Optical properties of oxidized single-wall carbon nanotubes

Optical properties of oxidized single-wall carbon nanotubes (SWCNTs) have attracted much attention because of the greater luminescence quantum yield than that of pristine CNTs, showing the possibility of optical applications such as near-infrared single-photon emitters and bioimaging. To advance the fundamental understanding of the optical properties, we theoretically investigated the energetics and the optical transitions for complex oxygen (O) adsorption structures on (6,5) CNTs, including adsorption of two O atoms. For CNTs adsorbed by isolated O atoms, four groups of optical transition levels were obtained below E-11. We also found two additional groups of optical transition levels for adsorption structures of two O atoms, whose related adsorption structures are more stable than the isolated O-adsorption structures. These results explain the multiple emission peaks and their irradiation time dependence in the photoluminescence (PL) spectra for CNTs oxidized by ultraviolet ozone, providing a possible mechanism for significant brightening of the emission whose wavelength range is ideal for biological imaging. Our results are also consistent with the PL measurements of SWCNTs oxidized by O-2 molecules during single chirality separation processes. This comprehensive understanding is essential for further applications of oxidized SWCNTs. (C) 2016 Elsevier Ltd. All rights reserved.