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Optical signatures of quantum dot excitons in carbon nanotubes

We report optical studies of quantum dot excitons in individual suspended carbon nanotubes at cryogenic temperatures. Narrow optical linewidths, strongly suppressed spectral wandering, and photoluminescence lifetimes in the range of nanoseconds emerge as key signatures of exciton localization. We infer exciton quantum dot formation with a characteristic length of a few exciton Bohr radii. Localization inhibits exciton diffusion and protects the exciton from dephasing by structural or environmental inhomogeneities as well as from exploring nonradiative quenching sites. In consequence, quantum dot excitons in carbon nanotubes exhibit intrinsic radiative lifetimes, long coherence times and a quantum yield of 100%. Our results underpin the potential of carbon nanotube excitons for both fundamental studies and applications that scale advantageously with enhanced spectral resolution and coherence.