Rational Design of the Metal‐Free KBe2BO3F2⋅(KBBF) Family Member C(NH2)3SO3F with Ultraviolet Optical Nonlinearity

The first fluorosulfonic ultraviolet (UV) nonlinear optical (NLO) material, C(NH₂)₃SO₃F, is rationally designed by taking KBe₂BO₃F₂ (KBBF) as the parent compound. C(NH₂)₃SO₃F features similar topological layers as KBBF by replacing inorganic (BO₃)^3? with organic C(NH₂)₃⁺ trigonal units and BeO₃F with SO₃F^? tetrahedra. Therefore, C(NH₂)₃SO₃F is a metal‐free UV NLO crystal. Benefiting from the coplanar configuration of the C(NH₂)₃⁺ cationic groups, it possesses a large SHG response of 5×KDP and moderate birefringence of 0.133@1064 nm. Besides, it has a short UV cutoff edge of 200 nm. The calculated results reveal the shortest SHG phase‐matching wavelengths can reach 200 nm. These findings highlight the exploration of metal‐free compounds as nontoxic and low‐cost UV NLO materials as a new research area.     

Design of the Ionic Organic Nonlinear Optical Material NH4[LiC3H(CH3)O4] with Ultrawide Band Gap and Moderate Birefringence

Ionic organic crystals containing organic planar π-conjugated units has become one of the hot spots as nonlinear optical (NLO) materials. However, although this type of ionic organic NLO crystals commonly have remarkable second harmonic generation (SHG) responses, they also suffer from overlarge birefringences and relatively small band gaps that be hardly beyond 6.2 eV. Herein, a flexible π-conjugated [C₃H(CH₃)O₄]²⁻ unit was theoretically revealed, showing great potential for designing NLO crystals with balanced optical properties. Accordingly, through the reasonable NLO-favourable layered design, a new ionic organic material, NH₄[LiC₃H(CH₃)O₄], was successfully obtained. As expected, it achieves not only a large SHG effect (4×KDP), but also a suitable birefringence (0.06@546 nm) and an ultrawide band gap (>6.5 eV). This study provides a new flexible π-conjugated NLO-active unit, contributing to design more ionic organic NLO materials with excellent balanced optical properties.     

LiMII(IO3)3 (MII=Zn and Cd): Two Promising Nonlinear Optical Crystals Derived from a Tunable Structure Model of α‐LiIO3

Excellent nonlinear optical materials simultaneously meet the requirements of large SHG response, phase‐matching capability, wide transparency windows, considerable energy band‐gap, good thermal stability and structure stability. Herein, two new promising nonlinear optical (NLO) crystals LiM^II(IO₃)₃ (M^II=Zn and Cd) are rationally designed by the aliovalent substitution strategy from the commercialized α‐LiIO₃ with the perfect parallel alignment of IO₃ groups. Compared with parent α‐LiIO₃ and related A^I₂M^IV(IO₃)₆, the title compounds exhibit more stable covalent 3D structure, and overcome the racemic twinning problem of A^I₂M^IV(IO₃)₆. More importantly, both compounds inherit NLO‐favorable structure merits of α‐LiIO₃ and show larger SHG response (≈14× and ≈12×KDP), shorter absorption edge (294 and 297 nm) with wider energy band‐gap (4.21 and 4.18 eV), good thermal stability (460 and 430 °C), phase‐matching behaviors, wider optical transparency window and good structure stability, achieving an excellent balance of NLO properties.     

Rational Design of the Metal-Free KBe2BO3F2⋅(KBBF) Family Member C(NH2)3SO3F with Ultraviolet Optical Nonlinearity

The first fluorosulfonic ultraviolet (UV) nonlinear optical (NLO) material, C(NH₂)₃SO₃F, is rationally designed by taking KBe₂BO₃F₂ (KBBF) as the parent compound. C(NH₂)₃SO₃F features similar topological layers as KBBF by replacing inorganic (BO₃)³⁻ with organic C(NH₂)₃⁺ trigonal units and BeO₃F with SO₃F⁻ tetrahedra. Therefore, C(NH₂)₃SO₃F is a metal-free UV NLO crystal. Benefiting from the coplanar configuration of the C(NH₂)₃⁺ cationic groups, it possesses a large SHG response of 5×KDP and moderate birefringence of 0.133@1064 nm. Besides, it has a short UV cutoff edge of 200 nm. The calculated results reveal the shortest SHG phase-matching wavelengths can reach 200 nm. These findings highlight the exploration of metal-free compounds as nontoxic and low-cost UV NLO materials as a new research area.     

Chain-like [Sx] (x=2–6) Units Realizing Giant Birefringence with Transparency in the Near-Infrared for Optoelectronic Materials

Birefringent crystals are requisite optical devices in laser and modern opto-electronic fields. Development of excellent birefringent materials is still challenging. Herein, the linear or chain-like [S_x] (x=2–6) species were theoretically proved to be the origin of the large birefringence, and could be regarded as birefringent genes. Besides, the metal polysulfide family was first proposed to be rich birefringent materials source, among which Cs₂S₆ realizes giant birefringence 0.58@1064 nm together with a wide band gap of 1.70 eV (based on the generalized gradient approximation). Moreover, the first dual-anion group polysulfide Na₄Ba₃(S₂)₄S₃ was obtained, showing wide infrared transmission range (0.5–6.2 μm), wide band gap (2.3 eV), and large birefringence (0.37 at 1064 nm). This work provides a new guiding thought for exploring large birefringence crystals in the future.     

KCs2[Pb2Br5(HCOO)2]: A Polar 3D Lead-Bromide Framework Exhibiting Strong Second-Harmonic Generation Response

The discovery of new nonlinear optical (NLO) crystals with excellent properties is in urgently demand because of their ability to generate coherent light. Herein, we report an unique NLO lead bromide formate, KCs₂[Pb₂Br₅ (HCOO)₂], which has been synthesized by a mix-solvothermal method. KCs₂[Pb₂Br₅(HCOO)₂] exhibits strong phase-matching second-harmonic generation (SHG) response (6.5×KDP), large birefringence (0.16@ 1064 nm), and a wide transparent window in most visible light and mid-IR region. Interestingly, KCs₂[Pb₂Br₅(HCOO)₂] features a polar 3D lead-bromide framework in which adjacent Pb−Br layers containing coplanar Pb₆Br₆ rings are not only parallel to each other, but also orient in the same direction. These oriented arrangements are responsible for the strong SHG response and large birefringence that are elucidated by both local dipole moment and theoretical calculations. This research provides a new strategy to explore subsequent NLO crystals.     

(Na0.74Ag1.26)BaSnS4: A New AgGaS2-Type Nonlinear Optical Sulfide with a Wide Band Gap and High Laser Induced Damage Threshold

The development of high-power solid-state lasers is in urgent need of infrared (IR) nonlinear optical (NLO) materials with wide band gaps and high laser-induced damage thresholds (LIDTs). Herein, a new compressed chalcopyrite-like IR NLO crystal (Na_0.74Ag_1.26)BaSnS₄ was successfully synthesized using a facile high-temperature solid-state method. Its structure can be considered as a variant of chalcopyrite AgGaS₂ (AGS)-type ones. It features a three-dimensional framework constructed by corner-sharing {[(Na/Ag)S₄]⁷⁻}_∞ layers and isolated SnS₄ tetrahedra with negative cavities occupied by counter ion Ba²⁺. (Na_0.74Ag_1.26)BaSnS₄ exhibits phase-matchable moderate SHG response (0.31 × AGS), wide band gap (3.70 eV), and high LIDT (6.44 × AGS). Theoretical calculations reveal that the NLO response of (Na_0.74Ag_1.26)BaSnS₄ is mainly originated from the synergetic effects of AgS₄ and SnS₄ tetrahedra, and the inclusion of alkaline and alkaline earth metals is responsible for the wide band gap and high LIDT. Moreover, the discovery of this chalcopyrite-like compound will provide a feasible design strategy for the exploration of new promising IR NLO materials.     

Darstellung und Eigenschaften von Blei(lV)-selenit,Pb(SeO3)2, und der Alkali-triselenitoplumbate(IV), M2[Pb(SeO3)3])

Inhaltsübersicht. Blei(IV)-acetat reagiert in wäßriger Essigsäure mit seleniger Säure zu Blei(IV)-selenit, Pb(SeO₃)₂, welches unter geeigneten Versuchsbedingungen mit Alkaliselenitlösungen in die Alkalitriselenitoplumbate(IV), M₂[Pb(SeO₃)₃] übergeführt werden kann (M = NH₄, K, Rb, Cs). Die dargestellten Verbindungen sind kristallin. Preparation and Properties of Lead(IV) Selenite, Pb(SeO₃ )₂, and the Alkali Triselenito-plumbates(IV), M₂[Pb(SeO₃)₃] Lead(IV) acetate reacts in aqueous acetic acid with selenious acid to yield lead(IV) selenite, Pb(SeO₃)₂. Using suitable conditions of preparation lead(IV) selenite reacts with alkali-selenites to yield alkali triselenito-plumbates(lV). M₂[Pb(SeO₃)₃]. All the prepared compounds are cristalline.     

Pr4(SeO3)2(SeO4)F6 und NaSm(SeO3)(SeO4): Selenit‐Selenate der Selten‐Erd‐Elemente

Pr₄(SeO₃)₂(SeO₄)F₆ and NaSm(SeO₃)(SeO₄): Selenite‐Selenates of Rare Earth Elements Light green single crystals of Pr₄(SeO₃)₂(SeO₄)F₆ have been obtained from the decomposition of Pr₂(SeO₄)₃ in the presence of LiF in a gold ampoule. The monoclinic compound (C2/c, Z = 4, a = 2230.5(3), b = 710.54(9), c = 835.6(1) pm, β = 98.05(2)°, R_all = 0.0341) contains two crystallographically different Pr³⁺ ions. Pr(1)³⁺ is attached by six fluoride ions and two chelating SeO₃^2– groups (CN = 10), Pr(2)³⁺ is surrounded by four fluoride ions, three monodentate SeO₃^2– and two SeO₄^2– groups. One of the latter acts as a chelating ligand, so the CN of Pr(2)³⁺ is 10. The selenite ions are themselves coordinated by five and the selenate ions by four Pr³⁺ ions. The coordination number of the F^– ions is three and four, respectively. The linkage of the coordination polyhedra leads to cavities in the crystal structure which incorporate the lone pairs of the selenite ions. The reaction of Sm₂(SeO₄)₃ and NaCl in gold ampoules yielded light yellow single crystals of NaSm(SeO₃)(SeO₄). The monoclinic compound (P2₁/c, Z = 4, a = 1066.9(2), b = 691.66(8), c = 825.88(9) pm, β = 91.00(2)°, R_all = 0.0530) contains tenfold oxygen coordinated Sm³⁺ ions. The oxygen atoms belong to five SeO₃^2– and two SeO₄^2– ions. Two of the SeO₃^2– groups as well as one of the SeO₄^2– groups act as a chelating ligand. The sodium ions are surrounded by five SeO₄^2– ions and one SeO₃^2– group. One of the selenate ions is attached chelating leading to a coordination number of seven. Each selenite group is coordinated by six (5 × Sm³⁺ and 1 × Na⁺), each selenate ion by seven cations (5 × Na⁺ and 2 × Sm³⁺).     

Syntheses,characterization and nonlinear optical properties of a bismuth subcarbonate Bi2O2CO3

A novel nonlinear optical (NLO) material Bi₂O₂CO₃ has been successfully developed by the hydrothermal method. It was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, high resolution transmission electron microscopy (HRTEM), UV–vis–NIR diffuse reflectance spectrum (DRS) and photoluminescence (PL) spectra. The band gap was determined to be 3.42 eV, and the PL properties of Eu³⁺ doped Bi₂O₂CO₃ under UV excitation have also been investigated. The powder second-harmonic generation (SHG) measurement performed on the ground crystal indicates that the NLO efficiency is approximately 5 times as large as that of KDP (KH₂PO₄) standard. In addition, the origin of large SHG for Bi₂O₂CO₃ was also researched according to its crystal structure.     

A New Nonlinear Optical Material with N(CN)2− Anion

Discovering new functional genes and developing high-performance materials are the goals being pursued by scientists. In this work, we successfully obtained a second-order nonlinear optical (NLO) material via the aqueous solution method, Y[N(CN)₂]₄[NH(C₂H₅)₃] ⋅ 3H₂O, which is the first NLO material with the anionic group N(CN)₂⁻. Remarkably, this material is not only strongly NLO-active at 1064 nm with a response of about 2.8 × KH₂PO₄, but also possesses a short UV absorption edge of 250 nm. In-depth first-principles calculations illustrate well that the optical properties are mainly from the strong interaction of N, C and Y atoms. This result indicates that the N(CN)₂⁻ anion may be a new NLO functional gene. This work enriches the diversity of NLO functional genes and materials.     

K2ZnSn3Se8: A Non‐Centrosymmetric Zinc Selenidostannate(IV) Featuring Interesting Covalently Bonded [ZnSn3Se8]2− Layer and Exhibiting Intriguing Second Harmonic Generation Activity

Non‐centrosymmetric zinc selenidostannate(IV) K₂ZnSn₃Se₈ was synthesized. It features interesting covalently bonded [ZnSn₃Se₈]²⁻ layers with K⁺ cations filling in the interlayer voids. The phonon spectrum was calculated to clarify its structural stability. Based on the X‐ray diffraction data along with the Raman spectrum, the major bonding features of the title compound were identified. According to the UV/vis‐NIR spectroscopy, K₂ZnSn₃Se₈ possesses a typical direct band gap of 2.10 eV, which is in good agreement with the band structure calculations. Moreover, our experimental measurements and detailed theoretical calculations reveal that K₂ZnSn₃Se₈ is a new phase‐matchable nonlinear optical material with a powder second harmonic generation (SHG) signal about 0.6 times of that of AgGaS₂.     

Designing Silicates as Deep-UV Nonlinear Optical (NLO) Materials using Edge-Sharing Tetrahedra

Discovering new deep-ultraviolet (DUV) nonlinear optical (NLO) materials is currently a great challenge. The reported DUV NLO materials are almost exclusively borates or phosphates. Silicates—the largest constituent of the earth's crust—are excluded owing to their weak second harmonic generation (SHG) response. We report a silicate, Li₂BaSiO₄, with edge-sharing LiO₄–SiO₄ tetrahedra that achieves the balance between a short UV absorption edge, below 190 nm, and a large SHG response, 2.8×KDP. The SHG intensity is the largest for silicates without second-order Jahn–Teller cations, and exceeds that of non-isomorphic Li₂SrSiO₄ by more than an order of magnitude. As such Li₂BaSiO₄ may be seen as a promising DUV-UV NLO material. This research indicates that edge-sharing tetrahedra is a new design parameter for discovering new DUV NLO materials.     

Prediction of Fluorooxoborates with Colossal Second Harmonic Generation (SHG) Coefficients and Extremely Wide Band Gaps: Towards Modulating Properties by Tuning the BO3/BO3F Ratio in Layers

Fluorooxoborates have inspired investigations of deep‐ultraviolet (DUV) nonlinear optical (NLO) materials that can meet the multiple criteria. Herein, five stable structures with the composition of BaB₂O₃F₂ (I–V) are discovered using the ab initio evolutionary algorithm. Among them, BaB₂O₃F₂‐I has been synthesized experimentally and confirms the reliability of the method. All of the predicted structures possess extremely wide band gaps (8.1–9.0 eV). Moreover, four new structures exhibit giant second harmonic generation (SHG) coefficients (>3×KDP, d₃₆=0.39 pm V^?1). A novel type of the [BOF] layer with BO₃:BO₃F ratio of [1:1] is found in BaB₂O₃F₂‐II and BaB₂O₃F₂‐III. While BaB₂O₃F₂‐IV and BaB₂O₃F₂‐V are solely composed of the BO₃F group and have colossal SHG coefficients (ca. 4×KDP). It gives the direct evidence that the BO₃F group could generate strong SHG effect. Most importantly, the influences of BO₃:BO₃F ratio and their number density on band gap, birefringence and SHG effects are investigated.     

Syntheses,characterization and nonlinear optical properties of sodium–scandium carbonate Na5Sc(CO3)4·2H2O

A novel nonlinear optical (NLO) material Na₅Sc(CO₃)₄·2H₂O has been synthesized under a subcritical hydrothermal condition. The structure is determined by single-crystal X-ray diffraction and further characterized by TG analyses and UV–vis–NIR diffuse reflectance spectrum. It crystallizes in the tetragonal space group P-421c, with a = b = 7.4622(6) Å, C = 11.5928(15) Å. The Second-harmonic generation (SHG) on polycrystalline samples was measured using the Kurtz and Perry technique, which indicated that Na₅Sc(CO₃)₄·2H₂O was a phase-matchable material, and its measured SHG coefficient was about 1.8 times as large as that of d₃₆ (KDP). The results from the UV–vis diffuse reflectance spectroscopy study of the powder samples indicated that the short-wavelength absorption edges of Na₅Sc(CO₃)₄·2H₂O is about 220 nm, suggesting that this crystal is a promising UV nonlinear optical (NLO) materials.     

Sb6O7(SO4)2: A Promising Ultraviolet Nonlinear Optical Material with an Enhanced Second-Harmonic-Generation Response Activated by SbIII Lone-Pair Stereoactivity

The stereochemical activity of lone pairs (SCALP) in a cation favors the formation of acentric materials and can enhance the second-harmonic-generation (SHG) response and/or the birefringence. By introducing functional Sb^III into sulfates, an anhydrous sulfate of Sb₆O₇(SO₄)₂ ( 1 ) is explored. Sb³⁺ cations are in seesaw configurations and in-phase aligned in a 3D asymmetric dense structure. Compound 1 exhibits an enhanced phase-matching SHG response, a moderate birefringence, a wide transparency window, and considerable environmental stabilities, which result in it being a promising UV nonlinear optical (NLO) material. Theoretical studies reveal that the stereoactive lone pairs on Sb³⁺ cations make the predominant contribution to the SHG effect. This work will attract more interest from scientists for research into SCALP-cation-based NLO materials.     

Perfectly Encoding π-Conjugated Anions in the RE5(C3N3O3)(OH)12 (RE=Y,Yb, Lu) Family with Strong Second Harmonic Generation Response and Balanced Birefringence

Nonlinear optical (NLO) crystal, which simultaneously exhibits strong second-harmonic-generation (SHG) response and desired optical anisotropy, is a core optical material accessible to the modern optoelectronics. Accompanied by strong SHG effect in a NLO crystal, a contradictory problem of overlarge birefringence is ignored, leading to low frequency doubling efficiency and poor beam quality. Herein, a series of rare earth cyanurates RE₅(C₃N₃O₃)(OH)₁₂ (RE=Y, Yb, Lu) were successfully characterized by 3D electron diffraction technique. Based on a “three birds with one stone” strategy, they enable the simultaneous fulfillment of strong SHG responses (2.5–4.2× KH₂PO₄), short UV cutoff (ca. 220 nm) and applicable birefringence (ca. 0.15 at 800 nm) by the introduction of rare earth coordination control of π-conjugated (C₃N₃O₃)³⁻ anions. These findings provide high-performance short-wavelength NLO materials and highlight the exploration of cyanurates as a new research area.     

Quadruple-Bidentate Nitrate-Ligated A2Hg(NO3)4 (A=K,Rb): Strong Second-Harmonic Generation and Sufficient Birefringence

The design of efficient nonlinear optical (NLO) crystals continues to pose significant challenges due to the difficulty of assembling polar NLO-active modules in an optimal additive fashion. We report herein the first NLO-active mercuric nitrates A₂Hg(NO₃)₄ (A=(KHNO), Rb (RHNO)), for which assembly is induced by ionic polarization of the d¹⁰ cations. The two new crystalline compounds are isostructural, featuring interesting pseudo-diamond-like structures with parallel [Hg(NO₃)₄] modules, and leading to strong powder second-harmonic generation (SHG) responses of 9.2 (KHNO) and 8.8 (RHNO) times that of KH₂PO₄. In combination with the simple solution preparation of centimeter-scale crystals, sufficient birefringence, and short ultraviolet (UV) cutoff edges, these attributes make KHNO and RHNO promising candidates for UV NLO materials. Theoretical calculations and single-crystal structure analysis reveal that the newly-developed highly condensed and distorted [Hg(NO₃)₄] module, with an Hg²⁺ cation that is quadruply bidentate nitrate-ligated, is crucial for the significant SHG responses. This work highlights the potential importance of modules with multiple bidentate ligands for the development of high-performing next-generation NLO materials.     

Perfectly Encoding π-Conjugated Anions in the RE5(C3N3O3)(OH)12 (RE=Y,Yb, Lu) Family with Strong Second Harmonic Generation Response and Balanced Birefringence

Nonlinear optical (NLO) crystal, which simultaneously exhibits strong second-harmonic-generation (SHG) response and desired optical anisotropy, is a core optical material accessible to the modern optoelectronics. Accompanied by strong SHG effect in a NLO crystal, a contradictory problem of overlarge birefringence is ignored, leading to low frequency doubling efficiency and poor beam quality. Herein, a series of rare earth cyanurates RE₅(C₃N₃O₃)(OH)₁₂ (RE=Y, Yb, Lu) were successfully characterized by 3D electron diffraction technique. Based on a “three birds with one stone” strategy, they enable the simultaneous fulfillment of strong SHG responses (2.5–4.2× KH₂PO₄), short UV cutoff (ca. 220 nm) and applicable birefringence (ca. 0.15 at 800 nm) by the introduction of rare earth coordination control of π-conjugated (C₃N₃O₃)³⁻ anions. These findings provide high-performance short-wavelength NLO materials and highlight the exploration of cyanurates as a new research area.     

Li[LiCs2Cl][Ga3S6]: A Nanoporous Framework of GaS4 Tetrahedra with Excellent Nonlinear Optical Performance

A large nonlinear optical (NLO) coefficient and a wide band gap are two crucial but contradictory parameters that are difficult to achieve simultaneously in a single infrared (IR) NLO compound. A salt‐inclusion chalcogenide (SIC), Li[LiCs₂Cl][Ga₃S₆] ( 1 ), was prepared that presents a nanosized tunnel framework constructed from monotype chalcogenide tetrahedra. Highly oriented covalent GaS₄ tetrahedra in the host lead to a moderate second harmonic generation response (0.7 AgGaS₂), and ionic guests effectively broaden the band gap to the widest value (4.18 eV) among all IR NLO chalcogenides, thereby achieving a remarkable balance between NLO efficiency and band gap.