Abstract:

Silica glasses containing different contents of Al₂O₃, Yb₂O₃ and P₂O₅ were fabricated by Sol-Gel method combined with high temperature vacuum sintering. Changes in UV transmission, fluorescence spectra under the UV excitation, and X-ray photoelectron spectra (XPS) of Yb4d caused by P⁵⁺ and Al³⁺ ions co-doping in Yb³⁺-doped silica glasses were comparatively investigated. The related mechanisms were discussed. Results show that the strong absorption bands in the range of 190 nm to 300 nm in Al³⁺/Yb³⁺/P⁵⁺-doped silica glasses are largely due to the charge-transfer (CT) from O^2- to Yb³⁺, the positions of CT-absorption bands as well as binding energy of Yb4d are shifted to the higher energy with increasing electro-negativity of the second coordination element (Al, Si, P) of Yb³⁺ ions. In addition, introduction of Al³⁺ into Yb³⁺-doped silica glass leads to the reduction of Yb³⁺ to Yb²⁺ ions under vacuum sintering condition. The characteristic absorption of Yb²⁺ ions is located at 330 nm. Nevertheless, further incorporation P⁵⁺ into Al³⁺/Yb³⁺-co-doped silica glass with mole ratio of P⁵⁺/Al³⁺>1 can effectively suppress the formation of Yb²⁺. The IR luminescence (976 nm) under UV excitation originates from a relaxed CT transition, and the visible luminescence (525 nm) is ascribed to 5d→4f transition of Yb²⁺. The results provide a guidance on technology optimization and composition design for fabricating high-performance Yb³⁺-doped fiber.

Key words: Yb3+-doped silica glasses, UV absorption bands, charge-transfer, Yb2+