Revealing photoluminescence mechanisms of single CsPbBr/CsPbBr core/shell perovskite nanocrystals.

CsPbBr nanocrystals (NCs) encapsulated by CsPbBr has attracted extensive attention due to good stability and high photoluminescence (PL) emission efficiency. However, the origin of photoluminescence (PL) emission from CsPbBr/CsPbBr composite materials has been controversial. In this work, we prepare CsPbBr/CsPbBr core/shell nanoparticles and firstly study the mechanism of its photoluminescence (PL) at the single-particle level. Based on photoluminescence (PL) intensity trajectories and photon antibunching measurements, we have found that photoluminescence (PL) intensity trajectories of individual CsPbBr/CsPbBr core/shell NCs vary from the uniform longer periods to multiple-step intensity behaviors with increasing excitation level. Meanwhile, second-order photon correlation functions exhibit single photon emission behaviors especially at lower excitation levels. However, the PL intensity trajectories of individual CsPbBr NCs demonstrate apparent "burst-like" behaviors with very high values of (0) at any excitation power. Therefore, the distinguishable emission statistics help us to elucidate whether the photoluminescence (PL) emission of CsPbBr/CsPbBr core/shell NCs stems from band-edge exciton recombination of CsPbBr NCs or intrinsic Br vacancy states of CsPbBr NCs. These findings provide key information about the origin of emission in CsPbBr/CsPbBr core/shell nanoparticles, which improves their utilization in the further optoelectronic applications.