Department of Chemistry, University of California, Berkeley, and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460, United States.
J Phys Chem B. 2011 May 12;115(18):5201-11. doi: 10.1021/jp106250a. Epub 2010 Nov 23.
We report a femtosecond transient absorption spectroscopic study on the (6, 5) single-walled carbon nanotubes and the (7, 5) inner tubes of a dominant double-walled carbon nanotube species. We found that the dynamics of exciton relaxation probed at the first transition-allowed state (E(11)) of a given tube type exhibits a markedly slower decay when the second transition-allowed state (E(22)) is excited than that measured by exciting its first transition-allowed state (E(11)). A linear intensity dependence of the maximal amplitude of the transient absorption signal is found for the E(22) excitation, whereas the corresponding amplitude scales linearly with the square root of the E(11) excitation intensity. Theoretical modeling of these experimental findings was performed by developing a continuum model and a stochastic model with explicit consideration of the annihilation of coherent excitons. Our detailed numerical simulations show that both models can reproduce reasonably well the initial portion of decay kinetics measured upon the E(22) and E(11) excitation of the chosen tube species, but the stochastic model gives qualitatively better agreement with the intensity dependence observed experimentally than those obtained with the continuum model.
我们报告了一项飞秒瞬态吸收光谱研究，研究对象是（6,5）单壁碳纳米管和一种主要的双壁碳纳米管物种的（7,5）内管。我们发现，当激发给定管类型的第一跃迁允许态（E(11)）时，激发出的激子弛豫动力学表现出明显较慢的衰减，而当激发其第二跃迁允许态（E(22)）时，衰减速度比通过激发第一跃迁允许态（E(11)）时要快。对于 E(22)激发，我们发现瞬态吸收信号的最大幅度呈线性强度依赖性，而对于 E(11)激发，相应的幅度与激发强度的平方根线性相关。通过开发连续模型和考虑相干激子湮灭的随机模型，对这些实验结果进行了理论建模。我们的详细数值模拟表明，这两种模型都可以合理地再现所选管类型的 E(22)和 E(11)激发后测量的衰减动力学初始部分，但与连续模型相比，随机模型与实验观察到的强度依赖性更符合定性。
