Microwave hydrothermal synthesis and white up-conversion emission of NaGd(WO4)2:(Yb3+/Tm3+/Ho3+) phosphors

NaGd(WO4)2:(Yb3+/Tm3+/Ho3+) phosphors were synthesized by the microwave hydrothermal process. In the synthesis, different amounts of glycerine were added. The samples were characterized by XRD, SEM, and fluorescence spectrometer. The XRD and SEM results indicate that the different amounts of glycerine in the synthesis have no obvious influence on crystallites, but have obvious influence on sizes. Under the 980 nm excitation, NaGd(WO4)2:(Yb3+/Tm3+/Ho3+) phosphors show three emission bands peaking at 476, 542 and 656 nm. The CIE chromaticity coordinates suggest that all samples show white light emission. Based on the luminescent properties of samples, the possible mechanisms for the white UC emission are speculated.