2 μm mid-infrared optical spectra of Tm3+-doped germanium gallate glasses

Glasses with the composition of 65GeO2-12Ga2O3-10BaO-8Li2O-5La2O3 (molar ratio) doped with 1.526 wt.%, 3.006 wt.%, 5.836 wt.%, 11.028 wt.%, and 15.678 wt.% Tm2O3, respectively, were fabricated by conventional melting method. According to the absorption spectra and the Judd-Ofelt theory, the J-O strength parameters (Ω2, Ω4, Ω6) were calculated, with which the radiative transition probabilities, branching ratios and radiative lifetimes were obtained. The infrared emission spectra (with 808 nm LD excitation) at ∼1.47 and ∼1.8 μm of various concentrations of Tm3+-doped glasses were studied. The emission intensity at ∼1.8 μm reached to the maximum when the Tm2O3-doping concentration was near to be ∼3.006 wt.% (1.0 mol.%), and then decreased as doping concentration increased further. The mechanism of the fluorescence intensity change was explained with the cross-relaxation effect and the concentration quenching effect of Tm3+. Meanwhile, according to McCumber theory, the absorption and emission cross-sections corresponding to the 3F4→3H6 transitions of Tm3+ at 1.8 μm was obtained. For Tm3+-doped germanate glasses, the maximum emission cross-section reached a value higher than that reported for fluorozircoaluminate glasses. It is expected to be a favorable candidate host for ∼2.0 μm mid-infrared laser because the glass shows favorable optical spectra.