Glass-forming region-guided Zn(PO3)2-AlF3-NaF fluorophosphate glasses for broadband 1.5 μm emission in Yb3+/Er3+ co-doped bulk and fibers

Glass-forming region guided design gives a stable Zn(PO 3 ) 2 -AlF 3 -NaF fluorophosphate host (ΔT ≈ 166 °C) for fiber drawing. • Fluorine as a network modifier creates a low-phonon environment, boosting 1.5 μm emission. • Broadband 1.5 μm emission in bulk (47.2 nm) and fiber (ASE 1450–1650 nm, 0.187 dB/cm). Driven by the rapid growth of AI, 5G/6G, and chip-scale LiDAR, broadband 1.5 μm gain media with high efficiency and fiber compatibility are urgently needed. However, the structure-spectroscopy correlation governing the luminescence performance of Er 3+ /Yb 3+ co-doped glasses remains insufficiently understood. In this work, a Zn(PO 3 ) 2 -AlF 3 -NaF fluorophosphate glass composition (ZAFPN15) was selected based on a previously reported glass-forming region and characterized from atomic structure to fiber-level performance. Molecular dynamics simulations indicate that fluorine predominantly acts as a network modifier and that Er 3+ ions are predominantly coordinated by fluorine (Er–F coordination number ≈ 7.73). The local phonon energy around Er 3+ ions is estimated to be below 500 cm⁻ 1 , much lower than the nominal maximum phonon energy (∼1260 cm⁻ 1 ). The optimized glass exhibits a measured emission cross-section of 0.54 × 10⁻ 20 cm 2 at 1535 nm with an effective linewidth of 47.2 nm, together with a low inversion threshold (∼0.2). Fiber fabrication from this glass shows amplified spontaneous emission (ASE) spanning 1450–1650 nm with a propagation loss of 0.187 dB/cm at 1535 nm. These results demonstrate that this specific fluorophosphate glass composition can be processed into an active fiber with broadband near-infrared emission, and the structural data offer a possible explanation for the observed emission properties.