Optical and structural properties of Er doped Si'O IND.2'-Ge'O IND.2'-'Al IND.2''O IND.3' gels, nanopowders and waveguides through the Sol-Gel process - Maia, Lauro J. Q.; Faria Filho, Fausto M.; Gonçalves, Rogéria Rocha; Ribeiro, Sidney J. L. (International Sol-Gel Conference, 2011)