Luminescence centres in silica nanowires

Three broad cathodoluminescence bands centred at similar to 2.02 eV ( red), similar to 2.78 eV ( blue), and similar to 3.45 eV ( ultraviolet) have been observed from silica nanowires synthesized by thermal evaporation at high temperature. The luminescence intensities of both the red and ultraviolet bands decrease upon electron-beam irradiation, while the intensity of the blue band increases with both irradiation time and specimen temperature. The red, blue, and ultraviolet bands are identified as radiative transitions involving the following centres: nonbridging oxygen hole centres, oxygen-deficient centres, and peroxy linkage. The varying time- and temperature-dependent luminescence intensities can be explained by the mutual transformation of these defects, which is driven by the irradiation- and heat-induced migration and desorption of radiolytic oxygen.