Sol-gel fabrication and photoluminescence properties of SiO ₂@Gd ₂O ₃:Eu ³⁺ core-shell particles

A uniform nanolayer of europium-doped Gd ₂O ₃ was coated on the surface of preformed submicron silica spheres by a Pechini sol-gel process. The resulted SiO ₂@Gd ₂O ₃:Eu ³⁺ core-shell structured phosphors were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL) spectra as well as kinetic decays. The XRD results show that the Gd ₂O ₃:Eu ³⁺ layers start to crystallize on the SiO ₂ spheres after annealing at 400 °C and the crystallinity increases with raising the annealing temperature. The core-shell phosphors possess perfect spherical shape with narrow size distribution (average size: 640 nm) and non-agglomeration. The thickness of the Gd ₂O ₃:Eu ³⁺ shells on the SiO ₂ cores can be adjusted by changing the deposition cycles (70 nm for three deposition cycles). Under short UV excitation, the obtained SiO ₂@Gd ₂O ₃:Eu ³⁺ particles show a strong red emission with ⁵D ₀- ⁷F ₂ (610 nm) of Eu ³⁺ as the most prominent group. The PL intensity of Eu ³⁺ increases with increasing the annealing temperature and the number of coating cycles.