Synthesis of thermally stable and highly luminescent spherical shaped ligand-free Cs4PbBr6 nanospheres with a single polar solvent

We demonstrate a simple method to synthesis thermally stable and green luminescent ligand-free Cs4PbBr6 nanospheres (NS) with a polar solvent. In this approach, a single polar solvent, N,N-dimethylformamide (DMF) is sufficient enough to convert precursors into cubic shaped ligand-free Cs4PbBr6 crystals. Further, the morphology of cubic shaped Cs4PbBr6 crystals is reformed into spherical shaped Cs4PbBr6 NS by prolonged DMF washing (overnight stirring, 15 h). Besides, the reduction in average particle size of spherical shaped Cs4PbBr6 NS (similar to 70 nm) to one-fourth to the original size of cubic Cs4PbBr6 crystals (similar to 310 nm). The ligand-free spherical shaped Cs4PbBr6 NS showed a high photoluminescence quantum yield of 42.5%, which could compete the conventional ligand mediated Cs4PbBr6 crystals. Moreover, spherical shaped Cs4PbBr6 NS exhibited a high thermal stability even at 200 degrees C without sacrificing luminescence intensity. Hence, it is foreseen that this approach brings a new strategy to prepare ligand-free Cs4PbBr6 NS as a promising material in optoelectronic devices.