Influence of B₂O₃ on Structure and Optical Properties of Yb³⁺ Doped Phosphate Glasses

The Yb³⁺ doped borophosphate glasses were prepared by the melt-quenching method. The effect of B₂O₃ on optical properties was investigated, and stark splitting of Yb³⁺ was obtained by fitting the absorption and emission spectra. Based on fitting results, the crystal field strength parameter N_J and asymmetry of the surrounding ligand structure were calculated which was used to explain the change of luminescence properties and Yb³⁺ local environment with the help of structure information. The results show that B₂O₃ is good for enlarging the Stark splitting of Yb³⁺ and changing the local environment. Compared with the previous single PO₄ ligand, the difference in bond length of BO₄-Yb and PO₄-Yb will increase the asymmetry of Yb³⁺. In addition, the electronegativity of P is stronger than that of B, and the reciprocity between P and O in PO₄ is stronger than that of BO₄, so the interaction between BO₄ and Yb³⁺ is stronger than that between PO₄ and Yb³⁺. Therefore, when x_\rmB_2O_3>10% was applied, the degree of asymmetry and N_J increased, which enhanced the fluorescence intensity around Yb³⁺. Besides, with the increase of B₂O₃ mole fraction, the introduced B₂O₃ all exist in the form of BO₄, and BPO₄ structure units are formed by alternating connection with PO₄. Therefore, B₂O₃ could connect phosphate long chains and glass network transfers from chain structure to three-dimensional space which contributes to enhance the chemical stability and improve the environment of Yb³⁺. Borophosphate glass is expected to be a high power ytterbium-doped matrix material.