Exciton relaxation in single wall carbon nanotubes

Ultrafast exciton dynamics is measured in films of functionalized single wall carbon nanotubes embedded in PMMA with time resolution down to sub-10-fs. Ultrafast bleaching decay and photoinduced absorption formation (depending on probe wavelength) are observed and assigned to decay of the second (or higher) exciton into the first exciton. The time constant of the relaxation process is ≈40 fs. The origin of the phenomenon is discussed within the one-dimensional semiconductor picture.