Synthesis of CaWO_4:Er~(3+)@SiO_2 and CaWO_4:Tm~(3+)@SiO_2 nano-particles via a combustion pathway and study of their optical properties

摘要

Use of citric acid as a chelating agent and fuel, ammonium nitrate as fuel, boric acid as flux material and silica as supports, CaWO_4:Ln~(3+)@SiO_2 (Ln = Er and Tm) nanoparticles were synthesized via a combustion reaction at 800 °C. Characterization of the samples was performed by X-ray diffractometer (XRD), reflectance UV-Vis spectrophotometer, fluorescence spectrophotometer (PL) and transmission electron microscope (TEM). XRD patterns showed that tetragonal crystalline structure of scheelite and silica supports were formed, and that the formation of a silica support could enhance the luminescence intensity of CaWO_4:Ln~(3+). The reflectance UV-Vis and PL spectra indicated the broad absorption band of WO_4~(2-) groups about 240 nm, the WO_4~(2-) wide excitation band with maximum at 240 nm, a broad emission band of WO_4~(2-) with maximum about 420 nm, and characteristic emissions of Ln~(3+) ions. According to the TEM analysis, CaWO_4:Er~(3+)@SiO_2 and CaWO_4:Tm~(3+)@SiO_2 nanoparticles have almost the same morphology with average particle sizes about 50 nm.