Nonradiative Energy Transfer from CsPbBr3 Nanocrystals to CdSe/CdS Nanocrystals for Efficient Light Down Conversion

Semiconductor nanocrystals ( NCs) are emerging luminescent materials with superior optical properties. However, the light-conversion application of NCs is restricted by reabsorption-induced fluorescent quenching. Here, a NC-NC Forster resonance energy transfer (FRET) system is developed by employing large CsPbBr3 NCs as donors and CdSe/CdS NCs as acceptors. The FRET systems using toluene and octadecene as solvents show decreases of 10% and 14%, respectively, in the integrated photoluminescence (PL) intensity, far below the reabsorption loss observed in concentrated CdSe/CdS NCs (>30%) at the same color purity. Notably, we demonstrate by transient absorption measurements that the styrene-mediated FRET system involves a Dexter energy transfer process, which enables the harvesting of triplet excitons and leads to an additional PL enhancement at system level by a maximum of 40% instead of fluorescence quenching. The remarkably improved lightconversion efficiency and antiquenching property make the proposed NC-NC system superior in light down-conversion applications.