Highly Emissive Zero-Dimensional Cesium Lead Iodide Perovskite Nanocrystals with Thermally Activated Delayed Photoluminescence.

We utilized a modified reverse-microemulsion method to develop highly emissive and photostable zero-dimensional (0D) Cs 4 Pb(Br 1- x I x ) 6 perovskite nanocrystals (PNCs). We employed single-particle photoluminescence (PL) spectroscopy to explore blinking statistics and demonstrate single-photon emission from individual PNCs. Low-temperature blinking and photon correlation studies revealed a transition from single- to multiphoton emission with progressively longer "delayed" PL components, reaching ∼70 ns at room temperature and representing a distinctive behavior to previously known iodide PNCs. Such thermally activated PL emission is explained by the existence of defect-related "reservoir" states, feeding back into the PNC's emissive state and providing multiple photons within a single excitation cycle. This work establishes a new member in the 0D class of perovskite materials, studies its photophysical properties, and reveals its potential for future optoelectronic applications.