Green-to-Blue Triplet Fusion Upconversion Sensitized by Anisotropic CdSe Nanoplatelets

Green-to-blue photon upconversion bears great potential in photocatalytic applications. Current hybrid inorganic–organic upconversion schemes commonly utilize spherical CdSe nanocrystals, but size polydispersity could influence efficiencies in future solid-state applications. In this contribution, we introduce anisotropic CdSe nanoplatelets as triplet sensitizers. Here, quantum confinement occurs in only one direction, erasing effects stemming from size polydispersity. Additionally, their high quantum yields, giant oscillator strengths, and large absorption cross sections could prove useful in a triplet sensitization scheme. We investigate the triplet energy transfer process from the CdSe nanoplatelets to the surface-bound triplet acceptor 9-anthracenecarboxylic acid and the resulting upconversion in 9,10-diphenylanthracene. We further investigate the influence of nanoplatelet stacking and singlet back-transfer on the observed upconversion efficiency. We obtain an upconversion quantum yield of 5.4% at a power density of 11 W/cm2 using the annihilator 9,10-diphenylanthracene and a low efficiency threshold Ith of 237 mW/cm2.