Fluorophosphate (FP) laser glass offers high rareearth solubility, low nonlinear refractive index, and a large Abbe number, making it a promising gain medium for high-power fiber lasers. The determination of the glass-forming region is fundamental to developing new laser glass systems. Previous studies have relied heavily on trialanderror approaches, yielding only limited data at prohibitive cost in terms of manpower, finances, and material resources. In this work, thermodynamic calculations are employed to investigate the glass-forming region of multicomponent FP glass systems. The results reveal that thermodynamic calculations can effectively predict the glass-forming region of FP glasses. Moreover, differences in cation field strength and interactions with anions are identified as critical factors governing the glassforming ability and structural stability of FP glasses. Based on these theoretical predictions, a ytterbiumdoped, high-gain FP laser glass and fiber are designed and fabricated through compositional optimization, and initial 1.0 μm laser output is successfully demonstrated.

The thermodynamic calculations are based on the free energy balance between liquid and solid phases in binary systems. By solving the equilibrium equation, the melting temperature is obtained as a function of composition, and the eutectic point is determined by locating the minimum of this function. For ternary and higher-component systems, the binary eutectic points are treated as “quasi-compounds”, and the calculation is performed iteratively to construct the theoretical glass-forming region. The predicted regions were validated against experimental data reported in the literature. Raman spectroscopy combined with peak-fitting analysis was used to quantify Qn species, while density and refractive index measurements were carried out for physical property evaluation. Yb³⁺-doped FP glasses and fibers were then fabricated based on the predicted glass-forming region, and their laser performance was characterized.

Quantitative comparison between predicted and experimental glass-forming regions shows overlap ratios of 74.5%, 100%, and approximately 100% for the three systems examined, confirming that the method effectively locates the main compositional range of glass formation. Raman analysis reveals a transition from Q²-dominated chain structures at high phosphate contents to Q⁰/Q¹ units at low phosphate contents, with the Q² fraction decreasing from 73.4% to 8.4% as phosphate content drops from 80%(mole fraction) to 40%. Cation field strength is identified as a critical factor: the higher field strength of Zn²⁺ (0.43) relative to Ba²⁺ (0.24) leads to stronger network bonds but greater sensitivity to composition variation, resulting in a narrower glass-forming region. Guided by the theoretical predictions, Yb³⁺-doped FP fibers were fabricated with a peak gain coefficient of 5.56 dB/cm at 1064 nm and stable dual-wavelength laser emission at 1023.3 nm and 1031.5 nm under 974 nm pumping.

This work demonstrates that thermodynamic calculations based on eutectic point prediction provide a valid pre-screening tool for locating glass-forming regions in multicomponent FP systems. Cation field strength governs the glass-forming window and structural stability. Guided by theoretical predictions, Yb³⁺-doped FP fibers were successfully fabricated with stable 1.0 μm laser output, validating the effectiveness of this combined theoretical-experimental approach for developing novel laser glass materials.