Luminescence properties and exciton dynamics of core–multi-shell semiconductor quantum dots leading to QLEDs

Abstract

In this study, we grew CdSe core quantum dots (QDs) along with CdSe/ZnS/ZnS and CdSe/CdS/CdS core–multi-shell semiconductor QDs via successive ionic layer adsorption and reaction. The effects of the shell layers on the optical properties and exciton dynamics of the QDs were examined using steady-state and time-resolved measurements together with transient absorption (TA). The photoluminescence (PL) intensity and quantum yield (QY) of the synthesized QDs were enhanced by shell growth. The QY of the QDs increased from 23% to 41% with shell growth due to the decrease in nonradiative recombination sites, which was attributed to surface passivation by the shell layer. The average PL lifetime decreased with shell growth. This effect might be related to the reduction of electron and hole densities on the QD surfaces. The TA spectra show bleaching and photoinduced absorption, corresponding to the state-filling effect and trap states, respectively. The findings are essential for understanding the growth and applications of core–multi-shell QDs.