Cathode-Luminescence from Extrinsic Impurities in Bundles of Carbon Nanotubes: A Possible Role

Luminescence spectra obtained by electron bombardment of carbon nanotubes bundles show anUV signal centered at about 380 nm. We show that these transitions are extrinsic to nanotubes, in the sense that they are not linked to any carbon compound or structure, but are caused by the residual catalyst material used in the growth process. A possible role of such luminescence attributable to impurities is also discussed. In fact our luminescence measurements, in association with laserablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and X-ray photoelectron spectroscopy(XPS), permit us to assign these spectral bands to Zn and Al oxides. Our conclusions, supportedby data in literature, and the comparison with the quantitative results obtained by LA-ICP-MSspectrometry (which detects ppm) allows us to define cathode-luminescence analysis as a goodtechnique to control cleanness and purity of carbon nanotube samples.