LAUSR

We have developed a facile colloidal synthesis approach for nearly monodisperse CsX (X = Cl, Br, I) nanocrystals with truncated octahedral shape and simple cubic structure. Upon the partial exchange of Cs+ with Pb2+ ions, these particles can be transformed to fluorescent CsPbX3 (X = Cl, Br) nanocrystals. The CsBr case has been studied extensively: the transformation of CsBr to CsPbBr3 goes through core/shell CsBr/CsPbBr3 nanocrystals as intermediate structures. In the early stages of the transformation, i.e. for CsBr NCs with thin CsPbBr3 shells, the particles exhibit a strong blue-shifted emission compared to the bulk band gap of CsPbBr3 due to the presence of quantum confined CsPbBr3 domains on the surface of the CsBr particles. These confined perovskite domains are unstable, as the emission red-shifts with time. Also, the nanocrystals undergo significant inter-particle aggregation over time if the cation exchange process is not completed. The full transformation scheme, however, yields stable and mon-o...