Photoluminescence Side Band Spectroscopy of Individual Single-Walled Carbon Nanotubes

Abstract

Photoluminescence spectra of single-walled carbon nanotubes (SWCNTs) have been recorded and analyzed for selected individual nanotubes and structurally sorted bulk samples to clarify the nature of secondary emission features. Room temperature spectra show, in addition to the main peak arising from the E11 bright exciton, three features at lower frequency, which are identified here (in descending order of energy difference from E11 emission) as G1, X1, and Y1. The weakest (G1) is interpreted as a vibrational satellite of E11 involving excitation of the ∼1600 cm–1 G mode. The X1 feature, although more intense than G1, has a peak amplitude only ∼3% of E11. X1 emission was found to be polarized parallel to E11 and to be separated from that peak by 1068 cm–1 in SWCNTs with natural isotopic abundance. The separation remained unchanged for several (n,m) species, different nanotube environments, and various levels of induced axial strain. In 13C SWCNTs, the spectral separation decreased to 1023 cm–1. The measured...