From structural evolution to property regulation: The role of fluorine in neodymium-doped phosphate glasses

Phosphate laser glasses often face a trade-off between enhanced optical performance and chemical durability. The integration of fluorine into phosphate laser glasses presents a promising strategy for tailoring their properties, yet a comprehensive understanding of the underlying structural evolution and its correlation with macroscopic performance remains incomplete. This work investigates a series of neodymium-doped phosphate glasses with incremental substitution of F ‒ for O 2‒ Structural analyses (Raman, FTIR, NMR, XPS) reveal that F atoms preferentially coordinates with Al, saturating the Al(6) sites near [Al(OP) 4 F 2 ] at a critical F/Al ratios of 2.86. Beyond this, excess F depolymerizes the phosphorus network, converting Q 2 to Q 1 units. This transition suggests property trends: doping below the threshold (F/Al < 2.86) enhances chemical durability, hardness, and reduces the nonlinear refractive index, while higher concentrations induce degradation. Spectroscopically, F increases Nd 3+ site ionicity without compromising the stimulated emission cross-section, confirming its utility for designing high-performance laser glasses.