Band Gap Fluorescence from Individual Single-Walled Carbon Nanotubes

TLDR

Fluorescence across the band gap of semiconducting carbon nanotubes has been observed, but aggregation into bundles quenches fluorescence and broadens absorption spectra. Individual nanotubes were isolated by sonicating a sodium dodecyl sulfate dispersion and centrifuging to remove bundles, ropes, and catalyst, leaving each tube encased in a cylindrical micelle. At pH < 5, individual nanotubes exhibit band‑gap selective protonation of their side walls, as seen in absorption and emission spectra, and this protonation can be readily reversed by base or UV light.

Abstract

Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light.