Cathodoluminescence of crystalline and amorphous SiO2 and GeO2

Cathodoluminescence (CL) and its temperature-dose behaviour are presented for different crystalline and amorphous modifications of SiO2 and GeO2 as well as for Ge-doped SiO2 layers. The crystalline samples include four-fold coordinated Si and Ge in hexagonal quartz and quartz-like crystals, respectively, as well six-fold coordinated atoms in tetragonal rutile-like crystals. The detected luminescence bands, in general, are attributed to three optical active luminescence centres: the two-fold coordinated silicon (=Si:) and germanium (=Ge:) centre, respectively, the non-bridging oxygen hole centre (NBOHC) and the self trapped exciton (STE). The first ones, the oxygen deficient centres (ODC), are especially developed in both, in the tetragonal crystal rutile-like modifications as well as in glassy states. The huge violet luminescence in Ge-implanted SiO2-layers is attributed to the two-fold coordinated Ge in the silica matrix.