Optical and Dynamic Properties of Water-Soluble Highly Luminescent CdTe Quantum Dots

Abstract

CdTe quantum dots (QDs) were synthesized in aqueous solution using thioglycolic acid (HS−CH₂COOH,\nTGA) as a stabilizer. The phenomenon of “on” and “off” luminescence intermittency (blinking) of CdTe\nQDs in PVA and trehalose was investigated by single-molecule optical microscopy, and we identified that\nthe intermittencies of single QDs were correlated with the interaction of water molecules absorbed on the\nQD surface. The “off” times, the interval between adjacent “on” states, remained essentially unaffected with\nan increase in excitation intensity. Every QD showed a similar power law behavior for the “off” time distribution\nregardless of the excitation intensity and aqueous environment of the QDs. In the case of “on” time distribution,\npower law behavior with an exponential cutoff tail is observed at longer time scales. The time traces indicated\nthat the “on” time was inversely proportional to the excitation intensity; the duration of “on” time became\nshorter with increasing excitation intensity. An increase in the duration of “on” time was observed in trehalose\nwith respect to that in PVA. We obtained a clear decrease in the power law exponent when PVA was replaced\nwith trehalose. These observations indicate that the luminescence blinking statistics of water-soluble single\nCdTe QDs is significantly dependent on the aqueous environment, which is interpreted in terms of passivation\nof the surface trap states of QDs.