Red-Emission Harvesting Unlocked by Pressure-Enhanced Crystal Field and Mn–Mn Coupling

The lack of red emission component with a high color rendering index (CRI) results in a harsh white light-emitting diode. Here, a high-pressure strategy is introduced to achieve a marked piezochromism that shifts from green to red in zero-dimensional (0D) manganese halide (C 6 H 14 N 2 )MnCl 4 . Note that after the pressure is released, the red emission with intense intensity can be stabilized at ambient conditions. The CRI and color purity of the red emission for the quenched (C 6 H 14 N 2 )MnCl 4 are significantly improved to 72 and 85.9% from the initial 14 and 66.5%, respectively. The irreversible pressure-induced amorphization highly contributes to the quenched high-efficiency red emission through the strengthening of the crystal field and Mn–Mn coupling, associated with the shortening of the Mn─Cl bond length and Mn–Mn distance. This work unravels the underlying mechanism of piezochromism from green to red, and retention of intense red emission from the Mn-based metal halides, greatly facilitating the development of new-generation amorphous-state luminescent materials.