UV and gamma radiation damage in silica glass and fibres doped with germanium and cerium

Ultraviolet-induced absorption during very short continuous exposure in Ge-doped optical fiber

“…Based on the results drawn from the literature [6,11], we suggest that only Ge(1) centers have an OA band which extends into the visible region. The previous assumption is consistent with the thermal annealing experiments which reveal that the absorption intensity starts to decay at around 150°C [12] and is completely bleached for annealing temperature higher than 400°C [13]. This annealing process indicates that the GeE 0 defect is not the absorbing specie because it begins to bleach at around 450°C [12].…”

“…In particular, among these defects there are two Ge paramagnetic centers, Ge (1) and Ge (2), which are photoinduced in Ge-doped fiber by irradiation with UV light [7]. The Ge (1) center is assigned to a four-fold 0022 Ge atom having trapped an electron whereas the structure of Ge(2) is still debatable [6,8,9]. The GeE 0 type center is not included in this study.…”

Étude des processus photochimiques primaires dans les fibres optiques germanosilicates lors d'une insolation ultraviolette

“…• C [15]. Cette température d'activation permet d'exclure les défauts GeE' qui, eux, commenceà blanchir autour de 400…”

“…• C [15]. Il s'agirait plus probablement des centres Ge(1) et Ge(2) qui sont connus pour blanchirà des températures voisines de 150…”

Ge and Sn Doping in Silica: Structural Changes, Optically Active Defects, Paramagnetic Sites

“…Later on, different groups agreed with the attribution of the Ge(3) signal to axial E' -Ge sites, whereas an alternative assignment was proposed for the orthorhombic Ge(l) signal [36]. Specifically, the Ge(1) signal was ascribed to electrons trapped in fourfold coordinated Ge sites following two arguments: a) the s-character of the wavefunction estimated from the hfs splitting is larger than 30%, similarly to some amphoteric impurities (as P and As) embedded in silica with coordination order higher than 3 and with electron-trap character [36,37]; b) the radiation-induced growth of the Ge(l) signal in Ce 3 + co-doped samples is correlated with the change of oxidation state of Ce 3 + ions during irradiation showing the presence of electron trapping processes [38]. Recent theoretical calculations -giving an estimated hfs splitting in good agreement with the experiment -apparently support the electron trapping features of fourfold coordinated Ge sites, although the same approach gives similar results in the case of GeOz, in contradiction with the experimental evidence [39].…”