Effect of anionic group[SiO_(4)]^(4-)/[PO_(4)]^(3-) on the luminescence properties of Dy^(3+)-doped tungstate structural compounds

Novel scheelite structures of Li_(2)Ca(WO_(4))_(2),Li_(2)Ca_(2)(WO_(4))(SiO_(4)),and LiCa_(2)(WO_(4))(PO_(4))fluorescent materials were successfully prepared using a high-temperature solid-phase process.The compounds were characterized by X-ray diffraction and energy dispersive spectroscopy.The tests revealed that the substitution of[WO_(4)]^(2-)by[SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron in tungstate had no significant influence on the crystal structure of the Li_(2)Ca(WO_(4))_(2).When Dy^(3+) ions were introduced as an activator at an optimum doping concentration of 0.08 mol%,all of the as-prepared phosphors generated yellow light emissions,and the emission peak was located close to 576 nm.Replacing[WO_(4)]^(2-) with [SiO_(4)]^(4-) or [PO_(4)]^(3-) tetrahedron significantly increased the luminescence of the Li_(2)Ca(WO_(4))_(2) phosphors.Among them,the LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor had the best luminescence properties,decay life(r=0.049 ms),and thermal stability(87.8%).In addition,the as-prepared yellow Li_(2)Ca(WO_(4))_(2):0.08Dy^(3+),Li_(2)Ca_(2)(WO_(4))(SiO_(4)):0.08Dy^(3+),and LiCa_(2)(WO_(4))(PO_(4)):0.08Dy^(3+) phosphor can be used to fabricate white light emitting diode(LED)devices.