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.