Structure and optical properties of perovskite-embedded dual-phase microcrystals synthesized by sonochemistry

Cesium lead halide perovskite (CsPbX3, X=Cl, Br, I) nanocrystals embedded in Cs4PbX6 or CsPb2X5 matrices have received interests due to their excellent optical properties. However, their precise endotaxial structures are not known, and the origin of photoluminescence remains controversial. Here we report a sonochemistry technique that allowed us to synthesize high-quality CsPbBr3-based microcrystals in all ternary phases, simply by adjusting precursor concentrations in a polar aprotic solvent, N,N-dimethylformamide. The microcrystals with diverse morphologies enabled us to visualize the lattice alignments in the dual-phase composites and confirm CsPbBr3 nanocrystals being the photoluminescent sites. We demonstrate high solid-state quantum yield of >40% in Cs4PbBr6/CsPbBr3 and lasing of CsPbBr3 microcrystals as small as 2 mu m in size. Real-time optical analysis of the reaction solutions provides insights into the formation and phase transformation of different CsPbBr3-based microcrystals. The origin of the excellent photoluminescence properties of embedded cesium lead halide perovskite nanocrystals remains to be fully understood. Here the authors visualize lattice alignments in dual-phase Cs4PbBr6 and CsPb2Br5 composites synthesized by sonochemistry and find that the CsPbBr3 nanocrystals are responsible for the luminescence.