'Er POT. 3+' doped phosphoniobate glasses and planar waveguides: structural and optical properties - Barbosa, A. J.; Dias Filho, F. A.; Maia, L. J. Q.; Messaddeq, Younnes; Ribeiro, S. J. L.; Gonçalves, Rogéria Rocha (Journal of Physics Condensed Matter, 2008)