Environment effect on cross-polarized excitons in carbon nanotubes

Effects of environmental dielectric materials on cross-polarized excitons of semiconducting carbon nanotubes are theoretically studied in an effective-mass scheme. When a nanotube is surrounded by a medium, the bright exciton, shifted to the high-energy side by depolarization effect, becomes weaker and disappears with the increase of the dielectric constant. When a nanotube contains a medium inside, the bright exciton becomes more eminent. The dark exciton, brightened due to electron-hole asymmetry, is enhanced with the increase of the dielectric constant both for outside and inside materials. Consequently, the relative intensity of the brightened dark exciton normalized by the bright exciton is strongly enhanced by environmental screening, in particular, for outside materials.