(n,m)-assigned absorption and emission spectra of single-walled carbon nanotubes

Spectroscopic studies of SWNT samples enriched in individual, surfactant-suspended nanotubes have revealed distinct absorption and emission transitions for more than 30 different semiconducting (n,m) species. Through the combined use of pattern analysis, qualitative model calculations, and resonance Raman measurements of radial breathing mode frequencies, (n,m) indices were assigned to the first- and second-van Hove optical transitions of 33 different species. The results show large systematic deviations from a simple dependence of transition wavelength on tube diameter, suggesting the presence of substantial excitonic effects in addition to trigonal warping patterns. Tight-binding models are not successful in simulating the results. An experimental, model-free plot of transition energy vs. nanotube diameter is now available. It is advisable to use this in preference to theoretically constructed Kataura plots, which contain substantial errors. Optical spectroscopy will also prove a valuable tool for selective, sensitive, rapid, and nondestructive analysis of bulk nanotube samples.