Light emission excited by scanning tunnelling microscopy (STM) has been observed on multiwall
carbon nanotubes. The photon yield depends on the scanned tube but it is constant all along the tube.
Simultaneous photon spectroscopy evidences emitted wavelengths in the 600−1000 nm range in good
agreement with previous field emission data. Emission characteristics are independent of substrate and of STM tip. We discuss how these new results are consistent with radiative transitions involving localized
states in carbon nanotubes.