Silicon Oxide Modified with Gadolinium and Europium Oxides—Synthesis, Properties and Application Prospects

Abstract

The SiO₂, Gd₂O₃–SiO₂ and Eu₂O₃–SiO₂ were synthesized by two ways: using the silicon oxide isolated from kaolin and using the silicon oxide obtained by hydrolysis of tetraethoxysilane. Agar-agar (polysaccharide) was added as a structure-forming agent and the freeze-drying was used for obtaining powders. DSC and TG up to 700°С revealed endothermic effects corresponding to the loss of free moisture, the decomposition of metal hydroxide and hydroxogroups (≡Si–OH) from the silica surface. The powders calcined at 700°С are X-ray amorphous. The morphology of the samples was studied using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The hydrodynamic size of the particles synthesized from kaolin, determined using DLS method, exceeds the particle size established by TEM. The hydrodynamic size of the nanoparticles obtained from tetraethoxysilane is within the particle size determined by TEM. The agglomerates formed by particles synthesized from tetraethoxysilane are less strong than those obtained from kaolin. In the Eu₂O₃–SiO₂ system obtained using tetraethoxysilane, nanocrystallinity with a particle size of 8–40 nm was detected. The luminescence excitation spectra for the Eu₂O₃–SiO₂ samples synthesized by both ways differ in the ratio of the supersensitive ⁵D₀–⁷F₂ and magnetodipole ⁵D₀–⁷F₁ transition bands. For the Gd₂O₃–SiO₂ nanopowder obtained from tetraethoxysilane, an increase in the ⁵D₀–⁷F₂ intensity, as well as the appearance of a second ⁵D₀–⁷F₁ peak were observed.