Excitation Energy Dependence of Fluorescence Intermittency in CdSe/ZnS Core-Shell Nanocrystals
Excitation Energy Dependence of Fluorescence Intermittency in CdSe/ZnS Core-Shell Nanocrystals
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DOI：
10.1021/jp8104216
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发表时间：
2009-07-16
影响因子：
3.7
通讯作者：
Drndic, Marija
中科院分区：
文献类型：
--
作者：
Crouch, Catherine H.;Mohr, Robert;Drndic, Marija
我们报告的测量的激发能量依赖的单个CdSe/ZnS核/壳纳米晶体（NC）的荧光强度，使用两种不同尺寸的NC和三种不同的激发能量。最低的激发能量对应于在其光学带隙处激发较小尺寸的NC，因此我们检查在带隙处和在带隙以上的不同能量处的激发。我们发现，关断时间的概率分布遵循幂律与指数约-1.5，无论NC的大小或激发能量。准时概率分布遵循截断幂律，幂律指数再次不依赖于大小或能量。具有可比的吸收率，截断时间为较大的纳米晶体是非常相似的激发时，无论是270或480 meV以上的带隙，但缩短近紫外线激发1 eV以上的带隙。对于较小的纳米晶体，截断时间是可比的，无论是在带隙或270 meV以上激发。我们的研究结果支持一个光谱扩散控制的模型闪烁，并与激发态的准连续流形的存在与改变发射动力学以上的1 P（e）状态是一致的，他们还表明在非常高的过剩能量的发射动力学的变化。
We report measurements of the excitation energy dependence of the fluorescence intermittency of single CdSe/ZnS core/shell nanocrystals (NCs), using two different sizes of NCs and three different excitation energies. The lowest excitation energy corresponds to exciting the smaller size NC at its optical band gap, so we examine both excitation at the band gap and at varying energies above the band gap. We find that off-time probability distributions follow a power law with exponent roughly - 1.5 regardless of NC size or excitation energy. The on-time probability distributions follow a truncated power law with a power-law exponent that again does not depend on size or energy. With comparable absorption rate, the truncation times for the larger nanocrystals are very similar when excited either 270 or 480 meV above the band gap but shorten for near-ultraviolet excitation 1 eV above the band gap. For the smaller nanocrystals, the truncation times are comparable whether excited at the band gap or 270 meV above. Our findings support a spectral diffusion-controlled model for blinking and are consistent with the existence of a quasicontinuous manifold of excited states with altered emission dynamics above the 1P(e) state; they also indicate a change in emission dynamics at very high excess energy.