Synthesis and transformation of zero-dimensional Cs₃BiX₆ (X = Cl, Br) perovskite-analogue nanocrystals

The unique structure of zero-dimensional (0D) perovskite-analogues has attracted a great amount of research interest in recent years. To date, the current compositional library of 0D perovskites is largely limited to the lead-based Cs₄PbX₆ (X = Cl, Br, and I) systems. In this work, we report a new synthesis of lead-free 0D Cs₃BiX₆ (X = Cl, Br) perovskite-analogue nanocrystals (NCs) with a uniform cubic shape. We observe a broad photoluminescence peak centered at 390 nm for the 0D Cs₃BiCl₆ NCs at low temperatures. This feature originates from a self-trapped exciton mechanism. In situ thermal stability studies show that Cs₃BiX₆ NCs remain stable upon heating up to 200 °C without crystal structural degradation. Moreover, we demonstrate that the Cs₃BiX₆ NCs can transform into other bismuth-based perovskite-analogues via facile anion exchange or metal ion insertion reactions. Our study presented here offers the opportunity for further understanding of the structure-property relationship of 0D perovskite-analogue materials, leading toward their future optoelectronic applications.