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Two alkali tin(II) phosphates, namely, Rb[SnF(HPO4)] and Rb(Sn3O)2(PO4)3, were synthesized through mild hydrothermal methods. They belong to the orthorhombic Pnma and Pbcn space groups, respectively. Rb[SnF(HPO4)] features a layered structure based on 1D [SnF(HPO4)]∞ chains interconnected by hydrogen bonds, with Rb+ cations located at the interlayer space. For Rb(Sn3O)2(PO4)3, each pair of [Sn3O]4+ clusters is bridged by a pair of [P(1)O4]3- tetrahedra to build a 1D [Sn-P-O]∞ chain. These 1D [Sn-P-O]∞ chains are further cross-linked though [P(2)O4]3- tetrahedra to construct a 3D network with 7- and 10-membered-ring channels. The tin(II) ions in Rb[SnF(HPO4)] and Rb(Sn3O)2(PO4)3 with stereochemically active lone pairs (SCALPs) significantly enhance the birefringences of metal phosphates: Δn = 0.147@1064 nm for Rb[SnF(HPO4)] and 0.082@1064 nm for Rb(Sn3O)2(PO4)3.

An organic-inorganic hybrid polyiodate, namely, [o-C5 H4 NHOH]2 [I7 O18 (OH)]⋅3 H2 O (I), featuring a novel branched polyiodate chain has been obtained by evaporation method. [o-C5 H4 NHOH]2 [I7 O18 (OH)]⋅3 H2 O (I) crystalizes in the polar space group Ia and features an [I7 O18 (OH)] ∞2- branched polyiodate chain in which [I3 O9 ]3- trimers are grafted on the same side of the one-dimensional (1D) chain based on [I4 O11 (OH)]3- tetramers. The asymmetric organic amine groups are beneficial to the polymerization of iodate groups and inducing the formation of the non-centrosymmetric (NCS) structure. Compound I exhibits a rather large Second-Harmonic- Generation (SHG) signal of 8.5×KH2 PO4 (KDP) upon 1064 nm laser radiation, a moderate band gap of 3.90 eV and a high laser-induced-damage-threshold (LIDT) of 182.34 MW cm-2 , hence it is a promising new SHG material. The relationship between the structures of the organic amine groups and the overall structures has been also analyzed.

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., A novel salt-inclusion fluoroiodate nonlinear optical material, [GaF(H2O)][IO3F], is derived from CsIO2F2 through polycation substitution, and it exhibits an intense SHG effect of 10 times that of KH2PO4 and improved overall performance.

A new anhydrous rare-earth metal iodate fluoride, Ce(IO3)2F2, was rationally designed and synthesized. Ce(IO3)2F2 features unique zigzag ∞[CeF2]2+ chains that are bridged by IO3– groups, creating a...

Explorations of new types of borates are important because of their promising application in diverse fields. A new bismuth-containing boroselenite, Bi2[B2(SeO3)6], has been obtained through high-te...

Playing a crucial role in light-emitting diode (LED) illumination sources, the blue light-emitting materials are commonly obtained by doping rare-earth metal ions. Considering the high price, non-r...

Two new antimonous phosphates, namely Ba3Sb2(PO4)4 and Cd3Sb2(PO4)4(H2O)2, have been successfully prepared through mild hydrothermal reactions. Ba3Sb2(PO4)4 features a 1D [Sb(PO4)2]3- chain structure separated by Ba2+ cations while Cd3Sb2(PO4)4(H2O)2 presents a 2D [Sb(PO4)2]3- layered structure with Cd2+ located at the interlayer space. The [Sb(PO4)2]3- chain in Ba3Sb2(PO4)4 is the first example of 1D antimonous phosphate structure, and Cd3Sb2(PO4)4(H2O)2 represents the first d10 transition metal antimonous phosphate. Based on UV-vis-NIR spectra, both Ba3Sb2(PO4)4 and Cd3Sb2(PO4)4(H2O)2 can display large optical band gaps (4.30 and 4.36 eV, respectively). But their transparent ranges are quite different because of the coordination water of Cd3Sb2(PO4)4(H2O)2 (500-2000 and 500-1300 nm for Ba and Cd compounds). The anhydrous Ba3Sb2(PO4)4 shows high thermal stability in the nitrogen atmosphere (900 °C). Because of the incorporation of the lone pair cation of Sb(III), the birefringence of Ba3Sb2(PO4)4 and Cd3Sb2(PO4)4(H2O)2 has been enhanced to 0.086 and 0.053 at 532 nm, respectively.

Cyanurate motifs are emerging functional basic blocks (FBBs) for nonlinear optical (NLO) materials and birefringent materials. Herein, we report two new potassium lead(II) hydroisocyanurates, namely, K2Pb(H2C3N3O3)4(H2O)4 (I) and K3Pb(H2C3N3O3)5(H2O)6 (II). I and II belong to acentric Cm and centric C2/m, respectively. Compound I features a novel 3D network formed by 2D [K2PbO8(H2O)4]12− anionic layers interconnected by (H2C3N3O3)− anions. The 2D [K2PbO8(H2O)4]12− anionic layer is composed of 1D chains of edge-sharing K(1)O6 and K(2)O8 being further interconnected by 8-coordinated Pb2+ ions. Compound II exhibits a characteristic 3D framework based on 2D [K3PbO11(H2O)6]17− anionic layers interlinked through (H2C3N3O3)− groups, and the 2D [K3PbO11(H2O)6]17− anionic layer is based on K–O/H2O chains bridged by Pb2+ ions. Powder second harmonic generation (SHG) measurements of I revealed a moderate SHG response of approximately 2.6 × KDP with a type I phase-matching behavior under 1064 nm laser radiation. Theoretical calculations of I and II revealed their birefringence to be 0.325 and 0.193@532 nm, respectively. Their impressive optical properties mainly stem from stereochemically active lone pair (SCALP) Pb2+ cations and the planar π-conjugated (H2C3N3O3)− groups.

Our exploration of novel inorganic solids with large birefringence in the d10 Metal–Te4+–SO42− system afforded four new sulfate tellurites, Ga2(TeO3)(SO4)(OH)2, In2(TeO3)2(SO4)(H2O), Zn4(Te3O7)2(SO4)2(H2O) and Hg3(Te3O8)(SO4). Notably, Hg3(Te3O8)(SO4) exhibits the largest birefringence at 532 nm (0.184) and 1064 nm (0.166) among the reported metal sulfate tellurites.

Fluorine, as the most electronegative element, can replace the oxygen ligands of functional groups under given conditions. These fluoride groups are more or less different from the pure oxide groups in composition, symmetry, polarizability, transmittancy, etc. The rational use of these differences is expected to improve the probability of noncentrosymmetric structures and the comprehensive performance of second-harmonic-generation (SHG) materials. In this feature article, we introduce the recent developments in fluoride selenite and tellurite SHG materials together with highlighting our contributions, including Se(IV) and Te(IV) compounds with (i) d0 transition metal oxyfluoride octahedron, (ii) IIIA metal oxyfluoride octahedron, (iii) fluoride lone pair cation polyhedron, and (iv) other fluoride polyhedron. The future perspectives of fluoride selenite and tellurite SHG materials are also discussed.

The first polar molybdenum oxyfluoride in selenite and tellurite systems, namely, Ba(MoO2F)2(SeO3)2 and Ba(MoO2F)2(TeO3)2, was achieved successfully by partial fluorination of MoO6 octahedra under ...

The first polar alkaline-earth metal molybdenum iodate, Ba2[MoO3(OH)(IO3)2]IO3, with a Λ-shaped [MoO3(OH)(IO3)2]3– functional motif, was rationally designed. A zero-dimensional (0D) [MoO3(OH)(IO3)2...

The first mixed alkali-metal gallium iodate-fluoride, namely, LiGaF2(IO3)2, was successfully obtained under hydrothermal conditions. The structure of LiGaF2(IO3)2 features a novel two-dimensional (2D) [GaF2(IO3)2] layer composed of [Ga2F4(IO3)6]4 dimers further bridged by (IO3) groups. LiGaF2(IO3)2 exhibits a wide band gap of 4.33 eV, corresponding to the ultraviolet (UV) absorption edge of 230 nm. Calculations of linear optical property revealed that LiGaF2(IO3)2 has a remarkably large birefringence of 0.181 @1064 nm and 0.206@532 nm, indicating that it is a potential birefringent material that could be used from visible to UV region. This study provides a new method for the future discovery of promising optical crystals.

The search of novel second-harmonic generation crystals in gallium selenite systems results in three new compounds of MGa2(SeO3)4 (M = Sr, Pb) and BiGa(SeO3)3. The isostructural MGa2(SeO3)4 (M = Sr...

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.

The combination of d0 transition metal oxofluorides with iodate anions helps to synthesize polar crystals. Herein, a novel polar crystal, K3V2O3F4(IO3)3, which is the first metal vanadium iodate with two types of V5+-centered polyhedra (VO4F2 octahedron and VO3F2 trigonal bipyramid), has been prepared hydrothermally. It crystallizes in the polar space group of Cmc21 and its structure displays an unprecedented 0D [V2O3F4(IO3)3]3− anion, which is composed of Λ-shaped cis-[VO2F2(IO3)2]3− and [VO2F2(IO3)]2− anions interconnected via the corner-sharing of one oxo anion. The synergy gained from the VO4F2, VO3F2 and IO3 groups resulted in K3V2O3F4(IO3)3 exhibiting both a strong second-harmonic generation (SHG) response (1.3 × KTiOPO4) under 2050 nm laser irradiation and a large birefringence (0.158 @ 2050 nm). This study provides a facile route for designing SHG materials by assembling various vanadium oxide-fluoride motifs and iodate anions into one compound., K3V2O3F4(IO3)3, which is the first metal vanadium iodate containing two different V-centered polyhedra, exhibits a strong SHG effect of 1.3 × KTP and a large birefringence of 0.158 @ 2050 nm.

Two bismuth iodate sulfates crystallizing in the monoclinic space group P21/c, namely, Bi(IO3)(SO4) and CdBi(IO3)(SO4)2, were synthesized via solvothermal reactions. Bi(IO3)(SO4) features 2D [Bi(SO4)]+ layers, which are further linked by the IO3− groups to form a 3D network. CdBi(IO3)(SO4)2 exhibits 1D [IO3]− chains built from IO43− groups via corner-sharing and is the first example of a polyiodate sulfate as far as we know. These [IO3]− chains are interconnected by Bi3+ cations into [Bi(IO3)]2+ layers parallel to the bc plane, whereas the neighbouring Cd2+ cations are interconnected by bridging SO42− anions into [Cd(SO4)2]2− layers, also parallel to the bc plane. These cationic and anionic 2D layers are held together through Bi–O–S bridges into a complicated 3D framework. Bi(IO3)(SO4) and CdBi(IO3)(SO4)2 show wide band gaps of 3.91 and 4.03 eV and large birefringence values of 0.087 and 0.100 at 1064 nm, respectively. Our work indicates that the introduction of iodate group and lone pair cations, such as Bi3+, into metal sulfates can greatly enhance their birefringent properties.

Due to the intriguing chemical variability and structure-property flexibility, molecular materials with striking multifunctional characteristics, including tunable physical, chemical, optical, and electronic properties, have aroused wide attention. Recently, great advances have also been made in designing molecular ferroelastics with optoelectronic properties. However, the band gaps of the most typical ferroelastics are far in excess of 2.0 eV, which severely hinder their further applications. And this corresponds to the inherent incompatibility of ferroelastics. Herein we report an organometallic compound, ferrocenium tetrachloroferrate (

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.

Two new inorganic metal borate derivatives, Sr5TeO2(BO3)4 and NaSr5(BO3)(SiO4)2, have been obtained through a high temperature solid reaction method. Sr5TeO2(BO3)4 crystallizes in a tetragonal space group of P4/mnc featuring a three-dimensional (3D) structure composed of a porous 3D strontium framework stabilized by the unique zero-dimensional (0D) [TeO2(BO3)4]10− anions. NaSr5(BO3)(SiO4)2 crystallizes in a monoclinic space group of P21/c with a 3D structure consisting of a splendid strontium 3D framework strengthened by isolated BO3 and SiO4 groups. The sodium cations located in the empty space of the structure. Thermal stability analyses, optical property measurements and theoretical studies of the compounds were performed. Refractive index calculations revealed that the birefringence of Sr5TeO2(BO3)4 and NaSr5(BO3)(SiO4)2 is 0.048 and 0.029, respectively, at 1064 nm.

A cesium bismuth germanate, Cs2Bi2O(Ge2O7) (CBGO), was synthesized by a traditional high-temperature solid-state reaction. Its structure features a 3D network composed of a 1D chains composed of Bi2O8 dimers that are further bridged by Ge2O7 dimers, forming tunnels of seven member rings (MRs) that are filled by the Cs+ cations. CBGO exhibits extraordinary larger second harmonic generation (SHG) response of about 13.7 times that of KDP (KH2PO4) under 1064 nm laser radiation and 1.1 times that of KTP (KTiOPO4) under 2.05 mu m laser radiation, which is the highest among all of the metal germanates reported so far. CBGO possesses a moderate birefringence (0.073 at 1064 nm) and is phase matchable. Furthermore, CBGO melts congruently and exhibits high thermal stability.

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.

A new ultraviolet nonlinear optical material, namely LiHgPO4, was synthesized using the mild hydrothermal method. The structure of LiHgPO4 features novel double layers constructed by severely distorted HgO6 octahedra and PO4 tetrahedra, which are further interconnected by LiO4 tetrahedra to form a three-dimensional structure. LiHgPO4 exhibits a very strong second harmonic generation (SHG) response of 11.0 times that of KH2PO4 and a relatively large birefringence (0.068 at 1064 nm) among the reported SHG-active phosphates. Theoretical calculations revealed that the introduction of the Hg2+ in a highly distorted HgO6 octahedral geometry is crucial to produce the strong SHG response and large birefringence.

Two new barium polyiodate compounds in the alkali-earth system, namely, HBa2.5(IO3)6(I2O5) (Fdd2) and HBa(IO3)(I4O11) (P1) have been obtained through hydrothermal reaction. Interestingly, the stru...

The first examples of bismuth fluoride selenites with d0 -TM/TeVI polyhedrons, namely, Bi4 TiO2 F4 (SeO3 )4 (1), Bi4 NbO3 F3 (SeO3 )4 (2), Bi4 TeO4 F2 (TeO3 )2 (SeO3 )2 (3), Bi2 F2 (MoO4 )(SeO3 ) (4) and Bi2 ZrO2 F2 (SeO3 )2 (5) have been successfully synthesized under hydrothermal reactions by aliovalent substitution. The five new compounds feature three different types of structures. Compounds 1-3, containing TiIV , NbV and TeVI respectively, are isostructural, exhibiting a new 3D framework composed of a 3D bismuth oxyfluoride architecture, with intersecting tunnels occupied by d0 -TM/TeVI octahedrons and selenite/tellurite groups. Interestingly, compound Bi4 TeO4 F2 (TeO3 )2 (SeO3 )2 (3) is the first structure containing SeIV and mixed-valent TeIV /TeVI cations simultaneously. Compound 4 features a new 3D structure formed by a 3D bismuth oxyfluoride network with MoO4 tetrahedrons and selenites groups imbedded in the 1D tunnels. Compound 5 displays a novel pillar-layered 3D open framework, consisting of 2D bismuth oxide layers bridged by the [ZrO2 F2 (SeO3 )2 ]6- polyanions. Theoretical calculations revealed that the five compounds displayed very strong birefringence. The birefringence values of compounds 1-3, especially, are above 0.19 at 1064 nm, which are larger than the mineral calcite. Based on the structure and property analysis, it was found that the asymmetric SeO3 groups (and TeO3 in compound 3) displayed the largest anisotropy, compared with the bismuth cations and the d0 -TM/Te polyhedra, which is beneficial to the birefringence.

ConspectusSecond-harmonic-generation (SHG) causes the frequency doubling of light, which is very useful for generating high-energy lasers with specific wavelengths. Noncentrosymmetry (NCS) is the first requirement for an SHG process because the SHG coefficient is zero (χ2 = 0) in all centrosymmetric structures. At this stage, developing novel NCS crystals is a crucial scientific topic. Assembling polar units in an addictive fashion can facilely form NCS crystals with outstanding SHG performance. In this way, our group has obtained many different NCS crystals with extremely large SHG intensities (>5 × KDP or 1 × KTP). In this Account, we first provide a brief review of the development of SHG materials and concisely highlight the features of the excellent SHG materials. Then, we present four facile and rational molecular design strategies: (1) Traditional BO33--based crystals feature short absorption edges but usually suffer from relatively weak SHG performance (

Metal selenites and tellurites have demonstrated excellent second-harmonic generation (SHG) properties in inorganic solid compounds, such as strong SHG efficiency, a wide transparent range, appropriate birefringence, etc. During the past ten years, important progress has been achieved in this field. The largest SHG efficiency of selenites and tellurites reached 13.5 × KDP (BiFSeO3) and 2 × KTP (CdTeMoO6), respectively. The shortest UV absorption edge of tellurites has been pushed to 205 nm in BaF2TeF2(OH)2 successfully. In terms of the chemical compositions, research studies are no longer concentrated on d0 transition metal compounds only, and the most electronegative fluorine has been used increasingly to widen the optical bandgaps and enrich the structural types of the materials. This paper reviewed the recent developments of selenite and tellurite based SHG materials. Challenges in creating new high powered SHG materials and perspectives for future work are presented.

Three new acentric Sc-based borates, K6ACaSc2(B5O10)3 (A = Li, Na, Li0.7Na0.3; space group R32), have been obtained and characterized. They are isostructural, and all exhibit three-dimensional [Sc2(B5O10)3]9- anionic architecture composed of B5O10 clusters and ScO6 octahedra with the alkali- and alkaline-earth-metal cations occupying the cavities and keeping the charge balance. These compounds possess moderate second-harmonic-generation (SHG) responses (∼0.2×β-BaB2O4 at 532 nm and ∼0.4×KH2PO4 at 1064 nm) with phase-matching abilities and importantly display short cutoff edges below 200 nm. Furthermore, the relationship between the crystal structure and the SHG property has also been discussed based on the theoretical calculations.

By using hydrofluoric acid as a solubilizer, the first alkali-metal niobium iodate and an alkali-earth metal niobium iodate, i.e. (H3O)HCs2Nb(IO3)9 and SrNbO(IO3)5, have been obtained. An obvious cation-controlled polarity shift is observed in the Ae/A-Nb5+-IO3 system. (H3O)HCs2Nb(IO3)9 gives a strong second harmonic generation (SHG) signal about 6 times that of KH2PO4 (KDP), making it a promising nonlinear optical (NLO) material.

Herein, we reported two alkali metal molybdenum(VI) iodates, namely, NaMoO3(IO3) and γ-KMoO3(IO3) with 1D and 3D [MoO3(IO3)]− anionic architectures, respectively. The novel 1D chain in NaMoO3(IO3) and the 3D network in γ-KMoO3(IO3) are constructed by the 0D Λ-shaped cis-[MoO4(IO3)2]4− building units interconnected by bridging IO3− anions as well as the corner-sharing of oxo anions. Importantly, the polar γ-KMoO3(IO3) exhibits a very large second-harmonic generation (SHG) effect of 12 × KH2PO4 (KDP) under 1064 nm laser radiation, a high laser-Induced damage threshold value (52 × AgGaS2), and a moderate birefringence of 0.087@1064 nm, whereas the centrosymmetric NaMoO3(IO3) has a large birefringence of 0.208@1064 nm. This study further proves the useful route of exploring promising optical materials via assembling the 0D basic building units into higher dimensional anionic architectures.

Three new cadmium(II) tartratoborates, namely, Cd5[(C4H2O6)2B]2(H2O)8·3H2O (1), K2Cd4[(C4H2O6)2B]2(H2O)2 (2), and Li0.92K1.08Cd1.5[(C4H2O6)2B](H2O)2 (3), have been successfully synthesized by the hydrothermal method. Compounds 1–3 belong to centric C2/c, acentric Pc, and the polar C2, respectively. Through based on the same hybrid borate–tartrate [(C4H2O6)2B]5– anions, they exhibit different structures. The [(C4H2O6)2B]5– anion is composed of two tartrate anions and a B(OH)4– unit. Compound 1 features a novel 3D network formed by 2D {Cd3[(C4H2O6)2B]2(H2O)2}4– anionic layers and [Cd2O10] dimers, forming tunnels of large 14-MRs which are filled by the non-coordination water molecules. Compound 2 has a characteristic 3D network based on {Cd2[(C4H2O6)2B]}− units interlinked via carboxylate groups, forming tunnels of 11-MRs, half of which stuffed with the K+ ions. Compound 3 features 2D {Cd4[(C4H2O6)4B]}3+ layers which are separated by K/Li ions. Luminescent studies suggest that they emit blue light. Compounds...

A new nonlinear optical material, the first fluoride selenite nitrate PbCdF(SeO3)(NO3), was successfully synthesized by traditional solid state reactions. This compound crystallizes in the polar space group of Pca21, and its structure features a novel 2D layered structure consisting of 1D lead nitrate chains and 2D cadmium selenite layers. PbCdF(SeO3)(NO3) exhibits a phase-matchable SHG efficiency of about 2.6 times that of KDP and a wide band gap of 4.42 eV. Its laser damage threshold was measured to be 135.6 MW/cm2, which is comparative to that of the reported Li7(TeO3)3F with a short ultraviolet cutoff edge. Theoretical calculation confirmed that the synergistic effects of all the four functional units make PbCdF(SeO3)(NO3) a remarkable SHG material.

Three new d10 transition metal selenites containing PO4 tetrahedron, namely, Cd7(HPO4)2(PO4)2(SeO3)2 (1), Cd6(PO4)1.34(SeO3)4.66 (2) and Zn3(HPO4)(SeO3)2(H2O) (3), have been synthesized by hydrothermal reaction. They feature three different structural types. Compound 1 exhibits a novel 3D network composed of 3D cadmium selenite open framework with phosphate groups filled in the 1D helical tunnels. The structure of compound 2 displays a new 3D framework consisted of 2D cadmium oxide layers bridged by SeO3 and PO4 groups. Compound 3 is isostructural with the reported solids of Co3(SeO3)3-x(PO3OH)x(H2O) when x is equal to 1.0. Its structure could be viewed as a 3D zinc oxide open skeleton with SeO3 and HPO4 polyhedra attached on the wall of the tunnels. They represent the only examples in metal selenite phosphates in addition to the above cobalt compounds. Optical diffuse reflectance spectra revealed that these solids are insulators, which are consistent with the results of band structure computations based on DFT algorithm.

Two new lead(II) borate-sulfate mixed-anion compounds, namely, Pb4(BO3)2(SO4) and Pb2[(BO2)(OH)](SO4), have been prepared by using high-temperature melt method or hydrothermal reaction. These compounds exhibit two different types of 3D structures composed of the same anionic units of BO3 triangles and SO4 tetrahedra which are interconnected by lead(II) cations. In Pb4(BO3)2(SO4), the lead(II) ions are bridged by borate anions into 3D [Pb4(BO3)2]2+ architectures with 1D tunnels of 8-member rings along the a-axis, which are filled by the sulfate anions. In Pb2[(BO2)(OH)](SO4), the lead(II) ions are interconnected by borate and sulfate anions into 2D Pb-B-O and Pb-S-O layers parallel to the ab plane, respectively, and these layers are further condensed into the 3D lead(II) borate-sulfate framework. TGA and DSC studies indicate that Pb4(BO3)2(SO4) is congruently melting with a melting point of 689 °C whereas Pb2[(BO2)(OH)](SO4) decomposes at approximately 335 °C. UV/Vis/NIR optical diffuse reflectance spectrum measurements reveal the optical band gaps of 4.03 and 4.08 eV for Pb4(BO3)2(SO4) and Pb2[(BO2)(OH)](SO4), respectively. Furthermore, the electronic structures of Pb4(BO3)2(SO4) have also been calculated.

A series of new compounds in the A/Ae-Ge4+-IO3 system, namely, A2Ge(IO3)6 (A = Li, Na, Rb, or Cs) and BaGe(IO3)6(H2O), have been obtained by introducing GeO6 octahedra into a ternary metal iodate system. The structures of all five new compounds feature a zero-dimensional [Ge(IO3)6]2– anion composed of a GeO6 octahedron connecting with six IO3 groups, the alkali or alkali-earth cations acting as spacers between these anions and maintaining charge balance. Interestingly, the isomeric Li2Ge(IO3)6 and Na2Ge(IO3)6 are noncentrosymmetric (NCS), whereas the isostructural Rb2Ge(IO3)6 and Cs2Ge(IO3)6 are centrosymmetric. BaGe(IO3)6(H2O) is the first NCS alkali-earth germanium iodate reported. Powder second-harmonic generation (SHG) measurements show that Li2Ge(IO3)6, Na2Ge(IO3)6, and BaGe(IO3)6(H2O) crystals are phase-matchable and display very large SHG signals that are approximately 32, 15, and 12 times that of KH2PO4, respectively, under 1064 nm radiation and 2, 0.8, and 0.8 times that of KTiOPO4, respectively,...

Using hydrothermal reactions, three series of rare-earth borate-sulfates, namely, RE(SO4)[B(OH)4](H2O) (RE = La (1), Sm (2), Eu (3)), RE(SO4)[B(OH)4](H2O)2 (RE = Pr (4), Nd (5), Sm (6), Eu (7), Gd (8)), and RE(SO4)[B(OH)4](H2O)·H2O (RE = Tb (9), Dy (10), Ho (11), Er (12), Tm (13), Yb (14), Lu (15), Y (16)), have been synthesized, which represent the first rare-earth borate-sulfate mixed-anion compounds. All these compounds possess the same fundamental building anionic units of SO4 and B(OH)4 tetrahedra; however, they exhibit three different types of two-dimensional (2D) layered structures composed of 1D RE–B–O and RE–S–O chains. The rare-earth borate chains are similar in all compounds, while the rare-earth sulfate chains differ in each type of compound due to the various coordination modes of sulfate groups. On the basis of the measured UV–vis diffuse reflectance spectra, the optical band gaps of compounds 2, 3, 6, and 7 are estimated to be 4.66, 4.53, 4.62, and 4.50 eV, respectively. Luminescence studie...

Here, the combination of the strong electropositive lithium and the most electronegative fluorine with the TeO3 group afforded the first lithium fluoride tellurite, namely, Li7(TeO3)3F (P63), which was synthesized by solid-state reactions. Its structure features a novel three-dimensional anionic framework of [Li7O9F]12– composed of LiO3F and LiO4 tetrahedra with one-dimensional hexagonal tunnels of 12-membered rings along the c-axis, filled by the “isolated” ψ-TeO3 tetrahedra. Notably, this compound displays the largest band gap of 4.75 eV among all of the non-centrosymmetric metal-tellurites reported so far, as well as strong second harmonic generation (SHG) responses (3 × KH2PO4 @1064 nm, 0.2 × β-BaB2O4 @532 nm) and a large laser damage threshold (73 × AgGaS2). Furthermore, theoretical calculations reveal that the LiO4 and LiO3F tetrahedra also contribute significantly to the SHG response (∼30%).

Partial substitution of iodate anions in La(IO3)3 by OH- or NO3- anion led to acentric La3(IO3)8(OH) and chiral La(IO3)2(NO3). The structure of La3(IO3)8(OH) can be seen as a complex three-dimensional (3D) network composed of two-dimensional [La3(IO3)2(OH)]6+ cationic layers that are further bridged by remaining iodate anions, or alternatively as a 3D network composed of one-dimensional [La3(IO3)6(OH)]2+ cationic columns being further interconnected by additional iodate anions, while the structure of La(IO3)2(NO3) can be seen as a novel 3D structure with planar NO3 groups serving as linkage between the [La3(IO3)6]3+ triple layers. Compared to La(IO3)3, both compounds show considerably wide band gaps and enhanced thermal stability. La(IO3)2(NO3) shows a moderate second harmonic generation (SHG) response of ∼0.6 times that of KDP (KH2PO4), a wide band gap of 4.23 eV, and a high LDT value (22 × AgGaS2). Optical property measurements, thermal analysis, as well as theoretical calculations on SHG origin, were performed. It can be deduced that partial substitution of iodate anions can be a facile route to design new noncentrosymmetric metal iodates with novel structure and potential application.

The first series of metal phosphate iodates, namely, M(IO3)(HPO4)(H2O) (M = Sc 1, Fe 2, Ga 3, In 4), have been obtained through hydrothermal syntheses. The title compounds are isomorphic and crystallize in the monoclinic space group C2/c (No. 15). Their structures feature a three-dimensional (3D) network composed of 1D [M(HPO4)(H2O)]+ chains that are further bridged by IO3 groups, forming 1D tunnels based on eight-membered rings along the b-axis. Magnetic measurements revealed antiferromagnetic coupling interactions between magnetic centers in compound 2. The UV absorption spectra measurements revealed that compound 2 exhibits a broad absorption peak at about 427 nm. The TGA studies and IR spectra for compounds 1–4 were also performed.

To develop new mid-infrared (MIR) nonlinear optical (NLO) materials, which can overcome the low laser damage threshold (LDT) of the commercial MIR-NLO crystals (AgGaS2 , AgGaSe2 and ZnGeP2 ) and simultaneously keep the large NLO susceptibility, is necessary for high-power MIR laser frequency conversion technology. To improve the LDT, a new strategy of increasing lattice stability was adopted. Here, the strongly covalent structural unit of the PS4 tetrahedron was introduced into AgGaS2 (AGS), and that led to the isolation of the first compound in AgI -GaIII -PV -S system, namely, AgGa2 PS6 (Cc). It retains a large SHG efficiency (1.0×AGS) with phase-matchable ability, and also exhibits an improved LDT (5.1×AGS), indicating AgGa2 PS6 is a new promising MIR-NLO crystal. Moreover, a novel 3D framework of [Ga2 PS6 ]- , with triangular-shaped channels, as well as interesting single triangular geometry of AgS3 -both of which are very rare in reported sulfides-was discovered in AgGa2 PS6 . Furthermore, theoretical calculations, and lattice energy and thermal expansions analyses suggest that the PS4 group makes a large contribution to the large SHG efficiency and high LDT.

Two new phosphates, non-centrosymmetric (NCS) (H3O)Ca2Zn3.5(PO4)4 and centrosymmetric (CS) Ba2Cd3(PO4)2(HPO4)2 have been prepared by hydrothermal reactions. The single-crystal X-ray structural analyses have shown that they crystallized in space group P−421c and P21/c, respectively·(H3O)Ca2Zn3.5(PO4)4 features a three-dimensional (3D) network structure composed of ZnO4 and PO4 tetrahedra that are interconnected via corner-sharing, forming 1D channels of 6-MRs and 8-MRs which are filled by Ca2+ and H3O+ cations, respectively. Ba2Cd3(PO4)2(HPO4)2 features a layered [Cd3(PO4)2(HPO4)2]4- composed of 1D chain of edge-sharing CdO6 octahedra that are further bridged by PO4 tetrahedra with Ba2+ cations filling the interlayer spaces. Luminescent studies suggest that (H3O)Ca2Zn3.5(PO4)4 emits blue light. Optical diffuse reflectance spectra show the experimental band gaps for (H3O)Ca2Zn3.5(PO4)4 and Ba2Cd3(PO4)2(HPO4)2 are 5.67 eV and 5.68 eV, respectively. The UV cut-off edge of title compounds are around at 218 nm·(H3O)Ca2Zn3.5(PO4)4 exhibits a very weak SHG response.

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 [001] 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.

Two new vanadium tellurites, VTeO4(OH) (1) and Ba2V4O8(Te3O10) (2), have been synthesized successfully with the use of hydrothermal reactions. The crystal structures of the two compounds were determined by single-crystal X-ray diffraction. Compound 1 crystallizes in the polar space group Pca21 (No. 29) while compound 2 crystallizes in the centrosymmetric space group C2/c (No. 15). The topography of compound 1 reveals a two-dimensional, layered structure comprised of VO6 octahedral chains and TeO3(OH) zig-zag chains. Compound 2, on the contrary, features a three-dimensional [V4O8(Te3O10)]4- anionic framework with Ba2+ ions filled into the 10-member ring helical tunnels. The [V4O8(Te3O10)]4- anionic network is the first 3D vanadium tellurite framework to be discovered in the alkaline-earth vanadium tellurite system. Powder second harmonic generation (SHG) measurements indicate that compound 1 shows a weak SHG response of about 0.3×KDP (KH2PO4) under 1064 nm laser radiation. Infrared spectroscopy, elemental analysis, thermal analysis, and dipole moment calculations have also been carried out.

An excellent SHG iodate, LiMg(IO3)3, has been obtained via the aliovalent substitution of defect-containing MIV sites with ordered Mg2+., 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.