Photoluminescence microscopy of carbon nanotubes grown by chemical vapor deposition: Influence of external dielectric screening on optical transition energies

Photoluminescence (PL) laser microscopy was applied to determine optical transition energies E₁₁ and E₂₂ of individual semiconducting single-walled carbon nanotubes (SWNTs) suspended on top of carbon nanotube ``forests,'' grown by chemical vapor deposition (CVD) on silicon substrates. A uniform increase of E₁₁ and E₂₂ energies by 40--55 and 24--480.3em0exmeV, respectively, was found for 19 different $(n,m)$ nanotube species suspended in air or a vacuum---relative to SWNTs in a reference water-surfactant dispersion. CVD-grown SWNTs embedded in paraffin oil and 1-methylnaphthalene show nearly the same PL peak positions as SWNTs in aqueous dispersion, indicating similar dielectric screening of excitons in SWNTs in these media.