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Borates have emerged as a significant resource for exploring birefringent materials in the UV frequency region. The π‐conjugated planar anions, such as the [BO3], [B2O5], and [B3O6] units, exhibiting strong polarizability anisotropy, are traditionally good structural models. Both fluorination and hydroxylation have been proven effective strategies to modulate the optical properties of the planar anions. Controlling the ratio between F and OH is the key to realizing a balanced performance between birefringence and bandgap. Based on a fluorination mechanism proposed recently, a novel hydroxyfluorooxoborate (C3N2H5)B3O3F2(OH)2 with an optimal F/OH ratio of 1/1 is synthesized. During the synthesis, another strategy known as “cation activation” is also employed, which further increases birefringence by introducing active cation units. With its superior performance, this compound exhibits a short UV cutoff edge at 214 nm and a substantial birefringence of 0.205 at 546 nm, surpassing the commercial birefringent crystal α‐BBO (0.122@532 nm). The synergy between F/OH‐ratio optimization and cation activation offers a practical methodology for developing UV birefringent materials.

The approach of synergistically combining mixed chromophores has garnered significant attention attributed to its ability to leverage the advantages of both groups and design novel nonlinear optical (NLO) materials. Herein, Sr(NO3)(NH2SO3)·H2O, a noncentrosymmetric compound, which represents the first reported nitrate sulfamate compound, is successfully designed and synthesized. The compound features zigzag [SrNO10(H2O)]∞ infinite layers, forming a honeycomb‐like graphene topology in its layered structure. The unique arrangement results in an excellent second harmonic generation response, 5.1 times that of KH2PO4, and an optimized birefringence of 0.06650 at 532 nm. In addition, the presence of interlayered covalent [NH2SO3] groups facilitates improved crystal growth habits, resulting in a large single crystal measuring 19.0 × 17.0 × 3.5 mm3. In this discovery, a new class of NLO materials is introduced and the scope of structural chemistry is significantly expanded.

Abstract Birefringent materials play indispensable roles in modulating the polarization of light and are vital in the laser science and technology. Currently, the design of birefringent materials operating in the deep-ultraviolet region (DUV, λ ≤200 nm) is still a great challenge. In this work, we developed a new DUV birefringent crystal LiBO2 based on [BO2]∞ infinite chains in the Li-B-O system, which simultaneously achieves the shortest UV cutoff edge (164 nm) and the largest birefringence (≥0.168 at 266 nm) among all the reported borate-based DUV birefringent materials. Single crystals of LiBO2 with dimensions up to Ø55 × 34 mm3 were grown by the Czochralski method, providing access to large-sized single crystal with low cost. Moreover, it has a high laser damage threshold and stable physicochemical properties. These outstanding characters unambiguously support that LiBO2 can be an excellent birefringent material for DUV application.

The design of new materials with special performances is still a great challenge, especially for the deep-ultraviolet nonlinear optical materials in which it is difficult to balance large bandgaps and strong second harmonic generation responses due to their inverse relationship. Cation variation not only influences the whole structure frameworks but also directly participates in the formation of electronic structures, both of which could lead to the uncontrollability of the properties of the designed materials. Here, a novel approach, aiming at purposeful and foreseeable material designs, is proposed to characterize the role of cations. By the verification of several series of borates, the influences of cation variation on property changes are explored systematically. Accordingly, a feasible strategy of designing deep-ultraviolet nonlinear optical materials by substituting barium for lead has been concluded, which could obviously blue-shift the ultraviolet cutoff edge and maintain the relatively strong second harmonic generation response (more than 2 times of KH2PO4), achieving the property optimization, and especially works efficiently in fluorooxoborates. The property optimization design strategy and the cation characterization method are not only helpful in exploring nonlinear optical materials but also enlightening in material design and selection.

Borates offer extended structural diversity and promise in diverse applications. Here the authors report a borate with linear BO2 units as well as NMR spectroscopy characterization that provides a quantitative basis for identification of BO2 units in polycrystalline and non-crystalline samples.

Abstract Design and fabrication of new infrared (IR) nonlinear optical (NLO) materials with balanced properties are urgently needed since commercial chalcopyrite‐like (CL) NLO crystals are suffering from their intrinsic drawbacks. Herein, the first defect‐CL (DCL) alkali‐earth metal (AEM) selenide IR NLO material, DCL‐MgGa2Se4, has been rationally designed and fabricated by a structure prediction and experiment combined strategy. The introduction of AEM tetrahedral unit MgSe4 effectively widens the band gap of DCL compounds. The title compound exhibits a wide band gap of 2.96 eV, resulting in a high laser induced damage threshold (LIDT) of ≈3.0 × AgGaS2 (AGS). Furthermore, the compound shows a suitable second harmonic generation (SHG) response (≈0.9 × AGS) with a type‐I phase‐matching (PM) behavior and a wide IR transparent range. The results indicate that DCL‐MgGa2Se4 is a promising mid‐to‐far IR NLO material and give some insights into the design of new CL compound with outstanding IR NLO properties based on the AEM tetrahedra and the structure predication and experiment combined strategy.

Abstract Understanding and exploring the functional modules (FMs) consisting of local atomic groups can promote the development of the materials with functional performances. Oxygen‐containing tetrahedral modules are popular in deep‐ultraviolet (DUV) optical materials, but their weak optical anisotropy is adverse to birefringence. Here, the fluorooxosulfate group is proved as a new birefringence‐enhanced FM for the first time. The birefringence of fluorooxosulfates can be 4.8–15.5 times that of sulfates with the same metal cations while maintaining a DUV band gap. The polarizing microscope measurement confirms the birefringence enhancement by using the millimeter crystals experimentally. The theoretical studies from micro and macro levels further reveal a novel universal strategy that the fluorine induced anisotropic electronic distribution in fluorooxo–tetrahedral group is responsible for the enhancement of birefringence. This study will guide the future discovery of DUV optical materials with enlarged birefringence.

Nonlinear optical crystals suitable for the UV spectral region could simplify short-wavelength generation and make it more efficient. Here, the authors design and demonstrate that one of two asymmetric borate polymorphs exhibits promising optical and mechanical properties for generating UV light.

Abstract Mid-Infrared nonlinear optical (Mid-IR NLO) crystals with excellent performances play a particularly important role for applications in areas such as telecommunications, laser guidance, and explosives detection. However, the design and growth of high performance Mid-IR NLO crystals with large NLO efficiency and high laser-damage threshold (LDT) still face numerous fundamental challenge. In this study, two potential Mid-IR NLO materials, Rb2LiVO4 (RLVO) and Cs2LiVO4 (CLVO) with noncentrosymmetric structures (Orthorhombic, Cmc21) were synthesized by high-temperature solution method. Thermal analysis and powder X-ray diffraction demonstrate that RLVO and CLVO melt congruently. Centimeter sized crystals of CLVO have been grown by the top-seeded solution growth method. RLVO and CLVO exhibit strong second harmonic generation (SHG) effects (about 4 and 5 times that of KH2PO4, respectively) with a phase-matching behavior at 1.064 μm, and a wide transparency range (0.33–6.0 μm for CLVO). More importantly, RLVO and CLVO possess a high LDT value (~28 × AgGaS2). In addition, the density functional theory (DFT) and dipole moments studies indicate that the VO4 anionic groups have a dominant contribution to the SHG effects in RLVO and CLVO. These results suggest that the title compounds are promising NLO candidate crystals applied in the Mid-IR region.

Abstract The conflict between beneficial layered structure for performances and layered growth habits in KBe2BO3F2 (KBBF) always restricts its practical applications. A beryllium‐free KBBF family member, Zn2BO3(OH), is explored to feature the same topological layer with KBBF by replacing [BeO3F]5− with [ZnO3(OH)]5− and excellent UV performances. It exhibits a second harmonic generation response of about 1.5 × KH2PO4 with the UV cutoff edge of 204 nm. The birefringence of Zn2BO3(OH) in the visible region is about 0.067, which is larger than those of commercial UV crystals LiB3O5, CsB3O5, and CsLiB6O10. Additionally, it has excellent thermal and water‐resistant stabilities. Owing to the removal of interlayer cations, Zn2BO3(OH) shows better growth habits than KBBF while achieving the balance between beneficial layered structure and layer tendency.

Borates have been regarded as a rich source of functional materials due to their diverse structures and wide applications. Therein, zincobrates have aroused intensive interest owing to the effective structural and functional regulation effects of the strong-bonded zinc cations. In recent decades, numerous zincoborates with special crystal structures were obtained, such as Cs3Zn6B9O21 and AZn2BO3X2 (A = Na, K, Rb, NH4; X = Cl, Br) series with KBe2BO3F2-type layered structures were designed via substituting Be with Zn atoms, providing a feasible strategy to design promising non-linear optical materials; KZnB3O6 and Ba4Na2Zn4(B3O6)2(B12O24) with novel edge-sharing [BO4]5− tetrahedra were obtained under atmospheric pressure conditions, indicating that extreme conditions such as high pressure are not essential to obtain edge-sharing [BO4]5−-containing borates; Ba4K2Zn5(B3O6)3(B9O19) and Ba2KZn3(B3O6)(B6O13) comprise two kinds of isolated polyborate anionic groups in one borate structure, which is rarely found in borates. Besides, many zincoborates emerged with particular physicochemical properties; for instance, Bi2ZnOB2O6 and BaZnBO3F are promising non-linear optical (NLO) materials; Zn4B6O13 and KZnB3O6 possess anomalous thermal expansion properties, etc. In this review, the synthesis, crystal structure features and properties of representative zincoborates are summarized, which could provide significant guidance for the exploration and design of new zincoborates with special structures and excellent performance.

A series of new infrared nonlinear optical (IR NLO) materials, LiRe3MS7 (Re = Sm, Gd; M = Si, Ge), have been successfully synthesized in vacuum-sealed silica tubes via a high-temperature solid-state method. All of them crystallize in the non-centrosymmetric space group P63 of the hexagonal system. In their structures, LiS6 octahedra connect with each other by sharing common faces to form infinite isolated one-dimensional ∞[LiS3]n chains along the 63 axis. ReS8 polyhedra share edges and corners to construct a three-dimensional tunnel structure with ∞[LiS3]n chains located inside. Remarkably, LiSm3SiS7 shows promising potential as one new IR NLO candidate, including a wide IR transparent region (0.44–21 μm), a high laser damage threshold (LDT) (3.7 × benchmark AgGaS2), and a good NLO response (1.5 × AgGaS2) at a particle size between 88 μm and 105 μm. Dipole-moment calculation was also used to analyze the origin of NLO responses for title compounds.

The exploration of high-performance mid- and far-infrared (IR) nonlinear optical (NLO) crystals is an urgent need. Herein, a new Hg-based selenide Hg7P2Se12 (HPSe) is designed and synthesized by a rigid and flexible units coupled strategy. It is interesting that in the compound, three types of NLO-active units, including linear [HgSe2], triangular [HgSe3], and tetrahedral (MSe4) (M= Hg/P) groups, simultaneously exist. It shows a wide transparency range (0.84-22.8 µm), large SHG response (1 x AGS), high laser-induced damage threshold (≈ 2 x AGS), and a large birefringence (0.102 @2090 nm). Moreover, the compound melts congruently along with good crystal growth habits, and single crystals with a maximum size of ≈ 7 x 5 x 2 mm³ are obtained. Theoretical analyses confirm that the large NLO response originates from the synergistic effects of Hg-Se units, (PSe4) and nonbonding electrons. The results indicate that HPSe is a promising mid- and far-IR NLO material, and inspire a path to finding new classes of IR NLO materials that are different from traditional chalcopyrite materials by grouping the linear, planar, and tetrahedral units. [ABSTRACT FROM AUTHOR]