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

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 degrees C revealed endothermic effects corresponding to the loss of free moisture, the decomposition of metal hydroxide and hydroxogroups (equivalent to Si-OH) from the silica surface. The powders calcined at 700 degrees C 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 D-5(0)-F-7(2) and magnetodipole D-5(0)-F-7(1) transition bands. For the Gd2O3-SiO2 nanopowder obtained from tetraethoxysilane, an increase in the D-5(0)-F-7(2) intensity, as well as the appearance of a second D-5(0)-F-7(1) peak were observed.

Automated summary

SiO2, Gd2O3-SiO2, and Eu2O3-SiO2 were synthesized using silicon oxide isolated from kaolin and silicon oxide obtained by hydrolysis of tetraethoxysilane. Agar-agar was added as a structure-forming agent and freeze-drying was used to obtain powders. The calcined powders are X-ray amorphous. The morphology of the samples was studied using TEM and DLS. The nanoparticles obtained from tetraethoxysilane have a smaller particle size and weaker agglomerates compared to those synthesized from kaolin. Different luminescence excitation spectra were observed for the Eu2O3-SiO2 samples synthesized using different methods.