We studied the dynamics of excitons in individual semiconducting single-walled carbon nanotubes (SWNTs) using time-resolved photoluminescence (PL) spectroscopy. The PL decay from nanotubes of the same (n,m) type was found to be mono-exponential, however, with lifetimes varying between less than 20 ps and 200 ps from nanotube to nanotube. Competition of non-radiative decay of excitons is facilitated by a thermally activated process, most likely a transition to a low-lying optically inactive trap state that is promoted by a low-frequency phonon mode [1]. Near-field PL imaging with a spatial resolution better than 15 nm was used to visualize the spatial extent of luminescent excited states along SWNTs. The PL from micelle-encapsulated SWNTs on mica is typically extended along the nanotube up to several hundreds of nanometers. For SWNTs on glass, we observe highly localized PL from short segments of about 20 nm in length indicating bound excitons [2].
[1] A. Hagen et al., Phys. Rev. Lett. 95, 197401 (2005)
[2] A. Hartschuh et al., Nano Lett. 5, 2310 (2005)