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 E-22 and E-11 excitons, in specific nanotubes. Among other features, PL excitation and emission satellites at similar to(E-11+95) and similar to(E-11-200) meV, respectively, were resolved. We show that the E-22 exciton primarily decays (>= 80%) to the optical E-11 exciton. A minor decay pathway likely involves relaxation into dark deep excitonic states, which weakly emit at similar to 40 and similar to 140 meV below E-11. In addition, we report PL polarization measurements, supporting assignment of transverse E-12,E-21 photoexcitations, and PL quantum yields for (n,m) nanotubes in toluene-polymer dispersions.