TSSG Growth and Thermal Field Optimization of Er³⁺:NaSrY(Mo_1–xW_xO₄)₃ Crystals: Structure Evolution and Anion-Substitution-Induced Disorder

In this study, a series of Er³⁺:NaSrY(Mo_1–xW_xO₄)₃ (x = 0.1, 0.3, 0.5) crystals were successfully grown using the top-seeded solution growth (TSSG) method. The effects of partial substitution of Mo⁶⁺ by W⁶⁺ on the crystal structure, electronic structure, and the 1.55 μm luminescence properties of Er³⁺ were systematically investigated. The growth temperature field was optimized through finite element simulations, enabling the determination of the optimal crucible position and seed rod rotation rate. X-ray diffraction and Rietveld refinement results indicate that W doping induces lattice expansion and shifts the diffraction peaks toward larger angles. First-principles calculations and diffuse reflectance spectroscopy reveal that W doping effectively tunes the bandgap of the material. The spectroscopic results indicate that when the W doping concentration reaches x = 0.3, the absorption capability of Er³⁺ at 980 nm is significantly enhanced, with an absorption cross section of 4.75 × 10^–21 cm². Meanwhile, the emission band around 1.55 μm exhibits remarkable broadening, with the full width at half-maximum (fwhm) increasing to 98.3 nm and the corresponding emission cross section reaching 12.1 × 10^–21 cm². Combined with the fluorescence lifetime and gain cross-section analysis, the crystal demonstrates a relatively low lasing threshold and excellent gain performance. These results suggest that Er³⁺:NaSrY(Mo_1–xW_xO₄)₃ (x = 0.1, 0.3, 0.5) crystals are promising candidates for broadband tunable near-infrared laser gain media.