ONE- AND TWO-QUANTUM UV PHOTO-REACTIONS IN PURE AND DOPED SILICA GLASSES. 2. GERMANIUM OXYGEN DEFICIENT CENTERS (GODC)

摘要

The results of our spectroscopic studies clearly demonstrate the following important features of photo-excitation and photo-decomposition of germanium oxygen deficient centers (GODC) in germanosilicate glasses: 1. Oscillator strength for UV absorption (S_0-S_1 transition) of GODC is relatively low f=0.03 with respect to that of SODC (f=0.14). This is one of the reasons of relatively low effeciency of UV photodecomposition of GODC in comparison with SODC. 2. The photo-reaction from T_1 state dominates in one-quantum photochemistry of GODC, when excited both via singlet-singlet and singlet-triplet transition. 3. The UV absorption and photoluminescence spectra of GODC are inhomogeneous by nature. This is caused by small variation of GODC structure, due to the different 4. Different groups of GODC have different photo-reactivities (photochemical inhomogeneity). Both chemical and spectral inhomogeneity results in strong non-exponentially of GODC photodecay with UV dose. 5. The strong enhancement of GODC one-quantum photo-reaction yield with GeO_2 concentration takes place in hydrogen unloaded germanosilicate preforms and fibers. This is explained by the effect of Ge ~(4+) in the first coordination sphere of GODC on photo-reaction probability. 6. The loading with hydrogen results in significant enhancement of both one-quantum and two-quantum pathways of GODC. 7. At low-intensity (one-quantum) excitation, the reaction of triplet-excited GODC with hydrogen dominates, and there is no more effect of GeO_2 concentration on photo-reaction yield. 8. Two-quantum (two-step) photo-ionization of GODC is one of the dominant pathways of high intensity UV laser decomposition of GODC. 9. At high-intensity excitation, competition of one- and two-quantum photo-reaction pathways takes place, and the dominant pathway is controlled to great extent by Ge concentration.