Solvent- and Wavelength-Dependent Photoluminescence Relaxation Dynamics of Carbon Nanotube sp3 Defect States
Solvent- and Wavelength-Dependent Photoluminescence Relaxation Dynamics of Carbon Nanotube sp3 Defect States
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DOI：
10.1021/acsnano.8b02909
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发表时间：
2018-08-01
期刊：
影响因子：
17.1
通讯作者：
Doorn, Stephen K.
中科院分区：
文献类型：
--
作者：
He, Xiaowei;Velizhanin, Kirill A.;Doorn, Stephen K.
通过低水平共价功能化将光致发光sp(3)缺陷态引入到单壁碳纳米管（SWCNTs）中，由于缺陷位点充当激子陷阱，产生了新的光物理行为和功能。对不同介质环境下的弛豫动力学进行评估，有助于对缺陷态弛豫路径和电子结构进行更完整的描述。在这里，我们利用螺旋包裹聚合物作为将（6,5）SWCNTs与4-甲氧基苯共价官能团悬浮在溶剂体系中的途径，溶剂体系包括H2O、D2O、甲醇、二甲基甲酰胺、四氢呋喃和甲苯，介质常数范围从80到3。测量了缺陷态光致发光衰减随发射波长和溶剂环境的变化。发射衰减呈双指数，短寿命组分约为65 ps，长寿命组分约为100 ~ 350 ps。随着发射波长的增加，短和长衰变组分均增加，而只有长寿命组分表现出溶剂依赖性。我们证明了波长依赖是缺陷态激子热脱陷产生可移动E-11激子的结果，为缺陷态居群的损失提供了重要的机制。较深的阱态（即波长较长的阱态）导致热损失率降低。短寿命组分的不依赖于溶剂的行为与它作为在明暗缺陷态之间重新分配激子居群的特征时间的分配是一致的。长寿命组分的溶剂依赖性被证明与通过电子到振动的能量传递机制的弛豫一致，其中能量在多声子衰变过程的互补机制中共振地损失到溶剂振动。
Photoluminescent sp(3) defect states introduced to single wall carbon nanotubes (SWCNTs) through low-level covalent functionalization create new photo physical behaviors and functionality as a result of defect sites acting as exciton traps. Evaluation of relaxation dynamics in varying dielectric environments can aid in advancing a more complete description of defect-state relaxation pathways and electronic structure. Here, we exploit helical wrapping polymers as a route to suspending (6,5) SWCNTs covalently functionalized with 4-methoxy-benzene in solvent systems including H2O, D2O, methanol, dimethylformamide, tetrahydrofuran, and toluene, spanning a range of dielectric constants from 80 to 3. Defect state photoluminescence decays were measured as a function of emission wavelength and solvent environment. Emission decays are biexponential, with short lifetime components on the order of 65 ps and long components ranging from around 100 to 350 ps. Both short and long decay components increase as emission wavelength increases, while only the long lifetime component shows a solvent dependence. We demonstrate that the wavelength dependence is a consequence of thermal detrapping of defect-state excitons to produce mobile E-11 excitons, providing an important mechanism for loss of defect-state population. Deeper trap states (i.e., those emitting at longer wavelengths) result in a decreased rate for thermal loss. The solvent-independent behavior of the short lifetime component is consistent with its assignment as the characteristic time for redistribution of exciton population between bright and dark defect states. The solvent dependence of the long lifetime component is shown to be consistent with relaxation via an electronic to vibrational energy transfer mechanism, in which energy is resonantly lost to solvent vibrations in a complementary mechanism to multiphonon decay processes.