Pb5(GeO4)(Ge2O7) and Pb3.32Ca1.68(GeO4)(Ge2O7): Two Nonlinear Optical Germanates Induced by Diverse PbOx Polyhedra

Pentanary Oxythiogermanates Ba3MGe3O2S8 (M = Ca, Zn) Featuring [Ge3O2S8]8- Trimers and {[MGe3O2S8]6-}∞ Chains: Structural Chemistry and Physical Properties

Oxychalcogenides are increasingly attracting wide attention because they contain multiple anions that may combine the advantages of oxides and chalcogenides. In this work, two new pentanary oxythiogermanates, Ba3MGe3O2S8 [M = Ca (1), Zn (2)], were synthesized by a high-temperature solid-state reaction. They crystallize in the orthorhombic space group Pnma, and their structures contain isolated [Ge3O2S8]8- units constructed by one [GeO2S2] and two [GeOS3] tetrahedra that link with M2+ ions to build the {[MGe3O2S8]6-}∞ chain, representing a new type of oxythiogermanate. Notably, a [ZnS5] square pyramid exists in 2. Their structural chemistry and relationship with relevant structures are analyzed. 1 and 2 exhibit wide band gaps of 3.93 and 2.63 eV, birefringences of 0.100 and 0.089 at 2100 nm, respectively, and also obvious photocurrent responses. This work may be extended to a family of AE3MIIMIV3O2Q8 (AE = alkali-earth metal; MII = Ca, Zn, Cd, Hg; MIV = Si, Ge, Sn; Q = S, Se), and further systematic survey on them can be performed to enrich the study of multifunctional oxychalcogenides.

Li13YGe4O16: A Mid-infrared Rare-Earth Germanate Nonlinear Optical Crystal Featuring a Broad Transmission Range and an Enlarged Band Gap

Germanate is garnering increasing attention in the field of optoelectronics owing to its competitive optical transparency and robust stability. Herein, a novel lithium-rich rare-earth germanate, Li13YGe4O16, was fabricated for the first time using a high-temperature solution approach. This compound adopts the asymmetric space group Cmc21 (no. 36), characterized by isolated [YO6] and [GeO4] structural motifs with Li+ cations located in the channel. Notably, Li13YGe4O16 presents a short ultraviolet cutoff edge at 240 nm, indicative of an enlarged band gap of 4.96 eV and showcases a wide mid-infrared transmission region exceeding 6.0 μm. Moreover, Li13YGe4O16 features exceptional thermal stability and moderate second harmonic generation (SHG) intensity. Additionally, a theoretical analysis suggests that the distorted [YO6] octahedra. [GeO4] and [LiO4] tetrahedra play a significant role in the optical activities of Li13YGe4O16. These attributes endow Li13YGe4O16 with the potential to serve as a new mid-IR nonlinear optical (NLO) crystal and enrich the structural chemistry of germanates.

The first quaternary rare-earth oxythiogermanate with second-harmonic generation and ferromagnetic behavior

The discovery of new functional materials is attractive since they have the opportunity to change some important fields. Of these materials, oxychalcogenides constitute an increasing type of nonlinear optical (NLO) material. Herein, a new rare-earth oxythiogermanate Eu₃GeOS₄ crystallizing with a polar orthorhombic Pca2₁ structure is studied. Its three-dimensional structure is constructed from unique [EuOS₆] monocapped trigonal prisms and isolated [GeOS₃] tetrahedra, featuring a new type of oxysulfides. Its band gap is 2.05 eV, and it exhibits obvious second-harmonic generation (SHG) response and high laser-induced damage threshold. In addition, Eu₃GeOS₄ exhibits Curie-Weiss ferromagnetic behavior in the high-temperature region. The SHG effect is ascribed to the synergistic effect of [EuOS₆] and [GeOS₃] units based on theoretical calculation results. This work is the first investigation of quaternary rare-earth oxythiogermanates as NLO materials.

The First UV Nonlinear Optical Selenite Material: Fluorination Control in CaYF(SeO3 )2 and Y3 F(SeO3 )4

It is a great challenge to develop UV nonlinear optical (NLO) material due to the demanding conditions of strong second harmonic generation (SHG) intensity and wide band gap. The first ultraviolet NLO selenite material, Y₃ F(SeO₃ )₄ , has been obtained by control of the fluorine content in a centrosymmetric CaYF(SeO₃ )₂ . The two new compounds represent similar 3D structures composed of 3D yttrium open frameworks strengthened by selenite groups. CaYF(SeO₃ )₂ has a large birefringence (0.138@532 nm and 0.127@1064 nm) and a wide optical band gap (5.06 eV). The non-centrosymmetric Y₃ F(SeO₃ )₄ can exhibit strong SHG intensity (5.5×KDP@1064 nm), wide band gap (5.03 eV), short UV cut-off edge (204 nm) and high thermal stability (690 °C). So, Y₃ F(SeO₃ )₄ is a new UV NLO material with excellent comprehensive properties. Our work shows that it is an effective method to develop new UV NLO selenite material by fluorination control of the centrosymmetric compounds.

Pb2Cl2(HPO3)(H2O) and Pb3Br2(HPO3)2: Two Phosphite Halides with 3D Structural Networks and Enlarged Birefringence

Compounds constructed by mixed anions are widely favorable for their diverse crystal structures and physical performances. Here, two lead phosphite halides, Pb₂Cl₂(HPO₃)(H₂O) (1) and Pb₃Br₂(HPO₃)₂ (2), were obtained by facile hydrothermal reactions. Both compounds crystallize in the space group Pnma. 1 exhibits a 3D structure composed of HPO₃ units, PbCl₄O₃ pentagonal bipyramids, and PbO₃ pyramids. 2 also shows a 3D framework built by HPO₃ units, PbO₂Br₄ octahedron, PbO₅ and PbO₃Br₂ square pyramids. By introducing halogen anions to the lead phosphite system, 1 and 2 show enhanced birefringences of 0.083 and 0.072 at 1064 nm, respectively, compared with 0.023@1064 nm for Pb₂(HPO₃)₂. In this work, syntheses, crystal structures, optical properties, and theoretical calculation results have been studied in detail.