We study the excitonic recombination dynamics in an ensemble of (9,4) semiconducting single-wall carbon nanotubes by high-sensitivity time-resolved photoluminescence experiments. Measurements from cryogenic to room temperature allow us to identify two main contributions to the recombination dynamics. The initial fast decay is temperature independent and is attributed to the presence of small residual bundles that create external nonradiative relaxation channels. The slow component shows a strong temperature dependence and is dominated by nonradiative processes down to 40 K. We propose a quantitative phenomenological modeling of the variations of the integrated photoluminescence intensity over the whole temperature range. We show that the luminescence properties of carbon nanotubes at room temperature are not affected by the dark/bright excitonic state coupling.

We report on environmental effects on the optical properties of single-wall carbon nanotubes in a gelatin-based composite material designed to foster their photoluminescence. We show that the dielectric screening of excitons due to the surrounding medium is responsible for a sizeable shift of the luminescence lines which hardly depends on the tube geometry. In contrast, the temperature dependence (from 4 to 300 K) of the luminescence is clearly chirality dependent : the first and second excitonic lines shift in opposite directions with a magnitude that can be related quantitatively to a strain-induced modification of the electronic structure due to an expansivity mismatch between the nanotube and the matrix.PACS numbers: