Here, the combination of the strong electropositive lithium and the most electronegative fluorine with the TeO group afforded the first lithium fluoride tellurite, namely, Li(TeO)F (P6), which was synthesized by solid-state reactions. Its structure features a novel three-dimensional anionic framework of [LiOF] composed of LiOF and LiO tetrahedra with one-dimensional hexagonal tunnels of 12-membered rings along the c-axis, filled by the "isolated" ψ-TeO tetrahedra. Notably, this compound displays the largest band gap of 4.75 eV among all of the non-centrosymmetric metal-tellurites reported so far, as well as strong second harmonic generation (SHG) responses (3 × KHPO @1064 nm, 0.2 × β-BaBO @532 nm) and a large laser damage threshold (73 × AgGaS). Furthermore, theoretical calculations reveal that the LiO and LiOF tetrahedra also contribute significantly to the SHG response (∼30%).

Er3+/Yb3+/Pr3+: SrGdGa3O7 crystal was firstly grown by Czochralski method. Detailed spectroscopic analyses of Er3+/Yb3+/Pr3+: SrGdGa3O7 were carried out. Besides better absorption characteristic, the spectra of Er3+/Yb3+/Pr3+: SrGdGa3O7 show weaker up-conversion and near-infrared emissions as well as superior mid-infrared emission in comparison to Er3+: SrGdGa3O7 and Er3+/Yb3+: SrGdGa3O7 crystals. Furthermore, the self-termination effect for Er3+ 2.7 μm laser is suppressed successfully because the fluorescence lifetime of the 4I13/2 lower level of Er3+ decreases markedly while that of the upper 4I11/2 level changes slightly in Er3+/Yb3+/Pr3+: SrGdGa3O7 crystal. The sensitization effect of Yb3+ and deactivation effect of Pr3+ ions as well as the energy transfer mechanism in Er3+/Yb3+/Pr3+: SrGdGa3O7 crystal were also studied in this work. The introduction of Yb3+ and Pr3+ is favorable for achieving an enhanced 2.7 μm emission in Er3+/Yb3+/Pr3+: SrGdGa3O7 crystal which can act as a promising candidate for mid-infrared lasers.

In this paper, we reported a multiwavelength passively Q-switched Yb 3 :GdAl 3 BO 3 4 solid-state laser with topological insulator Bi 2 Te 3 as a saturable absorber (SA) for the first time, to the best of our knowledge. Bi 2 Te 3 nanosheets were prepared by the facile solvothermal method. The influence of three Bi 2 Te 3 densities on the laser operation was compared. The maximum average output power was up to 57 mW with a pulse energy of 511.7 nJ. The shortest pulsewidth was measured to be 370 ns with 110 kHz pulse repetition rate and 40 mW average power. The laser operated at three wavelengths simultaneously at 1043.7, 1045.3, and 1046.2 nm, of which the frequency differences were within the terahertz wave band. Our work suggests that solvothermal synthesized Bi 2 Te 3 is a promising SA for simultaneously multiwavelength laser operation.

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