Fabrication and photoluminescence properties of core-shell structured spherical SiO2@Gd2Ti2O7:Eu3+ phosphors

A sol-gel technique was used to prepare Gd2Ti2O7:Eu3+-coated submicron silica spheres (SiO2@Gd2Ti2O7:Eu3+). The resulted SiO2@Gd2Ti2O7:Eu3+ core-shell particles were characterized by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive x-ray spectra (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, as well as kinetic decays. The XRD results demonstrate that the Gd2Ti2O7:Eu3+ layers begin to crystallize on the SiO2 spheres after annealing at 800 degrees C and the crystallinity increases with raising the annealing temperature. The obtained core-shell phosphors have perfect spherical shape with narrow size distribution (average size similar to 620 nm), non-agglomeration, and smooth surface. The thickness of the Gd2Ti2O7:Eu3+ shells on the SiO2 cores could be easily tailored by varying the number of deposition cycles (60 nm for four deposition cycles). Under the irradiation of 310 nm ultraviolet, the SiO2@GdTi2O7:Eu3+ samples show strong emission of Eu3+. For the samples annealed from 600 to 800 degrees C, the emission is dominated by 613 nm red emission ascribed to D-5(0)-F-7(2) transition of Eu3+, while for those annealed from 900 to 1000 degrees C, the emission is dominated by 588 nm orange emission due to D-5(0)-F-7(1) transition of Eu3+. The PL intensity of Eu3+ increases with increasing the annealing temperature and the number of coating cycles.