Optical properties of Ge-oxygen defect center embedded in silica films

The photo-luminescence features of Ge-oxygen defect centers in a 100nm thick Ge-doped silica film on a pure silica substrate were investigated by looking at the emission spectra and time decay detected under synchrotron radiation excitation in the 10-300 K temperature range. This center exhibits two luminescence bands centered at 4.3eV and 3.2eV associated with its de-excitation from singlet (S1) and triplet (T1) states, respectively, that are linked by an intersystem crossing process. The comparison with results obtained from a bulk Ge-doped silica sample evidences that the efficiency of the intersystem crossing rate depends on the properties of the matrix embedding the Ge-oxygen defect centers, being more effective in the film than in the bulk counterpart.Comment: 10 pages, 3 figures, in press on J. Non cryst. solids (2007

Photodarkening of Infrared Irradiated Yb3+-Doped Alumino-Silicate Glasses: Effect on UV Absorption Bands and Fluorescence Spectra

The photodarkening phenomenon in alumino-silicate glass preforms, doped with different ytterbium concentrations, was studied. The UV band, comprised between 180 and 350 nm, was examined before and after irradiation at 976 nm. The non-linear dependence of 240 nm band with concentration after infra-red irradiation was demonstrated and ascribed predominantly to Yb3+ pair's interaction. The emission spectrum after the excitation in UV spectral region showed increased intensity after photodarkening, probably due to Yb2+ ions creation. Phenomenological photodarkening model and the possible existence of several defect types are presente

Assessment of Potential Risk for Kola's Population from Radiological Impact of Accident on Spent Nuclear Fuel Facilities

With financial support from the Swedish Board för Civil Emergency Preparedness (ÖCB).Nuclear Problems, Risks Perceptions of, and Social Responses to, Nuclear Waste in the Barents Regio