Highly Efficient Blue Emission from Self-Trapped Excitons in Stable Sb³⁺-Doped Cs₂NaInCl₆ Double Perovskites

Highly efficient blue-emitting three-dimensional (3D) lead-free halide perovskites with excellent stability have attracted worldwide attention. Herein, a doping route was adopted to incorporate Sb³⁺ ions into the Cs₂NaInCl₆ for decorating the electronic band structure. Due to the moderate electron-phonon coupling, the Sb³⁺-doped Cs₂NaInCl₆ double perovskites showed a narrow and relatively unusual blue emission of self-trapped excitons (STEs). Density functional theory (DFT) calculation indicated that the doped Sb³⁺ ions could break the parity-forbidden transition rule and modulate the density of state (DOS) population effectively to boost the PLQY of STEs drastically. The optimized Sb³⁺:Cs₂NaInCl₆ exhibited a PLQY of up to 75.89% and excellent stability under the consecutive illumination of 365 nm UV light for 1000 h. This kind of highly efficient lead-free Sb³⁺-doped Cs₂NaInCl₆ double perovskites may overcome the bottlenecks of severe toxicity and insufficient stability and therefore have an extensive application in the scarce blue photonic and optoelectronic fields.