“…Wang and Ohwaki proposed a mixed lead fluorogermanate glass from which a glass ceramic could be obtained displaying transparency comparable to the mother glass [9]. Tick and co-workers extended the work to some SiO 2 -Al 2 O 3 based compositions [10] and, during the last several years, different authors have been working with somewhat related rareearth-doped systems [11][12][13][14][15][16][17][18][19][20][21]. In all these papers, the exceptional optical properties of these new composite materials have been evaluated where the rare-earth containing bPbF 2 crystalline phase is often obtained at the nanometric scale.…”