Photoluminescence from an individual single-walled carbon nanotube

Photoluminescence (PL) and photoluminescence excitation (PLE) spectra are obtained from individual single-walled carbon nanotubes (SWNTs). Individual SWNT spectra are compared with spectra from ensembles. The PL spectrum of an individual SWNT in air at room temperature has a single asymmetric peak of width typically 10 to 15 meV, with no detected background. Both absorption and emission are strongly polarized along the tube axis. Photoluminescence excitation spectroscopy on single SWNTs clearly confirms the unique, one-to-one association of optical absorption resonances with individual emission peaks. Resonances in the PLE spectra are typically $\ensuremath{\approx}30\mathrm{meV}$ wide, with the PL intensity enhanced tenfold over nonresonant excitation. Whether for emission or absorption, the peak shape and peak width are almost the same for a single nanotube as they are for the corresponding species in a large ensemble. That is, there is no significant inhomogeneous broadening. While ensemble measurements are complicated by the superposition of many PL peaks from many different species, single nanotube spectra clearly isolate a single peak and are thus simpler to interpret.