Dual‐Channel Sensibilization of Bi ³⁺ Boosts Near‐Unity Photoluminescence Quantum Yield Rare‐Earth‐Free Halide Perovskite for Energy‐Saving Agricultural Cultivation Film

ABSTRACT The development of low‐cost, rare‐earth‐free light conversion materials is critical for sustainable agriculture. Herein, we report a Bi 3+ /Mn 2+ co‐doped lead‐free double perovskite Cs 2 Ag 0.8 Na 0.2 InCl 6 synthesized via an environmentally friendly mechanochemical method. The phosphor exhibits a broad‐spectrum emission (400–800 nm) with a full width at half maximum (FWHM) of 206 nm, attributed to the synergistic effect of Bi 3+ ‐activated self‐trapped excitons (STEs) and Mn 2+ 4 T 1 → 6 A 1 transitions. Bi 3+ doping not only extends the absorption range to the UVA region (350–400 nm) but also enhances the photoluminescence quantum yield (PLQY) to 99.3% through Bi 3+ →STE and Bi 3+ →Mn 2+ energy transfer. A sunlight conversion film fabricated by incorporating the phosphor into Ecoflex‐0031 silica gel shows excellent mechanical stability (tensile elongation retained over 16 days) and environmental durability. Plant growth experiments with chives and hydrocotyle vulgaris demonstrate significant improvements under the film: chive stem length increased by 136%, hydrocotyle leaf width by 37%, and fresh weight by 17%. This work highlights the potential of Bi 3+ /Mn 2+ co‐doped perovskites as efficient, low‐cost light conversion agents for energy‐saving agricultural cultivation film.