UV absorption bands and its relevance to local structures of ytterbium ions in Yb3+/Al3+/P5+-doped silica glasses

Abstract

Yb3+, Yb3+/Al3+, Yb3+/P5+, and Yb3+/Al3+/P5+ doped silica glasses were prepared via the sol-gel method combined with high-temperature sintering. The amorphous nature of as-prepared glasses was confirmed by the X-ray diffraction analysis. The composition dependent ultraviolet (UV) absorption changes in the glasses were correlated with the local structure of Yb3+ ions that was obtained by pulsed electron paramagnetic resonance (EPR). In situ photoluminescence evolution and continuous wave EPR spectrum of color centers induced by a 193-nm UV laser were recorded, and the role of UV absorption bands in the photodarkening process was discussed. The results indicated that the strong UV absorption bands in the range of 190–290 nm were primarily attributed to the charge-transfer (CT) transition from O2– to Yb3+ and the position of CT bands shifted to a higher energy level with increases in the electronegativity of next nearest neighbor atoms (Al/Si/P) of Yb3+ ions. Furthermore, the results revealed that excitation into the CT bands leads to the generation of oxygen hole centers and Yb2+ ions. The study is useful for understanding the underlying mechanism of photodarkening in Yb3+-doped high-power laser fibers.