Short Edge Research Articles

SrCl2·6H2O: An Alkaline-Earth-Metal Chloride Hexahydrate as Deep-Ultraviolet Nonlinear-Optical Crystal with the {[Sr(H2O)6]2+}∞ Cationic Framework.

Exploring deep-ultraviolet (DUV) nonlinear-optical (NLO) materials is significant for the conversion of high-frequency laser. Herein, two alkali-earth-metal halide hexahydrates, SrX2·6H2O (X = Cl, Br), were obtained, and the centimeter-sized single crystals of SrCl2·6H2O were grown by a slow evaporation method. Both of them crystallize in the trigonal space group P321, and their crystal structures show {[Sr(H2O)6]2+}∞ cationic chains, with isolated Cl- or Br- anions interspersed between the chains. SrCl2·6H2O exhibits a moderate second-harmonic-generation response (0.4 × KDP) at 1064 nm and can realize phase matching. Importantly, SrCl2·6H2O has a short ultraviolet cutoff edge (<200 nm). Crystal growth, crystal structures, optical performances, and theoretical calculations of the title and related compounds have been discussed in this work. This study enriches the understanding of metal halide hydrates as NLO materials in the DUV region.

Bi2O2Se Nanowire/MoSe2 Mixed-Dimensional Polarization-Sensitive Photodiode with a Nanoscale Ultrafast-Response Channel.

In recent years, polarization-sensitive photodiodes based on one-dimensional/two-dimensional (1D/2D) van der Waals (vdWs) heterostructures have garnered significant attention due to the high specific surface area, strong orientation degree of 1D structures, and large photo-active area and mechanical flexibility of 2D structures. Therefore, they are applicable in wearable electronics, electrical-driven lasers, image sensing, optical communication, optical switches, etc. Herein, 1D Bi2O2Se nanowires have been successfully synthesized via chemical vapor deposition. Impressively, the strongest Raman vibration modes can be achieved along the short edge (y-axis) of Bi2O2Se nanowires with high crystalline quality, which originate from Se and Bi vacancies. Moreover, the Bi2O2Se/MoSe2 photodiode designed with type-II band alignment demonstrates a high rectification ratio of 103. Intuitively, the photocurrent peaks are mainly distributed in the overlapped region under the self-powered mode and reverse bias, within the wavelength range of 400-nm. The resulting device exhibits excellent optoelectrical performances, including high responsivities (R) and fast response speed of 656 mA/W and 350/380 μs (zero bias) and 17.17 A/W and 100/110 μs (-1 V) under 635 nm illumination, surpassing the majority of reported mixed-dimensional photodiodes. The most significant feature of our photodiode is its highest photocurrent anisotropic ratio of ∼2.2 (-0.8 V) along the long side (x-axis) of Bi2O2Se nanowires under 635 nm illumination. The above results reveal a robust and distinctive correlation between structural defects and polarized orientation for 1D Bi2O2Se nanowires. Furthermore, 1D Bi2O2Se nanowires appear to be a great potential candidate for high-performance rectifiers, polarization-sensitive photodiodes, and phototransistors based on mixed vdWs heterostructures.

Mixed Alkali Metal and Alkaline Earth Metal Scandium Borate Birefringence Material with Layered Structure and Short Ultraviolet Cutoff Edge.

Birefringent crystals are essential in the domains of linear and nonlinear optics that need light wave polarization control. Rare earth borate has become a popular study material for ultraviolet (UV) birefringence crystals due to its short cutoff edge in the UV area. RbBaScB6O12, a two-dimensional layered structure compound with the B3O6 group, was effectively synthesized through spontaneous crystallization. The UV cutoff edge of RbBaScB6O12 is shorter than 200 nm, and the experimental birefringence is 0.139 @ 550 nm. Theoretical research indicates that the large birefringence originates from the synergistic impact of the B3O6 group and the ScO6 octahedron. RbBaScB6O12 is an outstanding candidate material for birefringence crystals in the UV and even deep UV regions due to its short UV cutoff edge and significant birefringence.

Na4[B6O9 (OH)3](H2O) Cl: A Deep-Ultraviolet Transparent Nonlinear Optical Borate Chloride with {[B6O9 (OH)3]3-}∞ Chains.

The development of nonlinear-optical (NLO) crystals with short ultraviolet cutoff edges is significant and challenging. Here, a new sodium borate chloride, Na4[B6O9 (OH)3](H2O) Cl, was successfully obtained by the mild hydrothermal method, which crystallizes in a polar space group Pca21. The structure of the compound is characterized by {[B6O9 (OH)3]3-}∞ chains. Measurements of optical properties indicate the compound exhibits a deep-ultraviolet (DUV) cutoff edge (≤200 nm) and moderate second harmonic generation response (0.4 × KH2PO4). It presents the first DUV hydrous sodium borate chloride NLO crystal and the first sodium borate chloride possessing a one-dimensional B-O anion framework. Probing into the connection of structure and optical properties has been performed based on theoretical calculations. These results are instructive for designing and obtaining new DUV NLO materials.

ASb(SO4)2 (A = Rb, Cs): Two short-wave UV antimony sulfates exhibiting large birefringence

Herein, two antimony sulfates, named RbSb(SO4)2 (1) and CsSb(SO4)2 (2), have been successfully synthesized with the introduction of Sb3+ cation with stereochemically active lone pairs (SCALP) into sulfates by the conventional hydrothermal method. Both two compounds endow short UV absorption edges (281 nm and 278 nm, respectively) and large birefringence ([email protected] nm and [email protected] nm, respectively), which means that they are promising short-wave ultraviolet (UV) optical materials. Interestingly, though both of the two compounds exhibit similar 1D chained structures, and possess the same functional moieties including SbO4 seesaws and SO4 tetrahedral groups, they exhibit significantly opposite macroscopic symmetries, i.e., compound 1 crystallizes in a centrosymmetric (CS) manner (P21/n) and compound 2 in a noncentrosymmetric (NCS) manner (P212121), due to the size of cations [r(Rb+) = 1.56 Å, r(Cs+) = 1.67 Å] affects the orientation of SCALP of the adjacent Sb3+.

Two New Aluminoborates with 3D Porous-Layered Frameworks.

Two new aluminoborates, NaKCs[AlB7O13(OH)]·H2O (1) and K4Na5[AlB7O13(OH)]3·5H2O (2), have been hydro(solvo)thermally made with mixed alkali metal cationic templates. Both 1 and 2 crystallize in the monoclinic space group P21/n and contain similar units of [B7O13(OH)]6- cluster and AlO4 tetrahedra. The [B7O13(OH)]6- cluster is composed of three classical B3O3 rings by vertex sharing, of which two of them connect with AlO4 tetrahedra to constitute monolayers, and one provides an O atom as a bridging unit to link two oppositely orientated monolayers by Al-O bonds to form 3D porous-layered frameworks with 8-MR channels. UV-Vis diffuse reflectance spectra indicate that both 1 and 2 exhibit short deep-UV cutoff edges below 190 nm, revealing that they have potential applications in deep-UV regions.

KHC2O4·B(OH)3: A nonlinear optical crystal with large birefringence in the short‐wavelength ultraviolet region

AbstractExploring nonlinear optical crystals with large birefringence in the short‐wavelength ultraviolet (SWUV) regions (≤300 nm) is a valuable pursuit. Herein, KHC2O4·B(OH)3, which is composed of infinite [HC2O4]− and [B(OH)3] chains, was successfully grown via the slow evaporation method. The [HC2O4]− and [B(OH)3] chains endow KHC2O4·B(OH)3 with the largest birefringence (0.164@1064 nm) of all B(OH)3‐containing compounds that have been reported in the SWUV regions. Moreover, it possesses a moderate second‐harmonic generation response (0.3 × KH2PO4) and a short UV cutoff edge of 254 nm. The electron localization function diagram indicates the large birefringence originates from the HC2O4 and B(OH)3 groups. This work provides a new method to investigate crystals with large birefringence in the B(OH)3‐based oxalate system.

Phosphates with Two Types of Isolated P–O Groups: Noncentrosymmetric Na6Sr2Bi3(PO4)(P2O7)4 and Centrosymmetric Cs2CaBi2(PO4)2(P2O7)

Inorganic phosphates are of great interest, because of their rich structural chemistry and multiple functional properties. Compared with the phosphates that only contain the solely condensed P-O groups, the phosphates with various condensed P-O groups are less reported, especially for the noncentrosymmetric (NCS) ones. Here, two new bismuth phosphates, Na6Sr2Bi3(PO4)(P2O7)4 and Cs2CaBi2(PO4)2(P2O7), were synthesized by the solid-state reaction and both structures contain two types of isolated P-O groups. Remarkably, Na6Sr2Bi3(PO4)(P2O7)4 crystallizes in the tetragonal space group P4̅21c, which represents the first NCS bismuth phosphate with PO4 and P2O7 groups. Detailed structural comparisons among Bi3+-containing alkali/alkaline-earth metal phosphates show that the ratios of cations/phosphorus profoundly influence the condensed degree of P-O groups. Ultraviolet-visible-near-infrared (UV-vis-NIR) diffusion spectra show that both compounds have the relatively short UV cutoff edges. And Na6Sr2Bi3(PO4)(P2O7)4 has a second-harmonic generation response of 1.1 × KDP. The first-principles calculations are carried out to understand the structure-performance relationship.

Designing a Strong Second-Harmonic Generation Polar Iodate by the Structure-Directing Properties of the “Tumbler-like” [Zn(IO3)(I2O5(OH))] Polyanions

Materials with second-harmonic generation (SHG) properties have attracted great attention in the field of photon technology. However, synthesis of materials with strong SHG responses and polar structure still faces enormous challenges. Herein, a new iodate K2Zn(IO3)3(I2O5(OH))(IO2(OH))(H2O) (KZIOH) was synthesized by coupling distorted ZnO6 octahedra with three diverse asymmetrical chromophores to assemble “tumbler-like” clusters, [Zn(IO3)(I2O5(OH))], which was the first noncentrosymmetric (NCS) and polar iodate containing isolated [IO3], [I2O5(OH)], and [IO2(OH)]. KZIOH exhibits the strongest SHG response (∼12 × KH2PO4 (KDP)@1064 nm) among the polyiodates with two or more types of isolate units and a short ultraviolet cutoff edge (262 nm). It also possesses a moderate birefringence (0.055@532 nm) and a wide band gap (4.0 eV), indicating KZIOH is a promising SHG material. Theoretical calculations and crystal structure analysis show that the asymmetric and top-heavy configurations of I–O groups around Zn-centered octahedral units with the aid of hydrogen bonding favor its polar structure and strong SHG response.

AKTeO2(CO3) (A = Li, Na): The First Carbonatotellurites Featuring a Zero-Dimensional [Te2C2O10]4– Cluster and a Wide Band Gap

The first carbonatotellurites, AKTeO2(CO3) (A = Li, Na), have been successfully synthesized by using boric acid as the mineralizer. AKTeO2(CO3) (A = Li, Na) crystallize in the monoclinic space group P21/n (no. 14), and their structures exhibit the novel zero-dimensional (0D) [Te2C2O10]4- clusters, in which two [TeO4]4- groups form a [Te2O6]4- dimer via edge-sharing, with each side of the dimer attached by a [CO3]2- group via a Te-O-C bridge. The alkali metal cations occupy the voids between the 0D clusters and maintain the charge balance. The ultraviolet-visible-near-infrared diffuse reflectance spectra show that the short absorption cut-off edges of LiKTeO2(CO3) (LKTC) and NaKTeO2(CO3) (NKTC) are 248 and 240 nm, respectively, and LKTC exhibits the largest experimental band gap (4.58 eV) among all of the tellurites containing the π-conjugated anionic groups reported. Theoretical calculations revealed that they exhibit moderate birefringences of 0.029 and 0.040@1064 nm, respectively.

Design, crystal growth and characterizations of novel bis morpholinium zinc bromide single crystals for optoelectronic applications

A novel metal-organic third-order nonlinear optical (NLO) material with promising excellent properties in the crucial solar blind UV region. For the first time, high NLO active metal-organic complex of bis-morpholinium zinc bromide (BMZB) single crystal has been rationally designed and single crystals have been grown by slow evaporation solution technique (SEST). Remarkably, the grown crystal exhibits competitive and even superior physical properties including high thermal stability and wider transparency than the standard NLO single crystal. The title compound crystallizes in the monoclinic crystal system with the space group of P21/cc and four molecules are accumulated in the unit cell (unit cell parameters are a = 6.7860 (6) Å, b = 16.6239 (2) Å, c = 14.8875 (2) Å, β = 94.937 (3)° and Z = 4). Further, the phase purity and the crystallinity of the grown sample were analyzed through powder X-ray diffraction (PXRD) analysis. The Fourier transform infrared (FTIR) spectroscopy analysis has been used to determine the presence of multifarious functional groups in the grown crystal. The recorded optical transmittance spectrum reveals that the BMZB crystal possesses good optical transparency in the range between deep ultraviolet (UV) and near-infrared (NIR) regions. Intriguingly, the short cut-off edge of the grown crystal is found to be about 227 nm which is more favorable for developing modern photonic and optoelectronic devices in the solar blind UV region. The thermal and mechanical stabilities of the grown crystals have been studied using Vickers microhardness and thermogravimetry (TG) and differential thermal analysis (DTA) respectively. Moreover, key requirements for designing practical NLO devices such as large laser damage threshold (LDT) and excellent third-order NLO response have been observed in the grown single crystal. Therefore, our findings open up a new avenue to the rational design of thermally stable and large NLO active metal-organic complexes for practical NLO applications.

Guided Wave-Based Damage Detection of Square Steel Tubes Utilizing Structure Symmetry

Square steel tube, which is widely used in civil engineering, can suffer from a wide variety of damages and aging defects, thus its nondestructive testing (NDT) has attracted wide attention. This work proposes an ultrasonic guided wave (UGW)-based damage detection method for square steel tubes using structure symmetry. Firstly, the dispersion characteristics of square steel tubes are obtained using the semi-analytical finite element (SAFE) method, after which the optimal guided wave modes for damage located on the long and short edges of the steel tube are selected by modal analysis. Then, using the symmetry of the square steel tube’s section, the symmetric layout scheme of the transmitters and the receivers is designed; on this basis, a signal processing strategy for damage detection is proposed by subtracting the receiving signals obtained from symmetric positions. Finally, the effectiveness of the proposed damage detection method is verified by numerical simulations and laboratory experiments. The results show that the proposed method has good inspection accuracy for crack and hole damages on both the long and short edges of square steel tube because the dispersion effect and clutters can be reduced utilizing structure symmetry. It is worth mentioning that the inspection effect for corner holes can be enhanced by modifying the position of the receivers.

CaB2O2F4: A Novel [BOF2]∞-Based Structural Template with a Strong Second Harmonic Generation Response and Large Band Gap

Nonlinear optical (NLO) materials are significant for their crucial role in the development of modern optoelectronic and laser technology. Recently, fluorooxoborates have aroused the widespread attention for their tight relationship between the micro-properties of functional [BOxF4–x](x+1)– (x = 0, 1, 2, and 3) modules and macroscopic performances. Nevertheless, whether fluorooxoborates with the anionic groups only composed of condensed [BO2F2] units exhibit a strong second harmonic generation (SHG) response remains unclear. Here, eight possible synthetic structures with the [BOF2]∞ chain in the CaB2O2F4 system were predicted by using evolutionary algorithm crystal structure prediction techniques. Among them, CaB2O2F4-I, II, IV, and V are centrosymmetric and CaB2O2F4-III, VI, VII, and VIII are non-centrosymmetric structures. Hence, CaB2O2F4-VI (C2) possesses an extremely short ultraviolet cutoff edge (147 nm) and the largest SHG coefficient among reported non-centrosymmetric fluorooxoborates only consisting of the [BO2F2] group. Also, the origin of the SHG coefficient was analyzed in detail through theoretical calculation.

The First UV Nonlinear Optical Selenite Material: Fluorination Control in CaYF(SeO3 )2 and Y3 F(SeO3 )4.

It is a great challenge to develop UV nonlinear optical (NLO) material due to the demanding conditions of strong second harmonic generation (SHG) intensity and wide band gap. The first ultraviolet NLO selenite material, Y3 F(SeO3 )4 , has been obtained by control of the fluorine content in a centrosymmetric CaYF(SeO3 )2 . The two new compounds represent similar 3D structures composed of 3D yttrium open frameworks strengthened by selenite groups. CaYF(SeO3 )2 has a large birefringence (0.138@532 nm and 0.127@1064 nm) and a wide optical band gap (5.06 eV). The non-centrosymmetric Y3 F(SeO3 )4 can exhibit strong SHG intensity (5.5×KDP@1064 nm), wide band gap (5.03 eV), short UV cut-off edge (204 nm) and high thermal stability (690 °C). So, Y3 F(SeO3 )4 is a new UV NLO material with excellent comprehensive properties. Our work shows that it is an effective method to develop new UV NLO selenite material by fluorination control of the centrosymmetric compounds.

Structural Motif Cosubstitution Strategy for Designing Fluoroaluminoborate with the Sr2Be2B2O7-Type Double-Layered Structure.

The cosubstitution strategy often was applied to design borate optical crystal materials. Revealingly, a fluoroaluminoborate Sr2Al2.18B5.82O13F2 with Sr2Be2B2O7 (SBBO) double-layered like configuration has been rationally designed and successfully synthesized based on structural motif cosubstitution strategy via the high-temperature solution method. In Sr2Al2.18B5.82O13F2, a structural motif, the [Al2B6O14F4] unit, with edge-sharing [AlO4F2] octahedra was filled in interlamination of double-layer structure. The research indicates that Sr2Al2.18B5.82O13F2 features a short ultraviolet cutoff edge (<200 nm) and moderate birefringence (∼0.058 @ 1064 nm). As the first reported linker in the interlamination of double-layer structures, the [Al2B6O14F4] unit enlightens the synthesis and discovery of new layered structures in borates.

Ba1.09Pb0.91Be2(BO3)2F2: The First Pb-Containing Beryllium Borate Fluoride with Trigonal Prismatic PbO6 and 2D [Be3B3O6F3]∞ Layers.

Ba1.09Pb0.91Be2(BO3)2F2 (BPBBF), a previously unreported lead-containing beryllium borate fluoride, has been successfully grown through a high-temperature flux method. Its structure is solved by single-crystal X-ray diffraction (SC-XRD), and it is optically characterized via infrared, Raman, UV-vis-IR transmission, and polarizing spectra as well. SC-XRD data suggests that it can be indexed by a trigonal unit cell (space group P3m1) with lattice parameters a = 4.7478(6) Å, c = 8.3856(12) Å, Z = 1, and V = 163.70(5) Å. This material could be considered as a derivative of the Sr2Be2B2O7 (SBBO) structural motif. It consists of 2D [Be3B3O6F3]∞ layers in the crystallographic ab plane, with divalent Ba2+ or Pb2+ cations serving as spacers among the adjacent layers. Ba and Pb were found to adopt a disordered arrangement in the trigonal prismatic coordination within the BPBBF structural lattice, which is evidenced by both structural refinements against SC-XRD data and energy dispersive spectroscopy. The UV absorption edge (279.1 nm) and birefringence (Δn = 0.054@ 546.1 nm) of BPBBF are confirmed by UV-vis-IR transmission and polarizing spectra, respectively. The discovery of this previous unreported SBBO-type material, BPBBF, along with other reported analogues such as BaMBe2(BO3)2F2 (M = Ca, Mg, and Cd), provide a prodigious example for tuning the bandgap, birefringence, and short UV absorption edge via simple chemical substitution.

Li3B8O13X (X = Cl and Br): Two New Noncentrosymmetric Crystals with Large Birefringence Induced by BO3 Units

Enthusiasm for the exploration of nonlinear alkali metal borates remains high. Focusing on the Li-B-O-X (X = Cl and Br) system, two examples of noncentrosymmetric borates, Li3B8O13Cl and Li3B8O13Br, were obtained using a high-temperature solution method under vacuum conditions. Structurally, the Li3B8O13X crystals exhibit two independent alternately arranged three-dimensional B-O network structures formed by the basic building block unit B8O16. The performance measurements demonstrate their short ultraviolet cutoff edges. The theoretical calculation indicates that the BO3 units dominate the contribution to their large optical anisotropy with the birefringence, 0.094 and 0.088@1064 nm for Li3B8O13Cl and Li3B8O13Br, respectively.

Controlling the Nonlinear Optical Behavior and Structural Transformation with A-Site Cation in α-AZnPO4 (A=Li, K).

Regulating the crystal structure by A-site cation substitution is one of the effective methods to explore high-performance nonlinear optical (NLO) materials. Herein, two non-centrosymmetric (NCS) compounds, α-MZnPO4 (M=Li, K) with short UV absorption edges 221 and 225nm, are obtained by performing A-site cation substitution method. It is noteworthy that α-LiZnPO4 (α-LZPO) achieves >10 times second harmonic generation (SHG) response (2.3×KDP) enhancement compared with that of α-KZnPO4 (α-KZPO) (0.2×KDP), which is the only case among phosphates with different A-site cations. By structural comparison, it is found that the A-site cations play important roles for anion rearrangements, and further the structure features of the two compounds by designing two suppositional crystal models as well as performing other theoretical calculations are analyzed. The study confirms the feasibility to design promising NLO materials with strengthen SHG response and structural stability in orthophosphate system.

Near infrared voltage sensitive dyes based on chromene electron donors.

Excellent hemicyanine voltage sensitive dyes (VSDs) are available for optical electrophysiology over a wide spectral range out to the far red. Near infrared fluorescent VSDs would be advantageous because they allow deeper light penetration into tissue because of decreased light scattering and also because they can be used in combination with other fluorescent indicators or optogenetic actuators. The usual approach to constructing long wavelength chromophores is to lengthen the π-system; however, this is generally accompanied by a significant decrease in fluorescence quantum efficiency and can also decrease aqueous solubility, making it difficult to deliver the probes to the target tissue. The VSDs developed in our lab are generally composed of an amino-naphthyl electron donor moiety linked to a pyridinium acceptor. Here we show that replacing the naphthalene with chromene induces a 60-80 nm red-shift in the absorption and emission spectra while maintaining the structure at the same size and fluorescence quantum yield at the same level. The voltage sensitivity of these chromene-based VSDs is also comparable to our older VSDs and they display opposite polarity sensitivity when excited at the short and long wavelength edges of the absorbance spectra; thus they can be used in dual wavelength ratio measurements to eliminate artifacts from motion and bleaching. We have tested one of these VSDs in voltage imaging of a whole murine heart at 730 nm, by far the longest wavelength reported in voltage imaging. It resolves action potentials in single sweep scans with 10.1% ΔF/F per action potential. Chromene-based electron donors are likely to find wide applications in generating long wavelength hemicyanines or cyanines. (Supported by NIH grant MH116830. Conflict of Interest statement: LML, CDA, and PY are founders and owners of Potentiometric Probes LLC.)

Structure and Characterization of K2Na3B2P3O13, a New Nonlinear Optical Borophosphate with One-Dimensional Chain Structure and Short Ultraviolet Cutoff Edge.

Nonlinear optical (NLO) crystals, being the primary medium for laser wavelength conversion, are crucial in all-solid-state lasers. Borophosphates offer more structural varieties than pure borates and phosphates, and they have become popular as NLO crystal candidates. Through spontaneous crystallization, we acquired a noncentrosymmetric alkali metal borophosphate crystal material, K2Na3B2P3O13 (KNBPO). KNBPO crystallizes in the orthorhombic Cmc21 space group with the following unit cell parameters: a = 13.9238(18) Å, b = 6.7673(8) Å, c = 12.1298(15) Å, and Z = 4, and its structure is characterized by a fundamental building unit 1∞ [B2P3O13] chain structure made up of bridging oxygen linkages between BO4 and PO4 tetrahedra. KNBPO has a short ultraviolet (UV) cut-off edge (<186 nm), a congruent melting characteristic, good thermal stability, and a moderate second harmonic generation response roughly 0.42 times that of KH2PO4. Theoretical calculations reveal that the optical properties of the compound mainly originate from BO4 and PO4 units. Due to the short UV cut-off edge, KNBPO can be used as a potential NLO material in the UV and even deep UV regions, and it enhances the structural variety of borophosphates, which has a reference value for scholars investigating similar materials.