Light emission from nanostructures exhibits rich quantum effects and hasbroad applications. Single-walled carbon nanotubes (SWNTs) are one-dimensional(1D) metals or semiconductors, in which large number of electronic states in anarrow range of energies, known as van Hove singularities, can lead to strongspectral transitions. Photoluminescence and electroluminescence involvinginterband transitions and excitons have been observed in semiconducting SWNTs,but are not expected in metallic tubes due to non-radiative relaxations. Here,we show that in the negative differential conductance regime, a suspendedquasi-metallic SWNT (QM-SWNT) emits light due to joule-heating, displayingstrong peaks in the visible and infrared corresponding to interbandtransitions. This is a result of thermal light emission in 1D, in starkcontrast with featureless blackbody-like emission observed in large bundles ofSWNTs or multi-walled nanotubes. This allows for probing of the electronictemperature and non-equilibrium hot optical phonons in joule-heated QM-SWNTs.
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