Local symmetry disruption via lanthanide co-doping in Cs2NaYCl6: Enhanced charge transfer and exciton binding

Lanthanide ions (Ln 3+ ) co-doped lead-free metal halide double perovskites exhibit significant potential in photoluminescence modulation, yet the luminescence synergy mechanism between co-doped Ln 3+ ions needs further exploration. In this study, we systematically investigated the electronic structure properties of the Ln 3+ single-doped (Ln 3+  = Tb 3+ , Eu 3+ , Yb 3+ , Ho 3+ , Er 3+ ) and co-doped (Tb 3+ +Eu 3+ , Yb 3+ +Ho 3+ , Yb 3+ +Er 3+ ) models based on Cs 2 NaYCl 6 double perovskites (DPs) using density functional theory (DFT). The results reveal that appropriate Ln 3+ co-doping further breaks the local symmetry compared with single doping, regulates the ionicity of Na + , and enhances the charge transfer transition of Cl − →Ln 3+ . In addition, co-doping strategies elevate exciton binding energy by approximately 25 %–38 %, promoting exciton radiative recombination. Experimental verification via hydrothermal-synthesized Ho 3+ ,Yb 3+ co-doped Cs 2 NaYCl 6 crystals confirmed a 27.4 % enhancement in absolute photoluminescence quantum yield (PLQY) under 360 nm photoexcitation compared to Ho 3+ single-doped, validating the theoretical prediction of optimized charge-transfer transitions. This study provides a theoretical reference for regulating the luminescence properties of lanthanum ion-doped double perovskite materials.