Continuous Wave Photon Upconversion from a Copper Selenide Nanocrystal Film

Photon upconversion is of great interest for improving the efficiency of silicon photovoltaic cells, for biological imaging, and for thermal management strategies. Currently, the vast majority of materials being developed for solar upconversion are composed of rare and expensive elemental compounds. Moving forward, the development of earth abundant, non-toxic materials that efficiently convert near infrared light into visible light would be ideal. Copper selenide-based materials meet these criteria, and are of great interest due to their unique thermoelectric and plasmonic properties. In particular, doped copper selenides (Cu2−xSe) have tunable near infrared localized surface plasmon resonances, large Seebeck coefficients, and low thermal conductivity, with a range of chemical and thermoelectric applications. Here, we observe another interesting application of this material in the upconversion of near infrared light from a silica xerogel film containing degenerately doped Cu2−xSe nanocrystals, with an onset flux of ∼ 1.96 ± 0.29 kW/cm^2 and at least 1% quantum yield. Our investigations suggest a plasmon-driven thermal mechanism likely plays a role in this upconversion process.