Active planar waveguides based on sol-gel 'Er POT. 3+'-doped Si'O IND.2'-Zr'O IND.2' for photonic applications: morphological, structural and optical properties - Gonçalves, Rogéria Rocha; Guimarães, J. J.; Ferrari, J. L.; Maia, L. J. Q.; Ribeiro, S. J. L. (Journal of Non-Crystalline Solids, 2008)