Origins of Red Emission from ZnS:Cu Colloidal Nanocrystals and Potential Applications for Quantum Information Science

Colloidal ZnS:Cu nanocrystals (NCs) are prototypical colloidal nanophosphors in bio-imaging and optoelectronic applications thanks to their bio-compatibility and broadly tunable luminescence properties. Visible luminescence from ZnS:Cu colloidal NCs is typically dominated by green and blue peaks (denoted G-Cu and B-Cu), with observations of red (R-Cu) luminescence from nanocrystalline ZnS:Cu remaining extremely limited. Here, we present a synthetic method for obtaining colloidal ZnS:Cu NCs that emit primarily R-Cu. We use time- and temperature-resolved luminescence spectroscopies to study the emission mechanism, which provides advanced knowledge of the electronic structure produced by defects in ZnS:Cu that is critical for controlling the luminescence properties of this material. We also discuss the applicability of colloidal nanocrystals containing color centers to quantum information science, where electronically isolated defect states can serve as optically addressable spin qubits.