Switchable biexcitons in perovskite-like RbCu2Br3 crystals driven by thermally induced phase transition

The difficulties in precise composition synthesis, large-scale growth, and environmental friendliness of halide perovskites and their derivatives, as well as the lack of research on their basic physical properties, hinder their application in the field of optoelectronics. Here, through a liquid-phase method, we have synthesized large-size (20 × 5 × 2 mm) and high-quality perovskite-type RbCu2Br3 crystals with a one-dimensional electronic structure for the first time. Interestingly, as temperature decreases, the light emitted by the RbCu2Br3 crystals shows a transition from blue light to dazzling orange light, and the crystals show double exciton radiative recombination of photoluminescence and radioluminescence at low temperatures. It is found that the crystal structure symmetry is broken due to the superposition of thermally-induced local deviations of the crystal field resulting in a structural transition from the Cmcm to Pnma phase with low symmetry. This work can help to enrich the categories of copper-based halides, and provide new perspectives for the research on the photophysical properties and applications of such materials.