Highly Efficient Manganese Bromides with Reversible Luminescence Switching through Amorphous–Crystalline Transition

While luminescent stimuli-responsive materials (LSRMs) have become one of the most sought-after materials owing to their potential in optoelectronic applications, the use of earth-scarce lanthanides remains a crucial problem to be solved for further development. In this work, two manganese-based LSRMs, (<i>R</i>)-(+)-1-phenylethylammonium manganese bromide, (R-PEA)₂MnBr₄, and (<i>S</i>)-(-)-1-phenylethylammonium manganese bromide, (S-PEA)₂MnBr₄, are successfully demonstrated. Both (R-PEA)₂MnBr₄ and (S-PEA)₂MnBr₄ show a kinetically stable red-emissive amorphous state and a thermodynamically stable green-emissive crystalline state at room temperature, where the fully reversible transition can be done through melt-quenching and annealing processes. Based on this property, a reusable manganese-halide-based time-temperature indicator is demonstrated for the first time. Furthermore, an X-ray scintillator with a low limit of detection (18.1 nGy/s) and a high spatial resolution limit (30.0 lp/mm) are achieved by exploiting the high transparency of amorphous states. These results uncover the multifunctionality of manganese halides and pave the way for upcoming research.