Sm3S3BO3: The First Sulfide Borate without S–O and B–S Bonds

A Rare-Earth-Based Borate Optical Crystal with Enlarged Dihedral Angles of Distinct [BO3] Groups Exhibiting a Wide UV Transparent Range

Borates, as advanced optical materials, have garnered wide interest due to their diverse structural configurations and great potential for applications in the ultraviolet (UV) regions. Herein, we synthesized a new rare-earth borate crystal, namely, K2NaYB2O6, which is classified as one of the ABReB2O6 compounds, where A and B represent alkali metal and Re denotes rare-earth metal. K2NaYB2O6 adopts in the monoclinic space group P21/c (No. 14), showcasing a three-dimensional (3D) framework composed of a planar triangular configuration of [BO3] units and distortive [YO7] polyhedra. Notably, both dihedral angles between distinct [BO3] units reach 79.6°, which represents an unprecedented structural feature in monoclinic ABReB2O6-type crystals. Moreover, the compound has a short UV absorption edge at around 204 nm, corresponding to a wide band gap of approximately 5.67 eV. Additionally, it possesses a moderate birefringence of 0.028 at 1064 nm. Further analysis utilizing theoretical calculations suggests that the optical behaviors of K2NaYB2O6 are mainly governed by its basic structural unit [BO3] triangles and distorted [YO7] polyhedra. These findings enrich the structure chemistry of rare-earth borates and offer valuable insights for the design of optical crystals in the UV wavelength range.

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.

Rational Design of Novel Promising Infrared Nonlinear Optical Materials: Structural Chemistry and Balanced Performances

ConspectusSecond-order nonlinear optical (NLO) materials are currently a hot topic in modern solid-state chemistry and optics because they can produce coherent light by frequency conversion. Noncentrosymmetric (NCS) structure is not only the prerequisite for NLO materials but also a challengeable issue because materials tend to be centrosymmetric (CS) in terms of thermodynamical stability. Among NLO materials, an excellent infrared (IR) candidate should simultaneously meet several strict key conditions including a large NLO coefficient, high laser-induced damage threshold (LIDT), phase-matchable (PM) behavior, and so on. Achieving a balance between the large NLO effect and high LIDT is difficult, as they have contradictory requirements for chemical bonds. Considering the urgent need of the high-power IR laser market and the drawbacks of the available ones, exploring new high-performance IR NLO crystals is necessary while challenging. In this Account, we first briefly introduce the status and advancement of IR NLO crystals and emphasize the criteria of an excellent candidate. Then, we will introduce five simple methods developed by us to discover practical NLO candidates through understanding of the chemical composition-structure-NLO performance relationship. (1) A rarely investigated system with simple chemical compositions as new-type NLO crystals, namely, adducts containing S8 molecules, are developed. Combining a chairlike S8 unit with other units through van der Waals forces has successfully obtained several high-performance NLO adducts. (2) The main trend in exploring new NLO crystals is that the chemical composition is more and more diversified and the structure is more and more complex, and expensive and chemically active alkaline and alkaline earth metals are usually introduced as counter cations. In contrast, the research on systems with simple chemical compositions, simple structures, and low costs has been continuously ignored. The binary M2Q3 (M = Ga, In; Q = S, Se) family with rich acentric modifications has been systematically investigated, and they all exhibit strong SHG effects and high LIDTs. (3) We first proposed the concept of inducing CS structures transformed to NCS ones by partial cation substitution to design novel NLO crystals. Considering the huge number of CS structures in the database compared to the number of NCS structures, it is an attractive method to apply CS structures as the parents to obtain potential NLO materials via partial-substitution-induced symmetry breaking. A series of chalcogenides with high NLO performances have been successfully obtained by us in this way. (4) We investigated the first NLO-active rare earth (RE) chalcophosphates and developed this family systematically, and they demonstrate wonderful comprehensive NLO properties. (5) We created a novel mixed-anion system for NLO applications, namely, chalcogenide borates. Usually, mixed-anion compounds can engender a synergistic effect to obtain desired IR NLO properties. Our recent progress on this system suggests that chalcogenide borates are potential candidates for IR NLO applications, although the study is still in its infancy. Finally, we state the current problems of IR NLO materials and give some perspectives for their future development.

NaREP2Se6 (RE = Y, Sm, Gd-Dy): Quaternary Rare-Earth Selenophosphates with Unique 3D {[REP2Se6]-}∞ Framework Built by RESe8 and P2Se6 Motifs and Multiple Properties

Rare-earth (RE) chalcophosphates have been widely studied because of their abundant structures. Here, five new RE selenophosphates, NaREP2Se6 (RE = Y, Sm, Gd-Dy), were synthesized by a facile RE oxide-boron-selenium solid-state route. They crystallize in the triclinic P1̅ space group, featuring three-dimensional (3D) structures constructed by RESe8 and P2Se6 motifs, different from common 2D RE chalcophosphates A-RE-P2-Q6 (A = alkali metal; Q = S, Se) system. Their structural chemistry and relationship with related phases are analyzed. Both the size of A and the coordination geometry of RE have important influences on the system's structures. Their optical band gaps are tunable from 1.79 to 2.50 eV, and they exhibit diverse magnetic behaviors, including Van-Vleck-type paramagnetism, antiferromagnetism, and ferromagnetism. Their photocurrent responses and thermal stabilities are analyzed as well. Calculation results suggest that the RESe8 and P2Se6 units make a great contribution to the optical properties. This work enriches the chemistry and multifunctional properties of RE chalcophosphates.

Cation Regulation to Investigate the Chalcogenide Borate RE6Nb2MgSB8O26 (RE = La-Nd) Family

Chalcogenide borates have been developed and are considered an attractive system due to their favorable physical properties such as magnetism and nonlinear optical effects. Here, isostructural RE₆Nb₂MgSB₈O₂₆ (RE = La-Nd) compounds in the title family have been obtained through cation regulation in rare-earth and VB group metals. This family crystalizes in the centrosymmetric P3̅ space group and features 3D frameworks formed by {[Mg(NbB₄O₁₃)₂]^16-}_∞ polyanionic layers and QRE₆ octahedra. The structural chemistry was characterized and theoretical calculations were performed to understand the structural merit of this family. In addition, RE₆Nb₂MgSB₈O₂₆ possess the largest band gaps among known rare-earth chalcogenide borates, and they all show antiferromagnetic-like behaviors.

Hexagonal In2Se3: A Defect Wurtzite-Type Infrared Nonlinear Optical Material with Moderate Birefringence Contributed by Unique InSe5 Unit

The balance between second harmonic generation (SHG) intensity and laser-induced damage threshold (LIDT), together with phase-matchable behavior, is the key point for exploration of novel nonlinear optical (NLO) materials. In this work, the NLO property of defect wurtzite-type hexagonal-In₂Se₃ (γ) is extensively explored first. It exhibits a strong SHG intensity of 2.6 × AgGaS₂ (AGS) at 2.1 μm, and a high powder LIDT of 7.3 × AGS. From wurtzite to γ-In₂Se₃, the birefringence changes from 0.003 to 0.075, resulting in the phase-matchable phenomenon of γ-In₂Se₃. This is well ascribed to the contribution of the unique InSe₅ unit in γ-In₂Se₃ from the result of birefringence calculation and analysis.

A Series of Chalcogenide Borates RE6Ta2MgQB8O26 (RE = Sm, Eu, Gd; Q = S, Se) Featuring a B4O10 Cluster

New compounds with multiple anions are receiving increasing interest in view of their diverse structures and physical properties. Here we report four isostructural hexanary RE₆Ta₂MgQB₈O₂₆ (RE = Sm, Eu, Gd; Q = S, Se), belonging to the rare chalcogenide borates. Their structures feature an unprecedented [B₄O₁₀]^8- unit comprised of one BO₄ and three BO₃ units. Their 3D structures are constructed by the connection between QRE₆ octahedra and the _∞{[Mg(TaB₄O₁₃)₂]^16-} polyanionic layer. Density functional theory calculations on the electronic structure and a birefringence of 4 are also performed.

[(Ba19Cl4)(Ga6Si12O42S8)]: a Two-Dimensional Wide-Band-Gap Layered Oxysulfide with Mixed-Anion Chemical Bonding and Photocurrent Response

Mixed-anion compounds play an essential part in modern structural chemistry. In this Communication, an unprecedented hexanary oxysulfide, [(Ba₁₉Cl₄)(Ga₆Si₁₂O₄₂S₈)] (FJ-1), was synthesized at 1073 K by a standard solid-state method, which is a new phase in the AE/M^III/M^IV/O/Q/X (AE = alkaline-earth metal; M^III = group 13 metal; M^IV = group 14 metal; Q = chalcogen; X = halogen) system. FJ-1 adopts a new structure type and crystallizes in the orthorhombic system with space group Cmcm. In the structure, unique two-dimensional [Ga₆Si₁₂O₄₂S₈]^34- layers formed by the familiar [SiO₄] species and unusual heteroligand [GaO₂S₂] and [GaO₃S] tetrahedra extend the intralayer linking. Significantly, a photoelectrochemical test revealed that FJ-1 is photoresponsive under ultraviolet illumination. Moreover, density functional theory calculations were employed to gain insight into the relationship between the electronic structure and optical properties. Such work will be conducive to the structural diversity of gallium coordination chemistry by exploration of the new mixed-anion functional chalcohalides.

Synthesis and crystal structure of the rare earth borogermanate EuGeBO5

The synthesis and crystal structure of the rare earth borogermanate EuGeBO5 are reported. It is synthesized by high-temperature solid-state reaction and crystallizes in the monoclinic space group P21/c (no. 14) with the unit cell parameters a=4.8860(5), b=7.5229(8), c=9.9587(10) Å, and β=91.709(3)°. Its crystal structure features a polyanion-type layer (GeBO5)3− constructed by BO4 and GeO4 tetrahedra connected alternatingly. Eu3+ ions are located in cavities and are coordinated by eight O atoms. Various structures of the related compounds REMM′O5 (RE=rare earth metal; M=Si, Ge, and Sn; M′=B, Al, and Ga) are also discussed.

Thioborates: potential nonlinear optical materials with rich structural chemistry

This review summarizes thioborates and their structural motifs ranging from zero-dimension to three-dimension. The most commonly observed building units of these examples are planar-triangle BS₃ and tetrahedron BS₄. Thioborates possess advantages with respect to their structural diversity, optical nonlinearity, laser-induced damage threshold and transparency range, and represent potentially a rich supply of new nonlinear optical materials.

Band gap tuning from an indirect EuGa2S4 to a direct EuZnGeS4 semiconductor: syntheses, crystal and electronic structures, and optical properties

Novel EuZnGeS₄, with a direct band gap, can be obtained via simple substitution from EuGa₂S₄, with an indirect band gap.

Na6Si3S8O: the first example of a sulfide silicate exhibiting unusual tri-polymerized [Si3S8O]6−units without S–O bonds

A new sulfide silicate – Na₆Si₃S₈O – featuring novel tri-polymerized [Si₃S₈O]⁶⁻units without common S–O bonds has been verified as a promising birefringent material.

A series of pentanary inorganic supramolecular sulfides (A3X)[MB12(MS4)3] (A = K, Cs; X = Cl, Br, I; M = Ga, In, Gd) featuring B12S12 clusters

A series of multinary thiogallate- or thioindate-closo-dodecaborates synthesized by solid state reactions demonstrate second-harmonic generation behaviors.

Crystal and electronic structures, and optical and magnetic properties of novel rare-earth sulfide borates RE3S3BO3 (RE = Sm, Gd)

Systematic study of RE₃S₃BO₃ (RE = Sm, Gd) compounds with a novel structure type is demonstrated.

Crystal and electronic structures, and photoluminescence and photocatalytic properties of α-EuZrS3

Novel crystalline α-EuZrS₃ shows Eu²⁺ photoluminescence and is photocatalytically active towards the decomposition of methylene blue under visible light or simulated sunlight irradiation.

Synthesis, crystal structure and second-order nonlinear optical property of a novel pentanary selenide (K3I)[InB12(InSe4)3]

A novel pentanary selenide (K₃I)[InB₁₂(InSe₄)₃] (P6₃22) features InSe₄ tetrahedron consolidated B₁₂ icosahedron and 1-D chain constructed by InSe₆ octahedron and B₁₂Se₁₂ cluster. It is an indirect semiconductor with the energy gap of 1.15 eV and second harmonic generation-active.