In addition to the well-established need for highly reliable space power systems, there has been recently renewed interest in developing practical new materials capable of efficient thermal-to-electric conversion of high grade heat sources (up to 1300 K), generated through fossil fuel combustion or as a waste exhaust stream. Si-Ge alloys have remained the State-of-the-Art since the late 1960s, but their thermoelectric performance is fairly low, even when operating across large temperature differentials. In addition, the significant Ge content precludes their use for large scale terrestrial applications due to cost considerations. New classes of higher performance materials that happen to contain large amount of rare earth elements (such as Ce, La and Yb) have been developed over the last few years. They typically share similar favorable characteristics for their use as high temperature thermoelectric materials: a semi-metallic behavior, with low to very low lattice thermal conductivity values and reasonably large thermopower values at near their peak operating temperatures. We present an overview of recent research efforts and discuss approaches for tuning the properties of these rare earth compounds through suitable chemical substitutions coupled with guidance from first principle electronic structure simulations. An assessment of the maturity of selected materials and challenges in scaling up for potential integration into high efficiency long life and thermally stable thermoelectric power generation devices is provided.

La3-xTe4 is an n-type state of the art thermoelectric material with a ZTmax~1.4 @ 1000 oC and has a demonstrated reliability and performance in devices. However, the material behaves as a brittle ceramic and suffers from chipping and cracking during processing and service. Efforts to develop La3-xTe4 as a cermet composite is explored as a means to improve material robustness and device yield. The Vickerâ?Ts hardness as a function of load will be reported for various composite loading fraction and the fracture toughness will be correlated from the length of the cracks emanating from the corners of the Vickerâ?Ts indents. Results on the equibiaxial flexural strength will be discussed for the various composites. In addition, special attention will be paid to the effects of the inclusions on the thermoelectric properties to provide a basis for optimization between thermoelectric and mechanical performance.

Preferential oxidation of CO with oxygen in presence of high hydrogen amounts (PROX reaction) is a process needed to purify hydrogen obtained from fossil or renewable feedstocks before using it in polymer membrane fuel cells. Copper oxide dispersed on cerium dioxide has shown good catalytic activity for this process, with the advantage over other current catalysts containing precious metals (like Pt or Au) of having lower cost. In previous works [1] we have shown that the active species in this catalyst are formed by small Cu oxide nanoparticles lying, initially as CuO, on the ceria carrier surface. Now we show that its properties can be improved by modifying the underlying ceria nanoparticle shape and, consequently, the crystallographic plane exposed by it. Hydrothermal preparations are shown to produce in controlled way ceria crystals with nanocube or nanorod shapes which respectively expose (100) or (110)+(100) faces and have specific surfaces SBET= 20 or 59 m2/g, while a traditional ceria nanomaterial made by precipitation in an inverse microemulsion presents rounded shapes exposing mainly (111) faces (plus some (100) ) together with a surface area SBET=130 m2/g. These samples are shown to contain different types of surface carbonate and OH groups (shown by the IR spectra), which characteristics are modeled with DFT calculations. When 1% CuO (by weight) is dispersed on these samples, different configurations of the Cu-containing species are obtained, as shown by Cu2+ EPR spectra and by the IR features of the Cu-adsorbed carbonyls appearing during in situ (operando) experiments made in reaction conditions under CO + O2 + H2 gas mixture. Particularly interesting is the fact that with the ceria nanocube-supported catalyst the measured selectivity for CO oxidation (for one same CO conversion level) is higher, i.e. less H2 is burned (wasted), than for the other samples, which makes this catalyst potentially more interesting for this application. DFT modeling indicates that the interaction between CuO nanoparticles and the underlying ceria surface is stronger when the latter exposes the less stable and more reactive (100) face. [1] D. Gamarra et al. J. Phys. Chem. C 111 (2007) 11026; and references therein.

Li7La3Zr2O12 thin films were successfully prepared by pulsed laser deposition technique for the first time. The crystalline features and optical properties of the as-deposited and post-annealed thin films were revealed by X-ray diffraction and UV-VIS spectrometer, respectively. The films deposited at room temperature were amorphous and they gradually crystallized by post-annealing. The as-deposited films showed an optical band gap of 5.13 eV which decreased to 3.64 eV after annealing at 1000 °C. The films deposited at room temperature exhibited a high ionic conductivity of 1.02Ã-10-6 S/cm, which is comparable with the best value of LiPON. In order to investigate LLZO as a solid electrolyte, a thin film battery using LLZO as the solid electrolyte and LiCoO2 as the cathode was deposited by PLD on Nb doped SrTiO3 substrate. This thin film battery with copper anode was found to be rechargeable. Therefore, LLZO is a very promising solid electrolyte for thin-film lithium ion batteries.

Solid oxide fuel cells (SOFCs) provide a promise for the future whereby the harnessing of our natural hydrocarbon energy resources can shift from inefficient and polluting combustion - mechanical methods to high-efficiency electrochemical conversion. SOFCs and other solid-state electrochemical devices depend on the ability to transport chemical species in the solid-state and actively participate in chemical reactions at their surface. These properties require particular crystallographic structures and defects that typically are achieved by the use of rare earth dopants. We will review material property requirements, their dependence on dopant radii, polarizability, and charge, and propose strategies to deal with potential shortages in rare earth materials.

The chemical reactivity of a material is pivotal to applications spanning, for example, catalysis, sensor, fuel cell, biomedical. Here we show how the chemical reactivity of ceria can be controlled as a function of nanoarchitecture and strain. Moreover, as strain is a continuous variable, the approach offers the promise of tuneable reactivity. We consider a variety of ceria architectures to illustrate including: ceria nanoparticles (0 dimensional), nanorods (1D), nanosheets (2D), and nanoporous (3D).

Rare-earth oxides of cerium, gadolinium, and praseodymium have shown promise as potential component materials in intermediate temperature (500 â?" 700 °C) solid oxide fuel cells (IT-SOFCs). Ceria (CeO2) doped with aliovalent cations has high ion conductivity in this temperature range. IT-SOFCs are of growing interest in part due to their potential for high energy conversion efficiency, fuel flexibility, and relatively high power density in mobile applications. In order to scale this technology, inexpensive synthesis methods for mixed oxides of rare-earths are needed which can deliver uniform material with highly tunable composition. Here we investigate the variation in ion conductivity with dopant concentration for a series of Pr-doped, Gd-doped and Pr/Gd-co-doped materials synthesized using a spray-drying technique. Bulk and grain boundary ionic conductivity are determined based on impedance measurements conducted as a function of temperature. Grain size distribution, composition, and microstructure are a consequence of processing and are expected to affect ion conductivity; thus we will present data on these parameters determined using scanning electron microscopy with energy dispersive x-ray spectroscopy. Furthermore, we characterize dopant and impurity segregation, which are expected to affect grain boundary composition, structure, and contribution to total ionic conductivity. We investigate these effects using high spatial resolution electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope. Finally, we discuss correlations between the spray-drying process, nanostructure and compositional heterogeneity, and ion conductivity.

We synthesized mono-dispersed polystyrene colloidal nanospheres by free-soap emulsion polymerization. The colloidal particles diameter can be controlled by changing the polymeric reaction condition, which can act as building blocks to prepare diverse functional materials. Further, three-dimensional colloidal crystal films with excellent fluorescent property are fabricated by self-organization of the monodisepred colloidal particles. The films have been characterized by SEM, DLS, UV-vis spectroscopy and luminescence spectroscopy and so on. The colloidal crystal film indicates a photonic band gap, which depends on the diameter and size-dispersing of the nanospheres building blocks. Due to the photonic band gap and the luminescent properties, the colloidal crystals films imply special optical properties. On the other hand, we studied the luminescent properties affected by the colloidal crystals structure, and investigated the two kinds properties of colloidal crystals together, then feedback to the preparation process to obtain with the optical modulation function of the polymer colloidal crystals films, which present potential applications in fabricating optical devices, data storage, chemical and biological sensors, and color displays.

Nanocolloids and nanocrystals doped with ions of rare-earth elements have recently attracted a lot of attention of the scientific community - due to unique physical, chemical and optical properties attributed to nanometer size of the particles. They have great potential of being used in applications spanning from new types of lasers, especially blue and UV, phosphorous display monitors, optical communication, and fluorescence imaging. Here we present the results of synthesis and optical spectroscopy of hexagonal-phase NaYF₄: Tm³⁺, Yb³⁺ nanocrystals with significant NIR-to-visible upconversion fluorescence. The nanocrystals can be potentially used as a new laser filling medium in photonic crystal fibers. The nanocrystals were synthesized using simple co-precipitation procedure in the presence of ethylenediaminetetraacetic acid (EDTA). The size of the nanoparticles in the colloid was measured using the atomic force microscope. The freshly prepared nanophosphor, being pumped with a 980-nm laser, exhibited very weak up-conversion fluorescence. However, after annealing at a temperature of 600^oC, the nanophosphor produced blue upconversion fluorescence visible by the naked eye at room light. The optical fluorescence spectroscopy indicated that the upconversion fluorescence had spectral peaks at 376 nm, 476 nm, 646 nm, 696 nm and 803 nm. The obtained nanocolloids were incorporation into the HC19-1550-01 micro-structured photonic crystal fiber and their properties as a filling laser media were investigated.

Due to high stability of Si-O bonds, the series of barium-silicate compounds are famous for host materials of photoluminescent compounds. The crystal structure of Ba2SiO4, each SiO4 tetrahedral are isolated in the lattice. On the other hand, SiO4 tetrahedral of Ba4Si6O16 and Ba5Si8O21 are corner sharing each other. The Ba2+ ions of Ba2SiO4, Ba4Si6O16 and Ba5Si8O21 are located 2, 4 and 3 kinds of asymmetric position, respectively. Recently, Ba2SiO4:Eu2+ is used as the photoluminescent materials for white LEDs. In this paper, we reported the luminescence property of Ba2SiO4:Eu2+, Ba4Si6O16:Eu2+ and Ba5Si8O21:Eu2+.

Core-shell nanostructures provide a wide array of physio-chemical properties which make them attractive candidates for drug delivery and biomedical applications. The core and shell can be of the same or of different materials which provide the final nanostructure with distinctive properties. In this regard, we have developed a material system that consists of silica nanoparticles decorated by ceria nanostructures. Because of the versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for applications in drug delivery. The silica particles of size ~50nm were synthesized by the StÃ-ber synthesis method and ceria nanoparticles of size ~2-3nm were attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous precipitation of ceria nanoparticles which were attached to silica surface by Si-O-Ce bonding. The formation of ceria nanoparticles on the surface of silica were characterized by various spectroscopic and electron microscopy techniques such as dynamic light scattering (DLS), fourier transform infrared spectroscopy (FTIR), angle resolved X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the surface of silica. The angle resolved XPS analysis indicates that ceria nanoparticles are located on the surface of silica and possess mixture of +3 and +4 chemical states. The FTIR spectroscopic analysis is consistent with the formation of Si-O-Ce bonding. As an initial phase of biological testing, we carried out concentration dependent cytotoxicity studies on a Raw 264.7 macrophage cell line. Cell viability was measured by the alamar blue assay. The cells were incubated with silica/ceria nanostructures at four different concentrations (5, 25, 50 and 100µg/ml) for 24 hours. The cell viability was measured and compared to control cells (untreated) which show minimal toxicity up to 50µg/ml.

Inorganic erbium-doped glasses are widely used in telecommunications due to the sharp intra-atomic 4I13/2 â?' 4I15/2 transition in the 4f orbital of erbium resulting in an emission at ~ 1.5 µm, which is the low loss window of silica optical fibres. The erbium concentration limit of about 10^20 ions/cm3 in inorganic erbium-doped glasses and the low absorption coefficient of the Er3+ ions, imply that long lengths of fibre are required. Organic erbium complexes present higher absorption cross sections due to the photosensitization of erbium by the organic conjugated ligands and broader emission bands than those of the free Er3+ ions. Such properties open the possibility to develop compact, low power and broadband infrared emitting devices. We present the study of two organic fluorinated erbium complexes exhibiting 1.5 µm luminescence lifetime from few microseconds to several hundreds of microseconds measured on sublimed powder state. These luminescence lifetimes are mainly due to the different chemical structure of ligands which modulates the quenching processes. Both organic complexes have been deposited by vacuum sublimation technique. This deposition method allows the realization of an erbium-doped thin film without the help of an organic polymer matrix, which is also a potential source of vibrationnal luminescence quenching. We report the synthesis, the sublimation process, and the characterization of the thin films. The chemical structures of the complexes are checked by FTIR and NMR. Chemical integrity of the thin films after vacuum deposition is determined by FTIR. The morphology of the thin films is characterized by X-ray diffraction experiments. The optical properties of thin films are determined by spectroscopic ellipsometry, UV-Vis-NIR absorption spectroscopy and time resolved NIR luminescence spectroscopy. The authors gratefully acknowledge the French National Research Agency (ANR) for the financial support through the VERSO program METAPHOTONIQUE.

Mesoporous matrix is an interesting host to prepare new luminescence systems; the porous network can be tune and provides an interesting way to control the geometry of the luminescence center. Our goal is to study the d-f energy transference from d-block element to lanthanide ion, as antenna effect, to sensitize near-infrared emission upon photo-excitation of the transition metal. The mesoporous role was offering a confined environment to Ru(III)/Nd(III), thus assisting the energy transfer process. Ordered mesoporous SiO2 particles have been synthesized by spray pyrolysis (at few minutes) with a careful control of precursors, as alkoxide hydrolysis and surfactants concentration and, in addition, the choice of the structure-directing agents may control the dimension porous. The d-f system was attained by the different complex synthesis; first, a ruthenium complex by bipyridine silylated ligand, and neodymium complex by thenoyltrifluorodiketonate silylated ligand; second, a Ru(III)/Nd(III) binuclear complex with silylated ligand. In the first one, the mononuclear complexes were grafted onto silica, and the close environment to energy transference was determined by the porous dimension. In the second one, the interaction metal-lanthanide was achieved by the binuclear system and, in both case, the complexes were covalently bonded to the silica host. The materials obtained were characterized by scanning electron microscopy, transmission electron microscopy, elemental analysis, thermogravimetric analysis and Fourier transform infrared spectroscopy. The near-infrared emission luminescence was observed by the photo-excitation in the metal-to-ligand charge transfer state of the Ru(III) complex.

The novel mesoporous structure based on SiO2/TiO2 host was prepared and, this synthesis allowed the porous network control, by the choice of surfactant and adjustment of synthesis procedure. However, in this propose, the Si/Ti ions ratio may help tuning the structural parameters and supplying a new environment for interesting phosphors. The Si/Ti molar ratios were ranged from 15 to 3, and all samples were characterized by different methods, as scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), nitrogen adsorption-desorption analysis, FTIR and UV-vis spectroscopies. The samples were doped with Eu(III) Beta-diketonate complex, these complexes were targets of intensive studies to determine the intramolecular energy-transfer processes, and theoretical models were used to describe geometric and spectroscopic properties of lanthanide complex. In our system, all samples presented correlation peaks attributed to the mesostructured porous and, the divers cell parameters acquired were correlated at the Si/Ti molar variation, as characterized by SAXS. The luminescence spectra suggest the influence of inorganic network upon the closely chemical environments around of europium ions, which results from the Si/Ti-complex interactions. In conclusion, the mesoporous material may provide different confined environments for the Eu complex of interest.

Rare earth doped semiconductor materials are of special interests due to their potential applications in optoelectronic devices. Among the rare earth elements, erbium (Er) is the most widely studied material that the inner shell transition from 4I11/2 â?' 4I15/2 produces photon emission at 1.54 um that corresponds to the absorption minima of silica fiber. ZnO is an ideal candidate for the doping of Er that thermal quenching effect is less significant. Besides, the optimum doping concentration of Er in ZnO is close 1 at. %. In this study, we prepared Er doped ZnO (Er:ZnO) with Er concentration from 0.1 to 3.5 at. % by dual beam ion beam sputter deposition at room temperature. Experimental results show that the as-deposited Er :ZnO with Er concentration of 1.1 at. % exhibits the highest carrier concentration of 2.3 Ã- 1019 cm-3. However, the as-deposited samples show little or no 1.54 um emission at all. The 0.5 at. % sample shows the strongest 1.54 um emission after annealing at 700C while all the film becomes semi-insulting. This suggests that the formation of an asymmetric tetrahedral structure around the Er ions which favors the photoluminescence at 1.54 um may have an advert impact on carrier concentration of Er:ZnO films.

Since the 1960â?Ts, rare earth vanadate phosphors have attracted attention for visualization applications due to their high stabilities, high emission colour purities and high luminescence yields. The rare earth vanadates are isosctructural to the rare earth phosphates, thus presenting monoclinic (monazite) or tetragonal (xenotime) crystal structures, which makes possible the development of mixed phosphate-vanadate phosphors with several advantageous luminescent properties. The improvement of the quality of such compounds as luminescent materials is still a very important research topic, since the optimization of the main matrix components (mainly lanthanum, yttrium or gadolinium), of the phosphorus/vanadium ratio, and of the activator concentration are primordial for the applicability of these solids in visualization devices. In this sense, this work shows the application of a polymeric precursor synthesis (modification of Pechini method) for the obtainment of nanosized rare earth phosphovanadates of several compositions, in order to elucidate the spectroscopic behaviour of these solids. The synthesized powders were characterized by scanning electron microscopy, X-ray diffractometry, and vibrational and electronic (luminescence) spectroscopies. The effect of the vanadium concentration (1, 5, 10, 20, and 50% V in YPO4) on the luminescence of Eu3+ was studied with regard to the symmetry of the occupied sites, quantum efficiencies/quantum yields, chromaticities, luminescence lifetimes and Judd-Ofelt intensity parameters. Moreover, the methodology was also applied for the obtainment of a blue phosphor ((Y,Gd)(P,V)O4:Tm3+), with high emission colour purity, high emission intensity and broad excitation bands in the UV range. In this way, very efficient nanosized red and blue phosphovanadate phosphors with well controlled composition can be prepared through a simple technique, which allows for the correlation of the matrix composition with the spectroscopic behaviour of the powders. The authors thank the Brazilian agencies CAPES, CNPq/inct-INAMI, and FAPESP. References [1] W.M. Yen, S. Shinoya, H. Yamamoto (Eds); Phosphor Handbook 2nd Ed., CRC Press, Boca Raton, 2007. [2] P.C. de Sousa Filho, O.A. Serra, J. Fluoresc. 18 (2008) 329

The Er3+ ion is a key component in many optical applications including lasing media and fiber optic communications. One limiting aspect is the weak absorption of some of the pertinent energy levels. Yb3+ has been found to be a strong activator for the near-infrared 4I11/2 level of Er3+ for three reasons. The energies of the 4I11/2 of Er3+ and the 2F5/2 of Yb3+ are closely matched. The 2F5/2 level has a much stronger absorption strength and has a lifetime that is much longer (~1ms) than the 4I11/2 level of Er3+ (~10μs in silicates). Due to the commercial availability of 980nm diode lasers, efficient cw excitation of Er3+ ions can be accomplished when using Yb3+as an activator. In this work, sol-gel silicate glasses containing various concentrations of Er3+ and Yb3+are used to study the dynamics of Yb-Er energy transfer at room temperature. Sol-gel synthesis provides a convenient, low temperature means for preparing optically transparent amorphous materials. Tetramethoxysilane (TMOS) was the alkoxide precursor used in the formation of these silica sol-gels. Because the initial preparation was a room temperature liquid (sol), the inclusion of rare earth additives was easily accomplished even to higher degrees of concentration than in traditional, monolithic, melt glasses. By controlling thermal and atmospheric parameters as the gel dried and densified, high-quality structural and optical properties could be achieved. One attractive aspect of sol-gel synthesis is that optical properties of a densified gel, heated to temperatures near ~1000°C, approach that of traditional glasses produced by thermally quenching molten material of much higher temperature. Dynamics of Yb-Er energy transfer is studied by observing green emission from the 2H11/2 and 4S3/2 levels of Er3+ after 5-ns pulsed laser excitation of the 2F5/2 level of Yb3+ at 978nm. The time-scale of this excitation is similar to the GHz bandwidth of fiber optic communication. Due to the relatively short laser pulse and weak absorption of the Er3+ ion, direct pumping of the Er3+ ion produces only very weak upconverted fluorescence. With the addition of Yb3+, the fluorescence intensity increases by several orders of magnitude. This upconversion process is interesting because energy is deposited in a group of Yb3+ions which sequentially transfers energy to a nearby Er3+ ion. Two excited Yb3+ions must stepwise transfer their energy. We have found that rare earths most commonly reside on the pore surfaces of these glasses. Thus, energy migration among the Yb3+ions and subsequent transfer to an Er3+ ion is mitigated by the porous nature of the sol-gel glass. Among other results, fluorescence decay profiles will be presented which demonstrate an increased characteristic decay time of the 4F7/2 level as the concentration of Yb3+ is increased, an effect due to a longer feeding time from the excited Yb3+ population.

The Rare Earths exploitation in Brazil started in 1885 with the extraction of monazite from the Prado shores, in the state of Bahia[1]. Until 1896, it was freely used as ship ballast and sold for less than US$10/ton. Its destination was Europe, where Th and Ce nitrates were used to produce incandescent gas mantles. In the 50â?Ts, Brazil, through ORQUIMA, a private company, dominated the whole process and managed to obtain quite pure oxides (99.9 - 99.99%), having even exported Eu2O3 for the production of metal bars for the neutron absorption control in the the world's first nuclear submarine, the Nautilus. In 1962, as an intern at ORQUIMA, along with Pawel Krumholz[2], we produced 10 g of Lu2O3 (> 99.9%), the largest amount of such compound ever produced at that time! The company, which came to process up to 2,000 tons of monazite a year was nationalized in the early 60â?Ts and obsoleted until it was restricted to only extracting the monazite and producing a low purity RE and CeO2 concentrate. The production was practically disabled in 2002. All technological and human resources investment was virtually lost and when the RE started to have greater added value in the 70â?Ts and 80â?Ts, Brazil had no market competitiveness anymore. In the largest deposits of China, an intimate mixture of monazite and bastnasite occurs together with other minerals. Since the 50â?Ts, the Chinese have been investing in extraction processes that involve careful flotation systems interspersed with electromagnetic procedures[3]. In 1990, the world production was approximately 25,000 tons and China accounted for less than half. However, the low cost of the RE produced by China since the 90â?Ts, and a greater environmental control made producers from countries like the USA (Molycorp) and Australia (Lynas) close down all their activities at the end of the last century. At first, at low cost and with no environmental concern, China has come to dominate the market for these twenty years and currently sells over 97% of the RE compounds (mainly oxides and metals). But the growing domestic demand caused by the mastering of the technologies that enabled the manufacturing of final products (wind turbines, phosphors, batteries etc.) besides the environmental constraints have made China raise the average price of RE more than ten times in the last two years, besides establishing exportation quotas for oxides and metals. Nowadays, USA, EU and Japan governments are taking actions in order to be independent of Chinese exportation. Molycorp and Lynas should alone by the end of 2012 be able to supply almost their own needs. Several mining companies around the world (South Africa, Korea, Canada, Brazil, etc.) are also involved in RE mineral extraction, mainly the heavy ones. [1] O.A. Serra, J. Braz. Chem. Soc. 22 (2011) 809. [2] P. Krumholz in E.J.S. Vichi, Quim. Nova 6 (1983) 152. [3] Y. Zongsen, C. Minbo; Rare Earth Elements and Their Applications, Metallurgical Industry Press, Beijing, 1995.

Scarcity and possible future shortages of key elements used in modern technology has come into the focus of public interest. One of the most imminent challenges of modern materials science is the development of new materials with less critical elements that have comparable or better functionalities than those currently used. Taking into account interdisciplinary aspects (e.g., criticality of resources, economic merits) at an early stage of research has to be a key priority in future materials Research and Development. We illustrate this approach¹ by applying it to the prototypical example of materials with extremely high dielectric constant. These materials could pave the way for a new generation of electronic components, e.g., capacitors with outstanding energy-storage capabilities. Here, we demonstrate the prospects of several materials (BaTiO₃ doped with rare earth², CaCu₃Ti₄O₁₂³, and La_2-xSr_xNiO₄⁴) from a perspective of materials science, resource strategy and resource management providing three filters that have to be passed by a material to be suitable for application as, e.g., multilayer ceramic capacitor. Criteria for the material science filter are based on technically relevant properties only whereas criticality of materials is considered in the resource strategy filter. The final filter deals with economic aspects of the resources and of processing techniques. By combining these filters and estimating the time-dependent criticality of the resources and economic aspects, we arrive at a recommendation for a specific material to be selected for a defined application. ¹ S. Krohns et al., Nature Materials (in press). ² M.-J. Pan & C. A. Randall, IEEE Electrical Insulation Magazine 26, 44 (2010). ³ C. C. Homes et al., Science 293, 673 (2001). ⁴ S. Krohns et al., Appl. Phys. Lett. 94, 122903 (2009).

The rare-earth (R) tri-tellurides RTe_3 host an unidirectional, incommensurate CDW already well above room temperature for all R elements lighter than Dy, while in the heavy rare-earth tri-tellurides (i.e., R=Tm, Er, Ho, Dy) the corresponding transition temperature, T_CDW1, lies below 300 K and decreases with increasing R mass. In the latter systems, a further transition to a bidirectional CDW state occurs at T_CDW2, ranging from 180 K for TmTe_3 to 50 K for DyTe_3. We will present a large wealth of data collected with different spectroscopic methods, as x-ray diffraction, and infrared and Raman spectroscopy as a function of both temperature and externally applied pressure. First of all, our x-ray investigations allow us to extract the lattice constants and the CDW modulation wave-vector. We observe that the intensity of the CDW satellite peaks tend to zero with increasing pressure, thus providing direct evidence for a pressure-induced quenching of the CDW phase. With optical reflectivity method, we consistently discover that the CDW gap of RTe_3 progressively collapses when the lattice constant is reduced. Finally, we will present novel Raman scattering experiments as a function of temperature on DyTe_3 and on LaTe_3 at 6 GPa, which clearly display the emergence of the collective CDW amplitude excitations for both the uni- and bidirectional states.

Volume collapse in rare earth systems--due to delocalization and bonding of 4f electrons at extreme pressures--has been a hotly debated topic for several decades because the theory of f-electron correlations is a huge scientific challenge. Advances in x-ray spectroscopy at high pressure allow us to examine the physics underpinning these collapses with unprecedented detail and make for a stringent test of the latest theoretical treatments. In this presentation, we will lay out the x-ray techniques, present our results on rare earth metals and compare to explicit predictions from dynamical mean field theory.

Epitaxial rare earth monpnictide (RE-V) nanostructures embedded within a III-V semiconductor matrix are of great interest due to a number of exciting electrical and magnetic properties, including phonon scattering for high ZT thermoelectric, sub-picosecond carrier lifetimes for terahertz devices, and strong exchange coupling between 4f, valence, and conduction electrons near the Fermi level. To date, most work on this nanocomposite system has focused on embedded RE-V nanoparticles, e.g. ErAs or ErSb nanoparticles embedded in GaAs (001) and GaSb (001). Here we demonstrate the growth of highly anisotropic ErSb nanorods embedded in GaSb (001) during molecular beam epitaxial growth of ErGaSb by codeposition. These nanorods are continuous throughout the ErGaSb layer, their axes are parallel to the [001] growth direction, and they self-assemble into ordered arrays aligned along the [-110] direction. Additionally, the resulting ErGaSb nanocomposite is single crystalline with a continuous Sb-subblate, with no observable defects across the ErSb/GaSb interfaces. Using a combination of molecular beam epitaxy (MBE) and in-situ scanning tunneling microscopy (STM), we have investigated the growth mechanisms that result in embedded nanorod formation. We show that the atomic scale growth mechanisms are driven by surface diffusion and wetting characteristics that enable the surface to remain remarkably smooth during growth. Furthermore through control of surface diffusion we demonstrate morphologies ranging from pristine nanorods to branched nanotrees. We have used scanning tunneling spectroscopy (STS) and angle resolved photoemission spectroscopy (ARPES) to measure the electronic bandstructure of embedded RE-V nanostructures of varying dimensions, namely 0D nanoparticles, 1D nanorods, and 2D thin films. Despite the predictions of simple effective mass models [1], the ErAs and ErSb nanostructures remain semimetallic and no bandgap is opened even with reduced dimensions. We used tunneling spectroscopy to measure changes in the local density of states across the ErAs/GaAs interface and propose that the interface atomic structure results in electronic states that prevent the opening of a band gap [2]. In order to obtain more detailed information on the band structure, we used ARPES to measure the band dispersion as a function of ErAs film thickness and have identified surface/interface bands that may be responsible for preserving metallic behavior. The variety of self assembled structures and preservation of metallic behavior make RE-V/III-V a promising system for high quality epitaxial semimetal/semiconductor nanocomposite interconnects, photonic crystals, and plasmonic structures. [1] M. A. Scarpulla, J. M. O. Zide, J. M. LeBeau, C. G. Van De Walle, A. C. Gossard, and K. T. Delaney, APL. 92, 173116 (2008). [2] J. K. Kawasaki, R. Timm, K. Delaney, E. Lundgren, A. Mikkelsen, and C. J. Palmstrøm, PRL. 107, 036806 (2011).

Rare-earth elements are currently soaring in value due to a restricted supply. This is problematic given that rare-earth materials form the basis for a wide range of technologies, including wind turbines, hybrid car engines, high-efficiency batteries, and lasers. In order to advance rare-earth materials and potentially substitute 4f electron elements with other species, a core understanding of the electronic, magnetic, and crystal structure of the elements must be formed. Here we use aberration-corrected transmission electron microscopy and synchrotron-based nonresonant inelastic x-ray scattering (NIXS) to probe the electronic structure of the light lanthanide metals Ce, Pr, and Nd. X-ray and electron scattering results are in agreement for dipole transitions (k = 1), with the high energy resolution and signal-to-noise of electron energy-loss spectroscopy (EELS) in the TEM allowing measurement of the complex and subtle excitation spectra of rare-earth materials. NIXS, with the ability to probe electronic structure at large momentum transfer, yields spectra with multipole information (k = 3 and 5). The momentum transfer dependence of the x-ray scattering is extracted and compared against atomic calculations. Together, EELS and NIXS results validate the applicability of the screened trivalent atomic model often used for rare-earth materials, with NIXS providing a direct test of the theoretically predicted atomic radial wave functions.

We have used atomic-level computer simulations to study the relationship between ionic conductivity and radiation tolerance of rare-earth pyrochlores and doped ceria. The materials studied include gadolinium titanate, gadalinium zirconate and samaria-doped ceria. Defect diffusion, radiation-induced amorphization, and the oxidation state of Ce were systematically examined. The results reveal a link between ionic conductivity and radiation tolerance in pyrochlore compounds. The results shed light on experimental findings of radiation effects in pyrochlores, and the charge state of Ce in ceria.

Many unique properties and applications of rare earth (RE) compounds are characterized and determined by the f-electron crystal field (CF). However, CF effects are usually rather small for f electron: the CF splitting is at the order of 0.1 eV, compared to several eV for d-electrons. Therefore accurate theoretical description of RE crystal field is challenging. We present a first-principles method of CF calculation based on an improved LDA+U method. By careful cancellation of errors, the method can reach relatively high accuracy for the CF parameters. As a demonstration we calculate the experimentally well-characterized RE:LaF₃ system, which has low point-group symmetry and a large number of CF parameters, representing a stringent test of theory. The predicted CF excitation energies of Ce:LaF₃ agree within about 10 meV with experiment, and within several meV if the errors in the free-ion parameters are excluded. Work is underway to apply the method to other materials for solid-state lighting and laser applications.

Rare-earth based scintillators in general and lanthanum bromide in particular represent a challenging class of materials due to pronounced spin-orbit coupling and subtle interactions between d and f states that cannot be reproduced by standard electronic structure methods such as density functional theory. In this contribution we present a detailed investigation of the electronic band structure of LaBr3 using the quasi-particle self-consistent GW (QPscGW) method. This parameter-free approach is shown to yield an excellent description of the electronic structure of LaBr3. Specifically we are able to reproduce the correct level ordering and spacing of the 4f and 5d states, which are inverted with respect to the free La atom, the band gap as well as the spin-orbit splitting of La-derived states. We then use the QPscGW results to benchmark several computationally less demanding techniques including hybrid exchange-correlation functionals and several flavors of the GW method. We explicitly take into account spin-orbit coupling at all levels of the theory and employ maximally localized Wannier functions to interpolate quasi-particle energies. Our results demonstrate the applicability and reliability of the QPscGW approach for rare-earth halides. They furthermore provide an excellent starting point for investigating the electronic structure of rare-earth dopants such as Ce and Er not only in LaBr3 but also in other systems.

The study of exchange-coupled systems has focused an intense research activity for several years since they may exhibit interesting properties as spring magnet behavior or exchange bias effect. These properties are induced by the interface exchange coupling between two different magnetic materials. Among these systems, the RE-Fe₂ (RE is a rare earth element) Laves phase superlattices are of great interest for potential applications as well as for the theoretical understanding of the magnetic coupling in these materials [1]. DyFe₂/YFe₂ superlattices are heterostructures that consist of hard (DyFe₂) and soft (YFe₂) ferrimagnetic phases. The hard magnetic phase tends to resist magnetization reversal in high fields owing to its high anisotropy, while the soft phase possesses large magnetization. Depending on the layers thicknesses and on the temperature, the field dependence of the magnetization depth profile is complex. In particular, while the behavior of the superlattices dominated by the DyFe₂ magnetization displays as expected domain walls in the YFe₂ (soft) layers, in some cases, the domain walls are essentially located in the DyFe₂ (hard) layers. This situation is encountered for DyFe₂ (3nm)/YFe₂ (12nm) when the hysteresis loops is measured at T=200K [2]. We have performed Monte Carlo simulations of the hysteresis loops at several temperatures in the case of superlattices magnetically dominated by the DyFe₂ layers or by the YFe₂ layers, depending on their respective thicknesses. The model used consists in a face-centered cubic lattice of Heisenberg spins including three energetic contributions: the exchange interactions between nearest-neighbor atoms, the magnetocrystalline anisotropy which holds mainly on the Dy sites and the Zeeman interaction with the applied magnetic field. The numerical simulations allow to obtain a good qualitative description of the field induced reversal of the magnetization especially concerning the localization and the extent of the domain walls in function of the temperature. The results obtained are in good agreement with the experimental ones. References [1] E.E. Fullerton, J.S. Jiang, M. Grimsditch, C.H. Sowers, and S.D. Bader, Phys. Rev. B 58, 12193 (1998). [2] M.R. Fitzsimmons, S. Park, K. Dumesnil, C. Dufour, R. Pynn, J.A. Borchers, J.J. Rhyne, and Ph. Mangin, Phys. Rev. B 73, 134413 (2006)

There has been a recent explosion of interest in upconverters (UC) for device and sensing applications, owing to the introduction of efficient, solvent-dispersible nanocrystalline UC materials (NaYF₄) activated by trivalent lanthanide ions (Ln³⁺). The use of upconverters in a nanocrystalline form dramatically increases their processability, in terms of incorporation into composite materials, and provides high spatial resolution and biocompatibility for sensing applications. However, it is difficult to directly measure the quantum efficiency of these materials, and the effect of materials parameters on efficiency (such as particle size, capping ligand, composite matrix) is poorly understood. A rate-equations model has been constructed which describes the mechanism of NIR-to-visible upconversion in NaYF₄ :Er, Yb in terms of the microscopic rate constants relevant to the upconversion mechanism. This model can be used to determine NIR-to-visible quantum efficiency from accessible spectroscopic data, and can isolate the effects of nanoparticle size, doping concentrations, etc. on the individual mechanistic steps. The model correctly predicts the less-than-quadratic dependence of UC intensity on excitation power long before the high-power limit is reached. The use of the model in characterizing the potential for enhancing upconversion using plasmonic surfaces will also be discussed.

Cerium oxide (ceria) nanoparticles are widely studied for their current and potential use in catalytic, energy, environmental protection and bio-medical applications. The performance of ceria in many of these applications depends on the ability of cerium to switch between +3 and +4 oxidation states. Our research involves examination of the properties of ceria nanoparticles as they apply to materials science research and impact biological systems. We have synthesized ceria nanoparticles by several solution growth processes as well as examined the impacts of the wide variety of other processes described in the literature. This paper summarizes some of our observations of the impact that synthesis route, processing conditions, storage and environmental conditions have on the properties of ceria nanoparticles. An examination of the biological impacts of ceria nanoparticles indicates that larger faceted ceria particles that have been heated are more likely to have adverse consequences, while smaller particles synthesized at room temperature and never removed from solution often have anti-oxidative behaviors. Smaller particles are highly dynamic in nature changing their oxidation state not just as a function of size, but also as a function of aging (time) and environmental conditions. During particle nucleation and growth in solution, both the particle size and oxidation state change with time. This type of observation suggests that interpretations of experimental results based primarily on particle size will be misleading at best. It is possible to vary the rates of oxidation state change by varying the properties of the solution used for synthesis. We have also found that small variations in synthesis such as changing the source of chemicals, altering the water source or changing from clean glassware to sterilized plastic containers for biological studies can alter the character of particles formed as well as their stability. Smaller particles are particularly susceptible to change and Raman and XRD studies suggest that these changes can be more complex than initially anticipated. Because synthesis, analysis and relevant operational conditions often place particles in different environments, understanding how particles change as a function of time in different environments is essential to predicting their properties. In such cases, aging time and environmentally induced changes in particles may play a significant role in the results reported and hence lead to discrepancies reported in various studies.

Cerium oxide nanoparticles (nanoceria) exert outstanding anti-oxidant effects in vivo acting as well tolerated anti-age and anti-inflammatory agents, potentially being innovative therapeutic tools. This is especially important, since the etiology or development of many serious diseases imply oxidative stress, and the search of reliable and effective antioxidant therapy is a focus of current pharmacological research. Nanoceria are redox-active owing to the co-existence of Ce3+ and Ce4+ oxidation states and to the fact that Ce3+ defects, and the compensating oxygen vacancies, are more abundant at the surface. However, the biological antioxidant mechanisms of nanoceria are still unclear. We are performing a pioneering study on such mechanisms [Celardo et al., 2011, Nanoscale 3:1411-20]. We selected a model of two human leukocyte cell lines, the monocytic U937 and the T lymphocytic Jurkat, focusing on the mechanisms through which nanoceria affect the oxidative status and proneness to apoptosis induced by a set of cell damaging agents. We found that nanoceria reduce the oxidative status and the extent of damage-induced apoptosis, including DNA-damaging agents, metabolic inhibitors, UV irradiation and oxidations. We demonstrated a direct cause-effect relationship between the cell anti-radical and pro-survival effects of nanoceria, showing that nanoceria only affect apoptosis occurring via redox-dependent pathways, possibly acting at the level of glutathione metabolism, whereas apoptosis induced via the physiological pathway remains unaltered. To understand which of the surface defects of nanoceria (i.e., Ce3+ ions or oxygen defects) is responsible of such effects, we doped nanoceria with increasing amount of Sm; this doping dose-dependently decreased Ce+3 and increased oxygen vacancy contents, leaving the other features unaltered. Sm-doped nanoceria progressively lose the biological effects, demonstrating that Ce+3/Ce+4 redox reactions are responsible for the outstanding in vivo properties of nanoceria [Celardo et al., 2011, ACS Nano, 5:4537-49]. A major obstacle to the in vivo use of nanoceria as therapeutic agents is the tendency to form huge aggregates in aqueous solutions, since such aggregates may promote fatal adverse effects. We are exploring the possibility of approaching this problem avoiding using any functionalization, which may alter or mask nanoceria function. Preliminary observations show that aggregates formed after suspending nanoceria in water may be separated from colloidal particles, which remain quite stable in water and retain all of the nanoceria biological activity.

Hydrogen peroxide (H₂O₂) is considered as an important analyte because of its importance in clinical diagnosis and chemical warfare. H₂O₂ is produced as a byproduct of several enzymatic reactions that can be used as diagnostic tools for detection of the onset of various biological conditions. Thus direct or indirect detection of H₂O₂ is one of the central themes in design and fabrication of various biosensors. Herein, an enzyme-free detection of H₂O₂ is demonstrated based on the colorimetric response of ceria nanoparticles (CNPs) from their redox reaction with H₂O₂. The colorimetric response originates from the charge transfer from oxygen 2p states to empty 4f and 5d states of cerium that changes with change in the Ce³⁺/Ce⁴⁺ratio of nanoparticles upon oxidation with H₂O₂. This colorimetric sensitivity of CNPs towards H₂O₂ increases significantly with decreasing crystallite size of CNPs due to an increase in total surface area as well as Ce³⁺/Ce⁴⁺ ratio on the surface of CNPs. To retain high surface area and Ce³⁺/Ce⁴⁺ ratio a single layer of 3-5nm CNPs was immobilized on transparent glass slides. Prior to immobilization the glass surface was modified by adsorption of poly(4-vinylpyridine) (PVP) to obtain self-assembled monolayers (SAMs) of PVP. During self-assembly nitrogen from one of the pyridine rings in PVP binds to the glass surface and unbound nitrogen from alternate pyridine rings can be used for immobilization of nanoparticles. Surface immobilization of nanoparticles on modified glass slides was achieved by the interaction of ceria nanoparticles with PVP-SAMs by dipping the PVP modified glass slides in varying concentration of CNPs. X-ray photoelectron spectroscopy was used to confirm PVP-SAMs formation and immobilization of nanoparticles. Cluster-free and uniform immobilization of nanoparticles was confirmed from atomic force microscopy and helium ion microscopy. UV-Visible measurements from CNPs immobilized on PVP SAMs showed a concentration dependent increase in absorbance from CNPs exposed to various concentrations of H₂O₂ demonstrating the spectrophotometric detection at micromolar concentrations. The size dependent colorimetric response from CNPs was verified by DFT calculations which suggest that small size of nanoceria as well as oxygen molecules from the solution are necessary for the colorimetric response.

We developed a predictive toxicological paradigm for safety assessment of metal oxide nanoparticles through high throughput screening analysis of mammalian tissue culture cells and zebrafish embryos. While the multi-parametric cellular assay reflects generation of toxic oxidative stress in accordance to metal oxide band gap characteristics, the effects on zebrafish embryos and larvae is more directly related to metal ion release with affects on the hatching enzyme or induction of heat shock stress responses in transgenic animals. Use of the cellular hazard profiling for comparative studies in the lungs of BL/6 mice demonstrated an excellent correlation between the in vitro property-activity relationships and the pro-inflammatory effects in the lung. We propose that it should be possible to classify oxide nanoparticle toxicity in the lung according to band gap energy levels and the relationship to biological oxidative stress. Finally, we will also demonstrate that for a metal oxide such as CeO2, its lack of toxicity as a spherical nanoparticle cannot be used to predict its toxicity in the form of a nano wire, which triggers cellular injury based on lysosomal damage.

A significant enhancement of the visible and near-infrared emission from NaYF4 nanoparticles was achieved by coating them with a plasmonic metal shell, creating a valuable composite material for labeling in biology and other applications [1-2]. The NaYF4 matrix contained ytterbium sensitizer and an Erbium (Er) or Thulium (Tm) activator. Plasmonic enhanced up-conversion emission in Tm is increased by about a factor of eight, and is observed for visible and near-infrared wavelengths. For achieving enhanced near-infrared emission from these phosphors we have tuned the sensitizer (Yb) composition in NaYF4 and LnF3 (Ln= Gd and Y) hosts. Gd was chosen as a host element, as it is a known down-converter. We have developed a protocol to convert the cubic-NaYF4 nanoparticle to either an hexagonal NaYF4 or a YF3 nanoparticle without affecting the gold shell and exhibiting higher emission efficiencies. This allowed a good comparison of NIR emissions from two different host that were prepared identically with and without gold coating. 1. L. Sudheendra, Volkan Ortalan, Sanchita Dey, Nigel D. Browning and I.M. Kennedy Chem. Mater., 23 (2011) 2987 2. Wei Deng, L Sudheendra, Jiangbo Zhao, Junxiang Fu, Dayong Jin, Ian M Kennedy and Ewa M Goldys, Nanotechnology 22(2011) 325604

Erbium-Ytterbium codoped nanophosphor systems are explored for high efficiency upconversion. The NIR to visible upconversion from 1550 nm and 980 nm excitation are of particular interest to us for biomedical applications such as imaging, sensing, and photodynamic therapy. Variations in synthesis method and rare earth concentration are carried out in sodium and barium based phosphor materials. The spectroscopic properties of the material dry and in biologically appropriate solution are taken, and the quantum efficiencies are calculated. After bioconjugation, the particles are injected into mice to demonstrate that cancer imaging with a near-infrared excitation source is possible.

Fluorescence-based imaging tests have emerged as a powerful tool for visualization of many biological events and detection of numerous biomarkers. The optical probes currently used in clinics give fluorescence in the visible region. It overlaps with autofluorescence of substrates and decreases the sensitivity of the test significantly. They also require short wavelength excitation for strong signals, which leads to severe photobleaching of samples. Complexes of lanthanide ions, such as Yb3+, have been proposed as such alternative optical probes due to their sharp emission in the NIR region. The emission is "sensitized" by energy transfer from the excited state (often are triplet states) of a chromophore that is coordinated to the lanthanide ion, followed by its relaxation to the ground state with unique emission in the NIR region. The key challenge for their application in bio-imaging is the need of a suitable chromophore that is capable of sensitizing lanthanide emission efficiently under long wavelength excitation. In this report, we will present a new class of chromophores that can sensitize the near-infrared emission of lanthanide ions efficiently under long wavelength light excitation, i. e. > 550 nm. The results will demonstrate the potential of these compounds as optical probes for medical diagnosis and imaging.

The promising potential of spintronics research has led to an increased interest in ferromagnetic materials with semiconducting behavior. Although it is accepted that gadolinium nitride (GdN) is ferromagnetic, reports on the nature of the electronic structure of GdN have ranged from insulating to semi-metallic. This lack of agreement in the literature is likely due to a wide variation in the quality of the analyzed samples and the inability to consistently synthesize high-quality GdN films. Here we report our finding of the surface electronic structure of high-quality [100]-textured GdN thin films made by a chemical vapor deposition method. The demonstrated ability to synthesize high-quality thin films has allowed for a detailed inverse photoelectron spectroscopy (IPES) study to elucidate the surface band structure of GdN. The results of our study indicate that the band gap of the GdN surface is about a few meV. These findings agree well with the predictions of a small density of states at the Fermi level and an overlap of bands at the gamma point from our density functional theory calculations for GdN slab models of eleven to twenty layers.

A detailed photodissociation mechanism for laser assisted metal-organic chemical-vapor deposition (LCVD) process using gadolinium cyclopentadienyl-type precursors, e.g. tris(cyclopentadienyl)Gd(III) (Gd(CP)3) and tris(tetramethylcyclopentadienyl)Gd(III) (Gd(TMCP)3), was elucidated using photoionization time-of-flight mass spectrometry. The collisionless environment of the molecular beam source revealed a series of unimolecular steps, starting with dissociation of an intact CP or TMCP ligand. The ligand-to-metal charge transfer (LMCT) process causes metal-reduction and intact-ligand dissociation steps, producing neutral GdLn and neutral L organic ligand. In the meanwhile, a competing step, where neutral GdLn fragments undergo directly photoionization to GdLn+, also occurs, resulting to high mass fragments ions in the mass spectrum. Another observation is that during the last ligand fragmentation different varieties of gadolinium fragments were formed, prominently the gadolinium carbides, which is helpful to understand the metal-carbides formation mechanism during the LCVD process.

The photodissociation process of lanthanum tri(methylsilyl)amide, La(TMSA)3, as an excellent precursor for thin film deposition by the LCVD method, was investigated by using the photoionization time-of-flight mass (PI-TOF) spectrometry. The mass spectra results reveal that there are two different photodissociation pathways, taking responsible for the dissociation mechanisms of La(TMSA)3 and TMSA ligand respectively. For the dissociation of La(TMSA)3, there are also two different competing dissociation mechanisms. The ligand-to-metal charge transfer (LMCT) process causes metal-reduction and neat intact TMSA ligand dissociation steps, producing of neutral La(TMSA)n (n = 1, 2) fragments and neutral TMSA ligand. The other observation is that during the ligand fragmentation, a parallel dissociation pathway is the breaking down of the TMSA ligand itself, with part of which is still attached to the mental ion. The investigation of the photodissociation mechanism gives a clear explanation on the observed peaks in the PI-TOF mass spectra and a better understanding how lanthanum nitride or silicide is formed during the thin film deposition by the LCVD method.

Chitosan, a natural biopolymer derived from shellfish, has established its applicability in numerous studies including, tissue scaffolds, topical antimicrobial agents, glucose biosensors and drug delivery platforms. Among these applications, biosensors utilizing chitosan have been championed due its excellent film-forming ability, biocompatibility, good adhesion, non-toxicity, and susceptibility to chemical modification due to the presence of plentiful amino groups and hydroxyl groups. The challenge in development of many biosensing materials is that they should offer robust and tunable characteristics (fluorescence, magnetic, thermal, etc.) while remaining biocompatible. In this work, a facile method was developed to synthesize a biocompatible hetero-nanoparticle which inherently displays multifunctionality based on a few interchangable components. As an example of the interchangable nature of the components, we will present a system composed of rare earth metal oxide (REMO) nanoparticles, Er doped Y₂O₃, with the attachment of gold nanostructures using chitosan. The resulting REMO/CHIT-Au⁰ hybrid nanoparticles are capable of displaying tunable optical properties due to the surface plasmon resonance absorption of the gold nanoparticles useful to optoacoustic applications. An overview of the nanostructure components will be given followed by morphological and spectroscopic analyses. The results of the characterizations are the focus of our future work towards the applicability of these systems to biological sensing, detection and contrast agents.

The efficiency of a solar cell can be increased significantly with a process, in which infrared photons are converted to visible photons. It is known that intermediate excited states with long lifetimes are needed for fulfilling these requirements. Rare earth ions are known for discrete energy levels and relatively long excited state lifetimes. When doped in a low phonon matrix such as glass, glass ceramics, phosphor etc non-radiative losses can be reduced and increase the fluorescence efficiency. Our preliminary study on rare earth doped glass and phosphors are efficient to convert 1550 nm to 980 nm, which can be absorbed by a conventional single crystalline silicon solar cell.

There are growing interests in the development of novel optical materials/engineering process based on organic/inorganic hybrid materials doped with rare-earth metals to satisfy a set of our increasing demands in nanotechnology. In this work, we introduce a family of highly fluorinated hybrid silicate glasses at the molecular-composite level, whose domain sizes are at the nanometer-scale. It was molecularly designed and synthesized for optical device materials, especially laser device materials. By modifying the Si-O-Si polymeric network, we prepared a hybrid glasses with controlled porosities to dope uniform rare-earth metals or semiconductors. We demonstrate hexylene- or fluoroalkylene-bridged polysilsesquioxane doped with both of Er+3 ions and CdSe nano-particles. In photoluminescent experiments, a significant enhancement in fluorescent intensity at 1540 nm has been observed from the organically modified glasses doped with Er+3 ions and CdSe phases. NMR experiments show a dramatically enhanced degree of condensation and a low level of hydroxyl environment in the fluoroalkylene-bridged glass matrix. The presence of CdSe nano-particles, by virtue of their low phonon energy, also appears to significantly influence the nature of the surrounding environment of Er+3 ions in those modified silicate systems, resulting in the increased fluorescent intensity.

Tb and Yb co-doped oxyfluoride glasses were fabricated in a lithium-lanthanum-aluminosilicate matrix (LLAS) by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. LaF3 nanoparticles (NPs) were formed in the glass-ceramic samples. Visible to near-infrared down-conversion quantum cutting was studied for samples with different thermal annealing times. Laser light at 488 nm was used to excite Tb3+ ions while Yb3+ ions were excited by energy transfer from the excited Tb3+ ions. Strong emission at 940 â?" 1020 nm was observed. It has been found that the emission at 940 â?" 1020 nm increases significantly from the glass-ceramic compared to that of the as-prepared glass. This result suggests that significant rare-earth ions were incorporated in LaF3 NPs in the glass-ceramic. Because the Yb3+ emission at 940 â?" 1020 nm is matched well with the band gap of crystalline Si, the quantum cutting effect may have its potential application in silicon-based solar cells.

The conversion efficiency of silicon based photovoltaic cells is currently around 20%. One major loss mechanism leading to low conversion efficiency is the thermalization of charge carriers generated by absorption of high-energy photons, typically UV and visible. A solution to reduce these losses has been proposed and consists in the absorption of high-energy incident photons by a luminescent conversion layer deposited in front of the solar cell and their conversion into two NIR photons able to be absorbed by silicon. This could be achieved by using a transparent matrix doped with a couple of rare-earth ions. Pr3+ - Yb3+ is considered as the most promising couple for quantum-cutting. The expected process is a two-step mechanism : Pr3+ (3P0 â?' 1G4, 1G4 â?' 3H4) â?' Yb3+ (2Ã-{3F7/2 â?' 3F5/2}). Pr3+ shows a low absorption cross-section, therefore sensitization of its 3Pj levels is necessary to obtain significant light yield. On the contrary Ce3+ ion shows a high absorption cross-section and could thus be used as a sensitizer. Energy transfer between Ce3+ and Pr3+ has already been demonstrated in a thin film of CaYAlO4 [1], so here we focus on energy transfer in CaYAlO4 doped with Ce3+, Pr3+, and Yb3+. We show that transfer from Pr3+ toward Yb3+ occurs. We present and discuss quantum yield measurement on thin films of CaYAlO4 doped with Ce3+, Pr3+, and Yb3+ deposited by PLD. Based on our results, and considering the fact that back-transfer from Yb3+ to Pr3+ is a very likely process because the 1G4 level of Pr3+ ion lies just below the 3F5/2 level of Yb3+, we discuss the possibility that quantum-cutting occurs in this matrix. [1] A. Guille, A. Pereira, G. Breton, A. Bensalah-Ledoux, B. Moine, Sensitization of Yb3+ with Pr3+ and Ce3+ in CaYALO4 for NIR quantum-cutting, submited to the Journal of Applied Physics on 22.09.2011

Ceria (CeO2) is a technologically important material, with diverse applications ranging from support materials for catalysts, based on precious and transition metals, to oxygen-ion-conducting electrolytes for intermediate-temperature solid-oxide fuel cells (IT-SOFC). However, the sintering temperature required for obtaining dense CeO2 membranes has been a significant technological challenge, especially in the implementation in IT-SOFCs. In 2010, Basu et al. [1] reported a novel co-precipitation technique for the synthesis of CeO2 using hexamethylene tetramine (HMTA) as the precipitant. The method, carried out at operating temperatures between 60 and 90oC, yielded nano-scale CeO2 powder that was crystalline at the precipitate stage and could therefore result in a significant lowering of the subsequent processing temperatures required. Suresh et al. [2] also reported that the use of cobalt as the sole dopant in Ba(Ce,Zr)O3 resulted in a bifunctional material with catalytic activity and potential mixed protonic-electronic conductivity. The use of Co and other transition metals in CeO2 has largely been limited to being sintering aids. Hence, there is scope for research on the use of these metals as primary dopants in CeO2, which could result in a novel class of bifunctional catalytic electro-ceramics. The aim of the present study is to adapt the aforementioned synthesis technique to the synthesis of CeO2 doped, or co-doped, with different transition metals. Materials with nominal compositions of Ce1-xMxO2-δ (x = 0.00 to 0.15; M = Co, Mn etc.) were synthesized from nitrate precursors using HMTA-based co-precipitation. The precipitates were heat-treated at higher temperatures and X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) were carried out on both the heat-treated powders and the as-synthesized precipitates in order to determine the evolution of phase distribution, particle size and particle morphology. The materials were also synthesized using solid-state reaction and analyzed using XRD and TEM in order to provide a comparison between the different synthesis techniques. [1] Basu et al., Applied Surface Science, 256 (2010) 3772 [2] Suresh et al., Journal of Materials Science, 45 (2010) 3215

Detection of trace levels of non-ubiquitous radioactive isotopes using radiometric methods requires sensitive materials coupled with well-tuned electronics to identify real, potentially threatening, interaction events in a noisy natural background. The rare earth element cerium coupled with lithium in the Elpasolite structured halide offers the ability to detect both γ-rays and thermal neutrons. Elpasolites are a complex class of compounds with the chemical composition A₂BMX₆ where A and B are monovalent cations, M is a trivalent cation, and X is a monvalent anion. The structure is a substitutional variant of a cubic perovskite where the cation valences are altered to maintain electroneutrality. Optical and crystallographic properties from growths of Cs₂LiCeCl₆ and Rb₂LiCeBr₆ Elpasolites will be reported. Detection sensitivity is expected to increase with larger crystal size and quality. Methods for handling and encapsulating this hygroscopic material will also be discussed.

In this paper we investigate the infrared-to-visible upconversion luminescence in bulk crystals and nanocolloid filled photonic crystal fiber with ytterbium and erbium co-doped, ytterbium and holmium co-doped and ytterbium and praseodymium co-doped NaYF₄ upconversion phosphors. The phosphors were prepared by using simple co-precipitation synthetic method. The initially prepared phosphors have very weak upconversion fluorescence. The fluorescence significantly increased after the phosphor was annealed at a temperature of 600⁰C to obtain the hexagonal-phase. Nanocolloids of this phosphor were obtained using polar and non polar solvents and they were utilized as laser filling medium in photonic crystal fibers. The size of the nanoparticles in the colloids was measured using the atomic force microscope. Under 980 nm laser excitation very strong upconversion signals were obtained for the ytterbium and erbium co-doped phosphor at 408 nm, 539 nm and 655 nm, for the ytterbium and holmium co-doped phosphor at 541 nm, 646 nm and 751 nm. Efficiency, pump power dependency and decay life time study of the upconverted emissions were conducted to understand the upconversion mechanisms. The reported nanocolloids are good candidates for fluorescent biosensing applications and also as a new laser filling medium in fiber lasers.

Ceramic proton conductors are extensively studied for their potential use as electrolyte in electrochemical devices such as fuel cells, electrolysers and gas sensors. We are searching for strategies to control the proton conductivity activation energy in order to make better fuel cell electrolyte. Recent data show that the activation energy scales linear with the lattice parameter, suggesting that an enlarged lattice volume â?" for example thin films with epitaxial strain - can promote proton conductivity. To comprehend the crystalline and vibronic structure, optical Raman spectroscopy and XRD were studied on the compressively strained BaCe0.8Y0.2O3-δ (BCY20) proton conductors, indicating that lattice softening results in better proton mobility; also the lattice softening may be anisotropic. This may provide a general guideline for the development of epitaxial strained proton conducting thin film systems with high proton mobility and low activation energy using tensile strain.

Lanthanide sesquioxides Ln2O3 are a group of compounds of particular importance for a variety of technical applications due to their electronic and magnetic properties. Intriguingly, a range of physical properties of X2O3 have been found to periodic in the lanthanide series X=La,...,Lu. Prokofiev et al[1] have shown that the band gaps from photoemission experiments are periodic and exhibit four distinct dips for Ce, Eu, Tb and Yb, which arise due to 4f levels entering the forbidden gap. Common density functional theory (DFT) approaches in the frame of the local-density (LDA) and generalized gradient approximation (GGA) fail to reproduce both the magnitude and the periodicity of the optical band gaps of Ln2O3 sesquioxides due to the inherently bad description of strongly correlated electrons. Jiang et al. showed that an a posteriori G0W0 self-energy correction on LDA+U calculations can restore the experimental results, but such approaches are computationally expensive and unsuitable for total energy calculations. We have investigated the band structures of all 15 Ln2O3s by means of hybrid DFT[3]. Here, many-body effects are introduced by mixing a fraction of Hartree-Fock exchange into the LDA/GGA exchange-correlation, which leads to a general improvement of the prediction of physical properties. We show that (i) the three hybrid functionals HSE, HSE06[4] and sX-LDA[5] substantially improve on the purely local functionals and can restore the observed periodicity of the optical gaps and the observed plateau between Ho2O3 and Tm2O3. (ii) The obtained band gaps for HSE06 are in good agreement with experimental values (typically within 0.2-0.4 eV) for almost all investigated lanthanide oxides. (iii) The HSE06 gaps are mostly superior to those reported for the more sophisticated G0W0@LDA+U[2] approach. (iv) The band gaps from HSE are typically ~0.3 eV smaller than those from HSE06 and of similar accuracy as the G0W0@LDA+U values. (v) sX-LDA predicts the 4f levels at higher energies than the other two functionals, thus being particularly good for materials with no occupied 4f levels in the band gap. [1] A. M. Prokofiev, A. Shelykh, and B. Melekh, VIER Journal of Alloys and Compounds 242, 41 (1996) [2] H. Jiang, R. I. Gomez-Abal, P. Rinke, and M. Scheffler, Phys. Rev. Lett. 102, 126403 (2009) [3] A. Seidl, A. Görling, P. Vogl, J. A. Majewski, and M. Levy, Phys. Rev. B 53, 3764 (1996) [4] J. Heyd, G. E. Scuseria, and M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003) [5] D. M. Bylander and L. Kleinman, Physical Review B 41, 7868 (1990); S. J. Clark and J. Robertson, Phys. Rev. B 82, 085208 (2010)

Ab-initio calculations have been performed to examine the magnetic ordering of Gd ions when incorporated in a ZnO matrix. Following trends reported experimentally we examine whether ferromagnetic exchange interaction between the Gd ions is an intrinsic property of the ZnO matrix [1], carrier mediated [2], or mediated via Zn vacancy point defects. Our results indicate that when Gd ions are located in Zn substitutional sites there is no coupling between the rare earth ions. The introduction of carriers, in the form of electrons or holes, into the system does not alter the aforementioned result. Furthermore, introducing a Zn vacancy in various locations relative to the dopant atoms and in different charge states (-2, -1, 0, +1, and +2) continues to show no difference between the computed ferromagnetic and antiferromagnetic energies. Our density functional theory simulations thus show that for all of the aforementioned scenarios there is no exchange interaction between the magnetic dopants [3]. [1] K. Potzger, et al., Journal of Applied Physics 99, 063906 (2006). [2] M. Subramanian, et al., Journal of Applied Physics 108, 053904 (2010). [3] M. Ungureanu, et al., Superlattices and Microstructures 42, 231 (2007).

Pyrochlore structured rare earth oxides with the general composition Ln2X2O7 display a vast range of properties ranging from ionic conductivity to spin-ice systems. The varying properties stems from the large flexibility of the pyrochlore structure, both in terms of composition and defect chemical-wise [1]. For instance Ca-doped La2Zr2O7 has been shown to display a significant protonic conductivity at elevated temperatures, with a proton transport number close to unity in the temperature range 473-873 K [2], whereas bulk Er2Ti2O7 displays no contributions from protons to the overall conductivity [3]. In the present study we aim to discuss the effect of Ln and X-site substitution on proton related defect properties through the Ln2X2O7 (Ln=La-Lu and X=Zr, Sn, Ti ) series of oxides. In this work, we apply Density functional theory (DFT) calculations in combination with the Nudged Elastic Band (NEB) method and Molecular Dynamics (MD) simulations to elucidate relative stabilities of proton related defects, defect-acceptor association, vibrational and mobility trends through the series. The computational work is supplemented with experimental, thermogravimetric (TG) analyses of the hydration trends through the series. Both from the DFT calculations and the TG measurements, the enthalpy of hydration of oxygen vacancies becomes less exothermic with decreasing radii of the Ln ion for all Ln2X2O7 series (X=Ti, Sn, Zr), in-line with previous experiments. From the MD/NEB analyses, we determine a proton jump process involving both rotation and jump of the protonic defect to be the rate limiting step for proton diffusion. Further, both the activation energy of proton mobility and the vibrational properties of the protonic defects depends on the size of the Ln ions. Finally, the observed trends are discussed in terms of bonding nature, structure and general composition of the included pyrochlore oxides. 1.Subramanian et al, Progress in Solid State Chemistry, 1983. 15(2): p. 55-143. 2.Omata, T., et al., Solid State Ionics, 1997. 104(3-4): p. 249-258. 3. Fjeld et al., Solid State Ionics (October 2008), 179 (33-34), pg. 1849-1853

La2Ce2O7 has been studied for several decades for the use as an ionic conductor in solid oxide fuel cells and oxygen sensors [1-3]. The material is known as a pure oxygen ion conductor at high temperatures, but has recently attained attention, due to experimental findings of a significant protonic conductivity, with protons as the main charge carrier below 400°C [4]. Earlier work on structural characterization concludes that this ternary oxide adopts the disordered fluorite structure [4,5]. However, in a recent work, the complexity of the structure is emphasized and raise question regarding the variety of experimental results indicating more or less ordering towards the pyrochlore structure. They claim that La2Ce2O7 is shown to be stable in the pyrochlore structure based on first principal calculations [6], hence placing La2Ce2O7 on the other side of the ionic radius ratio border between the stability regions of disordered fluorite and pyrochlore. The difference between disordered fluorite with no short-range order and the long range ordered pyrochlore is of great importance when studying inherent oxygen deficiency and investigating hydration thermodynamics, as well as transport properties of protons in the material. In this work, we focus on investigating the materials structural features and defect chemistry through First Principles total energy calculations. Structural ordering is studied by comparing its formation energy with cation and anion ordering range between the disordered fluorite and pyrochlore structure. Further, we focus on the local arrangement of various point defects in the material, encompassing protonic defects, oxygen vacancies, aliovalent dopants and their mutual association complexes (i.e. defect clustering). The formation energies of the possible defects are evaluated and their relative stabilities compared. Also migration paths for the various point defects are studied. Density functional theory (DFT) calculations in combination with the Nudged Elastic Band (NEB) method and Molecular Dynamics (MD) simulations are applied for modeling of the system and results are compared with indications obtained by experimental results performed by others in our research group. [1] H. L. Tuller andA. S.Nowick, J. Electrochem. Soc. 122, 255 (1975). [2] T. Kudo and H. Obayashi, J. Electrochem. Soc. 122, 142 (1975). [3] J. S. Bae, W. K. Choo, and C. H. Lee, J. Eur. Ceram. Soc. 24, 1291 (2004). [4](To be published)Ionic conductivity and hydration of the inherently oxygen-deficient La2Ce2O7-δ, V. Besikiotis, R. Haugsrud, T. Norby, Department of Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, FERMiO, Gaustadalleen 21, NO-0349 Oslo, Norway. [5] Knop, F.B.a.O., Can. J. Chem, 45(6), 609-614. (1967). [6] D. E. P. Vanpoucke, P. Bultinck, S. Cottenier, V. Van Speybroeck, and I. Van Driessche, Phys. Rev. B 84, 054110 (2011)

Impedance spectroscopy on the hydrated proton conductor BZY10 at high T shows that bulk proton conductivity activation energy scales with the strain parameter ε, as achieved by hy-drostatic pressures up to 2 GPa, suggesting that large lattices favor proton diffusivity. At high T, Eb increases upon pressure by 40%. The grain boundary activation energy Eg is around twice as Eb, indicating higher proton mobility in grain boundaries as a result of pressure induced sintering. Bragg reflections in Y-resonant XRD of BZY10 reveal that Y is organized in a superstruc-ture. Comparison with neutron diffraction superstructure reflections in protonated/deuterated BZY10 suggests that both superstructures are linked, and that protons move in the landscape imposed by the Y. The thermal expansion decreases abruptly for protonated BZY10, coinciding with lateral proton diffusion and suggesting a correlation of structural changes and proton conductivity. In-situ EIS was used to study strain on the proton conductivity of BCY by applying hydrostatic pressure up to 1.25 GPa. Increased bulk conductivity activation energy was found with increasing p during volume change, confirming the suggested correlation between lattice volume and proton diffusivity. BCY20 under hydration and strain was analyzed with high p Raman spectroscopy and high p XRD. The p dependent variation of the bending modes is suppressed upon hydration, affect-ing directly proton transfer by changing electron density of the oxygen. Compressive strain causes hardening of stretching bonds, with the pressure coefficient being the same for the dry and hydrated sample. The activation barrier for proton conductivity is raised, in line with recent findings using high p,T EIS. Hydration also offsets slightly the stretching modes towards higher wave numbers, revealing an increase of the bond strength. Some reflections do not change during pressurizing and thus reveal that the oxygen occupying the O2 site displaces only along b-axis. The increasing Raman frequency thus implies that phonons become hardened and increase the vibration energy upon compressive strain, whereas phonons are relaxed in the b-axis, and thus reveal softening of modes. Lattice toughening raises therefore a barrier for proton transfer and thus anisotropic conductivity. The experimental findings of the interaction of protons with the ceramic host lattice under external strain may provide a general guideline for yet to develop epitaxial strained proton conducting thin film systems with high proton mobility and low activation energy. We will also present very recent ambient pressure high temperature XPS data as well as high-pressure quasi elastic neutron scattering data. References: Q. Chen et al. Journal of Physical Chemistry C, in press http://pubs.acs.org/doi/pdf/10.1021/jp208525j Q. Chen et al. J. Eur. Ceram. Soc. (2011) 31, 2657. Q. Chen et al. Appl. Phys. Lett. 97, 041902 (2010). A. Braun et al. J. Appl. Electrochem. 2009, 39, 471.

GdN is an intrinsic magnetic semiconductor and possess excellent optical, electronic and magnetic properties which make promising material for creating new functionalities in semiconductor spintronics and magneto-optical devices. Recently, the magneto-optical effects in AlN/GdN/AlN heterostructures have demonstrated in our earlier studies [H. Yoshitomi et al., PRB83, 155202 (2011)]. Here we demonstrate a detailed study on the cooperative phenomena of optical and magnetic properties of AlN/GdN/AlN heterostructures grown by using a reactive radio-frequency magnetron sputtering technique performed under molecular-beam epitaxial quality with a base pressure less than 5Ã-10-6 Pa . The ultra-high vacuum conditions during growth of GdN enable us to curtail oxophilicity character. The temperature dependent optical absorbance measurements have been carried out to evaluate the direct optical band gap at the X point through the Tauc plots for the heterostructures. For the first time, the optical absorbance studies have demonstrates an exceptional spin-splitting in valance and conduction bands in GdN below the Curie temperature. The optically induced spin-splitting energy has enhanced by decreasing temperature below Tc and is an evidence of transformation from subtle to stalwart ferromagnetic behaviour. This remarkable investigation has explained in terms of long range ferromagnetic ordering of magnetic moments. The spin-splitting energy is slightly increased from 45 K to 30 K and the difference is merely Î"E=12 meV. This slight difference pertaining to the marginally increase of magnetic moments, leads to soft ferromagnetic behaviour. In addition to that the spin splitting energy drastically increases from 25 K to 3 K and the difference is Î"E=172 meV. This startling increase convincing that there is rapid increase of magnetic moments caused by long range correlation of spins. The magnetization measurements have undertaken to investigate the short and long range ordering of magnetic moments for the heterostructure. When the temperature decreased to below 45 K, the magnetization began to gradually increase and saturated at ~6 μB/Gd3+ at B = 2.0 mT. This value is slightly smaller than the theoretically expected value of 7 μB/Gd3+. This could be interpreted by magnetic anisotropy induced by the external magnetic field. The unprecedented spin splitting phenomena including with great tendency to generate spin polarized electrons in GdN have inspired to offer new frontier in spin filtering and magneto-optical devices.

In view of achieving room temperature ferromagnetism in Gd doped ZnO thin films towards improving its diluted magnetic semiconducting (DMS) properties for spintronic applications [1-3], we have prepared few Gd doped ZnO thin films and studied their structural and magnetic properties. All the thin film samples were prepared on sapphire substrates by PLD technique employing a KrF excimer laser (λ= 248 nm) at different O2 pressures and substrate temperatures. XRD and HR-SEM analyses revealed that all the films were polycrystalline and quasi epitaxial, oriented along the c-axis of the ZnO. The XRD patterns showed no trace of any secondary phase. Magnetization measurements carried out using a SQUID-VSM showed that 0.5at% Gd doped Zno was not ferromagentic. Gd 1at% and 5at% doped ZnO thin films were ferromagnetic at room temperature however, at 5K they exhibited a superparamagnetic like behaviour. The origin of the room temperature ferromagnetism, its intrinsicality or a possibility of coexistence of a magnetic and a superparamagnetic phase are being analysed using different microstructure, magento-transport and spectroscopic studies. References: 1) T. Dietl, H. Ohno, F. Matsukura, J. Cibert, D. Ferrand, Science, 287 (2000) 1019-1022 2) H. Ohno, F. Matsukara and Y. Ohno, JSAP International 5 (2002) 4-13 3) S. J. Pearton, C. R. Abernathy, M. E. Overberg, G. T. Thaler, and D. P. Norton, N. Theodoropoulou and A. F. Hebard, Y. D. Park, F. Ren and J. Kim and L. A. Boatner J. Appl. Phys. 93 (2003) 1-13

Near room temperature magnetic cooling, based on the magnetocaloric effect (MCE), is an emerging technology that has the potential to achieve significantly higher efficiency than conventional vapour compression. Its future relies heavily on the availability and ease of processing of high performance magnetic refrigerant materials. The first condition posed on the magnetic refrigerants â?" a large (giant) MCE â?" guides us to the use of materials experiencing a first-order magnetic phase transition. Extensive research activity has concentrated on optimising the magnetic properties of such materials by chemical composition modification, while little effort has been made in terms of microstructure design to overcome such detrimental effects of the first order transition as large hysteresis and poor mechanical stability. Among the materials with a first order transition, the La(Fe,Si)₁₃ compound occupies a special place. The abundance of its main constituents, iron and silicon, and substantially higher availability of light rare-earth lanthanum, as compared to heavy rare-earth gadolinium (a benchmark material against which performance of other materials is frequently compared), as well as the possibility of adjusting the Curie temperature by partial substitution of Fe by Co and/or by hydrogenation makes this material a promising magnetic refrigerant. The compound has also a low intrinsic hysteresis. The frequently observed hysteresis in the LaFe_13-xSi_x alloys is of microstructure-driven nature [1] and can be reduced by introducing porosity and by decreasing grain size from the micro- to nanometer range [2]. While porosity provides long-term stability by sacrificing only a small fraction of the MCE value, the thermal conductivity of porous alloys decreases significantly. Here, we demonstrate the use of electrochemical methods for the preparation of novel high-performance composite materials consisting of the active magnetic phase La(Fe,Si)₁₃ in a ductile, high thermal conductivity Cu matrix. We further show that electrochemical treatment is a powerful method in the processing of LaFe_13-xSi_x for near-room temperature applications and provides a significant advance in the area of magnetic refrigeration. This research was supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme. [1] J. Lyubina, R. Schäfer, N. Martin, L. Schultz, O. Gutfleisch, Adv. Mater. 22 (2010) 3735. [2] J. Lyubina, J. Appl. Phys. 109 (2011) 07A902.

Pr2Co7 alloys with high coercivity were synthesized by mechanical alloying and subsequent annealing. X-ray diffraction analysis by Rietveld method was used to determine their structure and lattice constants. The crystallization, phase components and magnetic properties of the alloys were investigated systematically. For samples annealed at TA = 800 °C, the main phase of those alloys is hexagonal of the Ce2Ni7 type structure whereas at TA = 1050 °C, the main one is rhombohedral of the Gd2Co7 type structure. The coercivity increases with annealing temperature reaching a maximum for TA = 800 °C. The highest is equal to 18 kOe at 293 K and 23 kOe at 10 K. This leads to the formation of a magnetically hard Pr2Co7 phase. This high coercivity is attributed to the high anisotropy field of the Pr2Co7 phase and its nanoscale grain size.

The remanent magnetization (Mr) and the coercive field (Hc) are the two main parameters determining the performance of hard magnetic materials. Highest values are obtained in the rare earth-transition metal based magnets (Sm-Co and RFeB, R=rare-earth). Demand for RFeB magnets is increasing rapidly for use in hybrid cars and wind mills. The high coercivities required for such applications are currently achieved by partial substitution of heavy rare earth elements (Dy, Tb) for light rare earth ones (Nd, Pr). The heavy rare earths (HRE) being strategic elements, there is now a major drive to develop HRE-free RFeB magnets with sufficiently high coercivities. Better understanding of the mechanisms which determine Hc is needed for the development of such materials. In the idealistic Stoner-Wohlfarth model the coercive field Hc is equal to the anisotropy field, HA. In real systems, Hc is typically 5-10 times weaker than HA (µ0HA = 8T in Nd2Fe14B). Conceptually, it is understood that an essential link exists between coercivity and microstructure. Experimentally, the challenge is to identify the nature of this link. Thick hard magnetic films, in which the nanostructure can be modified through a variation in processing parameters, constitute model systems for coercivity studies. Coercive field values of up to 2.7 T, which are significantly higher than what has been reported for bulk HRE free magnets, have been obtained in NdFeB films containing trace quantities of Cu. Such films are characterized by Nd-rich grain boundary phases, the continuity of which is attributed to a redistribution of the phase while it is in liquid form, under the influence of compressive stress, during a post-deposition annealing step. Such a Nd-rich grain boundary phase would favor exchange decoupling of the hard magnetic grains. It may also favorably modify the intrinsic magnetic properties of the surface of these grains. The coercive field and activation volume are measured from low temperature up to 400 K. The link existing between these quantities are discussed in the framework of the so-called global model. Their experimental values are shown to be in excellent agreement with those derived from micromagnetic modeling. The angular dependence of the coercivity is compared to calculated predictions. Ab initio calculations indicate that part of what was previously attributed to structural defect, is actually intrinsic to the material. In view of enhancing further the coercive field of hard magnets, the concept of superferrimagnetism, in which the hard magnetic grains would be antiferromagnetically coupled to a ferromagnetic or ferrimagnetic grain boundary phase, is proposed. The question arises whether materials can be developed, with suitably controlled nanostructures, permitting the full realization of this concept. Finally, prospects for developing new hard magnetic materials, containing a greatly reduced amount of rare-earth elements, will be discussed.

New coating technology enables the fabrication of low cost structural health monitoring and tamper indication devices that can be employed to strengthen both national and international safeguards objectives. There is particular interested in exploring new coating materials and techniques that would allow for quick and reliable verification of device authenticity and integrity through â?ocharacteristicâ? optical coatings. Synthesis of fluorescent functional coatings by chemical solution deposition using both alumina and silica host matrices has been performed to incorporate dopants (Er⁺³ and Tb⁺³) which exhibit fluorescence on the surface of the ceramic specimens. These dopants have been identified as possible candidates due to their unique optical response (UV excitation with visible emission) and have been successfully incorporated into the alumina and silica films. Fluorescence microscopy was used to investigate the photoluminescence properties of the doped matrixes and reveals unique properties. Techniques for the deposition of the Er⁺³ and Tb⁺³ doped alumina gels on alumina ceramics with tailored thickness in the micron range including dip coating and spin coating will also be discussed. The structural evolution of the coatings with time, temperature and dopant concentration was evaluated using FTIR, Raman, XRD, UV-Vis and Fluorescence spectroscopy. The combination of fluorescence and spatial-Raman spectroscopy help in offering a non-invasive way to detect tampering of devices. The optimal performance which balances durability, emission intensity (synergy effects of co-doped gels and ceramics with hidden emission properties) and ease of processing will be reported.

5%Eu:YPO4.xH2O (x=0.5-1) nanocrystals were successfully synthesized by a solvothermal method. Thenoyltrifluoroacetonate (TTFA) was used to replace a small fraction of the oleate capping ligand on the as-prepared 5%Eu:YPO4.xH2O (x=0.5-1) nanocrystals in order to sensitize the emission of Eu3+ ions. The resulting samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), UV-Vis absorption spectroscopy, photoluminescence (PL) spectroscopy and time-resolved luminescence spectroscopy. XRD analysis indicates that the samples are crystalline with a hexagonal phase. The oleate capped 5%Eu:YPO4.xH2O (x=0.5-1) nanocrystals nanoparticles have very interesting structure, which is a zeolite structure with a porous surface. The morphology and quality of the nanoparticles remains unchanged upon ligand exchange. FTIR spectra indicate that, after ligand exchange, the capping ligand is still primarily oleate, such that good dispersion in chloroform is maintained. The colloidal dispersions show the characteristic emission of Eu3+ 5D0-7FJ (J=0-4) when excited at the TTFA absorbance band (350 nm). Ligand excitation at 350 nm results in Eu3+ emission that is 88 times brighter than that obtained by direct Eu3+ excitation at 394 nm with a 1.2 mol% TTFA on the surface of the nanoparticles. The ability to sensitize emission from these nanocrystals greatly increases their potential for application in display and lighting fields.

Polycrystalline ceramics are desired materials for applications in demanding environments because they offer high hardness, high melting points and chemical stability. Moreover, their development as transparent materials has seen a recent resurgence in activity due to their viability as optical-structural materials as well asfor light emitting applications such as laser host materials. Historically, there has been much effort devoted to doping ceramic host materials with rare-earths with a particular reliance on thermodynamic equilibrium processing techniques, i.e. the Czochralski and verneuil techniques for single crystal variants, and pressureless sintering and hot isostatic pressing for polycrystalline counterparts. Some dopants cannot be added through equilibrium techniques however. If we consider rare-earth doping of aluminum oxide for example, we find that the dopant levels are limited by the rare-earth solubilities in the host at equilibrium. Because rare-earth dopant solubility in alumina is very low, ~10-4%, the functionality of transparent alumina as a rare- earth host material for photoluminescent purposes is negated although alumina possesses a good thermal conductivity and transparency. Thus, little attention has been given to producing rare-earth doped bulk transparent ceramics with non-equilibrium processing techniques. Here we report on the application of the Current Activated Pressure Assisted Densification (CAPAD) technique for the production of rare-earth doped aluminum oxide transparent polycrystals to dopant levels as high as a few atomic percent We have investigated the effects of processing temperature, and pressure on the resultant sample density, microstructure, and on optical properties, e.g. transmission, reflectance, absorbance, and photoluminescence.

Phenomena related to the interaction of light with rare earth emitters (RE) coupling to metallic nanoparticles (MN) have been attracting large intention due to their relevance for a variety of applications such colored displays, optical amplifiers, as well as photovoltaic devices1. The addition of MN in RE doped matrix was used to promote the emission enhancing or quenching2. These effects are due either to local field enhancement around RE3 or to energy transfer2 between MN and RE emitters. These two mechanisms are a function of the correlation between metal Plasmon resonance and emitter energy level, and a function of the structure geometry i.e. size and shape of MN and distance between MN and emitter. In this work, we investigate the effect of the distance d between MN and RE emitters on their emission. This study needs positioning emitters at controlled distance of MN. The main technique used in the literature is the doping with MN of RE doped matrix like in glass2 and as the concentration increases the distance between MN and RE increases statistically. In our knowledge the investigation on a single RE particle is not been published due probably to the weak emission of RE doped nanoparticles4. Another approach is to use multilayer structure consisting on MN layer and emitter film separated by a passive spacer. It is important to distinguish the studies of MN island film effect5 and metal mirror effect, which is more studied6. In this study the composite films containing MN were prepared by the alternate pulsed laser deposition technique, which allows the deposition of multilayer in a single step. Passive Y2O3 and emitting Eu:Y2O3 targets have been used. Two metal targets have been tested, Ag and Al, to adjust the Plasmon resonance to the absorption of Eu3+ ions in f-f dipolar electric transition or in Eu-O transfer charge. The most critical aspect of this approach is the fine control of the thickness of each layer. For each material, the deposition rate was first determined by m-lines and/or profilometric technique in order to adjust precisely the number of pulses. MN layers growth was observed by Transmission Electron Microscopy and absorption analysis. Varying the spacer thickness, we monitor over which distance the RE emission is enhanced. By comparing near-field simulations3 with experiments, we establish the relationship between the properties of the composite films (MN size, distance d) and the electrical field surrounding RE. Two effects are demonstrated: the first one at short distance (< 30nm) modelled by an interaction with a single MN and the second one at longer distance modelled by the interaction between a MN group. 1 J.C.G. Bunzli & al J. Rare earths 25 (2007) 257 2 M. Eichelbaum & al Adv. Funct. Mater 19 (2009) 2045 3 G. Colas des Francs & al Opt. Exp. 16 (2008) 17654 4 P. Anger & al Phys. Rev. Lett. 96 (2006) 113002 5 C.Lin & al J. Lumin. 130 (2010) 1907 6 S. Karaveli & R. Zia Phys. Rev. Lett. 106 (2011) 193004

The findings from this investigation contribute to developing a material that interacts uniquely to different types and doses of radiation. The current work explores the radiation effects of YAG and pyrochlore structures under proton and alpha irradiation. The phosphor does not act as a scintillator, but rather it records the damage that can be queried at any time after exposure. We chose yttrium aluminum garnet doped with cerium (YAG:Ce) because it is used in many applications and thus its fabrication and properties are well understood. The pyrochlore lanthanum zirconate doped with europium (LAZ:Eu) was also chosen because its crystal structure is different and consequently its photoluminescent response to due radiation-induced damage is unique. Luminescent intensity or radiation interaction events can be improved by changing the composition of the materials. For example, substituting gallium for aluminum in YAG magnifies the radiation cross-section and increases the sensitivity to radiation-induced displacement damage. Radiation interactions change the crystal structure of the phosphor and result in the permanent damage we measure. Photoluminescent spectroscopy is used to recover the information about the damage. Typical results show degradation in the intensity of the spectra, changes in the relative peak intensities, or even peaks red- or blue-shifting mechanism. At 3x10^6 particles/mm^2 of alpha particle exposure there is significant photoluminescent intensity degradation. Proton bombardment between 1x10^14 and 1x10^16 particles/mm^2 show approximately exponential decrease of the emission spectra as well. These results provide strong indication that our materials are being damaged by the radiation and that the radiation effects can be quantified.

A new type of neutron detection scintillator based on rare-earth activated transparent glass-ceramic will be reported. ⁶Li-based scintillating glass has been an attractive neutron detection material due to its low-cost, large-volume production capability and easy shaping of elements. However, glass typically exhibits relatively low light yields, due to the amorphous structure and the presence of many defects which form trapping sites responsible for non-radiative recombinations. By introducing nanocrystals into the glass-matrix, luminescence efficiency can be potentially improved while the scintillatorâ?Ts transparency remains high. In this paper, Ce³⁺ activated gadolinium halide nanocrystal embedded glass-ceramic scintillators were developed by an economic melt-quench method followed by annealing. The nanocrystals were formed in-situ by phase separation and precipitation from the supersaturated precursor glass and uniformly distributed in the glass matrix. Such materials provide a desirable low phonon energy halide environment for the activator ions while maintaining the advantages of oxide glasses, including high mechanical strength, chemical durability, and thermal stability. The ⁶Li content, Ce³⁺ doping concentration and processing conditions were optimized to improve the light output based on photoluminescence and alpha particle excitation measurements. The neutron scintillation properties will be investigated and compared to conventional ⁶Li-based scintillating glass.

Binary europium chalcogenides (EuX: X = S, Se, Te) and ternary lead europium chalcogenides (Pb_xEu_yX) have been studied for many years for their potential employment in diverse applications, such as optical isolators, infrared diode lasers and spintronics devices, due to their tunable optical and semi-magnetic properties. Among the Pb_xEu_yX ternary compounds, lead europium sulfide (Pb_xEu_yX) is likely to be most suitable for applications that call for dilute magnetic semiconductors because they can form a completely miscible alloy system with tunable energy band gaps over a wide range. Europium telluride provides an intriguing system to explore size-dependent effects within antiferromagnetic materials. We report the structural and composition dependent magnetic properties of Pb_xEu_yX and EuTe nanomaterials. The crystallinity of the nanocrystals was affirmed by X-ray diffraction and transmission electron microscopy, whereas the magnetic characteristics were probed by vibrating sample magnetometry. Pb_xEu_yX nanocrystals exhibited paramagnetic properties down to 2K, whereas comparably-sized PbS was diamagnetic and EuS was ferromagnetic at these temperatures. For EuTe, we observed finite size effects that induced the formation of a superantiferromagnetic state.

In the last decade, Tetrathiafulvalene derivatives have been associated to d metal ions to elaborate multifunctional materials which possess magnetic and electrical properties. The 4f lanthanides exhibit exiting specific luminescent properties. In particular, lanthanide complexes with a-diketones have focused a large attention due to their potential applications in the design of chelate lasers, efficient organic and polymer light emitting diodes (OLEDs and PLEDs). The irradiation of the [Yb(hfac)3(TTF-CONH-2-Py-N-oxide)2] compound in the HOMO-LUMO+1/+2 charge transfer bands provokes the emission of both donor and Yb(III) ion. We have shown that the donor is an efficient organic antenna for the sensitization of Yb(III) luminescence.[1] Lanthanide ions are also well-known to exhibit strong magnetic anisotropy and so they are considered as good candidates for the elaboration of Single Molecule Magnets (SMM). We have associated the tetrathiafulvalene-3-Pyridine-N-oxide ligand to the Ising Dy(III) ions producing a centrosymmetric dinuclear complex in which the magnetic moments are antiferromagnetically coupled. Surprisingly, the complex behaves as a SMM with strong frequency dependent out-of-phase signal of the ac magnetic susceptibility.[2] [1] F. Pointillart et al. Chem. Eur. J. 2010, 16, 11926. [2] F. Pointillart et al. Chem. Eur. J. 2011, 17, 10397.

The phenomenon of luminescence enables a variety of purposes ranging from biotechnology to photovoltaics. This research has developed printed thin polymer films containing lanthanide doped nanoparticles that convert near-infrared light to a visible wavelength region. In this work, lanthanide-doped, sodium yttrium fluoride (β-NaYF4: 3%Er, 17%Yb) nanocrystals were prepared and dispersed in a solvent consisting of 90 vol% toluene and 10 vol% methyl benzoate. Poly (methyl methacrylate) polymer was dissolved in the solvent, in addition to the nanocrystals. These inks were printed using direct-write techniques. For large area printing, a Sono-Tek Exacta Coat 3 axis robot with an Impact EDGE print head system was used, while an Optomec Maskless Mesoscale Materials Deposition system was used to print fine lines. Substrates used included Kapton®, bond paper and glass. For large area printing, a stencil was manufactured and the nanocrystal-containing inks were printed over the stencil using the Sono-Tek system. The stencil pattern was also put into CAD software and printed using the Optomec system. The upconversion from these printed patterns was observed using a 980 nm laser and both types of patterns produced yielded very strong green light which matched the desired patterns. In addition to stencil printing, QR codes were generated and these codes were then printed using the Optomec system. The upconversion from these codes was easily read using a smart phone. These codes were also printed using rare-earth doping giving blue, red and green colors. The printed materials were found to be quite robust to bending and folding of the flexible substrate. On many substrates, these printed traces are difficult to detect, making them very useful for covert and semi-covert security printing applications.

Nitride ceramics, particularly some III-nitrides are wide band gap semi-conductors that could be useful in high power light emitting applications since they have high thermal conductivity. Doping nitrides with rare earths (RE) offers the possibility of photoluminescence and longer duty cycles and/or higher average power photonic devices. However it has been challenging to produce RE doped nitrides using conventional techniques. Here we apply the current activated pressure assisted densification (CAPAD) process in order to densify bulk polycrystalline nitrides. Results on AlN samples that were consolidated to near full density and doped with RE dopants, Gd, Tb, Dy will be presented. Optical properties of the materials such as Transparency, absorption and Photo luminescence spectra will be presented.

Since practically the beginning of the laser, some of the most successful lasers have relied on rare earth ions, principally in the form of trivalent cations in crystalline or fiber hosts. Most trivalent lanthanides have several strong emission lines, and the wavelengths of these lines differ substantially among the lanthanides, providing some flexibility in laser wavelength selection. Their absorption and emission lines are narrow, making it relatively easy to achieve large cross sections (for gain at the laser wavelength and for absorption of pump light) in systems with attractively long upper state lifetimes. Lasers based on these ions are studied by many groups and used in many applications. Today, I will present a few examples from the work of our team at the Army Research Laboratory, highlighting the interrelation between spectroscopic properties and laser behavior. I will concentrate on bulk solids, though rare-earth-doped fiber lasers are also extremely important to us and to the broader community. One system to be discussed is Nd:YAG, particularly ceramic YAG, which can accommodate higher Nd3+ concentrations than can single crystal YAG. Studies of concentration quenching clarify its mechanism, and help to identify the useful concentration limits for practical laser operation. Another important rare earth laser ion is Yb3+. It can perform well at far higher concentrations than can Nd3+, and comparison of spectroscopic and laser properties help to show that systems such as Yb:Y2O3 and Yb:Sc2O3 are promising laser materials for room temperature and cryogenic operation. For some applications, it is highly desirable to use lasers operating at wavelengths to which the human eye is comparatively resistant to damage, yet the rare earth ion transitions in the relevant wavelength ranges tend to be less efficient than the one-micron transitions of Nd3+ and Yb3+. We are investing substantial effort in the study and optimization of resonant diode-pumped laser operation of Er3+-doped solids at wavelengths near 1.5 microns. Working with diode laser manufacturers, we have achieved very encouraging laser performance from Er:YAG at both cryogenic and room temperatures, pumping at wavelengths that minimize heat deposition in the gain medium. At cryogenic temperatures, hosts such as Sc2O3 are even more promising than YAG, for reasons having to do with spectroscopic details that will be discussed.

Colloidal nanocrystals doped with rare-earth ions can exhibit visible upconversion luminescence when excited with near-infrared (NIR) laser excitation, enabling their use as non-toxic, low-autofluorescence, and non-photobleaching probes in cells and tissue. Current upconverting nanoparticle probes, however, utilize canonical phosphor materials (e.g. NaYF4:Yb, Er) that exhibit multiple 4f-to-4f radiative transitions that are difficult to alter and that complicate multi-color applications. One method to achieve selective emission from upconverting materials is to promote or quench specific radiative transitions utilizing energy transfer between multiple lanthanide dopants. However, optimizing the large number of experimental parameters that dictate efficient energy transfer can be an intractable task via traditional bulk or colloidal synthetic methods. We present an automated method for the combinatorial screening and optimization of multiply doped upconverting nanocrystals with spectrally selective luminescence. The solution-phase chemistry of colloidal nanomaterials facilitates the use of a high-throughput liquid handling robot to prepare large libraries of 500 µl-scale reactions in which the composition and concentration of the dopants are varied. The common host matrix of the nanoparticles and the similar chemistry of the lanthanides enable the parallel high-temperature synthesis of the materials in 96-well plates. For high-throughput spectral characterization, we developed an upconversion luminescence microplate reader with eight NIR laser excitation lines. Integrating this data with photophysical models, we have isolated spectrally selective rare earth dopant combinations and have identified the critical energy transfer mechanisms that determine this selective behavior.

The field of luminescence from rare-earth (RE) ions has been very active during the past decade. The triply charged ions europium (Eu³⁺), terbium (Tb³⁺) and cerium (Ce³⁺) have been used in phosphors to produce the visible emission of saturated red, green and blue required for colour displays. Simultaneously intensive research on erbium (Er³⁺) doped materials has been conducted in order to develop lasers and amplifiers for telecommunication applications due to its emission centred at 1.5 μm. More recently the potential to control the material configuration at the nanoscale has opened new opportunities for the design of materials with optimized functional response. In this context colloidal sol-gel method is a powerful route to obtain stable and homogeneous sols of nanoparticles of controlled size. The use of these nanocrystalline based structures provides an additional control on the gap of the material, and in turn to control the so called sensitization process of the RE-ion. This sensitization process takes place when RE ions are incorporated in a wide-band-gap material (e.g. TiO₂). In this process when the doped material is excited with a photon with higher energy than that of the bandgap, the subsequent exciton recombination in the host is able to transfer its energy to the intra-f-shell of the RE ion, therefore significantly enhancing the RE effective absorption cross-section. In this work the optical response of Eu- and Er-doped TiO₂ nanoparticulate sols and thin films prepared by spin-coating are investigated. Sols with RE concentrations from 1 to 3 % have been prepared. The nanoparticle size in the sols ranges from 5 to 8 nm. Optical spectroscopy techniques (absorption, reflection and ellipsometry) and photoluminescence are used to monitor the properties of the films in order to determine structural and morphological features. It has been found that the bandgpap and porosity of the prepared thin films differs from that of the bulk TiO₂. The use of post-annealing treatments to optimize their optical and photoluminescence response will be discussed.

Lithium codoping is now a common way of improving optical efficiency in lanthanide-activated oxide luminescent materials; however, the reported mechanisms by which Li⁺ enhances upconversion are numerous, ambiguous, and often speculated. In this work, we have identified the major mechanisms by which Li⁺ enhances upconversion in Y₂SiO₅:Pr³⁺, using crystallographic and spectroscopic techniques in the form of diffraction/Rietveld refinement, photoluminescence spectroscopy, and electron microscopy. By isolating the effects, the relative contribution to the efficiency gain of each mechanism was quantified. Results show that 10 at.% doping with Li⁺ improves UV emission 9-fold and is attributed to crystallite enlargement, induction of a phase change, and increasing inter-ion separation of the Pr³⁺ activator.

Y2O3:Eu3+, is a very important phosphor in high efficiency compact fluorescence lamps and liquid crystal displays (LCDs). After the successful discovery of carbon nanotube in 1991, much interest has been focused on one-dimensional nanostructures of different shapes such as wire, rod-like and tubular forms. Shape modulated rare- earth oxides have potential application in several fields like high performance magnets, luminescence devices, catalysts, and other functional materials. The phonon density-of-states of the host material can be significantly modified according to the size and shape of the particles. Consequently, these changes of nonradiative relaxation probabilities (multiphonon emission) affect the photoluminescence (PL) lifetime, which in turn influences the luminescence intensity. Precise control of the size and shape thus allows manipulation of the luminescence properties of the doped samples, as desired. A facile hydrothermal route has been demonstrated for the synthesis of Eu3+ doped Y2O3 with distinct and well controlled morphologies viz, hexagonal prism-like, sheet-like and rod-like. Electrolytes seem to have a profound effect on the morphological evolution of Eu3+ doped Y2O3. NH4NO3, NaNO3, KNO3, KCl and NH4Cl in the presence of NH4OH have been found to be suitable reagents for the preparation of different shaped yttria. Samples have been characterized by XRD and SEM. It has been observed that the crystal structure of precursor has a crucial effect on the shape of the product. The anisotropic structure of monoclinic yttrium oxide hydroxide nitrate [Y4O(OH)9NO3] was found to be responsible for the one dimensional growth. A dissolution-recrystallization mediated growth has taken place to produce the hexagonal-prism like morphological variety. The coordinating property of NH3 molecule obtained from NH4OH has a vital role for the evolution of hexagonal prism â?" like morphology. NH4NO3 in the presence of NH4OH provides the common ion NH4+ which causes the existence of large amount of NH3 in the system, can produce the hexagonal-prism like morphological varieties. The formation of irregular shaped particle in the presence of NH4NO3 and NaOH clearly demonstrates the role of NH3 in the growth process. After morphological study of the prepared samples, their photoluminescence properties were investigated. One significant outcome of the photoluminescence study involved a detailed observation of the variations in the relative intensity of the stark components of 5D0â?"7F2 transition of Eu3+ embedded in different shaped hosts. It has been observed that the host morphology plays a crucial role on the symmetry around the rare-earth ion as a result of which, the intensity ratio of stark components of different transitions of Eu3+ in different samples varies with change in host morphologies. The observation was subsequently explained on the basis of change in the local symmetry of the dopant ion, due to the change in the host morphology.