Near-infrared photoluminescence of single-walled carbon nanotubes prepared by the laser vaporization method

Single-walled carbon nanotubes (SWNTs) prepared by pulsed laser vaporization, dispersed, and surfactant-stabilized in near-infrared transparent D2O Show weak photoluminescence (PL) from similar to 1300 up to > 1750 nm corresponding to the lowest electronic interband transitions of semiconducting tubes. The characteristic features of this PL, such as a multiple peak emission and a strong excitation wavelength dependence (investigated for lambda(exc) from 457 up to 1064 nm), are similar to those reported recently for SWNTs with smaller diameters of around 1 nm (O'Connell et al. Science 2002, 297, 593). The luminescence is significantly polarized with an anisotropy value r of up to 0.32, depending on the excitation and emission wavelengths. The PL data can be used for the structural assignment of emitting tubes; however, in agreement with the results of O'Connell et al., these data are only qualitatively consistent with the tight-binding model widely applied for SWNTs. The luminescence is sensitive to chemical treatment/interactions of SWNTs; much weaker and broader PL was observed above 1300 nm for dispersions of acid-treated tubes in D2O, whereas raw SWNTs in N,N-dimethylformamide show practically no PL. The Raman spectra of dispersed SWNTs differ from those of the solid samples.