A new polar alkaline earth-rare earth iodate: Ba2Ce(IO3)8(H2O).

A new alkaline earth-rare earth iodate, Ba2Ce(IO3)8(H2O), has been synthesised by a hydrothermal method and its structure has been determined by single-crystal X-ray diffraction. Ba2Ce(IO3)8(H2O) crystallises in the polar space group Pna21 (No. 33) with unit cell parameters of a = 15.5042(5) Å, b = 7.8841(3) Å, c = 19.5359(8) Å, V = 2388.00(15) Å3, and Z = 4. The structure of Ba2Ce(IO3)8(H2O) is characterised by zero-dimensional (0D) [Ce(IO3)8(H2O)]4- units separated by Ba2+ cations. Large crystals of Ba2Ce(IO3)8(H2O) with dimensions of a few millimetres have been grown. The UV-vis-NIR transmission spectroscopy measurements of the compound showed that it has a short wavelength absorption edge at 381 nm. Ba2Ce(IO3)8(H2O) exhibits a relatively weak second-harmonic-generation (SHG) response, about 0.2 times that of KDP, which is mainly due to the fact that the polarisation effects of the IO3 groups in the structure largely cancel each other out. The relationships between the structure and the physical properties of Ba2Ce(IO3)8(H2O) have also been calculated theoretically. Ba2Ce(IO3)8(H2O) has a band gap of 2.44 eV, which is determined by the Ce-O and I-O interactions and is larger than those of many simple metal iodates. The introduction of alkaline earth metals favours an increase in band gap. Our work shows that the SHG and birefringence properties are closely related to the arrangement of the functional groups in the compounds.

CsHfF4(IO3): A Hafnium Iodate Exhibiting a Strong Second-Harmonic-Generation Effect and a Wide Band Gap Achieved by Mixed-Ligand Acentric Coordination.

A new polar hafnium iodate, CsHfF4(IO3), was successfully designed and synthesized by integrating fluorinated hafnium-oxygen polyhedra (HfF6O2) and IO3- anionic functional groups. Owing to the weak electronic effect of Hf4+ and the bond-network-induced out-of-center distortion of the HfF6O2 dodecahedra, CsHfF4(IO3) achieves a good balance between a strong second-harmonic-generation effect (3.5 × KH2PO4) and a rather large band gap (4.47 eV), which is the largest among the d0 transition-metal iodates. In addition, CsHfF4(IO3) possesses a wide transparent region (0.27-9.9 µm), a large birefringence for phase-matching (0.161), and a high laser-induced damage threshold (55.41 MW cm-2, 26 × AgGaS2) and is nonhygroscopic. This work indicates that the integration of mixed-ligand acentric coordination polyhedra and functional groups containing lone electron pairs is an effective strategy for developing novel inorganic nonlinear-optical materials with balanced overall properties.

Growth and Optical Properties of Large-Sized NaVO2(IO3)2(H2O) Crystals for Second-Harmonic Generation Applications.

Large-sized crystals of the quaternary iodate NaVO2(IO3)2(H2O) (NVIO) with centimeter-scale dimensions (23 mm × 18 mm × 6 mm as a representative) have been successfully grown by the top-seeded hydrothermal method. Linear optical properties have been measured, including the optical transmission spectrum and refractive index. The NVIO crystal possesses an optical window with high transmittance (above 80%) over the range of 500-1410 nm and exhibits strong optical anisotropy with large birefringence Δn (nz - nx) of 0.1522 at 1064 nm and 0.1720 at 532 nm. Based on the measured refractive indices, the phase-matching conditions for second-harmonic generation (SHG) have been calculated, and SHG devices have further been fabricated along the calculated type I and type II phase-matching directions of (θ = 39.0°, φ = 3.8°) and (θ =53.8°, φ = 1.3°). Laser experiments of extra-cavity frequency doubling have been performed on these NVIO devices. It has been confirmed that the effective SHG conversion from 1064 to 532 nm could be achieved with an energy conversion efficiency of 8.1%. Our work demonstrates that large-sized NVIO crystals are promising in the frequency-doubling application.

Two Indium Iodate-Nitrates with Large Birefringence Induced by Hybrid Anionic Functional Groups and Their Favorable Arrangements.

Two new indium iodate-nitrates, In(IO3)2(NO3) (1) and [In(IO3)(OH)(H2O)](NO3) (2), were rationally designed through the integration of hybrid anionic functional units. They exhibit large birefringences (1, 0.269; 2, 0.188, at 532 nm) and wide band gaps (1, 4.08 eV; 2, 4.39 eV), which is attributed to the synergistic effect of two types of birefringence-active units, namely, lone-pair IO3 and π-conjugated NO3 anionic groups. Through the substitution of OH and H2O of 2 with IO3, the hydrogen bonds of 2 are eliminated and the birefringence of 1 is greatly enhanced, highlighting the intriguing role of isovalent substitution in the discovery of fascinating optical materials.

Ba2[FeF4(IO3)2]IO3: a promising nonlinear optical material achieved by chemical-tailoring-induced structure evolution.

A new noncentrosymmetric iron-iodate-fluoride Ba2[FeF4(IO3)2]IO3 was ingeniously obtained based on the centrosymmetric Ba[FeF4(IO3)] through chemical tailoring. Ba2[FeF4(IO3)2]IO3 exhibits a strong phase-matchable second-harmonic generation effect, a large band gap, and a wide mid-infrared transparent window. The chemical tailoring design based on oxide-fluoride anions affords a feasible approach to design nonlinear optical materials.

[GaF(H2O)][IO3F]: a promising NLO material obtained by anisotropic polycation substitution.

A novel salt-inclusion fluoroiodate [GaF(H2O)][IO3F] derived from CsIO2F2 was ingeniously obtained through anisotropic polycation substitution. Because the catenulate [GaF(H2O)]2+ framework serves as a template for the favorable assembly of the polar [IO3F]2- groups and contributes to the nonlinear coefficient, [GaF(H2O)][IO3F] exhibits a greatly improved second-harmonic generation (SHG) effect of 10 times that of KH2PO4 (KDP) and a considerable band gap of 4.34 eV compared to the parent compound CsIO2F2 (3 × KDP, 4.5 eV). Particularly, to the best of our knowledge, [GaF(H2O)][IO3F] has the largest laser-induced damage threshold (LDT) of 140 × AgGgS2 of the reported iodates. All these results signify that [GaF(H2O)][IO3F] is a promising nonlinear optical (NLO) crystal. This work also proposes that anisotropic polycation substitution is an effective approach to optimize the SHG effect and develop excellent NLO materials.

CsVO2 F(IO3 ): An Excellent SHG Material Featuring an Unprecedented 3D [VO2 F(IO3 )]- Anionic Framework.

The first alkali-metal vanadium iodate fluoride, CsVO2 F(IO3 ), with a novel 3D anionic framework, has been rationally designed and hydrothermally synthesized. The 3D [VO2 F(IO3 )]- framework in CsVO2 F(IO3 ) is built from 0D Λ-shaped cis-[VO3 F(IO3 )2 ]4- polyanions via corner-sharing of oxo anions and bridging of the iodate groups. CsVO2 F(IO3 ) displays both a strong second-harmonic generation (SHG) 1.1 times as strong as KTiOPO4 (KTP) under 2.05 µm laser radiation and high laser-induced damage threshold (LIDT) of 107.9 MW cm-2 . This work provides a new route to design SHG crystals with stable 3D anionic structures from low-dimensional structural building units.

A new iodate-phosphate Pb2(IO3)(PO4) achieving great improvement in birefringence activated by (IO3)- groups.

The first divalent-metal iodate-phosphate, Pb2(IO3)(PO4), has been prepared via the strategy of introducing (IO3)- into phosphate. The structure features a unique 3D network where [Pb(IO3)]∞+ and [Pb(PO4)]∞- layers are alternatively interconnected. The birefringence of Pb2(IO3)(PO4) is greatly increased to 0.060 at 1064 nm.

REI5 O14 (RE=Y and Gd): Promising SHG Materials Featuring the Semicircle-Shaped I5 O14 3- Polyiodate Anion.

The first examples of rare-earth polyiodates, namely, REI5 O14 (RE=Y and Gd), have been prepared by hydrothermal reactions of RE2 O3 and H5 IO6 in H3 PO4 (≥85 wt % in H2 O), with extremely high yields (>95 %). They crystalize in the polar space group Cm and feature a brand-new semicircle-shaped [I5 O14 ]3- pentameric polyiodate anion composed of two IO3 and three IO4 polyhedra. Remarkably, both compounds exhibit very large second-harmonic generation (SHG) signals (14× and 15×KH2 PO4 (KDP) upon 1064 nm laser radiation for Y and Gd compounds, respectively). Our work shows that the hydrothermal reaction in a phosphoric acid medium facilitates the formation of rare-earth polyiodates.

LiMg(IO3)3: an excellent SHG material designed by single-site aliovalent substitution.

An excellent second harmonic generation (SHG) material, LiMg(IO3)3 (LMIO), has been elaborately designed from Li2MIV(IO3)6 (MIV = Ti, Sn, and Ge) by aliovalent substitution of the central MIV cation followed by Wyckoff position exchange. The new structure sustains the ideal-alignment of (IO3)- groups. Importantly, LMIO exhibits an extremely strong SHG effect of roughly 24 × KH2PO4 (KDP) under 1064 nm laser radiation or 1.5 × AgGaS2 (AGS) under 2.05 µm laser radiation, which is larger than that of α-LiIO3 (18 × KDP). The replacement of MIV with Mg2+ without d-d electronic transitions induces an obviously larger band gap (4.34 eV) with a short absorption edge (285 nm). This study shows that single-site aliovalent substitution provides a new synthetic route for designing SHG materials.

Two Barium Gold Iodates: Syntheses, Structures, and Properties of Polar BaAu(IO3)5 and Nonpolar HBa4Au(IO3)12 Materials.

Two new barium gold iodates, namely, BaAu(IO3)5 and HBa4Au(IO3)12, have been prepared. BaAu(IO3)5 crystallizes in the polar space group Pca21, whereas HBa4Au(IO3)12 crystallizes in the centrosymmetric space group P21/c. BaAu(IO3)5 consists of unique polar [Au(IO3)4]- anions whose four iodate groups are located at both sides of the AuO4 plane and the polarity points in the [001̅] direction. BaAu(IO3)5 displays strong second-harmonic-generation (SHG) effects about 0.6KTiOPO4 (KTP) and is phase-matchable. Thermal properties, optical spectra analyses, and theoretical calculations are also reported.

Bi(IO3 )F2 : The First Metal Iodate Fluoride with a Very Strong Second Harmonic Generation Effect.

The first metal iodate fluoride, Bi(IO3 )F2 , with a strong second harmonic generation (SHG) effect has been prepared. Bi(IO3 )F2 crystallizes in the polar space group C2 and features a three-dimensional [BiF2 ]+ cationic framework with IO3 groups capping the inner walls of the one-dimensional tunnels. This [BiF2 ]+ cationic framework acts as a template for the assembly of the polar IO3 units in a favorable superposed fashion, which leads to the polar structure of the material. Bi(IO3 )F2 displays a rather wide transmittance window (0.3-11 µm) and exhibits a very strong SHG response that is about 11.5 times larger than that of KH2 PO4 (KDP) under 1064 nm laser radiation and the same as that of KTiOPO4 (KTP) under 2.05 µm laser radiation. Preliminary investigations indicate that Bi(IO3 )F2 is a promising nonlinear optical material in the visible and mid-IR region.

New Series of Polar and Nonpolar Platinum Iodates A2Pt(IO3)6 (A = H3O, Na, K, Rb, Cs).

A new series of platinum iodates, namely, α-(H3O)2Pt(IO3)6, ß-(H3O)2Pt(IO3)6, and A2Pt(IO3)6 (A = Na, K, Rb, Cs), have been synthesized. Interestingly, among these six stoichiometrically identical compounds, α-(H3O)2Pt(IO3)6 is polar, whereas other compounds are nonpolar and centrosymmetric. They all consist of zero-dimensional [Pt(IO3)6](2-) molecular units separated by H3O(+) or A(+) cations. All of the lone electron pairs of the IO3(-) groups are aligned and almost point to one direction for α-(H3O)2Pt(IO3)6, whereas IO3(-) groups are located trans to each other in other compounds. The material, α-(H3O)2Pt(IO3)6, exhibits very strong second harmonic generation (SHG) effects, approximately 1.2 × KTiOPO4 (KTP), and is phase-matchable. Thermogravimetric analysis, elemental analysis, infrared spectra, UV-vis spectra, nonlinear optical properties, and theoretical calculations are also reported.

Explorations of new second-order nonlinear optical materials in the ternary rubidium iodate system: noncentrosymmetric ß-RbIO3(HIO3)2 and centrosymmetric Rb3(IO3)3(I2O5)(HIO3)4(H2O).

Two new rubidium iodates, namely, ß-RbIO3(HIO3)2 (1, P1) and Rb3(IO3)3(I2O5)(HIO3)4(H2O) (2, P21/c), have been synthesized by hydrothermal reaction and their structures determined by single-crystal X-ray diffraction. Compound 1 exhibits IO3(-) anions and neutral HIO3 molecules which are interconnected by Rb(+) cations into three-dimensional structure. Compound 2 features a two-dimensional layered structure formed by IO3(-) anions and neutral HIO3 and dimeric I2O5 molecules interconnected by Rb(+) cations. Large bulk crystal of 1 with dimensions of several millimeters has been grown. UV-vis-NIR transmission spectroscopy measurements on a slab of a polished crystal of 1 indicated that the crystal possesses a short-wavelength absorption edge onset at 305 nm. Powder second-harmonic generation (SHG) measurements on sieved crystals revealed that 1 is a type I phase-matchable material with an SHG response about 1.5 times that of KH2PO4. The Vickers hardness of crystal of 1 has been measured to be 110 HV, and the laser-induced damage threshold has been confirmed to be 18.26 J/cm(2) with a laser wavelength of 1064 nm and a pulse duration of 10 ns. Moreover, thermal stabilities and vibrational spectra for both 1 and 2 have also been studied.

Explorations of a series of second order nonlinear optical materials based on monovalent metal gold(III) iodates.

The syntheses, crystal structures, and characterizations of a series of monovalent metal gold(III) iodates, namely, α-NaAu(IO3)4, ß-NaAu(IO3)4, RbAu(IO3)4, α-CsAu(IO3)4, ß-CsAu(IO3)4, and AgAu(IO3)4 are reported. Their structures feature Au(IO3)4(-) anions that are separated by alkali metal ions or silver(I) ions. The Au(IO3)4(-) anions in the polar α-NaAu(IO3)4, RbAu(IO3)4, and α-CsAu(IO3)4 are polar with all four iodate groups being located only above (or below) the AuO4 square plane (cis- configuration). α-NaAu(IO3)4, RbAu(IO3)4, and α-CsAu(IO3)4 display moderate strong Second-Hamonic Generation (SHG) responses of 1.17 ×, 1.33 ×, and 1.17 × KTP (KTiOPO4), respectively, and all three materials are type-I phase-matchable. The Au(IO3)4(-) anions in centrysymmetric ß-NaAu(IO3)4, ß-CsAu(IO3)4, and AgAu(IO3)4 are nonpolar with the four iodate groups of the Au(IO3)4(-) anion being located both above and below the AuO4 square plane (trans- configuration). IR and UV spectra, luminescent and ferroelectric properties have also been measured. Theoretical calculations of their optical properties based on density functional theory (DFT) methods were performed by using the CASTEP total-energy code.

Zn2(VO4)(IO3): a novel polar zinc(II) vanadium(V) iodate with a large SHG response.

The synthesis, crystal and electronic structures, and optical properties of the first zinc(II) vanadium(V) iodate, namely, Zn2(VO4)(IO3), are reported. Zn2(VO4)(IO3) crystallizes in the noncentrosymmetric (NCS) and polar space group Pc (No. 7) with a = 5.2714(8) Å, b = 10.0402(11) Å, c = 5.5070(8) Å, ß = 101.326(10)°, and Z = 2. It displays a novel three-dimensional (3D) network structure composed of ZnO5, ZnO6, VO4, and IO3 polyhedra. One-dimensional (1D) chains of edge-sharing ZnO5 polyhedra and 1D chains of corner-sharing ZnO6 octahedra along the c-axis are interconnected via corner-sharing into a two-dimensional (2D) zinc oxide layer, and such layers are bridged by both VO4 tetrahedra and IO3 groups into a 3D network. The polarity in the structure is imparted by the alignment of the stereochemically active lone pairs of the iodate anions along the c-axis. The second harmonics generation (SHG) measurements on powder samples of Zn2(VO4)(IO3) under 1064-nm laser radiation revealed a large response of ∼6 × KDP, which is Type I phase-matchable. Thermal stability and optical properties, as well as theoretical calculations based on DFT methods, were also performed.

Tl(VO)2O2(IO3)3: a new polar material with a strong SHG response.

The synthesis, crystal and band structures and optical characterizations of a new polar thallium(I) vanadyl iodate, namely Tl(VO)2O2(IO3)3, are reported. Tl(VO)2O2(IO3)3 crystallizes in the orthorhombic polar space group Ima2 (No. 46) with a = 14.1143(17), b = 10.2116(12), c = 8.0319(9) Å, V = 1157.6(2) Å(3) and Z = 4. The structure of Tl(VO)2O2(IO3)3 exhibits a 1D [(VO)2O2(IO3)3](-) chain in which neighboring distorted VO6 octahedra are interconnected by both bridging oxo and iodate anions. The SHG measurements on Tl(VO)2O2(IO3)3, using a 2050 nm laser radiation, showed a moderate strong SHG response of 1.2 × KTP(KTiOPO4). Furthermore, the material is phase-matchable. Theoretical calculations based on DFT methods were performed by using the total-energy code CASTEP.

Explorations of new second-order nonlinear optical materials in the potassium vanadyl iodate system.

Four new potassium vanadyl iodates based on lone-pair-containing IO(3) and second-order Jahn-Teller distorted VO(5) or VO(6) asymmetric units, namely, α-KVO(2)(IO(3))(2)(H(2)O) (Pbca), ß-KVO(2)(IO(3))(2)(H(2)O) (P2(1)2(1)2(1)), K(4)[(VO)(IO(3))(5)](2)(HIO(3))(H(2)O)(2)·H(2)O (P1), and K(VO)(2)O(2)(IO(3))(3) (Ima2) have been successfully synthesized by hydrothermal reactions. α-KVO(2)(IO(3))(2)(H(2)O) and ß-KVO(2)(IO(3))(2)(H(2)O) exhibit two different types of 1D [VO(2)(IO(3))(2)](-) anionic chains. Neighboring VO(6) octahedra in the α-phase are corner-sharing into a 1D chain with the IO(3) groups attached on both sides of the chain in a uni- or bidentate bridging fashion, whereas those of VO(5) polyhedra in the ß-phase are bridged by IO(3) groups into a right-handed helical chain with remaining IO(3) groups being grafted unidentately on both sides of the helical chain. The structure of K(4)[(VO)(IO(3))(5)](2)(HIO(3))(H(2)O)(2)·H(2)O contains novel isolated [(VO)(IO(3))(5)](2-) units composed of one VO(6) octahedron linked to five IO(3) groups and one terminal O(2-) anion. The structure of K(VO)(2)O(2)(IO(3))(3) exhibits a 1D [(VO)(2)O(2)(IO(3))(3)](-) chain in which neighboring VO(6) octahedra are interconnected by both oxo and bridging iodate anions. Most interestingly, three of four compounds are noncentrosymmetric (NCS), and K(VO)(2)O(2)(IO(3))(3) displays a very strong second-harmonic generation response of about 3.6 × KTP, which is phase matchable. It also has high thermal stability, a wide transparent region and moderate hardness as well as an excellent growth habit. Thermal analyses and optical and ferroelectric properties as well as theoretical calculations have also been performed.

A series of new alkali metal indium iodates with isolated or extended anions.

Systematic explorations of new phases in the A(I)-In(III)-I(V)-O system by hydrothermal reactions led to five new compounds, namely, AIn(IO(3))(4) (A = Li, Na), Rb(3)In(IO(3))(6) and A(2)HIn(IO(3))(6) (A = Rb, Cs). The structure of AIn(IO(3))(4) (A = Li, Na) contains one-dimensional [In(IO(3))(4)](-) chains separated by Li(+) or Na(+) cations. In both compounds, each In(3+) cation is octahedrally coordinated by six IO(3)(-) anions, neighboring In(3+) cations are interconnected by bidentate bridging iodate anions into 1D chains. The structures of Rb(3)In(IO(3))(6) and A(2)HIn(IO(3))(6) (A = Rb, Cs) all feature isolated [In(IO(3))(6)](3-) anions with alkali metal ions (and H(+) ions) as spacers. Both optical diffuse reflectance spectrum measurements and band structure calculations based on DFT methods indicate that LiIn(IO(3))(4), NaIn(IO(3))(4), and Rb(2)HIn(IO(3))(6) are insulators.