Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, USA.
Department of Electrical and Computer Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin 53706, USA.
Nat Commun. 2015 Apr 13;6:6732. doi: 10.1038/ncomms7732.
Thin film networks of highly purified semiconducting carbon nanotubes (CNTs) are being explored for energy harvesting and optoelectronic devices because of their exceptional transport and optical properties. The nanotubes in these films are in close contact, which permits energy to flow through the films, although the pathways and mechanisms for energy transfer are largely unknown. Here we use a broadband continuum to collect femtosecond two-dimensional white-light spectra. The continuum spans 500 to 1,300 nm, resolving energy transfer between all combinations of bandgap (S1) and higher (S2) transitions. We observe ultrafast energy redistribution on the S2 states, non-Förster energy transfer on the S1 states and anti-correlated energy levels. The two-dimensional spectra reveal competing pathways for energy transfer, with S2 excitons taking routes depending on the bandgap separation, whereas S1 excitons relax independent of the bandgap. These observations provide a basis for understanding and ultimately controlling the photophysics of energy flow in CNT-based devices.
高度纯化半导体碳纳米管（CNT）的薄膜网络正在被探索用于能量收集和光电设备，因为它们具有出色的传输和光学性质。这些薄膜中的纳米管紧密接触，允许能量流过薄膜，尽管能量转移的途径和机制在很大程度上是未知的。在这里，我们使用宽带连续光源收集飞秒二维白光光谱。连续光源的范围为 500 到 1300nm，能够分辨所有带隙（S1）和更高（S2）跃迁之间的能量转移。我们观察到 S2 态上超快的能量再分配，S1 态上的非福斯特能量转移以及能级的反相关。二维光谱揭示了能量转移的竞争途径，S2 激子根据带隙分离选择途径，而 S1 激子的弛豫则与带隙无关。这些观察结果为理解和最终控制基于 CNT 的器件中的能量流动的光物理提供了基础。
