Triple molybdate scheelite-type upconversion phosphor NaCaLa(MoO4)3:Er3+/Yb3+: structural and spectroscopic properties

Abstract

Triple molybdate NaCaLa_(1−x−y)(MoO₄)₃:xEr³⁺,yYb³⁺ (x = y = 0, x = 0.05 and y = 0.45, x = 0.1 and y = 0.2, x = 0.2 and y = 0) phosphors were successfully synthesized for the first time by the microwave sol–gel method. Well-crystallized particles formed after heat treatment at 900 °C for 16 h showed a fine and homogeneous morphology with particle sizes of 2–3 μm. The structures were refined by the Rietveld method in the space group I4₁/a. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the NaCaLa_0.7(MoO₄)₃:0.1Er³⁺,0.2Yb³⁺ and NaCaLa_0.5(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 three 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.