Photoluminescence Properties of the CdSe Quantum Dots Accompanied with Rotation of the Defocused Wide-Field Fluorescence Images

Abstract

By tracking the dynamics of the emitting field of single CdSe/ZnS core−shell quantum dots (QDs), the defocused image (DI), i.e., emission pattern of some QDs was observed to rotate after blinking- off periods in our previous paper. To gain insight into this phenomenon, here we have extended the observation time to 350 s and traced the DIs of a number of individual QDs under different environments. It has been found that the “active” QDs (of which the DI changes) blink less frequently than the “normal” QDs and remain dark most of the observation time. Upon illumination in air, the occurrence probability of the DI rotation in the CdSe core QDs was observed to be as high as 18%. For those CdSe QDs passivated with ZnS shells, the occurrence probability dropped to 3%. When they were protected further by the PVA or PMMA film, the probability dropped to as low as ∼5‰. We propose that the surface defects of the QDs could form a type of carrier traps, which may influence the electron cloud and lead to a relatively high occurring probability of the “self-rotation” of the DI. Further, it seems that the surface defects could affect the recapture of the ejected carrier of the QDs and result in a longer mean off -time for the “active” QDs.