Coexisting Dielectric and X-ray Response in a Nitrate-Bridged Perovskite-Type Bimetal Rare-Earth Hybrid Semiconductor

M^IRE^III-based nitrate-bridged double perovskite-type hybrid materials are an emerging class of multifunctional materials that exhibit intriguing physical properties. While the synthesis and structural phase transitions of these compounds, including (TMA)₂NaPr(NO₃)₆ (TMA⁺ = tetramethylammonium cation, 1), have been recently established, their potential in electronic applications remains largely unexplored. Herein, we focus on the functional characterization of 1, which exhibits a reversible phase transition at T_tr = 306 K, dynamic dielectric response, and semiconducting behavior with an indirect band gap of 3.81 eV at 335 nm. Furthermore, 1 exhibits a luminescent property with a fluorescence lifetime of 29.09 ns. More importantly, an X-ray detector fabricated from a single crystal of 1 demonstrates a sensitivity of 27 μC·Gy_air^-1·cm^-2 and a minimum detectable dose rate of 0.038 mGy_air·s^-1 at an ultralow bias of 1 V. This performance surpasses that of commercial amorphous selenium-based direct-type detectors (XR100SDD and BrillianSe). This work not only demonstrates the multifunctionality of 1, including dielectric response, fluorescence, and X-ray response but also opens potential applications for developing novel optoelectronic and sensing devices.