Strategies to Maximize the Dopant‐To‐Exciton Emission Ratio in Mn‐Doped CsPbCl ₃ Nanocrystals

Abstract Doping CsPbCl ₃ perovskite nanocrystals (NCs) with Mn ²⁺ has gained attention due to their interesting emission properties. However, the photoluminescence (PL) spectra of these NCs display both dopant and exciton emission peaks. It is critical to achieve color purity for light–emitting diode (LED) applications, but the factors that govern this remain unclear. Herein, a systematic investigation of the factors determining the exciton‐to‐dopant energy transfer process in Mn ² ⁺‐doped CsPbCl ₃ NCs is presented to reveal how the exciton‐to‐Mn ² ⁺ emission ratio can be maximized. These findings indicate that this process is not only affected by dopant concentration and halide (Cl/Br) composition, but also by the co‐dopants used, as well as surface passivation. These factors can potentially account for the discrepancies in the exciton‐to‐dopant emission ratios across the literature. These results show that post‐synthetic surface passivation of Mn ² ⁺‐doped CsPbCl ₃ NCs with quaternary ammonium salt, such as dimethyldidodecylammonium chloride (DDACl), drastically enhances the exciton‐to‐Mn ² ⁺ emission ratio, achieving a two‐fold increase. Ultrafast pump‐probe spectroscopy surprisingly reveals that the passivation can introduce shallow trap states that enhance energy transfer to dopant sites and influence overall luminescence efficiency through non‐radiative decay processes. This study sets guidelines for maximizing dopant emission in doped perovskite NCs.