Exciton Effects of Optical Transitions in Single-Wall Carbon Nanotubes

Absorption spectra have been measured in the near-infrared region for a thin-film sample of single-wall carbon nanotubes of 1.2–1.5 nm diameter. Two absorption peaks are observed at 0.7 and 1.2 eV. The observed spectrum has been compared with the calculation based on the tight-binding model taking into account the distribution of diameter and the helical arrangement of tubes. We have found that a one-dimensional exciton effect plays an important role in the fundamental optical transition of semiconducting single-wall carbon nanotubes.