Tailoring Narrow‐Band Green Photoluminescence in Manganese Hybrid Halides via Solvent‐Free Mechanosynthesis and Anion Exchange for Advanced Optical Applications

Solvent‐free mechanochemical synthesis represents an eco‐friendly and highly efficient strategy toward functional materials, eliminating organic solvents, shortening synthetic durations, and enabling rapid construction of unprecedented crystalline structures via solid‐state grinding. Manganese hybrid halides (Br 4 and Br 2 I 2 ) were successfully prepared via a facile solvent‐free mechanosynthesis combined with Br − /I − anion exchange. The as‐synthesized samples exhibit tunable narrow‐band green photoluminescence (518 nm for Br 4 , 533 nm for Br 2 I 2 ) with a full width at half maximum of ≈44 and 47 nm. Photoluminescence properties confirm that anion exchange modulates the Mn 2+ crystal field environment, realizing PL tunability based on the spin‐forbidden d ‐ d transition. Benefiting from their superior luminescent properties, the samples were successfully applied in backlight LED, multi‐level fluorescent anti‐counterfeiting, latent fingerprint detection and X‐ray imaging. The present research establishes a sustainable and scalable synthetic strategy toward high‐performance Mn 2+ ‐based hybrid halides, and further extends their practical utilization in optoelectronic applications and analytical detection.