Intense and wide mid-infrared luminescence in bismuth-germanate glass co-doped with Ho3+/Er3+/Yb3+ ions

In this work, we focused on the possibility of obtaining intense and wide emission in the mid-infrared spectral range. The bismuth-germanate oxide glasses have been co-doped with erbium, holmium and ytterbium ions. Glasses have been synthesized in terms of high mid-infrared transmittance and low hydroxides content using low vacuum atmosphere (50-70 mBar). In order to maximize the mid-infrared luminescence, optimization of the rare earth ions content has been conducted. The highest emission intensity in the mid-IR has been observed in sample co-doped with molar concentration 0.1 Ho2O3/0.7 Er2O3/0.25 Yb2O3 under 980 nm laser diode excitation. Moreover, rare earth ions system enables to observe broadband mid-infrared luminescence in the range of 2.7-2.9 μm due to the energy transfer and emission band overlap phenomena. Furthermore, wide emission band (FWHM = 193 nm) and high energy transfer efficiency (η = 66.84%) from Yb3+ to Er3+ and Ho3+ ions are favorable from the perspective of further applications in mid-infrared fiber amplifiers and lasers.