Green Upconversion Luminescence of Li+∕Er3+∕Yb3+ Tridoped CaWO4 and Effects of Er3+ Concentration

Li + /Er 3+ /Yb 3+ tridoped CaWO 4 polycrystalline powders were prepared by a solid-state reaction method and their upconversion (UC) luminescence properties were investigated in detail. Under 980 nm laser excitation, CaWO 4 :Li + /Er 3+ /Yb 3+ powder exhibited weak red emission near 680 nm and strong green UC emission peaks at 530 and 550 nm, which were due to the transitions of Er 3+ ( 4 F 9/2 , 2 H 11/2 , 4 S 3/2 ) → Er 3+ ( 4 I 15/2 ), respectively. The optimum doping concentration of Er 3+ was investigated based on crystal structural variation and concentration quenching induced by energy transfer of cross relaxation process in CaWO 4 . Moreover, the effects of Er 3+ concentration on UC emission intensity ratios ( 4 S 3/2 → 4 I 15/2 versus 2 H 11/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 ) were studied in detail.