Volkán-Kacsó Sándor
Noyes Laboratory of Chemical Physics, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
J Chem Phys. 2014 Jun 14;140(22):224110. doi: 10.1063/1.4881460.
A theoretical method is proposed for the calculation of the photon counting probability distribution during a bin time. Two-state fluorescence and steady excitation are assumed. A key feature is a kinetic scheme that allows for an extensive class of stochastic waiting time distribution functions, including power laws, expanded as a sum of weighted decaying exponentials. The solution is analytic in certain conditions, and an exact and simple expression is found for the integral contribution of "bright" and "dark" states. As an application for power law kinetics, theoretical results are compared with experimental intensity histograms from a number of blinking CdSe/ZnS quantum dots. The histograms are consistent with distributions of intensity states around a "bright" and a "dark" maximum. A gap of states is also revealed in the more-or-less flat inter-peak region. The slope and to some extent the flatness of the inter-peak feature are found to be sensitive to the power-law exponents. Possible models consistent with these findings are discussed, such as the combination of multiple charging and fluctuating non-radiative channels or the multiple recombination center model. A fitting of the latter to experiment provides constraints on the interaction parameter between the recombination centers. Further extensions and applications of the photon counting theory are also discussed.
提出了一种理论方法来计算在一个时间间隔内的光子计数概率分布。假设为双态荧光和稳态激发。一个关键特性是一个动力学方案，它允许广泛的一类随机等待时间分布函数，包括幂律，展开为加权衰减指数之和。在某些条件下，解是解析的，并且找到了“亮”态和“暗”态积分贡献的精确且简单的表达式。作为幂律动力学的应用，将理论结果与来自多个闪烁的CdSe/ZnS量子点的实验强度直方图进行了比较。这些直方图与围绕“亮”最大值和“暗”最大值的强度状态分布一致。在或多或少平坦的峰间区域也揭示了一个状态间隙。发现峰间特征的斜率以及在某种程度上的平坦度对幂律指数敏感。讨论了与这些发现一致的可能模型，例如多重充电和波动的非辐射通道的组合或多重复合中心模型。将后者拟合到实验中对复合中心之间的相互作用参数提供了限制。还讨论了光子计数理论的进一步扩展和应用。
