fluorophosphate, and fluoride glasses

In this study, we explore the photodarkening mechanisms of Tb3+-activated silica, phosphate, fluorophosphate, and fluoride glasses. The glasses were prepared by either conventional melting or sol-gel combined with high temperature sintering. The absorption, emission spectra, lifetime, and electron paramagnetic resonance (EPR) spectra of Tb3+-activated host glasses are systematically characterized before and after X-ray irradiation. The results show that the formation of Tb4+ ions and the oxygen-related hole defects are two key factors which led to the photodarkening in visible region of above glasses after X-ray irradiation. Evaluating from the change of absorption, emission intensity and lifetime at 540 nm, fluoride glass demonstrated a superior photodarkening resistance among four kinds of glasses. It is a preferred host material for lasing operation at visible wavelengths. Our findings offer insight into the photodarkening mechanism of different Tb3+-activated glasses which find applications in fiber lasers at visible wavelengths.