Organic–Inorganic Hybrid Manganese(II) Halides with Reversible Thermochromic Luminescence for Anti-Counterfeiting and X-ray Imaging

Thermochromic scintillators with high electron and hole generation capacity after X-ray irradiation have gained significant attention for anticounterfeiting and X-ray imaging applications. However, achieving luminescent compounds with highly efficient and reversible thermochromic luminescence and radioluminescence remains a significant challenge. In this study, we reported two novel and cost-effective zero-dimensional (0D) Mn(II)-based halide hybrids, designated as (4-PP)₂MnX₄ (4-PP = 4-phenylpyridine; X = Cl, Br), with bright narrow-band green emissions and remarkably high photoluminescence quantum yields of 90.7% and 94.6%, respectively. Notably, a distinct and reversible thermochromic behavior, shifting from green to red emission with temperature variation, was observed under ambient conditions. Furthermore, (4-PP)₂MnX₄ (X = Cl, Br) demonstrated impressive steady-state X-ray light yields of 42 000 and 48 000 photons MeV^-1, alongside low detectable limits of 79.2 and 56.6 nGyair s^-1. The combination of pronounced color changes and exceptional radiative properties positions these materials as promising candidates for anticounterfeiting applications and in situ thermally responsive X-ray imaging. This research marks a significant advance in the design of high-efficiency thermochromic materials, offering a blueprint for future research into multifunctional thermochromic scintillators tailored for advanced X-ray imaging technologies.