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

The photoluminescence of green-emitting Cs4PbBr6 crystals has shown superior stability over that of standard CsPbBr3 phase towards 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 c axis and the cooling rate of precursor was found a key factor to manipulate the emitter density, which was reported for the first time to the best of our knowledge. Through an ultra-slow cooling procedure, a full-body emitting crystal of high PL QY up to 83% was obtained. Importantly, the PL QY was found temperature-insensitive in a broad range from 80 K to 300 K despite of strong phonon-electron coupling effect. The lifetime displayed a linear relationship to temperature, which suggested a 2D quantum-well feature of excitons according to Rosales model. This work provided many new evidences and insights into the PL origin of Cs4PbBr6, representing a step forward to approaching the nature of emitters in low dimensional perovskites.