Tang Jau, Marcus R A
Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA.
J Chem Phys. 2005 Aug 1;123(5):054704. doi: 10.1063/1.1993567.
The light-induced spectral diffusion and fluorescence intermittency (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 -32 power law for the blinking statistics of the fluorescence intermittency, 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 -12 instead of -32. Quantitative analyses are made of the experimental data on spectral diffusion and on the asymmetric blinking statistics for the "on" and "off" events. Causes for deviation of the exponent from the ideal value of -32 are also discussed. Several fundamental properties are determined from the present experimental data, the diffusion correlation 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.
利用扩散控制电子转移（DCET）模型对半导体纳米晶体量子点的光致光谱扩散和荧光间歇性（闪烁）进行了理论研究，该模型考虑了能量空间中的光致一维扩散过程。与具有简单指数动力学的传统电子转移反应不同，该模型自然地导致了间歇性的幂律统计。我们对光谱展宽及其与光能密度的比例关系、荧光间歇性闪烁统计的-32幂律、“亮”周期幂律行为的弯曲尾部破坏、“暗”周期缺乏弯曲尾部（但最终会在稍后时间出现）以及弯曲尾部对光强度和温度的依赖性提出了一种可能的解释。该DCET模型预测了一个临界时间t(c)（电子耦合强度和其他量的函数），使得对于短于t(c)的时间，幂律指数为-12而不是-32。对光谱扩散以及“开”和“关”事件的不对称闪烁统计的实验数据进行了定量分析。还讨论了指数偏离理想值-32的原因。从目前的实验数据、扩散相关时间、斯托克斯位移以及其他基于分子的量的组合中确定了几个基本性质。建议进行特定实验以进一步测试该模型、提取其他分子性质并阐明量子点中光致电荷转移动力学的更多细节。
