Structural and optical characterization of Er3+/Yb3+-doped LiNbO3

We report the dependence of the unit-cell parameters and the extraordinary and ordinary refractive indices of Er/Yb-codoped LiNbO3 crystals. Both properties depend in a non-monotonic manner on the Er/Yb content. A singularity was observed at concentrations of 1.1-1.2 mol.% in the crystal (0.6-0.7 mol.% in the melt). In the same way the Er and Yb concentration influences the periodically poled lithium niobate formation. The observed behavior of refractive indices and unit-cell parameters of Er/Yb-codoped LiNbO3 crystals could be explained in terms of the RE-ion concentration affecting the Li-vacancy concentration and the RE-ion positions in the crystal.