Time-resolved photoluminescence of single wall carbon nanotubes

Time-resolved photoluminescence measurements are performed on ensembles of isolated (6,5) single wall carbon nanotubes after a selective picosecond excitation of the second transition of the semiconducting nanotubes. These measurements give insight into the carrier dynamics in the bright nanotubes. The carrier dynamics in bright nanotubes is non exponential reflecting the inhomogeneous distribution of life times. However two contributions to the relaxation are distinguishable within the experimental resolution : a fast component of the order of 10~ps and a smaller long living component of about 100 ps. When cooling the sample down to 10 K, the relative weight of the slow component increases with a characteristic temperature of 150 K. Only a small increase of about 30\% of the quantum yield is observed at low temperature. No clear relation between emission energy and life time is observed. In light of recent publications these results suggest that the monoexponential relaxation process in one single nanotube might be either fast or slow and that the proportion of both kind of processes is modified by the temperature with a typical energy of 15~meV.