Photoluminescence and Lasing of Cs4PbBr6 Micro‐Flakes and Micro‐Flowers with Embedded CsPbBr3 Nanocrystals

Herein, a controlled synthesis route with precise growth tunability of perovskite Cs4PbBr6 micro‐flakes and micro‐flowers with embedded CsPbBr3 nanocrystals (Cs4PbBr6@CsPbBr3) is elaborated. This room‐temperature synthesis scheme initiates the nucleation and growth process of the majority crystalline phase of Cs4PbBr6 with a few CsPbBr3 impurities as confirmed by the X‐ray diffraction studies. The microstructures and shape control are further investigated by scanning electron microscopy (SEM) and the high‐resolution transmission electron microscopy (HRTEM). The results depict hexagonal Cs4PbBr6 micro‐flakes with embedded CsPbBr3 that can spontaneously self‐assemble into micro‐flowers with varying external conditions. This approach gives access to perovskite semiconductors with both structural and excellent optical properties by correlating the dimensionality with quantum confinement effects. The photoluminescence, absorption, and time‐resolved photoluminescence spectroscopy confirm that such as‐synthesized materials exhibit bright green emission with an optical bandgap of 2.3 eV. Lasing action is obtained under an excitation wavelength of 400 nm at 10 K where the light intensity and lifetime are examined at different pump fluences. There exist two linear regions corresponding to spontaneous emission and lasing, respectively. The lower lasing threshold of 27 μJ cm−2 per pulse is obtained and the corresponding Q factor is estimated to be 1090.