Interplay of spectral diffusion and phonon-broadening in individual photo-emitters: the case of carbon nanotubes

At cryogenic temperatures, the photoluminescence (PL) spectrum of nano-emitters may still be significantly broadened due to interactions with the environment. The interplay of spectral diffusion (SD) and phonon broadening in this context is still a debated issue. Singlewall carbon nanotubes (SWNTs) are a particularly relevant system to address this topic as they show intense spectral diffusion and undergo a high exciton-phonon coupling due to their one-dimensional geometry. Here, we investigate the correlations between the spectral diffusion of the main line and that of the wings in SWNTs quantitatively and demonstrate that the photoluminescence spectrum undergoes spectral jumps as a whole, without distortions. This behavior suggests that the spectral shape of SWNT PL is defined by exciton-phonon interactions and that spectral diffusion results in an additional flat broadening. The methodology developed here can be used to investigate a broad range of non-Lorentzian emitters undergoing spectral diffusion.