Synergistic Zn2+–Sb3+ Doping Enables Unity Photoluminescence Quantum Yield in Zero-Dimensional Manganese Halide toward Flexible Temperature Sensing

Zero-dimensional manganese halides offer distinctive luminescence but are limited by nonradiative losses, constraining their efficiency and tunability. Herein, we demonstrate a synergistic Zn2+ and Sb3+ doping strategy in (C8H20N)2MnCl4 to overcome these limitations. Initial Zn2+ alloying optimized the inter-Mn2+ distance, suppressing nonradiative energy transfer and boosting the inherent green Mn2+ emission (525 nm) to a 92.5% PLQY. Subsequent incorporation of trace Sb3+ ions created dual emissive centers, enabling broad white-light emission and a record PLQY of 98.4%. Combined spectroscopic and computational studies confirm that Sb3+ occupies both Mn2+ and Zn2+ sites, introducing specific defect states that steer energy into both triplet and singlet self-trapped exciton channels, alongside the Mn2+ transition. The optimized material exhibits superior thermal stability with a high activation energy barrier. Leveraging these properties, we fabricated a mechanically durable fluorescent film that serves as a highly sensitive temperature sensor (maximum relative sensitivity of 5.190% K–1), withstanding rigorous folding tests. This work establishes a potent doping paradigm for engineering high-performance 0D emissive halides and showcases their viable integration into flexible optoelectronic devices for advanced sensing applications.