Sb2O2SeO3 and Sb2O(SeO3)2: Two-Layered Antimony(III) Selenites with Enhanced Birefringence.

Two antimony selenites, Sb2O2SeO3 and Sb2O(SeO3)2, were synthesized by simultaneously incorporating stereochemically active lone pair electrons containing SeO32- and Sb3+. These compounds are structured with [SbOx] polyhedra and [SeO3] units within a two-dimensional framework. Both of them exhibit cutoffs at 300 and 330 nm within the ultraviolet (UV) range and demonstrate significant birefringence, with indices of 0.069 and 0.126 at 546 nm, respectively. These properties highlight their potential as UV birefringent materials. Structural analyses and theoretical calculations reveal that their exceptional birefringence results from the synergistic interactions between SeO32- anions and Sb3+ cations.

Gradual Increase in Birefringence of Antimony Oxalates through Precise Tuning of the Sb3+/[C2O4]2- Ratio.

Birefringent crystals play a crucial role in modulating and controlling the polarization of light in the optical communication and laser industries. Recently, adopting appropriate strategies to enhance the birefringence of crystals has become a prominent area of research focus. Herein, four UV antimony oxalate birefringent crystals, namely, K5Sb2(C2O4)5.5·3H2O, BaSb(C2O4)2.5·3H2O, Na4Sb2O(C2O4)4·6H2O, and Na3Sb(C2O4)2F2·2H2O, have been successfully synthesized. These compounds feature a similar zero-dimensional (0D) cluster structure and share the same functional groups, including π-conjugated [C2O4]2- groups and Sb3+-based distorted polyhedra with stereochemically active lone pairs (SCALPs). Interestingly, we achieved a stepwise increase in birefringence by precisely controlling the Sb3+/[C2O4]2- ratio, ultimately resulting in the compound Na3Sb(C2O4)2F2·2H2O exhibiting a large birefringence (0.21@546 nm). Additionally, we confirmed that the synergistic effects between the π-conjugated [C2O4]2- groups and the distorted polyhedra based on Sb3+ are responsible for the excellent optical properties observed in the reported compounds.

Two Short-Wave UV Beryllium Selenites Exhibiting Diverse Optical Properties Stemming from Functional Group Arrangements.

The arrangement of functional groups exerts a crucial role in determining the characteristics of compounds. In this study, we synthesized two novel short-wave ultraviolet (UV) nonlinear optical (NLO) crystals: KBe2(SeO3)2(OH)·H2O and K2Be(SeO3)2. Interestingly, the two compounds show the same SeO3 triangular pyramids and K-O polyhedra. However, the two compounds exhibit distinct beryllium-oxygen anion groups: BeO3(OH) for KBe2(SeO3)2(OH)·H2O and BeO4 for K2Be(SeO3)2. This results in the SeO3 groups within the structure having different orientations, ultimately leading to the two compounds exhibiting completely different optical properties. KBe2(SeO3)2(OH)·H2O displays a large second harmonic generation (SHG) effect equivalent to 2× KH2PO4 (KDP), coupled with a large birefringence of 0.078 at 546 nm. In contrast, the SHG effect and birefringence of K2Be(SeO3)2 are only 0.33× that of KDP and 0.024 at 546 nm, respectively. Structural analyses and theoretical calculations indicate that these pronounced differences in optical properties stem from variations in the arrangement of the SeO3 functional groups. This study not only sheds light on the correlation between crystal structure and optical behavior but also presents a hopeful avenue for the advancement of materials in the short-wave UV spectrum.

Two Short-Wave UV Antimony(III) Sulfates Exhibiting Large Birefringence.

In the present work, we have successfully obtained two new UV antimony-based sulfates, NH4Sb(SO4)2 and Ca2Sb2O(SO4)4, by a conventional hydrothermal method. Interestingly, both compounds share similar structural building blocks, such as SbO4 seesaws and SO4 tetrahedra, yet they endow discrepant birefringence values measured at 546 nm with values of 0.150 and 0.114, respectively, owing to the different distortions of the SbO4 groups with SCALP electrons. Moreover, both compounds display large band gaps (4.32 and 4.43 eV, respectively), so they can be used as short-wavelength UV birefringent materials. Moreover, NH4Sb(SO4)2 is a noncentrosymmetric compound, showing a frequency doubling effect of 0.2 × KDP. Detailed structural analyses and calculations confirm the source of superior optical performance and the reasons for the different birefringence of the two compounds. This work provides ideas for the following discovery of antimony-based optical materials with excellent properties.

Enhanced UV Nonlinear Optical Properties in Layered Germanous Phosphites through Functional Group Sequential Construction.

This study pioneers a novel strategy for synthesizing solar-blind ultraviolet (UV) nonlinear optical (NLO) crystals through functional groups sequential construction, effectively addressing the inherent trade-offs among broad transmittance, enhanced second-harmonic generation (SHG), and optimal birefringence. We have developed two innovative van der Waals layered germanous phosphites: GeHPO3, the first Ge(II)-based oxide NLO crystal which exhibits a black phosphorus-like structure, and K(GeHPO3)2Br, distinguished by its exceptional birefringence and graphene-like structure. Significantly, GeHPO3 exhibits a remarkable array of NLO properties, including the highest SHG coefficient recorded among all NLO crystals for phase-matching and generating 266 nm coherent light via quadruple frequency conversion. It delivers a potent SHG intensity, surpassing KH2PO4 (KDP) by 10.3 times at 1064 nm and ß-BaB2O4 by 1.3 times at 532 nm, complemented by a distinct UV absorption edge at 211 nm and moderate birefringence of 0.062 at 546 nm. Comprehensive theoretical analysis links these exceptional characteristics to the unique NLO-active GeO34- units and the distinctive, highly ordered layered structures. Our findings deliver essential experimental insights into the development of Ge(II)-based optoelectronic materials and present a strategic blueprint for engineering structure-driven functional materials with customized properties.

Unearthing Superior Inorganic UV Second-Order Nonlinear Optical Materials: A Mineral-Inspired Method Integrating First-Principles High-Throughput Screening and Crystal Engineering.

Natural minerals, with their adaptable framework structures exemplified by perovskite and lyonsite, have sparked substantial interest as potential templates for the design of advanced functional solid-state materials. Nonetheless, the quest for new materials with desired properties remains a substantial challenge, primarily due to the scarcity of effective and practical synthetic approaches. In this study, we have harnessed a synergistic approach that seamlessly integrates first-principles high-throughput screening and crystal engineering to reinvigorate the often-overlooked fresnoite mineral, Ba2 TiOSi2 O7 . This innovative strategy has culminated in the successful synthesis of two superior inorganic UV nonlinear optical materials, namely Rb2 TeOP2 O7 and Rb2 SbFP2 O7 . Notably, Rb2 SbFP2 O7 demonstrates a comprehensive enhancement in nonlinear optical performance, featuring a shortened UV absorption edge (260 nm) and a more robust second-harmonic generation response (5.1×KDP). Particularly striking is its significantly increased birefringence (0.15@546 nm), which is approximately 30 times higher than the prototype Ba2 TiOSi2 O7 (0.005@546 nm). Our research has not only revitalized the potential of the fresnoite mineral for the development of new high-performance UV nonlinear optical materials but has also provided a clearly defined roadmap for the efficient exploration of novel structure-driven functional materials with targeted properties.

Cd2 Nb2 Te4 O15 : A Novel Pseudo-Aurivillius-Type Tellurite with Unprecedented Nonlinear Optical Properties and Excellent Stability.

Oxides are emerging candidates for mid-infrared (mid-IR) nonlinear optical (NLO) materials. However, their intrinsically weak second harmonic generation (SHG) effects hinder their further development. A major design challenge is to increase the nonlinear coefficient while maintaining the broad mid-IR transmission and high laser-induced damage threshold (LIDT) of the oxides. In this study, it is reported on a polar NLO tellurite, Cd2 Nb2 Te4 O15 (CNTO), featuring a pseudo-Aurivillius-type perovskite layered structure composed of three types of NLO active groups, including CdO6 octahedra, NbO6 octahedra, and TeO4 seesaws. The uniform orientation of the distorted units induces a giant SHG response that is ≈31 times larger than that of KH2 PO4 , the largest value among all reported metal tellurites. Additionally, CNTO exhibits a large band gap (3.75 eV), a wide optical transparency window (0.33-14.5 µm), superior birefringence (0.12@ 546 nm), high LIDT (23 × AgGaS2 ), and strong acid and alkali resistance, indicating its potential as a promising mid-IR NLO material.

Two Mixed-Alkali-Metal Selenates as Short-Wave Ultraviolet Nonlinear-Optical Materials.

Two novel mixed-alkali-metal selenate nonlinear-optical (NLO) crystals, Na3Li(H2O)3(SeO4)2·3H2O (I) and CsLi3(H2O)(SeO4)2 (II), have been successfully synthesized by an aqueous solution evaporation method. Both compounds feature the unique layers constructed of the same functional moieties including SeO4 and LiO4 tetrahedra: [Li(H2O)3(SeO4)2·3H2O]∞3- layers in I and [Li3(H2O)(SeO4)2]∞- layers in II. The titled compounds display wide optical band gaps of 5.62 and 5.66 eV, respectively, according to the UV-vis spectra. Interestingly, they exhibit significantly different second-order nonlinear coefficients (0.34 × KDP and 0.70 × KDP, respectively). Detailed dipole moment calculations manifest that the large disparity can be attributed to the difference in the dipole moment of the crystallographically independent SeO4 and LiO4 groups. This work confirms that alkali-metal selenate system is an excellent candidate for short-wave ultraviolet NLO materials.

Two van der Waals Layered Antimony(III) Phosphites as UV Optical Materials.

Herein, two new Sb3+-based phosphites, Sb2O2(HPO3) (I) and Sb2O(HPO3)2 (II), were successfully obtained by ingeniously combining Sb3+-based polyhedra containing stereochemically active lone pair (SCALP) and HPO3 polar groups. Both reported compounds exhibit unique 2D van der Waals layered structures, [Sb4O4(HPO3)2]∞ and [Sb2O(HPO3)2]∞, respectively, which favors compounds with large optical anisotropy. Interestingly, the different curvatures of the two layers resulted in the two title compounds showing significantly different birefringences (0.079@546 and 0.046@546 nm, respectively). Both compounds endow wide optical band gaps (4.32 and 4.54 eV, respectively), which indicates their potential as promising ultraviolet (UV) birefringent crystals. The synthesis of the two title compounds enriched Sb3+-based phosphites in the UV region and provided guidance for the subsequent synthesis of superior optical materials.

Data Mining and Graph Network Deep Learning for Band Gap Prediction in Crystalline Borate Materials.

Crystalline borates are an important class of functional materials with wide applications in photocatalysis and laser technologies. Obtaining their band gap values in a timely and precise manner is a great challenge in material design due to the issues of computational accuracy and cost of first-principles methods. Although machine learning (ML) techniques have shown great successes in predicting the versatile properties of materials, their practicality is often limited by the data set quality. Here, by using a combination of natural language processing searches and domain knowledge, we built an experimental database of inorganic borates, including their chemical compositions, band gaps, and crystal structures. We performed graph network deep learning to predict the band gaps of borates with accuracy, and the results agreed favorably with experimental measurements from the visible-light to the deep-ultraviolet (DUV) region. For a realistic screening problem, our ML model could correctly identify most of the investigated DUV borates. Furthermore, the extrapolative ability of the model was validated against our newly synthesized borate crystal Ag3B6O10NO3, supplemented by the discussion of an ML-based material design for structural analogues. The applications and interpretability of the ML model were also evaluated extensively. Finally, we implemented a web-based application, which could be utilized conveniently in material engineering for the desired band gap. The philosophy behind this study is to use cost-effective data mining techniques to build high-quality ML models, which can provide useful clues for further material design.

Centrosymmetric Rb2Sb(C2O4)2.5(H2O)3 and Noncentrosymmetric RbSb2(C2O4)F5: Two Antimony (III) Oxalates as UV Optical Materials.

Herein, we have successfully synthesized two rubidium antimony (III) oxalates, namely, Rb2Sb(C2O4)2.5(H2O)3 and RbSb2(C2O4)F5, utilizing a low-temperature hydrothermal method. These two compounds share a similar chemical composition, consisting of Sb3+ cations with active lone pair electrons, alkali metal Rb+ ions, and planar π-conjugated C2O42- anions. However, they exhibit different symmetries, Rb2Sb(C2O4)2.5(H2O)3 is centrosymmetric (CS), while RbSb2(C2O4)F5 is noncentrosymmetric (NCS), which should be caused by the presence of F- ions. Notably, the NCS compound, RbSb2(C2O4)F5, demonstrates a moderate second-harmonic generation (SHG) response, approximately 1.3 times that of KH2PO4 (KDP), and exhibits a large birefringence of 0.09 at 546 nm. These characteristics indicate that RbSb2(C2O4)F5 holds promising potential as a nonlinear optical material for ultraviolet (UV) applications. Detailed structural analysis and theoretical calculations confirm that the excellent optical properties arise from the synergistic effects between Sb3+ cations with SCALP and planar π-conjugated [C2O4]2- groups.

Hg3(SeO3)2(SO4): A UV Nonlinear Optical Mercury Selenite Sulfate Constructed by Neat [Hg6O8(SeO3)4]∞ Layers and SO4 Tetrahedra.

A novel mercury selenite sulfate named Hg3(SeO3)2(SO4) has been successfully synthesized under a mild hydrothermal method. Hg3(SeO3)2(SO4) crystallizes in a monoclinic space group P21 and features a unique three-dimensional (3D) frame structure formed by [Hg6O8(SeO3)4]∞ layers and SO4 tetrahedra, which enables it to exhibit a comprehensive performance of a moderate second-harmonic generation (SHG) response of approximately 1.3 times that of baseline KH2PO4 (KDP), a moderate birefringence (0.118@546 nm), and a wide band gap (4.70 eV), which indicates that it has potential for application as an ultraviolet (UV) nonlinear optical material. Detailed theoretical calculations show that the Hg2+-based polyhedra with large polarizability and deformability and the SeO3 groups with stereochemically active lone pair (SCALP) electrons are the main contributors to moderate optical properties.

A2Hgx(SeO3)y (A = K, Rb, Cs): Three Alkali Metal Mercury Selenites Featuring Unique 1D [HgOm(SeO3)n]∞ Chains.

Herein, three alkali metal mercury selenites, K2Hg2(SeO3)3, Rb2Hg2(SeO3)3, and Cs2Hg3(SeO3)4, were successfully obtained by a hydrothermal method. The three compounds featured same one-dimensional (1D) [HgOm(SeO3)n]∞ chain structure that consisting of distorted Hg-O polyhedra and SeO3 triangular pyramids with stereochemically active lone pair (SCALP) electrons. Interestingly, the rich coordination environment of Hg atoms and the size difference of alkali metal cations lead to diverse arrangement of SeO3 groups, which makes them exhibit different birefringence. The band gaps of the three compounds indicate that they are potential ultraviolet (UV) optical materials. Detailed theoretical calculations demonstrate that the combined effects of SeO3 triangular pyramids and Hg-O polyhedra are responsible for the optical characteristics of the reported compounds.

Layered Perovskite-like Nitrate Cs2Pb(NO3)2Br2 as a Multifunctional Optical Material.

A novel alkali metal lead halide nitrate, Cs2Pb(NO3)2Br2, has been successfully synthesized via a hydrothermal method. Interestingly, the title compound features a distinctive Ruddlesden-Popper perovskite-like layered structure, which induces the outstanding multifunctional optical properties, including a large birefringence (0.147@546 nm) and broad light-orange emission. Detailed structural analysis and theoretical calculations revealed that the large birefringence originates from the p-π interaction between the Pb2+ cations and NO3 groups and that the excellent luminescence properties derive from the distortion of PbO4Br4 polyhedra. This work not only enriches the variant structure types of layered perovskites but also guides the further exploration of all-inorganic multifunctional optical materials.

Enhanced Second-Harmonic-Generation Response in a KH2PO4-Type Calcium Nitrate Carboxylate with Unusual Three-Dimensional Inorganic and Organic Connections.

An organic carboxylate ligand was employed in the synthesis of a nonhygroscopic nitrate-based nonlinear-optical (NLO) material. The hybrid-framework solid has unusual three-dimensional inorganic and organic connections with high thermal stability. Sharing similar structural features with the well-known NLO material KH2PO4 (KDP), this compound shows an enhanced second-harmonic-generation (SHG) response of about 1.6 times that of KDP. Theoretical calculations were carried out to reveal the origin of its SHG response.

SbHPO3F: 2D van der Waals Layered Phosphite Exhibiting Large Birefringence.

A novel antimony(III)-based phosphite, SbHPO3F, featuring a unique two-dimensional (2D) van der Waals layered structure, has been successfully designed and synthesized via the simultaneous employment of optically active moieties including SbO3F seesaw and tetrahedral HPO3 groups. Its optimized layered arrangement formed by the alternating connection of 4-membered rings (4-MRs) and 8-MRs endows the title compound with desirable optical properties including a large birefringence and short ultraviolet (UV) cutoff edge, implying that it is a potential UV birefringent material.

Corrugated 1D Hybrid Metal Halide [C6H7ClN]CdCl3 Exhibiting Broadband White-Light Emission.

Organic-inorganic hybrid metal halides (OIMHs) exhibiting white-light emission are a splendid class of emitters and are regarded as desired phosphors for solid-state lighting applications. Here we report a single-component white-light-emitting hybrid metal halide, namely, [C6H7ClN]CdCl3 (C6H7ClN = 4-(chloromethyl)pyridinium), which features a corrugated 1D anionic double chain composed of edge-shared CdCl6 octahedrons and exhibits broadband white-light emission with a photoluminescence quantum yield of 12.3% under 365 nm UV light irradiation. Density functional theory calculations and temperature-dependent emission spectral analysis unveil that the broadband emission of [C6H7ClN]CdCl3 is ascribed to self-trapped excitons. Moreover, a single-component white-light-emitting diode device with a correlated color temperature of 5214 K and color rendering index of 83.7 can be fabricated via coating [C6H7ClN]CdCl3 on a 365 nm UV light-emitting diode chip. Such a promising luminescent material provides guidance for the design and synthesis of OIMHs with unique structures and desired properties.

Homochiral Hybrid Organic-Inorganic Cadmium Chlorides Directed by Enantiopure Amino Acids.

Homochiral cadmium chlorides were prepared under mild conditions using enantiopure amino acids as structure-directing agents. They feature a lacunary hexagonal CdCl2 lattice as well as a one-dimensional perovskite structure. The coexistence of protonated and zwitterionic amino acids between cadmium chloride chains is quite rare. These compounds are nonlinear optically active solids showing a moderate second-harmonic-generation response. Theoretical calculations were performed to reveal the origin of their nonlinear-optical properties.

Enhanced Interlayer Interaction and Second-Harmonic-Generation Response in a KBe2BO3F2-Type Inorganic-Organic Hybrid Zinc Borate.

A new inorganic-organic hybrid zinc borate was prepared under hydrothermal conditions. This compound is the first KBe2BO3F2 (KBBF) derivative with zinc borate layers linked by mononegatively charged amino acids. Notably, it exhibits a relatively large second-harmonic-generation response of about 2.0 times that of KBBF and a moderate birefringence for phase matching in the UV region. The enhanced interlayer interaction was evaluated by theoretical calculations based on density functional theory.

High-Performance Sulfate Optical Materials Exhibiting Giant Second Harmonic Generation and Large Birefringence.

Discovering novel sulfate optical materials with strong second-harmonic generation (SHG) and large birefringence is confronted by a great challenge attributed to the intrinsically weak polarizability and optical anisotropy of tetrahedral SO4 groups. Herein, two superior-performing sulfate optical materials, namely, noncentrosymmetric Hg3 O2 SO4 and centrosymmetric CsHgClSO4 ⋅ H2 O, have been successfully synthesized through the introduction of a highly polarizable d10 metal cation, Hg2+ . The unique component layers in the reported compounds, [Hg3 O2 SO4 ]∞ layers in Hg3 O2 SO4 and [HgClSO4 (H2 O)] ∞ - layers in CsHgClSO4 ⋅ H2 O, induce enlarged birefringence in each sulfate. Remarkably, Hg3 O2 SO4 exhibits a very large SHG response (14 times that of KH2 PO4 ), which is the strongest efficiency among all the reported nonlinear optical sulfates. Detailed theoretical calculations confirm that the employment of highly polarizable Hg2+ is an effective strategy to design superior optical materials with large birefringence and strong SHG response.