Color tunability of intense upconversion emission from Er3+ –Yb3+ co-doped SiO2–Ta2O5 glass ceramic planar waveguides - Ferrari, Jefferson Luis; Lima, Karmel de Oliveira; Pecoraro, Edison; Ferreira, Rute A. S.; Carlos, Luís D.; Gonçalves, Rogéria Rocha (Journal of Materials Chemistry, 2012)