Synthesis and characterization of 'Er IND.2''O IND.3'-'Al IND.2''O IND.3'-'Y IND.2''O IND.3'-Si'O IND.2' compounds from the sol-gel process - Mendes, A. C.; Siu Li, Máximo; Hernandes, Antônio Carlos; Carvalho, J. F.; Maia, L. J. Q. (International Sol-Gel Conference, 2009)