Pressure‐Treated Engineering to Harvest Enhanced Green Emission in Mn‐Based Organic–Inorganic Metal Halides at Ambient Conditions

Abstract In the pressure‐induced emission enhancement paradigms, harvesting enhanced emission on the basis of original color is still largely hampered due to the recovery or decrement of emission intensity upon decompression. Here, a pressure‐treated strategy is reported to achieve the remarkable green emission enhancement of organic–inorganic metal halide (OIMH) [PP14] 2 [MnBr 4 ] ( N ‐butyl‐ N ‐methylpiperidinium [PP14] + ) at ambient conditions. After a cycle of 1 atm to 15.2 GPa, the [PP14] 2 [MnBr 4 ] shows a 1.67‐fold enhancement in the photoluminescence quantum yield from 54.5% to 90.8%, and green emission monochromaticity is unexpectedly retained. The restriction of motion freedom of [MnBr 4 ] 2− by increased Br···H interactions is highly responsible for the intense emission. Furthermore, [PP14] 2 [MnBr 4 ] exhibits significant piezochromism that shifts from green to red, and an ultrabroad tunability of 185 nm is observed below 12.5 GPa. The enhancement of the crystal field splitting energy and the reduction of the relaxation from the low‐energy excited state 4 T 1 to the ground state 6 A 1 that is caused by the shrinkage of MnBr bond result in the red shift of emission. This work sheds light on the effects of pressure treatment in boosting emission enhancement and facilitates the design of new OIMHs with the desired emission properties.