Abstract

Sesquioxides A₂O₃(A = Y, Lu, or Sc) are well-known laser host media for doping with rare-earth ions such as thulium (Tm³⁺) [1]. They belong to the cubic class (space group $Ia\overline{3}$) and are available both as single-crystals and transparent ceramics. The sesquioxides combine good thermal properties, low phonon energies and strong crystal-fields for the dopant ions leading to large Stark splitting of their multiplets. The latter results in broadband emission properties of these materials. Tm³⁺-doped sesquioxides are used for efficient and high-power lasers at 2 µm utilizing the ³F₄ → ³H₆ transition [1]. However, another transition of Tm³⁺ ions, ³H₄ → ³H₅, recently gained attraction, as it enables emission in the mid-infrared (MIR) at 2.3 – 2.5 µm [2]. In the present work, we aimed to assess the potential of Tm³⁺-doped sesquioxide single-crystals and ceramics for MIR laser sources, for the first time, to the best of our knowledge.

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