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Anomalous Temperature-Dependent Exciton–Phonon Coupling in Cesium Lead Bromide Perovskite Nanosheets

The role of exciton–phonon coupling in light emission in cesium lead bromide (CsPbBr3) nanosheets is investigated with combined photoluminescence spectroscopy and the multimode Brownian oscillator model. A good agreement between theory and experiment in the low temperature range of 5–40 K enables us to determine several key parameters, including the dimensionless Huang–Rhys factor characterizing the exciton–longitudinal-optical phonon coupling strength and the damping constant accounting for the phonon bath (quasi-continuous acoustic phonons) dissipation. It is found that the Huang–Rhys factor of the free excitons peculiarly tends to diminish upon increasing the temperature in the interested low temperature range. However, the damping constant shows a linear increase with temperature in the interested temperature range. These new findings may deepen the understanding of the exciton–phonon coupling in CsPbBr3 nanosheets and relevant solids.