Shell-dependent blinking and ultrafast carrier dynamics in CdxZn1-xSeyS1-y@ZnS core/shell quantum dots

Abstract

Fluorescent semiconductor quantum dots (QDs) are promising nanocrystals with excellent optical properties for applications in many fields. However, the severe blinking of QDs limits their practical applications that rely on single-dot emission. In this study, the shell-dependent blinking behavior and ultrafast carrier dynamics in CdxZn1-xSeyS1-y@ZnS core/shell QDs with smooth interface were investigated by using single particle fluorescence imaging and time-resolved spectroscopy. Our observations indicate that the on-time fraction of emission blinking for CdxZn1-xSeyS1-y QDs can be effectively increased with capping the ZnS shell. Meanwhile, the ultrafast dynamics including the hot carrier relaxation within hundreds of femtoseconds, carriers capture by defect states in tens of picoseconds, and electron-hole nonradiative recombination with several nanoseconds have been clearly identified for the as-prepared QDs with different shell thickness. We found that above carrier dynamics demonstrate an obvious dependence of ZnS shell thickness due to the effective isolation of the internal carriers in the CdxZn1-xSeyS1-y core from the decreased interfacial defects. These findings suggest that the capping shell can effectively regulate the carrier dynamics and blinking behavior, and improve the optical properties of CdxZn1-xSeyS1-y @ZnS QDs, which are significant for understanding the correlation between the structure and optical properties of fluorescent QDs.