Luminescence properties of individual (6,5) single-walled carbon nanotubes (SWNTs) were studied using continuous wave and time-resolved spectroscopy. Nanotubes synthesized by different methods (HiPco and CoMoCat) and dispersed in two different ionic surfactants were examined either in aqueous environments or deposited on surfaces. SWNT preparations leading to the highest luminescence intensities and narrowest spectral widths exhibit the longest luminescence decay times. This highlights the role of the nanotube environment and synthesis methods in the nonradiative relaxation processes of the excitonic recombination. Samples of HiPco nanotubes dispersed in sodium deoxycholate contained the brightest nanotubes in aqueous environments.