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 image groups and the PL spectra showed the image wide excitation band, broad emission band of image and characteristic emissions of Ln3+ ions. The average particle sizes were determined by TEM, which are about 50 nm.