Non-linear optical response and relaxation dynamics in double-walled carbon nanotubes

Relaxation dynamics of photoexcited carriers in individually suspended double-walled carbon nanotubes in solution have been investigated using femtosecond pump-probe spectroscopy. The average diameters of inner and outer tubes are 1.4 and 2.2 nm, respectively. The absorption spectrum reveals distinct band-to-band transitions in nanotubes with different diameters and chiralities. The differential absorption spectra measured by the pump-probe experiments show absorption bleaching and two-component decay behavior. The fast and slow components indicate carriers relaxation between the inner and outer tubes and non-radiative recombination of electrons and holes at the bottoms of the bands, respectively.