Excitation channels of the 4.3 eV photoluminescence in Ge-SiO2

Photoluminescence (PL) excitation spectra of the 4.2 eV alpha emission in Ge-doped silica were obtained at 290 and 9 K in the range 4.5-10 eV by synchrotron radiation excitation. The vacuum ultra-violet excitation pattern turns out to be different from that previously observed in pure silica. Four excitation bands were resolved at 4.9, 5.2, 6.4 and 7.2 eV. PL lifetime data were also analyzed to characterize the radiative relaxation channels. Data on differently prepared samples suggest to assign each excitation band to a distinct type of defect site. Nevertheless, the same results indicate the presence of only two types of PL sites, one of which possessing both intra- and inter-center excitation channels, possibly involving tunneling and defect conversion mechanisms