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

摘要： Compared with CsPbBr3 nanocrystals (NCs), the study of the structure and physical properties of Cs4PbBr6 and CsPb2Br5 NCs is not sufficient. In this paper, CsPbBr3, CsPb2Br5, and Cs4PbBr6 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 were investigated. It is found that rhombohedral Cs4PbBr6 was created at low temperature with low Pb/Cs ratios and short reaction time. CsPbBr3 phase was then obtained with increasing Pb/Cs ratios at high temperature through the reaction of Cs4PbBr6 and PbBr2. The evolution of phase composition occurred with time to create CsPbBr3, CsPb2Br5, and Cs4PbBr6 NCs. For a Pb/Cs molar ratio of 3, CsPbBr3 were firstly obtained at 180 °C. However, resulting sample is CsPb2Br5 phase after 120 min. The excesses PbBr2 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), rhombohedral Cs4PbBr6 phase was obtained and then reacted with PbBr2 to fabricate cubic CsPbBr3 nanosheets with sizes of several hundred nanometers. With changing phase composition, cubic, rod, rhombohedral morphologies were created. The PL properties of the NCs depended strongly on the phase composition. As a result, CsPbBr3 NCs reveal highly bright PL with narrow and symmetrical PL spectra (PL peak at 520 nm). In contrast, No PL was observed for Cs4PbBr6 and CsPb2Br5 phases. The results provide a possibility to well control the growth for the application of cesium lead halide NCs.