Chirality Dependence of Triplet Excitons in (6,5) and (7,5) Single-Wall Carbon Nanotubes Revealed by Optically Detected Magnetic Resonance
[2];
[2];
[3];
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- Department of Physics, University of Antwerp, Universiteitsplein 1, 2610Antwerp, Belgium, Department of Chemistry, University of Antwerp, Universiteitsplein 1, 2610Antwerp, Belgium
- Department of Physics, University of Antwerp, Universiteitsplein 1, 2610Antwerp, Belgium
- Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado80401, United States
- Chemistry Division, Physical Chemistry and Applied Spectroscopy Group (C-PCS), Los Alamos National Laboratory, Los Alamos, New Mexico87544, United States
The excitonic structure of single-wall carbon nanotubes (SWCNTs) is chirality dependent and consists of multiple singlet and triplet excitons (TEs) of which only one singlet exciton (SE) is optically bright. In particular, the dark TEs have a large impact on the integration of SWCNTs in optoelectronic devices, where excitons are created electrically, such as in infrared light-emitting diodes, thereby strongly limiting their quantum efficiency. Here, we report the characterization of TEs in chirality-purified samples of (6,5) and (7,5) SWCNTs, either randomly oriented in a frozen solution or with in-plane preferential orientation in a film, by means of optically detected magnetic resonance (ODMR) spectroscopy. In both chiral structures, the nanotubes are shown to sustain three types of TEs. One TE exhibits axial symmetry with zero-field splitting (ZFS) parameters depending on SWCNT diameter, in good agreement with the tighter confinement expected in narrower-diameter nanotubes. The ZFS of this TE also depends on nanotube environment, pointing to slightly weaker confinement for surfactant-coated than for polymer-wrapped SWCNTs. A second TE type, with much smaller ZFS, does not show the same systematic trends with diameter and environment and has a less well-defined axial symmetry. This most likely corresponds to TEs trapped at defect sites at low temperature, as exemplified by comparing SWCNT samples from different origins and after different treatments. A third triplet has unresolved ZFS, implying it originates from weakly interacting spin pairs. Aside from the diameter dependence, ODMR thus provides insights in both the symmetry, confinement, and nature of TEs on semiconducting SWCNTs.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of Antwerp (Belgium)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
- Grant/Contract Number:
- AC36-08GO28308
- OSTI ID:
- 1914345
- Alternate ID(s):
- OSTI ID: 1922618; OSTI ID: 1924495
- Report Number(s):
- NREL/JA-5K00-83760
- Journal Information:
- ACS Nano, Journal Name: ACS Nano Vol. 17 Journal Issue: 3; ISSN 1936-0851
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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