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

1D Cu(I)-based chiral organic-inorganic hybrid material with second harmonic generation and circular polarized luminescence

In recent years, organic-inorganic hybrid materials have demonstrated exceptional performance in nonlinear optics, attracting widespread attention. However, there are relatively few examples of coordination compounds synthesized with Cu as the metal center that exhibit excellent nonlinear optical properties. In this study, we successfully synthesized a pair of enantiomers named R/S-Cu2I2 by reacting chiral ligands with CuI. The crystal structure reveals a one-dimensional copper-iodide chain structure built by Cu2I2 clusters, and its ordered arrangement in space provides not only a strong second harmonic generation (SHG) signal (1.24 × KDP) but also a large birefringence (0.15@1064 nm). Under excitation at 395 nm, the crystals exhibit red fluorescence peaked at 675 nm. The CD spectra of R/S-Cu2I2 show a distinct mirror-symmetric Cotton effect, and their CPL signals are corresponding and opposite in the emission range, with a maximum glum of approximately ±2.5 × 10-3. Theoretical calculations using density functional theory were also carried out to enhance our understanding of the correlation between their structures and optical properties.

Chromium iodate: the structure and origin of optical second harmonic generation

Iodate crystal materials are some of the important candidates for mid-infrared nonlinear optical (NLO) crystals. Almost all the structures and NLO properties of monometallic iodates have been studied, except for a few difficult to synthesize crystalline phases. In this work, crystalline Cr(IO3)3 was synthesized and its optical properties were studied. Cr(IO3)3 has a strong powder second-harmonic generation (SHG) effect (1.3 × AgGaS2) and a large birefringence (0.24) at 2100 nm. Theoretical calculations indicate that the 3d orbital of Cr3+ is strongly involved in the SHG process, and the contribution of the metal cation centered unit CrO6 to the SHG response is much greater than that of the non-metal cation centered unit IO3. This study provides a new case among the few NLO materials in which the SHG response is dominated by metal cation centered groups.

Investigation of second-order NLO properties of novel 1,3,4-oxadiazole derivatives: a DFT study

CONTEXT

In this study, we have developed four new chromophores (TM1-TM4) and performed quantum chemical calculations to explore their nonlinear optical properties. Our focus was on understanding the impact of electron-donating substituents on 1,3,4-oxadiazole derivative chromophores. The natural bond orbital analysis confirmed the interactions between donors and acceptors as well as provided insights into intramolecular charge transfer. We also estimated dipole moment, linear polarizability molecular electrostatic potential, UV-visible spectra, and first hyperpolarizability. Our results revealed that TM1 with a strong and stable electron-donating group exhibited high first hyperpolarizability (β) 293,679.0178 × 10-34 esu. Additionally, TM1 exhibited a dipolar moment (μ) of 5.66 Debye and polarizability (α) of 110.62 × 10-24 esu when measured in dimethyl sulfoxide (DMSO) solvent. Furthermore, in a benzene solvent, TM1 showed a low energy band gap of 5.33 eV by using the ωB97XD functional with a 6-311 +  + G(d, p) basis set. Moreover, our study of intramolecular charge transfers highlighted N, N dimethyl triphenylamine and carbazole as major electron-donating groups among the four 1,3,4-oxadiazole derivative chromophores. This research illustrates the potential applications of these organic molecules in photonics due to their versatile nature.

METHODS

The molecules were individually optimized using different functionals, including APFD, B3LYP, CAM B3LYP, and ωB97XD combined with the 6-311 +  + G (d, p) basis set in Gaussian 16 software. These methods encompass long-range functionals such as APFD and B3LYP, along with long-range corrected functionals like CAM B3LYP and ωB97XD. The employed functionals of APFD, B3LYP, CAM B3LYP, and ωB97XD with the 6-311 +  + G (d,p) basis set were used to extract various properties such as geometrical structures, dipole moment, molecular electrostatic potential, and first hyperpolarizability through precise density functional theory (DFT). Additionally, TD-DFT was utilized for obtaining UV-visible spectra. All studies have been conducted in both gas and solvent phases.

Anhydrous Aluminum Iodate: Strong Second Harmonic Generation Effect Contributed by Unbonded and Antibonding Orbitals

Exploring materials that balance the second harmonic generation (SHG) effect and laser-induced damage threshold (LIDT) is the frontier of nonlinear optical (NLO) crystal research at present. In this work, the NLO property of anhydrous aluminum iodate is extensively explored and discussed first. It exhibits a strong SHG intensity of 18.3 × KH2PO4 (KDP) and a high-powder LIDT of 1.4 × KDP at 1064 nm. Combining experimental and theoretical studies at the atomic level and electronic levels, it is found that the cations in the structure are replaced by cations with small radius and high valence, enabling the production of materials with large SHG responses. Unbonded and antibonding orbitals play a crucial positive role in the SHG response of the structure, whereas bonding orbitals produce a large negative contribution. This provides a scarce example of materials in which bonding orbitals make significant negative contributions.

From NaGa(IO3)3F to NaGa(IO3)2F2 and NaGa(IO3)4: The Effects of Chemical Substitution between F- Anions and IO3- Groups on the Structures and Properties of Gallium Iodates

Introducing F- anions or substituting F- anions with IO3- groups has been proven to be ideal strategies for designing novel noncentrosymmetric (NCS) and polar materials, yet systematic investigation into the effect of F- anions or the substitution of IO3- for F- anions on structures and properties remains rarely explored. Herein, two new gallium iodates, NaGa(IO3)2F2 (1) and NaGa(IO3)4 (2), were successfully designed and synthesized based on NaGa(IO3)3F by introducing more F- anions and replacing F- anions with IO3 groups, respectively. Structurally, in compound 1, the adjacent [GaF3(IO3)3]3- polyanions are connected in an antiparallel manner, resulting in a complete cancellation of local polarity. While in compound 2, all IO3 groups in 2D [Ga(IO3)4]∞- layers are aligned, leading to large macroscopic polarization. Additionally, chemical substitution also results in a qualitative improvement in the functional properties of compound 2. It possesses strong SHG response (12 × KDP @1064 nm) and broad optical transparency, coupled with large birefringence (0.21 @1064 nm), showcasing its promise as a promising nonlinear optical (NLO) crystal. The effects of chemical substitution between F- anions and IO3- groups on the structures and properties are discussed in detail.

K(NH4)Zn2(PO4)2: a Beryllium-Free Sr2Be2B2O7 Derivative with Enhanced Interlayer Connectivity

A novel zinc phosphate derivative of Sr2Be2B2O7 (SBBO), K(NH4)Zn2(PO4)2 (KNZP), featuring [Zn2P2O8]∞2- double layers akin to the [Be2B2O7]∞4- layers in SBBO, was successfully synthesized via a moderate hydrothermal method. Through the substitution of BeO4 and BO3 with ZnO4 and PO4, the issue of toxicity has been effectively resolved, while the enhanced interlayer interactions facilitated by covalent and hydrogen bonding in KNZP overcome the inherent structural instability. Notably, KNZP exhibits a wide transparent window and a moderate second-harmonic generation (SHG) intensity, reaching 0.7 times that of KH2PO4 (KDP), rendering it type-I phase-matchable, indicating that it is a promising UV nonlinear optical (NLO) material.

LiGa(IO3 )4 : An Excellent NLO Material with Unprecedented 2D [Ga(IO3 )4 ]∞ - Layer Synthesized by Aliovalent Substitution

Nonlinear optical (NLO) crystals are indispensable for the solid-state lasers for their ability to expand wavelength spectral to the regions where the directing lasing is difficult or even impossible, yet the rational design of a high-performance NLO crystal remains a great challenge owing to the severe structural and properties' requirements. Herein, a new noncentrosymmetric (NCS) and polar gallium iodate, LiGa(IO3 )4 , with a novel 2D anionic layer, is successfully designed and synthesized by the aliovalent substitution strategy based on classic α-LiIO3 . The 2D [Ga(IO3 )4 ]∞ - layer in LiGa(IO3 )4 is built from the GaO6 octahedra and highly polarizable units IO3 . Compared with its parent compound, the partial replacement of A-site Li+ cation with main group Ga3+ cation facilitates LiGa(IO3 )4 to possess excellent NLO properties, including the large second-harmonic generation (SHG) response (14 × KH2 PO4 (KDP) @ 1064 nm), wide bandgap (4.25 eV), large birefringence (0.23 @ 1064 nm), and wide optical transparency from UV to mid-IR. These reveal that LiGa(IO3 )4 will be a promising NLO crystal.

α- and β-(C4H5N2O)(IO3)·HIO3: Two SHG Materials Based on Organic-Inorganic Hybrid Iodates

Organic-inorganic hybrid nonlinear optical (NLO) materials are highly anticipated because of the integration of both merits of the organic and inorganic moieties. Herein, the 2-pyrimidinone cation (C4H5N2O)+ has been incorporated into the iodate system to form two polymorphic organic-inorganic hybrid iodates, namely, α- and β-(C4H5N2O)(IO3)·HIO3. They crystallize in different polar space groups (Ia and Pca21), and their structures feature one-dimensional (1D) chain structures composed of (C4H5N2O)+ cations, IO3- anions, and HIO3 molecules interconnected via hydrogen bonds. α- and β-(C4H5N2O) (IO3)·HIO3 exhibit strong and moderate second-harmonic-generation (SHG) responses of 6.4 and 0.9 × KH2PO4 (KDP), respectively, the same band gaps of 3.65 eV, and high powder laser-induced damage threshold (LIDT) values [51 and 57 × AgGaS2 (AGS)]. The results of theoretical calculations revealed that the large SHG effect of α-(C4H5N2O)(IO3)·HIO3 originated from the IO3 and HIO3 groups. This work indicates that (C4H5N2O)+ is a potential group for designing new NLO materials with brilliant optical performances.

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.

Polar Bismuth Selenite Iodate Oxide BiSeIO6 with Three Types of Lone Pair Cations in One Structure

Novel bismuth selenite iodate oxide BiSeIO₆ was synthesized in a mild hydrothermal condition. BiSeIO₆ was crystallized in the polar space group Pna2₁ of an orthorhombic system. The crystal structure features a three-dimensional framework composed of three types of lone pair cations with distorted BiO₇ polyhedra, SeO₃ pyramids, and IO₃ pyramids in one structure. Interestingly, BiSeIO₆ exhibits a strong and phase-matchable second-harmonic generation (SHG) of ∼6 times that of KH₂PO₄ (KDP). Dipole moment analysis shows that all three local acentric groups of BiO₇, SeO₃, and IO₃ cooperatively contribute to the large macroscopic polarization and thereby strong SHG efficiency of BiSeIO₆. In addition, BiSeIO₆ has a broad transparency range from 0.35 to 11 μm, indicating its promising nonlinear optical applications from visible to mid-infrared bands.

PbBi(SeO3)2F and Pb2Bi(SeO3)2Cl3: Coexistence of Three Kinds of Stereochemically Active Lone-Pair Cations Exhibiting Excellent Nonlinear Optical Properties

Stereochemically active lone-pair (SCALP) cations are one attractive type of nonlinear optical (NLO)-active units because of their large microcosmic polarizability and anisotropy. Currently, the single and/or dual lone-pair cation-based noncentrosymmetric (NCS) oxides have been extensively investigated and verified to be one class of outstanding NLO materials. From the perspective of function optimization, the integration of three kinds of SCALP cations into one crystal may synergistically improve the NLO properties, which is greatly expected but unexplored to date. Herein, by introducing flexible metal halide bonds to guarantee the stereochemical activity and overcome the energetically favorable antiparallel arrangements of lone-pair cations, the first type of three lone-pair-cation (Pb2+, Bi3+, and Se4+)-coexisting NCS oxides PbBi(SeO3)2F (I) and Pb2Bi(SeO3)2Cl3 (II) was obtained. As expected, both compounds show outstanding NLO properties, such as the strong second-harmonic-generation signal (10.5× and 13.5 × KDP), large birefringence (0.103 and 0.186), relatively wide energy band gaps (3.75 and 3.45 eV), and good physicochemical stability. Theoretical calculations demonstrated the effect of three lone-pair-cation-based polyhedra and the halide anion on NLO properties.

Mixed-Anion-Oriented Design of LnMGa3S6O (Ln = La, Pr, and Nd; M = Ca and Sr) Nonlinear Optical Oxysulfides with Targeted Property Balance

Nonlinear optical (NLO) crystals are of importance on extending infrared (IR) laser wavelengths. Considering their performance drawbacks in commercial IR NLO crystals, a recent challenge in exploring new excellent IR NLO crystals is how to break the inherent conflict between a wide bandgap (E_g ≥ 3.0 eV) and large NLO effect (d_ij ≥ 0.5 × AgGaS₂) and simultaneously enlarge the birefringence (Δn) for a requisite phase-matching (PM) behavior. For that reason, rational combination of mixed-anion functional groups into a crystal structure affords the successful design and synthesis of six LnMGa₃S₆O (Ln = La, Pr, and Nd; M = Ca and Sr) NLO oxysulfides. Among them, LaMGa₃S₆O satisfy the property-balance demand (E_g: 3.21-3.27 eV and d_ij: 0.9-1.0 × AgGaS₂) as promising PM NLO crystals through gathering their property advantages between LaMGa₃O₇ and LaMGa₃S₇ by mixed-anion-oriented performance engineering. A study on the structure-property relationship indicates that heteroleptic (Ln/M)S₇O and GaS₃O anionic groups are proven as promising NLO-active units and offer a great synergistic effect on the NLO origin. This work as a visualized model not only provides a first clear cognition on varying properties from oxide to sulfide to oxysulfide but also highlights the feasibility of mixed-anion-oriented design of new NLO candidates with balanced performances.

Cd2(IO3)(PO4) and Cd1.62Mg0.38(IO3)(PO4): metal iodate-phosphates with large SHG responses and wide band gaps

The first NLO-active metal iodate-phosphates, namely, Cd₂(IO₃)(PO₄) and Cd_1.62Mg_0.38(IO₃)(PO₄) (1 and 2), with three types of NLO groups, have been reported. 1 and 2 are isostructural and the structure of 1 features a 3D network formed by the Cd₄(IO₃)_8/4(PO₄)_6/3 groups. 1 and 2 with strong SHG signals of 4 × and 3.5 × KH₂PO₄ are promising SHG materials in the visible region.

Lead Tellurite Crystals BaPbTe2O6 and PbVTeO5F with Large Nonlinear-/Linear-Optical Responses due to Active Lone Pairs and Distorted Octahedra

The exploration of nonlinear-/linear-optical crystal materials with high performance is an extremely difficult research project. Herein, the two new lead tellurite crystals BaPbTe₂O₆ and PbVTeO₅F were successfully obtained through a facile hydrothermal synthesis strategy. BaPbTe₂O₆ lies in the noncentrosymmetric (NCS) and chiral orthorhombic space group P2₁2₁2₁, featuring a unique _∞¹[PbTe₂O₆] chain consisting of the PbO₄ and TeO₃ building units, while PbVTeO₅F belonging to the centrosymmetric (CS) orthorhombic space group Pbca manifests a 2D layer made up of _∞¹[PbO₄F₂] chains and novel [V₂Te₂O₁₀F₂] clusters. Further, a systematic analysis of lead tellurites finds that the coordination geometries of the Pb atom exert a considerable influence on the connection modes of Pb-O and Te-O building units. BaPbTe₂O₆ shows a great second-harmonic-generation (SHG) effect of ∼5× the benchmark KH₂PO₄ (KDP) and a large optical birefringence of 0.086 at 590 ± 3 nm. PbVTeO₅F demonstrates a remarkably larger birefringence of 0.142 at 590 ± 3 nm, benefiting from the introduction of the VO₅F octahedral unit. Theoretical studies reveal that the large SHG and birefringence in BaPbTe₂O₆ can be attributed to TeO₃ and PbO₄ polyhedra with active lone pairs, while the remarkably enlarged birefringence in PbVTeO₅F is attributable to the highly distorted octahedral VO₅F. The functional orientations of active building units may offer a practical insight into the design of the desired optical functional materials.

Unprecedented mid-infrared nonlinear optical materials achieved by crystal structure engineering, a case study of (KX)P2S6 (X = Sb, Bi, Ba)

Three superior type-I phase-matching middle infrared nonlinear optical materials (Ea > 4.0 eV, dij > 2× AGS, LDT > 8× AGS) were achieved via crystal structure engineering.

From oxides to oxysulfides: the mixed-anion GeS3O unit induces huge improvement in the nonlinear optical effect and optical anisotropy for potential nonlinear optical materials

Oxysulfides combining intrinsic performance advantages between sulfides (strong NLO response) and oxides (wide optical bandgap) are proposed as potential infrared (IR) NLO materials. Theoretical calculation shows that the mixed-anion GeS₃O tetrahedron has a stronger polarizability anisotropy and hyperpolarizability than that of the typical GeO₄ unit. Based on this, two Sr₂MGe₂S₆O (M = Zn, Cd) oxysulfides with the GeS₃O unit show dozens of times improvement in critical birefringence and the NLO effect compared with those of isostructural Sr₂ZnGe₂O₇. Moreover, structure–property study further verifies that the mixed-anion GeS₃O ligand is a useful NLO-active unit and can offer great influence over the NLO origin. This research result also gives us a feasible design strategy and research system to explore new IR NLO candidates.

The mixed-anion GeS₃O unit induces huge improvement in the optical anisotropy and NLO response from Sr₂ZnGe₂O₇ oxide to Sr₂MGe₂S₆O oxysulfides.

BaI3O9H: a new alkaline-earth metal hydroxy iodate with two groups

A new alkali metal hydroxyl iodate BaI3O9H with a three-dimensional network structure and a moderate birefringence of 0.073 at 1064 nm.

KCs2Pb2(HCOO)2Cl5: A Lead Formate with Strong Second-Harmonic-Generation Response Obtained by an Anionic Substitution

Nonlinear optical (NLO) materials are playing an increasingly vital role in laser science and technology. Herein, we report a new lead formate, KCs₂Pb₂(HCOO)₂Cl₅, successfully synthesized by using mild mix-solvothermal methods. By the anionic substitution of a [CH₃COO] group with a [HCOO] group, the dipole moment of the distorted [PbCl₄O₂] polyhedron is increased. In contrast, polarization from the anionic group and the volume of the unit cell are reduced. Hence, KCs₂Pb₂(HCOO)₂Cl₅ possesses a strong second-harmonic-generation (SHG) response of 4.2 times that of KH₂PO₄ (KDP), a transparent window covering 0.43-1.87 μm, a large band gap of 3.52 eV, and moderate birefringence (0.11@1064 nm). Systematic theoretical calculations illustrate the origin of the linear and nonlinear optical properties of KCs₂Pb₂(HCOO)₂Cl₅. This research provides a viable strategy for the design and synthesis of new NLO crystals.

Synthesis and Characterization of Novel Nanoparticles of Lithium Aluminum Iodate LiAl(IO3)4, and DFT Calculations of the Crystal Structure and Physical Properties

Here we report on the non-hydrothermal aqueous synthesis and characterization of nanocrystalline lithium aluminum iodate, LiAl(IO₃)₄. Morphological and compositional analyses were carried out by using scanning electron microscopy (SEM) and energy-dispersive X-ray measurements (EDX). The optical and vibrational properties of LiAl(IO₃)₄ have been studied by UV-Vis and IR spectroscopy. LiAl(IO₃)₄ is found to crystallize in the non-centrosymmetric, monoclinic P2₁ space group, contrary to what was reported previously. Theoretical simulations and Rietveld refinements of crystal structure support this finding, together with the relatively high Second Harmonic Generation (SGH) response that was observed. Electronic band structure calculations show that LiAl(IO₃)₄ crystal has an indirect band gap Egap=3.68 eV, in agreement with the experimental optical band gap Egap=3.433 eV. The complex relative permittivity and the refraction index of LiAl(IO₃)₄ have also been calculated as a function of energy, as well as its elastic constants and mechanical parameters. LiAl(IO₃)₄ is found to be a very compressible and ductile material. Our findings imply that LiAl(IO₃)₄ is a promising material for optoelectronic and non -linear optical applications.

[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.

Sr2Pb(BeB5O10)(BO3): An Excellent Ultraviolet Nonlinear-Optical Beryllium Borate by the Pb-Modified Construction of a Conjugated System and Lone-Pair Effect

The design of material by chemical and/or crystalline modification of a classic structure model benefits not only the optimized physical properties but also the controllability and efficiency. Herein, a new nonlinear-optical (NLO) beryllium borate crystal, Sr₂Pb(BeB₅O₁₀)(BO₃) (SPBBO), is successfully designed and synthesized by chemical and crystalline modification of the perovskite-like K₃B₆O₁₀Cl NLO crystal. SPBBO displays a 3D BeB₅O₁₀^3- open-framework structure composed of interconnecting BeB₅O₁₃ groups with filled cationic Sr/Pb and anionic BO₃ groups, which exhibits the striking enhancement of the second-harmonic-generation (SHG) response (8 × KDP) and birefringence (0.10) compared to the parent model. Replacement of K by Sr and Pb with a lone pair and replacement of Cl by conjugated BO₃ result in the synergistic conjugation of Pb with host BeB₅O₁₀^3- and filled BO₃ groups, contributing to the striking enhancement of the SHG and birefringence. Single-crystal measurements show that SPBBO has a short UV absorption edge of 280 nm with a wide energy band gap of 4.35 eV and an outstanding laser-induced resistant behavior with a remarkably high laser-induced damage threshold of 2100 MW cm^-2. The excellent properties indicate that the SPBBO crystal is a very promising UV NLO functional material.

Tin Chloride Sulfates A3Sn2(SO4)3-xCl1+2x (A = K, Rb, Cs; x = 0, 1) as Multifunctional Optical Materials

The series of alkali-metal tin chloride sulfates A₃Sn₂(SO₄)_3-xCl_1+2x (A = K, Rb, Cs; x = 0, 1), K₃Sn₂(SO₄)₃Cl, Rb₃Sn₂(SO₄)₂Cl₃, and Cs₃Sn₂(SO₄)₂Cl₃, were successfully synthesized through an improved mild hydrothermal method. Interestingly, in addition to the cation size effect, the structure-directing effect of anions induces different symmetries in the three title compounds, with K₃Sn₂(SO₄)₃Cl being noncentrosymmetric, while Rb₃Sn₂(SO₄)₂Cl₃ and Cs₃Sn₂(SO₄)₂Cl₃ are centrosymmetric. Powder second-harmonic generation (SHG) measurements indicate that K₃Sn₂(SO₄)₃Cl is a nonlinear optical material that is type I phase matchable with a weak SHG response (0.1× KDP). Photoluminescence tests reveal that the three title compounds emit strong greenish yellow, orange, and salmon light, respectively, under UV excitation, indicating that they are promising inorganic solid fluorescent materials. Simultaneously, a detailed structural analysis of all the known tin(II) halide sulfates has been performed, which will guide the systematic exploration of high-performance tin(II)-based functional materials in the future.

Cd3(IO3)(IO4)F2·0.1CdO: A Nonlinear-Optical Crystal with the Introduction of Fluoride into Iodate Containing Both [IO3]- and [IO4]3- Groups

A new d¹⁰ transition-metal iodate fluoride, namely, Cd₃(IO₃)(IO₄)F₂·0.1CdO, was successfully designed and synthesized via the mid-infrared hydrothermal method. It crystallizes in the polar space group R3m and features the coexistence of the [IO₃]^- and [IO₄]^3- groups. Cd₃(IO₃)(IO₄)F₂·0.1CdO has a strong second-harmonic-generation response of about 3.0 times that of KDP(KH2PO4), large birefringence (0.133 at 546.1 nm), and a wide energy band gap (4.00 eV). In addition, the power laser damage threshold (LDT) measurement indicated that it possesses a high LDT of 84.29 MW/cm², which is about 30 times that of AgGaS₂. These superior properties showed that Cd₃(IO₃)(IO₄)F₂·0.1CdO may be an excellent nonlinear-optical crystal for visible and mid-infrared application.

SrTi(IO3)6·2H2O and SrSn(IO3)6: distinct arrangements of lone pair electrons leading to large birefringences

Three new iodates SrTi(IO₃)₆·2H₂O, (H₃O)₂Ti(IO₃)₆, and SrSn(IO₃)₆ have been synthesized via a facile hydrothermal method. The three compounds have zero-dimensional crystal structures composed of one [MO₆]⁸⁻ (M = Ti, Sn) octahedron connected with six [IO₃]⁻ trigonal pyramids. However, the particular coordination of Sr²⁺ cations results in distinct arrangements of lone pair electrons in an [IO₃]⁻ trigonal pyramid, which leads to large birefringences. More importantly, this work enriches the species crystal chemistry for [M(IO₃)₆]²⁻ (M = Ti, Sn) clusters-containing iodates.

The distinct arrangements of [IO₃]⁻ trigonal pyramids lead to larger birefringences in SrTi(IO₃)₆·2H₂O and SrSn(IO₃)₆ than that in (H₃O)₂Ti(IO₃)₆.

Na3Bi(IO3)6: An Alkali-Metal Bismuth Iodate with Intriguing One-Dimensional [BiI6O18] Chains and Pressure-Induced Structural Transition

An alkali-metal bismuth iodate, Na₃Bi(IO₃)₆, was successfully obtained by the hydrothermal method for the first time and contains intriguing one-dimensional [BiI₆O₁₈] chains. High-pressure Raman spectra were carried out to investigate the structural transition of Na₃Bi(IO₃)₆. Electronic states and anisotropic optical responses were also investigated by theoretical calculations.

An inherently kidney-targeting near-infrared fluorophore based probe for early detection of acute kidney injury

Acute kidney injury (AKI) is common in hospital patients. Delayed diagnosis and treatment of AKI due to the lack of efficient early diagnosis is an important cause of its high mortality. While fluorescence imaging seems promising to non-intrusively interrogate AKI-related biomarkers, the low kidney contrast of many fluorophores conferred by their relatively low abundance of distribution in the kidney limits their application for AKI detection. Herein, we discovered a near-infrared fluorophore with inherent kidney-targeting ability. Based on this fluorophore, a fluorogenic probe (KNP-1) was developed by targeting peroxynitrite (ONOO^-), which is upregulated at the early onset of AKI. KNP-1 exhibits desirable kidney distribution after intravenous administration and is fluorescent only after activation by ONOO^-. These properties lead to excellent kidney contrast imaging results. KNP-1 is capable of detecting both nephrotoxin-induced and ischemia-reperfusion injury-induced AKI in live mice. Temporally resolved imaging of AKI-disease model mice with KNP-1 suggests a gradual increase in renal ONOO^- levels with disease progression. Notably, the upregulation of ONOO^- can be observed at least 24 h earlier than the clinically popular sCr and BUN methods. Blocking ONOO^- generation also proves beneficial. These results highlight the applicability of this inherently tissue targeting-based strategy for designing probes with desirable imaging contrast; potentiate ONOO^- as a biomarker and target for AKI early diagnosis and medical intervention; and imply the clinical relevance of KNP-1 for AKI early detection.

Bi32Cd3P10O76: a new congruently melting nonlinear optical crystal with a large SHG response and a wide transparent region

Large size single crystal Bi₃₂Cd₃P₁₀O₇₆ with a large SHG response (4 × KDP) and a wide transmission range covering 0.36–4.9 μm.

Pressure-dependent modifications in the optical and electronic properties of Fe(IO3)3: the role of Fe 3d and I 5p lone–pair electrons

The electronic and transport properties of Fe(IO3)3 have been characterized under compression. A nice correlation of bandgaps of iodates to orbital configuration is proposed giving an explanation for the 2.1 eV bandgap of Fe(IO3)3.

High-Pressure Spectroscopy Study of Zn(IO3)2 Using Far-Infrared Synchrotron Radiation

We report the first high-pressure spectroscopy study on Zn(IO3)2 using synchrotron far-infrared radiation. Spectroscopy was conducted up to pressures of 17 GPa at room temperature. Twenty-five phonons were identified below 600 cm−1 for the initial monoclinic low-pressure polymorph of Zn(IO3)2. The pressure response of the modes with wavenumbers above 150 cm−1 has been characterized, with modes exhibiting non-linear responses and frequency discontinuities that have been proposed to be related to the existence of phase transitions. Analysis of the high-pressure spectra acquired on compression indicates that Zn(IO3)2 undergoes subtle phase transitions around 3 and 8 GPa, followed by a more drastic transition around 13 GPa.

Simple New Method for the Preparation of La(IO3)3 Nanoparticles

We present a cost- and time-efficient method for the controlled preparation of single phase La(IO₃)₃ nanoparticles via a simple soft-chemical route, which takes a matter of hours, thereby providing an alternative to the common hydrothermal method, which takes days. Nanoparticles of pure α-La(IO₃)₃ and pure δ-La(IO₃)₃ were synthesised via the new method depending on the source of iodate ions, thereby demonstrating the versatility of the synthesis route. The crystal structure, nanoparticle size-dispersal, and chemical composition were characterised via angle- and energy-dispersive powder X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy.

Methylation Design Strategy to Trigger a Dual Dielectric Switch and Improve the Phase Transition Temperature

Phase transitions of hybrid materials have aroused widespread concern and call for an in-depth study on its structure design, because the structure and characteristics are closely related, which promote potential applications in the field of temperature sensors, dielectric switches, and actuators. However, designing materials with multiple phase transitions and a high phase transition temperature (Tr) remains a huge challenge. In order to deal with this key hurdle, we tried to regulate the structural components and successfully synthesized [MASD]₂[CdCl₄] (1, MASD = 8-methyl-5-azoniaspiro[4,5]decane), which displays multiple phase transitions occurring at 273.8 K and 395.9 K separately. The Tr has significantly increased compared with the parent compounds reported previously. As the temperature sensitivity of compound 1 is constant at different frequencies, it can be applied for detectors or sensors under frequency-independent or wide frequency conditions. Moreover, methylation design strategy evidently triggered the dual dielectric switch and improved the Tr, which opens a new path for finding and adjusting ideal materials of multiple phase transition.

From Ag2 Zr(IO3 )6 to LaZr(IO3 )5 F2 : A Case of Constructing Wide-band-gap Birefringent Materials through Chemical Cosubstitution

Two mixed-metal zirconium iodates were prepared and studied as a case of chemical cosubstitution. The structure of Ag₂ Zr(IO₃ )₆ (P2₁ /c) features 0D [Zr(IO₃ )₆ ]^2- anion group and 1D [Ag(IO₃ )₂ ]^- anionic chain, with the [Zr(IO₃ )₆ ]^2- anion groups interconnected by Ag⁺ ions into 3D network; LaZr(IO₃ )₅ F₂ (P2₁ /n) features 0D [Zr(IO₃ )₅ F₂ ]^3- anion group and 2D [La(IO₃ )₅ ]^2- anionic layer, with the [Zr(IO₃ )₅ F₂ ]^3- groups interlinked by La³⁺ ions into 3D structure. Notably, LaZr(IO₃ )₅ F₂ is the first zirconium iodate fluoride reported. Wide optical band gaps of 3.77 and 4.13 eV are given for Ag₂ Zr(IO₃ )₆ and LaZr(IO₃ )₅ F₂ , respectively. Theoretical calculations confirmed that the weak d-d transition of Zr⁴⁺ in the band structure leads to a moderate band gap of Ag₂ Zr(IO₃ )₆ , and the introduction of F^- into the zirconium iodate compound results in a large band gap of LaZr(IO₃ )₅ F₂ . Both of the compounds are birefringent materials with birefringences of 0.064 @1064 nm and 0.082 @1064 nm, respectively.

Enhanced Proton Conductivity by Aliovalent Substitution of Cadmium for Indium in Dimethylaminium-Templated Metal Anilicates

Metal-organic frameworks (MOFs) with excellent proton conducting ability are crucial to fuel cells, chemical sensors, and redox flow batteries, but achieving them remain a challenge because of the difficulty in simultaneous fulfillment of large number of proton carriers, high mobility of protons, and long-term durable proton conduction. To explore a simple, efficient, and general route toward highly proton-conducting MOFs, we propose herein an aliovalent substitution metal strategy for isostructural aminium-templated MOFs which benefit the acquisition of rich proton sources without modifying ligands or exchanging protic organic molecules. This idea is verified by 100-fold enhancement of conductivity in compounds (Me₂NH₂)₂[Cd(mdhbqdc)₂] (Cd-BQ) and (Me₂NH₂) (Me₂NH)[In(mdhbqdc)₂] (In-BQ) (H₂mdhbqdc = dimethyl 3,6-dihydroxy-2,5-benzoquinone-1,4-dicarboxylic acid) that feature three-dimensional diamond-like structures with two-dimensional intersected channels. Accompanied by the in situ formation of an anilicate ligand, a great number of -OH groups are grafted onto the inner wall of pores, which interact with neutral Me₂NH and/or protonated Me₂NH₂⁺ cations via N-H···O hydrogen bonds. The high concentration of protons and dynamics of protic amines in the porous framework readily leads to a moderate conductivity of In-BQ (2.10 × 10^-4 S cm^-1, at 303 K under 95% RH) and an activation energy of 0.73 eV (95% RH). It should be noted that the aliovalent substitution of Cd(II) for In(III) results in the doubling of dimethylaminium proton carriers in Cd-BQ, indicating more frequent hopping and multiple proton-transfer pathways. This indication is supported by a very high protonic conductivity of 2.30 × 10^-2 S cm^-1 and a reduced activation energy of 0.48 eV under the same conditions. Molecular dynamics simulations visually elucidate the fact that compared with In-BQ, aliovalent-substituted Cd-BQ has shorter proton-migration distances, which in combination with more proton numbers results in more frequent hopping and sliding of protons, in agreement with the experimental results.

Large nonlinear optical effect in tungsten bronze structures via Li/Na cross-substitutions

By a simple cross-substitution of A-site Li/Na in tetragonal tungsten bronze (TTB) structures, we successfully synthesized a new niobate compound, Pb2.15(Li0.25Na0.75)0.7Nb5O15, with a superstructure. This compound exhibits a strong second harmonic generation (SHG) up to ∼47 × KDP. The large SHG response is related to strengthened local distortion, manifesting cross-substitution as a possibly general route to improve the NLO effect in stiff and low symmetric structures.

M4LiBe4P7O24 and M4Li(Li3P)P7O24 (M = Cs, Rb): deep-ultraviolet nonlinear-optical phosphates with a tetrahedra-substituted paracelsian-like framework

Paracelsian-like beryllophosphates M₄LiBe₄P₇O₂₄ and tetrahedra-substituted phases M₄Li(Li₃P)P₇O₂₄ (M = Cs, Rb) undergo structural transformation originating from the nature of tetrahedral cations.

From centrosymmetric to noncentrosymmetric: intriguing structure evolution in d10-transition metal iodate fluorides

Two new d10-transition metal iodate fluorides, centrosymmetric ZnIO3F and noncentrosymmetric CdIO3F, were successfully synthesized by intriguing structure evolution. Both compounds have higher thermal stability and CdIO3F has a large SHG response and wide band gap. Our study may afford a viable route to design materials with excellent NLO functions.