Fluorophosphate Glasses with High Terbium Content for Magneto-optical Applications

Fluorophosphate glasses are investigated following the composition law (1 – x )(70NaPO 3 – 30BaF 2 ) – x TbF 3 with x = 35, 40, 45, and 50 mol %. Bubble-free vitreous rods of 5 cm length and 4 mm in diameter are obtained without crystallization from 35 to 50 mol % of TbF 3 by using the conventional melt-quenching process. The maximum content of Tb 3+ ions successfully dissolved in these glasses corresponds to an ionic density of 8.88 × 10 21 ions cm –3, which is the highest value ever reported in a fluorophosphate glass matrix, to our knowledge. Thermal, structural, and optical properties were characterized respectively by DSC, Raman spectroscopy, prism coupling technique, UV–visible-NIR, and Verdet constant measurement. The increase of the terbium content from 35 to 50 mol % in the glass results in an increase of its glass transition temperature ( T g ) from 352 to 390 °C, a decrease of its thermal stability against crystallization (Δ T ) from 153 to 73 °C, and an increase of both its refractive index and Verdet constant, respectively. A maximum value of Verdet constant of −78 rad T –1 m –1 at 650 nm is measured in the sample containing 50 mol % of TbF 3 .