Pressure‐Induced Multi‐Stage Emission Modulation with Remarkably Enhanced Luminescence in 1D Halide Double Perovskite Sb 3+ ‐Doped TMA 2 NaInCl 6

ABSTRACT Doping with ns 2 metal ions tailors photophysical pathways in metal halides, activating and engineering luminescence in intrinsically non‐emissive matrices. Here, trace Sb 3+ doping transforms the non‐emissive 1D halide double perovskite TMA 2 NaInCl 6 (TMA + = C 4 H 12 N + ) into yellow broadband emission, originating from Sb 3+ of the triplet state 3 P 1 to ground state 1 S 0 radiative recombination. To overcome doping limitations, high pressure is applied to Sb 3 ⁺:TMA 2 NaInCl 6 , leveraging the structural flexibility to explore and enhance emission properties. Notably, high pressure induces multi‐stage emission evolution, characterized by two successive enhancement‐reduction processes before and after a pressure‐driven phase transition, stemming from varying lattice distortion. Throughout compression, both emission intensity and relative photoluminescence quantum yield (RPLQY) remain above ambient values, due to pressure‐induced structural regulation that improved radiative recombination while suppressing nonradiative losses. Specifically, emission intensity at 8.9 GPa reaches 5.3‐fold that at ambient conditions, while RPLQY at 25.1 GPa shows a 27.4‐fold enhancement. Moreover, increased local inorganic octahedron distortion under pressure induces distinct color changes and emission peak shifts, reflecting pressure modulation of the excited state. This work elucidates the emission mechanism of Sb 3+ ‐doped 1D halide double perovskite and offers guidance for designing metal halides with brighter emission, broader tunability, and improved RPLQY under external stimuli.