Emission characteristics of near-stoichiometric Er∕Yb-codoped LiNbO3 crystals

Abstract

Polarized visible, near-infrared, and 980-nm up-conversion emission characteristics in near-stoichiometric Z-cut Er(0.6mol%)∕Yb(0.3mol%)-codoped LiNbO3 crystals, prepared by vapor-transport-equilibration (VTE) technique, were investigated and discussed in comparison with corresponding as-grown crystal, thermally calcined ErNbO4 powder, as well as Z-cut only Er(2.0mol%)-doped LiNbO3 crystal that was subjected to the same VTE procedure as one of the Er∕Yb-codoped crystals. The VTE-induced crystalline phase transformation is discussed in combination with optical absorption results reported previously. The percentage of Er3+ ions present in the crystals as the ErNbO4 phase is evaluated based upon the optical absorption and the emission data at 1.5μm. An empirical expression for evaluating the Li composition in a near-stoichiometric Er(/Yb)-doped LiNbO3 crystal from the narrowing percentage of the σ- or α-polarized 1530nm emission peak is established based upon the emission spectra of singly Er-doped VTE LiNbO3 crystals. From the measured absorption band areas and the Judd-Ofelt theory, the influence of the VTE treatment on the Er3+ spectroscopic property was studied. The experimentally observed VTE effect on the emission intensity is conducted with the theoretical results of the transition probability. Both the theoretical and experimental results reveal that the VTE treatment results in the lengthening of the 1.5μm lifetime as much as 15%. A mechanism that the VTE treatment induces the crystalline phase transformation and the reduction of both OH− and intrinsic defect contents is proposed to explain the VTE effect on the lifetime.