Observation of excited-state excitons and band-gap renormalization in hole-doped carbon nanotubes using photoluminescence excitation spectroscopy

The higher Rydberg states of the E₁₁ exciton in undoped and hole-doped single-walled carbon nanotubes (SWCNTs) were studied using one- and two-photon photoluminescence excitation spectroscopy. Increasing the hole-dopant concentration resulted in a redshift of the first excited state (2g) and a blueshift of the ground state (1u) of the E₁₁ exciton. From the redshift of higher Rydberg states, we found that a reduction of the band-gap energy occurs in hole-doped SWCNTs. These findings show that the exciton and electronic band structures are modified by the presence of a small number of holes in the SWCNT one-dimensional structures.