Photoluminescence saturation independent of excitation pathway in air-suspended single-walled carbon nanotubes

Photoluminescence (PL) spectroscopy is a useful probe of excitonic interactions in optically excited nanostructures. Under intense optical excitation, the diffusion-annihilation of excitons in single-walled carbon nanotubes (SWCNTs) results in strong nonlinear PL. This behavior has been observed in a number of samples and has, until recently, been believed to be independent of excitation pathway. Contrary to this assumption, recent studies show that nonlinear PL in encapsulated SWCNTs, excited resonant to E-22, is not dominated by diffusion-annihilation but instead by laser induced quenching sites. In this paper, we show that, unlike encapsulated SWCNTs, air-suspended SWCNT PL saturation is independent of excitation pathway, validating the use of a diffusion model for excitons generated via E-22 excitation. In addition, we show that the diffusion of excitons in air-suspended SWCNTs is independent of atmospheric adsorbates, strengthening the assertion that in this system exciton diffusion is intrinsic and not disorder limited.