Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Passivated nanoparticles of europium(III)-doped yttrium, lanthanum and gadolinium oxides were synthesized by a modified sol-gel method and their luminescent properties were studied. The passivation of the nanoparticles surface is confirmed by infrared spectroscopy. Gadolinium and yttrium oxides crystalize as cubic phases while the lanthanum oxide has hexagonal phase. The emission spectra of the samples show broad transitions attributed to europium(III) ions probably due to structure disorder caused by the size and also by the high surface/volume ratio of the nanoparticles. The Judd-Ofelt intensity parameters were obtained from the emission spectra. The passivation of the nanoparticles surface, with trioctylphosphine oxide, does not significantly alter the values of Omega(2) and Omega(4) parameters and slightly increases the emission quantum efficiency of the nanoparticles that possesses lower values of Omega(2) parameter than bulk samples.3827942801Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)