Photoluminescence Centers in VAD SiO2 Glasses Sintered under Reducing or Oxidizing Atmospheres

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Abstract
Two types of diamagnetic luminescence centers were found in VAD SiO2 glass sintered under reducing atmospheres. One of the PL centers, which had an excitation band at 5.17 eV (240 nm) and two emission bands, at 4.2 eV (295 nm) and 3.1 eV (400 nm), was mainly detected in the glasses sintered under H2/He atmosphere. The intensity of the luminescence increased with the partial pressure of hydrogen of the atmosphere. The other PL center, which had an excitation band at 5.06 eV (245 nm) and at least two emission bands at 4.2 eV (295 nm) and around 3.0 eV (413 nm), has been predominantly observed in the sample melted under vacuum. On the basis of the atmosphere dependence of PL and optical absorption measurements in the VUV region, the former was assigned to Si (II) dissolved in a silica network. The Si cluster, in which the number of direct Si-Si bonds exceeded 4, was proposed as a possible candidate for the latter.