Resonance Raman of oxygen dangling bonds in amorphous silicon dioxide

We investigate the origin of a resonance Raman band induced by ionizing radiation in amorphous silicon dioxide (silica glass), which can be detected under ultraviolet laser excitation. A silica sample, rich of oxygen-excess related defects, was prepared by treating some length of a pure-silica-core multimode fiber in an O₂ atmosphere (at high temperature and pressure) and by irradiating it with X-rays at 10 MGy(SiO₂) dose. A micro-Raman study revealed a gaussian band peaking at 896 cm⁻¹ with a full width at half maximum of 32 cm⁻¹, which could be detected by exciting the sample with the 325-nm line of a HeCd laser. This spectral feature is absent in the Raman spectra performed with the 442-nm line of the same laser. On the basis of several experimental evidences and some complementary literature data, the 896 cm⁻¹ band is assigned to a resonance Raman scattering of oxygen dangling bonds, often called non-bridging oxygen hole centers.