  The influence of water-filling on the photoluminescence (PL) properties of
SWCNTs is studied by ensemble and single-molecule PL spectroscopy. Red-shifted
PL and PL excitation spectra are observed upon water filling for 16 chiralities
and can be used to unambiguously distinguish empty SWCNTs from filled ones. The
effect of water-filling on the optical transitions is well reproduced by a
continuum dielectric constant model previously developed to describe the
influence of the nanotube outer environment. Empty nanotubes display narrower
luminescence lines and lower inhomogeneous broadening, signatures of reduced
extrinsic perturbations. The radial breathing mode (RBM) phonon side band is
clearly observed in the PL spectrum of small diameter empty tubes and a strong
exciton-phonon coupling is measured for this vibration. Biexponential PL decays
are observed for empty and water filled tubes, and only the short living
component is influenced by the water-filling. This may be attributed to a
shortening of the radiative lifetime of the bright state by the inner
dielectric environment.
