Upconversion photoluminescence properties of SrY2(MoO4)4:Er3+/Yb3+ phosphors synthesized by a cyclic microwave-modified sol–gel method

SrY2−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) have been successfully synthesized by a cyclic microwave-modified sol–gel method, and the upconversion photoluminescence properties have been investigated. Well-crystallized particles showed a fine and homogeneous morphology with particle sizes of 1–3 μm. Under excitation at 980 nm, SrY2(MoO4)4:Er3+/Yb3+ particles exhibited a strong 525-nm, weak 550-nm emission bands in the green region, and a very weak 655-nm emission band in the red region. The possible mechanism of the green and red emissions was discussed in detail under consideration of a two-photon process. The Raman spectra of the particles indicated the presence of strong peaks at both higher and lower frequencies.