Ultrafast Laser Studies of Two-Photon Excited Fluorescence Intermittency in Single CdSe/ZnS Quantum Dots
Ultrafast Laser Studies of Two-Photon Excited Fluorescence Intermittency in Single CdSe/ZnS Quantum Dots
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DOI：
10.1021/acs.nanolett.5b01139
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发表时间：
2015-12-01
期刊：
影响因子：
10.8
通讯作者：
Nesbitt, David J.
中科院分区：
文献类型：
--
作者：
Early, Kevin T.;Nesbitt, David J.
单量子点条件下的双光子荧光显微术已经由几个小组报道，（1-3）具有关于荧光不稳定性或“闪烁”的动力学和动力学的对比观察。在这里，我们调查的功率依赖性，动力学和统计的两个光子激发的荧光光谱从单个的CdSe/ZnS量子点在固体PMMA膜作为在800 nm处的子带隙激光强度的函数。在所有激发功率下观察到荧光猝灭性，并且验证了入射激光功率对散粒噪声限制的荧光强度的二次（n = 1.97（3））依赖性，确认了来自单光子激发过程的基本上为零的背景贡献。这样的分析允许从数据中定量地提取单量子点的双光子吸收截面，这与从以前的双光子FCS测量中获得的结果吻合得很好。对于所有激发功率，观察到严格的逆幂律分布的关态停留时间，平均幂律指数< m（off）> = 1.65（4），与单光子激发条件下观察到的行为非常一致。最后，超二次（n = 2.3（2）），而不是四次（n = 4）的功率依赖性被观察到的导通状态闪烁停留时间，我们动力学分析和解释的一种新的2 + 1的“热”激子电离/闪烁机制，由于部分饱和的单光子子带隙激发的双光子单激子状态。动力学结果与来自“热”激子态的量子点光电离量子产率（4（1）× 10（-6））一致，与双激子态的俄歇电离效率的实验估计（10（-6）-10（-5））相当。
Two-photon fluorescence microscopy of single quantum dots conditions has been reported by several groups,(1-3) with contrasting observations regarding the kinetics and dynamics of fluorescence intermittency or "blinking". Here, we investigate the power dependence, kinetics, and statistics of two photon-excited fluorescence intermittency from single CdSe/ZnS quantum dots in a solid PMMA film as a function of sub-bandgap laser intensity at 800 nm. Fluorescence intermittency is observed at all excitation powers and a quadratic (n = 1.97(3)) dependence of the shot noise-limited fluorescence intensity on the incident laser power is verified, confirming essentially zero background contribution from one-photon excitation processes. Such analyses permit two photon absorption cross sections for single quantum dots to be extracted quantitatively from the data, which reveal good agreement with those obtained from previous two-photon FCS measurements. Strictly inverse power law-distributed off-state dwell times are observed for all excitation powers, with a mean power law exponent < m(off)> = 1.65(4) in excellent agreement with the behavior observed under one-photon excitation conditions. Finally, a superquadratic (n = 2.3(2)) rather than quartic (n = 4) power dependence is observed for the on-state blinking dwell times, which we kinetically analyze and interpret in terms of a novel 2 + 1 "hot" exciton ionization/blinking mechanism due to partially saturated 1-photon sub-bandgap excitation out of the two-photon single exciton state. The kinetic results are consistent with quantum dot photoionization quantum yields from "hot" exciton states (4(1) x 10(-6)) comparable with experimental estimates (10(-6)-10(-5)) of Auger ionization efficiencies out of the biexcitonic state.