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Title: Photoluminescence Side Band Spectroscopy of Individual Single-Walled Carbon Nanotubes

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 E11 bright exciton, three features at lower frequency, which are identified here (in descending order of energy difference from E11 emission) as G1, X1, and Y1. The weakest (G1) is interpreted as a vibrational satellite of E11 involving excitation of the ~1600 cm-1 G mode. The X1 feature, although more intense than G1, has a peak amplitude only ~3% of E11. X1 emission was found to be polarized parallel to E11 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 X1 band as emission from the dark K-momentum exciton, whose energy we find to be ~230 cm-1 above E11. The remaining sideband, Y1,more » is red-shifted ~300 cm-1 from E11 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 E11 peaks, with widths inversely related to SWCNT diameter. 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
Authors:
; ; ;
Publication Date:
OSTI Identifier:
1330140
Report Number(s):
NREL/JA-5900-67219
Journal ID: ISSN 1932-7447
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry. C; Journal Volume: 120; Journal Issue: 41
Publisher:
American Chemical Society
Research Org:
NREL (National Renewable Energy Laboratory (NREL), Golden, CO (United States))
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY single-walled carbon nanotubes; photoluminescence; exciton; phonon; isotopic enrichment