Nanocrystal Size and Quantum Yield in the Upconversion of Green to Violet Light with CdSe and Anthracene Derivatives

We investigate the parameters affecting the upconversion of visible light in a hybrid organic inorganic system based on CdSe nanocrystal (NC) sensitizers, 9-anthracene carboxylic acid (9-ACA) transmitter, and diphenylanthracene (DPA) annihilator. Seven wurtzite CdSe NCs ranging in photoluminescence quantum yield (PLQY) from 2.0% to 11%, and in diameter from 2.7 to 5.1 nm, were used in combination with the 9-ACA and DPA molecules. Using 2.7 nm diameter CdSe NCs, we show that the upconversion quantum yield has a quadratic to linear dependence on NC sensitizer concentration. Additionally, upconversion efficiency correlates positively with 9-ACA surface coverage on CdSe NCs and NC PLQY but negatively with particle size. This work clearly illustrates the path toward designing nanocrystal-molecule combinations with high upconversion efficiency that have potential applications in the fields of bioimaging, solar energy conversion, and data storage.