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

Abstract

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 ∼2.75, ∼3.5, and ∼4.5 µm, corresponding to the 4I11/2 → 4I13/2, 4F9/2 → 4I9/2 and 4I9/2 → 4I11/2 transitions, respectively. Temperature-dependent fluorescence spectra and decay times were recorded for the 4I9/2 level, which was resonantly excited at ∼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 α were determined to be 9.15 × 108 s−1 and 5.58 × 10−3 cm, respectively. The obtained parameters were subsequently used to describe the temperature dependence of the ∼4.5 µm mid-IR emission lifetime in a temperature range of 12 - 300 K. The stimulated emission cross-section of the 4I9/2 → 4I11/2 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 × 10−20 cm2 at room temperature and 0.21 × 10−20 cm2 at 77 K.