Structural Dependence of Excitonic Optical Transitions and Band-Gap Energies in Carbon Nanotubes

Abstract

The optical transitions of semiconducting carbon nanotubes have been ascribed to excitons. Here we use two-photon excitation spectroscopy to measure exciton binding energies, as well as band-gap energies, in a range of individual species of semiconducting SWNTs. Exciton binding energies are large and vary inversely with nanotube diameter, as predicted by theory. Band-gap energies are significantly blue-shifted from values predicted by tight-binding calculations.

Screening of Excitons in Single, Suspended Carbon Nanotubes

“…We develop a simple scaling relationship between the exciton binding energy and the external dielectric function and thus quantify the effect of screening. Our results imply that the underlying particle interaction energies change by hundreds of meV.The long predicted presence of excitons with large binding energies in carbon nanotubes (CNT) 1,2,3,4,5 has been experimentally confirmed by recent two-photon experiments 6,7,8 . With binding energies of hundreds of meV and Coulomb energies highly sensitive to screening due to the one dimensional nature of CNTs, one expects that the measured optical transition energies should change significantly with changes in the dielectric environment.…”

Optimizing sonication parameters for dispersion of single-walled carbon nanotubes

“…For semiconducting SWCNTs, there are two main peaks known as the S 11 and S 22 transitions [27]. The S 11 and S 22 peaks are centered at 976 nm and 551 nm, respectively, and are related to semiconducting (6, 5) SWCNTs [27][28]. Fig.…”

“…In order to increase the accuracy in the analysis of the absorption spectra of the CoMoCat SWCNTs, the optical absorption induced by the 1 w/v% aqueous DOC solution has been subtracted. For semiconducting SWCNTs, there are two main peaks known as the S 11 and S 22 transitions [27]. The S 11 and S 22 peaks are centered at 976 nm and 551 nm, respectively, and are related to semiconducting (6, 5) SWCNTs [27][28].…”

Photoluminescence sidebands of carbon nanotubes below the bright singlet excitonic levels

“…͑Our unpublished data show that the E 11 energy difference of the same chirality tubes between "PFO" and "PFO-BT" samples is much smaller.͒ The exciton binding energy, the energy difference between the band gap and the E 11 level, of ͑6,5͒ tubes is known to be ϳ400 meV. 13 This means that the overall Coulomb interaction that determines the magnitude of the e-h interaction is changed by ϳ2% due to the environment. By a first approximation, the magnitude of ⌬ is considered to be modified by a similar proportion.…”