Triple-Kagomé-Layer Slabs of Mixed-Valence Rare-Earth Ions Exhibiting Quantum Spin Liquid Behaviors: Synthesis and Characterization of Eu9MgS2B20O41

Na2CeF6: A Highly Laser Damage-Tolerant Double Perovskite Type Ce(IV) Fluoride Exhibiting Strong Second-Harmonic Generation Effect

Perovskite structure compounds are significant candidates for designing new optical function materials due to their structural variability. Here, an inorganic tetravalent cerium fluoride, Na2CeF6, is derived from the perovskite structure through double-site cation co-substitution. Na2CeF6 crystalizes in the non-centrosymmetric space groupP 6 ¯ 2 m ${P}^{\bar{6}}2m$ . Edge-sharing connected NaF9 and CeF9 polyhedra build the whole 3D structure of Na2CeF6. Importantly, it represents the first Ce(IV) fluoride nonlinear optical (NLO) crystal and can produce a strong and phase-matchable second-harmonic generation (SHG) effect of ≈2.1 times that of KH2PO4 (KDP), making it the strongest among non-lone pair electron metal fluoride system. Further, it exhibits a high laser-induced damage threshold (LIDT) of 74.65-76.25 MW cm-2, which is over 20 times that of AgGaS2. It also exhibits a wide transparent region (0.5-14.3 µm). This work provides a facile route for exploring high-performance halide NLO materials.

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.

A Non-π-Conjugated Molecular Crystal with Balanced Second-Harmonic Generation, Bandgap, and Birefringence

Traditional nonlinear optical (NLO) crystals are exclusively limited to ionic crystals with π-conjugated groups and it is a great challenge to achieve a subtle balance between second-harmonic generation, bandgap, and birefringence for them, especially in the deep-UV spectrum region (Eg  > 6.20 eV). Herein, a non-π-conjugated molecular crystal, NH3 BH3 , which realizes such balance with a large second-harmonic generation response (2.0 × KH2 PO4 at 1064 nm, and 0.45 × β-BaB2 O4 at 532 nm), deep-UV transparency (Eg > 6.53 eV), and moderate birefringence (Δn = 0.056@550 nm) is reported. As a result, NH3 BH3 exhibits a large quality factor of 0.32, which is evidently larger than those of non-π-conjugated sulfate and phosphate ionic crystals. Using an unpolished NH3 BH3 crystal, effective second-harmonic generation outputs are observed at different wavelengths. These attributes indicate that NH3 BH3 is a promising candidate for deep-UV NLO applications. This work opens up a new door for developing high-performance deep-UV NLO crystals.

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.

Mixed Alkali Metal and Alkaline Earth Metal Scandium Borate Birefringence Material with Layered Structure and Short Ultraviolet Cutoff Edge

Birefringent crystals are essential in the domains of linear and nonlinear optics that need light wave polarization control. Rare earth borate has become a popular study material for ultraviolet (UV) birefringence crystals due to its short cutoff edge in the UV area. RbBaScB₆O₁₂, a two-dimensional layered structure compound with the B₃O₆ group, was effectively synthesized through spontaneous crystallization. The UV cutoff edge of RbBaScB₆O₁₂ is shorter than 200 nm, and the experimental birefringence is 0.139 @ 550 nm. Theoretical research indicates that the large birefringence originates from the synergistic impact of the B₃O₆ group and the ScO₆ octahedron. RbBaScB₆O₁₂ is an outstanding candidate material for birefringence crystals in the UV and even deep UV regions due to its short UV cutoff edge and significant birefringence.

Na4[B6O9 (OH)3](H2O) Cl: A Deep-Ultraviolet Transparent Nonlinear Optical Borate Chloride with {[B6O9 (OH)3]3-}∞ Chains

The development of nonlinear-optical (NLO) crystals with short ultraviolet cutoff edges is significant and challenging. Here, a new sodium borate chloride, Na₄[B₆O₉ (OH)₃](H₂O) Cl, was successfully obtained by the mild hydrothermal method, which crystallizes in a polar space group Pca2₁. The structure of the compound is characterized by {[B₆O₉ (OH)₃]^3-}_∞ chains. Measurements of optical properties indicate the compound exhibits a deep-ultraviolet (DUV) cutoff edge (≤200 nm) and moderate second harmonic generation response (0.4 × KH₂PO₄). It presents the first DUV hydrous sodium borate chloride NLO crystal and the first sodium borate chloride possessing a one-dimensional B-O anion framework. Probing into the connection of structure and optical properties has been performed based on theoretical calculations. These results are instructive for designing and obtaining new DUV NLO materials.

Luminescence Properties of Green Phosphor Ca2Ga2(Ge1-xSix)O7:y%Eu2+ and Application

Rare earth luminescent materials demonstrate significant advantages in lighting and energy saving, and detection etc. In this paper, a series of Ca₂Ga₂(Ge_1-xSi_x)O₇:y%Eu²⁺ phosphors were synthesized by high-temperature solid-state reaction and characterized by X-ray diffraction and luminescence spectroscopy methods. The powder X-ray diffraction patterns reveal that all the phosphors are isostructural with a space group of P4¯21m. The excitation spectra of Ca₂Ga₂(Ge_1-xSi_x)O₇:1%Eu²⁺ phosphors exhibit significant overlapping of the host and the Eu²⁺ absorption bands, which facilitates Eu²⁺ absorbing the energy to increase its luminescence efficiency when excited by visible photons. The emission spectra show that the Eu²⁺ doped phosphors have a broad emission band with a peak centered at 510 nm arising from the 4f⁶5d¹→4f⁷ transition. Variable temperature fluorescence reveals that the phosphor has a strong luminescence at low temperature but has a severe thermal quenching effect when temperature rises. The optimal Ca₂Ga₂(Ge_0.5Si_0.5)O₇:1.0%Eu²⁺ phosphor shows promise for application in the field of fingerprint identification based on the experimental results.

Mixed Rare-Earth Chalcogenide Borate Eu9-xRExMgS2B20O41 (RE = Sm, Gd) Featuring a 3D {[B20O41]22-}∞ Framework Connected by [B6O9(O0.5)6]6- and [B7O13(O0.5)3]8- Clusters

Rare-earth (RE) chalcogenide borates are very rarely discovered in view of the difficulties in synthesis though they have demonstrated attractive physical performances. Here, the first mixed RE chalcogenide borates Eu_5.4Sm_3.6MgS₂B₂₀O₄₁ (1) and Eu₃Gd₆MgS₂B₂₀O₄₁ (2) are synthesized by combining RE, sulfur, and borate ions into one structure. They crystallize in the centrosymmetric hexagonal space group P6₃/m, and their 3D honeycomb-like {[B₂₀O₄₁]^22-}_∞ open frameworks are built by [B₆O₉(O_0.5)₆]^6- and [B₇O₁₃(O_0.5)₃]^8- polyanionic clusters and consolidated by Mg²⁺ ions; both of which are formed by BO₄ tetrahedra and BO₃ planar triangles. The coordination modes of RE ions are rare REO₆S₂ bicapped trigonal prisms and REO₈S irregular polyhedra, and their band gaps are determined to be 2.25 and 2.22 eV, respectively. They exhibit antiferromagnetic interactions and distinct photocurrent responses. The corresponding theoretical calculations are also performed. The study of 1 and 2 perhaps stimulates interest in exploring new functional RE chalcogenide borates.

Eu2 P2 S6 : The First Rare-Earth Chalcogenophosphate Exhibiting Large Second-Harmonic Generation Response and High Laser-Induced Damage Threshold

Metal chalcogenophosphates are receiving increasing interest, specifically as promising infrared nonlinear optical (NLO) candidates. Here, a rare-earth chalcogenophosphate Eu₂ P₂ S₆ crystallizing in the monoclinic noncentrosymmetric space group Pn was synthesized using a high-temperature solid-state method. Its structure features isolated [P₂ S₆ ]^4- dimer, and two types of EuS₈ bicapped triangular prisms. Eu₂ P₂ S₆ exhibits a phase-matchable second-harmonic generation (SHG) response ≈0.9×AgGaS₂ @2.1 μm, and high laser-induced damage threshold of 3.4×AgGaS₂ , representing the first rare-earth NLO chalcogenophosphate. The theoretical calculation result suggests that the SHG response is ascribed to the synergetic contribution of [P₂ S₆ ]^4- dimers and EuS₈ bicapped triangular prisms. This work provides not only a promising high-performance infrared NLO material, but also opens the avenue for exploring rare-earth chalcogenophosphates as potential IR NLO materials.

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.

Material research from the viewpoint of functional motifs

As early as 2001, the need for the ‘functional motif theory’ was pointed out to assist the rational design of functional materials. The properties of materials are determined by their functional motifs and by how they are arranged in the materials. Uncovering the functional motifs and their arrangements is crucial in understanding the properties of materials and rationally designing new materials of desired properties. The functional motifs of materials are the critical microstructural units (e.g. constituent components and building blocks) that play a decisive role in generating certain material functions, and could not be replaced with other structural units without losing or significantly suppressing the relevant functions. The role of functional motifs and their arrangements in materials with representative examples was presented. These examples could be classified into six types of material microscopic structures on a length scale smaller than ∼10 nm with maximum subatomic resolution, i.e. the crystal, magnetic, aperiodic, defect, local, and electronic structures. The method of functional motif analysis could be employed in the function-oriented design of materials, as elucidated by taking infrared nonlinear optical materials as an example. Machine learning is more efficient in predicting material properties and screening materials with high efficiency than high-throughput experimentation and high-throughput calculations. In extracting the functional motifs and finding their quantitative relationships, developing sufficiently reliable databases for material structures and properties is imperative.

KNa0.78Eu0.27In3.80B12S12: A Novel Hexanary Thioborate Featuring B12S12 Cluster and Diverse InSx (x = 4, 5, 6) Units

Thioborates combine the advantages of sulfides and borates, are a new type of multifunctional inorganic materials with versatile structural features. Here, a thioborate KNa0.78Eu0.27In3.80B12S12 crystallizing with a new structure-type was...

BaSc2(HPO3)4(H2O)2: A New Nonlinear Optical Phosphite Exhibiting 3D [Sc2(HPO3)4]2- Anionic Framework and Phase Matchable SHG Effect

Phosphite materials have aroused widely attention for their diverse open-frameworks and promising magnetic and optical performances. Here, the first barium scandium phosphite, BaSc2(HPO3)4(H2O)2, was obtained via a facile hydrothermal route....

KEu2In3B12S13: A Novel Type of Thioborate Featuring B12S12 Cluster and Unique In6S6 12-membered Ring

Both borates and sulfides are important inorganic multifunctional materials. Encouraged by this background, thioborates attract broad interest. However, their investigations are highly hindered by the available ones’ scarcity and new...

NaRbB3 O4 F3 : A New Fluorooxoborate with a Short UV Cutoff Edge Enriching the Structural Chemistry of Borate

The combination of RbB₃ O₄ F₂ and NaF generates a new member of fluorooxoborates, NaRbB₃ O₄ F₃ , with a wide transparency range from the IR to DUV region. NaRbB₃ O₄ F₃ shows a three-dimensional (3D) structure composed of 1D [B₃ O₄ F₃ ]_∞ chains, [NaO₃ F₃ ] and [RbO₅ F₅ ] polyhedra. The structural evolution from NaRbB₃ O₄ F₃ to RbB₃ O₄ F₂ , as well as the structural comparison between NaRbB₃ O₄ F₃ and its identical stoichiometry compound, Li₂ B₃ O₄ F₃ were discussed in detail. The IR spectrum verifies its structural validity. The spectral measurement shows that the reflectance has no obvious change in the range of 175-300 nm, and its cutoff edge is below 175 nm. In addition, theoretical calculations are carried out to understand its electronic structure and optical properties.

A Geometrically Frustrated Family of MIIMIIIF5(H2O)2 Mixed-Metal Fluorides with Complex Magnetic Interactions

Inverse weberites are of interest as geometrically frustrated magnetic materials due to their unique cation arrangement. We have synthesized nine isostructural materials that adopt the inverse weberite crystal structure, which consists of cross-linked kagome layers. These materials, having the general formula M^IIM^IIIF₅(H₂O)₂ (M^II = Co, Mn, Ni, Zn; M^III = Ga, Cr, Fe, V), were synthesized using mild hydrothermal conditions, which yielded phase-pure samples after optimization of the reaction conditions. Their crystal structures and optical, thermal, and magnetic behavior were characterized using single-crystal X-ray diffraction, UV-vis spectroscopy, thermogravimetric analysis, and measurement of the magnetic susceptibility and isothermal magnetization data, respectively. Three distinct types of magnetism were observed, including simple paramagnetism, antiferromagnetism, and canted antiferromagnetism; the last type is accompanied by a high frustration index fin the range 4.16-8.09. We demonstrated that the magnetic behavior of inverse weberites depends on the presence or absence of unpaired-electron-containing cations on the two distinct crystallographic sites, which can be employed for the prediction of the magnetic properties of other compounds in this rich and diverse family.

"Size or mass" which plays a role? An investigation on the optical and ultrasonic properties of chitosan-lanthanide composites

In this present exploration, chitosan doped with different lanthanide oxides such as CeO₂, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃ and Ho₂O₃ has been prepared and its optical and thermodynamical properties were studied as a function of the ion size of the lanthanide element and its atomic masses. From the refractive index measurement, the space-filling factor and polarizability have been obtained. The propagation of ultrasonic waves like ultrasonic velocity and its derived quantities such as relaxation strength (r_s), adiabatic bulk modulus (K_s), acoustic impedance (Z) and adiabatic compressibility (β) have been obtained for different Chitosan-Lanthanide oxides (Ch-LnO). FTIR studies confirm the formation of different Ch-LnO. The variation of all the said properties with ion size is opposite to that of atomic mass due to lanthanide contraction. The results are presented and discussed in a detailed manner.

Expanding the chemistry of borates with functional [BO2]- anions

More than 3900 crystalline borates, including borate minerals and synthetic inorganic borates, in addition to a wealth of industrially-important boron-containing glasses, have been discovered and characterized. Of these compounds, 99.9 % contain only the traditional triangular BO₃ and tetrahedral BO₄ units, which polymerize into superstructural motifs. Herein, a mixed metal K₅Ba₂(B₁₀O₁₇)₂(BO₂) with linear BO₂ structural units was obtained, pushing the boundaries of structural diversity and providing a direct strategy toward the maximum thresholds of birefringence for optical materials design. ¹¹B solid-state nuclear magnetic resonance (NMR) is a ubiquitous tool in the study of glasses and optical materials; here, density functional theory-based NMR crystallography guided the direct characterization of BO₂ structural units. The full anisotropic shift and quadrupolar tensors of linear BO₂ were extracted from K₅Ba₂(B₁₀O₁₇)₂(BO₂) containing BO₂, BO₃, and BO₄ and serve as guides to the identification of this powerful moiety in future and, potentially, previously-characterized borate minerals, ceramics, and glasses.

Bi2[B2(SeO3)6]: A Metal Boroselenite with a Unique Zero-Dimensional [B2(SeO3)6]6- Anionic Group and Large Birefringence

Explorations of new types of borates are important because of their promising application in diverse fields. A new bismuth-containing boroselenite, Bi₂[B₂(SeO₃)₆], has been obtained through high-temperature solid-state reaction in a closed system. Bi₂[B₂(SeO₃)₆] possesses a zero-dimensional [B₂(SeO₃)₆]^6- anionic group that does not belong to any types of reported boroselenites. Besides, Bi₂[B₂(SeO₃)₆] is the first boroselenite with lone-pair electrons containing a metal ion as the countercation. More interestingly, on the basis of the first-principles calculations, this compound displays a large birefringence (0.090) at 1064 nm.

A series of oxysulfides RE2M2S3O4 (RE = Y, Tm; M = Zr, Hf) featuring a unique MS3O4 motif and {[M2S3O4]8-}∞ wrinkle layer

Inorganic salts with multiple anions have recently received increasing interest in view of their structural diversity and multifunctional properties, and oxysulfides are one type of such salts. Here, three novel oxysulfides Y₂Zr₂S₃O₄ (1), Y₂Hf₂S₃O₄ (2), and Tm₂Z₂S₃O₄ (3) are obtained by high-temperature solid-state reactions. They crystallize with the orthorhombic space group Pbam and their three-dimensional structures featuring MS₃O₄ (M = Zr, Hf) motifs built an unprecedented {[M₂S₃O₄]^8-}_∞ wrinkle layer. Their optical band gaps are determined and 3 shows antiferromagnetic-like behavior. Theoretical calculations suggest their direct band gaps and the electron transfer between the frontier orbitals mainly occurred from S-3p and O-2p, to Y-4d and Zr-4d/Hf-5d orbitals.

Spin-frustration with two quasi-degenerated spin states of a copper(II) heptanuclear complex obtained from an amino acid ligand

The Cu(ii) heptanuclear complex (Cu7atac) was synthesised using the hydrated amino acid ligand 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (Hatac·H2O). Single crystal X-ray diffraction analysis revealed a μ3-hydroxo bridged Cu(ii) heptanuclear complex, consisting of two triangular subunits and one Cu(ii) ion as a bridge with the formula [Cu7(atac)6(μ3-OH)2(NO3)2(H2O)10](NO3)4. The magnetic behaviour of this discrete 0D complex shows strong antiferromagnetic couplings between Cu(ii) mediated by N,N bonding and an anti-anti modes of the carboxylate anion of the ligand atac-. The magnetic data were fitted considering a 3J model. To support the model used to fit the magnetic data of the Cu7atac complex, theoretical calculation methods (complete active space self-consistent field, CASSCF, density functional theory (DFT) using the UKS TPSS/Def2-TZVP//Def2-SVP level and periodic boundary conditions (PBC) using PBE/DZVP-MOLOPT-GTH) were performed to obtain the spin states, spin density map and J couplings. The theoretical results suggest that Cu7atac is a spin-frustrated complex in the ground state, in which the doublet spin state co-exists with the quartet spin state.

Co3(SeO3)(SO4)(OH)2: A Selenite-Sulfate Compound with a Distorted Kagomé Lattice

A new selenite-sulfate compound Co₃(SeO₃)(SO₄)(OH)₂ was prepared using a typical hydrothermal reaction. This compound is found to crystallize in an orthorhombic space group of Pnma, featuring a 2D distorted kagomé structure composed of linear and zigzag Co-chains, in which the magnetic ions construct different isosceles-triangles. Our results of magnetic and specific heat measurements confirm a canted antiferromagnetic order at T_N ∼ 29 K. Further, the successive field-induced metamagnetic transitions can be observed at H_c1 ∼ 1 T, H_c2 ∼ 23 T, and H_c3 ∼ 27 T, respectively. A clear magnetic hysteresis loop with a coercive field (H_c) of ∼1.4 T is also observed.

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.

Two Covalent Ultraviolet Nonlinear Optical Crystals

Nonlinear optical (NLO) crystals are the vital components of laser science and technology, as they can convert lasers in common wavelengths into new wavelength bands for ultraviolet (UV), IR, and even terahertz laser output. Known UV NLO crystals mainly focus on crystals containing cations, but covalent crystals have rarely been reported. Here we report two covalent NLO crystals, B₂ O₃ I and B₂ O₃ II. According to the first-principles calculations, B₂ O₃ I and II have extremely short absorption edges of about 134 nm and 141 nm, large NLO coefficients of d₂₂ =1.38 pm/V and d₂₄ =0.702 pm/V, as well as sufficient birefringences of 0.037 and 0.031, respectively. Notably, the absorption edges are almost the shortest among NLO crystals. Meanwhile, the NLO coefficients are evidently larger than that of another well-known covalent NLO crystal α-SiO₂ and are comparable to those of the commercial UV NLO crystal LiBO₃ with Li⁺ cation. Furthermore, the birefringences are significantly larger than that of α-SiO₂ , which are favorable to the phase matching for both crystals. These results reveal that B₂ O₃ I and B₂ O₃ II are excellent candidates for UV NLO applications. In-depth calculations are carried out to reveal the origin of excellent NLO properties. These covalent crystals provide a new direction for the research of UV NLO crystals.

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.

A highly distorted HgS4 tetrahedron-induced moderate second-harmonic generation response of EuHgGeS4

The first Eu,Hg-based chalcogenide EuHgGeS₄ exhibits phase-matchable SHG activity with an intensity ∼0.9 times that of AgGaS₂.