Effect of P⁵⁺ on spectroscopy and structure of Yb³⁺/Al³⁺/P⁵⁺ co-doped silica glass

Two series of silica glasses [(95.9−x)SiO₂–4Al₂O₃–xP₂O₅–0.1Yb₂O₃ (in mol%, x=0–10) and (92−y) SiO₂–4Al₂O₃–4P₂O₅–yYb₂O₃ (in mol%, y=0–0.2)] were prepared by sol–gel method combined with high-temperature sintering. The relationship between the glass structure and spectroscopic properties is investigated. Significant alterations in density, refractive index, absorption and emission cross sections, fluorescence lifetime, and scalar crystal field N_J are observed at a molar ratio of P⁵⁺/Al³⁺=1 due to the transformation of P⁵⁺ structure type from AlPO₄-like to PO₄ units. This structural change is clearly observed in Raman spectra. In addition, NMR experimental results suggest that Yb³⁺ is mainly located in AlPO₄-like but not SiO₄ units at a molar ratio of P⁵⁺/Al³⁺=1, and also Raman spectra reveals the presence of P=O linkage in samples with molar ratio of P⁵⁺/Al³⁺>1. This further demonstrates that it is due to the formation of P=O site but not the simple addition of P₂O₅ in Yb³⁺/Al³⁺/P⁵⁺ co-doped silica glass to significantly decrease the absorption and emission cross sections of Yb³⁺. It reflects in the change of Yb³⁺ Stark splitting, and is revealed by the decline of Yb³⁺ asymmetry degree. - Highlights: • Silica glasses doped with P⁵⁺, Yb³⁺, Al³⁺ were successfully prepared. • Their optical and spectroscopic properties were measured at room temperature. • Structure–property relationships of these glasses were investigated