Energy transfer processes in (Er3+–Yb3+)-codoped germanate glasses for mid-infrared and up-conversion applications

Luminescence characteristics of Er3+-activated, Yb3+-sensitised GeO2–Na2O–Nb2O5 heavy metal germanate glasses have been investigated in the context of searching active media for laser devices. Optical absorption, emission spectra and decay time measurements have been performed at room temperature on these materials. Intense 1540 nm infrared fluorescence and visible emission bands at 533, 554, and 660 nm were observed under continuous wave excitation at 980 nm.An efficient energy transfer from Yb3+ to Er3+ ions, increasing as a function of Yb3+ concentration, favours the Er3+ 1.54 μm eye-safe laser emission in these materials.The power dependence study of the upconverted emissions gives evidence of a bi-photonic process. Moreover, the Yb3+ codoping enhances the up-conversion efficiency. Decay time measurements have been examined in the purpose of elucidating the possible mechanisms involved in this process.The experimental results are in good agreement with an effective Yb3+-to-Er3+ nonradiative energy transfer.