Enhancing Initial Surface Adsorption for Doped Lead‐Free Copper(I) Halide Microcrystals Through a Moderate Lewis Base Ligand

Abstract Doping Mn 2+ in newly emerged lead‐free metal halides to access versatile optoelectronic applications is highly desired. However, understanding the chemical pathway of Mn 2+ doping and precisely controlling it remains challenging. Here, the crucial role of the initial surface adsorption of Mn 2+ in doping kinetics is demonstrated, and the adsorption step is effectively optimized by a moderate Lewis base ligand. The results show that not only the doping concentration of Mn 2+ in Cs 3 Cu 2 I 5 is modulated flexibly but also the produced Cs 3 Cu 2 I 5 :Mn 2+ microcrystals exhibit tuned photoluminescence/radioluminescence properties, indicating their applicability in anti‐counterfeiting and X‐ray imaging. Systematic experimental and theoretical outcomes reveal that the moderate Lewis base ligand dually links Mn 2+ (hard acid) and Cu + (soft acid) on the matrix surface, which improves the initial surface adsorption of the dopant and further promotes the doping step. This study contributes a simple strategy for simply controlling Mn 2+ doping in Cu(I)‐based halides and also opens a new avenue for understanding the fundamentals of doping dynamics in metal halide systems.