Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
Nat Chem. 2013 Oct;5(10):840-5. doi: 10.1038/nchem.1711. Epub 2013 Jul 21.
Semiconducting carbon nanotubes promise a broad range of potential applications in optoelectronics and imaging, but their photon-conversion efficiency is relatively low. Quantum theory suggests that nanotube photoluminescence is intrinsically inefficient because of low-lying 'dark' exciton states. Here we demonstrate the significant brightening of nanotube photoluminescence (up to 28-fold) through the creation of an optically allowed defect state that resides below the predicted energy level of the dark excitons. Emission from this new state generates a photoluminescence peak that is red-shifted by as much as 254 meV from the nanotube's original excitonic transition. We also found that the attachment of electron-withdrawing substituents to carbon nanotubes systematically drives this defect state further down the energy ladder. Our experiments show that the material's photoluminescence quantum yield increases exponentially as a function of the shifted emission energy. This work lays the foundation for chemical control of defect quantum states in low-dimensional carbon materials.
半导体碳纳米管有望在光电和成像领域得到广泛应用，但它们的光子转换效率相对较低。量子理论表明，由于存在低能“暗”激子态，纳米管的光致发光本质上是低效的。在这里，我们通过创建一个低于预测的暗激子能级的光允许的缺陷态，证明了纳米管光致发光（高达 28 倍）的显著增强。从这个新状态发出的光产生的光致发光峰比纳米管原来的激子跃迁红移多达 254 meV。我们还发现，将电子受体取代基连接到碳纳米管上，会将这个缺陷态在能量梯级上进一步向下驱动。我们的实验表明，材料的光致发光量子产率随发射能量的偏移呈指数增长。这项工作为在低维碳材料中化学控制缺陷量子态奠定了基础。
