Temperature-Dependent Photoluminescence of Ag₂Se Quantum Dots

Abstract

The time-resolved photoluminescence spectroscopy was employed to analyze the optical properties of Ag2Se quantum dots with different diameters at temperatures of 80–360 K. The photoluminescence lifetime measurement disclosed that in the low-energy electronic structure there were two dominating emissive “in-gap” states associated with surface defect and intrinsic states, which were further confirmed by Gaussian fitting of the photoluminescence spectra. The temperature-dependent emission peak energy was fitted to phenomenological equations to extract the average phonon energy, the Huang–Rhys factor, and the excitonic acoustic phonon coupling coefficient. The relatively large phonon energy and small Huang–Rhys factor were demonstrated, which induced the small variation of emission peak energy in the low-temperature range. Meanwhile, the photoluminescence line width increased with temperature and was analyzed based on the standard equation describing the temperature dependence of the width of the ground state exciton. The variation of both the photoluminescence peak and line broadening was mostly due to the exciton to acoustic phonon coupling.