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 ⁴I_11/2 → ⁴I_13/2, ⁴F_9/2 → ⁴I_9/2 and ⁴I_9/2 → ⁴I_11/2 transitions, respectively. Temperature-dependent fluorescence spectra and decay times were recorded for the ⁴I_9/2 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 ⁴I_9/2 → ⁴I_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 × 10⁻²⁰ cm² at room temperature and 0.21 × 10⁻²⁰ cm² at 77 K.

中文翻译：

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用于中红外激光的低声子掺ErBaF ₂单晶的光谱表征

我们介绍了掺有Er ³⁺离子的低最大声子能主体材料，氟化钡（BaF ₂）的光谱性质。在800nm处，二以下的光学激发³⁺：的BaF ₂表现出广泛的中红外发射带为中心在~2.75，〜3.5，和~4.5微米，对应于⁴我_11/2 → ⁴我_13/2，⁴ ˚F _9/2 → ⁴余_9/2和⁴余_9/2 → ⁴我_11/2过渡，分别。记录了⁴ I _9/2能级的随温度变化的荧光光谱和衰减时间，该能级在〜800 nm处共振激发。利用众所周知的能隙定律推导了几个紧密间隔的Er ³⁺跃迁的多声子衰变率，确定了与主体相关的能隙定律参数B和α为9.15×10 ⁸ s ^-1和5.58×10 ^-3 cm。所获得的参数随后用于描述的温度范围内12的~4.5微米的中红外发光寿命的温度依赖性- 300 K的刺激的发射横截面⁴余_9/2 →^据我们所知，Er ³⁺离子的⁴ I _11/2跃迁是首次得出，据我们所知，室温下为0.11×10 ^-20 cm ²，室温为0.21×10 ^-20厘米²在77 K.