Water‐Induced Reversible Luminescence and Efficient Radioluminescence in Multifunctional Manganese(II) Halides

Organic–inorganic hybrid manganese(II) halide materials have attracted attention for their stimuli‐responsive luminescence switching, making them promising candidates for anticounterfeiting applications. Furthermore, these materials have also emerged as efficient scintillators due to their remarkable X‐ray absorption properties. Herein, we developed a novel zero‐dimensional manganese(II) halide, (pr‐ted) ₂ MnBr ₄ ·H ₂ O (pr‐ted = 1‐propyl‐1,4‐diazabicyclo[2.2.2]octan‐1‐ium), which exhibits water‐molecule‐induced reversible photoluminescence transformation. Specifically, thermal dehydration of (pr‐ted) ₂ MnBr ₄ ·H ₂ O induces a structural transition to anhydrous (pr‐ted) ₂ MnBr ₄ , accompanied by a distinct emission color change from red to green. Remarkably, the original hydrated phase can be fully restored upon re‐exposure to moisture, demonstrating excellent reversibility. Based on this unique property, we successfully applied (pr‐ted) ₂ MnBr ₄ ·H ₂ O in information encryption–decryption, optical anticounterfeiting, and optical logic gate. Additionally, both (pr‐ted) ₂ MnBr ₄ ·H ₂ O and (pr‐ted) ₂ MnBr ₄ exhibit outstanding scintillation performance, with measured light yields of 30,120 photons MeV ⁻¹ and 26,320 photons MeV ⁻¹ , respectively. This work provides a strategic approach for designing multifunctional manganese(II) halide materials.