Evolution of Morphology, Phase Composition, and Photoluminescence of Cesium Lead Bromine Nanocrystals with Temperature and Precursors

Compared with CsPbBr 3 nanocrystals (NCs), the study of the structure and physical properties of Cs 4 PbBr 6 and CsPb 2 Br 5 NCs is not sufficient. In this paper, CsPbBr 3, CsPb 2 Br 5, and Cs 4 PbBr 6 NCs were prepared by a hot-injection method using oleylamine (OAm) and oleic acid (OA) without adding other ligands. The evolution of phase composition, morphology, and photoluminescence (PL) property was investigated. It is found that rhombohedral Cs 4 PbBr 6 was created at low temperature with low Pb/Cs ratios and short reaction time. The CsPbBr 3 phase was then obtained with increasing Pb/Cs ratios at high temperature through the reaction of Cs 4 PbBr 6 and PbBr 2 . The evolution of phase composition occurred with time to create CsPbBr 3, CsPb 2 Br 5, and Cs 4 PbBr 6 NCs. For a Pb/Cs molar ratio of 3, CsPbBr 3 was first obtained at 180 °C. However, the resulting sample is the CsPb 2 Br 5 phase after 120 min. The excess PbBr 2 is a key for such phase change because no similar phenomenon was observed in the case of molar ratio of Pb/Cs of 2. At low temperature (e.g., 140 and 160 °C), the rhombohedral Cs 4 PbBr 6 phase was obtained and then reacted with PbBr 2 to fabricate cubic CsPbBr 3 nanosheets with sizes of several hundred nanometers. With changing phase composition, cubic, rod, and rhombohedral morphologies were created. The PL properties of the NCs depended strongly on the phase composition. As a result, CsPbBr 3 NCs reveal highly bright PL with narrow and symmetrical PL spectra (PL peak at 520 nm). In contrast, no PL was observed for Cs 4 PbBr 6 and CsPb 2 Br 5 phases. The results provide a possibility to well control the growth for the application of cesium lead halide NCs.