Spectroscopic study of Er-doped Ga 2 Ge 5 S 13 glass for mid-IR laser applications

We present mid-IR spectroscopic characterization of the low-phonon chalcogenide glass, Ga 2 Ge 5 S 13 (GGS) doped with Er 3+ ions. Under the excitation at ∼800 nm, Er 3+ :GGS exhibited broad mid-IR emission bands centered at ∼2.7, ∼3.5, and ∼4.5 µm at room temperature. The emission lifetime of the 4 I 9/2 level of Er 3+ ions in GGS glass was found to be millisecond-long at room temperature. The measured fluorescence lifetimes were nearly independent of temperature, indicating negligibly small nonradiative decay rate for the 4 I 9/2 state, as can be expected for a low-maximum-phonon energy host. The transition line-strengths, radiative lifetimes, fluorescence branching ratios were calculated by using the Judd-Ofelt method. The peak stimulated emission cross-section of the 4 I 9/2 → 4 I 11/2 transition of Er 3+ ion was determined to be ∼0.10×10 −20 cm 2 at room temperature.