Unlocking Near 100% PLQY: The Impact of Post‐Treatment on Emission Efficiency of Mn²⁺: CsPbCl₃ Nanocrystals

Abstract Mn 2+ doped CsPbCl 3 nanocrystals (Mn 2+ :CsPbCl 3 NCs) show immense promise in lighting and display technologies owing to their outstanding optical characteristics. Nonetheless, high defect density, inefficient Mn 2+ doping, and poor structural robustness pose considerable challenges in the synthesis of Mn 2+ :CsPbCl 3 NCs with high photoluminescence quantum yield (PLQY) and long‐term stability. This study introduces an eco‐friendly room‐temperature post‐treatment method utilizing MgCl 2 /oleylamine solution, boosting the total PLQY of the NCs from 65% to 98%, including a 30% increase for Mn 2+ emission. Additionally, the post‐treatment significantly improves the NCs’ resilience against UV light, retaining 80% of their initial PL intensity after 120 hours of UV exposure. Comprehensive analyses including density functional theory simulation and temperature‐dependent PL spectra suggested that the PLQY enhancement is due to the improved Mn 2+ doping efficiency and the effective passivation of native vacancy defects. The stability of the NCs is enhanced by replacing Pb 2+ with Mg 2+ and Mn 2+ , mitigating lattice distortions within the [PbCl 6 ] 4− octahedral framework. The color rendering index of white light‐emitting diodes fabricated with the post‐treated Mn 2+ :CsPbCl 3 NCs achieves an exceptional value of 98. This work offers novel insights into the fabrication of high‐PLQY Mn 2+ :CsPbCl 3 NCs, advancing the practical deployment of perovskite nanomaterials in various industries.