Room‐Temperature Precipitation of Highly Stable Sb 3+ Doped Cs 3 LuCl 6 Microcrystals for Flexible X‐ray Imaging

ABSTRACT Lead‐free all‐inorganic metal halides are promising scintillators due to their self‐trapped exciton (STE) luminescence, large Stokes shifts, and robust stability. However, achieving a balance among scalable synthesis, X‐ray absorption capability, high light yield (LY), and stability of all‐inorganic metal halide microcrystals (MCs) remains extremely challenging. Here we introduce Sb 3+ into a Cs 3 LuCl 6 host with a high effective atomic number and synthesize Sb 3+ ‐doped Cs 3 LuCl 6 MCs by room‐temperature precipitation. The incorporation of Sb 3+ generates localized [SbCl 6 ] 3− units that regulate self‐trapped exciton emission, yielding optimized Cs 3 LuCl 6 : 0.7%Sb 3+ MCs that exhibit broadband green emission, a large Stokes shift of 142 nm and a near‐unity photoluminescence quantum yield of 97.4%. The MCs also exhibit outstanding X‐ray absorption capability, a high LY of 26318 photons/MeV, a low detection limit of 437 nGy/s, and exceptional irradiation stability (retaining 115% of initial RL intensity after 1 h of cyclic irradiation). The fabricated flexible Cs 3 LuCl 6 : Sb 3+ MCs @ polydimethylsiloxane film further enables clear visualization of intricate internal structures with a spatial resolution of 10.8 lp/mm. These results demonstrate the potential of Sb 3+ ‐doped Cs 3 LuCl 6 as a highly efficient, stable, and lead‐free scintillator and establish a scalable, low‐temperature synthetic route toward advanced flexible X‐ray imaging systems.