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 F-2(7/2) -> F-2(5/2) transition. The tellurite glasses have a relatively low phonon energy (similar to 700 cm(-1)) among oxides, high refractive index (similar to 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. (C) 2010 Elsevier B.V. All rights reserved.