AbstractThe 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.