Influence of surface states on blinking characteristics of single colloidal CdSe-CdS/ZnS core-multishell quantum dot

摘要

We carefully characterized the fluorescence blinking of single colloidal CdSe-CdS/ZnS core-multishell quantum dots (QDs) with different surface modifications, including octadecylamine (ODA) coated QDs dispersed in chloroform, aqueous 3-mercaptopropionic acids (3MPA) coated QDs in HEPES solution treated by Ca2+ ions and ethylene glycol tetraacetic acid (EGTA, Ca2+ chelator), and aqueous 3MPA-QDs treated by glycerol. It was found that the on- and off-state probability density distributions displayed different rules. The off-state probability density distributions of all QDs complied well with the inverse power law, while the on-state probability density distributions bended upwards in log-log scale, and the degree of the upwards-bending correlated strongly with QD surface modification and fluorescence brightness of the single QD. Further autocorrelation analysis revealed that the fluorescence time series of a single QD was more random when the single QD showed a stronger fluorescence. Realistic numerical simulations with input parameters from quantum mechanical calculations showed that the QD exciton was first generated by an excitation photon; It radiatively recombined to give QD's fluorescence response, i.e., the on-state, which displayed the upwards-bended on-state probability density distribution profile; The electron and/or the hole of the photoexcited exciton in the QD core, after tunneling to the QD surface, randomly walked through the two-dimensional network of the QD surface states, resulting in the off state probability density distribution profile of the inverse power law. Surface modification modified the QD surface-state network, in turn modifying the on/off probability density distribution profiles. Our findings provide us with a novel highway of applying colloidal QDs to study microscopic physical, and chemical, processes in many fields including in vivo and in vitro imaging, sensing and labelling. (C) 2017 Elsevier Inc. All rights reserved.