  Carbon nanotubes are quantum sources whose emission can be tuned at
telecommunication wavelengths by choosing the diameter appropriately. Most
applications require the smallest possible linewidth. Therefore, the study of
the underlying dephasing mechanisms is of utmost interest. Here, we report on
the low-temperature photoluminescence of high crystalline quality individual
single-wall carbon nanotubes synthesized by laser ablation (L-SWNTs) and
emitting at telecommunication wavelengths. A thorough statistical analysis of
their emission spectra reveals a typical linewidth one order of magnitude
narrower than that of most samples reported in the literature. The narrowing of
the PL line of L-SWNTs is due to a weaker effective exciton-phonon coupling
subsequent to a weaker localization of the exciton. These results suggest that
exciton localization in SWNTs not only arises from interfacial effects, but
that the intrinsic crystalline quality of the SWNT plays an important role.
