Yb³⁺/Al³⁺-co-doped silica fibers are the most significant gain medium in high-power lasers to obtain the femtosecond laser pulse with 100 J peak energy. However, high melting temperature and high refractive index may restrict their application.

B₂O₃ can effectively lower the viscosity of glass melt and affect the optical properties of rare-earth ions. Most previous work focuses on the properties of the ytterbium doped glasses with different compositions while the underlying reasons are rarely reported.

A research team led by prof. HU Lili in Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (SIOM, CAS) has built an intuitive model of structure and properties evolution during the substitution of SiO₂ by B₂O₃ in Yb³⁺/Al³⁺/B³⁺-co-doped silica glasses. The study was published in Journal of the American Ceramic Society.

In their research, the homogeneous Yb³⁺/Al³⁺/B³⁺-co-doped silica glasses with various B₂O₃ concentration were prepared via a sol-gel method and subsequently high temperature sintered under vacuum. Yb³⁺-doped, Y³⁺/Al³⁺/B³⁺-co-doped, B³⁺-doped silica and borosilicate glasses were simultaneously fabricated for comparison. The network structure of Yb³⁺/Al³⁺/B³⁺-co-doped silica glasses was systematically analyzed via FT-IR, Raman, ²⁹Si, ²⁷Al and ¹¹B Magic Angle Spinning NMR spectra, as well as ²⁷Al{¹¹B} and ¹¹B{²⁷Al} Rotational Echo Double Resonance experiments.

The generation of Yb-O-B bonds at the cost of partial Yb-O-Al/Si ones should account for the decrement in the scalar crystal field parameters, Yb³⁺ asymmetry degree and Yb³⁺ cross-sections when B₂O₃ was lower than 2 mol%. They found that further increased B atoms preferred to connect with Si and Al rather than Yb. Consequently, the above parameters were basically unchanged and B₂O₃ addition could continuously decrease the refractive index and density.

This research can provide a valuable reference to fabricate the Yb³⁺-doped silica fibers with low numeral aperture.

This work was supported by the National Natural Science Foundation of China, the Natural Science Foundation of Shanghai and Shanghai International Cooperation Fund.

Yb³⁺/Al³⁺/B³⁺-co-doped silica fiber. (Image by SIOM)

Article website:
https://doi.org/10.1111/jace.17155

Contact:
Mr. CAO Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: caoyong@siom.ac.cn