Spectroscopic characterization of low-phonon Er-doped BaF2 single crystal for mid-IR lasers

We present spectroscopic properties of the low-maximum-phonon energy host material, barium fluoride (BaF2) doped with Er3+ ions. Following optical excitation at 800 nm, Er3+:BaF2 exhibited broad mid-IR emission bands centered at similar to 2.75, similar to 3.5, and similar to 4.5 mu m, corresponding to the I-4(11/2) -> I-4(13/2), F-4(9/2) -> I-4(9/2) and I-4(9/2) -> I-4(11/2) transitions, respectively. Temperature-dependent fluorescence spectra and decay times were recorded for the I-4(9/2) level, which was resonantly excited at similar to 800 nm. The multi-phonon decay rates of several closely spaced Er3+ transitions were derived using the well-known energy-gap law, and the host-dependent energy-gap law parameters B and a were determined to be 9.15 x 10(8) s(-1) and 5.58 x 10(-3) cm, respectively. The obtained parameters were subsequently used to describe the temperature dependence of the similar to 4.5 mu m mid-IR emission lifetime in a temperature range of 12 - 300 K. The stimulated emission cross-section of the I-4(9/2) -> I-4(11/2) transition of Er3+ ion was derived for the first time among the known fluoride hosts, to the best of our knowledge, and found to be 0.11 x 10(-20) cm(2) at room temperature and 0.21 x 10(-20) cm(2) at 77 K. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement