Site-selective study of the 1.8 eV luminescence band in glassy GeO₂

Photoluminescence (PL) band around 1.8 eV in γ-irradiated glassy GeO₂ was studied by site-selective excitation at 1.8 eV. At T < 50 K a vibronic line at 701 cm^-1 appears in the emission spectra. This line is similar to the 890 cm^-1 local vibration seen in the site-selective emission spectra of the 1.9 eV PL center in glassy SiO₂, which is attributed to non-bridging oxygen hole center (NBOHC, a dangling oxygen bond). The vibrational frequencies scale well with the reduced mass and force constants of Si-O and Ge-O quasimolecules. This finding confirms the similarity between both centers and the assignments of the 1.8 eV PL center in GeO₂ and 1.9 eV PL center in SiO₂ to NBOHC. However, NBOHC is not the sole cause of the PL of GeO₂ in the 1.8 eV region and different defect centers may contribute too.