Optical band gap and photoluminescence in heavily Tb3+ doped GeO2-B2O3-SiO2-Ga2O3 magneto-optical glasses

In this study, germanium borosilicate magneto-optical (MO) glasses (GeO2-B2O3-SiO2-Ga2O3-xTb2O3) doped with different concentrations of Tb3+ ions were prepared by melt quenching technique. Structural, physical properties, optical properties and luminescent properties of obtained glasses were investigated in detail. Raman spectrum of the MO glasses shows that co-existence of trigonal [BO3], tetrahedral [BO4] and [GeO4] units were the main network structure and the increasing of Tb2O3 in glass promoted the conversion of BO3 into BO4. The aforementioned structural change observed in MO glasses as a function of Tb3+ ion concentration is reflected by the increase of glass density and decrease of molar volume. The obtained MO glasses exhibits a large of Verdet constant (at 632.8 nm) ranging from −49.98 to −120.54 Rad/T/m in a positive correlation with Tb3+ ion concentration. The value of Urbach energy (ΔE) and optical band gap (Eobg) shows a negative correlation with Tb3+ ion concentration. The luminescent intensity in 5D4 fluorescent level decreases with the increase of Tb3+ ions concentration, and the concentration quenching is found when changing the content of Tb2O3 from 15 mol% to 30 mol%.