Hydrothermal synthesis and upconversion luminescence of NaGd(WO4)2 co-doped with Ho3+ and Yb3+

The Ho3+/Yb3+ co-doped NaGd(WO4)2 phosphors with different concentrations of Yb3+ were prepared by a facile hydrothermal route. X-ray diffraction and scanning electron microscopy were used to study the structure of the samples. The upconversion (UC) emission spectra of the samples were measured under 980 nm excitation with different pumping power. Intense red luminescence at 625-675 nm, weak blue luminescence at 458-492 nm, green luminescence at 523-565 nm and near infrared luminescence at 736-770 nm emitted by Ho3+ were observed, and their emission intensities changed with the Yb3+ concentration. The transition mechanisms of the UC luminescence were also discussed.