Luminescence of fused silica: Observation of theO2−emission band

Phosphorescence (PP) and photoluminescence (PL) spectra on type-I and type-II fused silica have been measured. Comparison among them shows that the same bands are present in the PL and PP spectra; the only exception is the ‘‘resonant’’ emission excited in the $B_2$ absorption band (∼5.1 eV) which is always absent in the PP spectrum. At low temperature in one of the PL emission bands, structures have been found whose energy spacing, ∼1250 ${\mathrm{cm}}^{\mathrm{-}1}$, appears to identify the luminescent center as the ${\mathrm{O}}_2$ ${\mathrm{}}^{\mathrm{-}}$ molecular ion.