White-Light Emission and Diffusion of Self-Trapped Excitons in Antimony- and Bismuth-Based Hybrid Perovskites

Lead halide perovskites have set the stage for the emergence of main-group metal halide materials as promising candidates for next-generation optoelectronics, spanning applications like solar cells, light-emitting diodes, lasers, sensors, and photo-catalysis. Within these materials, efficient light-emission arises from self-trapped excitons, where excitations create transient defects in the crystal lattice that effectively capture excitons.<br/><br/>However, the complex interplay of factors, including ground- and excited-state lattice distortions, lattice softness, and electron-phonon coupling strength, presents a challenge in establishing the structure-property relationship. This complexity hinders the targeted design of optical properties and necessitates a deeper exploration of the influence of elemental composition and anion dimensionality.<br/><br/>In this study, we investigate two families of antimony and bismuth halide compounds that systematically vary in composition, anion dimensionality, connectivity, and the organic cation. These compounds possess crystal structures that facilitate self-trapped exciton formation, resulting in broad photoluminescence spectra with pronounced Stokes shifts. Our analysis identifies the relevant factors influencing bright white-light emission and quantifies the electron-phonon coupling strength, expressed by the Huang-Rhys factor (ranging from 5 to 22 in these materials). Furthermore, we investigate the diffusion of self-trapped excitons through temporally- and spatially resolved photoluminescence spectroscopy.<br/><br/>The insights gained from this research deepen our understanding of the emission mechanisms in hybrid halide perovskites, promising to guide the development of advanced optoelectronic materials.