Germanosilicate glass–ceramics for non-linear optics

Glass samples in the GeO2·SiO2·Nb2O5·K2O system, with different K2O/Nb2O5 ratios, were prepared, and glass–ceramics were obtained by controlled crystallization. Characterization included density measurements (Archimedes’ method), differential thermal analysis, X-ray diffraction (XRD), and Raman and UV–Visible spectroscopies. Crystal volume fractions were estimated from density measurements, while XRD was used to estimate the crystal size, by the Scherrer formula. XRD and Raman data showed that a K2O/Nb2O5 ratio of 1 promoted the formation of the crystalline phase K3.8Nb5Ge3O20.4 and transparent glass–ceramics could be obtained with a crystalline fraction of 79 % and an average crystal size of 19 nm, while a K2O/Nb2O5 ratio of 2 promoted the formation of KNbO3 crystalline phase, and a translucent glass–ceramic was obtained with a crystalline fraction of 27 % and a crystal size of 14 nm. The Maker fringe method was used to compare the second-harmonic generation efficiency of the glass–ceramics with a Y-cut quartz reference.