Optical nonlinearities and ultrafast carrier dynamics in semiconductor nanocrystals
Optical nonlinearities and ultrafast carrier dynamics in semiconductor nanocrystals
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DOI：
10.1021/jp9944132
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发表时间：
2000-07-06
影响因子：
3.3
通讯作者：
Klimov, VI
中科院分区：
文献类型：
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作者：
Klimov, VI
可见光和红外光谱范围内的飞秒瞬态吸收已被应用于研究具有各种表面钝化的 CdSe 纳米晶体 (NC) 中的载流子动力学和共振光学非线性机制。在逐渐升高的泵浦强度下记录的 NC 漂白光谱中，可以清楚地观察到由费米统计控制的 1S、1P 和 1D 类原子电子轨道的顺序填充。我们观察到电子-空穴 (e-h) 空间分离强烈影响电子带内动力学。这种依赖性表明涉及 e-h 相互作用的非声子能量弛豫机制。观察到在初始带内弛豫之后的阶段中电子和空穴弛豫行为的显着差异。与电子弛豫相比，电子弛豫对表面钝化的质量敏感（即受表面缺陷捕获的影响），在具有不同表面性质的NC中，初始激发空穴态的减少动力学是相同的，这表明这些动力学是由于弛豫到本征NC态所致。在多粒子激发状态下，观察到对应于不同的多个 e-h 对状态的弛豫率的量化。这种效应可以用量子限制俄歇复合来解释。
Femtosecond transient absorption in the visible and infrared spectral ranges has been applied to study carrier dynamics and mechanisms for resonant optical nonlinearities in CdSe nanocrystals (NCs) with a variety of surface passivations. Sequential filling of the 1S, 1P, and 1D atomic-like electron orbitals, governed by Fermi statistics, is clearly observed in the NC bleaching spectra recorded at progressively higher pump intensities. We observe that electron-hole (e-h) spatial separation strongly affects electron intraband dynamics. Such dependence indicates a nonphonon energy relaxation mechanism involving e-h interactions. A strong difference in electron and hole relaxation behavior in the stage following initial intraband relaxation is observed. In contrast to electron relaxation, which is sensitive to the quality of surface passivation (i.e., is affected by trapping at surface defects), depopulation dynamics of the initially-excited hole states are identical in NCs with different surface properties, suggesting that these dynamics are due to relaxation into intrinsic NC states. In the regime of multiparticle excitation, a quantization of relaxation rates corresponding to different multiple e-h pair states is observed. This effect is explained in terms of quantum-confined Auger recombination.