Ab Initio Study on Oxygen Doping of (5,4), (6,4), (6,5), and (8,6) Carbon Nanotubes

Abstract

Oxygen doping of single-wall carbon nanotubes (SWCNTs) exposed to ozone and light has attracted attention because of their greater luminescence quantum yield than that of pristine CNTs. The luminescence at E 11 *, which is red-shifted from E 11 for pristine CNTs, originating from the oxidation appears to be also observed for small-diameter CNTs in chirality separation experiments without a particular oxidation treatment. To understand this phenomenon, we performed ab initio calculations for the adsorption of oxygen molecules (O 2 ) onto realistic models of chiral CNTs. We found that the energy barrier from the physisorption of O 2 to the chemisorption is lower than that of the reverse reaction for (6,4) nanotubes, whereas the relation is opposite for (8,6) nanotubes, consistent with the distinct luminescence peak at E 11 * observed for (6,4) nanotubes and with the lack of a pronounced luminescence peak for larger-diameter (8,6) nanotubes in the chirality separation experiments. As also proposed for ozone oxidation, one of the final products was found to be the isolated ether structure, whose ground state band gap is slightly narrower than that of pristine CNTs.

Carbon Nanotube Photoluminescence Modulation by Local Chemical and Supramolecular Chemical Functionalization

“… ,,,,,− Hereafter, the energy values of the intrinsic exciton PL peak and the red-shifted PL peak are referred to as E 11 and E 11 *, respectively. The red-shifted PL feature of the doped nanotubes has been attributed to a reduced band gap and exciton energy of the dopant-induced local states. ,,,− Microscopically, these defects were attributed to ether- or epoxide-type oxygen adducts ,,, that induce local midgap states with specific energies depending on the details of the local chemical structures (Figure ). This was further confirmed by comparing the experimental results of the individual SWCNTs by density functional theory (DFT) calculations .…”

Determination of Precise Redox Properties of Oxygen-Doped Single-Walled Carbon Nanotubes Based on in Situ Photoluminescence Electrochemistry

“…The electronic states of the O-doped site have been investigated based on theoretical calculations. − Mu et al carried out calculations utilizing the GW method and the Bethe–Salpeter equation (GW+BSE), in which the O-doping induces an ∼10 meV shift in the electronic states, and the resulting large Stokes shift is important for the E 11 * emission . Ma et al compared the PL of single O-doped SWNTs to that of nondoped SWNTs at low temperature and observed a wide range of shifts in the PL peaks.…”

Solvent- and Wavelength-Dependent Photoluminescence Relaxation Dynamics of Carbon Nanotube sp3 Defect States

“…Low-level covalent functionalization of semiconducting single-wall carbon nanotubes (SWCNTs) by oxygen, aryl, and alkyl groups, with the latter two classes creating sp 3 defects, introduces new photoluminescent emitting states that are strongly red-shifted from the emission commonly observed from the nanotube band-edge E 11 exciton state . In addition to being the source of new photophysical behaviors, these states are drawing significant interest as the basis for emerging functionality, with possibilities including enhanced sensing and imaging, ,, photon upconversion, − and potential to act as room-temperature single photon emitters. , Many of these behaviors arise due to localization of the diffusive band-edge exciton at the defect site. − The localized exciton adopts a modified electronic structure defined by the molecular dopant forming the defect. ,,− Localization also modifies photoluminescence (PL) saturation behavior. ,, A particularly important signature of the exciton localization at defect sites is that, because the exciton is no longer free to diffusively sample PL quenching sites along the length of the carbon nanotube, its PL lifetime is significantly extended. − , …”