Mid-infrared emission properties of the Tm3+-doped sesquioxide crystals Y2O3, Lu2O3, Sc2O3 and mixed compounds (Y,Lu,Sc)2O3 around 1.5-, 2- and 2.3-μm

Tm3+-doped sesquioxides Y2O3, Lu2O3 and Sc2O3 are well known for their emissions around 2 μm (3F4 →3H6 transition). We study here their absorption and emission properties, both at 2 μm and at 1.5 μm (3H4 → 3F4) and 2.3 μm (3H4 → 3H5), by considering that the totality of the Tm3+ ions or only part of them are contributing to the line intensities. The study is also extended to the Tm3+-doped mixed compounds LuYO3, LuScO3 and YScO3. The results obtained in terms of radiative lifetimes and branching ratios, as derived from a Judd-Ofelt analysis of the absorption data, thus appear to be more consistent with the measured fluorescence decays, by assuming that only 75% of the Tm3+ ions, those sitting into C2 symmetry sites, are involved in the absorption and the emission spectra. The registered emission spectra are then calibrated in cross section unit and some of them compared between each other depending on the method (reciprocity, modified reciprocity or Füchtbauer method) which is used. Calculations are finally carried out to predict the cross section of important excited-state transitions which are involved in the two-step excitation pumping of the 3H4 emitting level around 1.05 μm (3F4 → 3F2,3) and 1.45 μm (3F4 → 3H4).