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

Nanocrystalline CaWO 4 and Eu 3+ (Tb 3+)-doped CaWO 4 phosphor layers were coated on non-aggregated, monodisperse and spherical SiO 2 particles by the Pechini sol-gel method, resulting in the formation of SiO 2 @CaWO 4 , SiO 2 @CaWO 4 :Eu 3+ /Tb 3+ core-shell structured particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL), low-voltage cathodoluminescence (CL), time-resolved PL spectra and lifetimes were used to characterize the core-shell structured materials. Both XRD and FT-IR indicate that CaWO 4 layers have been successfully coated on the SiO 2 particles, which can be further verified by the FESEM and TEM images. The PL and CL demonstrate that the SiO 2 @CaWO 4 sample exhibits blue emission band with a maximum at 420 nm (lifetime = 12.8 µs) originated from the WO 2− 4 groups, while SiO 2 @CaWO 4 :Eu 3+ and SiO 2 @CaWO 4 :Tb 3+ show additional red emission dominated by 614 nm (Eu 3+ : 5 D 0-7 F 2 transition, lifetime = 1.04 ms) and green emission at 544 nm (Tb 3+ : 5 D 4-7 F 5 transition, lifetime = 1.38 ms), respectively. The PL excitation, emission and time-resolved spectra suggest that there exists an energy transfer from WO 2− 4 to Eu 3+ and Tb 3+ in SiO 2 @CaWO 4 :Eu 3+ and SiO 2 @CaWO 4 :Tb 3+ , respectively. The energy transfer from WO 2− 4 to Tb 3+ in SiO 2 @CaWO 4 :Tb 3+ is more efficient than that from WO 2− 4 to Eu 3+ in SiO 2 @CaWO 4 :Eu 3+ .