Photophysics of carbon nanotubes in organic polymer-toluene dispersions: Emission and excitation satellites and relaxation pathways

We have prepared toluene-polymer dispersions of single-walled carbon nanotubes (SWNTs) containing only one or a few specific semiconducting $(n,m)$ species. These have large helical angles and manifest a high discrimination against larger-diameter SWNTs, metallic species, and nanotube aggregates. Such $(n,m)$-narrowed dispersions proved especially valuable for identification of low-intensity photoluminescence (PL) features as well as relaxation pathways, e.g., for the optically active E₂₂ and E₁₁ excitons, in specific nanotubes. Among other features, PL excitation and emission satellites at ~(E₁₁+95) and ~(E₁₁-200) meV, respectively, were resolved. We show that the E₂₂ exciton primarily decays (≥80%) to the optical E₁₁ exciton. A minor decay pathway likely involves relaxation into ``dark'' deep excitonic states, which weakly emit at ~40 and ~140 meV below E₁₁. In addition, we report PL polarization measurements, supporting assignment of transverse E12,21 photoexcitations, and PL quantum yields for $(n,m)$ nanotubes in toluene-polymer dispersions.