On-line investigation of laser-induced aggregation and photoactivation of CdTe quantum dots by fluorescence correlation spectroscopy

In this work, the laser-induced aggregation and subsequent photoactivation process of mercaptopropionic acid (MPA)-capped CdTe QDs was on-line studied with fluorescence correlation spectroscopy technique (FCS). It was observed that under laser irradiation, certain QDs facilely aggregated together and photoactivation process occurred. The aggregation process was dependent on sizes of QDs. Smaller QDs were more apt to aggregate together. The buffer types and concentrations markedly affected the photoactivation process. The higher concentration of salt would suppress the aggregation and photoactivation process of QDs significantly. Meanwhile, the photoactivation process was also closely associated with the concentration of QDs. Only when the concentrations of QDs were over the certain concentration (called as "photoactivation critical concentration") could the photoactivation of QDs occur under laser irradiation. Finally, a simple model was summarized to explain the photoactivation process of MPA-capping CdTe QDs.