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