Sol-gel synthesis and green upconversion luminescence in BaGd2(MoO4)4:Yb3+,Er3+ phosphors

Yb3+/Er3+ codoped BaGd2(MoO4)4 phosphor powders were prepared by the Sol-gel method and the upconversion luminescence properties were investigated in detail. Under 980 nm semiconductor laser excitation, BaGd2(MoO4)4:Yb3+,Er3+ phosphor exhibits green upconversion luminescence with peaks at 530 and 550 nm, which are due to the transitions of Er3+ (2H11/2) → Er3+ (4I15/2) and Er3+ (4S3/2) → Er3+ (4I15/2), respectively. Both of the two green emission lines are produced by populating Er3+ ions to the excited state through a two-photon process. By monitoring the intensities of the green upconversion luminescence, the optimum conditions for the Sol-gel synthesis were determined when the molar ratio of citric acid to total chelate metal cations was 2:1 and the sintering temperature was at 1073 K. The concentration quenching effect for Er3+ was found at the optimum doping concentration of 6 mol%, and the critical distance for the neighboring Er3+ was determined to be about 21.5 Å.