Semiconducting single-walled carbon nanotubes (SWCNTs) often exhibit distinctive spectral features due to a complex dark exciton manifold. One of those features, the K-momentum dark exciton (KDE) state, has been of significant recent interest because of the unique photophysics required to brighten the nominally optically forbidden state. Although the energy of the KDE state relative to the bright singlet excitonic state (E₁₁) is currently understood, how the KDE state is efficiently populated, and its resulting dynamics, is not. Time-correlated single photon counting (TCSPC) and kinetic modeling were used to study the dynamics of the KDE state as temperature and lattice defect concentration varied. Photoluminescence (PL) time decays corresponding to the KDE state exhibited biexponential character with average lifetime values roughly 6 times longer than those of the typical E₁₁ state. As temperature was lowered or as the SWCNT lattice became more defective, the KDE state lifetime values increased by nearly 3 times, reaching values as high as ∼400 ps. This trend strongly suggested that the dark singlet excitonic state (D₁₁) situated a few millielectronvolts below the bright plays a significant role in KDE dynamics. Transition times between the E₁₁ and D₁₁ states, as well as dark-to-bright excitonic conversion efficiencies, were extracted by using a kinetic analysis of the experimentally determined KDE state time decays. Together, the experimental results and kinetic modeling strongly suggest that mixing between the bright and dark singlet excitonic states is the driving force that dictates KDE state dynamics.

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单壁碳纳米管暗激子光致发光动力学

由于复杂的暗激子流形，半导体单壁碳纳米管 (SWCNT) 通常表现出独特的光谱特征。其中一个特征，即K动量暗激子 (KDE) 状态，最近引起了人们的极大兴趣，因为它需要独特的光物理学来使名义上的光学禁止状态变亮。尽管 KDE 态的能量相对于亮单重激子态 (E ₁₁) 目前了解，KDE 状态是如何有效填充的，以及由此产生的动态，还不是。时间相关单光子计数 (TCSPC) 和动力学模型用于研究 KDE 状态随温度和晶格缺陷浓度变化的动力学。对应于 KDE 状态的光致发光 (PL) 时间衰减表现出双指数特征，平均寿命值比典型的 E ₁₁状态长大约 6 倍。随着温度降低或 SWCNT 晶格变得更加有缺陷，KDE 状态寿命值增加了近 3 倍，达到高达 400 ps 的值。这种趋势强烈表明暗单线态激子态 (D ₁₁) 位于亮度下方几毫电子伏特处，在 KDE 动力学中起着重要作用。E ₁₁和D ₁₁状态之间的转换时间以及暗到亮激子转换效率是通过使用对实验确定的 KDE 状态时间衰减的动力学分析来提取的。总之，实验结果和动力学模型强烈表明，明暗单线态激子态之间的混合是决定 KDE 态动力学的驱动力。