Green Aqueous Production of Lead‐Free Cs ₃ YCl ₆ Perovskite Microcrystals with Near‐Unity Quantum Yield for High Performance X‐ray Imaging

X‐ray imaging requires scintillators combining efficient X‐ray absorption, high light yield, fast decay, and environmental safety. This study presents high‐performance X‐ray scintillators based on Sb 3+ /Tb 3+ co‐doped Cs 3 YCl 6 microcrystals (MCs). These materials were synthesized via a scalable, green aqueous‐phase evaporation method. Broadband 1 S 0 → 3 P 1 absorption by Sb 3+ enables efficient energy transfer to Tb 3+ , achieving near‐unity photoluminescence quantum yield (PLQY). Under X‐ray excitation, these MCs demonstrate a light yield of 28 542 photons MeV −1 and a detection limit of 96.6 nGy air s −1 , together with excellent radiation stability. Flexible scintillating films fabricated from these MCs exhibit a spatial resolution of 12.3 lp mm −1 , enabling clear imaging of internal structures in capsules and electronic components. This work establishes an eco‐friendly, cost‐effective route for mass‐producing lead‐free scintillators suitable for low‐dose medical imaging and non‐destructive testing.