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

Green-to-blue photon upconversion bears great potential in photocatalytic applications. However, current hybrid inorganic-organic upconversion schemes utilizing spherical CdSe nanocrystals are limited by the additional tunneling barrier resulting from the necessity of surface-passivating shells. In this contribution, we introduce anisotropic CdSe nanoplatelets as triplet sensitizers. Here, quantum confinement occurs in only one direction, erasing effects stemming from energetic polydispersity. We investigate the triplet energy transfer from the CdSe nanoplatelets to the surface-bound triplet acceptor 9-anthracene in both solution and in solid-state upconversion devices fabricated by solution-casting. In solution, we obtain an upconversion quantum yield of (6±1)% at a power density of 11 W/cm^2­using the annihilator 9,10-diphenylanthracene, and a low efficiency threshold I_thof 200 mW/cm². Bilayer solid-state show low efficiency thresholds of 124 mW/cm², however, suffer detrimental effects from parasitic low-energy excimer formation. This indicates that the overall brightness of the UC device and the I_thdo not necessarily correlate. This system provides a new avenue towards investigating the role of exciton transport on the upconversion mechanism.