Narrow-Line Width Emission and Room Temperature Amplified Spontaneous Emission in Three-Dimensional Ge Halide Perovskites

High Resolution Image Download MS PowerPoint Slide We report the structural and optoelectronic properties of lead-free CsGeI 3 and CsGeBr 3 perovskites, unveiling the critical role of local symmetry distortions in defining their emission properties. CsGeBr 3 exhibits broad photoluminescence from self-trapped excitons, due to local octahedral distortion and a large distribution of the average bond lengths. On the contrary, by using temperature-dependent pair distribution function analysis and hybrid-functional molecular dynamics simulations, we demonstrate that CsGeI 3 adopts a monoclinic local structure responsible for its narrow near-infrared (NIR) emission (∼745 nm, FWHM ≈ 110 meV at room temperature), the narrowest reported for Ge-based perovskites and in line with tin iodide perovskites. Notably, the high level of structural order also supports the achievement of amplified spontaneous emission (ASE) at room temperature with an exceptionally low threshold (75 μJ/cm 2 ), positioning it as a promising candidate for lead-free NIR light-emitting and laser applications.