Bond differentiation manipulated lattice rigidity for enhanced luminescent Cs2AgSbCl6 through In3 + alloying

Sb-based metal halide double perovskites (MHDPs) are promising lead-free luminescent materials owing to their potential to exhibit a unique broadband self-trapped exciton emission. However, pristine Sb-based MHDPs are generally non-luminescent, limited by the severe lattice distortion from stereochemically active 5 s 2 lone pairs of Sb 3+ and concentration quenching from dense [SbCl 6 ] 3- center packing. Alloying is a powerful strategy to modulate the optical properties of MHDPs. Herein, a series of Cs 2 AgSb 1-x In x Cl 6 (x = 0–0.4) samples were synthesized via a vacuum solid-state reaction. Combined with first-principles calculations, we elucidated the effects of In 3+ incorporation on their structural, electronic, and optical properties. The results reveal that In 3+ alloying not only spatially separates [SbCl 6 ] 3- luminescent centers to suppress concentration quenching, but also drives electron density redistribution, forming bond differentiation between ionic In-Cl bonds and reinforced covalent Sb-Cl bonds. Thus, lattice rigidity increases, which alleviates excessive distortion of [SbCl 6 ] 3- octahedra, so as to reduce electron-phonon coupling strength. Consequently, non-radiative recombination caused by concentration quenching and excessive [SbCl 6 ] 3- octahedral distortion in Cs 2 AgSbCl 6 is largely suppressed with In 3+ alloying, which prolongs the photoluminescence lifetime from 0.37 μs (x = 0.05) to 1.23 μs (x = 0.3) and enables a transformation from non-luminescence to bright yellow-green emission across the Cs 2 AgSb 1-x In x Cl 6 (x = 0–0.4) system. The Cs 2 AgSb 0.7 In 0.3 Cl 6 sample exhibits the highest PL intensity with a PLQY of 11.88%. This study demonstrates that In 3+ alloying can simultaneously mitigate concentration quenching and lattice distortion in Sb-based MHDPs, providing a facile and effective strategy for developing high-performance lead-free luminescent materials.