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Title: Photoluminescence Dynamics of Aryl sp 3 Defect States in Single-Walled Carbon Nanotubes

Abstract

Photoluminescent defect states introduced by sp 3 functionalization of semiconducting carbon nanotubes are rapidly emerging as important routes for boosting emission quantum yields and introducing new functionality. Knowledge of the relaxation dynamics of these states is required for understanding how functionalizing agents (molecular dopants) may be designed to access specific behaviors. We measure photoluminescence (PL) decay dynamics of sp 3 defect states introduced by aryl functionalization of the carbon nanotube surface. Results are given for five different nanotube chiralities, each doped with a range of aryl functionality. We find the PL decays of these sp 3 defect states are biexponential, with both components relaxing on timescales of ~ 100 ps. Exciton trapping at defects is found to increases PL lifetimes by a factor of 5-10, in comparison to those for the free exciton. A significant chirality dependence is observed in the decay times, ranging from 77 ps for (7,5) nanotubes to > 600 ps for (5,4) structures. The strong correlation of time constants with emission energy indicates relaxation occurs via multiphonon decay processes, with close agreement to theoretical expectations. Variation of the aryl dopant further modulates decay times by 10-15%. The aryl defects also affect PL lifetimes of the freemore » E 11 exciton. Shortening of the E 11 bright state lifetime as defect density increases provides further confirmation that defects act as exciton traps. A similar shortening of the E11 dark exciton lifetime is found as defect density increases, providing strong experimental evidence that dark excitons are also trapped at such defect sites.« less

Authors:
 [1];  [1];  [1];  [2];  [1];  [2];  [1];  [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of Maryland, College Park, MD (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1375887
Report Number(s):
LA-UR-17-24661
Journal ID: ISSN 1936-0851
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 10; Journal Issue: 9; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY; Carbon nanotubes; diazonium salts; doping; exciton localization; photoluminescence; time-correlated single-photon counting

Citation Formats

Hartmann, Nicolai F., Velizhanin, Kirill A., Haroz, Erik H., Kim, Mijin, Ma, Xuedan, Wang, YuHuang, Htoon, Han, and Doorn, Stephen K. Photoluminescence Dynamics of Aryl sp 3 Defect States in Single-Walled Carbon Nanotubes. United States: N. p., 2016. Web. doi:10.1021/acsnano.6b02986.
Hartmann, Nicolai F., Velizhanin, Kirill A., Haroz, Erik H., Kim, Mijin, Ma, Xuedan, Wang, YuHuang, Htoon, Han, & Doorn, Stephen K. Photoluminescence Dynamics of Aryl sp 3 Defect States in Single-Walled Carbon Nanotubes. United States. doi:10.1021/acsnano.6b02986.
Hartmann, Nicolai F., Velizhanin, Kirill A., Haroz, Erik H., Kim, Mijin, Ma, Xuedan, Wang, YuHuang, Htoon, Han, and Doorn, Stephen K. 2016. "Photoluminescence Dynamics of Aryl sp 3 Defect States in Single-Walled Carbon Nanotubes". United States. doi:10.1021/acsnano.6b02986. https://www.osti.gov/servlets/purl/1375887.
@article{osti_1375887,
title = {Photoluminescence Dynamics of Aryl sp 3 Defect States in Single-Walled Carbon Nanotubes},
author = {Hartmann, Nicolai F. and Velizhanin, Kirill A. and Haroz, Erik H. and Kim, Mijin and Ma, Xuedan and Wang, YuHuang and Htoon, Han and Doorn, Stephen K.},
abstractNote = {Photoluminescent defect states introduced by sp3 functionalization of semiconducting carbon nanotubes are rapidly emerging as important routes for boosting emission quantum yields and introducing new functionality. Knowledge of the relaxation dynamics of these states is required for understanding how functionalizing agents (molecular dopants) may be designed to access specific behaviors. We measure photoluminescence (PL) decay dynamics of sp3 defect states introduced by aryl functionalization of the carbon nanotube surface. Results are given for five different nanotube chiralities, each doped with a range of aryl functionality. We find the PL decays of these sp3 defect states are biexponential, with both components relaxing on timescales of ~ 100 ps. Exciton trapping at defects is found to increases PL lifetimes by a factor of 5-10, in comparison to those for the free exciton. A significant chirality dependence is observed in the decay times, ranging from 77 ps for (7,5) nanotubes to > 600 ps for (5,4) structures. The strong correlation of time constants with emission energy indicates relaxation occurs via multiphonon decay processes, with close agreement to theoretical expectations. Variation of the aryl dopant further modulates decay times by 10-15%. The aryl defects also affect PL lifetimes of the free E11 exciton. Shortening of the E11 bright state lifetime as defect density increases provides further confirmation that defects act as exciton traps. A similar shortening of the E11 dark exciton lifetime is found as defect density increases, providing strong experimental evidence that dark excitons are also trapped at such defect sites.},
doi = {10.1021/acsnano.6b02986},
journal = {ACS Nano},
number = 9,
volume = 10,
place = {United States},
year = 2016,
month = 8
}

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  • Photoluminescence spectra of single-walled carbon nanotubes (SWCNTs) have been recorded and analyzed for selected individual nanotubes and structurally sorted bulk samples to clarify the nature of secondary emission features. Room temperature spectra show, in addition to the main peak arising from the E 11 bright exciton, three features at lower frequency, which are identified here (in descending order of energy difference from E 11 emission) as G 1, X 1, and Y 1. The weakest (G 1) is interpreted as a vibrational satellite of E 11 involving excitation of the ~1600 cm -1 G mode. The X 1 feature, althoughmore » more intense than G 1, has a peak amplitude only ~3% of E 11. X 1 emission was found to be polarized parallel to E 11 and to be separated from that peak by 1068 cm -1 in SWCNTs with natural isotopic abundance. The separation remained unchanged for several ( n,m) species, different nanotube environments, and various levels of induced axial strain. In 13C SWCNTs, the spectral separation decreased to 1023 cm -1. The measured isotopic shift points to a phonon-assisted transition that excites the D vibration. This supports prior interpretations of the X 1 band as emission from the dark K-momentum exciton, whose energy we find to be ~230 cm -1 above E 11. The remaining sideband, Y 1, is red-shifted ~300 cm -1 from E 11 and varies in relative intensity among and within individual SWCNTs. We assign it as defect-induced emission, either from an extrinsic state or from a brightened triplet state. In contrast to single-nanotube spectra, bulk samples show asymmetric zero-phonon E 11 peaks, with widths inversely related to SWCNT diameter. As a result, an empirical expression for this dependence is presented to aid the simulation of overlapped emission spectra during quantitative fluorimetric analysis of bulk SWCNT samples.« less
  • Addition of dithiothreitol (DTT) to a suspension consisting of either DNA or sodium dodecyl sulfate (SDS) wrapped single-walled carbon nanotubes (SWCNTs) caused significant photoluminescence (PL) brightening from the SWCNTs, while PL quenching to different extents was observed for other surfactant-SWCNT suspensions. PL lifetime studies with high temporal resolution show that addition of DTT mitigates non-radiative decay processes, but also surprisingly increases the radiative decay rate for DNA- and SDS-SWCNTs. There are completely opposite effects on the decay rates found for the other surfactant-SWCNTs and show PL quenching. Here, we propose that the PL brightening results from a surfactant reorganization uponmore » DTT addition. TOC« less
  • Variable temperature photoluminescence excitation spectroscopy of three (n,m) species of single-walled carbon nanotubes revealed that at resonant S 22 excitation, in addition to allowed excitonic optical transitions, several sidebands that should be forbidden based on selection rules were observed and appeared to have a strong temperature dependence. In particular, we found that a sideband located approximately 130 meV away from the bright S 11 exciton peak relating to the K-momentum dark exciton state, called X 1, decreased in intensity five-fold as the samples were cooled. Direct optical excitation of this dark state is nominally forbidden, thus calling into question howmore » the state is populated, and why it is so prominent in the photoluminescence spectrum. Interestingly, the ratio of the integrated photoluminescence intensities of X 1 to S 11 scales with a Boltzmann factor unrelated to the phonon that is thought to be responsible for depopulating the K-momentum dark exciton state: an in-plane transverse optical phonon, A 1’. Furthermore, photoluminescence spectra from individual (7,5) nanotubes show that only a small fraction exhibit the X 1 feature, with varying oscillator strength, thus suggesting that intrinsic processes such as phonon scattering are not responsible for populating the dark state. Alternatively, we suggest that populating the K-momentum dark exciton state requires scattering from defects, which is consistent with the increased magnitude of the X 1 feature for samples with increased sample purification and processing. Thus, the presence of an X 1 peak in photoluminescence is an extremely sensitive spectroscopic indicator of defects on single-walled carbon nanotubes.« less
  • By employing atomistic simulations based on empirical potential and density-functional theory, we study the irradiation of single-walled carbon nanotubes with a carbon ion. According to different impact locations on the surface of the nanotube, the incident threshold energies of defects formation are predicted to be 19, 35 and 45 eV, respectively. Moreover, the displacement threshold energy is investigated by using the collision dynamical method, and a reasonable value 17.59 eV is clarified by eliminating the thermal effect induced by the collision. Finally, the formation energy of a single vacancy is calculated by the ab initio method.
  • Understanding of the origin of some of the intermediate frequency modes (IFMs) in the Raman spectrum of carbon nanotubes has remained controversial in the literature. In this work, through controlled introduction and elimination of defects in carbon nanotubes, we attempt to isolate the IFMs due to structural defects from that of the combination modes in single walled carbon nanotubes (SWCNTs). Our investigations on pristine and defect engineered SWCNTs using ion-irradiation, thermal annealing, and laser processing show systematic changes in the IFMs in the range 400-1200 cm{sup -1} and its manipulation with the processing parameters. In particular, we found that themore » intensity of IFM at 929 cm{sup -1} scale up with the increasing defect concentration, while that at 668 cm{sup -1} follows opposite behavior. New IFM peaks were observed upon the creation of a controlled amount of structural defects through 30 keV N{sup +} ion irradiation. Elimination of defects through vacuum annealing results into reduction of intensity of some IFMs identified as defect related, while the intensity of characteristic combination modes correspondingly increases. Our results show that the IFMs observed at 709, 805, 868, 926, and 1189 cm{sup -1} are due to structural defects in the SWCNTs, while those in the range 400-550 cm{sup -1} and at 669 cm{sup -1} are due to the combination modes. Our x-ray photoelectron spectroscopy analysis on ion irradiated SWCNTs supports the Raman results.« less