Scalable Open‐Air Synthesis of Mg2+‐Doped Lead‐Free Cs3Cu2Cl5 Nanocrystals for High‐Performance Green LEDs

Cs3Cu2Cl5 nanocrystals (NCs) have emerged as promising optoelectronic materials owing to their efficient self‐trapped exciton (STE) emission. However, their limited environmental stability has significantly constrained their application in light‐emitting diodes (LEDs). In this work, a facile ambient‐air synthesis strategy is developed for Mg2⁺‐doped Cs3Cu2Cl5 NCs that simultaneously addresses both stability and emission efficiency challenges. Remarkably, optimal Mg2⁺ doping (20%) enhances the photoluminescence quantum yield (PLQY) from 28.69% to 59.3%. Comprehensive theoretical investigations through density of states (DOS) calculations and ab initio molecular dynamics (AIMD) simulations demonstrate that Mg2⁺ doping induces bandgap narrowing for enhanced radiative recombination while reinforcing the crystal lattice stability. When integrated with a UV LED chip, the optimized NCs enable the fabrication of high‐performance green LEDs exhibiting outstanding luminance (17 281 cd m−2) and excellent color stability (CIE coordinates: 0.354, 0.518). This study provides not only a practical synthetic approach for stable copper halide NCs but also valuable insights for designing efficient STE emitters for optoelectronic applications.