Sol–gel synthesis and photoluminescence properties of sphericalSiO2@LaPO4:Ce3+/Tb3+ particles with a core–shell structure

Abstract

LaPO4:Ce3+ and LaPO4:Ce3+, Tb3+ phosphor layers have been deposited successfully on monodispersed and sphericalSiO2 particles of different sizes (300, 500, 900 and 1200 nm) through asol–gel process, resulting in the formation of core–shell structuredSiO2@LaPO4:Ce3+/Tb3+ particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanningelectron microcopy (SEM), transmission electron microscopy (TEM), and general and time-resolvedphotoluminescence (PL) spectra as well as lifetimes were used to characterize the resultingSiO2@LaPO4:Ce3+/Tb3+ samples. The XRD results demonstrate that theLaPO4:Ce3+,Tb3+ layers begin to crystallizeon the SiO2 templatesafter annealing at 700 °C, and the crystallinity increases on raising the annealing temperature. Theobtained core–shell phosphors have perfectly spherical shape with a narrow sizedistribution, non-agglomeration, and a smooth surface. The doped rare-earthions show their characteristic emission in the core–shell phosphors, i.e.Ce3+ 5d–4fand Tb3+ 5D4–7FJ (J = 6–3) transitions, respectively. The PL intensity of theTb3+ increased on increasing the annealing temperature and theSiO2 core particle size. The energy transfer process fromCe3+ toTb3+ inSiO2@LaPO4:Ce3+,Tb3+ core–shell particles was studied using the time-resolved emission spectra.