Radiation-induced defects in europium and terbium doped glasses

Irradiation of glasses with sufficient high energy (x-ray, UV) releases electrons and holes which can be trapped by precursors in the matrix, leading to the formation of electron and hole defect centres. This results in undesired transmission losses of optical glasses [1]. Desired radiation-induced effects are refractive index change and persistent spectral hole burning by UV laser irradiation as well as radiation-stimulated fluorescence of active ions. These phenomena are used in novel photonic devices (see Refs in [2]). Polyvalent rare earth ions such as europium and terbium can interfere in the releasing and trapping of electrons. Their redox behaviour is closely connected with radiation-induced defect formation, Fundamental research in this field is of importance to favour or suppress defect formation as required. Furthermore, polyvalent rare earth ions are suitable indicators for examination of the mechanisms of defect formation. The influence of terbium and europium ions on radiation-induced defect formation has been studied in fluoride phosphate and phosphate glasses which are attractive materials for high performance optics and for photonic devices. Different melting conditions have been employed to adjust the redox state before irradiation. The defect centres have been examined by optical absorption, fluorescence and electron spin resonance (ESR) spectroscopy. X-rays and UV excimer laser at 248 nm have been used to create defects. Different mechanisms of defect formation have been found for x-ray and UV laser irradiation. The results on laser induced defect formation are promising for increasing the photosensitivity of glasses.