The photoluminescence excitation spectra of the 4.2eV alpha emission from Ge-doped silica were obtained at 290 and 9K, in the range of 4.5 to 10eV, by means of synchrotron radiation excitation. The vacuum ultra-violet excitation pattern was found to be different to that previously observed in pure silica. Four excitation bands were resolved, at 4.9, 5.2, 6.4 and 7.2eV. The photoluminescence lifetime data were also analyzed in order to characterize the radiative relaxation channels. Data on variously prepared samples suggested that each excitation band could be attributed to a distinct type of defect site. On the other hand, the same results indicated the presence of only 2 types of photoluminescence site, one of which possessed both intra-center and inter-center excitation channels; possibly involving tunnelling and defect conversion mechanisms.

B.Crivelli, M.Martini, F.Meinardi, A.Paleari, G.Spinolo: Solid State Communications, 1996, 100[9], 651-6