Revisiting the nanocrystal formation process of zero-dimensional perovskite

The nanocrystal (NC) form of zero-dimensional perovskite (Cs4PbBr6) has attracted a great deal of attention due to both its elusive green emission and phase-pure nature, which has posed a major challenge to the impurity theory used to explain CsPbBr3 being an emitter. In this work, we revisit the NC formation process in real time by using an in situ photoluminescence (PL) monitoring system. Through analyzing the evolution of the PL spectra, the formation process was divided into two stages, namely the nucleation stage and growing stage, which were well explained by the LaMer mechanism and the Ostwald ripening model. In addition, the Johnson–Mehl–Avrami (JMA) model was used to simulate the transformation from non-emissive Cs4PbBr6 to green-emitting Cs4PbBr6, and the ensuing activation energy (Ea = 39.0 ± 5.0 kJ mol−1) was extracted. Importantly, an accompanied transformation from “white spots” to “black spots” was observed, which suggested that the black spots were responsible for PL emission despite their amorphous nature. Our work represents a step forward in unraveling the PL origin of the Cs4PbBr6 phase, although the nature of the white and black spots remained elusive.