Optimization of Functional Building Blocks Generates a Substantial Improvement in Birefringence from Sn2OSO4 to Sn3O2(OH)(HSO4).

In this work, two tin(II)-based sulfates, Sn2OSO4 and Sn3O2(OH)(HSO4), were synthesized via the mild hydrothermal method. Both compounds employ the Sn2+ cation with stereochemically active lone pair (SCALP) electrons and non-π-conjugated tetrahedral anionic groups SO4 as the functional structural blocks. Interestingly, the experimental birefringence of Sn3O2(OH)(HSO4) is 0.169@546 nm, approximately 42 times larger than that of Sn2OSO4, which is 0.004@546 nm. Detailed structural analysis and theoretical calculations suggest that this significant birefringence difference arises from the optimization of functional building blocks in coordination environments and spatial arrangements. Furthermore, both compounds exhibit ultraviolet absorption edges at 308 and 307 nm, respectively. This indicates that Sn3O2(OH)(HSO4) has the potential to be a candidate for an ultraviolet (UV) birefringent crystal. This study offers inspiration for further exploration of tin(II)-based compounds with excellent comprehensive properties.

Gradual Increase in Birefringence of Antimony Oxalates through Precise Tuning of the Sb3+/[C2O4]2- Ratio.

Birefringent crystals play a crucial role in modulating and controlling the polarization of light in the optical communication and laser industries. Recently, adopting appropriate strategies to enhance the birefringence of crystals has become a prominent area of research focus. Herein, four UV antimony oxalate birefringent crystals, namely, K5Sb2(C2O4)5.5·3H2O, BaSb(C2O4)2.5·3H2O, Na4Sb2O(C2O4)4·6H2O, and Na3Sb(C2O4)2F2·2H2O, have been successfully synthesized. These compounds feature a similar zero-dimensional (0D) cluster structure and share the same functional groups, including π-conjugated [C2O4]2- groups and Sb3+-based distorted polyhedra with stereochemically active lone pairs (SCALPs). Interestingly, we achieved a stepwise increase in birefringence by precisely controlling the Sb3+/[C2O4]2- ratio, ultimately resulting in the compound Na3Sb(C2O4)2F2·2H2O exhibiting a large birefringence (0.21@546 nm). Additionally, we confirmed that the synergistic effects between the π-conjugated [C2O4]2- groups and the distorted polyhedra based on Sb3+ are responsible for the excellent optical properties observed in the reported compounds.

Sb2O2SeO3 and Sb2O(SeO3)2: Two-Layered Antimony(III) Selenites with Enhanced Birefringence.

Two antimony selenites, Sb2O2SeO3 and Sb2O(SeO3)2, were synthesized by simultaneously incorporating stereochemically active lone pair electrons containing SeO32- and Sb3+. These compounds are structured with [SbOx] polyhedra and [SeO3] units within a two-dimensional framework. Both of them exhibit cutoffs at 300 and 330 nm within the ultraviolet (UV) range and demonstrate significant birefringence, with indices of 0.069 and 0.126 at 546 nm, respectively. These properties highlight their potential as UV birefringent materials. Structural analyses and theoretical calculations reveal that their exceptional birefringence results from the synergistic interactions between SeO32- anions and Sb3+ cations.

Na4Sn4(C2O4)3F6 and NaSnC2O4F·H2O: two tin(II) fluoride oxalates display large birefringence.

Birefringent materials play an important role in laser techniques as an essential part of optical devices. Therefore, the exploration of high-performance birefringent materials has been a central focus of researchers. Herein, two tin(II) fluoride oxalates Na4Sn4(C2O4)3F6 and NaSnC2O4F·H2O were gained by the combination of birefringence-active groups of Sn2+ with stereochemically active lone pairs and planar π-conjugated [C2O4]2- groups. These groups assemble into low-dimensional structures of 0D [C2O4F4]6- clusters and 1D [SnC2O4F]∞- chains in Na4Sn4(C2O4)3F6, and double [Sn2(C2O4)2F2]∞2- chains in NaSnC2O4F·H2O, which gives rise to the large birefringence of 0.160@546 nm and 0.189@546 nm, respectively. Detailed structure-property analysis and theoretical calculations indicate that strong optical anisotropy can be induced by the rational arrangement of the Sn2+-polyhedra and [C2O4]2- groups.

Two Short-Wave UV Antimony(III) Sulfates Exhibiting Large Birefringence.

In the present work, we have successfully obtained two new UV antimony-based sulfates, NH4Sb(SO4)2 and Ca2Sb2O(SO4)4, by a conventional hydrothermal method. Interestingly, both compounds share similar structural building blocks, such as SbO4 seesaws and SO4 tetrahedra, yet they endow discrepant birefringence values measured at 546 nm with values of 0.150 and 0.114, respectively, owing to the different distortions of the SbO4 groups with SCALP electrons. Moreover, both compounds display large band gaps (4.32 and 4.43 eV, respectively), so they can be used as short-wavelength UV birefringent materials. Moreover, NH4Sb(SO4)2 is a noncentrosymmetric compound, showing a frequency doubling effect of 0.2 × KDP. Detailed structural analyses and calculations confirm the source of superior optical performance and the reasons for the different birefringence of the two compounds. This work provides ideas for the following discovery of antimony-based optical materials with excellent properties.

A2Hgx(SeO3)y (A = K, Rb, Cs): Three Alkali Metal Mercury Selenites Featuring Unique 1D [HgOm(SeO3)n]∞ Chains.

Herein, three alkali metal mercury selenites, K2Hg2(SeO3)3, Rb2Hg2(SeO3)3, and Cs2Hg3(SeO3)4, were successfully obtained by a hydrothermal method. The three compounds featured same one-dimensional (1D) [HgOm(SeO3)n]∞ chain structure that consisting of distorted Hg-O polyhedra and SeO3 triangular pyramids with stereochemically active lone pair (SCALP) electrons. Interestingly, the rich coordination environment of Hg atoms and the size difference of alkali metal cations lead to diverse arrangement of SeO3 groups, which makes them exhibit different birefringence. The band gaps of the three compounds indicate that they are potential ultraviolet (UV) optical materials. Detailed theoretical calculations demonstrate that the combined effects of SeO3 triangular pyramids and Hg-O polyhedra are responsible for the optical characteristics of the reported compounds.

Centrosymmetric Rb2Sb(C2O4)2.5(H2O)3 and Noncentrosymmetric RbSb2(C2O4)F5: Two Antimony (III) Oxalates as UV Optical Materials.

Herein, we have successfully synthesized two rubidium antimony (III) oxalates, namely, Rb2Sb(C2O4)2.5(H2O)3 and RbSb2(C2O4)F5, utilizing a low-temperature hydrothermal method. These two compounds share a similar chemical composition, consisting of Sb3+ cations with active lone pair electrons, alkali metal Rb+ ions, and planar π-conjugated C2O42- anions. However, they exhibit different symmetries, Rb2Sb(C2O4)2.5(H2O)3 is centrosymmetric (CS), while RbSb2(C2O4)F5 is noncentrosymmetric (NCS), which should be caused by the presence of F- ions. Notably, the NCS compound, RbSb2(C2O4)F5, demonstrates a moderate second-harmonic generation (SHG) response, approximately 1.3 times that of KH2PO4 (KDP), and exhibits a large birefringence of 0.09 at 546 nm. These characteristics indicate that RbSb2(C2O4)F5 holds promising potential as a nonlinear optical material for ultraviolet (UV) applications. Detailed structural analysis and theoretical calculations confirm that the excellent optical properties arise from the synergistic effects between Sb3+ cations with SCALP and planar π-conjugated [C2O4]2- groups.

A Novel Fusion Method for State-of-Charge Estimation of Lithium-Ion Batteries Based on Improved Genetic Algorithm BP and Adaptive Extended Kalman Filter.

The lithium-ion battery is the power source of an electric vehicle, so it is of great significance to estimate the state of charge (SOC) of lithium-ion batteries accurately to ensure vehicle safety. To improve the accuracy of the parameters of the equivalent circuit model for batteries, a second-order RC model for ternary Li-ion batteries is established, and the model parameters are identified online based on the forgetting factor recursive least squares (FFRLS) estimator. To improve the accuracy of SOC estimation, a novel fusion method, IGA-BP-AEKF, is proposed. Firstly, an adaptive extended Kalman filter (AEKF) is used to predict the SOC. Then, an optimization method for BP neural networks (BPNNs) based on an improved genetic algorithm (IGA) is proposed, in which pertinent parameters affecting AEKF estimation are utilized for BPNN training. Furthermore, a method with evaluation error compensation for AEKF based on such a trained BPNN is proposed to enhance SOC evaluation precision. The excellent accuracy and stability of the suggested method are confirmed by the experimental data under FUDS working conditions, which indicates that the proposed IGA-BP-EKF algorithm is superior, with the highest error of 0.0119, MAE of 0.0083, and RMSE of 0.0088.

Hg3(SeO3)2(SO4): A UV Nonlinear Optical Mercury Selenite Sulfate Constructed by Neat [Hg6O8(SeO3)4]∞ Layers and SO4 Tetrahedra.

A novel mercury selenite sulfate named Hg3(SeO3)2(SO4) has been successfully synthesized under a mild hydrothermal method. Hg3(SeO3)2(SO4) crystallizes in a monoclinic space group P21 and features a unique three-dimensional (3D) frame structure formed by [Hg6O8(SeO3)4]∞ layers and SO4 tetrahedra, which enables it to exhibit a comprehensive performance of a moderate second-harmonic generation (SHG) response of approximately 1.3 times that of baseline KH2PO4 (KDP), a moderate birefringence (0.118@546 nm), and a wide band gap (4.70 eV), which indicates that it has potential for application as an ultraviolet (UV) nonlinear optical material. Detailed theoretical calculations show that the Hg2+-based polyhedra with large polarizability and deformability and the SeO3 groups with stereochemically active lone pair (SCALP) electrons are the main contributors to moderate optical properties.

A flexible functional module to regulate ultraviolet optical nonlinearity for achieving a balance between a second-harmonic generation response and birefringence.

Rigid planar π-conjugated groups are adopted for designing ultraviolet (UV) nonlinear optical (NLO) materials extensively. However, for these UV NLO crystals, the realization of a strong second harmonic generation (SHG) response is commonly accompanied by undesired overlarge birefringence. Herein, we propose a new functional gene, the flexible π-conjugated (C3H2O4)2- group, for designing a UV NLO crystal with a balance between the SHG response and birefringence. Furthermore, the combination of low-coordinated and high-coordinated alkali cations with the flexible (C3H2O4)2- group results in finding a new mixed alkali malonate, KLi(C3H2O4)·H2O (KLMW). As expected, KLMW exhibits a strong SHG efficiency (3 × KDP) and moderate birefringence (0.103 @ 1064 nm). In addition, it has a short UV cut-off edge of 231 nm and can be conveniently grown from solution. More importantly, it realized fourth harmonic generation with type-I phase-matching. Therefore, these excellent properties make KLMW a potential practical UV NLO material.

Sharp Enhancement of Birefringence in Antimony Oxalates Achieved by the Cation-Anion Synergetic Interaction Strategy.

Birefringent materials with large birefringence play an important role in in laser science and technology owing to their ability to modulate polarized light. However, the lack of systematic and effective synthesis strategies severely hinders the development of novel superior birefringent materials. Herein, the cation-anion synergetic interaction strategy was proposed to successfully synthesize two excellent UV birefringent materials, RbSb(C2O4)F2·H2O and [C(NH2)3]Sb(C2O4)F2·H2O. Both compounds feature unprecedented [Sb(C2O4)F2]∞- anionic chains composed of planar π-conjugated [C2O4]2- units and a distorted SbO4F2 complex with stereochemically active lone pairs, which induce a large optical anisotropy. Remarkably, further enhancement of birefringence in [C(NH2)3]Sb(C2O4)F2·H2O was achieved via cation-anion synergetic interactions between the [C(NH2)3]+ cationic groups and [Sb(C2O4)F2]∞- anionic chains. It exhibited a giant birefringence of 0.323@546 nm, twice larger than that of its analogue RbSb(C2O4)F2·H2O (0.162@546 nm). A detailed structural analysis and theoretical calculations revealed that the cation-anion synergetic interaction strategy is an effective strategy for the efficient exploration of superior birefringent materials, which will guide the further exploration of new structure-driven functional materials.

Mg2In3Si2P7: A Quaternary Diamond-like Phosphide Infrared Nonlinear Optical Material Derived from ZnGeP2.

Balancing the second-harmonic generation (SHG) coefficient, band gap, and birefringence is a vital but addressable challenge for designing infrared nonlinear optical materials. By applying a "rigidity-flexibility coupling" strategy, a quaternary diamond-like phosphide, Mg2In3Si2P7, with wurtzite-type superstructure was successfully designed and synthesized. Remarkably, it achieved the rare coexistence of giant second-harmonic generation (2 × ZnGeP2 and 7.1 × AgGaS2), suitable band gap (2.21 eV), moderate birefringence (0.107), and wide IR transparent range (0.56-16.4 µm). First-principles calculations revealed that the giant SHG response and large birefringence can be attributed to the synergy of arrangement-aligned [InP4] and [SiP4] tetrahedra. This work not only opens a new avenue for designing advanced infrared nonlinear optical materials but also may spur more explorations on quaternary diamond-like pnictides.

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.

Unexpected aliovalent cation substitution between two NLO materials LiBa3Bi6(SeO3)7F11 and Ba3Bi6.5(SeO3)7F10.5O0.5.

One new combination, alkali-metal and alkaline earth-metal selenite fluoride, LiBa3Bi6(SeO3)7F11 (LBBSF) and its analogue Ba3Bi6.5(SeO3)7F10.5O0.5 (BBSF) were reported here for the first time. Unusual aliovalent cation substitution between them affected the layer thickness and made the bond strains of [SeO3] enhanced, thereby inducing greater distortions and affecting the SHG efficiencies. This work may provide thoughts for exploring new NLO materials.

Explorations of Second-Order Nonlinear Optical Materials in the Alkaline Earth Barbiturate System: Noncentrosymmetric Ca(H3C4N2O3)2·H2O and Centrosymmetric Sr(H5C8N4O5)2·4H2O.

Two new alkaline earth barbiturates, Ca(H3C4N2O3)2·H2O and Sr(H5C8N4O5)2·4H2O, were synthesized via the mild hydrothermal technique. For Ca(H3C4N2O3)2·H2O, the stacking (H3C4N2O3)- anions along the c axis are interconnected by CaO7 polydedra forming a three-dimensional structure. Also, for Sr(H5C8N4O5)2·4H2O, it has two-dimensional layers composed by SrO7 polyhedra and (H5C8N4O5)- anions. The (H5C8N4O5)- anions can be seen as two (H3C4N2O3)- anions connected each other via the N-C bond. Powder second-harmonic generation (SHG) measurements revealed that Ca(H3C4N2O3)2·H2O is a phase-matchable material with a moderate SHG response (ca. 1.15× that of KDP). Furthermore, the birefringence values of the two crystals were measured as 0.49 and 0.475 at 546.1 nm, respectively. The theoretical calculations showed that the SHG response and large birefringence were primarily caused by the (H3C4N2O3)- and (H5C8N4O5)- groups.

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.

A(H3C3N3O3)(NO3) (A = K, Rb): Alkali-Metal Nitrate Isocyanurates with Strong Optical Anisotropy.

The first alkali-metal nitrate isocyanurates, A(H3C3N3O3)(NO3) (A = K, Rb), were synthesized by the tactic of introducing (NO3)- into isocyanurate with a mild hydrothermal technique. They crystallized into the same monoclinic centrosymmetric (CS) space group P21/c, which featured a 2D [(H3C3N3O3)(NO3)]∞ layered structure separated by K+ and Rb+ cations, respectively. Both compounds exhibited short ultraviolet cutoff edges (λcutoff = 228 and 229 nm) and large birefringences (Δn = 0.253 and 0.224 at 546.1 nm). More importantly, in comparison with most of the isocyanurates and nitrates, they have better thermal stability with decomposition temperatures up to 319.8 and 324.4 °C. In addition, our theoretical calculations reveal that the π-conjugated groups play significant roles in improving the optical anisotropy. Remarkably, introducing a π-conjugated inorganic acid radical (NO3)- into isocyanurate is an extremely meaningful strategy to explore new UV birefringent crystals.

Sr[B(OH)4](IO3) and Li4Sr5[B12O22(OH)4](IO3)2: two unprecedented metal borate-iodates showing a subtle balance of enlarged band gap and birefringence.

Two unprecedented metal borate-iodates, Sr[B(OH)4](IO3) (SBIO) and Li4Sr5[B12O22(OH)4](IO3)2 (LSBIO), were synthesized via the strategy of introducing (IO3)- into borates. In particular, the LSBIO possessed a new B12O26 fundamental building block (FBB). The two compounds integrated the advantages of both pure iodates and borates, showing enlarged band gaps and birefringence. Moreover, diverse B-O FBBs achieved the modulation of birefringence. This work reported the first two examples of borate-iodates.

RE(H2C3N3O3)2·(OH)·xH2O (RE = La, Y and Gd): potential UV birefringent materials with strong optical anisotropy originating from the (H2C3N3O3)- group.

A new series of dihydro-isocyanurates, namely, RE(H2C3N3O3)2·(OH)·xH2O (RE = La, Y and Gd) was readily obtained by a mild hydrothermal technique using lithium hydroxide as a deprotonation agent. La(H2C3N3O3)2·OH·2H2O and Re(H2C3N3O3)2·OH·5H2O (Re = Y, Gd) crystallized in the centrosymmetric (CS) space groups P21/c and P1[combining macron], respectively. Their intricate 3D frameworks were built by cationic polyhedrons (LaO8N/ReO8) and (H2C3N3O3)- groups. The experiments and theoretical studies demonstrated that these compounds possessed short ultraviolet cut-off edges (≤240 nm) and large birefringences (Δn≥ 0.257@546.1 nm). In addition, the theoretical studies further revealed that the (H2C3N3O3)2- group plays a pivotal role in strengthening the optical anisotropy for all compounds.

A new 4-Amino-7-Nitro-2,1,3-Benzoxadiazole (ANBD)-Based Fluorescent Probe for the Detection of Hg2.

Based on the photoinduced electron transfer (PET) principle, 4-amino-7-nitro-2,1,3-benzoxadiazole (ANBD) has been used as a fluorophore to develop a new fluorescent probe, 4-(2-N,N-dimethylthioacetamide)amino-7-nitro-2,1,3-benzoxadiazole (2), for the detection of Hg2+. Upon the addition of Hg2+, a 46-fold fluorescence enhancement occurs. Moreover the probe 2 exhibits a high selectivity and sensitivity to Hg2+, even in the presence of other common metal ions. Under optimal reaction conditions, a good linearity can be obtained in the range of 0.5-2.5 µM, and the detection limit is 0.05 µM. In addition, the desulfurization reaction mechanism is proposed based on electrospray ionization mass spectrum. The present study is not only a supplement to the detection method of Hg2+, but also a merit to the development of ANBD-based fluorescent probes.