Optical spectroscopy of single‐walledcarbon nanotubes: From excitonic effects towards control of the radiative lifetime

Abstract

We have recently studied excitonic effects on the optical properties of single‐walled carbon nanotubes by means of two‐photon spectroscopy and time‐resolved photoluminescence spectroscopy. For nanotubes with diameters between 6.8 Å and 9.0 Å, the two‐photon spectra give evidence for large binding energies between 300 meV to 400 meV. Theoretical simulations of these spectra indicate that the lowest energy exciton state in nanotubes is an optically dark exciton, which has profound implications on the luminescence yield and exciton dynamics in single‐walled nanotubes. Indeed, time‐resolved photoluminescence measurements of individual nanotubes reveal low quantum yields and rather short exciton lifetimes ranging from 10 ps to 200 ps, which are affected by exciton relaxation between bright and dark states and non‐radiative exciton recombination. These results suggest that a control of the radiative lifetime of nanotube excitons may be a viable strategy for enhancing their luminescence yield. Here, we propose that exciton‐coupling to surface plasmon polaritons in metallic nanostructures may result in a substantial enhancement of the radiative exciton decay rate. Two‐photon luminescence excitation spectra of single‐walled carbon nanotubes. The luminescence intensity is plotted as a function of excitation and detection wavelength. The various two‐photon resonances are assigned to nanotube species with different chiral indices (n,m), as indicated in the figure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)