Abstract
Optical absorption spectra of the X-ray irradiated alkali borate glasses containing various kinds of halide ions were obtained. Halide ions in glasses form Vk centers (X2- centers, X=F, Cl, Br and I) and showed sharp absorptions in the visible or ultra violet range. In the K2O-B2O3-KCl glasses the intensity due to Cl2- center decreases with increasing concentration of potassium oxide and drops abruptly at about 20mol% potassium oxide. This behavior coincides with that observed in the previous study on Na2O-B2O3-NaCl glasses and is related to the structural change in the borate network with glass composition. The addition of fluoride or bromide ion to the Na2O-B2O3 glasses also generates F2- or Br2- center in the acidic range on X-ray irradiation. On the other hand, I2- center was created over the entire range of composition examined in this work. Thus it is expected that the iodide ion dissolves in the glasses in a distinguishable way owing to its large polarizing power. The absorption energies due to Vk centers in the glasses are larger than that seen in the corresponding alkali halides. By combining the above results with the Raman shift observed in the Cl2- center, it is concluded that the stability of Vk centers in glasses is larger than that in alkali halide crystals. Finally it is observed that halide ions in glasses also reduces the concentration of defect centers in mother glasses as scavenger ions.
