Bismuth-germanate glasses with low hydroxide content co-doped with Ho3+/Yb3+ ions have been investigated in terms of structural and spectroscopic properties. To reduce OH⁻ ions content and improve transmittance value at the wavelength of 3.1 µm, the glass synthesis has been carried out in low vacuum conditions (45-65 mBar). The composition of the host glass based on heavy metal oxides affects the maximum phonon energy (hωmax = 724 cm-1), which low value has a positive impact on the mid-infrared emission parameters. Emission band at the wavelength of 2.87 µm was observed in glass co-doped with mol% 0.25 Ho₂O₃/0.75 Yb₂O₃ under 980 nm high power laser diode wavelength excitation. Lifetime measurements of the Yb3+:²F5/2 quantum level indicate efficient Yb3+ → Ho3+ energy transfer (η = 61%). The developed active bismuth-germanate glass was used as the core of optical fibre operating in the mid-infrared region.
Keywords: 2.87 µm luminescence; Ho3+/Yb3+; bismuth-germanate glass; heavy metal oxide; mid-infrared emission; optical active fibre.