Study On Calcium Tungstate Spherical Luminescent Materials Doped With Rare Earth

Calcium tungstate material is self-activated material with a wide blue band. It is an excellent fluorescent material and a good matrix material as well. Critical factors that can affect the properties of luminescent material are its morphology and size. While most commercial phosphor is prepared by the high temperature solid-phase synthesis method at present, it is not only requiring a high temperature but is also hard to control the morphology of the phosphor, especially the crystal size which is not conducive to the applications of the devices. Calcium Tungstate Spherical Luminescent Materials Doped with Rare Earth with uniform size has a large specific surface area and a good density of stacking. These factors can make it possible to improve the luminescent efficiency of the material by reducing the scattering and the irregularity of the light-emitting layer.In this paper, unlike the high temperature solid-phase synthesis method, we use hydro thermal method preparing a series monodisperse spherical luminescent material of calcium tungstateat at a lower temperature160℃, such as CaWO4, CaWO4:Sm3+, CaWO4:Eu3+and CaWO4:Tb3+. We test the characterizations of its crystal structure, morphology and photology by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorescence spectra (PL) and other testing means。Based on the test results we studied the effects of different doping concentration, different reaction time and other changes in the phosphors with different rare earth doping. Most of them are related to the morphology and optical properties.First of all, we prepared blue spherical phosphor powder samples by sonochemical method and hydrothermal method. Both of the samples have formed a good spherical shape and a good structure of scheelite. But as to the crystallinity, the hydrothermal method is better than the sonochemical method, because its higher temperature and pressure can provides a good thermodynamic and kinetic conditions during the growing of the crystal. The samples have a relatively pure hue and perform well in luminescent, with emission peak located420nm, which is corresponding to the W6+-O2-charge transfer band.Secondly, we prepared CaWO4:Sm3+and CaWO4:Eu3+red spherical phosphor power samples by hydrothermal method with the scheelite tetragonal structure and a good spherical morphology. The size of the samples is about1.5μm-2μm The final emission peak is647nm and615nm respectively, corresponding to the electronic transitions of4G5/2-6H9/2of Sm3+and the electronic transitions of5D0-7F2Eu3+. Meanwhile based on the experiments of different doping concentrations, we can find that the samples of Sm3+perform best with the doping amount of6%; the samples of Eu3+perform best with the doping amount of4%.At last, we prepared CaWO4:Tb3+green spherical phosphor power samples by hydrothermal method. It has a good crystal structure with spherical morphology. The transition of5D4-7F5of Tb3+make the samples preform a strong emission at the peak of545nm. The experiments indicate that different doping concentrations and reaction time will influence its morphology and optical properties. And when the doping concentration of Tb3+is6%, we can get the best light-emitting properties with a green light emission at545nm.