Ba2ScBSi2O9: A Mixed-Coordination Borosilicate with a Low B/Si Ratio Exhibiting Enhanced Second Harmonic Generation Response.

Rational chemical substitution is an effective way to regulate structure and enrich property. Herein, a new noncentrosymmetric borosilicate, Ba2ScBSi2O9, was successfully synthesized by substituting CaO6 units in Ba2CaB2Si4O14 with ScO6 octahedra, with comparatively strong covalency. This substitution not only effectively prevents polymerization of the B-O groups, resulting in an intriguing structural transformation from tetrahedral-coordinated borosilicate of Ba2CaB2Si4O14 to mixed-coordinated borosilicate Ba2ScBSi2O9, but also enhances its second harmonic generation response (2 × KDP), that is nearly four times higher than its parent structure while keeping a short ultraviolet (UV) cutoff edge (λcutoff < 190 nm). In addition, the polar space group of Pca21 for Ba2ScBSi2O9 achieves its ferroelectric polarization reversal capability, which makes quasi-phase-matching technology possible to counteract the nonphase-matching caused by small birefringence of silicates. This work indicates the unique role of heterovalent substitution in regulating structure and performance, providing new insights for exploring borosilicate with versatile functionality.

La3Ga5M0.5Sn0.5O14, (M = Ge, Si): Design and Synthesis of Two Langasite Nonlinear Optical Materials with Large Second Harmonic Generation and Birefringence Induced by Distorted (Sn/M)O6 Octahedra.

Nonlinear optical (NLO) coherent light sources are widely applied in many areas of science and technology. As the core medium, the NLO material is required to have a wide transparent range, a large NLO response, and a high laser damaged threshold (LDT). It is common knowledge that langasite (La3Ga5SiO14, LGS) crystal has an underdeveloped second-harmonic generation (SHG) coefficient and a small birefringence, which seriously restrict its application in the NLO field, despite that it has a broad transmittance spectrum and a moderate LDT. Herein, we have successfully obtained novel langasite NLO crystals LGSS (La3Ga5Si0.5Sn0.5O14) and LGGS (La3Ga5Ge0.5Sn0.5O14), with short UV absorption edges of 209 and 212 nm, respectively. Incorporating heavy ions Sn4+ into the structure, a distorted BO6 octahedron was adjusted by the radius difference between Sn4+ and Si4+/Ge4+, which caused the strong SHG responses in LGSS (∼10.77 × KDP) and LGGS (∼9.23 × KDP) and increased birefringences of 0.034 and 0.025, respectively. Besides, they also had large energy band gaps (4.95 eV for LGSS, and 4.93 eV for LGGS), which allowed high LDTs with LGSS of 1.3 GW/cm2 and LGGS of 813 MW/cm2. This work demonstrates a new strategy to enhance SHG responses and birefringence for existing NLO materials and enriches langasite family crystals.

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.

Li3Na7B4P6O26: a new ultraviolet transparent congruently melting non-linear optical crystal.

The exploration of nonlinear optical crystals with ultraviolet (UV) transparent ranges and easy-to-grow large-size crystals is one of the current research interests. Herein, by combining borate and phosphate groups, a novel congruently melting alkali-mixed metal borophosphate, Li3Na7B4P6O26 (LNBPO) with UV transparency was successfully designed and synthesized using a high-temperature flux method. LNBPO crystallizes in the non-centrosymmetric (NCS) and polar orthorhombic space group Pca21 (no. 29), showcasing interesting (B2P3O13)∞ chains along the c axis. Notably, LNBPO has a moderate second harmonic generation (SHG) response (∼0.38 × KDP) and displays a wide transmission ranging from 0.22 to 3.68 µm, as measured by a [001]-oriented crystal wafer. Furthermore, a high-quality single crystal of LNBPO with sizes up to 14 × 14 × 12 mm3 was grown using the top-seeded solution growth method. The refractive indices of LNBPO were determined by applying the minimum deviation angle method. These results show that LNBPO possesses a phase-matching wavelength as short as 483 nm, indicating its potential as a new UV NLO crystal.

A bifunctional primitive strategy induces enhancements of large second harmonic generation and wide UV transmittance in rare-earth borates containing [B5O10] groups.

Strong second-harmonic generation (SHG) and a short ultraviolet (UV) cutoff edge are two crucial yet often conflicting parameters that must be finely tuned in the exploration of nonlinear optical (NLO) materials. In this study, two new rare earth borate NLO crystals, K7BaSc2B15O30 (KBSBO) and Rb21Sr3.8Sc5.2B45O90 (RSSBO), were rationally designed through a bifunctional primitive strategy to achieve an optimized balance between favorable SHG efficiency and UV transparency. As anticipated, both KBSBO and RSSBO exhibit a wide UV transparency window below 190 nm. Notably, these tailored crystals display strong SHG responses, with RSSBO achieving a remarkable enhancement in SHG efficiency (2 × KDP), surpassing that of most deep-UV rare earth borates containing [B5O10] groups known to date. Theoretical calculations and structural analyses reveal that the impressive SHG activities primarily stem from the [B5O10] groups and [ScO6] polyhedra. These findings suggest promising potential for KBSBO and RSSBO crystals as beryllium-free deep UV NLO materials.

Assembly of π-Conjugated [B3O6] Units by Mer-Isomer [YO3F3] Octahedra to Design a UV Nonlinear Optical Material, Cs2YB3O6F2.

Achieving the extreme balance of the key performance requirements is the crucial to breakthrough the application bottleneck for nonlinear optical (NLO) materials. Herein, by assembly of the π-conjugated [B3O6] functional species with the aid of structure-directing property of mer-isomer [YO3F3] octahedra, a new ultraviolet (UV) NLO material, Cs2YB3O6F2 with aligned arrangement of coplanar [B3O6] groups has been synthesized. The polar material exhibits the rare coexistence of the largest second harmonic generation response of 5.6×KDP, the largest birefringence of 0.091 at 532 nm, the shortest Type I phase-matching down to 200.5 nm and deep-ultraviolet transparency among reported acentric rare-earth borates with [B3O6] groups. Remarkably, benefiting from the enhanced bonding force among functional units [B3O6], a firm three-dimensional framework is constructed, which facilitates the growth of large crystals. This can be proved by a block shape crystal with dimensional of 6×5×4 mm3, indicating that it was a promising UV NLO crystal. This work provides a powerful strategy to design UV NLO materials with good performances.

LaMg6Ga6S16: a chemical stable divalent lanthanide chalcogenide.

Divalent lanthanide inorganic compounds can exhibit unique electronic configurations and physicochemical properties, yet their synthesis remains a great challenge because of the weak chemical stability. To the best of our knowledge, although several lanthanide monoxides epitaxial thin films have been reported, there is no chemically stable crystalline divalent lanthanide chalcogenide synthesized up to now. Herein, by using octahedra coupling tetrahedra single/double chains to construct an octahedral crystal field, we synthesized the stable crystalline La(II)-chalcogenide, LaMg6Ga6S16. The nature of the divalent La2+ cations can be identified by X-ray photoelectron spectroscopy, X-ray absorption near-edge structure and electron paramagnetic resonance, while the stability is confirmed by the differential thermal scanning, in-situ variable-temperature powder X-ray diffraction and a series of solid-state reactions. Owing to the particular electronic characteristics of La2+(5d1), LaMg6Ga6S16 displays an ultrabroad-band green emission at 500 nm, which is the inaugural instance of La(II)-based compounds demonstrating luminescent properties. Furthermore, as LaMg6Ga6S16 crystallizes in the non-centrosymmetric space group, P-6, it is the second-harmonic generation (SHG) active, possessing a comparable SHG response with classical AgGaS2. In consideration of its wider band gap (Eg = 3.0 eV) and higher laser-induced damage threshold (5×AgGaS2), LaMg6Ga6S16 is also a promising nonlinear optical material.

Pb3[O10Pb20](SiO4)4X10 (X = Cl, Br): The First Pb-Containing Halogen Silicates with Mirror-Symmetric Pseudo-Aurivillius Bilayers.

Two new congruently melting Pb-containing halogen silicates, Pb3[O10Pb20](SiO4)4X10 (X = Cl, Br), have been synthesized using a high-temperature solution method. Their crystal structures were determined by single-crystal X-ray diffraction, and both compounds crystallize in the orthorhombic space group Cmca. In both structures, the mirror-symmetric bilayer composed of Pb-O polyhedra is observed for the first time in Pb-containing silicates and belongs to α-PbO derivatives and is related to the Aurivillius phase. Thermal behavior analysis, UV-vis diffuse-reflectance spectroscopy, and IR spectroscopy were also performed. The Pb3[O10Pb20](SiO4)4Cl10 matrix was doped with Eu3+ ions as a dopant, and its potential application in fluorescence was confirmed from the resulting orange-red emission.

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.

Cs3In(In4Se7)(P2Se6): A Multi-Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting.

Non-centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro-optical technologies, yet their rational structural design remains a significant challenge. Here, we report a "group grafting" strategy for designing the first multi-chromophore selenophosphate, Cs3In(In4Se7)(P2Se6), that crystallizes in a NCS and polar space group of Cm. The structure features a unique basic building unit (BBU) [In(In4Se10)(P2Se6)], formed through "grafting [In4Se10] supertetrahedra on the root of [In(P2Se6)2] groups". Theoretical calculations confirm that this [In(In4Se10)(P2Se6)] BBU can achieve a "1+1>2" combination of properties from two chromophores, [In4Se10] supertetrahedron and ethane-like [P2Se6] dimer. That makes Cs3In(In4Se7)(P2Se6) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS2), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 µm), a significant birefringence (0.26 @1064 nm) as well as the congruently-melting property at ~700 °C. Therefore, Cs3In(In4Se7)(P2Se6) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that "group grafting" will be an effective strategy for constructing novel polar BBUs with multi-chromophore to design NCS structures and high-performance IR NLO materials.

From NaGa(IO3)3F to NaGa(IO3)2F2 and NaGa(IO3)4: The Effects of Chemical Substitution between F- Anions and IO3- Groups on the Structures and Properties of Gallium Iodates.

Introducing F- anions or substituting F- anions with IO3- groups has been proven to be ideal strategies for designing novel noncentrosymmetric (NCS) and polar materials, yet systematic investigation into the effect of F- anions or the substitution of IO3- for F- anions on structures and properties remains rarely explored. Herein, two new gallium iodates, NaGa(IO3)2F2 (1) and NaGa(IO3)4 (2), were successfully designed and synthesized based on NaGa(IO3)3F by introducing more F- anions and replacing F- anions with IO3 groups, respectively. Structurally, in compound 1, the adjacent [GaF3(IO3)3]3- polyanions are connected in an antiparallel manner, resulting in a complete cancellation of local polarity. While in compound 2, all IO3 groups in 2D [Ga(IO3)4]∞- layers are aligned, leading to large macroscopic polarization. Additionally, chemical substitution also results in a qualitative improvement in the functional properties of compound 2. It possesses strong SHG response (12 × KDP @1064 nm) and broad optical transparency, coupled with large birefringence (0.21 @1064 nm), showcasing its promise as a promising nonlinear optical (NLO) crystal. The effects of chemical substitution between F- anions and IO3- groups on the structures and properties are discussed in detail.

Rb8Nb10Ge6O41: a new niobium-germanate crystal featuring unique one-dimensional [Nb7O30]∞ chains and wide mid-IR transparency.

Germanate oxides have garnered considerable interest owing to their diverse structural configuration and intriguing properties. Herein, we present a novel niobium germanate crystal, Rb8Nb10Ge6O41, extracted through the process of spontaneous crystallization. It showcases a unique three-dimensional (3D) structural framework composed of one-dimensional (1D) twisted [Nb7O30]∞ chains and isolated [Ge3O9] rings, arising from the divergent polymerized manifestations of [NbO6] and [GeO4] basic building blocks, respectively, marking the first instance of such a topography in germanate materials. Notably, the title compound exhibits exceptional thermal stability up to 1250 °C with a good congruent melting nature. Moreover, it achieves a short ultraviolet edge at 306 nm and a favorable infrared edge cutoff exceeding 6.2 µm, thus indicating a wide transparency window. Additionally, this study elucidates the microscopic birefringence of Rb8Nb10Ge6O41 and clarifies the intricate relationship between its structure and properties. Our findings suggest that the polymerization of distinct structural motifs within a single compound is an effective strategy for exploring novel inorganic materials.

KNa2Lu(BO3)2: A Rare-Earth Borate Crystal Characterized by an Enhanced Birefringence and Wide Ultraviolet Transparency Range.

Borate materials are of significant interest due to their versatile structural configuration and competitive ultraviolet (UV) transparency range. In this study, we present a novel rare-earth borate crystal, KNa2Lu(BO3)2, synthesized for the first time through a facile spontaneous crystallization method. It adopts the centrosymmetric space group Pnma (no. 62) and yields a unique three-dimensional (3D) structural network formed by isolated [BO3] plane triangles and distorted [LuO7] polyhedra. This compound displays excellent thermal stability up to ∼990 °C, demonstrating a favorable congruent melting nature. Moreover, KNa2Lu(BO3)2 achieves a notably short UV absorption cutoff at approximately 204 nm, yielding a large band gap of 5.58 eV. Remarkably, it showcases an enlarged birefringence of 0.044 at 1064 nm, implying its potential as a birefringent material. Moreover, density functional theory calculations demonstrate that the optical characteristics are predominantly influenced by fundamental building blocks [BO3] triangles and distorted [LuO7] polyhedra. Our findings demonstrate the potential of KNa2Lu(BO3)2 in the development of a birefringent candidate and enrich the structural chemistry of rare-earth-based borates.

LiGa(IO3 )4 : An Excellent NLO Material with Unprecedented 2D [Ga(IO3 )4 ]∞ - Layer Synthesized by Aliovalent Substitution.

Nonlinear optical (NLO) crystals are indispensable for the solid-state lasers for their ability to expand wavelength spectral to the regions where the directing lasing is difficult or even impossible, yet the rational design of a high-performance NLO crystal remains a great challenge owing to the severe structural and properties' requirements. Herein, a new noncentrosymmetric (NCS) and polar gallium iodate, LiGa(IO3 )4 , with a novel 2D anionic layer, is successfully designed and synthesized by the aliovalent substitution strategy based on classic α-LiIO3 . The 2D [Ga(IO3 )4 ]∞ - layer in LiGa(IO3 )4 is built from the GaO6 octahedra and highly polarizable units IO3 . Compared with its parent compound, the partial replacement of A-site Li+ cation with main group Ga3+ cation facilitates LiGa(IO3 )4 to possess excellent NLO properties, including the large second-harmonic generation (SHG) response (14 × KH2 PO4 (KDP) @ 1064 nm), wide bandgap (4.25 eV), large birefringence (0.23 @ 1064 nm), and wide optical transparency from UV to mid-IR. These reveal that LiGa(IO3 )4 will be a promising NLO crystal.

Chiral and Polar Duality Design of Heteroanionic Compounds: Sr18 Ge9 O5 S31 Based on [Sr3 OGeS3 ]2+ and [Sr3 SGeS3 ]2+ Groups.

Chirality and polarity are the two most important and representative symmetry-dependent properties. For polar structures, all the twofold axes perpendicular to the principal axis of symmetry should be removed. For chiral structures, all the mirror-related symmetries and inversion axes should be removed. Especially for duality (polarity and chirality), all of the above symmetries should be broken and that also represents the highest-level challenge. Herein, a new symmetry-breaking strategy that employs heteroanionic groups to construct hourglass-like [Sr3 OGeS3 ]2+ and [Sr3 SGeS3 ]2+ groups to design and synthesize a new oxychalcogenide Sr18 Ge9 O5 S31 with chiral-polar duality is proposed. The presence of two enantiomers of Sr18 Ge9 O5 S31 is confirmed by the single-crystal X-ray diffraction. Its optical activity and ferroelectricity are also studied by solid-state circular dichroism spectroscopy and piezoresponse force microscopy, respectively. Further property measurements show that Sr18 Ge9 O5 S31 possesses excellent nonlinear optical properties, including the strong second harmonic generation efficiency (≈2.5 × AGS), large bandgap (3.61 eV), and wide mid-infrared transparent region (≈15.3 µm). These indicate that the unique microstructure groups of heteroanionic materials are conducive to realizing symmetry-breaking and are able to provide some inspiration for exploring the chiral-polar duality materials.

Rational Design of a Niobium Tellurite Crystal Nb2Te3O11 Exhibiting Good Overall Infrared NLO Performance by Structural Genetic Engineering.

Nonlinear optical (NLO) materials have aroused increasing interest owing to their promising applications in optoelectronic technologies. Herein, we present the synthesis of an acentric niobium tellurite crystal, Nb2Te3O11, extracted via a spontaneous crystallization approach. It adopts a unique three-dimensional (3D) structure constructed by the distorted [TeO3], [TeO4], and [NbO6] fundamental building units. The title compound undergoes incongruent melting at approximately 807 °C. Optical characterizations demonstrate that Nb2Te3O11 possesses an extended transparency window beyond 5 µm, along with a large band gap value of 3.1 eV. Moreover, the as-synthesized Nb2Te3O11 displays an appreciable second-harmonic generation (SHG) response of 2 × KDP and a notable birefringence of 0.11 under 1064 nm for achieving phase-matching. In addition, theoretical calculation investigations suggest that the intriguing optical properties are ascribed to the cooperative effect of three types of NLO-active motifs: [TeO3] pyramids, [TeO4] seesaws, and [NbO6] octahedra. These attributes provide new functional insights into Nb2Te3O11 and enrich the family of NLO crystals in the mid-infrared region.

Tailored Synthesis of Two Metal Borates KSrM3B2O9 (M = Al and Ga) Exhibiting Wide Ultraviolet Transparency.

Borate materials continue to command considerable attention due to their remarkable capacity for applications in deep ultraviolet (UV) wavelengths. Herein, two new metal borates KSrM3B2O9 (M = Al and Ga) were extracted via the application of flux techniques. These two crystals adopt a centrosymmetric space group P21/c (no. 14), showcasing a layered structural configuration composed of isolated [BO3] plane triangles and [AlO4]/[GaO4] tetrahedra. Thermal analysis revealed that KSrM3B2O9 (M = Al and Ga) exhibits an incongruent nature and possesses good thermal stability up to 1083 and 983 °C, respectively. Notably, these compounds display a short UV-transmission cutoff edge, approximately around 194 and 200 nm, accompanied by band gaps of 5.47 and 4.83 eV, respectively. Furthermore, KSrM3B2O9 (M = Al and Ga) demonstrates a moderate optical birefringence of 0.026 and 0.025, respectively. Additionally, first-principles calculations were employed to shed light on the intricate interplay between the structure and properties of these compounds.

Effective Faraday rotator based on the TbYO3 crystal with a high Verdet constant and a high thermal conductivity.

Facing the demand of high-power laser development, a high-quality magneto-optical crystal with a high Verdet constant and a high thermal conductivity is needed. Herein, an effective Faraday rotation based on a TbYO3 single crystal with a strong magneto-optical effect, grown by the laser floating zone method, is demonstrated for the first time, to the best of our knowledge. The TbYO3 crystal has the Verdet constant which is 2.16 times (106 rad·m-1 T-1) higher than that of the TGG crystal (49 rad·m-1 T-1) at 880 nm. Additionally, the TbYO3 crystal also has a thermal conductivity of 11.8 W·m-1·K-1 and a laser-induced damage threshold of 1.59 GW·cm-2. These advantages can allow the TbYO3 crystal to be an attractive magneto-optical material.

Improving the Luminescence Performance of Monolayer MoS2 by Doping Multiple Metal Elements with CVT Method.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) draw much attention as critical semiconductor materials for 2D, optoelectronic, and spin electronic devices. Although controlled doping of 2D semiconductors can also be used to tune their bandgap and type of carrier and further change their electronic, optical, and catalytic properties, this remains an ongoing challenge. Here, we successfully doped a series of metal elements (including Hf, Zr, Gd, and Dy) into the monolayer MoS2 through a single-step chemical vapor transport (CVT), and the atomic embedded structure is confirmed by scanning transmission electron microscope (STEM) with a probe corrector measurement. In addition, the host crystal is well preserved, and no random atomic aggregation is observed. More importantly, adjusting the band structure of MoS2 enhanced the fluorescence and the carrier effect. This work provides a growth method for doping non-like elements into 2D MoS2 and potentially many other 2D materials to modify their properties.

Rational Design of Noncentrosymmetric Organic-Inorganic Hybrids with a π-Conjugated Pyridium-Type Cation for High Nonlinear-Optical Performance.

Organic-inorganic hybrid materials have attracted increasing attention due to their unique superiority by combining the features of organic parts with inorganic parts. Herein, two organic-inorganic hybrid nonlinear-optical crystals, [C5H6O2N3]2[IO3]2 (I) and [C5H6O2N3][HSO4]·H2O (II), were successfully synthesized in aqueous solution by selecting 2-amino-3-nitropyridine as the cation and different anions of [IO3]- and [HSO4]-. The two compounds crystallized in the noncentrosymmetric space groups of P21 and P212121, respectively. I displays second-harmonic-generation (SHG) effects of 2.4 × KDP (KH2PO4) and a large birefringence (Δncal ∼ 0.22). Moreover, II exhibits a stronger SHG response of 5.2 × KDP, an enhanced band gap (2.81 eV), as well as a large birefringence (Δncal ∼ 0.25). This work points out a new feasible path for the rational design of high-performance organic-inorganic hybrid materials.