Real-Time Tracking of Emitter Generation in a Zero-Dimensional Perovskite

The photoluminescence of green-emitting Cs4PbBr6 crystals has shown superior stability over that of the standard CsPbBr3 phase toward many harsh conditions, including long-term storage, heat shock, light irradiation, and even multiple solvent rinsing. However, the understanding of its origin remained controversial, partially due to the lack of real-time observation on its initial formation stage. Here, this work reported the direct observation of emitter generation in the crystallization stage. Through the use of a home-made crystal incubator coupled with a fluorescent microscope, both the crystal growth and emitter emergence were tracked in a real-time manner. The emitter distribution was found oriented along the c axis and the cooling rate of the precursor was found as a key factor to manipulate the emitter density, which was reported for the first time to the best of our knowledge. Through an ultraslow cooling procedure, a full-body emitting crystal of high photoluminescence quantum yield (PL QY) up to 83% was obtained. The emitter emergence was accompanied with a release of strain as evidenced by Williamson–Hall fitting, and the PL evolution was further simulated with the Johnson–Mehl–Avrami model. Combined with the linear relationship of lifetime to temperature, a two-dimensional phase of disordered Csn+1PbnBr3n+1 was proposed as the emitter according to the Rosales model. Although the direct evidence of the emitter phase remains elusive, this work provided many new insights into the PL origin of Cs4PbBr6.