Recently, cesium bismuth halide perovskites have emerged as potential substitutes to their counterparts, cesium lead halide perovskites, owing to their low toxicity. However, the photophysics of cesium-bismuth halides nanocrystals (NCs) have not yet been fully rationalized because their structures remain highly debated. The ultraviolet-visible (UV-vis) absorption along with other photophysical properties such as the nature and lifetime of the excited states vary considerably across the previous reports. Here, we successfully synthesize pure Cs₃BiBr₆ and Cs₃Bi₂Br₉ NCs via a modified hot-injection method, where the structure can be easily controlled by tuning the reaction temperature. The UV-vis absorption spectrum of the pure Cs₃Bi₂Br₉ NCs features two characteristic peaks originating from the absorption of the first exciton and second exciton, respectively, which ultimately clarifies the debate in the previous reports. Using femtosecond transient absorption spectroscopy, we systematically investigate the excited state dynamics of the Cs₃Bi₂Br₉ NCs and reveal that the photoexcited carriers undergo a self-trapping process within 3 ps after excitation. More intriguingly, the Cs₃Bi₂Br₉ NCs prepared by this method show much better photostability than those prepared by the ligand-assisted reprecipitation process. Photodetectors based on these Cs₃Bi₂Br₉ NCs show a sensitive light response, demonstrating the definite potential for breakthrough optoelectronic applications.

最近，由于低毒性，铯铋卤化物钙钛矿已成为其对应物铯铅卤化物钙钛矿的潜在替代品。然而，铯-铋卤化物纳米晶体 (NC) 的光物理学尚未完全合理化，因为它们的结构仍存在很大争议。紫外-可见 (UV-vis) 吸收以及其他光物理特性（例如激发态的性质和寿命）在之前的报告中差异很大。在这里，我们通过以下方法成功合成了纯 Cs ₃ BiBr ₆和 Cs ₃ Bi ₂ Br ₉ NCs一种改进的热注射方法，可以通过调整反应温度轻松控制结构。_{纯Cs 3} Bi ₂ Br ₉ NCs的紫外-可见吸收光谱具有两个特征峰，分别来自第一激子和第二激子的吸收，这最终澄清了之前报告中的争论。使用飞秒瞬态吸收光谱，我们系统地研究了 Cs ₃ Bi ₂ Br ₉ NC 的激发态动力学，并揭示了光激发载流子在激发后 3 ps 内经历了自陷过程。更有趣的是，Cs ₃ Bi ₂ Br ₉通过这种方法制备的 NCs 显示出比配体辅助再沉淀过程制备的 NCs 更好的光稳定性。基于这些 Cs ₃ Bi ₂ Br ₉ NC 的光电探测器表现出灵敏的光响应，展示了突破性光电应用的明确潜力。