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A defect diamond-like mid-IR NLO material, AgIn5Se8, is synthesized and its NLO performance has been systematically studied for the first time.

An alkali metal gallium iodate, Cs3[Ga2O(I3O9)(IO3)4(HIO3)] (CGIO), was synthesized by the traditional hydrothermal method. Interestingly, CGIO revealed a novel I3O93− fundamental building block (FBB) constituted by two IO3 tetrahedrons and one IO5 polyhedron through sharing O atoms. The new I3O93− trimer forms a 0D [Ga2O(I3O9)(IO3)4(HIO3)]3− anion cluster together with the [Ga2O11]16− dimer and isolated IO3− units. The UV-vis-NIR diffuse reflectance spectrum of CGIO shows a wide bandgap of 4.05 eV, and the thermal stability could reach above 400 °C. First-principles calculations explicated that the optical properties of CGIO mainly originated from the iodate anion units with a calculated birefringence of 0.04 at 1064 nm.

Cation substitution of alkali metal (K+, Rb+) and anion group arrangement transition were successfully realized in Rb[Te2O4(OH)5] (RTOH) and K2[Te3O8(OH)4] (KTOH) with a wide band gap and moderate SHG effect.

A lead-free, high stability, all-inorganic Rb2CsBiCl6 single crystal with 0D structure was successfully grown. The introduction of Sb3+ can effectively narrow the band gap, resulting in a strong broad yellow emission with a high PLQY of 45.

Hybrid organic-inorganic metal halide (OIMH) perovskites are regarded as potential photoluminescent (PL) materials and have attracted intensive attention. Here, we select 1-methylpiperazine as an organic component and successfully obtain a two-dimensional (2D) Ge-based OIMH perovskite, (1-mpz)GeBr

The continuous exploration of multinary chalcogenide semiconductors has provided a variety of new functional materials. In this paper, four new quaternary chalcogenides AHgPS4 (A+ = Na+, K+, Rb+, Cs+) have been prepared by solid-state syntheses. These findings complement the lack of research on this quaternary system. Influenced by the size effect of cations and the coordination mode of Hg, the four compounds crystallize in four different space groups [NaHgPS4, P4n2; KHgPS4, Pnn2; RbHgPS4, P21/n; CsHgPS4, P212121] and show an interesting evolution from a 3D framework structure to a 1D chain structure. Moreover, all of these compounds feature noncentrosymmetric (NCS) structures except for RbHgPS4. The materials exhibit wide band gaps of 2.7 eV < Eg < 3.0 eV. The NCS- related second-harmonic-generation (SHG) property of NaHgPS4 and KHgPS4 was also studied. They display strong powder SHG responses (3.14 × AgGaS2 for NaHgPS4; 4.15 × AgGaS2 for KHgPS4), which indicate their intriguing potential as IR nonlinear-optical materials. Moreover, first-principles theoretical calculations were performed to understand the structure-property relationships of these materials.

Cyanurate crystals have recently become a research hot spot in birefringent materials owing to the large structural and optical anisotropy of the planar π-conjugated (HxC3N3O3)x-3 (x = 0-3) groups. In this study, two new Zn-based cyanurate crystals, Zn5(OH)4(C3N3O3)2 and MgZn4(OH)4(C3N3O3)2, were synthesized by the hydrothermal method. In Zn5(OH)4(C3N3O3)2, the d10 Zn2+ cations have three different coordinating environments, which has never been found in cyanurates. These compounds have wide band gaps (∼5 eV) and large birefringence (∼0.32 at 400 nm), indicating their potential as ultraviolet birefringence crystals.

Deep-ultraviolet (DUV) nonlinear optical (NLO) crystals are vital to the development of science and state-of-the-art technologies, but the exploration of these important optoelectronic materials is hindered by the contradiction between NLO effect and energy band gap as well as the sensitivity of DUV phase-matching to optical birefringence. Here, in order to achieve a well balanced DUV NLO performance, we chose the diamond-like structure as the prototype template for the material design and synthesized the first DUV NLO hydroxycarbonate crystal, LiZn(OH)CO3 . This compound simultaneously has a wide band gap (>6.53 eV), a strong second harmonic generation response (ca. 3.2×KDP), and a large birefringence (0.147 at 1064 nm) with the shortest DUV phase-matching capability (λPM

Birefringent crystals are very important optical materials, which are widely used in the fields of optics and communication. In this work, we reported a new iodate, NaGaI3O9F, synthesized by mild hydrothermal method. NaGaI3O9F crystallized in the monoclinic space group P21/c (No. 14) and it featured a novel ∞[Ga2(IO3F)2(IO3)4]2− layer stacked with Na+ cations located in the void maintaining charge balance. Notably, IO3− and IO3F2− anionic units appeared in the same time in the A–Ga–I–O/F (A = alkali metal) system. According to the experimental characterization and theoretical calculations, NaGaI3O9F showed a wide bandgap (4.27 eV) and large birefringence (Δnexp ∼ 0.203, Δncal = 0.197 at 1064 nm), indicating its potential use as a birefringent material.

Metal chalcogenides are an attractive subject for investigation owing to their wide application in optoelectronics. Here, we report the discovery of a new cadmium-based quaternary sulfide, Na4CdGe2S7, with a wide band gap of 3.35 eV. The microscopic structure of this compound features two-dimensional [Ge2CdS7]∞ layers, which were first found in metal sulfides. Remarkably, the Na/S ratio in Na4CdGe2S7 exceeds 50%, suggesting that it would have ecofriendly electrical applications, such as in sodium-ion-battery electrodes and fast ion conductors.

Nonlinear-optical (NLO) crystals, which can regulate the laser wavelength through a cascading second-harmonic-generation technique, have been widely utilized in the field of optoelectronics. In this work, we grew the NLO borate crystal Rb3YB6O12 (RYBO) using the spontaneous crystallization method. RYBO crystallizes in a chiral trigonal space group of R32 with a new type of structural arrangement built from Y-O short chains and B5O10 groups. It is significantly different from the known structure of chemical analogues Rb3REB6O12 (RE = Nd, Eu) not only in the halved unit cell parameter but also in the Y-O connection manner. The NLO response of RYBO is about 0.8KDP, 8-fold larger than that of KB5O8·4H2O with the same B5O10 groups because of the coexistence of two NLO-active units of the distorted YO6 octahedra and B5O10 anions. Thanks to the short ultraviolet (UV) cutoff, RYBO may have potential NLO applications in the UV and even deep-UV spectral regions.

Two novel zinc borate halides named Zn2BO3X·H2O (X = Cl, Br) were discovered through hydrothermal techniques. Both compounds are isomorphic and feature the layered structure similar to that of KBBF, consisting of the infinite planar [Zn2BO3X·OH2] (X = Cl, Br) layers. Compared with the weak ionic bond between adjacent layers in KBBF, the strong interaction of hydrogen bonds between layers in Zn2BO3X·H2O (X = Cl, Br) effectively enhances the interlayer force, contributing to eliminating the layering growth tendency. Optical measurements on these two NLO crystals revealed that they have a broad wavelength transparency window and a moderate NLO coefficient. Moreover, the theoretical calculations revealed that the linear and NLO properties primarily depended on the [BO3] and [ZnO3Cl/Br] groups in both crystals.

To discover the nonlinear optical (NLO) materials with strong second harmonic generation (SHG), the design of NLO-active molecular units with large polarization is considered as a common strategy. Herein, we propose that the local structural distortion induced with vacancies, apart from the NLO-active units, can be employed to improve the NLO effect in solids as well. Accordingly, a new tungsten bronze (TB) oxide, Pb

Two new isomorphic selenite bromides, namely Pb2GaF2(SeO3)2Br (1) and Pb2NbO2(SeO3)2Br (2), were synthesized by mild hydrothermal reactions. These two compounds crystallize in the noncentrosymmertric space group P21 and feature 3D structures consisting of 1D (Pb2Br)3+ cationic chains and 2D [Ga2F4(SeO3)4]6−/[Nb2O4(SeO3)4]6− anonic chains. As measured, 1 and 2 are phase-matchable and exhibit excellent second harmonic generation (SHG) responses of 4.5 and 1.4 times that of KDP, respectively. Moreover, these two compounds possess wide bandgaps (>3.17 eV) and high thermal stabilities (>425 °C), indicating their suitable performances as potential nonlinear optical materials. First-principle density functional theory (DFT) calculations were also performed to explicate the structure–property relationship.

Searching for new nonlinear optical active (NLO-active) units would greatly promote the development of NLO materials. Herein, we theoretically investigate a newly reported [B2P5]5− group which consisted of two corner-sharing [BP3]3− trigonal planar units. Attributed to the coplanar π-conjugated configuration and the unique connection mode, the [B2P5]5− group can achieve both the largest birefringence (Δn ∼ 0.68) and nonlinearity (d15 ∼ 57.14 pm V−1) among all inorganic planar NLO-active groups, which makes it a good NLO-active unit. Our analysis also reveals that the modulation of the electronegativity of constituent elements upon replacing with the elements in the same period can effectively improve the NLO responses, which would inspire a new direction for designing high performing NLO materials.

Nonlinear optical (NLO) materials have been playing significant roles in laser science and technology for converting laser wavelengths to spectral regions where normal lasers operated poorly. Inorganic planar π-conjugated groups possessing both large second harmonic generation (SHG) responses and optical anisotropy are one of the most desirable fundamental building units (FBUs) for NLO materials. Up to now, inorganic planar π-conjugated groups including [BO3], [B3O6], [CO3], [NO3], [HxC3N3O3] (x varying from 0 to 3), [BS3], [B3S6], [HgSe3], [AgSe3], and [B2P5] units are reported as NLO-active groups, which strongly enhance the structural diversity of NLO materials. In this review, the NLO materials containing inorganic planar π-conjugated groups are classified according to their shortest transparent regions, i.e. deep-ultraviolet (DUV, λ 780 nm) regions. On the basis of available experimental and calculated data, the structure–property relationships and potential applied wave ranges for different inorganic planar π-conjugated groups are discussed.

Birefringent crystals are very important optical materials, which are widely used in the fields of optics and communication. In this work, we reported a new iodate, NaGaI

Cyanurate crystals have recently become a research hot spot in birefringent materials owing to the large structural and optical anisotropy of the planar π-conjugated (H

The first alkaline-earth metal tin(II) phosphate, BaSn2 (PO4 )2 , has been discovered, which consists of layered structures constructed from strictly alternating [SnO3 ]4- and [PO4 ]3- moieties. This compound is expected to have a large birefringence with Δn≈0.071 at 1064 nm, owing to the presence of stereochemically active lone pair metal cations.

Infrared (IR) nonlinear optical (NLO) materials are of current interest owing to their technological applications in many military and civil fields. Metal halides are among the most favorable candidates for IR laser frequency conversion owing to their relatively large NLO effects, wide IR transparency and high laser damage thresholds (LDT). However, the comprehensive review for metal halides NLO materials is absent. Herein, we focus on the relationship between the structural features and NLO performances in the reported metal halide NLO materials. In particular, metal halides are classified according to the NLO-active [MXk] anionic units and NLO-active cations, i.e., they are sorted into traditional metal halides containing linear units, triangle pyramidal units, tetrahedral units, rectangular pyramidal units, five-coordinated pseudo-octahedra, six- and more-coordinated polyhedral units, organic-inorganic and supramolecular metal halides. The determination rules of these microscopic structures on NLO properties in metal halides are summarized and analyzed on the basis of the combination of available experimental data and first-principles results. From the deduced structure-property relationship, the development prospects for NLO metal halides are discussed.

The alkali metals Rb+ and Cs+ involving structural evolution from centrosymmetric (CS) to noncentrosymmetric (NCS) is investigated in the ASbF3Cl compounds. RbSbF3Cl crystallizes in the orthorhombi...

A new noncentrosymmetric mixed-alkaline borate, Li2CsB7O10(OH)4 (1), was made under solvothermal conditions. This layered boron oxide framework consists of unique bird-shaped [B7O12(OH)4]7- clusters with large 14-ring pores. Its second-harmonic-generation (SHG) signal is 2.5KDP (KH2PO4), with its short ultraviolet (UV) cutoff edge indicating that this crystal is a potential deep-UV transparent nonlinear-optical material.

A new mixed metal iodate compound, Ba3Ga2(IO3)12, is synthesized by a mild temperature hydrothermal method. Based on the single crystal XRD data, the crystal structure is solved and it shows that Ba3Ga2(IO3)12 crystallizes in the centrosymmetric trigonal space group of R (148) with unit cell parameters of a = b = 11.2465 A and c = 11.2217 A. In this compound, the [GaO6] and [IO3] units connect with each other to construct the isolated [GaI6O18] groups, which were only discovered in Ga(IO3)3. Interestingly, the [IO3] units in the [GaI6O18] group are directed along a circle in Ba3Ga2(IO3)12, while those in Ga(IO3)3 point perpendicular to the circle. Moreover, Ba3Ga2(IO3)12 is characterized by spectral analysis and first-principles calculations.

As a great deal of attention has been paid to studying the role of fluorine in functional oxyfluorides, the question that arises now is how to orderly incorporate the fluorine atoms into the compounds. Herein, we proposed an original strategy using [SeO3]2− anionic groups as the effective structure directing blocks to orderly introduce the F atoms into the [MOxFy] (M = metal) polyhedra. Accordingly, two ordered metal selenite fluorides with [MO3F3]7− groups, M2(SeO3)F2 (M = Zn, Cd), were successfully synthesized through hydrothermal reactions. The stabilities of these structures were confirmed by thermogravimetry tests, bond valence sum analysis and phonon spectrum calculations.

Van-der-Waals (vdW) deep-ultraviolet (DUV) nonlinear-optical (NLO) materials hold great potential to extend DUV NLO applications to two dimensions, but they are rare in nature. In this study, we propose a design principle to realize vdW DUV NLO materials via structural evolution from the non-vdW (BO3 )-(BeO3 F) layers in KBe2 BO3 F2 (KBBF) to the vdW (BO3 )-(BeO4 H) layers in berborite Be2 BO5 H3 (BBH) and the vdW (BO4 )-(BeO4 ) layers in beryllium metaborate BeB2 O4 (BEBO). Based on first-principles calculations, the fundamental NLO properties of BBH and BEBO demonstrate that a balanced DUV NLO performance can be achieved in these two systems. Importantly, BBH, a layered material existing in nature, can achieve an available DUV phase-matched output with strong second harmonic generation (SHG) for 177.3/193.7 nm DUV lasers, which is almost identical to that of KBBF. Remarkably, BEBO shows an excellent DUV SHG capacity and an even shorter phase-matching wavelength than KBBF. Therefore, the newly discovered vdW BBH and BEBO, once verified by experiments, could provide an ideal platform to study DUV NLO effects in three dimensions and two dimensions.

Deep-ultraviolet (DUV) nonlinear optical (NLO) crystals are vital to the development of science and state-of-the-art technologies, but the exploration of these important optoelectronic materials is hindered by the contradiction between NLO effect and energy band gap as well as the sensitivity of DUV phase-matching to optical birefringence. Here, in order to achieve a well balanced DUV NLO performance, we chose the diamond-like structure as the prototype template for the material design and synthesized the first DUV NLO hydroxycarbonate crystal, LiZn(OH)CO

Ultraviolet (UV) transparency, second harmonic effect and optical birefringence are three vital but mutually restrictive factors in the application of UV nonlinear optical (NLO) materials. It is difficult for traditional phosphates to achieve a good balance among these factors. In this communication, we propose that the structural evolution of the NLO motif from traditional phosphate to oxythiophosphate would enhance the birefringence and second harmonic generation (SHG) effect while maintaining wide UV transparency, which is confirmed by first-principles calculations and preliminary experimental measurements. Following this strategy, we predict that, compared with the well-known NLO phosphate KH2 PO4 , the oxythiophosphate KH2 PO3 S exhibits better balance for the UV NLO performance, including wide UV transparency (UV cutoff down to 203 nm), strong SHG effect (ca. 0.9 pm V-1 ), and large birefringence (ca. 0.1 at 1 μm) with short phase-matching SHG output wavelength (≈214 nm).

Metal chalcogenides are an attractive subject for investigation owing to their wide application in optoelectronics. Here, we report the discovery of a new cadmium-based quaternary sulfide, Na

Two new isomorphic selenite bromides, namely Pb2GaF2(SeO3)2Br (1) and Pb2NbO2(SeO3)2Br (2), were synthesized by mild hydrothermal reactions. These two compounds crystallize in the noncentrosymmertric space group P21 and feature 3D structures consisting of 1D (Pb2Br)3+ cationic chains and 2D [Ga2F4(SeO3)4]6-/[Nb2O4(SeO3)4]6- anonic chains. As measured, 1 and 2 are phase-matchable and exhibit excellent second harmonic generation (SHG) responses of 4.5 and 1.4 times that of KDP, respectively. Moreover, these two compounds possess wide bandgaps (3.17 eV) and high thermal stabilities (425 °C), indicating their suitable performances as potential nonlinear optical materials. First-principle density functional theory (DFT) calculations were also performed to explicate the structure-property relationship.

Nonlinear-optical (NLO) crystals, which can regulate the laser wavelength through a cascading second-harmonic-generation technique, have been widely utilized in the field of optoelectronics. In this work, we grew the NLO borate crystal Rb

Aimed to realize deep-ultraviolet (DUV, λ200 nm) second harmonic generation (SHG), herein we systematically investigate the scheme for screening DUV nonlinear optical (NLO) material "genes" from traditional borates to hydroxyborates. From our first-principles studies, it is demonstrated that, if hydroxyborate motifs can be aligned by reasonable layered crystallization types, the resulting crystal will exhibit potential DUV NLO capability. Guided by the theoretical analysis and prediction, two targeted hydroxyborates AEB

Lead-free zero-dimensional (0D) organic-inorganic metal halide hybrids have recently attracted special attention as luminescent materials. However, their structural stability is still a challenge for the further development. Here, we select Sn4+ as the B-site inorganic cation and obtain a new tin(IV)-based organic-inorganic metal halide hybrids (C6N2H16Cl)2SnCl6 with remarkable air stability. (C6N2H16Cl)2SnCl6 exhibits a blue broadband emission originating from self-trapping excitons (STEs) and the emission intensity remains stable for over three months. When the temperature rises to 450 K, the intensity of photoluminescence can maintain about 50%, indicating the good thermal stability of (C6N2H16Cl)2SnCl6. This work presents a new strategy toward the tin(IV)-based photoluminescent organic-inorganic metal halide hybrids with environmentally friendly, high stability characteristics.

A new non-centrosymmetric hydroxyl alkali metal borate LiNaRbB5O8(OH)2 has been grown under mild hydrothermal conditions at 220 °C. LiNaRbB5O8(OH)2 belongs to the orthorhombic space group Aba2, with a = 11.3017(5) A, b = 10.9956(5) A, c = 9.2860(4) A, and Z = 2. The crystal structure of LiNaRbB5O8(OH)2 consists of Li/Na–O, Rb–O polyhedra, and [B5O8(OH)2]3– groups. The transmittance spectrum of the LiNaRbB5O8(OH)2 exhibits an absorption edge less than 200 nm in the UV region. The powder second-harmonic generation coefficient in LiNaRbB5O8(OH)2 is about one-third that of KH2PO4 (KDP) based on the Kurtz-Perry method. First principle calculations based on band structure, density of states, and optical properties are used to better understand the relationship between electronic structure and optical properties.

Searching for new nonlinear optical active (NLO-active) units would greatly promote the development of NLO materials. Herein, we theoretically investigate a newly reported [B

A new diphosphate Rb2CaP2O7 is synthesized by solid-states reaction. This compound crystallizes in the monoclinic space group of P21/n, with unit cell parameters of a=10.0238(9) A, b=5.7861(5) A, c=13.0654(11) A and β=104.726°. In this compound the [P2O7]4- dimers and [CaO6]10- units are interconnected by sharing the corner O atoms to form a 3D framework, with Rb+ cations filling in the interstices to balance the charge. The thermal property, IR and Raman spectra, UV–Vis–NIR diffuse reflectance spectrum and electronic band structure in Rb2CaP2O7 are determined, demonstrating its congruently melted characteristic and wide transparency down to the deep-ultraviolet region. Moreover, the replacement of Rb by K atoms in Rb2CaP2O7 can keep the compound structure unchanged, and the exemplified K1.85Rb0.15CaP2O7 exhibits almost the same fundamental physicochemical properties as Rb2CaP2O7.

A new Sn-based halide compound, Rb4Sn3Cl2Br8, is synthesized by hydrothermal method. This compound crystallizes in orthorhombic noncentrosymmetric space group of Cmc21, and the structure is composed of one-dimensional [Sn4Cl2Br8]1∞ chains elongated in parallel to the a-axis. Interestingly, in the [Sn4Cl2Br8]1∞ chains the [SnBr5] and [SnClBr4] groups hold pyramidal configurations which are found for the first time in Sn-based metal halides. Rb4Sn3Cl2Br8 exhibits a high thermal stability (up to 270 °C) and a relatively large bandgap of 2.82 eV. This compound shows a phase-matchable powder second harmonic generation response of 0.5 times of KH2PO4 (KDP), and is the first phase-matchable Sn-based halide nonlinear optical material. The discovery of Rb4Sn3Cl2Br8 will be beneficial to further phase-matchable nonlinear optical materials exploration in Sn-based halides.

As the first family of Sn-based alkaline earth metal mixed halides, three new compounds, BaSn2F5X (X = Cl, Br, and I), are synthesized by hydrothermal method. These compounds are crystallized in the centrosymmetric space groups of P21/c, P4/nmm, and Pmma for BaSn2F5Cl, BaSn2F5Br, and BaSn2F5I, respectively, and their microscopic frameworks are all composed of the fundamental structural unit [SnF4]2– and its derivatives ([SnF4Cl]3– and [SnF5]3– groups). Interestingly, the structures in BaSn2F5X are significantly changed from one-dimensional (1D) to two-dimensional (2D) and then to 1D motifs as X varies from Cl, Br, to I. Structural analysis combined with theoretical calculations reveals that the structural diversities are caused by the difference of ionic radius and electronegativity of X– anions as well as the orientation of the lone-pair electrons on Sn2+ cations. Moreover, the optical, electronic, and thermal properties for these three compounds are determined. This work provides a representative exampl...

A computer-assisted materials design system is employed to predict three new deep-ultraviolet (DUV) nonlinear optical (NLO) fluorooxoborates, including BaB4O6F2, KB4O6F-I and KB4O6F-II, by the strategy of optimizing the arrangement of (BO3F)4- and (BO3)3- groups. In particular, KB4O6F-II features an optimal two-dimensional layer structure that exhibits excellent DUV NLO properties, almost exceeding the performance of the famous KBe2BO3F2 crystal.

A new alkali tin(II) halide compound, Na3Sn2F6Cl, is synthesized by hydrothermal method. This compound crystallizes trigonally in space group of R-3c (167), and processes a zero-dimensional (0D) structure consisted of Na+ cations, Cl− anions and the isolated [SnF3]- trigonal pyramids in which the stereochemically active 5s2 lone pair electrons are attached to the Sn2+ cations. Interestingly, the [SnF3]− trigonal pyramids are parallel arranged in the a-b plane, while oppositely arranged in line with rotation along the c- axis. Moreover, the energy bandgap, thermal stability and electronic structure of Na3Sn2F6Cl are characterized and the results reveal that this compound has and indirect bandgap of 3.88 eV and is stable under 270 °C.

A new perovskite stoichiometric alkali tin dihalides compound, Cs3Sn3F2Cl7, is synthesized by a hydrothermal method. This compound belongs to the monoclinic space group of P21/c with cell parameters of a = 9.5645(4) A, b = 14.2057(7) A, c = 13.5828(6) A, and β = 93.2450(10)°. Unlike the common perovskites in which octahedra are interconnected to be a three-dimensional network, Cs3Sn3F2Cl7 possesses a zero-dimensional structure consisting of Cs+ cations, isolated [SnCl3]− trigonal pyramids, and dimer structural units [Sn2F2Cl4]2–; the latter microscopic unit is found for the first time. The thermal stability and UV–vis–NIR diffuse reflectance spectroscopy in Cs3Sn3F2Cl7 are measured, and the electronic structure is calculated. Interestingly, the 5s2 lone-pair electrons on Sn2+ cations are stereochemically active, which results in a pretty good photocatalytic activity of the title compound.

Recently, a borate crystal Zn4B6O13 (ZBO) has been focused on since it exhibits novel isotropic near-zero thermal expansion behavior in a wide temperature range. In this work, the mechanical properties in ZBO are studied by high-pressure X-ray diffraction and first-principles calculations. It is found that ZBO possesses the highest mechanical hardness in all known borates whose mechanical properties have been measured. The very high mechanical strength in ZBO mainly originates from the resistance of strong Zn–O bonds to the rotation among BO4 tetrahedra in the unique sodalite-cage structure. Moreover, ZBO shows relatively high mechanical resistance to the axial and shear stress and exhibits high optical transparence in the ultraviolet spectral region under high pressure. Benefitting from these good properties, ZBO may find potential applications in high-precision optical facilities used at extreme conditions under complex environments.

Recently, the exploration of infrared nonlinear optical (IR NLO) materials has mainly focused on chalcogenide compounds. However, their practical applications are often hampered by the low laser damage thresholds (LDTs). It is known that wide band gaps can significantly enhance the LDTs of materials, and the introduction of alkali and alkaline earth cations would broaden the band gap. Accordingly, in this work two new compounds KSrPS4 and CsBaAsS4 with both alkali and alkaline earth cations were synthesized successfully. Both compounds crystallize in the space group Pnma (62) of the orthorhombic system, and the structures consist of isolated PnS4 (Pn = P, As) tetrahedra with the interstices occupied by K (or Cs) and Sr (or Ba) atoms, respectively. The band gaps of compounds were determined by different methods. The UV-visible diffuse reflectance spectra revealed that the band gaps of KSrPS4 and CsBaAsS4 are larger than 3.62 eV and 2.86 eV, respectively. The band gaps are primarily determined by the PnS4 tetrahedra.

A new category of five KBBF-analogy nonlinear optical (NLO) materials, AZn2BO3X2 (A = K, Rb, NH4; X = Cl, Br), are developed by the tetrahedron substitution of BeO3F for ZnO3X from KBe2BO3F2 (KBBF). They preserve the structural merits of KBBF, consisting of the infinite planar [Zn2BO3X2]∞ layers. Optical measurements on this series of NLO crystals reveal that they are phase-matchable in the visible and UV region with powder second-harmonic generation (SHG) responses being more than twice that of isostructural KBBF. First-principles calculations and atom-cutting analysis were carried out to demonstrate that enhanced SHG response originates from the cooperative effect of coparallel [BO3] triangles and distorted ZnO3Cl/Br tetrahedra. The theoretical calculations and experimental results show that AZn2BO3X2 exhibits a less-developed layer habit compared with KBBF. Especially, because of the existence of relatively strong hydrogen bond between NH4+ groups and [Zn2BO3Cl2]∞ layers, NH4Zn2BO3Cl2 crystal exhibits ...

A new deep-ultraviolet transparent alkali metal borophosphate KNa