On/Off Fluorescence Intermittency of Single Semiconductor Quantum Dots

Published

July 1, 2001

Author(s)

M Kuno, D P. Fromm, H F. Hamann, Alan Gallagher, David Nesbitt

Abstract

Single molecule confocal microscopy is used to investigate the detailed kinetics of fluoresence intermittency in colloidal H-VI (CdSe) semiconductor quantum dots. two distinct modes of behavior are observed corresponding to i) sustained on episodes (Τ_on) of rapid laser absorption/fluroesceince cycling, followed by ii) sustained off episodes (Τ_off) where essentially no light is emitted despite continuous laser excitation. Both the on-time and off-time probability densities follow an inverse power law, P(τ_on/off) viriation} 1/τ_on/off, over more than seven decades in probability density and five decades in time. Such inverse power law behavior is an unambiguous signature of highly disturbed rates (over 10⁵-fold) as opposed to isolated rate processes between sparse on and off configurations of the system. This intrinsically non-exponential power law behavior calls into question previous kinetic studies of average on (off) times, which for power law kinetics depends explicitly on experimental integration time and observation window. The large dynamic range of the current data permits several modes of fluorescence intermitttency to be critically evaluated. For example, the Auger electron hole pair ejection model is qualitatively inconsistent with the observedpower law behavior in both P(τ_on) and P(τ_off). Specifically, the inverse power law in P(τ_on) excludes any model based on a static configuration of trap sites, and highlights the crucial role of fluctuations in the QD environment. Finally, we offer a simple model based on the dynamical tunneling of carriers through fluctuating barriers which suggests an alternate way to characterize blinking kinetics.

Citation

Journal of Chemical Physics

Volume

115

Issue

No. 2

Pub Type

Journals

Keywords

distributed kinetics, inverse power law, nanocrystallites, quantum dots single molecule spectroscop

Citation

Kuno, M. , Fromm, D. , Hamann, H. , Gallagher, A. and Nesbitt, D. (2001), On/Off Fluorescence Intermittency of Single Semiconductor Quantum Dots, Journal of Chemical Physics (Accessed July 9, 2025)