Epoxide synthesis of binary rare earth oxide aerogels with high molar ratios (1:1) of Eu, Gd, and Yb

erogels containing rare earth elements are promising compounds for designing various functional materials, since they combine the properties of aerogels - high surface area and porosity, and the luminescent and catalytic properties of rare earth elements. A modified sol-gel method was developed to produce mixed rare earth oxide aerogels (Eu 2 O 3 /Gd 2 O 3 , Eu 2 O 3 /Yb 2 O 3 , and Gd 2 O 3 /Yb 2 O 3 ) with high metal to metal molar ratio (1:1) and individual (Eu 2 O 3 , Gd 2 O 3 , and Yb 2 O 3 ) aerogels. Rare earth nitrates, propylene oxide, and citric acid were used for the synthesis of monolithic halogen-free rare earth oxide aerogels. The aerogels obtained by supercritical drying in CO 2 possess mesoporous structure and high surface area (180–350 m 2 /g). Uniform distribution of elements in binary oxides was confirmed by EDX. Calcination at 600–800 °С causes crystallization of the amorphous aerogels. XRD patterns of the binary oxides after calcination corresponded to single phase cubic ( Ia3 ) structure of rare earth M 2 O 3 oxide, which indicated the formation of solid solutions. The Eu 2 O 3 /Gd 2 O 3 and Eu 2 O 3 aerogels demonstrate strong luminescence in visible region at near UV excitation, which was also observed after calcination of the aerogels at 800 °C. Graphical Abstract For the first time mixed aerogels (Eu 2 O 3 /Gd 2 O 3 , Eu 2 O 3 /Yb 2 O 3 , and Gd 2 O 3 /Yb 2 O 3 ) with high metal to metal molar ratio (1/1) were obtained by propylene oxide assisted hydrolysis of RE nitrates in presence of citric acid as a chelating agent. The aerogels after SC drying in CO 2 possess mesoporous structure with high surface area. Calcined at 600–800 °С aerogels have cubic lattice ( Ia3 ) of rare earth sesquioxide with crystallites diameter about 20–40 nm. XRD, IR spectroscopy and EDX analysis reveal uniform distribution of elements in material and formation of solid solutions after calcination of the mixed RE oxides. The Eu 2 O 3 /Gd 2 O 3 aerogels demonstrate red luminescence under near UV excitation.