Preparation of CaWO4:Ln3+@SiO2 (Ln=Tb, Dy and Ho) nanoparticles by a combustion reaction and their optical properties

The CaWO4:Ln3+@SiO2 (Ln=Tb, Dy and Ho) nanoparticles were synthesized via a combustion process at 800 °C, using citric acid as chelating agent and fuel, ammonium nitrate as fuel, boric acid as flux material and silica as supports. The persistent phosphor nanoparticles were characterized by X-ray diffraction (XRD), reflectance UV-vis and fluorescence spectroscopy (PL) and transmission electron microscopy (TEM) techniques. XRD patterns indicated that crystalline calcium tungstate with scheelite structure was produced. The reflectance UV-vis spectra showed the broad absorption band of WO42− groups and the PL spectra showed the WO42− wide excitation band, broad emission band of WO42− and characteristic emissions of Ln3+ ions. The average particle sizes were determined by TEM, which are about 50 nm.