  Carbon nanotubes have been observed to emit ultraviolet, visible and infrared
radiation when exposed to microwaves. We have performed experiments in which
both short (0.5 microns to 2 microns) and long (5 microns to 30 microns) single
and double walled carbon nanotubes were exposed to 2.46 GHz microwaves at a
pressure of 10^-6 Torr. Structural modifications of the-carbon nanotubes due to
microwave absorption have been studied using the Raman spectroscopy G-band and
D-band intensities, which suggest that microwave irradiation at relatively low
pressure results in an increase in nanotube defects, especially in the case of
the long nanotubes. Furthermore, a comparison of the spectra of the radiation
emitted from the nanotubes suggests that the longer nanotubes emitted radiation
of much greater intensity than the shorter nanotubes. Based on the results of
the experiments and results described in previous reports, the ultraviolet,
visible and infrared radiation emitted as the result of microwave absorption by
carbon nanotubes seems to be primarily blackbody radiation emitted due to Joule
heating. However, the presence of several broad photopeaks in the spectra of
the emitted radiation (which do not seem to be related to gases absorbed by the
nanotubes or the presence of catalyst particles) suggest that emissions are not
the result of Joule heating alone.
