Sol–gel synthesis and characterization ofSiO2@CaWO4,SiO2@CaWO4:Eu3+/Tb3+ core–shell structured spherical particles

Abstract

Nanocrystalline CaWO4 and Eu3+ (Tb3+)-doped CaWO4 phosphor layers were coated on non-aggregated, monodisperse and sphericalSiO2 particles by the Pechini sol–gel method, resulting in the formation ofSiO2@CaWO4,SiO2@CaWO4:Eu3+/Tb3+ core–shell structured particles. X-ray diffraction (XRD), Fourier transform infraredspectroscopy (FT-IR), field emission scanning electron microscopy (FESEM),transmission electron microscopy (TEM), photoluminescence (PL), low-voltagecathodoluminescence (CL), time-resolved PL spectra and lifetimes were used tocharacterize the core–shell structured materials. Both XRD and FT-IR indicate thatCaWO4 layers have beensuccessfully coated on the SiO2 particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstratethat the SiO2@CaWO4 sample exhibits blue emission band with a maximum at 420 nm(lifetime = 12.8 µs) originatedfrom the WO42− groups, while SiO2@CaWO4:Eu3+ and SiO2@CaWO4:Tb3+ show additional red emission dominated by 614 nm(Eu3+:5D0–7F2 transition,lifetime = 1.04 ms) and greenemission at 544 nm (Tb3+:5D4–7F5 transition, lifetime = 1.38 ms), respectively. The PL excitation, emission and time-resolved spectra suggest that there exists an energytransfer from WO42− to Eu3+ and Tb3+ in SiO2@CaWO4:Eu3+ andSiO2@CaWO4:Tb3+, respectively. Theenergy transfer from WO42− to Tb3+ inSiO2@CaWO4:Tb3+ is more efficientthan that from WO42− to Eu3+ in SiO2@CaWO4:Eu3+.