Native and radiation-induced photoluminescent defects in SiO2:: Role of impurities

We report photoluminescence (PL) data on amorphous SiO2 in the spectral range of the alpha (4.3 eV), beta (3.1 eV), and gamma (2.7 eV) emissions excited with synchrotron radiation. Differently prepared and treated samples are compared. Neutron irradiation gives rise to PL features distinct from those observed both in unirradiated Ge-doped silica and in samples with other impurities. Our data suggest that the defect-formation processes determine the different PL patterns observed in SiO2, while the usually proposed distinction between Si- and Ge-like centers is not relevant.