Pressure-Modulated Near-Infrared Photoluminescence of a Two-Dimensional Germanium Halide Perovskite

Two-dimensional (2D) metal halide perovskites have received considerable attention among researchers in recent years owing to their potential use in light-emitting diodes. However, deep-red and near-infrared (NIR) emissions are usually absent in such perovskites owing to their intrinsic quantum and dielectric confinement effects, warranting further exploration. Herein, we report the pressure-modulated NIR emission of a 2D perovskite, (benzimidazolium)2GeI4 [(BIM)2GeI4], the photoluminescence (PL) of which can be regulated from broadband NIR emission to tunable narrowband deep-red to NIR emission under hydrostatic pressure. The dramatic PL change is attributed to pressure-induced exciton transfer from self-trapped excitons to free excitons and structural rearrangement, which can be fully reversed upon pressure release. A remarkable reversible piezochromism from orange to red to black is also observed. This study extends the PL emission of 2D halide perovskites to the deep-red to NIR region through pressure engineering, demonstrating their potential use in red light emission applications and bioimaging.