A combined spectroscopic and theoretical study of the glasses SiO2, Na2O : SiO2 and Na2O : CaO : SiO2 has been carried out. For SiO, evidence is presented for the assignment of the sharp 10–2 eV peak as being due to a Wannier exciton, whilst peaks at higher energy stem from O 2p→Si 3d interband transitions. It is found that systematic changes in →2 and n occur as modifier cations are incorporated in SiO2. The first (exciton) peak is broadened by the modifiers and new absorption is found below 10 eV. Overall, the calculated joint density-of-states curves are in good agreement with the experimental curves of →2 E against E, where E is the photon energy.
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Ellis et al. (1979) studied this question.
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