Theory and experiments of pressure-tunable broadband light emission from self-trapped excitons in metal halide crystals

Hydrostatic pressure has been commonly applied to tune broadband light emissions from self-trapped excitons (STE) in perovskites for producing white light and study of basic electron-phonon interactions. However, a general theory is still lacking to understand pressure-driven evolution of STE emissions. In this work we first identify a theoretical model that predicts the effect of hydrostatic pressure on STE emission spectrum, we then report the observation of extremely broadband photoluminescence emission and its wide pressure spectral tuning in 2D indirect bandgap CsPb(2)Br(5 )crystals. An excellent agreement is found between the theory and experiment on the peculiar experimental observation of STE emission with a nearly constant spectral bandwidth but linearly increasing energy with pressure below 2 GPa. Further analysis by the theory and experiment under higher pressure reveals that two types of STE are involved and respond differently to external pressure. We subsequently survey published STE emissions and discovered that most of them show a spectral blue-shift under pressure, as predicted by the theory. The identification of an appropriate theoretical model and its application to STE emission through the coordinate configuration diagram paves the way for engineering the STE emission and basic understanding of electron-phonon interaction.

Automated summary

In this study, a theoretical model is proposed to predict the effect of hydrostatic pressure on the emission spectrum of self-trapped excitons (STE). The extremely broadband photoluminescence emission and its wide pressure spectral tuning are observed in 2D indirect bandgap CsPb(2)Br(5) crystals, and the experimental results are in good agreement with the theoretical predictions. Further analysis reveals the involvement of two types of STE and their different responses to external pressure. The investigation of published STE emissions shows a spectral blue-shift under pressure, consistent with the theoretical predictions.