Synthesis and luminescent properties of nanoparticles GdCaAl3O7:RE3+ (RE=Eu, Tb) via the sol–gel method

By using metal nitrates as starting materials and citric acid as complexing agent, GdCaAl3O7:Eu3+ and GdCaAl3O7:Tb3+ powder phosphors were prepared by a citrate-gel method. Thermal analysis (TG–DTG), X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results of the XRD indicated the precursor samples began to crystallize at 800 °C and the crystallinity increased with elevation the annealing temperature. TEM images showed that the phosphor particles were basically of spherical shape, with good dispersion about a particle size of around 40–70 nm. Upon excitation with UV irradiation, it is shown that there is a strong emission at around 617 nm corresponding to the forced electric dipole 5D0–7F2 transition of Eu3+, and at around 543 nm corresponding to the 5D4–7F5 transition of Tb3+. The dependence of photoluminescence intensity on Eu3+ (or Tb3+) concentration and annealing temperature were also studied in detail.