Sonochemical Preparation of Nanosized Rare-Earth Oxides

3 Sonochemical Preparation of Nanosized Rare-Earth Oxides 

A long list of oxides was prepared sonochemically. Almost all the above-mentioned oxides were synthesized in organic solvents. The other oxides that will be discussed from here on were all prepared in aqueous solutions. Submicron size spheres of silica and alumina prepared by well-known methods were coated sonochemically by nanoparticles of oxides of europium and terbium using the same concentration of ions [81]. We have also used sonochemistry to prepare nanoparticles of silica and alumina doped with the same rare-earth ions for comparison. The highest luminescence intensities were observed for europium and terbium doped in nanoparticles of alumina of dimension 20-30 run. The intensities are comparable or higher than in commercial phosphors. 

The synthesis of the rare-earth oxides was as follows europium oxide was dissolved in a minimum amount of nitric acid and evaporated to dryness. The dry nitrate was dissolved in 5 mL of water. The required amount of silica microspheres was put in a beaker with 30 mL of water and the europium nitrate solution was added. The sonication was carried out for 1 h in an open beaker kept in an ice bath. 5 mL of 25% aqueous ammonia was added dropwise during the sonication. The resulting product after sonication was washed extensively with water, centrifuged, and dried under vacuum. 

The preparation of the europium oxide-doped silica nano-particles (99.0S1O2-I.OEU2O3 mol%) was different. It was also carried out by the hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of H2O, ethanol, and a europium nitrate solution. 25% aqueous ammonia was added dropwise during the sonication. In this way, europium oxide incorporated into silica particles was obtained. 

Decay time measurements of EU2O3, and Tb203 doped and coated on alumina were conducted [82]. The luminescence of the alumina substrate was found to be much shorter than that of the rare-earth oxides. Differences between the decay times of the deposited and doped materials are accounted for by the stronger guest-host interaction and the absence of concentration quenching in the doped material. 

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