Te concentration-dependent carrier dynamics and electronic structure of ZnTe <i>x</i> Se1− <i>x</i> quantum dots

Abstract

Heavy-metal-free ZnTexSe1−x quantum dots (QDs) have attracted significant attention due to their potential to substitute Cd,Pb-based QDs for tunable emission in luminescent or display applications. In this work, a series of ZnTexSe1−x QDs capped with sequential shells including ZnSe and ZnS ranging from green to red emission are synthesized with broad Te concentration varying from x = 0.18 to 0.8. The photoluminescent properties and carrier dynamics are analyzed through combined spectral and structural characterization. The static and time-resolved photoluminescence (PL) spectra show reduced PL quantum yield and accelerated quenching kinetics owing to the synergistic effect of worse lattice mismatch and increased defects concentration at higher x values. In particular, the transient absorption (TA) spectra with regard to both single exciton and bi-exciton processes provide evidence that the energy level alignment between ZnTexSe1−x core and ZnSe shell evolves from type I to quasi-type II with increased Te concentration and leads to electron delocalization at the conduction band. Locations of the energy levels for each QD are also given in detail according to TA spectral analysis. Considering the crucial influence of the energy level structure on microscopic carrier dynamics and macroscopic optoelectronic properties, this work offers a deeper understanding of the specific carrier dynamics in ZnTexSe1−x-based QDs and supports their practical application in related optoelectronic devices.