Magneto-optical borogermanate glasses and fibers containing Tb³

New glass compositions containing high concentrations of Tb³⁺ ions were developed aiming at the production of magneto-optical (MO) fibers. This work reports on the structural and MO properties of a new glass composition based on (100 - x)(41GeO₂-25B₂O₃-4Al₂O₃-10Na₂O-20BaO) - xTb₄O₇. Morphological analysis (HR-TEM) of the sample with the highest concentration of Tb³⁺ ions confirmed the homogeneous distribution of Tb³⁺ ions and the absence of nanoclusters. All the samples presented excellent thermal stability against crystallization (ΔT > 100 °C). An optical fiber was manufactured by a fiber drawing process. The UV-Vis spectra of the glasses showed Tb³⁺ electronic transitions and optical windows varying from 0.4 to 1.6 μm. The magneto-optical properties and the paramagnetic behaviors of the glasses were investigated using Faraday rotation experiments. The Verdet constant (V_B) values were calculated at 500, 650, 880, 1050, 1330, and 1550 nm. The maximum V_B values obtained at 650 and 1550 nm for the glass with x = 18 mol% were -128 and - 17.6 rad T^-1 m^-1, respectively. The V_B values at 500 and 1550 nm for the optical fiber containing 8 mol% of Tb₄O₇ were - 110.2 and - 9.5 rad T^-1 m^-1, respectively, while the optical loss at around 880 nm was 6.4 dB m^-1.