Fabrication and photoluminescence properties of core-shell structured spherical SiO_2@Gd_2Ti_2O_7:Eu~(3+) phosphors

摘要

A sol-gel technique was used to prepare Gd_2Ti_2O_7:Eu~(3+)-coated submicron silica spheres (SiO_2@Gd_2Ti_2O_7:Eu~(3+)). The resulted SiO_2@Gd_2Ti_2O_7:Eu~(3+) 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 Gd_2Ti_2O_7:Eu~(3+) layers begin to crystallize on the SiO_2 spheres after annealing at 800 deg 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 -620 nm), non-agglomeration, and smooth surface. The thickness of the Gd_2Ti_2O7:Eu~(3+) shells on the SiO_2 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 SiO_2@Gd_2Ti_2O_7:Eu~(3+) samples show strong emission of Eu~(3+). For the samples annealed from 600 to 800 deg C, the emission is dominated by 613 nm red emission ascribed to ~5D_0-~7F_2 transition of Eu~(3+), while for those annealed from 900 to 1000 deg C, the emission is dominated by 588 nm orange emission due to ~5D_0-~7F_1 transition of Eu~(3+). The PL intensity of Eu~(3+) increases with increasing the annealing temperature and the number of coating cycles.