Bandgap tunable pure-phase zero-dimensional Cs4PbClxBr6-x perovskites with selective absorption and intrinsic ultraviolet emission

Zero-dimensional perovskite Cs4PbX6 possesses a unique crystal structure that sets it apart from the three-dimensional CsPbX3 perovskite, exhibiting a range of fascinating optical properties, and superior thermal and chemical stability compared to CsPbBr3. Its wide bandgap and narrowband absorption characteristics enable selective detection and applications involving deep ultraviolet to near-blind ultraviolet light. However, there are still challenges in achieving high-quality pure-phase nanocrystals, regulating bandgap and clarifying carrier transport mechanisms. In this study, a mild and controllable method was developed to synthesize high-quality pure-phase Cs4PbBr6, while kept size-independent bandgap. Subsequently, bandgap was tuned continuously from 3.94 to 4.35 eV by manipulating the halogen ratios, and still hold the pure-phase of zero-dimensional Cs4PbClxBr6-x. Furthermore, DFT calculations and an in-depth investigation of their emission demonstrated the localized electron states and exciton self-trapping mechanisms.