Yb³⁺/Al³⁺ co-doped silica glasses with different Ce₂O₃ contents were prepared using the sol–gel method combined with high-temperature sintering. Changes in refractive index, absorption, emission and fluorescence lifetime of these glasses caused by X-ray irradiation were recorded and analyzed systematically. It is found that co-doping with certain amount of Ce could greatly improve the radiation resistance without evident negative effects on the basic optical properties of the Yb³⁺ ions in the near-infrared region. The nature of the radiation-induced color centres and the mechanism by which Ce prevented the formation of these centres were studied using optical absorption, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) methods. Direct evidence confirmed that trapped electron centres (Yb²⁺/Si-E′/Al-E′) and trapped hole centres (Al-OHCs) were effectively inhibited by Ce doping, which was correlated to the coexistence of the redox couple Ce³⁺/Ce⁴⁺ in the glasses. These results are helpful to understand the micro-structural origin and the suppression mechanism by Ce co-doping of the photodarkening effect in Yb³⁺-doped silica fibers.

A series of Yb-doped silica glasses containing equimolar amounts of P₂O₅ and Al₂O₃ were prepared using a sol–gel method combined with high-temperature sintering. Raman spectroscopy confirmed the formation of AlPO₄ join with a P/Al ratio of 1. However, for a P/Al ratio slightly larger than 1, both the AlPO₄ join and P=O bond are formed. Based on the absorption, emission spectra, and electron paramagnetic resonance measurements, it was determined that the increase of the AlPO₄ join concentration in Yb-doped silica glass leads to (i) a decrease in the refractive index with a factor of 1.1005 × 10⁻⁴ (which allows for a low numerical aperture facilitating single-mode laser), (ii) the sustained spectroscopic properties of Yb³⁺, (iii) a decrease in Yb cluster concentration, and (iv) an improved radiation hardening performance (beneficial to high-power space lasers). These results suggest that Yb-doped Al₂O₃-P₂O₅-SiO₂ glass with an appropriate concentration of AlPO₄ join has potential applications in high-power space fiber lasers.

In this study, Er³⁺/Al³⁺ co-doped silica glasses with various Al/Er ratios ranging from 0 to 200 and a constant Er₂O₃ amount were prepared using the sol-gel method combined with high-temperature vacuum sintering. The absorption, emission spectra, and fluorescence lifetime of Er³⁺ ions were recorded and the absorption and emission cross sections were calculated. Using Raman, ²⁷Al and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS-NMR), ²⁷Al triple-quantum (TQ)-MAS-NMR, and electron paramagnetic resonance (EPR) spectroscopies, the physical and optical properties were correlated with the glass structural modifications due to the Al/Er ratio change. With the increase in the Al/Er ratio, the content of Al³⁺ ions around the Er³⁺ ions gradually increased. Meanwhile, the AlO₅ and AlO₆ polyhedrons increased at the expense of the AlO₄ and SiO₄ tetrahedrons, which resulted in an improved symmetry and better ionic Er–O bonds. These structural changes led to the site-to-site variations in the Er³⁺ local environment and the changes in the ligand field strength of the Er–O bonds. This, in turn, resulted in the inhomogeneous broadening of the absorption and emission spectra, with a blue shift of both absorption and emission peaks and a decrease in both absorption and emission at 1.53 μm. With the increase in Al/Er ratio, the full width at half maximum (FWHM) of the emission increased from 27.2 to 54.3 nm. The FWHM × emission cross section (${\sigma }_{emi}$ ) parameter for evaluating broadband amplification behavior was 30.1 × 10⁻²⁰ cm² · nm. This work reveals the close relationship between the glass structure and the spectroscopic properties of Er³⁺ ions and provides an important reference for the design of broadband amplifier materials in the field of optical communication.

In this work, Er/Al/Ge co-doped silica glasses with different GeO₂ content (0–3 mol%), as well as Ge/Al co-doped silica glasses, are prepared by combining the sol–gel and high-temperature sintering methods. Further, the effects of the GeO₂ content on the absorptions and emissions properties, and lifetimes of the glasses before and after 1KGy γ-ray irradiation are compared. The Er/Al/Ge co-doped silica fibers are prepared from a preform produced via modified chemical vapor deposition (MCVD) combined with nano sol-doping. The effects of Ge co-doping on the optical loss and amplifier gain of the Er-doped silica fibers (EDFs) before and after irradiation are also investigated. The related mechanism and species of the γ-ray radiation-induced color centers are revealed via radiation-induced-absorption (RIA) and continuous wave electron paramagnetic resonance (CW-EPR) spectroscopies. The results revealed that co-doping with GeO₂ considerably improves the radiation resistance of the glass and exerts a slight effect on the spectral properties of the Er/Al/Ge co-doped silica glasses before irradiation. The RIA and CW-EPR spectra revealed that the aluminum–oxygen hole center (AlOHC) defects reduce with increasing GeO₂ content because the intermediaries, the Ge-related oxygen-deficient centers (GeODC(I) and GeODC(II)), exhibit stronger abilities to trap the holes compared with the [AlO_4/2]⁻ group. This reduces the RIA level in the visible and near-infrared regions of the Er/Al/Ge co-doped silica glass. The irradiation experiment on the fiber further confirmed that the radiation resistance of EDFs can be considerably improved by Ge co-doping.