Ultrafast carrier dynamics in semiconductor quantum dots

Abstract

The dynamics of band-edge photoluminescence (PL) in CdS nanocrystals (NC’s) dispersed in a glass matrix are studied with the femtosecond up-conversion technique. The time-resolved PL spectra exhibit several discrete features (three of them are in the NC energy band gap) which are not pronounced in a cw PL spectrum. The initial stage of a PL decay is governed by a depopulation of the lowest extended states due to carrier trapping (localization) on the time scale of 1 ps. The low-energy bands originating from the extended-to-localized state transitions exhibit extremely fast buildup dynamics (rise time is 400–700 fs) which is explained by the preexisting occupation of the localized states. © 1996 The American Physical Society.