Temperature-dependent photoluminescence of PbS quantum dots in glass: Evidence of exciton state splitting and carrier trapping

We report experimental evidence of the lowest exciton state splitting and carrier trapping in PbS quantum dots (QDs) in glass matrix. Our measurements of photoluminescence (PL) of PbS QDs using steady-state and time-resolved PL spectroscopy reveal strong temperature dependences of the PL intensity and decay kinetics. We find that consistent quantitative description of our experimental results can be achieved using a simple model taking into account the lowest 1S-1S exciton state splitting and multiphonon-assisted carrier trapping to states outside a PbS QD. Using our model, we estimate the lowest exciton splitting energy and lifetimes of the dark and bright exciton states of PbS QDs. Consistent with our model, the PL transition energy of PbS QDs deviates at higher temperatures from the one predicted based on the bulk PbS band-gap dependence due to the lowest 1S-1S exciton state splitting. Temperature-induced broadening of the PL spectrum of PbS QDs is explained by the exciton-phonon interaction.