10 keV X-ray irradiation effects on phosphorus-doped fibers and preforms: Electron spin resonance and optical studies

In this paper, we study the radiation-induced point defects related to the Phosphorus element that is commonly used to improve the optical properties of silica-based glasses but is responsible of a dramatic increase of their radiation sensitivity. To this aim, the influence of X-ray irradiation on prototype phosphorus-doped canonical fibers and their related preforms was investigated by in-situ radiation induced attenuation (RIA), optical absorption (OA) and electron paramagnetic resonance (EPR) spectroscopy. The RIA spectra in the (1.5-5) eV range, can be explained by the presence of at least three absorption bands induced by radiation exposure. Additionally the X-dose dependence of such bands was studied. The main responsible defect for these absorption peaks was the POHC center, whose presence was also detected by EPR measurements both in irradiated fibers and preforms. Two narrow lines in EPR preform spectra, previously assigned to a variant of POHC center stable only at low temperature, were observed even at room temperature.