Pressure‐Induced Dual‐Emission of Mn‐Based Metal Halides (C₅H₆N)₂MnBr₄

Abstract Regulating the crystal structure of metal halides is important to tune their photoluminescence (PL) or govern the potential emergence of diverse physical properties. Here, an exceptional PL phenomenon characterized by dual‐emission bands in the Mn‐based metal halides (C₅H₆N)₂MnBr₄ is observed through hydrostatic pressure measurements. The results have confirmed that the dual‐emission bands centered at ≈518 and 650 nm arise from isolated Mn²⁺ ions and super‐exchange within Mn²⁺–Mn²⁺ dimers, respectively. (C₅H₆N)₂MnBr₄ displays remarkable piezochromic luminescence, accompanied by a red shift in dual‐emission. This phenomenon can be attributed to the enhancement of crystal‐field splitting energy and the reduction of relaxation from the low‐energy excited state ⁴T₁ to the ground state ⁶A₁. Meanwhile, the dual‐emission exhibits an anomalous increase ≈1.5–3.9 GPa, which is associated with reduced nonradiative losses during energy migration due to the decreased distance between the luminescent centers as a consequence of lattice contraction. Moreover, (C₅H₆N)₂MnBr₄ undergoes a phase transition at ≈1.5 GPa, and upon decompression, the high‐pressure phase partially recovers. This study not only provides insights into the luminescent properties of Mn‐based metal halides but also presents a novel approach to the design of multifunctional photoluminescent materials.