Mechanisms of fluorescence blinking in semiconductor nanocrystal quantum dots

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Abstract
The light-induced spectraldiffusion and fluorescenceintermittency (blinking) of semiconductor nanocrystal quantum dots are investigated theoretically using a diffusion-controlled electron-transfer (DCET) model, where a light-induced one-dimensional diffusion process in energy space is considered. Unlike the conventional electron-transfer reactions with simple exponential kinetics, the model naturally leads to a power-law statistics for the intermittency. We formulate a possible explanation for the spectral broadening and its proportionality to the light energy density, the − 3 ∕ 2 power law for the blinking statistics of the fluorescenceintermittency, the breakdown of the power-law behavior with a bending tail for the “light” periods, a lack of bending tail for the “dark” periods (but would eventually appear at later times), and the dependence of the bending tail on light intensity and temperature. This DCET model predicts a critical time t c (a function of the electronic coupling strength and other quantities), such that for times shorter than t c the exponent for the power law is − 1 ∕ 2 instead of − 3 ∕ 2 . Quantitative analyses are made of the experimental data on spectraldiffusion and on the asymmetric blinking statistics for the “on” and “off” events. Causes for deviation of the exponent from the ideal value of − 3 ∕ 2 are also discussed. Several fundamental properties are determined from the present experimental data, the diffusioncorrelation time, the Stokes shift, and a combination of other molecular-based quantities. Specific experiments are suggested to test the model further, extract other molecular properties, and elucidate more details of the light-induced charge-transfer dynamics in quantum dots.