Electronic Structure and Chemical Nature of Oxygen Dopant States in Carbon Nanotubes

Abstract

We performed low temperature photoluminescence (PL) studies on individual oxygen-doped single-walled carbon nanotubes (SWCNTs) and correlated our observations to electronic structure simulations. Our experiment reveals multiple sharp asymmetric emission peaks at energies 50-300 meV red-shifted from that of the E11 bright exciton peak. Our simulation suggests an association of these peaks with deep trap states tied to different specific chemical adducts. In addition, oxygen doping is also observed to split the E11 exciton into two or more states with an energy splitting <40 meV. We attribute these states to dark states that are brightened through defect-induced symmetry breaking. While the wave functions of these brightened states are delocalized, those of the deep-trap states are strongly localized and pinned to the dopants. These findings are consistent with our experimental observation of asymmetric broadening of the deep trap emission peaks, which can result from interaction between pinned excitons and one-dimensional phonons. Exciton pinning also increases the sensitivity of the deep traps to the local dielectric environment, leading to a large inhomogeneous broadening. Observations of multiple spectral features on single nanotubes indicate the possibility of different chemical adducts coexisting on a given nanotube.

Strong Acoustic Phonon Localization in Copolymer-Wrapped Carbon Nanotubes

“…55 In that work, undoped reference samples featured only one dominant peak in the E 11 regime as in our case, albeit with a broad linewidth of about 4 meV.…”

Strong reduction of exciton-phonon coupling in single-wall carbon nanotubes of high crystalline quality: Insight into broadening mechanisms and exciton localization

“…The asymmetry of this distribution, due to instrumental constraints, strongly suggests that even narrower PL lines could be observed in this sample. This FWHM distribution shows that L-SWNTs have a narrower PL emission than most solution processed SWNTs which show typical FWHMs of several meV [12,24,29,31]. Strikingly, these FWHM values seem comparable to and even narrower (at least in term of distribution) than those observed for most airbridging CVD SWNTs [31] and for most neutral polymerembedded SWNTs [9,25,32], i.e.…”

Room-temperature single-photon generation from solitary dopants of carbon nanotubes

“…By capturing excitons that might otherwise have recombined at quenching centres, thus allowing efficient radiative recombination instead, the covalent dopant states of SWCNTs dramatically enhance the photoluminescence emission efficiency (from ∼1% to 28%) and shift the photoluminescence of SWCNTs deeper into the near-infrared spectral regime (1.1-1.3 µm) 4,5,8,9 . These new transitions not only make envisioned applications of SWCNTs in optoelectronic, sensing and imaging technologies more feasible, but also present potential for room-temperature single-photon generation at telecom wavelengths 8,10,11 .…”

“…1b. They are therefore believed to have potential as single quantum emitters at room temperature 4,8,10 . Beyond enabling a new class of quantum light sources, these dopant-induced deep trap states of SWCNTs could present promising opportunities to couple a localized quantum two-level system with the unique mechanical and electrical transport properties of SWCNTs 17 .…”

“…Currently, both oxygen and diazonium doping are achieved through prolonged exposure of SWCNTs to doping agents in aqueous suspension 4,5 . Although doped SWCNTs emit reasonably stable photoluminescence in their native solution environment 4 , the photoluminescence signal shows rapid fluctuations both in intensity and wavelength when placed on solid-state substrates 10 . The photoluminescence also bleaches over a 10-30 min timescale when the tubes are subjected to intense laser excitation 10 .…”