Investigation of Exciton-Phonon Coupling in Cesium Lead Bromide Perovskite Nanosheets with photoluminescence

Variable-temperature photoluminescence (PL) spectra of cesium lead bromide (CsPbBr₃) nanosheets were measured in a low temperature range of 5 to 40 K. In this interested low temperature range the measured PL spectra exhibit a main zero-phonon peak and its longitudinal-optical (LO) phonon sideband, and are quantitatively simulated using the multimode Brownian oscillator (MBO) model. Good agreement between theory and experiment enables us to determine several key parameters characterizing the exciton−phonon coupling, including the dimensionless Huang-Rhys factor S accounting for the exciton-LO phonon coupling strength and the damping constant γ for the phonon bath (quasi-continuous acoustic phonons) dissipation. It is found that Huang-Rhys factor S peculiarly tends to diminish upon increasing the temperature, suggesting weakened exciton-LO phonon coupling in the interested low-temperature range. However, as often observed in solids, the damping constant γ in the nanosheets increases almost linearly with the rise of temperature. This study may shed some light on the complex exciton-phonon scattering mechanisms in solids.