Identification of an excitonic phonon sideband by photoluminescence spectroscopy of single-walled carbon-13 nanotubes

Abstract

We have studied photoluminescence (PL) and resonant Raman scatterings of single-walled carbon nanotubes (SWNTs) consisting of carbon-13 (SW 13 CNTs) synthesized from a small amount of isotopically modified ethanol. There was almost no change in the Raman spectra shape for SW 13 CNTs except for a downshift of the Raman shift frequency by the square-root of the mass ratio 12/13. By comparing photoluminescence excitation (PLE) spectra of SW 13 CNTs and normal SWNTs, the excitonic phonon sideband due to strong exciton-phonon interaction was clearly identified with the expected isotope shift.

Photoluminescence sidebands of carbon nanotubes below the bright singlet excitonic levels

“…So far, the phonon sideband at ϳ200 meV above the E ii levels has been well recognized and studied. [17][18][19][20][21][22] This phonon sideband was first predicted by Perebeinos et al 17 as a result of strong coupling between dipole-forbidden excitons above the E 11 level and K-point phonons ͑ϳ170 meV͒. This phonon is known to possess an in-plane transverse optical ͑TO͒ mode and is responsible for the D-band Raman feature in graphite and carbon nanotubes through a one-phonon emission double-resonance Raman process.…”

“…8 The strong confinement in the radial direction ͑ϳ1 nm͒ and the weak dielectric screening inside SWNTs give rise to very large exciton binding energies of ϳ0.5 eV, [9][10][11][12][13] which is much larger than those of InGaAs quantum wires 5,14 and larger than or comparable to those of -conjugated polymers. 15,16 So far, various groups have studied the ex-ph interactions in SWNTs both in terms of theory 17,18 and experiment [19][20][21][22] and have revealed the existence of a phonon sideband approximately 200 meV above the energy level of the singlet bright exciton ͑which has an s envelope and termed a "1u" state based on symmetry 12,13 but we simply call it "E ii " hereafter for the ith single-particle subband͒. [17][18][19][20][21][22] Techniques for preparing SWNT samples for optical studies have been rapidly improving recently.…”

“…15,16 So far, various groups have studied the ex-ph interactions in SWNTs both in terms of theory 17,18 and experiment [19][20][21][22] and have revealed the existence of a phonon sideband approximately 200 meV above the energy level of the singlet bright exciton ͑which has an s envelope and termed a "1u" state based on symmetry 12,13 but we simply call it "E ii " hereafter for the ith single-particle subband͒. [17][18][19][20][21][22] Techniques for preparing SWNT samples for optical studies have been rapidly improving recently. A technique that utilizes fluorene polymers to disperse SWNTs in organic solvents reported by Nish et al 23 is considered to be particularly important because of the strong selectivity to specific chiral types of SWNTs.…”

Carbon nanotubes for ultrafast fibre lasers

“…Nanotube isolation is critical due to the presence of both m-and s-CNTs in the solution and the tendency to form bundles, which causes radiationless intertube carrier transfer [204]. Photoluminescence excitation (PLE) allows not only to verify the presence of single-walled carbon nanotubes in a sample but also to determine the geometry of s-CNTs with a high accuracy, study their electronic and optical properties, interactions of single nanotubes in bundles [49] and with the environment [205].…”

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

“…Significant efforts have been devoted to produce and study isotope-enriched graphene-related materials [4][5][6][7][8][9][10][11][12][13]. For instance, isotope labeling provided direct evidence that the growth mechanism of graphene is substrate dependent and, furthermore, shed light on the rational design of chemical vapor deposition (CVD) synthesis methods [4][5][6][7][8].…”