Fluorescence properties and dehydration process of a novel high-gain Er3+/Yb3+ co-doped phosphate laser glass

In this study, a series of Er³⁺/Yb³⁺ co-doped P₂O₅-Al₂O₃-K₂O-BaO-MgO-Nb₂O₅ phosphate glasses were synthesized. Their physical and thermal properties, along with Raman and fluorescence spectra, were systematically characterized. Judd–Ofelt parameters were calculated to optimize the glass composition, rare-earth doping concentration, and dehydration processing conditions. Under excitation from a 980 nm LD laser, the Er³⁺/Yb³⁺ co-doped phosphate glasses exhibited strong fluorescence at 1.5 μm. The fluorescence lifetime increased from 1.18 ms to 4.03 ms as the Yb₂O₃ concentration was varied from 2 wt% to 16 wt%, with the Er₂O₃ content held constant at 1 wt%. The Yb³⁺ ion demonstrated strong absorption across the 800–1100 nm spectral range. The emission spectra of Yb³⁺ and the absorption spectra of Er³⁺ overlapped significantly, facilitating efficient energy transfer from Yb³⁺ to Er³⁺. To reduce the hydroxyl content in glass and improve its fluorescence properties, part of the BaO was replaced by BaCl₂. When the BaCl₂ substitution level was increased to 7.5 mol%, the fluorescence lifetime improved from 4.03 ms to 4.90 ms, and the hydroxyl absorption coefficient decreased from 13.68 cm⁻¹–12.45 cm⁻¹. Additionally, the effects of bubbling CCl₄ and POCl₃ on the hydroxyl absorption coefficient and fluorescence decay lifetime over varying bubbling times were investigated. For the Er³⁺/Yb³⁺-doped phosphate glass with a 1:16 ratio, the hydroxyl absorption coefficient dropped from 24.38 cm⁻¹ to 0.30 cm⁻¹ after dehydration with POCl₃ and dry O₂ for 40 min. Correspondingly, the fluorescence lifetime reached its peak value of 9.62 ms. The resulting Er³⁺/Yb³⁺ co-doped phosphate laser glasses demonstrated superior performance compared to existing commercial counterparts, with the longest fluorescence lifetime (9.62 ms), the highest unit-length gain (6.93 × 10⁻²¹ cm² ms), and a moderate excitation-emission cross section (7.2 × 10⁻²¹ cm²).