Glass formation, structure and property of Nd3+-doped Sr(PO3)2-Ba(PO3)2-AlF3-MgF2 glass for 0.9μm fiber lasers

Abstract

0.9 μm fiber lasers enable efficient generation of blue laser via second-harmonic conversion, which are essential light sources for applications such as undersea communications, laser displays, and biophotonic imaging. Glass fibers doped with Nd³⁺ ions serve as the gain medium for these lasers; however, the competition from the four-energy-level transition ⁴F_3/2→⁴I_11/2 remains a significant challenge. Fluorophosphate (FP) glass combines the high rare-earth solubility of phosphate glasses with the low phonon energy of fluoride, particularly benefiting from large crystal field strength that enhances the ⁴F_3/2→⁴I_9/2 transition. Nonetheless, crystallization and phase separation in FP glass pose substantial challenges for this multi-component glass system. Herein, a novel Nd³⁺-doped Sr(PO₃)₂−Ba(PO₃)₂−AlF₃−MgF₂ glass is reported. A thermodynamic approach was employed to predict the glass-forming region of the Sr(PO₃)₂−AlF₃−MgF₂ system, providing a robust design framework for FP compositions with superior glass-forming ability. Further investigations into the gradual substitution of Ba(PO₃)₂ to Sr(PO₃)₂ elucidate the structure-property relationship between the local network environment and Nd³⁺ emission at 0.9 µm. The optimized FP glass demonstrates remarkable stability against crystallization (ΔT>100 °C), a high branching ratio (47.2 %), a large emission cross-section (2.36 × 10⁻²⁰ cm²), an extended lifetime (334 μs), a high spectral quality factor (7.88 × 10⁻²⁴ cm²·s), and a broad gain bandwidth (10.71 × 10⁻²⁶ cm³) at 0.9 μm, surpassing previously reported glass hosts and establishing it as a highly promising host material for 0.9 μm fiber laser applications.