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. We have also used sonochemistry to prepare nanoparticles of silica and alumina doped by 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 nm. The intensities are comparative or higher than in commercial phosphors.

nanoparticles with an average size of 5 nm were synthesized by the hydrolysis of aluminum triisopropoxide under the influence of power ultrasound (100 W/cm 2 ) and in the presence of formic or oxalic acids as peptizers, followed by calcination. The structural and morphological properties of the as-prepared precursor hydroxides and calcined nanocrystalline powders were characterized by XRD, SEM, TEM, TGA, IR, and BET. The ultrasound-driven cavitation process has been shown to affect the agglomeration of the precursor nanoparticles by condensation of interparticle hydroxyls. The oxalate anions were strongly adsorbed on the surface of the precursor nanoparticles and thus retarded the ultrasounddriven condensation of interparticle hydroxyls. Formic acid showed a lesser degree of adsorption on the surface of the precursor particles. The ultrasound-driven agglomeration of the primary particles as well as the role of organic modifiers on the microstructural properties of the precursor and the target alumina phases have been discussed.

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