Preparation of CaLa2(MoO4)4:Er3+/Yb3+ phosphors via the microwave-modified sol–gel route and the upconversion of their photoluminescence properties

CaLa2 − x(MoO4)4:Er3+/Yb3+ phosphors with doping concentrations of Er3+ and Yb3+ (x = Er3+ + Yb3+, Er3+ = 0.05, 0.1, 0.2 and Yb3+ = 0.2, 0.45) were successfully prepared via the microwave-modified sol–gel route, and the upconversion of their photoluminescence properties was investigated. Well-crystallized particles, formed after heat-treatment at 900 °C for 16 h, showed a fine and homogeneous morphology with particle sizes of 2–10 μm. Under excitation at 980 nm, the upconversion intensities of CaLa1.7(MoO4)4:Er0.1Yb0.2 and CaLa1.5(MoO4)4:Er0.05Yb0.45 phosphors exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region and a very weak 655-nm emission band in the red region. The Raman spectra of the particles indicated the presence of strong peaks at higher frequencies (1026, 1092 and 1316 cm−1) and weak peaks at lower frequencies (236, 288, 365, 420 and 560 cm−1) induced by the disorder of the [MoO4]2− groups with the incorporation of the Er3+ and Yb3+ elements into the crystal lattice or by a new phase formation.