ABi2(IO3)2F5 (A=K,Rb, and Cs): A Combination of Halide and Oxide Anionic Units To Create a Large Second‐Harmonic Generation Response with a Wide Bandgap

A family of nonlinear optical materials that contain the halide, oxide, and oxyhalide polar units simultaneously in a single structure, namely ABi₂(IO₃)₂F₅ (A=K ( 1 ), Rb ( 2 ), and Cs ( 3 )), have been designed and synthesized. They crystallize in the same polar space group (P 2₁) with a two‐dimensional double‐layered framework constructed by [BiF₅]²⁻ and [BiO₂F₄]⁵⁻ units connected to each other by four F atoms, in which two [IO₃]⁻ groups are linked to [BiO₂F₄]⁵⁻ unit on the same side. A hanging Bi−F bond of [BiF₅]²⁻ unit is located on the other side via ionic interaction with the layer‐inserted alkali metal ions to form three‐dimensional structure. The well‐ordered alignments of these polar units lead to a very strong second‐harmonic generation response of 12 ( 1 ), 9.5 ( 2 ), and 7.5 ( 3 ) times larger than that of potassium dihydrogen phosphate under 1064 nm laser radiation. All of them exhibited a wide energy bandgap over 3.75 eV, suggesting that they will have a high laser damage threshold.     

(NH4)Bi2(IO3)2F5: An Unusual Ammonium‐Containing Metal Iodate Fluoride Showing Strong Second Harmonic Generation Response and Thermochromic Behavior

An ammonium‐containing metal iodate fluoride compound, (NH₄)Bi₂(IO₃)₂F₅, featuring a two‐dimensional double‐layered framework constructed by [BiO₂F₅]^6? and [BiO₄F₄]^9? polyhedra, as well as [IO₃]^? groups, was successfully synthesized. The well‐ordered alignment of these SHG‐active units leads to an extraordinary strong SHG response of 9.2 times that of KDP. Moreover, this compound possesses a large birefringence (Δn=0.0690 at 589.3 nm), a wide energy band gap (E_g=3.88 eV), and a high laser damage threshold (LDT; 40.2×AgGaS₂). In particular, thermochromic behavior was observed for the first time in this type of compound. Such multifunctional crystals will expand the application of nonlinear optical materials.     

Rb3VO(O2)2CO3: A Four‐in‐One Carbonatoperoxovanadate Exhibiting an Extremely Strong Second‐Harmonic Generation Response

A nonlinear optical (NLO) carbonatoperoxovanadate, Rb₃VO(O₂)₂CO₃, was synthesized through a simple solution‐evaporation method in phase‐pure form. Single‐crystal X‐ray diffraction revealed that the structure of Rb₃VO(O₂)₂CO₃ consists of important noncentrosymmetric (NCS) chromophores, that is, π‐delocalized (CO₃)^2? groups, a second‐order Jahn–Teller (SOJT) distortive V⁵⁺ cation, and π‐localized distorted O₂^2? groups, as well as charge‐balancing polarizable Rb⁺ ions. The powder second‐harmonic generation (SHG) measurements indicated that Rb₃VO(O₂)₂CO₃ is phase‐matchable (Type I) and exhibits a remarkably strong SHG response circa 21.0 times that of potassium dihydrogen phosphate (KDP), which is the largest efficiency observed among carbonate NLO materials. First‐principles calculation analysis suggests that the extremely large SHG response of Rb₃VO(O₂)₂CO₃ is attributed to the synergistic effect of the cooperation of all the constituting NCS chromophores.     

A2SnS5: A Structural Incommensurate Modulation Exhibiting Strong Second‐Harmonic Generation and a High Laser‐Induced Damage Threshold (A=Ba,Sr)

Structural modulations have been recently found to cause some unusual physical properties, such as superconductivity or charge density waves; however, thus‐induced nonlinear optical properties are rare. We report herein two unprecedented incommensurately modulated nonlinear optical sulfides exhibiting phase matching behavior, A₂SnS₅ (A=Ba, Sr), with the (3+1)D superspace groups P2₁2₁2(00γ)00s or P2₁(α0γ)0, featuring different modulations of the [Sn₂S₇]_∞ belts. Remarkably, Ba₂SnS₅ exhibits an excellent second harmonic generation (SHG) of 1.1 times that of the benchmark compound AgGaS₂ at 1570 nm and a very large laser‐induced damage threshold (LIDT) of 8×AgGaS₂. Theoretical studies revealed that the structural modulations increase the distortions of the Sn/S building units by about 44 or 25 % in A₂SnS₅ (A=Ba, Sr), respectively, and enhance significantly the SHG compared with α‐Ba₂SnSe₅ without modulation. Besides, despite the smaller E_g, the A₂SnS₅ samples exhibit higher LIDTs owing to their smaller thermal expansion anisotropies (Ba₂SnS₅ (1.51)<Sr₂SnS₅ (2.08)<AgGaS₂ (2.97)).     

两种具有二次谐波响应的紫外透过氨基磺酸盐A(NH2SO3)(A=Li、Na)

通过简便的蒸发方法得到了2种碱金属磺酸盐非线性光学(NLO)晶体,即Li(NH₂SO₃)和Na(NH₂SO₃)。Li(NH₂SO₃)以极性空间群Pca2₁(编号29)结晶。Li(NH₂SO₃)的结构可以描述为由[LiO₄]^7-多面体通过共角连接与NH₂SO₃^-四面体相互连接而形成的三维网络。Na(NH₂SO₃)以极性空间群 P2₁2₁2₁(编号 19)结晶。Na(NH₂SO₃)的结构可以描述为由扭曲的[NaO₆]^11-八面体通过共角连接与 NH₂SO₃-四面体相互连接而形成的三维网络。紫外可见近红外光谱表明,Li(NH₂SO₃)和 Na(NH₂SO₃)分别具有 5.25 和 4.81eV 的大光学带隙。粉末二次谐波发生(SHG)测量显示,Li(NH₂SO₃)和 Na(NH₂SO₃)的 SHG 强度分别为 KH₂PO₄的 0.32 倍和 0.31倍。第一原理计算证实,非线性光学性能主要来自氨基磺酸阴离子和碱金属氧阴离子多面体的协同作用。     

两种具有二次谐波响应的紫外透过氨基磺酸盐A(NH2SO3)(A=Li、Na)

通过简便的蒸发方法得到了 2种碱金属磺酸盐非线性光学(NLO)晶体, 即 Li(NH₂SO₃)和 Na(NH₂SO₃)。Li(NH₂SO₃)以极性空间群Pca2₁(编号 29)结晶。Li(NH₂SO₃)的结构可以描述为由[LiO₄]7-多面体通过共角连接与 NH₂SO₃^-四面体相互连接而形成的三维网络。Na(NH₂SO₃)以极性空间群 P2₁2₁2₁(编号 19)结晶。Na(NH₂SO₃)的结构可以描述为由扭曲的[NaO₆]^11-八面体通过共角连接与 NH₂SO₃^-四面体相互连接而形成的三维网络。紫外可见近红外光谱表明, Li(NH₂SO₃)和 Na(NH₂SO₃)分别具有 5.25 和 4.81 eV 的大光学带隙。粉末二次谐波发生(SHG)测量显示, Li(NH₂SO₃)和 Na(NH₂SO₃)的 SHG 强度分别为 KH₂PO₄的 0.32 倍和 0.31倍。第一原理计算证实, 非线性光学性能主要来自氨基磺酸阴离子和碱金属氧阴离子多面体的协同作用。     

Preparation of Porous Three‐Dimensional Quaternary Thioantimonates(III) ACuSb2S4 (A=Rb,Cs) through a Surfactant‐Thermal Method

Two novel porous three‐dimensional (3D) quaternary thioantimonates(III) ACuSb₂S₄ (A=Rb, Cs) were successfully synthesized by employing the neutral surfactant PEG‐400 (PEG=polyethyleneglycol) as reaction media, these are significantly different from the known quaternary A?Cu?Sb?S thioantimonates(III) with two‐dimensional (2D) crystal structures. This is the first time that crystalline quaternary chalcogenides have been prepared in surfactant media. Both experimental and theoretical studies confirm they are semiconductors with narrow band gaps. Our results demonstrated that the surfactant‐thermal strategy could offer a new opportunity to explore novel chalcogenides with diverse crystal structures and interesting physicochemical properties.     

Non‐centrosymmetric Selenides AZn4In5Se12 (A=Rb,Cs): Synthesis,Characterization and Nonlinear Optical Properties

Two new non‐centrosymmetric polar quaternary selenides, namely, RbZn₄In₅Se₁₂ and CsZn₄In₅Se₁₂, have been synthesized and structurally characterized. They exhibit a 3D diamond‐like framework (DLF) consisting of corner‐shared MSe₄ (M=Zn/In) tetrahedra, in which the A⁺ ions are located. Both compounds are thermally stable up to 1300 K and exhibit large transmittance in the infrared region (0.65–25 μm) with measured optical band gaps of 2.06 eV for RbZn₄In₅Se₁₂ and 2.11 eV for CsZn₄In₅Se₁₂. Inspiringly, they exhibit a good balance between strong second harmonic generation (SHG) efficiency (3.9 and 3.5×AgGaS₂) and high laser‐induced damage thresholds (13.0×AgGaS₂). Theoretical calculations based on density functional theory (DFT) methods confirm that such strong SHG responses originate from the 3D DLF structure.     

Pb2BO3I: A Borate Iodide with the Largest Second‐Harmonic Generation (SHG) Response in the KBe2BO3F2 (KBBF) Family of Nonlinear Optical (NLO) Materials

Borate halides are an ideal materials class from which to design high‐performance nonlinear optical (NLO) materials. Currently, borate fluorides, chlorides, and bromides are extensively investigated while borate iodide materials discovery remains rare because of the perceived synthetic challenges. We report a new borate iodide, Pb₂BO₃I, synthesized by a straightforward hydrothermal method. The Pb₂BO₃I chemical formula conceals that the compound exhibits a structure similar to the well‐established KBe₂BO₃F₂ (KBBF), which we show supports the highest second‐harmonic generation (SHG) at 1064 nm in the KBBF family, 10 × KH₂PO₄ (KDP), arising from the inclusion of Pb²⁺ and I^? and the crystal chemistry. Our work shows that KBBF‐related compounds can be synthesized incorporating iodide and exhibit superior NLO responses.     

Superlight and Superflexible Three‐Dimensional Semiconductor Frameworks A(X≡Y)4 (A=Si,Ge; X/Y=C,B, N) with Tunable Optoelectronic and Mechanical Properties from First‐Principles

Silicon carbide materials, as leading wide band gap semiconductors, hold significant importance in semiconductor technologies. Herein, diamond‐like 3D materials with low density, but high elasticity properties, have been designed from first‐principles calculations. They are porous single‐crystalline materials composed of sp³‐hybridized silicon (or germanium) and sp‐type C≡C (or B≡N) linear moieties; their stabilities are comparable to those of recently prepared SiC₄ materials. Moreover, such wide band gap semiconductors have strong absorption over a wide UV range and exhibit superlight, superflexible, and incompressible mechanical properties, and their optoelectronic and mechanical properties can be well tuned through structural modifications. Such features provide high potential for practicable application under extreme conditions, and suggest promising applications for the design of UV optoelectronic devices.     

A2SnS5: A Structural Incommensurate Modulation Exhibiting Strong Second-Harmonic Generation and a High Laser-Induced Damage Threshold (A=Ba,Sr)

Structural modulations have been recently found to cause some unusual physical properties, such as superconductivity or charge density waves; however, thus-induced nonlinear optical properties are rare. We report herein two unprecedented incommensurately modulated nonlinear optical sulfides exhibiting phase matching behavior, A₂SnS₅ (A=Ba, Sr), with the (3+1)D superspace groups P2₁2₁2(00γ)00s or P2₁(α0γ)0, featuring different modulations of the [Sn₂S₇]_∞ belts. Remarkably, Ba₂SnS₅ exhibits an excellent second harmonic generation (SHG) of 1.1 times that of the benchmark compound AgGaS₂ at 1570 nm and a very large laser-induced damage threshold (LIDT) of 8×AgGaS₂. Theoretical studies revealed that the structural modulations increase the distortions of the Sn/S building units by about 44 or 25 % in A₂SnS₅ (A=Ba, Sr), respectively, and enhance significantly the SHG compared with α-Ba₂SnSe₅ without modulation. Besides, despite the smaller E_g, the A₂SnS₅ samples exhibit higher LIDTs owing to their smaller thermal expansion anisotropies (Ba₂SnS₅ (1.51)<Sr₂SnS₅ (2.08)<AgGaS₂ (2.97)).     

CsZn2BO3X2 (X2=F2, Cl2, and FCl): A Series of Beryllium-Free Deep-Ultraviolet Nonlinear-Optical Crystals with Excellent Properties

Designing deep-ultraviolet (DUV) nonlinear-optical (NLO) crystals is one of the major current research interests, but it faces a great challenge. In order to overcome the problem of crystal growth and the toxicity of BeO raw materials in KBe₂BO₃F₂ (KBBF), the only applicable DUV NLO crystal so far, we substitute Be²⁺ cations with Zn²⁺ in the KBBF structure and modify the halogen anions, by which three new Zn-containing KBBF-like compounds, CsZn₂BO₃X₂ (X₂=F₂, Cl₂, and FCl), have been successfully synthesized. They all exhibit excellent NLO properties, including improved SHG responses (2.8–3.5×KDP) and short UV cut-off edges (<190 nm). In comparison with KBBF, CsZn₂BO₃X₂ (X₂=F₂, Cl₂, and FCl) are all chemically benign and have better growth habits, so they are all promising as DUV NLO crystals. Further study on structure–property relationships indicates that the mixing of halogen anions is a feasible strategy to enhance the SHG responses of the KBBF family.