Dual-Defect Engineering in Halide Nanocrystals Enables Synergistic Photochromism and Persistent Luminescence for X-Ray Colorimetric Imaging and Dynamic Anti-Counterfeiting

• • CsX (X = Cl, Br) nanocrystals exhibit dual-defect engineering with intrinsic and X-ray-induced chlorine vacancies, enabling simultaneous photochromism and persistent luminescence; X-ray irradiation at 20–70 kV induces reversible blue coloration with a color difference (ΔRL1) of 56.9% and a recovery rate (ΔRL2) of 98.1% upon visible light exposure within 30 s, ensuring high cycling stability for rewritable optical storage and anti-counterfeiting. • • Bromide incorporation deepens the energy level of intrinsic chlorine vacancies from 0.47–0.71 eV to 0.83 eV, producing persistent luminescence lasting over 30 minutes; this tunable defect depth is critical for optimizing afterglow performance in low-dose X-ray imaging and night-vision applications. • • The photochromic response is fully reversible under visible light, with a rapid bleaching time of 30 s, enabling fast write-erase cycles; this operational speed is essential for real-time X-ray colorimetric imaging and dynamic anti-counterfeiting where rapid response is required. • • The material system demonstrates excellent cycling stability, with a recovery rate of 98.1% after multiple cycles, indicating minimal fatigue; this durability is vital for long-term deployment in security marking and dosimetry, where repeated use without performance degradation is mandatory.