Increased Er3+ upconversion in tellurite fibers and glasses by co-doping with Yb3+

We report infrared-to-visible frequency upconversion in Er3+–Yb3+ co-doped TeO2–GeO2–PbO glasses and fibers. The upconversion is investigated as a function of the co-doping with different Yb3+ concentration. We observe an increase of the green and red upconversion intensities of up to 400 times with increasing Yb3+ concentration and explain the mechanism involved in the energy transfer process. The pump source is a diode laser emitting at 980 nm in resonance with the 2F7/2 → 2F5/2 transition. The tellurite glasses have a relatively low phonon energy (∼700 cm−1) among oxides, high refractive index (∼2), large transmission window (350 nm–6500 nm) and can be easily pulled into fibers. We also characterized fibers obtained from these compositions and measured similar characteristics when compared to bulk glasses.