Wounjhang Park, University of Colorado
John Capobianco, Concordia University
Andrew Ferguson, National Renewable Energy Laboratory
Dayong Jin, University of Technology, Sydney
Nano Convergence | Korea Nano Technology Research Society
National Renewable Energy Laboratory
ED4.1: Applications of Inorganic Upconversion Materials I
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 128 A
11:30 AM - *ED4.1.01
New Upconversion Schemes for Efficient Solar Harvesting and Biological Force Sensing
Jennifer Dionne 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Upconverting materials convert lower-energy photons to higher-energy photons. They can be used to harvest below-bandgap photons in photovoltaic cells, improving a single-junction cell’s efficiency beyond the Shockley-Queisser limit. They can also enable sensitive, background-free biological imaging in-vivo and new photodynamic medical therapies, since near-infrared light can penetrate approximately four times farther through biological tissue than visible light. Yet, despite their promise, current upconverters suffer from two significant limitations: 1) their efficiency is rather low, in many cases not exceeding a few percent, and 2) their upconverted intensity or color cannot be modulated with an external force or field. Here, we introduce high-efficiency and tunable upconverting materials that address each limitation, and show how they can be utilized for efficient solar energy generation and biological force sensing.
First, we develop a new upconverting scheme based on hot-carrier injection from a plasmonic absorber to an adjacent semiconductor. Low-energy photons incident on a plasmonic particle generate hot electrons and hot holes, which are injected into a semiconducting quantum well and subsequently radiatively recombine. Importantly, the bandgap of the quantum well can be higher than the energy of the incident photon, enabling upconversion. This scheme does not require coherent illumination, is a linear process, and can be broadband, paving the way towards high-efficiency upconversion.
Then, we develop upconverting nanoparticles that can be used as in vivo optical sensors of nano-to-microNewton forces. These upconverting force probes are small, bio-compatible, do not bleach or photoblink, need not be genetically encoded, and exhibit reversible changes in their color with an applied pressure. We deploy these nanoparticles in C. elegans to generate high-resolution in vivo force maps, focusing on the worm’s digestive cycle. These force-sensitive upconverting nanoparticles may help accelerate fundamental discoveries about intra- and inter-cellular mechanical signaling and serve as a new diagnostic tool for a variety of diseases.
12:00 PM - ED4.1.02
Photovoltaics—Upconversion Configurations versus Tandem Cells
Joop van Deelen 1 Show Abstract
1 , TNO, Eindhoven Netherlands
The potential of upconversion for various opto-electronic devices is tremendous. Unfortunately, the efficiency of upconversion is not ideal yet. For this reason, the photovoltaics (PV) industry has not invested in this direction so far. In this work detail the benefit of upconversion for PV, showing various single and tandem cell configurations and the impact of band gap tuning. For single junction solar cells, there is an optimal band gap at about 1.4 Ev. In case a highly efficient upconverter is used, this ideal band gap shifts to higher levels, because more of the photons in the spectrum can be utilized. For a wide range of bandgaps of solar cell material, we calculated what the potential contribution of upconversion materials could be and related that to various configurations of the solar cell and upconversion layers. Moreover, by comparing these various strategies with the potential of a dual junction tandem cell configuration, a compelling case is made for upconverters.
At 100% conversion efficiency, the upconverter with a single junction cell is more efficient than a dual junction tandem cell. Is was also found that a single junction cell with an upconverter that is ‘only’ 80% efficient has a similar efficiency as an ideal dual junction cell with optimized open circuit voltages. Because the single junction cell plus upconverter has more cost reduction potential than a dual junction cell configuration, this result shows that upconverters are certainly a route worthwhile to pursue. Additionally, it was investigated if a upconverter with two different photon energies would create a large surplus in efficiency. It was found that there is a further increase in efficiency, but very careful bandgap tuning with a tolerance < 0.02 Ev is needed to obtain the required matching, which makes this system rather sensitive for material and solar spectrum fluctuations and it is suggested that a simple upconverter is a more favourable strategy.
12:15 PM - *ED4.1.03
Optimization of Up-Conversion Photonic Markers Based on a La2O3 Host for Plastics Recycling and Anti-Counterfeiting Applications
Bryce Richards 1 , Guojun Gao 1 , Dmitry Busko 1 , Ian Howard 1 , Andrey Turshatov 1 Show Abstract
1 , Karlsruhe Institute of Technology (KIT), Eggenstein-Leopolds. Germany
Novel photonic markers based on trivalent rare-earth (RE3+) up-conversion (UC) materials offer promising market prospect as photonic markers for plastics recycling and anti-counterfeiting (PRAC). RE3+ UC materials exhibit many unique features such as: large anti-Stokes shift; high signal/noise ratio; good resistance to photo-bleaching and photochemical degradation; the availability of cheap NIR laser diodes for excitation; sharp UC emission lines; tailored UC emission color; long photo-luminescent (PL) lifetimes and low toxicity. These unique features, along with the abundant UC PL fingerprints over the broad spectral region endow them with the plentiful choices of photonic markers for PRAC.
Here, we summarize the recent developments of RE3+ UC materials with respect to: tailoring UC emission color over a wide spectral region from the NIR to visible to UV; intensity; intensity ratio; and Ln3+ lifetime. We systematically summarize the RE3+ and/or RE3+ combination choices, spectroscopic properties and the corresponding UC mechanisms for UC in NIR, red, orange, yellow, green, blue, violet and UV in the sequence of photon energy, such that best candidates can be chosen. Subsequently, recent advances for enhancing the UC PL intensity of a given band, the relative intensity ratio of multiple bands, as well as PL lifetimes are reviewed. Finally, the integration UC materials system into a photonic marker technology will be highlighted.
As an example, where a lanthanum oxide (La2O3) was co-doped with the following ion pairs: i) ytterbium-erbium (Yb3+-Er3+); ii) ytterbium-thulium (Yb3+-Tm3+); and iii) ytterbium-holmium (Yb3+-Ho3+) for the realization of blue ( Tm3+) , green (Ho3+, Er3+) , red (Er3+) and near-infrared ( Tm3+) emission upon excitation in the wavelength 935 - 980nm. Full optimization of doping concentrations was carried out, using the UC photoluminescent quantum yield (PLQY) as a figure-of-merit, and the spectral dependence on excitation power, as well as the range of colors that can be achieved (e.g. by varying the Yb3+ doping concentration alone), as well as PL lifetimes were investigated in detailed. This yielded oxide-based UC materials exhibit UC PLQY in the range of 2-5%.
ED4.2: Applications of Inorganic Upconversion Materials II
Tuesday PM, April 18, 2017
PCC North, 100 Level, Room 128 A
2:30 PM - *ED4.2.01
NIR Nanomaterials for Disease Diagnostics and Therapy
Fan Zhang 1 Show Abstract
1 , Fudan University, Shanghai China
Upconverting nanoparticles (UCNPs) present a new technology for optical imaging/detection which is a growing field with both diagnostic and drug discovery uses. Currently, fluorophores including fluorescent dyes/proteins and quantum dots (QDs) are used for fluorescence-based imaging and detection. These are based on ‘downconversion fluorescence’, emitting low energy fluorescence when excited by high energy light (such as UV or short wavelength visible light). Fluorophores in current use have several drawbacks: photobleaching, autofluorescence, short tissue penetration depth and tissue photo-damage. UCNPs emit detectable photons of higher energy in the visible range upon irradiation with near-infrared (NIR) light based on a process termed ‘upconversion’. UCNPs show absolute photostability, negligible autofluorescence, high penetration depth and minimum photodamage to biological tissues. They can be used for ultrasensitive interference-free biodetection because most biomolecules do not have upconversion properties.
3:00 PM - ED4.2.02
Orthogonal Near-Infraed Upconversion Co-Regulated Site-Specific O2 Delivery and Photodynamic Therapy for Hypoxia Tumor by Using Red Blood Cell Microcarriers
Peiyuan Wang 1 , Fan Zhang 1 Show Abstract
1 , Fudan University, Shanghai China
Pre-existing hypoxia in tumors can result in an inadequate oxygen supply during photodynamic therapy (PDT),which in turn hampers photodaynamic efficacy. To overcome this problem, we deleloped an orthogonal near-infared upconversion controlled red blood cell (RBC) microcarriers to selectively deliver O2 in hypoxia area. Moreover, this RBC microcarriers are able to overcome a series of complex biological barriers which inculding transporting across the inflamed endothelium,evading mononuclear phagocyte system, reducing reticuloendothelial system uptake. Based on these abilities, RBC microcarriers have efficient tumors accumulation and are capable of delivery a large amount of O2 for PDT under near-infared (NIR) irradiation to realized effective solid tumor eradication.
3:15 PM - ED4.2.03
Upconversion Nanoparticles Y2O3 and Gd2O3 Co-Doped with Er3+ and Yb3+ with Aminosilane-Folic Acid Functionalization for Breast and Cervix Cancer Cell Detection
Dalia Chavez 1 , Karla Juarez-Moreno 2 , Gustavo Hirata 2 Show Abstract
1 , CICESE, Ensenada, Baja California, Mexico, 2 CNyn, UNAM, Ensenada, Baja California, Mexico
The upconversion nanoparticles (UCNPs) possess the ability to absorb near infrared energy (980 nm) and upconvert it to emit in the visible spectra, in this research, the UNCPs emit in green (550 nm) and red (660 nm). The UCNPs were functionalized with aminosilanes and folic acid (UCNPs-NH2-FA) and analyzed by transmission electron microscopy, Fourier transform infrared spectroscopy and luminescence measurements. UCNPs-NH2-FA have a particle size of 70 ± 10 nm with a good luminescence spectrum in comparison with the bare ones. Cytotoxicity of different amounts between 0.001 µg/ml to 1 µg/ml of bare and functionalized UCNPs was measured with the colorimetric assay MTT in three cancer cell lines: human cervical adenocarcinoma (HeLa), human breast cancer cells MB-MDA-231 and human breast ductal carcinoma MCF7. Some concentrations of bare UCNPs were cytotoxic for cells, however after their functionalization they resulted to be non-cytotoxic. The functionalized UCNPs were able to bind to folate receptors which are overexpressed in cervical and breast cancers cells. It was demonstrated by confocal microscopy, that the functionalized UCNPs were internalized into the cancer cells, confirming the hypothesis that they can be used as biolabels for breast and cervical cancer cells.
3:30 PM - ED4.2.04
Upconversion Nanoparticles for Tumor Imaging
Mingyuan Gao 1 , Yi Hou 1 , Ruirui Qiao 1 Show Abstract
1 , Institute of Chemistry, Chinese Academy of Sciences, Beijing China
Through either passive or active targeting, functional nanoparticles have shown great potentials in visualizing tumors in vivo. In this presentation, we will present our recent investigations on multimodality imaging of tumor xenografts based on subcutaneous, intraperitoneal, orthotopic, and primary cancer mouse models. In addition, the particle-size dependent clearance pathway of nanoparticles will be discussed.[1-4]
C. Liu, Y. Qi, R. Qiao, Y. Hou, K. Chan, Z. Li, J. Huang, L. Jing, J. Du, and M. Y. Gao, Nanoscale, 2016, 8, 12579.
Y. Hou, J. Zhou, Z. Gao, X. Sun, C. Liu, D. Shangguan, W. Yang, and M. Y. Gao*, ACS Nano, 2015, 9, 3199.
R. Qiao, C. Liu, M. Liu, H. Hu, C. Liu, Y. Hou, K. Wu*, Y. Lin, J. Liang, M. Y.*, ACS Nano, 2015, 9, 2120.
C. Liu, Z. Gao, J. Zeng, Y. Hou*, F. Fang, Y. Li, R. Qiao, L. Shen, H. Lei, W. Yang, and M. Y. Gao, ACS Nano, 2013, 7, 7227.
3:45 PM - ED4.2.05
Develop Multi-Functional Contrast Agent for Deep Tissue In Vivo Bioimaging
Shihui Wen 1 2 , Du Li 1 2 , Deming Liu 1 2 , Dayong Jin 1 2 Show Abstract
1 Institute for Biomedical Materials and Devices, University of Technology Sydney, Sydney, New South Wales, Australia, 2 ARC Centre of Excellence for Nanoscale BioPhotonics (CNBP), Macquarie University, Sydney, New South Wales, Australia
The ultimate frontier in nanomaterials engineering is to realize their composition control with atomic scale precision to enable fabrication of nanoparticles with desirable size, shape and surface properties. Such control becomes even more useful when growing hybrid nanocrystals designed to integrate multiple functionalities. To achieving this aim in a family of rare-earth-doped nanomaterials, we recently verified the different roles of oleate anions (OA−) and molecules (OAH) in the crystal formation. Through the control over the ratio of OA− to OAH, directional inhibition, promotation or etching the crystallographic facets of the nanoparticles could be controlled. Here we demonstrate the development of facile one-dimensional nanomaterials synthesis that allows the integration of multiple components in a desired way for multimode bioimaging. This facile one-pot hot-injection method could enable the highly selectively controlled growth of different sodium lanthanide fluoride materials in longitudinal directions with atomic scale precision with tunable size, composition, and properties. This technique allows the upconversion luminescence signal, magnetic resonance imaging (MRI) and X-ray computed tomography (CT) signal logically integrated and optimized within one single versatile nanoplatform for multimode bioimaging. These findings suggest that the facile strategy developed here have the promising to get the desired heterogeneous nanocrystals as an all-in-one contrast agent for integrated and self-correlative multimodal bioimaging.
4:30 PM - *ED4.2.06
Upconverting Lipid Vesicles in Bioimaging and Photochemotherapy
Sylvestre Bonnet 1 , Sven Askes 1 Show Abstract
1 , Leiden University, Leiden Netherlands
Photopharmacology consists in the light activation of a medicinal compound in vivo in order to circumvent the biological action of a drug in space and time. In cancer research photopharmacology is notably regarded as a promising alternative to chemotherapy as side effects of most anticancer compounds limit treatment efficacy and are experienced as a heavy burden by cancer patients. The problem is that while many photosensitive compounds are sensitive to UV or blue light, which penetrates sub-optimally in biological tissues, red or NIR photon penetrate tissues much better but do not possess enough energy to trigger the required photochemistry. Triplet-triplet annihilation upconverting (TTA-UC) liposomes and polymersomes represent a promising family of upconverting drug delivery systems that allow for solving both problems at once. They produce blue light locally upon red light irradiation. The blue light is transferred radiatively or non-radiatively to the prodrug that becomes activated, without absorption by the surrounding tissues. My group recently showed that by incorporating in the membrane of liposomes and polymersomes a red light-absorbing photosensitizer and a blue emitter, red-to-blue upconversion was obtained that accelerated significantly the activation of anticancer metallodrugs. In this presentation I will also address the problem of the oxygen sensitivity of TTA-UC, which often stops working in presence of air. We recently demonstrated that addition of antioxidants allowed for obtaining stable red-to-blue upconversion in air for several hours. Overall, upconverting vesicles represent a promising way to activate photosensitive medicinal compounds within the photodynamic window.
5:00 PM - ED4.2.07
Bright and Force-Sensitive Upconverting Nanoparticles
Derek Wang 1 , Alice Lay 1 , Michael Wisser 1 , Randy Mehlenbacher 1 , Yu Lin 1 , Jennifer Dionne 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Lanthanide-based upconverters utilize real electronic states to absorb near-infrared light and convert it to visible light, making them useful for solar energy, security, and biological imaging applications. While most upconversion schemes are passive, systems that respond to external stimuli such as mechanical compression could enable precise studies of force distributions in microscale to nanoscale systems. Recently, we showed that sub-25 nm Mn- and Yb/Er-codoped cubic-phase NaYF4 nanoparticles exhibit a perceived emission color change from orange to red when subjected to forces on the nanonewton scale. However, due to the suboptimal crystal field environment provided by the cubic phase of NaYF4, the quantum yield of these nanoparticles was low, thereby limiting applications where bright force reporters are needed.
Here, we colloidally synthesize phase-pure hexagonal NaYF4 nanoparticles codoped with Mn2+ and Yb3+/Er3+ and characterize their optical response to mechanical compression. Modifying a scalable colloidal technique, we synthesize sub-25 nm, monodisperse, and bright hexagonal Mn- and Yb/Er-codoped NaYF4 nanoparticles by controlling the reactant composition, pH, and reaction time. Upon excitation with 980 nm light, the nanoparticles emit upconverted light centered at 525/540 nm (green) and 660 nm (red). Increasing Mn2+ doping from 0% to 2.1% yields enhancements in the red-to-green emission intensity ratio from 1.6 to 2.2, respectively. We then investigate the pressure dependence of upconversion up to 3 GPa (which corresponds to ~1 μN) using a diamond anvil cell coupled to a 980 nm excitation source. The upconverted emission of undoped Mn2+ particles demonstrates weak dependence on force. In contrast, the 2.1% Mn2+-doped nanoparticles exhibit a 13% change in the red to green ratio per micronewton of applied force – two orders of magnitude higher than the undoped nanoparticles. Additionally, these particles exhibit an enhanced green emission relative to the red emission with increasing pressure, a trend opposite that observed in cubic particles. All groups also exhibit reproducible color changes upon repeated cycling between 0 and ~1 μN. We explain these trends by using in situ x-ray diffraction to measure lattice changes upon compression and transient absorption to track the shift of the Mn2+ energy level with respect to Er3+. The bright emission, small size, micronewton force sensitivity, and cyclability of these particles demonstrate great promise for numerous optical force-reporting applications, such as mapping mechanotransduction in biological systems and mechanical strain in physical and engineered systems.
5:15 PM - *ED4.2.08
Security Applications of Upconverting Nanocrystals
Paul May 1 , Aravind Baride 1 , Jeevan Meruga 2 , Jon Kellar 2 , William Cross 2 Show Abstract
1 , University of South Dakota, Vermillion, South Dakota, United States, 2 , South Dakota School of Mines and Technology, Rapid City, South Dakota, United States
Recent advances in producing highly resolved, pre-defined patterns of upconversion (UC) nanophosphors via printing and other techniques present new opportunities for the use of these materials in sensing, theranostic, and security applications. The UC materials discussed here are invisible under ambient light and UV excitation, but become visible (or otherwise detectable) under NIR excitation. UC inks are activated by nanocrystals of β-NaYF4 which are doped with various combinations of trivalent lanthanide ions, Ln3+. We have demonstrated that covert upconversion QR codes printed using aerosol-jet technology (and subsequently adapted to inkjet technology), are readable using a near-IR laser, and can be successfully scanned using a smart phone. This research demonstrates that UC inks can be used to provide selected access to encoded information. We have also demonstrated an RGB additive-color printing system that produces highly resolved pre-defined patterns that are invisible under ambient lighting, but which are viewable as luminescent multi-color images under NIR excitation. Most recently, we have developed a print-and-read system based on NIR-to-NIR (980 nm-to-800 nm) upconversion luminescence. Remaining in the NIR spectral region for both excitation and emission has distinct advantages, because both excitation and emission wavelengths are able to penetrate highly scattering and / or visibly opaque media. Moreover, inexpensive CCD-based detectors and imaging devices exhibit peak sensitivity at the 800 nm emission wavelength of these nanocrystals. NIR-to-NIR images are easily captured, for example, using an inexpensive, modified point-and-shoot CCD camera, even at modest excitation power densities. Finally, we will discuss the potential for using metal-pattern-array substrates for significant enhancement of upconversion brightness through both plasmonic and optical mechanisms.
5:45 PM - ED4.2.09
Active Thermal Extraction and Temperature Sensing of Near-Field Thermal Radiation
Taeyong Kim 1 , Austin Minnich 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States
Recently, we proposed an active thermal extraction (ATX) scheme that enables thermally populated surface phonon polaritons to escape into the far-field. The concept is based on a fluorescence upconversion process that also occurs in laser cooling of solids (LCS). Here, we present a generalized analysis of our scheme using the theoretical framework for LCS. We show that both LCS and ATX can be described with the same mathematical formalism by replacing the electron-phonon coupling parameter in LCS with the electron-photon coupling parameter in ATX. Using this framework, we compare the ideal efficiency and power extracted for the two schemes and examine the parasitic loss mechanisms. This work advances the application of ATX to manipulate near-field thermal radiation for applications such as temperature sensing and active radiative cooling.
Wounjhang Park, University of Colorado
John Capobianco, Concordia University
Andrew Ferguson, National Renewable Energy Laboratory
Dayong Jin, University of Technology, Sydney
Nano Convergence | Korea Nano Technology Research Society
National Renewable Energy Laboratory
ED4.3: Synthesis and Characterizations of Inorganic Upconversion Materials
Wednesday AM, April 19, 2017
PCC North, 100 Level, Room 128 A
9:30 AM - *ED4.3.01
Lanthanide Upconversion Nanocrystals—Synthesis, Energy Transfer Management and Bioapplication
Chun-Hua Yan 1 , Hao Dong 1 , Ling-Dong Sun 1 Show Abstract
1 , College of Chemistry, Peking University, Beijing China
By virtue of the unique 4f electron configurations, lanthanide doped materials are considered ideal candidates for photon upconversion studies. As the size is confined into nanoscale, the inherent upconversion behaviors are well preserved, importantly, the energy transfer pathways can be flexibly managed. Upconversion emissions from lanthanide nanocrystals have been gaining a growing body of research interest in many interdisciplinary fields, for example, bioimaging, theranostic, and photovoltaic devices, etc. We present a versatile synthetic approach, namely thermal decomposition method, to prepare high-quality lanthanide upconversion nanocrystals, including fluorides, oxides, and oxyhalides, etc. Based on our preliminary mechanistic studies, lanthanide upconversion emission as well as excitation features have been effectively manipulated via core@shell nanostructures, upconversion/noble metal or organic dye nanocomposites, as well as tuning the local structure. Furthermore, in vivo bioimaging and photodynamic therapy were investigated with excitation in the harmless near infrared. Biotoxicity assessments showed the good biocompatibility of the lanthanide upconversion nanocrystals.
 Sun, L. D.; Wang, Y. F.; Yan, C. H. Acc. Chem. Res. 2014, 47, 1001.
 Dong, H.; Sun, L. D.; Yan, C. H. Chem. Soc. Rev. 2015, 44, 1608.
 Dong, H.; Du, S. R.; Zheng, X. Y.; Lyu, G. M.; Sun, L. D.; Li, L. D.; Zhang, P. Z.; Yan, C. H., et al. Chem. Rev. 2015, 115, 10725.
10:00 AM - ED4.3.02
Synthesis and Characterization of Er-Doped Indium Tin Oxide for Upconverting Transparent Conductor
Suehyun Cho 1 , Wounjhang Park 1 Show Abstract
1 , University of Colorado, Boulder, Colorado, United States
Upconverting materials doped with rare-earth ions have recently gained copious interest due to their interesting optical properties. They absorb near infrared (NIR) photons, upconverts them into visible photons through energy transfer upconversion (ETU). The upconverted luminescence has a wide range of potential applications ranging from high-contrast bioimaging to its applications in photovoltaic devices. For bioimaging applications, the upconversion mechanism provides and advantage over traditional fluorescent imaging agent because it utilizes the NIR excitation and hence minimizes autofluorescence. For its applications in photovoltaic devices, there has been a great interest to upconvert the photons below bandgap into photon energies above the bandgap. Upconverting, transparent, and conducting material will be of great interest particularly for photovoltaic devices.
Here we report successful syntheses of upconverting indium tin oxide (UC-ITO) nanoparticles doped with Er3+ ions by modifying the two previously proposed synthesis methods. First, we modified the ITO nanoparticle synthesis method via hydrolysis of metal carboxylates proposed by Gilstrap Jr. et al. The second synthesis method was a modification of nonhydrolytic synthesis of rare-earth oxide nanocrystals proposed by Si et al. The physical characteristics of UC-ITOs were examined via transmission electron microscopy (TEM), x-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). TEM revealed that the UC-ITO nanoparticles synthesized via modified Gilstrap method have uniform diameter of ~7nm while the particles synthesized via modified Si method have a diameter of ~30nm. XRD of the as-synthesized UC-ITO nanoparticles in both cases revealed identical peaks as commercial ITO without any annealing, hence proving successful synthesis of crystalline ITO nanoparticles. When comparing XRD peaks, UC-ITO particles synthesized via modified Si method show sharper and better defined peaks indicating better crystallinity.
Furthermore, the both UC-ITO nanoparticles show upconverted green and red luminescence upon 980nm laser excitation indicating successful doping of rare-earth ions. The UC-ITO particles synthesized via modified Si method showed better upconversion efficiencies than those of modified Gilstrap method. UC-ITO particles with various concentrations of tin and rare-earth ions were synthesized and characterized to find the optimal doping concentration for providing efficient upconversion as well as good conductivity. Finally, the UC-ITO nanoparticles were spun onto various substrates and annealed at 850 Co for 8 hours for thin film characterizations including ellipsometry, resistivity, and transmittance measurements.
10:15 AM - ED4.3.03
Microstructural Characterization of Rare-Earth Doped Fluoride Nanocrystals for Cold Brownian Motion
Xuezhe Zhou 1 , Guomin Zhu 1 2 , James De Yoreo 2 , Peter Pauzauskie 1 2 Show Abstract
1 , University of Washington, Seattle, Washington, United States, 2 Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Upconverting sodium-yttrium-fluoride (NaYF4) nanocrystals (NCs) are currently being investigated for a range of applications including deep-tissue bio-imaging, color displays, solar energy harvesting, and photocatalysis. Recent solid-state laser-refrigeration results have shown that single Yb(III) doped fluoride nanocrystals (NCs) can be refrigerated in aqueous media using single-beam near-infrared (NIR) laser-trapping1,2. These materials have enabled the first experimental demonstration of “Cold-Brownian-Motion” since Einstein’s seminal work on Brownian motion published in 1905 and suggest the potential of using β-NaYF4: 10%Yb3+ NCs for applications in localized optoelectronic device cooling or physiological laser refrigeration. Different sizes and morphologies of β-NaYF4 NCs can be achieved through a low-cost, reproducible hydrothermal approach. This talk will discuss recent ‘in situ’ and ‘ex-situ’ characterization techniques for these upconverting nanocrystals including Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray absorption spectroscopy (XAS) to elucidate the microstructural composition of these rare-earth-doped β-NaYF4 NCs. EXAFS measurements of ytterbium’s L3-edge for both cubic and hexagonal phases of NaYF4 NCs reveal the average spacing between rare-earth (RE) dopant-ions within the hosting crystal lattice. NEXAFS measurements of both carbon’s K-edge and fluorine’s K-edge also will be presented to show both the local electronic structure and absence of significant carbon doping in these hydrothermal fluoride NCs. Preliminary in-situ TEM results will be presented showing how cubic NaYF4 NCs may fuse and grow through an oriented attachment process during hydrothermal synthesis. ‘In-situ’ laser-trapping experiments are used to investigate real-time cation-exchange at the NC-solid/liquid interface. Finally, the radiative lifetime of Er(III) ions within single optically-trapped β-NaYF4 NCs will be presented for comparison with NC ensembles.
1. Roder, P. B., Smith, B. E., Zhou, X., Crane, M. J. & Pauzauskie, P. J. Laser refrigeration of hydrothermal nanocrystals in physiological media. Proc. Natl. Acad. Sci. 112, 15024–15029 (2015).
2. Zhou, X., Smith, B. E., Roder, P. B. & Pauzauskie, P. J. Laser Refrigeration of Ytterbium-Doped Sodium–Yttrium–Fluoride Nanowires. Adv. Mater. (2016). doi:10.1002/adma.201600406
10:30 AM - ED4.3.04
Scale-Up of the Synthesis of Upconversion Nanoparticles
Aravind Baride 1 , Mary Berry 1 , Paul May 1 Show Abstract
1 , University of South Dakota, Vermillion, South Dakota, United States
The potential applications of upconversion nanoparticles in bio-imaging, drug delivery, security printing, and photovoltaics has been previously demonstrated by many research groups. However, production of nanoparticles in large quantities is essential in order to take the applications beyond the laboratory demonstration phase. Scale-up of the laboratory-size reaction is the obvious first approach in large volume production of these nanocrystals. However, scaling-up the nanoparticle synthesis is challenging, because of the complex mass transport dynamics associated with seed formation and nanocrystal growth that subsequently affects nanocrystal morphology and size distribution. In this work, we develop a scaled-up synthesis procedure to produce tens of grams of β-NaYF4 nanoparticles in a relatively small reaction volume, retaining phase purity and morphology. The nanoparticles produced by the scale-up procedure have very narrow size distributions that enabled formation of higher-order self-assembly ‘super crystals’ merely by applying a drop-and-dry method. The scale-up procedure is suitable for producing nanocrystals in the 20-140 nm size range, which is suitable for the aforementioned applications.
10:45 AM - ED4.3.05
Upconversion Processes and Internal Net Optical Gain in Single-Cystal Erbium Chloride Silicate Nanowires
Hao Sun 1 , Leijun Yin 2 , Zhicheng Liu 2 , Yize Zheng 1 , Cun-Zheng Ning 1 2 Show Abstract
1 , Tsinghua University, Beijing China, 2 , Arizona State University, Tempe, Arizona, United States
Achieving high gain in the telecommunication wavelength range with compatible Silicon process techniques has a very beneficial impact on the on-chip photonic integration. Er-containing materials are one of the most important categories in rear-earth materials due to the favorable energy level structure of the trivalent erbium ion, which have been mostly exploited in a wide variety of optoelectronic applications, such as optical amplifiers, lasers and upcoversion solar cells, etc. Although devices with best optical gain performaces are being attained with Er-doped materials, the relative low Er-density limited the maximum achievable gain in typical Er-doped materials to only less than a few dB/cm. Great progress has been achieved in the synthesis of Er-compounds with relative high Er-density. However, the gain performances of Er-compounds have so far been significantly inferior to those of Er-doped materials, limited by the poor crystal qualities and short carrier lifetimes.
Recently, a silicon-compatible nanowire growth of Erbium Chloride Silicate (ECS) with single crystalline quality was reported with Er-concentration as high as ~ 1022 cm-3. ECS nanowires were grown on silicon via chemical vapor deposition method. Thanks to the excellent material quality, the ECS nanowire shows highest lifetime-density product among all the reported Er-containing materials, thus it has great potential to achieve significant gain for the fabrication of ultra-compact lasers or amplifiers. The fundamental challenge of Er-compound amplifiers or lasers has been to obtain both high Er-concentration and high optical gain. Upconversion process is typically known as the gain-limiting factor of optical amplifiers at ~ 1.5 µm, thus it is interesting to investigate the interplay of upconversion processes and optical gain, especially for such high Er-concentration. Here, we report on the optical characterizaion of single ECS nanowire with high Er-concentration, aiming to explore the intrinsic net gain. Upconversion photoluminescence spectroscopy was performed by coupling a 1532 nm laser into single ECS nanowire. ECS nanowire shows very intense upconversion emission at room temperature consisting of several distinct peaks. The scalings of upconversion processes with pump intensity in the near-infrared are characterized in detail. Fitting experimental results with rate equations allows determination of the cooperative upconversion coefficient. Pump-probe method was adopted to measure the signal enhancement of ECS nanowire, which gives over ~ 1000 dB/cm on-off gain at highest pump level. By performing power-dependent green upconversion emission measurement and tracing green emission decay, the absorption coefficient of 1532 nm laser was inferred to be over ~ 700 dB/cm. Therefore, over ~ 100s dB/cm internal net gain can be achieved. These results suggest that ECS nanowires could be indeed a promising material system for on-chip silicon-compatible light sources and amplifiers.
11:30 AM - ED4.3.06
Design and Synthesis of Upconversion Nanoparticles for Lifetime- and Intensity-Based Sensing Applications
Markus Buchner 1 , Sandy-Franziska Himmelstoss 1 , Verena Muhr 1 , Lisa Wiesholler 1 , Antje Baeumner 1 , Thomas Hirsch 1 Show Abstract
1 Institute of Analytical Chemistry, University of Regensburg, Regensburg Germany
Upconversion nanoparticles (UCNPs) represent a promising class of nanomaterials for bioanalytical applications due to their outstanding ability to convert near-infrared light (980 nm) into visible luminescence, enabling quasi-background free measurements, in conjunction with their multitude of narrow emission bands, high photostability, and chemical inertness. Many sensing applications require low power excitation, therefore it is essential to design and synthesize bright upconversion nanoparticles. This is a challenging task as the non-radiative pathways for deactivation of the upconversion luminescence for nanoparticles with surface attached molecules dispersed in liquids are yet not fully understood.
This talk will summarize our latest results on the possibilities to tune the brightness of the multiple, narrow emission bands of upconversion nanoparticles by the choice of the surface ligand individually, or even to shift the emission wavelength by attaching dyes onto the surface. These strategies include the synthesis of large batches, monodisperse nanoparticles with controlled size and core-shell architecture as well as surface functionalization to achieve colloidal stable particles. The fully characterized, bright upconversion nanoparticles are suitable candidates in bioanalytical sensing application. The advantage of photostability and the spectral overlap of the emission of UCNPs with the absorption band of coenzymes or co-factors of enzymes were exploited to achieve longtime online determination of biomarkers like L-lactate and glucose.
11:45 AM - *ED4.3.07
Controlling Photon Upconversion in Lanthanide-Doped Nanocrystals
Xiaogang Liu 1 Show Abstract
1 , National University of Singapore, Singapore Singapore
Lanthanide-doped nanoparticles exhibit unique luminescent properties, including a large Stokes shift, a sharp bandwidth of emission, high resistance to optical blinking, and photobleaching. Uniquely, they can also convert long-wavelength stimulation into short-wavelength emission. These attributes offer the opportunity to develop alternative luminescent labels to organic fluorophores and quantum dots. In recent years, researchers have taken advantage of spectral-conversion nanocrystals in many important biological applications, such as highly sensitive molecular detection and autofluorescence-free cell imaging. With significant progress made over the past several years, we can now design and fabricate nanoparticles that display tailorable optical properties. In particular, we can generate a wealth of color output under single-wavelength excitation by rational control of different combinations of dopants and dopant concentration. By incorporating a set of lanthanide ions at defined concentrations into different layers of a core-shell structure, we have expanded the emission spectra of the particles to cover almost the entire visible region, a feat barely accessible by conventional bulk phosphors. In this talk, I will highlight recent advances in the broad utility of upconversion nanocrystals for multimodal imaging, bio-detection, display and photonics.
12:15 PM - ED4.3.08
Inorganic Nanocrystals Functionalized Mesoporous Silica—From Symmetry to Asymmetry
Xiaomin Li 1 Show Abstract
1 Department of Chemistry, Laboratory of Advanced Materials, Fudan University, Shanghai China
Inorganic nanocrystals (NCs) functionalized mesoporous nanocomposites possess both unique properties of mesoporous nanomaterials and abundant optical, electrical, magnetic etc. properties of inorganic NCs. With the development of synthetic technology, the inorganic NCs functionalized mesoporous nanocomposites with symmetric and asymmetric structure have been widely developed. Like the anisotropic growth of the inorganic crystals, the mesostructures should be also oriented by surfactants micelles and further induce the anisotropic epitaxial growth of the ordered mesoporous to the asymmetric nanocomposites. By using this novel anisotropic growth strategy, series of asymmetric inorganic NCs functionalized mesoporous nanocomposites were developed, including Janus, Single-Hole Hollow, Nano-thermometer, Triblock Janus etc. Most importantly, the obtained asymmetric nanocomposites possess unique multiple independent surfaces, compositions, functions etc., which are ideally for the co-delivery of multi-guests with quite different properties (hydrophilicity/hydrophobicity, acidity/basicity, sizes etc.).
12:30 PM - ED4.3.09
Chemically and Structurally Flexible Hosts for Yb-Er Sensitizer-Activator Pairs
Federico Rabuffetti 1 , K. Tauni Dissanayake 1 , B. Dulani Dhanapala 1 Show Abstract
1 , Wayne State University, Detroit, Michigan, United States
Upconverting nanocrystals, which sequentially absorb multiple NIR photons and emit higher-energy NIR or visible photons, offer several potential advantages over molecular downconversion fluorophores traditionally employed in biophotonic applications such as imaging and sensing. However, their implementation as optical probes has been limited by their low quantum efficiency and lack of full-spectrum color tunability; these deficiencies stem from the occurrence of deleterious energy-transfer processes. Despite the key role played by the host lattice in mediating energy-transfer processes relevant to light upconversion, the ability to rationally manipulate its chemical composition and crystal structure to direct the flow of energy remains limited. Our group’s research aims bridging this fundamental knowledge gap by using upconverting nanocrystals that couple rare-earth activators (Yb-Er, Yb-Tm) to a family of host materials (MFX; M: Ca, Sr, Ba; X: Cl, Br, I) whose crystal structure can be rationally manipulated through chemical composition.
In this work, we present the synthesis, structural characterization, and infrared-to-visible light upconversion properties of semiconducting MFX (X: Cl, Br, I) nanocrystals codoped with Er and Yb. According to Rietveld and pair distribution function analyses, the average and local crystal structure conform to that expected on the basis of the P4/nmm tetragonal space-group. Excitation of Yb at 980 nm results in two-photon upconversion covering the 520-700 nm spectral range. The excited states of the Er activator in the MFX hosts exhibit a biexponential decay with lifetimes in the 0.01-0.2 and 0.3-0.4 ms ranges. Both, the chromaticity of the upconverted visible light and the excited-state dynamics can be tuned via chemical composition. Our findings prompt for an expansion of the library of upconverting nanocrystals into novel materials containing heavy halide anions.
12:45 PM - ED4.3.10
Crystal Structure, Point Symmetry and Absolute Upconversion Quantum Yield—Towards the Rational Design of Efficient Lanthanide-Doped Upconverting Nanocrystals
Damien Hudry 1 , Milinda Abeykoon 2 , Dmitry Busko 1 , Dmytro Nykypanchuk 3 , Eric Dooryhee 2 , Christian Kuebel 1 , Venkata Sai Kiran Chakravadhanula 1 , James Dickerson 3 , Bryce Richards 1 Show Abstract
1 , Karlsruhe Institute of Technology, Eggenstein-Leopoldsh Germany, 2 NSLS-II, Brookhaven National Laboratory, Upton, New York, United States, 3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Over the past decade, lanthanide-doped upconverting nanocrystals (Ln-doped UCNCs) have risen to be one of the most important classes of nanoscale materials due to their potential applications in technological fields as diverse as solid-state lasers, optical data storage, biological imaging and therapy, and solar energy conversion. Nevertheless, the low quantum efficiency of UCNCs represents a major cloud on the horizon. Although various strategies, such as surface passivation (core-shell), enhanced absorption (dye-sensitized, surface plasmon), and crystal field engineering (doping) were developed to enhance photon upconversion (UC), the absolute UC quantum yields (UCQY) reported to date remain very low, preventing the widespread penetration of UCNCs in any devices. As a consequence, there is an urgent need for the rational design of highly efficient UCNCs; which rely on the comprehensive understanding of all fundamental phenomena that influence the UC process in UCNCs.
Phonon energy of the host matrix and local symmetry are intrinsic characteristics of paramount importance to optimize the UC performance. The former is related to electronic excited-state dynamics, while the latter can modify the probability of occurrence of 4f-4f transitions. Quantifying the relationship between those intrinsic parameters and the absolute UCQY for various host matrices will inevitably lead to the emergence of selection rules that lead towards the discovery of highly efficient UCNCs. Our research group is currently investigating the relationship between the symmetry of a host matrix and its corresponding absolute UCQY through the use of synchrotron-based diffraction experiments coupled to both Rietveld and pair distribution function (PDF) analyses. In this presentation, the atomic scale structure and space group identification of bare NaGdF4:Yb:Er UCNCs will be first described for a size regime extending from 5 nm up to 15 nm. Then, the structural characteristics of the outer shell of core-shell systems such as NaGdF4:Yb:Er@NaYF4 will be revealed. Finally, the relationship between point symmetry and absolute UCQY will be explained for the first time. The problem was tackled through the synthesis of five ternary fluoride host matrices with various point symmetries (Oh, C3h, S4, Ci, and C1).
Detailed structural characterizations are of major interest to move forward with the comprehensive understanding of UC properties of UCNCs. Results that will be presented will help to pave the way towards the rational choice of host matrices that is a prerequisite for the design of highly efficient UCNCs.
ED4.4: Photonic Control of Upconversion
P James Schuck
Wednesday PM, April 19, 2017
PCC North, 100 Level, Room 128 A
2:30 PM - *ED4.4.01
Enhancing Lanthanide Upconversion with Molecular Concentrators, Micro Pillars and Energy-Looping Nanoparticle-Based Lasers
P James Schuck 1 , David Garfield 1 2 , Angel Fernandez-Bravo 1 , Elizabeth Levy 1 , Bining Tian 1 , Cheryl Tajon 1 , Edward Barnard 1 , Maysamreza Chamanzar 3 , Jillian Iafrati 4 , Michel Maharbiz 5 , Vikaas Sohal 4 , Nicholas Borys 1 , Emory Chan 1 , Bruce Cohen 1 Show Abstract
1 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States, 3 Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 4 , University of California, San Francisco, San Francisco, California, United States, 5 Electrical Engineering and Computer Science, University of California, Berkeley, Berkeley, California, United States
Though their unique optical properties are proving advantageous for numerous applications, an ongoing challenge facing uponverting nanoparticles remains achieving satisfactory upconverted signal and quantum yield while illuminating at low fluences. Here, I will describe the pros and cons of various strategies used to improve UCNP signals and efficiencies. I will follow this with a discussion of current efforts at our Facility aimed at applying these strategies for deep-tissue imaging, biosensing, optogenetics, and solar light harvesting. This will include demonstrations of imaging of ucpn-based micropillars through >2mm of tissue, continuous-wave multicolor upconverting microlasers, and sub-20nm UCNPs with >5% quantum yield.
3:00 PM - ED4.4.02
Plasmon-Enhanced Upconversion Luminescence in the Metal-Insulator-Metal Cylindrical Nanostrucutres
Gumin Kang 1 , Chenchen Mao 1 , Suehyun Cho 1 , Wounjhang Park 1 Show Abstract
1 Electrical, Computer & Energy Engineering, University of Colorado, Boulder, Colorado, United States
The unique luminescent properties of rare-earth ion doped upconversion materials make them very attractive candidates for various applications such as energy harvesting, biosensing and biomedical imaging. For wide spread use, however, the efficiency must be improved significantly. For this reason, there have been numerous studies on the use of photonic and plasmonic nanostructures to boost the efficiency of frequency upconversion.
In this study, we design cylindrical metal-insulator-metal (MIM) structures in which upconversion nanoparticle (UCNP) layer is sandwiched between two gold layers. By an extensive numerical modeling study, the thicknesses of gold and UCNP layers are optimized to possess strong surface plasmon resonance at 980 nm which is the excitation wavelength of UCNP. Furthermore, the surface plasmon mode in the optimized geometry has a field profile where the field is concentrated within the UCNP layer so that absorption and energy transfer process may be strongly enhanced. The optimum design shows 123x enhancement in intensity within the UCNP volume. For experimental demonstration, nanocrystals of NaYF4:Yb3+,Er3+ which is one of the most efficient upconversion materials, are synthesized and deposited on a thin layer of gold film. After an additional layer of gold is deposited on the upconversion nanoparticle layer, photoresist pattern is formed by laser interference lithography and a subsequent argon plasma etching process is used to fabricate nanoscale cylindrical MIM structures. The MIM structures show strong green and red photoluminescence under 980 nm excitation. Compared to unpatterned reference structure, they show a significant enhancement.
The additional advantage of the proposed structures is that the individual MIM structures can be lifted off and dispersed in an aqueous solution. The highly monodispersed plasmonic MIM structures suspended in solution can be for a variety of biomedical applications such as high contrast bio-imaging and photothermal therapy through the local heating of plasmonic structure induced by near infrared light. Moreover, one can envision solution-based fabrication of organic photovoltaic devices incorporating plasmon enhanced upconversion materials. The proposed fabrication process is cost-effective and scalable and thus offers a promising pathway to practical applications.
3:15 PM - ED4.4.03
Spectroscopic Imaging of NIR to Visible Upconversion from NaYF4:Yb3+,Er3+( Tm3+) Nanoparticles on Plasmonic Nano-Arrays
Jon Fisher 1 , Amy Hor 1 , Mary Berry 2 , Paul May 2 , Steve Smith 1 Show Abstract
1 , South Dakota School of Mines and Technology, Rapid City, South Dakota, United States, 2 Chemistry Department, University of South Dakota, Vermillion, South Dakota, United States
We investigate photonic and plasmonic enhancement of upconversion luminescence from NaYF4:Yb3+,Er3+(Tm3+) nano-particles supported by nano-arrays. Using spectroscopic imaging, we assess the spatial variations in upconversion luminescence from NaYF4:Er3+,Yb3+ nanoparticles embedded in PMMA on Au nano-arrays. Analysis of the statistical distribution of emission intensities in the spectroscopic images on and off the nano-arrays provides an estimate of the average enhancement factor independent of fluctuations in nanoparticle density. The nano-arrays support a surface plasmon (SP) resonance at 980nm, coincident with the peak absorption of the Yb3+ sensitizer. Spatially-resolved upconversion spectra show a 30X to 3X luminescence intensity enhancement on the nano-array compared to the nearby smooth Au surface, corresponding to excitation intensities from 1 W/cm2 to 300kW/cm2. Our analysis shows the power dependent enhancement in upconversion luminescence can be almost entirely accounted for by a constant shift in the effective excitation intensity, which is maintained over five orders of magnitude variation in excitation intensity. The variations in upconversion luminescence enhancement with power are modeled by a 3-level-system near the saturation limit, and by simultaneous solution of a system of coupled nonlinear differential equations, both analyses agree well with the experiments. We use the power dependent measurements to extract upconversion luminescence enhancement factors from candidate nano-arrays which are independent of excitation intensity.
4:30 PM - *ED4.4.04
Up-Conversion Technology—Are All Questions Answered?
Artur Bednarkiewicz 1 2 Show Abstract
1 , Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw Poland, 2 , Wroclaw Research Centre EIT+, Wroclaw Poland
Intentional design and engineering of photoluminescent properties of materials is currently at the forefront of fundamental research, as well as new applications and technology innovation. Up-converting colloidal nanoparticles have gained tremendous interest, which owes to their unique photo-physical properties. These properties, e.g. efficient anti-Stokes emission, long luminescence lifetimes, narrowband multicolor absorption and emission and recently new up-conversion schemes or mastering core-shell chemical architecture designs paves the way for many bio-medical applications. Although numerous proof-of-concept demonstrations of biosensing, bioimaging as well as theranostic treatments have been accomplished with upconversion technology, there are still questions which require more attention. For example, how can one improve the brightness? How to embed multifunctionality within single NPs? How shall we quantify and compare safety of NPs in the view of issues related to nanotoxicology definitions ? Are UCNPs completely safe for use in-vivo ? What are the factors, other than chemical composition, that may influence or induce toxicity of nanoparticles ? Some of these issues will be overviewed and discussed during the lecture.
The first part of the talk will focus on the influence of doping configuration and active-core@active-shell UCNPs chemical architecture on the up-conversion properties of b-NaYF4 NPs. Different materials were obtained and studied to understand fundamental aspects of energy transfer (e.g. between Yb@Ho or Ho@Yb ET), enhance cooperative energy up-conversion of Tb3+ under 800 nm (e.g. YbTb@Yb@YbNd NPs) or broaden temperature sensitivity range of optical nanotermometer (e.g. YbEr@YbNd NPs). The second part of the talk will outline the current understanding of nanotoxicity and indicate critical issues, such as NPs’ size, surface chemistry, NPs dissolution and RE toxicity, which shall be considered, when the UCNPs are to be used in vivo.
5:00 PM - ED4.4.05
Inhibited Spontaneous Emission in Nanocavities for More Efficient Energy Pooling Upconversion
Michael LaCount 1 , Mark T. Lusk 1 Show Abstract
1 , Colorado School of Mines, Golden, Colorado, United States
A fundamental constraint on exciton-based upconversions is the lifetime of the excitons themselves. This typically translates into a consideration of high-intensity light to carry out upconversions with any significant efficiency. An alternative, though, is to artificially increase exciton lifetimes by using nanocavities so as to inhibit spontaneous emission. This creates a singlet state with a lifetime more akin to that of a triplet exciton but without the added complexity associated with the creation and subsequent Dexter dynamics of triplets; these long-lived singlet states will exhibit energy transfer rates identical to their counterparts in a non-cavity environment. The cavity is tuned to the first donor excitation energy, but the donor itself is designed so that the reorganization that follows excitation reduces its emission energy below that supported by cavity modes—i.e. the Stokes shift puts the system out of resonance with the cavity. With spontaneous emission essentially removed as a competitor, the subsequent upconversion is made much more efficient.
The efficacy of inhibited spontaneous emission is computationally considered for molecular energy pooling, a three-body process in which two donors simultaneously transfer their energy to a spatially separated acceptor through the use of virtual states. It has recently been shown that there is no significant difference between the free-space coupling tensor and its cavity counterparts, but inhibited spontaneous emission breathes new life into the potential of cavity-based pooling.
Perturbation theory is used to derive expressions for the rates of all relevant processes, and these are populated with data obtained from ab initio calculations of an assembly of Fluorescein donors and Hexabenzocoronene acceptors. The equations are then embedded within a multi-path kinetic model to predict the steady state efficiency of upconversion. Our results demonstrate that dramatic increases in efficiency are possible by placing the molecular system within a tuned nanocavity.
 M. D. LaCount, D. Weingarten, N. Hu, S. Shaheen, J. van de Lagemaat, G. Rumbles, D. Walba and M. T. Lusk, Energy Pooling Upconversion in Organic Molecular Systems, Journal of Physical Chemistry A 119 4009-4016 doi:10.1021/acs.jpca.5b00509, arXiv 1503.07246 (2015)
 M. D. LaCount and M. T. Lusk, Electric dipole coupling in optical cavities and its implications for energy transfer, up-conversion, and pooling, Physical Review A 93 063811 doi: 10.1103/PhysRevA.93.063811, arXiv 1602.09048 (2016)
5:15 PM - ED4.4.06
Nanoplasmonic Upconverting Nanoparticles as Orientation Sensors for Single Particle Microscopy
Shuang Fang Lim 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
We show that the anisotropic disk shape of nanoplasmonic upconverting nanoparticles (NP-UCNPs) create changes in fluorescence intensity in the event of rotational motion. We determine the orientation by a three-fold change in fluorescence intensity, and define the response time and spatial resolution of the UCNP motion. We further show a strong dependence of the luminescence intensity on the particle orientation and polarization of the excitation light. This orientation dependence of the fluorescence will enable the detection of the rotational motion of biomolecules coupled to the nanoparticle.
5:30 PM - ED4.4.07
Disordered Media for Plasmonics-Driven Upconversion—Anderson Localization for Strong Near-Field
Seok Joon Kwon 1 Show Abstract
1 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Ever since theoretically proposed, Anderson localization has been studied in a variety of areas concerning localized wave phenomena in a random media from acoustic waves to quantum waves. Due to strong localization of waves, it has been conjectured that the constructive interferences of diffused electromagnetic waves as a form of accumulated multiple scattering in a disordered sub-wavelength nanostructures can contribute to the enhancement of near-field in 2D plane supporting strong plasmonic effects. In this study, we demonstrated 2D or 3D disordered plasmonic media comprised by sub-wavelength metallic nanoparticles or nanowires network targeting an induction of two- or three-order enhanced near-field, which finally results in two- or three-order enhanced intensity of emitted light by the near IR-to-visible light upconversion (UCL). For the 2D media, we fabricated self-assembled array of sub-100 nm Ag nanoparticles over a plasmonic substrate containing β-NaYF4:Yb3+/Er3+ UC nanoparticles, whereas for the 3D media, a randomly aligned network of micrometer-long Ag nanowires were employed for the plasmonic substrate. We experimentally and computationally observed and confirmed the formation of strong near-field of incident near IR at 980 nm around the respective nanostructures. We also observed reinforced near IR light absorption and green and red visible light emission by nano-antenna effects given by the randomized nanostructures for the plasmonic configurations. The strong near-field formation and enhanced UCL was effectively explained in the framework of the Anderson localization. We expect further editing and modifying of the plasmonic nanostructures pursuing better light extraction for various light emitting devices involving UCL.
5:45 PM - ED4.4.08
From Blue to Near-Infrared Continuous-Wave Upconverted Lasing Action from Lanthanide Doped Nanocrystals in Microcavities
Angel Fernandez-Bravo 1 , Elizabeth Levy 1 , Bining Tian 1 , Cheryl Tajon 1 , Edward Barnard 1 , Nicholas Borys 1 , Bruce Cohen 1 , Emory Chan 1 , P James Schuck 1 Show Abstract
1 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Despite their many advantages, upconverting nanoparticles (UCNPs) continue to suffer from a relative lack of brightness and efficiency. In this work, we show that by coupling specifically-engineered UCNPs to whispering gallery modes of 5 um-sized polystytrene microbeads, we achieve sufficient optical gain to enable continuous-wave (CW) upconverted lasing at multiple wavelengths. By optically pumping at 1064 nm, these upconverting microlasers leverage a resonant excited state absorption in Tm – the so-called “energy looping” excitation mechanism recently described in  – to achieve population inversion at the lowest thresholds reported to date. In contrast, we observe that pumping at similar CW powers with typical 980 nm excitation results in irreversible microcavity thermal damage, consistent with previous studies that require pulsed excitation and larger cavities to achieve UCNP-based lasing. Core-shell nanocrystals are systematically studied as microlasing media as a function of dopant type and concentration. In addition, we show that these 5 µm “energy looping” microlasers function even in aqueous environments, demonstrating their in vivo utility. These small lasers offer a bright, coherent local light source with minimal spatial requirements for high-quality feedback, and may greatly extend the broad functionality of UCNPs from background free imaging, theranostics, and volumetric displays, to active waveguiding, photonics structure assembly and deep-tissue optogenetics.
 E. S. Levy, A. Fernandez-Bravo, E. M. Chan, et al., “Energy-Looping Nanoparticles: Harnessing Excited-State Absorption for Deep-Tissue Imaging,” ACS Nano 10, 8423 (2016)
ED4.5: Poster Session: Photon Upconversion Materials
Thursday AM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - ED4.5.01
A General Strategy for Ligand Exchange on Upconversion Nanoparticles
Wei Kong 1 Show Abstract
1 , City University of Hong Kong, Hong Kong Hong Kong
Lanthanide-doped upconversion nanoparticles with a suitable surface coating are appealing for biological applications. As high quality upconversion nanoparticles are typically prepared in organic solvent and passivated by hydrophobic oleate ligands, a convenient and reliable method for surface modification of upconversion nanoparticles is thus highly desired to satisfy downstream biological investigations. In this work, we describe a facile and versatile strategy for displacing native oleate ligands on upconversion nanoparticles with a diversity of hydrophilic molecules. The successful coating of relevant ligands was confirmed by Fourier transform infrared spectroscopy, thermogravimetry analysis, and zeta potential measurement. The surface modified nanoparticles display high stability and good biocompatibility as revealed by electron microscopy, photoluminescence spectroscopy, and cytotoxicity assessment. Our study demonstrates that functional biomolecules such as biotin can be directly immobilized on the nanoparticle surface using this approach for quick and effective detection of streptavidin.
9:00 PM - ED4.5.02
Successful Fabrication of GaN Epitaxial Layer on Non-Catalytically-Grown Graphene for Photon Upconversion
Sungwon Hwang 1 Show Abstract
1 , Konkuk University, Chungju-si Korea (the Republic of)
Sapphire is widely used as a substrate for the growth of GaN epitaxial layer (EPI), but has several drawbacks such as high cost, large lattice mismatch, non-flexibility, and so on. Here, we first employ graphene directly grown on Si or sapphire substrate as a platform for the growth and lift-off of GaN-light-emitting-diode (LED) EPI, useful for not only recycling the substrate but also transferring the GaN-LED EPI to other flexible substrates. Sequential standard processes of nucleation/recrystallization of GaN seeds and deposition of undoped (u-) GaN/AlN buffer layer were done on graphene/substrate before the growth of GaN-LED EPI, accompanied by taping and lift-off of u-GaN/AlN or GaN-LED EPI. Upconversion photoluminescence (PL) from graphene quantum dots (GQDs) excited by a xenon lamp is artificial. It is essentially excited by the second-order diffraction light of wavelength λ/2 co-existing in the red light. Real upconversion PL from GQDs is observed under excitation with a femtosecond pulsed laser, implying that coherent photons with high enough power density can be upconverted into blue light via GQDs. This approach can overcome the limitations by the catalytic growth and transfer of graphene, and make the oxygen-plasma treatment of graphene for the growth of GaN EPI unnecessary.
This material is based upon work supported by the Ministry of Trade, Industry & Energy(MOTIE, Korea) under Industrial Technology Innovation Program. No.10067533 , 'Development of transfer printing equipment for micro LED chip for smart watch application and array transferring'
9:00 PM - ED4.5.03
Liquid-Phase Laser Ablation as a Method to Produce Upconverting Nanomaterials
Rosemary Calabro 1 , Doo Young Kim 1 , Dong-Sheng Yang 1 Show Abstract
1 Chemistry, University of Kentucky, Lexington, Kentucky, United States
Upconverting luminescent nanoparticles show promising uses in targeted drug delivery, bio-imaging and sensing, solar-energy harvesting, and security applications, among others. One common type of upconverting material is composed of a NaYF4 matrix with optically active trivalent lanthanide ions substituted for Y. This type of material utilizes the energy transfer upconversion mechanism where a Yb3+ sensitizer absorbs 980 nm photons and transfers its energy to an activator ion (Er3+, Nd3+, Dy3+, Ho3+, and Tm3+). Although thermal decomposition, coprecipitation, and solvothermal synthesis have widely been used for producing upconverting nanoparticles, these methods have limitations of toxic byproducts, high reaction temperatures, long reaction times, and/or poor control of morphology. We report liquid-phase laser ablation synthesis of NaYF4:Yb3+/Er3+ nanoparticles with various Yb3+/Er3+ ratios. In this synthesis, a target material is produced through coprecipitation, followed by annealing at 600 °C and then 532 nm pulsed nanosecond laser ablation in water. The laser causes the formation of plasma plumes that quickly expand, cool and condense into particles. The resultant particles show stronger emission at 652 and 669 nm and weaker bands at 407, 488, 523, 544, 556 nm. These emissions can easily be assigned to various atomic transitions of the Er3+ ion. Our experiments show that the Yb3+/Er3+ ratios and laser ablation parameters (laser power and wavelength as well as laser ablation duration) affect the upconversion efficiency, chemical structures, and sizes of the nanoparticles.
9:00 PM - ED4.5.04
Crystal Structure Features and Luminescent Properties of the Copper-Doped Ca-Eu Apatite
Mariam Pogosova 1 , Fardad Azarmi 1 2 Show Abstract
1 Center for Design, Manufacturing & Materials, Skolkovo Institute of Science and Technology, Moscow Russian Federation, 2 Mechanical Engineering Department, North Dakota State University, Fargo, North Dakota, United States
Inorganic pigments are known forthousands ofyears but there are still many areas remained forfuture investigation. Todays, pigments are widely used anywhere — since, almost every artificial object is colored. Therefore, huge amounts of different pigments are produced every year. Contemporary pigments are toxic whichlimits their implementation. Unfortunately, used pigments cannot be further recycled. In addition to this, modern technologies demand functionalized materials. Thus, modern pigments required to be nontoxic,with high qualities such as color stability, stability to the environmental factors, etc. and additional functional features.
Pigments based on the copper-doped apatite-type materials were discovered in 2001 with copper-doped strontium hydroxyapatite, which exhibit bright purple color. After that, the copper-doped barium and calcium hydroxyapatites were successfully achieved (with blueand magenta colors, respectively). It was foundfurther that the additional apatite-matrix modification results in the color change: copper-doped calcium-lithium, calcium-yttrium, calcium-bismuth, and calcium-lanthanum apatites are vine-red, khaki, sand yellow and pink, respectively. It wasestablished recentlythat two types of chromophore exist within copper-doped apatite matrix:
1. Intrachanneloxocuprate anion [O-Cu-O]—which is formed inside the hexagonal channels of apatite structure, presents in all mentioned apatite-type pigments;
2. Copper ion at the Ca(2) position, which is formed in the hexagonal channel’s walls, additionally presents in copper-doped calcium-lithium, calcium-yttrium, calcium-bismuth, and calcium-lanthanum apatites;
The combination of luminescent properties and stable color is realized in current work. Europium- and copper-doped calcium apatite was synthesized via solid state method. Europium-and-copper-doped materials demonstrate pink color and unusual luminescent properties, which are connected with the low symmetry crystal field influence. Chromophore and luminophore formation was analyzed and described. Conclusions are based on the data obtained from luminescent, Raman and diffuse reflectance spectroscopy results and the XRD phase analysis.
9:00 PM - ED4.5.05
NIR-to-NIR Upconversion Nanoparticle Applications in Security Printing, Fingerprint Imaging and Beyond
Aravind Baride 1 , Jeevan Meruga 2 , William Cross 2 , Jon Kellar 2 , Paul May 1 Show Abstract
1 , University of South Dakota, Vermillion, South Dakota, United States, 2 MET, South Dakota School of Mines and Technology, Rapid City, South Dakota, United States
Upconversion is a unique photo-physical phenomenon where absorption of multiple low-energy photons results in emission of high energy photons. Host nanocrystals doped with lanthanide ions are the most efficient upconversion materials. Upconversion nanoparticles have specific advantages in bio-imaging applications, because of greater tissue penetrability of NIR excitation light. In addition to bio-imaging, upconversion nanoparticles have been proposed for security printing applications. However, these systems require high excitation power density to achieve adequately bright luminescence, and the use of high excitation powers raises safety concerns. Therefore, more efficient upconverters are required that luminesce under relatively moderate excitation power density. In this work, we produce efficient and spectrally pure NIR (980nm)-to-NIR (800nm) upconverters that exhibit adequate brightness under moderate (50 mW/cm2) excitation power density. This is achieved by altering the doping composition of Yb/Tm in β-NaYF4 host crystals in conjunction with the use of CCD cameras, which have high sensitivity at 800 nm. The optimized NIR-to-NIR upconversion nanocrystals are used to demonstrate security printing and finger print imaging applications. The images of the NIR-to-NIR upconversion were captured exciting with power densities as low as 50 mW/cm2. This excitation power density is at least an order of magnitude lower than that is used to capture NIR-to-Vis (green) upconversion produced by Yb/Er doped upconversion nanoparticles. The advantage of using NIR-to-NIR UCNPs is that the printed images can be captured irrespective of type of background, e.g. white paper or dark paper. Because both the excitation (980 nm) and emission (800 nm) wavelengths fall within the biological window, these nanocrystals would be an ideal candidates for bio-imaging applications as well.
9:00 PM - ED4.5.06
Core-Shell Nd3+-doped Upconversion Nanoparticles with Enhanced Luminescence Properties for Bioanalytical Applications
Lisa Wiesholler 1 , Bettina Grauel 2 , Antje Baeumner 1 , Ute Resch-Genger 2 , Thomas Hirsch 1 Show Abstract
1 , University of Regensburg, Regensburg Germany, 2 , BAM Federal Institute for Materials Research and Testing, Berlin Germany
Lanthanide doped NaYF4 upconversion nanoparticles (UCNPs), excited in the near-infrared (NIR), are attractive in biological applications because of minimized luminescence background signal and deep tissue penetration. For many analytical techniques colloidal stability in aqueous solutions as well as small particle sizes are desirable. When the particles get smaller, the surface-to-volume ratio of these nanospheres is increased and therefore the upconversion efficiency decreases significantly due to non-radiative decay of the excited states of the lanthanide ions at the solvent-particle-interface. In principle, this can be overcome by stronger power density for the excitation of the particles. Nevertheless, 980 nm NIR excitation, which is mandatory for the most efficient UCNP-systems relying on Yb3+ sensitation, gets also absorbed by water. Heating of the sample will be the consequence.
Here we present a strategy to overcome these limitations. A synthesis of core-shell particles with Nd3+/Yb3+ doping in the shell and Yb3+/Er3+ or Yb3+/Tm3+ doping in the core was established to shift the excitation wavelength from 980 nm to 808 nm. By 808 nm excitation the overheating in aqueous solutions is minimized. The synthesis results in a large batch of up to 2 g of monodisperse high quality particles with diameters in the range of 30 nm and pure hexagonal crystal structure with oleic acid on the surface. A systematic study of the doping ratios and the core- and shell-thickness regarding the luminescence properties was performed. For all systems a significant enhancement in the upconversion luminescence by shifting the excitation wavelength to 808 nm was found. A growth of an additional inert shell on top of the particles minimizes the influence of surface defects and dangling bonds. Even thin shells of NaYF4 with an average thickness of 1 nm enhanced the intensity of the green emission by a factor of eight compared to the core particle excited by 980 nm.
The particles were transferred into aqueous solutions by a ligand exchange protocol and modified by a polymer coating. Colloidal stability in aqueous systems was confirmed by dynamic light scattering as well as by zeta potential measurements.
These small, monodisperse core-shell-shell particles with enhanced upconversion lumininescence can be easily functionalized with organic dyes for energy transfer-based sensors, or with bioreceptors for theranostic applications.
9:00 PM - ED4.5.07
The Dispersion Stability of Upconverting Nanoparticle Inks
Khadijah Cessac 3 , Paul May 2 , William Cross 1 , Jeevan Meruga 1 , Aravind Baride 2 , Jon Kellar 1 Show Abstract
3 Chemistry, Southern University and A&M College, Baton Rouge, Louisiana, United States, 2 Chemistry, University of South Dakota, Vermillion, South Dakota, United States, 1 , South Dakota School of Mines, Rapid City, South Dakota, United States
Being knowledgeable about ink stability and behavior under printing conditions is important because it allows scientists and companies to continuously learn key aspects to bettering ink formulations. An upconverting nanoparticle (UCNP)-based ink formulation was evaluated in the present investigation. In order for these inks to be used commercially in security printing, certain boundaries and expectations must be met. For example, water-based inks are desired because they are easy to produce, are environmentally friendly, and most importantly, are cost effective. While the security advantages of upconverting inks are quite beneficial, there is little literature on stability testing of these inks. Therefore, the purpose of this research was to first formulate a water-based ink that had suitable surface tension and viscosity for inkjet printing purposes, and then create a method to determine the stability of these UCNP inks. The surface tension and viscosity of the ink base were 40-41 mN/m and 1.0 cP, respectively. The stability testing included of surface tension and viscosity testing over time, and also a dispersion analysis of 0.3 wt% and 0.6 wt% nanoparticle inks in three storage conditions: cool (~4 C), warm (60 C), and ambient temperatures. To further analyze the observed values, comparison to thermal gravimetric analysis (TGA) was used as a reference.
9:00 PM - ED4.5.08
The Effects of Rapid Energy Migration on Upconversion Luminescence in β-NaYF4:Yb,Er Nanomaterials
Md Yeathad Hossan 1 , Molly Cleland 2 , John David Suter 1 , Mary Berry 1 , Paul May 1 Show Abstract
1 , University of South Dakota, Vermillion, South Dakota, United States, 2 Chemistry, Chadron State College, Chadron, Nebraska, United States
The NIR-to-visible upconversion (UC) quantum efficiency of β-NaYF4:Yb,Er has been reported to be as high as 7% in bulk materials.1 However, the quantum efficiency drops sharply as the crystal-size decreases to the nanoscale,2 presumably due to increased surface quenching effects. One effective way to minimize surface quenching is to add a passive shell of optically-inert un-doped material onto the core UC nanocrystals. We have studied the optical properties of core and core-shell β-NaYF4:Yb, Er UC nanocrystals to test models of the precise nature of the nanoscale effect and its relationship to surface quenching. The materials were characterized by TEM, absorbance spectroscopy, steady-state and time-resolved emission spectroscopy. A layer of inert-shell enhances the emission intensity as well as changes the time dependence of each emission wavelength. Our models suggest that the enhancement results from reducing surface quenching of Yb3+ (2F5/2) and Er3+ (4I11/2), energy levels which participate in rapid energy migration across tens of nanometers.3 Energy migration at the 1 micron energy level creates an equilibrium between interior and surface sites with the consequence of rapid depletion of the Yb3+ (2F5/2) and Er3+ (4I11/2) reservoir states throughout the crystal, which is then reflected in the rapid dynamics of green, blue, and red emission in nanocrystals.
(1) Anderson, R. B.; Smith, S. J.; May, P. S.; Berry, M. T. The Journal of Physical Chemistry Letters 2014, 5, 36.
(2) Boyer, J.-C.; van Veggel, F. C. J. M. Nanoscale 2010, 2, 1417.
(3) Fischer, S.; Bronstein, N. D.; Swabeck, J. K.; Chan, E. M.; Alivisatos, A. P. Nano Letters 2016.
9:00 PM - ED4.5.09
Real-Time Spectroscopic Monitoring of the Synthesis of Core/Shell β-NaYF4 Nanocrystals with Active and Passive Shells
Lance Kotter 2 , Paul May 1 , John Suter 1 , Md Yeathad Hossan 1 , Mary Berry 1 Show Abstract
2 Chemistry, University of Jamestown, Jamestown, North Dakota, United States, 1 , University of South Dakota, Vermillion, South Dakota, United States
Real-time spectroscopic monitoring (RTM) of upconversion luminescence is applied to study the reaction mechanism of the synthesis of core β-NaYF4:17% Yb, 3% Er nanocrystals and to subsequent shell addition to that core. Real-time spectroscopic monitoring of core synthesis and shell addition provides the ability to precisely characterize the time-evolution of the various stages of the reaction, show the transition between those stages, and accurately determine when the reaction has gone to completion (thereby avoiding unwanted ripening). Based on RTM data, our group has previously developed a quantitative model for describing the dynamics of nanoparticle growth and phase change during the synthesis of core β-NaYF4:17% Yb, 3% Er nanocrystals (J. Phys. Chem. C 2014, 118, 13238; J. Phys. Chem. C 2016, 120, 9482). Here, we extend the RTM studies to characterize the kinetics of shell formation on the core nanoparticle. Passive shells serve the purpose of increasing luminescence efficiency through reduced surface quenching. Active shells can also provide additional functionality by, for example, enabling excitation of luminescence at an alternative wavelength. Here, we characterize the kinetics of the addition of both a passive β-NaYF4 shell and an active β-NaYF4:10% Yb, 10% Nd to core β-NaYF4:17% Yb, 3% Er nanocrystals. The desired shell material is provided in the form of sacrificial α-phase nanoparticles following the method of van Veggel (J. Am. Chem. Soc. 2012, 134, 11068).
9:00 PM - ED4.5.10
Triplet-Triplet Annihilation Upconversion in Thin Film Polystyrene Copolymers
Abagail Williams 1 , Kaden Stevens 1 , Erin Crater 1 , Joseph Lott 1 Show Abstract
1 , The University of Southern Mississippi, Hattiesburg, Mississippi, United States
Interest in triplet-triplet annihilation upconversion (TTA-UC) has rapidly grown since its first demonstration is solid-state materials nearly a decade ago. Unlike other upconversion processes, which require higher-power coherent light, TTA can be used to transform low energy photons from low-power non-coherent light sources (i.e. sunlight) into higher energy light. Therefore, TTA-UC can be used in a wide range of applications from photovoltaics to bio-imaging. The current repertoire of mechanically robust materials capable of TTA-UC is limited. In addition, at low chromophore concentrations these materials suffer from low upconversion efficiencies due to limited molecular mobility. However, simply increasing the dye concentrations leads to adverse effects from aggregation. This work aims to mitigate these affects by copolymerizing 9-phenyl-10-(4-vinylphenyl)anthracene with styrene and employing processing methods aimed toward minimizing aggregation. Random poly(styrene-co-(9-phenyl-10-(4-vinylphenyl)anthracene)) (poly(St-co-DPA)) polymers were synthesized and their optical and thermal properties were analyzed using UV-vis to determine dye loading concentrations, fluorescence spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Upconversion properties of the polymers in conjunction with palladium octaethylporphryin (PdOEP) are analyzed in solution. Thin films comprised of the poly(St-co-DPA) and PdOEP were prepared using a spin casting method. Upconversion performance of the films was explored as a function of chromophore concentrations, and time resolved fluorescence measurements were used to probe the upconversion kinetics and efficiency of energy transfers.
9:00 PM - ED4.5.11
Distance Dependence of Gold-Enhanced Upconversion Luminescence in Au/SiO2/Y2O3:Yb3+, Er3+ Nanoparticles
W Ge 1 , XR Zhang 2 , M Liu 1 , ZW Lei 1 , Y.L. Lu 1 Show Abstract
1 Department of Materials Science & Engineering, University of Science and Technology of China, Hefei, Anhui, China, 2 , University of Science & Technology, Hefei, Anhui, China
W. Ge,1 X. R. Zhang,2 M. Liu, 1,* Z. W. Lei, 1 and Yalin Lu 1,2,3, *
1 CAS Key Laboratory of Materials for Energy Conversion; Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, P. R. China
2 Hefei National Laboratory for Physical Sciences at the Microscale, Hefei 230026, P. R. China
3 Laser Optics Research Center, Physics Department, United States Air Force Academy, CO 80840, USA
Key words: Plasmon coupling, Core/spacer/shell, Rare earth, Luminescence, Decay trace
We report a localized surface plasmon enhanced upconversion luminescence in Au/SiO2/Y2O3:Yb3+,Er3+ nanoparticles when excited at 980 nm. By adjusting the silica spacer’s thickness, a maximum 9.59-fold enhancement of the green emission was obtained. Effect of the spacer distance on the Au-Y2O3:Yb3+, Er3+ green upconversion mechanism was numerically simulated and experimentally demonstrated. In theory for radiative decay and excitation rates, they can be largely enhanced at the spacer thicknesses of less than 70 and 75 nm, respectively, and the quenching can be caused by the non-radiative energy transferring at the distance of less than 55 nm.
9:00 PM - ED4.5.12
Production and Characterization of Tb3+/Yb3+ Co-Activated AlN Thin Films for Down-Conversion Applications in Photovoltaic Cells
Karem Tucto Salinas 1 , Loreleyn Flores Escalante 1 , Jorge Guerra 1 2 , Amaru Toefflinger 1 , Rolf Grieseler 3 , Andres Osvet 2 , Miroslaw Batentschuk 2 , Roland Weingartner 1 Show Abstract
1 , Pontificia Universidad Catolica del Peru, Lima Peru, 2 , Institute of Materials for Electronics and Energy Technology (I-MEET), Friedrich-Alexander-Universität Erlangen–Nürnberg, Erlangen Germany, 3 , Institute of Materials Engineering and Institute of Micro and Nanotechnologies, Technische Universität Ilmenau, Ilmenau Germany
This work investigates down-conversion effect of Tb3+-Yb3+ co-doped aluminum nitride thin films at different dopant concentrations and annealing temperatures. Such photon energy conversion due to the transfer mechanisms between Tb3+ and Yb3+ is considered for its potential application in photovoltaic systems.
The thin films are deposited on silicon substrates by radio frequency magnetron sputtering. The structure and the luminescence properties of the films are investigated by using X-ray diffraction, Infrared absorption, cathodo- and photoluminescence spectroscopies. The concentration of these rare earths and temperature of annealing treatment influence the crystallization and phase formation of the host matrix. The efficient conversion of absorbed high energy photon into two emitted low energy photons is examined for different concentration of rare earths and annealing temperatures by means of extensive cathodoluminescence and life-time measurements.
9:00 PM - ED4.5.13
Red-Emitting Magnetic Mesocomposites of Ag-Decorated Fe3O4@SiO2 Nanoflowers Coated with Y2O3:Eu3+: Study of Iron Oxide Induced Luminescence Quenching
Latif Khan 1 , Luis Zambon 1 , Rodrigo Rodrigues 1 , Zahid Khan 1 , Hermi Brito 1 , Diego Muraca 2 3 Show Abstract
1 , University of Sao Paulo, Sao Paulo Brazil, 2 , Universidade Federal do ABC, Sao Paulo Brazil, 3 , UNICAMP - Universidade Estadual de Campinas, Sao Paulo Brazil
The preparation of bifunctional mesocomposites, co-assembling magnetic iron oxides or Ag-decorated Fe3O4@SiO2 nanoflowers and red-emitting Y2O3:Eu3+ entity into single nanostructures were reported through a new facile method. The magnetic properties of the iron-oxide@Y2O3:Eu3+, Fe3O4@SiO2@Y2O3:Eu3+ and Fe3O4@SiO2-Ag@Y2O3:Eu3+ nanomaterials are predominantly due to the iron oxide core particles, showing nonsuperparamagnetic behavior at room temperature as displayed by the MH and ZFC/FC magnetization curves. The Eu3+ doped Y2O3 exhibits well-defined narrow emission bands in the visible spectral range, rendering the bifunctional nanomaterials efficient red emission color. The iron oxides are usually luminescent quencher. Therefore the photoluminescence properties based on the emission spectral data and luminescence decay curves were studied. In addition, experimental intensity parameters (Ωλ), lifetimes (τ), emission quantum efficiencies (η) as well as radiative (Arad) and non-radiative (Anrad) decay rates were also calculated, in order to probe the local chemical environment of the Eu3+ ion and better understand the phenomena of iron oxide induced luminescence quenching. The higher value of the emission quantum efficiency for the α-Fe2O3@Y2O3:Eu3+ (1 mol%) (η = 74 %) among all the luminescent and magnetic mesocomposites suggests that α-Fe2O3 is induced lower luminescence quenching in Eu3+ ion then Fe3O4/γ-Fe2O3. Though, the thin layer of SiO2 spacer is caused of increase the quantum efficiency, whereas the Ag is further enhaunced the luminescence quenching by energy transfer form Eu3+ ion to the Ag nanoparticles, leading to lower emission quantum efficiency for the Fe3O4@SiO2-Ag@Y2O3:Eu3+ (1 mol%) material (η = 40 %) when compared to the Fe3O4@SiO@Y2O3:Eu3+ (1 mol%) counterpart one. These novel Eu3+ mesocomposites may act as a red emitting layer for magnetic and light converting molecular devices.
9:00 PM - ED4.5.14
A Hybrid Molecular-Nanocrystal Platform for Photon Upconversion
MingLee Tang 1 , Zhiyuan Huang 1 , Xin Li 1 , Melika Mahboub 1 Show Abstract
1 , University of California, Riverside, Riverside, California, United States
Third generation photovoltaics are inexpensive modules that promise power conversion efficiencies (PCEs) exceeding the thermodynamic Shockley-Queisser limit, perhaps by using up- or down-converters, intermediate band solar cells, tandem cells, hot carrier devices, or multi-exciton generation (MEG). Here, I introduce a hybrid platform comprised of semiconductor nanocrystals and organic semiconductor molecules that can efficiently upconvert light of visible and infrared wavelengths, at excitation densities below the solar flux. For example, colloidally synthesized core-shell lead sulfide -cadmium sulfide nanocrystals (NCs), in combination with tetracene derivatives, absorb near infrared (NIR) light and emit visible light at 560 nm with an upconversion quantum yield (QY) of 8.4 ± 1.0 %. This is achieved with 808 nm cw excitation at 3.2 mW/cm2, approximately three times lower than the available solar flux. The molecular and nanocrystal engineering here paves the way towards utilizing this hybrid upconversion platform in photovoltaics, photodetectors and photocatalysis.
Wounjhang Park, University of Colorado
John Capobianco, Concordia University
Andrew Ferguson, National Renewable Energy Laboratory
Dayong Jin, University of Technology, Sydney
Nano Convergence | Korea Nano Technology Research Society
National Renewable Energy Laboratory
ED4.6: Theory and Spectroscopy
Thursday AM, April 20, 2017
PCC North, 100 Level, Room 128 A
9:30 AM - *ED4.6.01
Real-Time Spectroscopic Monitoring and Mathematical Modelling of the Synthesis and Modification of NaYF4 Nanocrystals
Paul May 2 , Paul May 1 , Mary Berry 1 Show Abstract
2 Mathematics, South Dakota State University, Brookings, South Dakota, United States, 1 , University of South Dakota, Vermillion, South Dakota, United States
In order to understand the growth dynamics of doped-NaYF4 upconversion (UC) nanocrystals we have combined real-time spectroscopic monitoring of the upconversion luminescence with extraction of aliquots from the reaction mixture for electron microscopy. We have also developed a mathematical model that accurately describes the timeline for crystal growth, including the α→β phase transition that occurs during the synthesis. The model describes the growth dynamics in terms of crystal surface energies, lattice energies, and rate constants for growth and dissolution with reference to an Ostwald ripening model developed by Talpin et al. 
In the heat-up method, as employed in our laboratory, all precursor salts are combined in solvent and heated to 310 oC, at which temperature, the reaction mixture is maintained for approximately one hour before isolating the final β-phase product.  Following a very reproducible heat-up period of 30 minutes, low-level UC luminescence is immediately evident and TEM reveals the presence of copious small (~4-5 nm) α-phase particles. Following the heat-up time, there is a variable-time-length period (62 ± 22 min) of relative stasis in the UC luminescence intensity and in the nature of the extracted aliquots, which continued to exhibit pure α-phase crystals. Following this time interval is a period of rapid phase transition (α-to-β) accompanied by a rapid increase in UC intensity. This third period is very reproducibly accomplished in (10 ± 2 min). In the mathematical model presented here, the α particles formed during the heat-up period undergo Ostwald ripening and a slight broadening in size distribution. The α particles at the leading edge of the distribution reach a critical size where a phase transition from α to β is thermodynamically favored. Upon conversion to the less soluble β phase, the β particles begin to consume the smaller α particles, growing rapidly themselves and forcing the α-particle distribution to recede from that critical size.
The simple mathematical model described above accurately reproduces the experimentally-observed timing of the reaction stages and the evolving size distribution of the nanocrystals, suggesting the model may provide a platform for understanding how the dynamics change with solvent and surfactant concentration and for understanding the dynamics of shell addition.
 Talapin, et al., J. Phys. Chem. B 2001, 105, 12278-12285.  Suter et al., J. Phys Chem. C, 2014, 118, 13238–13247.
10:00 AM - ED4.6.02
Energy Transfer Dynamics in Dye-Sensitized Lanthanide-Doped Nanoparticles for Solar Upconversion
David Garfield 1 , Nicholas Borys 2 , Emory Chan 2 , Bruce Cohen 2 , P James Schuck 2 Show Abstract
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Lanthanide-doped upconverting nanoparticles (UCNPs), with long-lived, ladder-like excited states capable of efficiently converting multiple low-energy photons into a higher-energy photon, show unique promise across a range of applications from single-molecule imaging1 to solar energy harvesting. Three key attributes limiting their performance, however, are miniscule absorption cross-sections, narrow absorption bandwidths, and low quantum yields. To overcome these shortfalls, organic dye molecules with significantly stronger optical absorption can be attached to the surfaces of the UCNP to form hybrid antenna-upconverter architectures whereby optical energy is absorbed by the dye molecules and funneled to the lanthanide ions within the UCNP 2, 3, greatly enhancing both the effective absorption cross-section and bandwidth. However, the precise nature of the dye-UCNP energetic coupling mechanism has not been investigated, and while promising, this hybrid system suffers from poor photostability and rapid degradation. Using a comprehensive suite of steady-state and time-resolved spectroscopies on model dye-UCNP complexes, we elucidate several key aspects of the energy transfer mechanism, revealing critical insight and design rules towards maximizing the coupling efficiency and photostability in these systems. Evidence herein indicates that the excited triplet state of the dye mediates efficient energy transfer between the dye molecules and the UCNPs, where intersystem crossing between the singlet and triplet manifolds in the dye is enhanced by the heavy atoms of the UCNP. Because of the increased role of long-lived triplet states, oxygen-mediated quenching was suspected as a primary factor in photodegradation, and various oxygen exclusion techniques have yielded a much more stable system, with vastly improved upconversion performance. We report an integrated upconversion enhancement of 105 when exciting the dye molecule versus exciting the absorbing lanthanides directly at their respective peak absorptions. Furthermore, we report external quantum yields of 5.17% for dye-coated 12nm UCNPs, roughly 60-fold higher than the previous record for unshelled sub-20nm UCNPs. These improvements hold dramatic promise from solar efficiency improvements to background-free biological imaging.
1 Gargas, D. J.; Chan, E. M.; Ostrowski, A. D.; Aloni, S.; Altoe, M. V. P.; Barnard, E. S.; Sanii, B.; Urban, J. J.; Milliron, D. J.; Cohen, B. E.; et al. Engineering Bright Sub-10-nm Upconverting Nanocrystals for Single-Molecule Imaging. Nat. Nanotechnol. 2014, 9, 300−305.
2 Zou, W. Q., Visser, C., Maduro, J. A., Pshenichnikov, M. S. & Hummelen, J. C. Broadband dye-sensitized upconversion of near-infrared light. Nat. Photonics 2014, 6, 560–564.
3 Chen, G.; Damasco, J.; Qiu, H.; Shao, W.; Ohulchanskyy, T. Y.; Valiev, R. R.; Wu, X.; Han, G.; Wang, Y.; Yang, C.; Agren, H.; Prasad, P. N. Nano Lett. 2015, 15, 7400–7407.
10:15 AM - ED4.6.03
Effect of Nanoparticle Size on Time-Resolved Upconversion Resonance Energy Transfer
Verena Muhr 1 , Christian Wuerth 2 , Marco Kraft 2 , Antje Baeumner 1 , Ute Resch-Genger 2 , Thomas Hirsch 1 Show Abstract
1 , University of Regensburg, Regensburg Germany, 2 , BAM Federal Institute for Materials Research and Testing, Berlin Germany
Upconversion nanoparticles (UCNPs) offer new strategies for luminescence-based sensing. The potential of UCNPs to serve as donors in Förster resonance energy transfer (FRET) applications is intensely discussed, owing to their anti-Stokes shifted narrow emission bands, chemical inertness, photostability, and long luminescence lifetimes (> 100 µs).
Since FRET is distance dependent, the diameter of the particles is expected to affect the FRET efficiency. In order to identify the ideal particle architecture for FRET-based applications, we performed a systematic spectroscopic study of the influence of the UCNP size on the energy transfer using the organic dyes rose bengal and sulforhodamine B acting as model FRET acceptors for the green upconversion emission. High-quality Yb,Er-doped UCNPs with precisely controlled diameters between 10 and 43 nm were prepared using a high temperature synthesis. The monodisperse, oleate-capped particles were directly modified with the organic dyes by a two-step ligand exchange procedure, resulting in the shortest possible donor-acceptor distance. Successful FRET was demonstrated through the simultaneous drastic reduction of the luminescence intensity and the lifetime of the respective upconversion emission. In contrast to intensity measurements, time-resolved studies on both donor and acceptor luminescence allowed for the elimination of dependencies on excitation power density and particle concentration and for the discrimination between inner filter effects and FRET. The maximum FRET efficiency was observed at a particle diameter around 21 nm, which was attributed to an increasing fraction of the total amount of Er3+ donors inside the UCNPs being within Förster distance. Smaller UCNP diameters did not further improve the FRET efficiency, demonstrating the growing contribution of opposing effects, like the competition of non-radiative surface deactivation, at larger surface-to-volume ratios.
This comprehensive understanding of energy transfer processes at the surface of UCNPs is essential for the rational design of upconversion FRET platforms for applications in sensing, imaging, and theranostics with improved sensitivity, reliability and comparability. The energy transfer can also be utilized to shift the luminescence emission by the choice of the organic dye in order to explore applications that require specific emission wavelengths due to interfering substances, while still making use of the advantages of near-infrared excitation.
10:30 AM - ED4.6.04
Core/Shell Structured Upconversion Nanoparticles with Controllable Interfacial Energy Migration for Spectral and Lifetime Multiplexing
Ling-Dong Sun 1 , Hao Dong 1 , Chun-Huan Yan 1 Show Abstract
1 , Peking University, Beijing China
Lanthanide upconversion nanoparticles are especially attractive for optical multiplexing due to the flexible tunability of upconversion emission colors. However, effective confinement of energy migration in upconversion nanoparticles for releasing excitation dependent emissions still remains a great challenge. Here, we describe a series of core/shell structured upconversion nanoparticles with controllable interfacial energy migration between optically-inert and optically-active layers, which are integrated with different functionality. Importantly, these core/shell structured nanoparticles can give out distinctive emissions depending on excitation wavelength and power density. Such spectral correlation of near-infrared excitation enables a technology to differentiate the excitation source by upconversion emission color. Aside from spectral code, emission lifetime has been introduced into the core/shell structured nanoparticles to offer more code information, i.e., the nanoparticles can exhibit different emission color and lifetime in microseconds or milliseconds under varied excitation conditions. With these code-intensive upconversion nanoparticles, multiplexed high-resolution fingerprint imaging and tailing luminescence imaging were vividly demonstrated. The spectral and lifetime encoding strategy greatly broadens the scope of upconversion nanoparticles and other optical materials for multiplexing studies.
10:45 AM - ED4.6.05
Interface Energy Transfer Modeling on Alkali Rare-Earth Fluoride Related Core Shell Nanostructures—For Future Multi-Layer Core Shell Luminescence Materials
Bolong Huang 1 Show Abstract
1 , Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong Hong Kong
The development of highly controllable and energy efficient novel upconversion (UC) luminescence materials is imporant in the field of luminescence science. Core-shell nanostructured Lanthanide materials demonstrated tremendous potential in this regard due to their novel electronic structures. Their upconverted energy transfer dynamics and UC luminescence mechanisms as well as performance improvenemts require extensive studies.
Here we focus on electronic and optical properties at the interface of core-shell lanthanide materials with modulated by defect and impurity levels responsible for UC luminescence. The chemical trends of modulations are predicted by orbital-corrected ab-inito theoretical studies. By selective doping and/or native point defects engieering, we design the tailor-made interface models for UC nanoparticles to obtain the specific electronic structures responsible for the luminescence. Their photochemical properties and factors governing the UC luminescence will be analyzed. The chemical trends to improve the energy conversion will also established based on physical approaches.
Based on the energy conversion modelling to dictate their UC luminescence performance, we will unveil the physicochemical nature and improve the design of the new generation UC luminescence materials with higher intensity, longer duration time and improved greener energy efficiency.
We will discuss the band offsets and alignment for the interface system of heterogeneous core-shell of α-NaYF4. This work is a further step on our recent published work [J. Phys. Chem. C. 120 18848 (2016)]. Furthering on the discussions about interface bonding, band offsets, and formation energies, we figured out the significance of interface that play significant role for electrons transport to higher efficiency in energy conversions for upconversion luminescence. We also find out the initial surface formation energy that accommodates the shell materials for the core part. This is the determinant key size that tells the smallest sized core materials. We found the energy area density with related to core/shell thickness ratio follows the trend of Boltzman sigmoidal growth function. Based on the zero point energy area density, the smallest size of α-NaYF4 as core to absorb the shell materials such as SiO2 is approximately 4.59 Å in radius. This means that a critical supercell sized with 1.70×1.70×1.70 in spherical or 2.13×2.13×2.13 roughly in simple cubic approximation limits exists for forming the core to stably absorbing the first layer of shell. By the trend of physical chemistry, the calculations with density functional theory can suggest us in experiments that how the multi-layered core-shell structure is formed starting from the very beginning within minimum size. With this work, a route has been paved towards systematic study the energy conversion at the interface and to unveil the energy transfer mechanism in core-shell systems.
ED4.7: Applications of Organic Upconversion Materials
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 128 A
11:30 AM - *ED4.7.01
The Application of Photochemical Upconversion to Photovoltaics
Timothy Schmidt 1 Show Abstract
1 , UNSW, Sydney, New South Wales, Australia
Photovoltaic solar energy conversion devices waste a major part of the incident energy. For photon energies higher than the bandgap, the excess energy is converted into heat by thermalization of excited charge carriers, while light with sub-bandgap energies cannot be harvested at all. These effects dominate the fundamental losses of single-threshold photovoltaic (PV) devices, and restrain their conversion efficiency to 34% under the AM1.5G spectrum.
Sub-bandgap losses can be remedied by the application of photonic upconversion, whereby transmitted light is converted to light of higher energy, which can then be harvested by the cell and contribute to current generation. Based on detailed balance considerations it has been shown that upconversion can boost the maximum energy conversion efficiency to about 43% under one sun for a solar cell with a bandgap of 1.76 eV, and >50% under solar concentration Crystalline silicon cells could still reach about 38%, although the potential gain is smaller than for the high-bandgap devices.
An active field of research is the exploitation of triplet-triplet-annihilation in organic chromophores to achieve upconversion (TTA-UC). TTA-UC exploits the longevity of molecular triplet states. However, as the longevity diminishes with energy, TTA-UC is most readily applied to solar cells with bandgaps above about 1.5 eV. This talk will summarize the state-of-the-art in TTA-UC and its application to solar energy conversion.
Y. Y. Cheng, B. Fuckel, R. W. MacQueen, T. Khoury, Rgcr Clady, T. F. Schulze, N. J. Ekins-Daukes, M. J. Crossley, B. Stannowski, K. Lips, and T. W. Schmidt, "Improving the light-harvesting of amorphous silicon solar cells with photochemical upconversion," Energy & Environmental Science 5 (5), 6953-6959 (2012).
T. F. Schulze, J. Czolk, Y. Y. Cheng, B. Fuckel, R. W. MacQueen, T. Khoury, M. J. Crossley, B. Stannowski, K. Lips, U. Lemmer, A. Colsmann, and T. W. Schmidt, "Efficiency Enhancement of Organic and Thin-Film Silicon Solar Cells with Photochemical Upconversion," Journal of Physical Chemistry C 116 (43), 22794-22801 (2012).
Yuen Yap Cheng, Andrew Nattestad, Tim F. Schulze, Rowan W. MacQueen, Burkhard Fückel, Klaus Lips, Gordon G. Wallace, Tony Khoury, Maxwell J. Crossley and Timothy W. Schmidt "Increased upconversion performance for thin film solar cells: a trimolecular composition," Chem. Sci. 7 (1), 559-568 (2016)
12:00 PM - ED4.7.02
Intermediate Band Dye-Sensitised Solar Cells Utilising Triplet-Triplet Annihilation
Andrew Nattestad 1 , Catherine Simpson 2 1 , Rowan MacQueen 3 4 , Sameh Hamzawy 1 , Joe Gallaher 4 , Laszlo Frazer 4 , Tracey Clarke 5 1 , Attila Mozer 1 , Timothy Schmidt 4 Show Abstract
1 , University of Wollongong, Fairy Meadow, New South Wales, Australia, 2 Chemistry, Australian National University, Canberra, Australian Capital Territory, Australia, 3 , Helmholtz Zentrum Berlin, Berlin Germany, 4 Chemistry, UNSW, Sydney, New South Wales, Australia, 5 Chemistry, University College London, London United Kingdom
The inability to effectively utilise red-NIR light has been identified as a substantial challenge towards further enhancement of Dye-sensitised Solar Cell (DSC) efficiency. To this end, third generation concepts may offer a means to overcome this limitation, including multi-photon based approaches. The intermediate band concept can be applied to DSCs using the phenomenon of Triplet-Triplet Annihilation (TTA). This results in a device capable of generating photocurrent via two mechanisms, the first being the conventional one (photoexcitation of a bound dye (1), followed by charge injection). The second mechanism involves low energy photons being harvested by a second dye (2), which then undergoes intersystem crossing. Following this triplet energy transfer to dye 1 can occur. Two triplet state dye 1 molecules can annihilate resulting in a high enough energy state that charge injection can occur. Importantly, in spite of extending the range of spectral sensitivity, this process does not impinge upon the attainable device VOC, substantially increasing the maximum theoretical efficiency of the DSC.
12:15 PM - *ED4.7.03
Photon Upconversion Dye-Sensitized Solar Cells via Self-Assembled Multilayers
Kenneth Hanson 1 2 , Sean Hill 1 , Tristan Dilbeck 1 , Yan Zhou 1 Show Abstract
1 Department of Chemistry & Biochemistry, Florida State University, Tallahassee, Florida, United States, 2 Materials Science & Engineering, Florida State University, Tallahassee, Florida, United States
Photon upconversion by way of triplet-triplet annihilation (TTA-UC) is a compelling strategy for increasing solar cell efficiencies because it can occur even under low intensity, non-coherent, solar irradiation. In this presentation we demonstrate self-assembled bilayers of sensitizer and acceptor molecules on nanocrystalline metal oxide films as a new structural motif for facilitating molecular photon upconversion and directly incorporating TTA-UC into a dye-sensitized solar cell (DSSC). Under light intensities as low as two equivalent suns we demonstrate a 30% increase enhancement in the short circuit current relative to the sum of the sensitizer and acceptor monolayer devices. We will discuss the limitations of the current device and strategies for increasing the TTA-UC DSSC performance.
ED4.8: Novel Inorganic and Organometallic Chromophores for Photon Upconversion
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 128 A
2:30 PM - *ED4.8.01
Framing Upconversion Materials—Fluorescent Metal-Organic Frameworks
Angelo Monguzzi 1 Show Abstract
1 Material Science, Università degli Studi Milano-Bicocca, Milan Italy
The conversion of low-energy photons into radiation of higher energy is useful for bioimaging, 3D displays, photovoltaics and other applications. In particular, upconversion of the infrared portion of the solar spectrum (which is typically not absorbed by the optically active materials used in solar cells and photocatalytic systems) allows additional photons to be harnessed and boosts the efficiency of these devices. For this reason, low power photon up-conversion based on triplet-triplet annihilation (TTA-UC), which has been recently recognized as a potential viable approach towards enhancing the efficiency of sunlight-powered devices through sub-bandgap photon harvesting.
In TTA-UC, two emitter triplets indirectly populated by Dexter energy transfer from a suitable sensitizer, need to collide and experience annihilation within their lifetimes. TTA generates an excited emitter singlet with energy higher than the photon absorbed by the sensitizer, from which up-converted fluorescence is obtained. Since TTA and Dexter transfer undergo through electron exchange mechanism, triplets should come close within ~ 1 nm to allow molecular orbitals overlap. Indeed, efficient TTA-UC relies on molecular diffusion in low-viscosity solutions, allowing high collision rates between chromophores. However, the use of volatile organic solvents is not desirable for practical applications.
This fundamental problem can be solved by the use of condensed chromophore networks. Specifically, TTA-UC has been achieved in nanometric crystalline metal-organic frameworks (MOF) synthesized from metal ions and optically active bridging ligands containing chromophores. Since the triplet exciton diffusion in a crystal depends on the overlap of wavefunctions governing the Dexter energy transfer rate among iso-energetic centers, the highest diffusivity would be realized only under the condition where the chromophores are aligned in a crystalline order with properly controlled mutual orientation. Therefore, taking advantage of the MOFs designability, structural regularity and rigidity, several nanocrystals with different emitter alignments have been studied, with a benchmark combination of emitters and sensitizer. The efficient triplet energy migration and harvesting obtained in these ordered self-assemblies allows for 100% TTA yield under excitation intensity weaker than the sunlight, laying the foundation for realizing sunlight-powered TTA-UC devices. Moreover, very recent results outline a general modelling of the optical excitons photophysics in nano-sized MOFs, and suggest a practical methodology to realize industrially processable nanocomposites for technological applications.
3:00 PM - ED4.8.02
Looking for Molecular Erbium Complexes with Dual Emission for Molecular-Based Upconversion
Bahman Golesorkhi 1 , Yan Suffren 4 , Laure Guénée 2 , Homayoun Nozary 1 , Svetlana Eliseeva 3 , Stephane Petoud 1 , Andreas Hauser 4 , Claude Piguet 1 Show Abstract
1 Department of Analytical and Inorganic Chemistry, University of Geneva, Geneva, Geneva, Switzerland, 4 Department of Physical Chemistry, University of Geneva, Geneva Switzerland, 2 Laboratory of Crystallography, University of Geneva, Geneva Switzerland, 3 , Centre de Biophysique Moléculaire, CNRS UPR 4301, Orléans Cedex 2 France
Due to the wealth of closely spaced exited states that cover the infrared to ultraviolet range, trivalent Er(III) cations have been exploited as activators in linear optics for upconversion operating in nanoparticles and molecules. In order to explore the structural and electronic conditions required for the explicit induction of dual visible/NIR emissions in erbium coordination complexes, a series of mono- and dinuclear Er(III) complexes with polyaromatic tridentate ligands have been synthesized and structurally characterized. Photophysical investigations reveal an unusual dual VIS/NIR Er-centered emission sensitized via ligand excitation. Although the NIR emission arising from the Er(4I13/2→4I15/2) may be classified as ‘standard’, the ligand-sensitized nanosecond green emission occurring at 540 nm (Er(4S3/2→4I15/2)) observed in these Er(III) complexes is much more challenging and rarely reported for coordination complexes possessing high-energy oscillators. Combined with solid-state absorption and transmittance spectra of these Er(III) complexes, the special conditions required for implementing Er-centered upconverted emission in coordination complexes through different mechanisms called as ESA (excited-state absorption) and ETU (energy-transfer upconversion) in mononuclear and dinuclear complexes are discussed.
 Y. Suffren, B. Golesorkhi, D. Zare, L. Guénée, H. Nozary, S. V. Eliseeva, S. Petoud, A. Hauser, C. Piguet, Inorganic Chemistry 2016, 10.1021/acs.inorgchem.6b00700.
 F. Auzel, Chem. Rev. 2004, 104, 139-173.
3:15 PM - ED4.8.03
Efficient Infrared-to-Visible Upconversion with Sub-Solar Irradiance
Melika Mahboub 1 , MingLee Tang 1 2 , Zhi Yuan 3 Show Abstract
1 Materials Science and Engineering, University of California Riverside, Riverside, California, United States, 2 Chemical Science, University of California Riverside, Riverside, California, United States, 3 , University of California, Riverside, Riverside, California, United States
Power conversion loses in solar cells are due to thermalization and sub-bandgap light transmission. Photon upconversion, the ability to convert low energy photons to high energy photons, may provide the solution to transmission loss. Triplet-triplet annihilation (TTA)-based upconversion systems that utilize organic molecule face challenges in finding a stable molecule that can upconvert NIR efficiently despite the fact that more than 52% of the solar spectrum is NIR radiation. Introducing an efficient, photostable NIR upconversion system that can be operated on sub-solar fluxes is crucial for photovoltaic applications. Here we show that TTA-based upconversion with colloidally synthesized NCs as sensitizers can upconvert NIR light efficiently at sub-solar fluxes. PbS-CdS core-shell NCs, carboxylic acid tetracene, and rubrene act as sensitizer, transmitter, and annihilator. We report an 8.5% upconversion QY at 3.2 mW/cm2 flux density (three times lower than the available solar flux) excited with 808 nm cw. This is the highest efficiency ever reported for the Infrared-to-visible upconversion for excitation at sub-solar power densities. We believe the design here paves the way towards the practical use of photon upconversion in photocatalysis, photovoltaics, and photodetectors.
3:30 PM - ED4.8.04
Sandwich-Like Palladiumphthalocyanine—Highly Efficient NIR Sensitizer for Low Power Upconversion
Xiaomei Wang 1 , Changqing Ye 1 , Rongkang Hao 1 , Ping Yang 2 , Liwei Zhou 1 Show Abstract
1 , Suzhou University of Science and Technology, Suzhou, Jiangsu, China, 2 , Soochow University, Suzhou China
Triplet-triplet annihilation upconversion (TTA-UC) systems capable of generating short-wavelength radiation from long-wavelength light sources are very desirable because of their wide application potentials. For the purpose of solar energy and biomedicine applications, the upconversion systems of red-to-short wavelength light are more interesting since they can make the best of harvesting the sun light in near infrared (NIR) region and exploiting the NIR window for human body. Among red-to-short upconversion, the red-to-yellow has been investigated significantly, of which the typical pair of acceptor/sensitizer is almost entirely fixed on 5,6,11,12-tetraphenylnaphthacene (rubrene) doped with large planar peripherally substituted metalloporphyrins, such as metallated tetrabenzoporphyrins, metallated tetranaphthaloporphyrins, and metallated tetraquinoxalineporphyrins as well as metallated tetraanthraporphyrins, which need heavy and complicated synthesis process and show unpredictable triplet sensibilization.
3:45 PM - ED4.8.05
Interference-Enhanced Solid-State Infrared-to-Visible Upconversion Sensitized by Colloidal Nanocrystals
Mengfei Wu 1 , Joel Jean 1 , Lea Nienhaus 1 , Moungi Bawendi 1 , Vladimir Bulovic 1 , Marc Baldo 1 Show Abstract
1 Energy Frontier Research Center for Excitonics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Triplet-triplet annihilation sensitized by colloidal nanocrystals can convert infrared photons into visible photons at relatively low incident intensities. A solid-state device consisting of thin films of lead sulfide nanocrystals and rubrene doped with an emissive dye upconverts from wavelengths beyond λ = 1 μm to λ = 610 nm. We find that in a standard bilayer structure, however, the nanocrystal film must be kept nearly a monolayer thin to maximize internal quantum efficiency, resulting in low infrared absorption and hence low external quantum efficiency. Here we demonstrate a simple vertical geometry incorporating an optical spacer layer and a silver mirror to enhance nanocrystal absorption and organic emission through interference effects. We achieve an order-of-magnitude increase in front-face upconverted emission and a corresponding decrease in the threshold intensity of infrared excitation. Devices pumped at λ = 808 nm convert (7±1)% of absorbed photons into higher-energy emissive states. This work highlights the usefulness of optical management in solid-state upconverting devices and brings nanocrystal-sensitized upconversion a step closer to integration for photovoltaic and sensing applications.
ED4.9: Host Material Development for Organic Photon Upconversion
Thursday PM, April 20, 2017
PCC North, 100 Level, Room 128 A
4:30 PM - *ED4.9.01
Triplet-Triplet Annihilation Upconversion in the Aqueous and Dry Phases—Challenges, Solutions, and More Problems
Jaehong Kim 1 Show Abstract
1 , Yale University, New Haven, Connecticut, United States
This talk summarizes our group’s recent efforts in developing triplet-triplet annihilation (TTA) upconversion systems that can efficiency function in the aqueous and dry phases. Aqueous phase TTA-UC in a microcapsule configuration has been pursued to explore applications in environmental remediation field wherein sub-bandgap photons are utilized by semiconductor photocatalysts to produce reactive oxygen species that can degrade pollutants and inactivate pathogenic microorganisms. Alternatively, in situ synthesis of hydrogen peroxide by sub-bandgap semiconductor photocatalysis is also attempted. Another aqueous phase application focuses on bioimaging where TTA-UC system in a nano-scale capsule architecture, with antibodies immobilized on its surface, is utilized for multi-color cancer cell detection and targeted drug delivery. Dry phase application focused on utilizing rubbery polymer as a host of TTA-UC chromophores to enhance the solar energy conversion efficiency of dye-sensitized photoelectrochemical cells. The talk will discuss challenges we have faced toward these goals including the difficulty of avoiding oxygen quenching, successes made so far, and many problems that yet to be resolved for the efficient use of the light upconversion chemistry in various real world applications.
5:00 PM - ED4.9.02
Poly(Olefin Sulfone) Hosts for High-Efficiency Solid-State Triplet-Triplet Annihilation Up-Conversion
Andrey Turshatov 1 , Dmitry Busko 1 , Natalia Kiseleva 1 , Stephan Grage 1 , Ian Howard 1 , Bryce Richards 1 Show Abstract
1 , Karlsruhe Institute of Technologie (KIT), Eggenstein-Leopoldshafen Germany
In our work, we address the topic of photon up-conversion (UC) via triplet-triplet annihilation (TTA) mechanism, because since many years the TTA-UC is only the technology that can enable the spectral conversion under low-concentrated sunlight. TTA-UC occurs via the Dexter electron exchange mechanism and, thus, requires the dyes to be highly mobile to be efficient. Therefore, dyes are commonly dissolved in common organic solvents for that purpose. When the diffusion of dyes is arrested – which occurs in the solid state – the quantum yield of the TTA-UC mechanism is very low at ∼10-2 %. Thus, the combination of a macroscopically mechanically stiff material and the efficient TTA-UC remains a key research challenge.
One approach to achieve solid state TTA-UC is the embedding of dyes in a polymer host. It was demonstrated many times that to demonstrate a high TTA-UC efficiency, one needs a very soft polymer host with the glass transition temperature Tg << Tambient or very high concentration of dyes. Low Tg, however, significantly reduces mechanical properties of the material.
In order to overcome these disadvantages (low Tg of a host or extremely high dyes concentration), we performed synthesis and testing of several polymer hosts. In our work, we are describing the discovery that aliphatic poly(sulfone)s are excellent polymer hosts for the TTA-UC. These copolymers, especially poly(dodecyl sulfone) combine macroscopic rigidity (Tg > Tambient), nanoscale fluidity and outstanding oxygen barrier properties. A 50 μm thick film of poly(dodecyl sulfone) exhibits a TTA-UC quantum yield of 2.1 % (for the Pt-octaethylporphyrin/perylene pair) under ambient conditions. The similar quantum yield was measured when vacuum was applied. In addition to optical characterization, we used magic angle spinning solid-state NMR experiments to estimate the transverse relaxation time T2. The long 1H relaxation time T2 > 2 ms undoubtedly indicates enhanced nanoscale fluidity in the studied (co)polymers, despite the macroscopic rigidity.
In our opinion, starting from aliphatic poly(sulfone)s significant progress in the enhancement of the TTA-UC under ambient conditions can be achieved through proper design of the polymer materials.
5:15 PM - ED4.9.03
Thiol-Ene Click Chemistry for Solid State Triplet-Triplet- Annihilation
Joseph Lott 1 , Abagail Williams 1 Show Abstract
1 , University of Southern Mississippi, Hattiesburg, Mississippi, United States
Photon upconversion via the mechanism of triplet-triplet annihilation (TTA) offers the prospect of employing low-power and non-coherent excitation sources to drive the upconversion process. Solid-state materials capable of TTA present several significant challenges including limited solubility of the required chromophores and reduced molecular diffusion. Owing to the wide range of chemical compositions, tunable mechanical properties, and the ease of processing, polymeric materials have been at the forefront of solid-state materials for TTA. This study focuses on the use of thiol-ene ‘click’ chemistry to create elastomeric films for TTA. Functionalized derivatives of 9,10-diphenylanthracene bearing two vinyl groups were synthesized and covalently incorporated into thiol-ene films, along with palladium (II) octaethylporphine as the sensitizing moiety. Both emitter and sensitizer concentrations were systematically varied. The network formation was monitored using FTIR and NMR measurements and leaching experiments were conducted to quantify the amount of emitter chromophores not bonded into the network. The thermal and mechanical properties of the films were characterized using TGA, DSC, and DMTA. The upconverting performance was gauged using steady-state photoluminescence and lifetime measurements.
5:30 PM - ED4.9.04
Comparitive Study of Triplet-Fusion Induced Photon Energy Up-Converted Delayed Luminescence in Solution-Processable Blend Films of PtIIOctaethyl Porphyrin Model Composites
Panagiotis Keivanidis 1 , Hossein Goudarzi 2 Show Abstract
1 , Cyprus University of Technology, Limassol Cyprus, 2 Centre for Nano Science and Technology @PoliMi, Fondazione Istituto Italiano di Tecnologia, Milan Italy
Here we present results of time-gated photoluminescence (PL) spectroscopy as obtained by the comparative study of two types of model solid-state organic composites, both based on the organometallic sensitizer of (2, 3, 7, 8, 12, 13, 17, 18-octaethyl-porphyrinato) PtII (PtOEP); in Type A, PtOEP is mixed with the blue-light emitting derivative of 9,10 diphenyl anthracene (DPA) and a triplet energy transfer (TET) step from PtOEP to DPA is energetically allowed whereas in Type B, PtOEP is mixed with the blue-light emitting poly(fluorene) octyl (PF8) matrix and the TET step from PtOEP to PF8 is energetically forbidden. Both types of composites exhibit PtOEP triplet-triplet exciton annihilation-induced photon energy up-conversion (TTA-UC) in the blue after photoexcitation at 532 nm and their TTA-UC PL intensity is gradually enhanced upon cooling from 290 K to 100 K. The PtOEP phosphorescence kinetics of the two systems inform that the bimolecular rate constant γΤΤΑ of the PtOEP triplet excitons for Type A is γΤΤΑ-Type_A= 3.6 × 10-13 cm3 sec-1, whereas for Type B it lowers to γΤΤΑ-Type_B= 1.8 × 10-14 cm3 sec-1. Time-gated PL spectra for the DPA:PtOEP composite reveal that prior to the TET step from PtOEP to DPA a significant fraction of PtOEP triplet excitons annihilate in the PtOEP phase, leading to the activation of PtOEP delayed fluorescence at a photoexcitation fluence as low as 40 μJ pulse-1. Instead, no PtOEP delayed luminescence is observed for the case of PF8:PtOEP even when a photoexcitation fluence of 290 μJ pulse-1 is used. An all solution-based engineering protocol allows for the systematic tuning of the PtOEP phase-segregated content and of the PF8 beta-phase content in the DPA:PtOEP and the PF8:PtOEP composites, respectively. The PtOEP aggregate and the PF8 beta-phase species are monitored by their characteristic PL spectral signatures. We find that in a highly segregated PtOEP phase of DPA:PtOEP, the DPA TTA-UC PL intensity anticorrelates with the PL intensity of the PtOEP delayed fluorescence. In contrast, no obvious spectral evidence for PtOEP aggregation and no PtOEP delayed fluorescence are detected in PF8:PtOEP. For the latter, the TTA-UC PL signal of the PF8 matrix enhances as the PF8 beta-phase content increases.
Our study gains deep insight on the effect of intermolecular interactions in organic materials able to undergo TTA-UC in the solid-state. In next-generation TTA-UC composites of both Type A and Type B, efficient manipulation of the excited-state pathways can be enabled if simple rules are applied; in Type A systems, suitably decorated sensitizer moieties can alleviate the aggregation tendency and minimize TTA events in the segregated sensitizer phase without impeding the formation of networks that favour the necessary TET step. In Type B systems, TTA-induced energy pooling in the sensitizer phase is possible and the stored photon up-converted energy can be harvested by energy-acceptors of appropriate molecular conformation.