Glass structure and NIR emission of Er3+ at 1.5 μm in oxyfluoride BaF2–Al2O3–B2O3 glasses

• New oxyfluoride glasses with high amount of BaF2 and Al2O3 were synthesized.
• Glass structures were investigated by using XPS and Raman scattering spectroscopy.
• The glass structures are largely affected on crystallization behavior and optical properties.
• Er3+ in the glasses and glass–ceramics showed broad emission at 1.5 μm.

The glass structure, photoluminescence properties of Eu3+, Judd–Ofelt analysis, and near infrared emissions of Er3+ at 1.5 μm in the oxyfluoride glasses and glass–ceramics of 1Eu2O3- or 1Er2O3-doped 50BaF2–xAl2O3–(50 − x)B2O3 (x = 0–25 mol%) were investigated. It was clarified on the ground of Raman scattering spectroscopy and F1s and O1s XPS measurements that the glass with no Al2O3 (1Er2O3–50BaF2–50B2O3) is composed of BO3, BO2F and BO3F units with F–Ba bonds. The glasses with 25Al2O3 (1Er2O3–50BaF2–25Al2O3–25B2O3) is mainly composed of BO3− and Al(O,F)x units. Existence of non-bridging oxygen was not detected by O1s-XPS spectra. It was proposed that these structures are largely affected on crystallization behavior, e.g., the glass with no Al2O3 forms BaF2 and β-BaB2O4 due to Ba–F bonds and the glass with 25Al2O3 forms BaAlBO3F2 because the glass structure composed of BO3 and Al(O,F) units is similar to the BaAlBO3F2 crystal structure. Judd–Ofelt parameters of Er3+ and Eu3+ in the glasses showed almost the same values in Ω4 and Ω6 for each glass, on the other hand Ω2 decreased with addition of Al2O3. The emission spectra of Er3+ at 1.5 μm in the glasses and glass–ceramics with BaAlBO3F2 crystals showed broad peaks. It is proposed that oxyfluoride glasses and glass–ceramics based on the BaF2–Al2O3–B2O3 system have a high potential for optical device applications such as broadband optical amplifiers.