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Perovskite nanocrystals (PNCs) have attracted a lot of scientific interest in the recent years due to the extraordinary optical and electronic properties such as compositional and structural versatility, tunable bandgap, high photoluminescence (PL) quantum yield (QY) and facile chemical synthesis. Among them, all inorganic CsnPbXm perovskites have attracted particular attention due to enhanced light emission and photo/thermal stability. Lower dimensionality polymorphs can be formed by manipulation of chemical- synthesis conditions where Cs+ can stabilize 3D [PbX6] framework, resulting in 2D (nanosheet), 1D (nanowire) and 0D (nanodot) internal octahedra arrays within the bulk of the perovskite. The gamut of available experimental approaches are further expanded in colloidal PNCs where both external size quantization and internal 0D structure may combine to achieve “multidimensional” electronic properties that are engineered both on atomic scale and nanoscale. In this work, we explore the photon emission statistics from individual 3D (CsPbBr3) and 0D (Cs4PbBr6) PNCs in order to address the origin of their PL emission. Using time-correlated, time-stamped single photon counting (TCSPC) we obtain PL intensity trajectories and extract PL lifetimes and second–order correlation functions at different excitation levels. Blinking traces show “burst-like” intensity behavior, with large bin-to-bin fluctuations, akin to molecular fluorophores. Recorded single photon emission statistics indicate that some of the measured PNCs are single photon emitters, others contain several emissive centers with very similar lifetimes. Few of the PNCs exhibited effects of photobrightening – superlinear increase of PL emission intensity due to the activation of an additional number of emissive centers within the PNC. Such emission behavior, independent of the confinement effects afforded by quantization in the medium/large sized Cs-based PNCs, supports theoretical framework that points towards Br-vacancy states localized within isolated octahedra.
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