Gel-confined strain amplifies FRET efficiency toward red emission enhancement beyond pressure quenching

Manganese (Mn)-based metal halides, with their rich and well-defined emission mechanisms, have garnered substantial attention in luminescent materials. However, their red emission quantum yields generally lag behind green emission, making precise energy modulation an attractive yet challenging goal. Here, we engineer a pressure-triggered Förster resonance energy transfer (FRET) network within a Mn-based metal halide gel (Mn-MHG). This achieved anomalous red emission enhancement via external energy injection, with red emission intensity at 355% of ambient green emission intensity. During compression, pressure-induced matrix rigidification substantially isolated Mn-bromine tetrahedra, suppressing d-d coupling-induced nonradiative transitions. Concurrently, the gel matrix exhibited pressure-induced emission, with its blue-white band broadly overlapping the excitation spectrum of Mn-MHG, establishing it as an effective on-demand energy transfer donor. Notably, further compression reduced donor-acceptor distances, substantially increasing the effective FRET radius and energy transfer efficiency, thereby stabilizing the energy transfer pathway. At 6.7 gigapascals, Mn-MHG exhibited intense red emission, with intensity significantly exceeding its ambient green emission. These findings advance a design strategy for mechanoresponsive adaptive optoelectronic materials, leveraging dynamic FRET networks to bridge external control and inherent functionality.