Identification of an excitonic phonon sideband by photoluminescence spectroscopy of single-walled carbon-13 nanotubes

We have studied photoluminescence and resonant Raman scattering of single-walled carbon nanotubes (SWNTs) consisting of carbon-13 (SW(13)CNTs) synthesized from a small amount of isotopically modified ethanol. There was almost no change in the Raman spectra shape for SW(13)CNTs except for a downshift of the Raman shift frequency by the square root of the mass ratio 12/13. By comparing photoluminescence excitation spectra of SW(13)CNTs and normal SWNTs, the excitonic phonon sideband due to strong exciton-phonon interaction was clearly identified with the expected isotope shift. In addition to the direct experimental proof of the strong exciton-phonon interaction, we also found low-intensity "pure electronic" features whose origin has never been elucidated.