Revealing photoluminescence mechanisms of single CsPbBr₃/Cs₄PbBr₆ core/shell perovskite nanocrystals

CsPbBr₃ nanocrystals (NCs) encapsulated by Cs₄PbBr₆ has attracted extensive attention due to good stability and high photoluminescence (PL) emission efficiency. However, the origin of photoluminescence (PL) emission from CsPbBr₃/Cs₄PbBr₆ composite materials has been controversial. In this work, we prepare CsPbBr₃/Cs₄PbBr₆ 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 CsPbBr₃/Cs₄PbBr₆ 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 Cs₄PbBr₆ NCs demonstrate apparent "burst-like" behaviors with very high values of g ²(0) at any excitation power. Therefore, the distinguishable emission statistics help us to elucidate whether the photoluminescence (PL) emission of CsPbBr₃/Cs₄PbBr₆ core/shell NCs stems from band-edge exciton recombination of CsPbBr₃ NCs or intrinsic Br vacancy states of Cs₄PbBr₆ NCs. These findings provide key information about the origin of emission in CsPbBr₃/Cs₄PbBr₆ core/shell nanoparticles, which improves their utilization in the further optoelectronic applications.