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

Cesium lead halide perovskite (CsPbX 3 , X=Cl, Br, I) nanocrystals embedded in Cs 4 PbX 6 or CsPb 2 X 5 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 CsPbBr 3 -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 CsPbBr 3 nanocrystals being the photoluminescent sites. We demonstrate high solid-state quantum yield of >40% in Cs 4 PbBr 6 /CsPbBr 3 and lasing of CsPbBr 3 microcrystals as small as 2 µm in size. Real-time optical analysis of the reaction solutions provides insights into the formation and phase transformation of different CsPbBr 3 -based microcrystals.