A Thermally Robust Organic–Inorganic Hybrid Scintillator Enabled by RISC‐Assisted Mn 2+ Emission for High‐Temperature X‐Ray Imaging

Abstract Scintillators that sustain efficient radioluminescence at high temperatures are essential for next‐generation radiation imaging but remain a challenge, particularly for hybrid halide systems. Herein, an organic–inorganic hybrid scintillator is reported, ETPP 2 MnCl 4 , in which spatially isolated [MnCl 4 ] 2− tetrahedra are embedded within a 0D host–guest framework formed by bulky ETPP + cations. This architecture suppresses nonradiative relaxation and energy migration, yielding intense green emission from the Mn 2+ 4 T 1 (G)→ 6 A 1 (S) transition with a photoluminescence quantum yield of 45.2%. Remarkably, ETPP 2 MnCl 4 exhibits a thermally activated enhancement of radioluminescence, which is attributed to reverse intersystem crossing (RISC) from the triplet to singlet states of the organic ligand and then efficient energy transfer to Mn 2+ activators. As a result, it exhibits anti‐thermal‐quenching behavior, retaining 112% of its radioluminescence at 130 °C, and maintains over 92% of its emission intensity after prolonged high‐temperature and high‐dose irradiation. Under X‐ray excitation, the material delivers a light yield of 20 040 photons MeV −1 , a detection limit of 49.8 nGy air s −1 . and a spatial resolution of 12.2 lp·mm −1 . These findings demonstrate a previously unreported RISC‐assisted sensitization mechanism in hybrid scintillators and establish a design strategy that integrates triplet‐singlet conversion pathways with discrete metal halide emitters, positioning ETPP 2 MnCl 4 as a promising scintillator for extreme‐environmental applications.