Microwave synthesis and spectroscopic properties of ternary scheelite-type molybdate phosphors NaSrLa(MoO4)3:Er3+,Yb3+

Ternary scheelite-type molybdate NaSrLa(1-x-y)(MoO4)3:xEr3+,yYb3+ (x = y = 0, x = 0.1 and y = 0.2, x = 0.05 and y = 0.45, x = 0.2 and y = 0) phosphors were successfully synthesized by the microwave sol-gel method for the first time. Well-crystallized particles formed after the heat-treatment at 900 °C for 16 h showed a fine and homogeneous morphology with a particle size of 2-3 μm. The crystal structures were refined by the Rietveld method in space group I41/a. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under the excitation at 980 nm, the NaSrLa0.7(MoO4)3:0.1Er3+,0.2Yb3+ and NaSrLa0.5(MoO4)3:0.05Er3+,0.45Yb3+ particles exhibited a strong 525-nm emission band, a weaker 550-nm emission band in the green region and weak 655-nm, 490-nm and 410-nm emission bands in the red, blue and violet regions. The pump power dependence and Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail. The presence of Sr in NaSrLa(MoO4)3, in comparison with NaCaLa(MoO4)3 compound, leads to frequency shift mainly in the low region of Raman spectra. The MoO4 bending vibrations are most susceptible to changes in the distance between the nearest oxygen atoms in the nearest neighboring MoO4 groups.