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.

Linear Regulation of Red Emission in an Organic–Inorganic Manganese Bromide via Pressure

“…To better evaluate the potential of this compound for pressure sensing, we have compared its PLQY values, pressure sensitivity, pressure response range, and phase transition point with those from other Mn-based compounds (Table S5). ,− These results reveal that (TDMA)­MnBr 3 (H 2 O) 2 not only possesses a sensitive pressure response but also a high pressure–emission wavelength linear correlation and sufficient optical emission yields, which is favorable for pressure sensing in the red emission region.…”

“…The red-dotted regions show strong intramolecular hydrogen bonding interactions, mainly from the H···Br interactions between neighboring [MnBr 3 (H 2 O) 2 ] − octahedra or from H···Br interactions between TDMA + and [MnBr 3 (H 2 O) 2 ] − . The blue areas refer to the weaker van der Waals interaction, which distinctly indicate that the pressure significantly enhances the intramolecular hydrogen bonding interactions and thus has a significant effect on the structural stability of (TDMA)­MnBr 3 (H 2 O) 2 …”