Photoluminescence in VAD SiO2:GeO2 Glasses Sintered under Reducing or Oxidizing Conditions

Abstract
The atmosphere dependence of photoluminescence (PL) centers produced in SiO2:GeO2 glasses was examined by preparing VAD SiO2:GeO2 preform rods with changing the sintering atmosphere systematically from reducing to oxidizing. Four types of luminescence centers could be detected for samples sintered under H2/He=1/20, He or O2/He=1/10 atmospheres. The atmosphere dependence of luminescence intensity suggests that reduced species of Ge and/or Si are responsible for the luminescence centers. Ge(II) dissolved in a SiO2 network, which was characterized as a lone pair of electrons located on a Ge atom with 2 or 3 oxygen neighbors. Si(II) dissolved in a silica network, and the Si and/or Ge cluster and [chemical formula] or [chemical formula] were proposed for the possible structural models of PL centers.