Study On Radiation Induced Darkening Effect And Resistance Property Of Germanate Glass

Germanate glasses are important glass optical fiber matrices used for mid-infrared transmission and mid-infrared optical fiber laser. Particularly, barium gallo-germanate (BGG) glass, which has been an excellent glass matrix applied for 2.0 μm fiber laser, stands out for the combinations of comparatively low phonon energy, high rare-earth solubility, high laser induced damage threshold and good physicochemical and mechanical characteristics. However, for these fiber lasers used in harsh radiation environment such as space-based application, the BGG optical fiber darkening induced by gamma ray radiation often occurs, which causes continuous decrease in optical transmit characteristic, lifetime and reliability of these fiber lasers system. Up to now, the most researches about the gamma ray radiation induced darkening phenomenon mainly focused on rare earth or germanium doped silica glass fibers and phosphate glass fibers, very few reports pay attention to the BGG glass fiber. And the mechanism of gamma ray radiation-induced darkening has not been elucidated in detail yet.In this dissertation, the mechanism of the gamma ray radiation induced darkening in BGG glass and the influence of gamma ray radiation doses on the glass have been systematically studied. The methods of enhancing the γ-ray radiation resistance in BGG glass have been also investigated. The specific research contents and results are as follows:(1) According to the absorption spectra of unirradiated and γ-ray irradiated glasses, the gamma ray radiation-induced darkening in the BGG glass under many accumulated γ-ray doses levels has been investigated. A large optical excess loss band induced by γ-ray irradiation can be observed in the wavelength range from 260 to 800 nm. Meanwhile the radiation induced attenuation (RIA) increased with the increment of the accumulated γ-ray irradiation doses. When the γ-ray total does was up to 50 KGy, the RIA changes become saturated.(2) Optical transmittance spectra, electron paramagnetic resonance (EPR) and thermoluminescence (TL) spectra had been employed to investigate the gamma ray radiation- induced darkening in BGG glass. It was found that the main cause of the RIA was the forming of two kinds of Ge-related defects in the BGG glass, named Ge-related non-bridging oxygen hole center (Ge-NBOHC) and Ge-related electron centers (GEC). In addition, the absorption bands of the two defects have been separated and the absorptivity peaks of Ge-NBOHC and GEC defects were at 375 nm and 315 nm, respectively.(3) To improve the radiation resistance property of BGG glass, a method of doping the halogen, such as fluorine, chlorine and bromine in BGG glass, had been performed. By doping F, Cl and Br in the BGG glass, the RIA of the BGG glass can be reduced or even eliminated. The UV absorption edge of these halogen doping glass samples moved to long wavelength with the increase of doping concentration, indicating that the optimum concentrations of F, Cl and Br doped in the BGG glass to enhance the radiation resistance property were 1%,3% and 3%, respectively.(4) The radiation resistance property of doping variable valency Nb5+ions in BGG glass had been investigated. Owing to the Nb5+(?)Nb3+ interconversion in these doing samples after gamma ray radiation, the forming of Ge-NBOHC and GEC defects was inhibited. Thereby it can suppress the radiation-induced darkening effect and enhance the radiation resistance property of BGG glass. What is more, the optimum concentration of doping Mb205 in BGG glass to enhance the radiation resistance was 1.0%.