Optimization of Band Structure and Quantum-Size-Effect Tuning for Two-Photon Absorption Enhancement in Quantum Dots
Optimization of Band Structure and Quantum-Size-Effect Tuning for Two-Photon Absorption Enhancement in Quantum Dots
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DOI：
10.1021/nl1042209
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发表时间：
2011-03-01
期刊：
影响因子：
10.8
通讯作者：
Sargent, Edward H.
中科院分区：
文献类型：
--
作者：
Padilha, Lazaro A.;Nootz, Gero;Sargent, Edward H.
从理论和实验上研究了PbS量子点的双光子吸收截面，发现随着量子限制的增加，双光子吸收截面增强。这与我们先前对于CdSe和CdTe QD的结果相反，其中降低的态密度占主导地位并且导致2PA随着QD尺寸的减小而减小。定性地说，这种趋势可以通过PbS中导带和价带态的高度对称分布来理解，这导致在某些光谱区域中允许的2PA跃迁的积累。我们还测量了频率非简并2PA横截面是高达五倍以上的退化的情况下。我们使用一个k.p四带包络函数形式主义模型的双光子截面的增加趋势，由于量子限制，也由于共振增强的非简并的情况下。
The two-photon absorption, 2PA, cross sections of PbS quantum dots, QDs, are theoretically and experimentally investigated and are shown to be enhanced with increasing quantum confinement. This is in contrast to our previous results for CdSe and CdTe QDs where the reduced density of states dominated and resulted in a decrease in 2PA with a decrease in QD size. Qualitatively this trend can be understood by the highly symmetric distribution of conduction and valence band states in PbS that results in an accumulation of allowed 2PA transitions in certain spectral regions. We also measure the frequency nondegenerate 2PA cross sections that are up to five times larger than for the degenerate case. We use a k.p four-band envelope function formalism to model the increasing trend of the two-photon cross sections due to quantum confinement and also due to resonance enhancement in the nondegenerate case.