Borogermanate glasses with a high terbium oxide content

Glasses in Tb2O3–B2O3–GeO2 (TBG) system with high, up to 33 mol% Tb2O3 content, have been obtained, and their crystallization behavior, spectral and magneto-optical properties studied. It was found that Verdet constant V of TBG glasses for wavelength 632.8 nm reached very high values: more than 0.4 arc min/cm Oe. Transparent and colorless TBG glasses with low absorption coefficient a for working wavelength 1.064 μm were prepared by varying redox conditions of melting. It provided high magneto-optical figure of merit V/a exceeding the same option of industrial glasses. The melt temperature of TBG glasses obtained did not exceed 1450 °С. This temperature is much lower than that of silicate magneto-optical glasses, promoting homogeneity of glass melt and facilitating production of TBG optical quality glasses. The observed correlation between the Verdet constant and Tb3+ content indicates that the Borrelli's approach, explaining magneto-optical activity in glasses only by paramagnetic ion content, extends also to high concentrated rare earth oxide glasses.