NIR Luminescence from Deep-Level Traps in CsPbBr₃ Microcrystals

In this study, we report the first observation of a near-infrared (NIR) emission band from all-inorganic CsPbBr₃ and CsPb(Br/Cl)₃ perovskite microcrystals. By means of temperature- and power-dependent NIR and visible luminescence spectroscopy, we demonstrate that a fraction of the excited states in these materials relax through radiative transitions involving traps located deep within the band gap, leading to broadband NIR emission. The quantum yield of this deep trap emission is quantitatively determined for the first time and amounts to approximately 0.3% at room temperature. Furthermore, by examining the picosecond-to-nanosecond dynamics of the excited states, using time-resolved luminescence spectroscopy, we observe that the population of NIR initial states occurs on a 660 ps time scale, consistent with the capture of free carriers by deep trap sites. Hence, this work deepens our fundamental understanding of previously unexplored recombination channels in metal halide perovskite microcrystals.