Intensity-dependent bleaching relaxation in lead salt quantum dots

Abstract

Bleaching relaxation in lead salt (PbS) quantum dots (QDs) of various sizes and under different pump intensities has been studied. The observed bleaching relaxation features (particularly, shortening of the bleaching relaxation times with a decrease in the QD size and an increase of the pump-light intensity) are explained in the context of the proposed spectroscopic model. The model takes into account transitions of the excited-charge carriers both within the system of quantum-confined energy levels and the defect states of the QDs. The characteristic times of the direct electron-hole recombination, carriers trapping to the defect states, and their subsequent relaxation from these states as well as the cross sections of the ground-state and excited-state absorption of charge carriers can be evaluated from the experimental data for PbS QDs of different sizes and under different pumping conditions using this model.