Structure network topology and broadband 2.7 μm luminescence in Er3+/Pr3+ co-doped TeO2-BaF2-YF3 glass

Abstract

In this paper, Er³⁺/Pr³⁺ co-doped tellurite fluoride glass samples were prepared by high-temperature melting method, and the structural and optical properties of the glass samples were investigated and discussed by Raman spectroscopy, DSC mapping, absorption spectroscopy, and fluorescence spectroscopy with a view to obtaining a gain medium with good luminescence performance for the 2.7 μm band. The results of Raman spectroscopy show that the glass has a maximum phonon energy of 755 cm⁻¹. The lower maximum phonon energy is attributed to the introduction of F⁻, which leads to the breakage of the Te-O-Te bond in the structure and the formation of two kinds of bonds, O-Te-F and Te-F-Te, which makes the structure of TeO₄ gradually transformed into TeO₃₊₁ and TeO₃, and the fluoride–tellurite crystal system presents two phases of oxyfluoride (TeO₃F₂ and TeOF₂) based on the formation of α and β TeO₂ polymorphs. On the other hand, the change of structure network topology effectively inhibits the interaction between rare earth ions and reduces their nonradiative transitions probabilities, which provides a powerful environment for the mid-infrared band luminescence thus enhancing the infrared luminescence performance. The DSC pattern shows that the glass has a T_g of 355 °C and a ΔT as high as 118 °C, which suggests that the glass has a good thermal stability. The fluorescence spectra show that when the doping concentration of Er₂O₃/PrF₃ is 1 mol% and 2 mol%, the maximum fluorescence intensity of 2.7 μm is acquired. The fluorescence half-height width of the glass is 138 nm, and the effective fluorescence bandwidth of the glass is $\Delta {\lambda }_{eff}$ = 147.4 nm, which is a sufficient guarantee for the realization of the tunable laser of 2.7 μm with a wide $\Delta {\lambda }_{eff}$. The Judd-Ofelt intensity parameters were calculated by combining the absorption spectra, where the Ω₂,Ω₄,Ω₆, and spectral quality factor (χ = Ω₄/Ω₆) of the glass were 6.83 × 10⁻²⁰ cm², 2.49 × 10⁻²⁰ cm²,1.78 × 10⁻²⁰ cm², and 1.40, respectively. Meanwhile, the emission cross-section reached 6.37 × 10⁻²¹ cm², with maximum gain coefficients of 2.28 cm⁻¹, indicating that the glass sample has a low lasing threshold and is expected to produce efficient 2.7 μm luminescence. The results indicate that the Er³⁺/Pr³⁺ co-doped 70TeO₂-20BaF₂-10YF₃ glass is a promising laser glass material in the 2.7 μm band.