The effect of Mg2+ ion on the optical characteristics of rare-earth ion in CaWO4 polycrystal

Abstract

The Mg_xCa_(1-x)WO₄ polycrystals codoped with Er/Yb and Tm/Yb were prepared by the high temperature solid-state reaction method. The structural properties of Mg _x Ca_(1-x)WO₄ polycrystals codoped with Er³⁺ and Yb³⁺ ions were confirmed by the X-ray diffraction patterns. The effect of Mg²⁺ ion on the optical characteristics of Er³⁺ and Tm³⁺ ions in CaWO₄ polycrystals under 980 nm excitation was investigated. The strong blue and green upconversion emissions were observed for CaWO₄ polycrystal doped with 30 mol% Mg²⁺ ions. The Mg²⁺ ions affected the optical characteristics of Er³⁺ and Tm³⁺ ions in CaWO₄ host material through tuning the rate of cross relaxation process. Studies on the upconversion emission spectra and power pump dependence of Er/Yb:Mg_0.3Ca_0.7WO₄ polycrstals indicated that the inefficient cross relaxation processes of ⁴S_3/2 + ⁴I_15/2 → ⁴I_9/2 + ⁴I_13/2 and ⁴S_3/2 + ⁴I_15/2 → ⁴I_13/2 + ⁴I_9/2 between Er³⁺ ions were contribution to the increased green upconversion emission under 980 nm excitation.