Reversible colour changes in phosphoniobate glasses - Barbosa, A. J.; Gonçalves, R. R.; Dias Filho, F. A.; Shibuya, R. H.; Donoso, José Pedro; Magon, Claudio José; Messaddeq, Y.; Ribeiro, S. J. L. (International Symposium on Non-Crystalline Solids - ISNCS, 2005)