“All-Three-in-One”: A New Bismuth–Tellurium–Borate Bi₃TeBO₉ Exhibiting Strong Second Harmonic Generation Response

A new nonlinear optical (NLO) material, Bi₃TeBO₉ (BTBO), is successfully grown from high temperature solution method. BTBO crystallizes in a polar space group of <i>P</i>6₃ with a framework structure composed of [Bi₃O₉] blocks, with TeO₆ and BO₃ interconnection. It is interesting that in the BTBO structure three types of NLO-active units, including stereochemically active lone pair cations (Bi³⁺ cations), second-order Jahn–Teller distorted octahedra (TeO₆ octahedra) and π-orbital planar groups (BO₃ groups), simultaneously exist. The additive contribution from these three types of groups results in an extremely large second harmonic generation (SHG) response in BTBO (about 20 times that of KDP), exhibiting the largest SHG effect among the known borate NLO materials. The enhancement of the nonlinear optical property is elucidated by the first-principles analysis

Beryllium-Free Nonlinear-Optical Crystals A₃Ba₃Li₂Ga₄B₆O₂₀F (A = K and Rb): Members of the Sr₂Be₂(BO₃)₂O Family with a Strong Covalent Connection between the _<b>∞</b>²[Li₂Ga₄B₆O₂₀F]^9– Double Layers

Two gallium-based borates, K₃Ba₃Li₂Ga₄B₆O₂₀F (<b>I</b>) and Rb₃Ba₃Li₂Ga₄B₆O₂₀F (<b>II</b>), have been successfully grown in the M₂O (M = K, Rb)–LiF–B₂O₃ flux. They can be recognized as the element cosubstitutions of Sr for K/Rb and Ba and of Be for Li and Ga from Sr₂Be₂(BO₃)₂O (SBBO), which uses poisonous beryllium oxide during the synthesis and crystal growth process and also exhibits the problem of structural instability. The isostructural borates crystallize into the noncentrosymmetric space group <i>P</i>6̅2<i>c</i>, with <i>a</i> = 8.6398(12) Å and <i>c</i> = 16.827(3) Å for <b>I</b> and <i>a</i> = 8.7214(12) Å and <i>c</i> = 17.180(3) Å for <b>II</b>. In the structures, the basic anionic units are the BO₃ triangles and GaO₄ and LiO₃F tetrahydra. These anionic units bond together through O atoms, forming the infinitely extended _∞²[LiGa₂B₃O₁₂]^8– single layer at the <i>ab</i> plane. The adjacent layers are further coupled to the _∞²[Li₂Ga₄B₆O₂₀F]^9– double layers by means of bridged O and F atoms. Then the adjacent double layers are strongly joined together via O atoms of the GaO₄ tetrahedra to form a three-dimensional skeleton, with K/Rb and Ba atoms occupying the network for charge balance. <b>I</b> and <b>II</b> have considerable second-harmonic-generation responses of about 0.7 and 0.5 as large as that of KH₂PO₄, respectively. In addition, the first-principles calculations were conducted to confirm that they address the structural instability issues in SBBO

“All-Three-in-One”: A New Bismuth–Tellurium–Borate Bi₃TeBO₉ Exhibiting Strong Second Harmonic Generation Response

A new nonlinear optical (NLO) material, Bi₃TeBO₉ (BTBO), is successfully grown from high temperature solution method. BTBO crystallizes in a polar space group of <i>P</i>6₃ with a framework structure composed of [Bi₃O₉] blocks, with TeO₆ and BO₃ interconnection. It is interesting that in the BTBO structure three types of NLO-active units, including stereochemically active lone pair cations (Bi³⁺ cations), second-order Jahn–Teller distorted octahedra (TeO₆ octahedra) and π-orbital planar groups (BO₃ groups), simultaneously exist. The additive contribution from these three types of groups results in an extremely large second harmonic generation (SHG) response in BTBO (about 20 times that of KDP), exhibiting the largest SHG effect among the known borate NLO materials. The enhancement of the nonlinear optical property is elucidated by the first-principles analysis

AZn₂BO₃X₂(A = K, Rb, NH₄; X = Cl, Br): New Members of KBBF Family Exhibiting Large SHG Response and the Enhancement of Layer Interaction by Modified Structures

A new category of five KBBF-analogy nonlinear optical (NLO) materials, AZn₂BO₃X₂ (A = K, Rb, NH₄; X = Cl, Br), are developed by the tetrahedron substitution of BeO₃F for ZnO₃X from KBe₂BO₃F₂ (KBBF). They preserve the structural merits of KBBF, consisting of the infinite planar [Zn₂BO₃X₂]_∞ layers. Optical measurements on this series of NLO crystals reveal that they are phase-matchable in the visible and UV region with powder second-harmonic generation (SHG) responses being more than twice that of isostructural KBBF. First-principles calculations and atom-cutting analysis were carried out to demonstrate that enhanced SHG response originates from the cooperative effect of coparallel [BO₃] triangles and distorted ZnO₃Cl/Br tetrahedra. The theoretical calculations and experimental results show that AZn₂BO₃X₂ exhibits a less-developed layer habit compared with KBBF. Especially, because of the existence of relatively strong hydrogen bond between NH₄⁺ groups and [Zn₂BO₃Cl₂]_∞ layers, NH₄Zn₂BO₃Cl₂ crystal exhibits the best growth behavior along the <i>c</i> axis. These results show that they may have prospects as a kind of UV nonlinear optical material

Rational Design of Deep-Ultraviolet Nonlinear Optical Materials in Fluorooxoborates: Toward Optimal Planar Configuration

Rational Design of Deep-Ultraviolet Nonlinear Optical Materials in Fluorooxoborates: Toward Optimal Planar Configuratio

ε‑La(IO₃)₃: A Polar Iodate with High Thermal Stability and a Large Second-Harmonic-Generation Response Obtained by a Supercritical Hydrothermal Method

The synthesis conditions at high temperature and high pressure are favorable for exploring new compounds with novel structures and properties. In this work, a new polar iodate, ε-La(IO3)3, is obtained by a supercritical hydrothermal method with high temperature and high pressure (T = 400 °C and P ≈ 25 MPa). Different from the known phases, ε-La(IO3)3 crystallizes in the chiral space group P21, which features a three-dimensional framework with multiple IO3– groups stacked along different directions around the LaOx polyhedra. ε-La(IO3)3 possesses high thermal stability up to 525 °C and exhibits a wide band gap of about 4.05 eV. Attributed to its noncentrosymmetric arrangement, ε-La(IO3)3 is second-harmonic-generation (SHG)-active and the powder SHG response is measured to be 11.1 × KH2PO4 at 1064 nm in the 26–50 μm particle size range. This work has enriched the structural diversity of iodates and would further promote the materials’ exploration under a supercritical hydrothermal method

Midinfrared Nonlinear Optical Thiophosphates from LiZnPS₄ to AgZnPS₄: A Combined Experimental and Theoretical Study

Our earlier theoretical calculation and preliminary experiment highlighted LiZnPS₄ as a good mid-infrared (mid-IR) nonlinear optical (NLO) material. However, this compound suffers from problems including corrosion of the silica tubes, a pungent smell, deliquescence, and incongruent-melting behavior in the further single crystal growth and applications. In order to overcome these problems, herein, we investigate the analogues of LiZnPS₄ and propose that AgZnPS₄ would be a good candidate. The combination of experimental and theoretical study demonstrates that AgZnPS₄ exhibits a much stronger NLO effect than that of LiZnPS₄ despite the relatively smaller energy band gap. More importantly, AgZnPS₄ melts congruently with a melting point as low as 534 °C, much lower than those of traditional IR NLO crystals, and is nondeliquescent with enough stability in the air. Such a good crystal growth habit and chemical stability enable AgZnPS₄ to possess much better overall performance for the practical mid-IR NLO applications

Rational Design of the First Lead/Tin Fluorooxoborates MB₂O₃F₂ (M = Pb, Sn), Containing Flexible Two-Dimensional [B₆O₁₂F₆]_∞ Single Layers with Widely Divergent Second Harmonic Generation Effects

Molecular engineering design is a productive atomic-scale strategy to optimize crystal structure and develop new functional materials. Herein, the first lead/tin fluorooxoborates, MB₂O₃F₂ (M = Pb, Sn), were rationally designed by employing the nonlinear optical crystal Sr₂Be₂B₂O₇ (SBBO) as a parent model. Compared with the rigid [Be₆B₆O₁₅]_∞ double layers in SBBO, MB₂O₃F₂ have flexible two-dimensional [B₆O₁₂F₆]_∞ single layer, which not only keeps the NLO-favorable layered structure but also overcomes the structural instability issues of SBBO. Both compounds exhibited desired short UV cutoff edge. Interestingly, MB₂O₃F₂ exhibit widely divergent second harmonic responses, although they are isostructural and both contain stereochemically active lone-pair cations. Our first-principles calculations revealed that the SHG difference is mainly attributed to the different anisotropies of Pb and Sn SHG-active orbitals, which make constructive and destructive contributions to the SHG effects in PbB₂O₃F₂ and SnB₂O₃F₂, respectively

Ca₃Na₄LiBe₄B₁₀O₂₄F: A New Beryllium Borate with a Unique Beryl Borate _∞²[Be₈B₁₆O₄₀F₂] Layer Intrabridged by [B₁₂O₂₄] Groups

A novel beryllium borate, Ca₃Na₄LiBe₄B₁₀O₂₄F, has been discovered. It possesses a unique _∞²[Be₈B₁₆O₄₀F₂] layer composed of two opposite parallel [Be₄B₄O₁₂F]_∞ layers bridged with [B₁₂O₂₄] polyborates. The linkage of [B₁₂O₂₄] to other structural units is first found in anhydrous borates. In the _∞²[Be₈B₁₆O₄₀F₂] layer, multiple tunnels are arranged along different directions resided by the alkali and alkaline-earth cations. The compound remains stable in an ambient atmosphere from room temperature to the melting point at 830 °C and melts incongruently

Structural Evolution in BaSn₂F₅X (X = Cl, Br, I): A Family of Alkaline Earth Metal Tin Mixed Halides

As the first family of Sn-based alkaline earth metal mixed halides, three new compounds, BaSn₂F₅X (X = Cl, Br, and I), are synthesized by hydrothermal method. These compounds are crystallized in the centrosymmetric space groups of <i>P</i>2₁/<i>c</i>, <i>P</i>4/<i>nmm</i>, and <i>Pmma</i> for BaSn₂F₅Cl, BaSn₂F₅Br, and BaSn₂F₅I, respectively, and their microscopic frameworks are all composed of the fundamental structural unit [SnF₄]^2– and its derivatives ([SnF₄Cl]^3– and [SnF₅]^3– groups). Interestingly, the structures in BaSn₂F₅X are significantly changed from one-dimensional (1D) to two-dimensional (2D) and then to 1D motifs as X varies from Cl, Br, to I. Structural analysis combined with theoretical calculations reveals that the structural diversities are caused by the difference of ionic radius and electronegativity of X^– anions as well as the orientation of the lone-pair electrons on Sn²⁺ cations. Moreover, the optical, electronic, and thermal properties for these three compounds are determined. This work provides a representative example to show how microscopic ions influence the structures, thus in favor of the design for new mixed halides, a type of important functional materials with many optoelectronic applications