Radiation-induced defects in CoO- and NiO-doped fluoridephosphate glasses

Abstract

Irradiation-induced defect formation is a common phenomenon in glasses. The influence of the two polyvalent ions cobalt and nickel was studied in several model glasses, two of those were fluoride-phosphate glasses. These studies were done in order to contribute to the ongoing research on solarization. Dopants and impurities may influence the intensity of intrinsic defects and may cause the evolution of additional extrinsic defects. Sample plates of high-purity glasses, undoped and doped with CoO and NiO, were irradiated by UV lamps and X-rays. The formed defect centers displayed absorption bands in the UV-VIS range, which were recorded by absorption spectroscopy. As many defect centers are paramagnetic, EPR spectra of the irradiated samples were taken. The newly found optical bands and EPR signals evolving in the irradiated glasses are in part characteristic of intrinsic defects, which are different types of electron and hole centers connected with phosphate groups. The other signals arise from extrinsic defects, which are caused by the two dopant ions. Co2+ is photooxidized to (Co2+)+, and replaces some of the intrinsic hole centers (POHC), while Ni2+ is photoreduced to (Ni2+)-.