  The absorption cross section of highly luminescent individual single-walled
carbon nanotubes is determined using time-resolved and cw luminescence
spectroscopy. A mean value of 1x10-17 cm2 per carbon atom is obtained for (6,5)
tubes excited at their second optical transition, and corroborated by single
tube photothermal absorption measurements. Biexponential luminescence decays
are systematically observed, with short and long lifetimes around 45 and 250
ps. This behavior is attributed to the band edge exciton fine structure with a
dark level lying a few meV below a bright one.

Materials Science