Finding the Next Deep-Ultraviolet Nonlinear Optical Material: NH4B4O6F

The first lithium difluorophosphate LiPO2F2 with a neutral polytetrahedral microporous architecture

The first lithium difluorophosphate LiPO₂F₂ with a unique microporous architecture and improved optical properties was synthesized and characterized.

Na3B7O11F2: a new sodium-rich fluorooxoborate with a unique [B14O24F4] ring and a short ultraviolet absorption edge

A new sodium-rich fluorooxoborate Na₃B₇O₁₁F₂ features a novel large [B₁₄O₂₄F₄] ring formed by two corner-shared [B₇O₁₃F₂] groups, each containing two [B₃O₇] anionic units linked by a [BO₂F₂] group.

Investigation on two new antimony-based quaternary chalcogenides: Na6CdSb4S10 and Na3CdSbSe4

Two new Sb-based chalcogenides exhibiting interesting structural features and optical properties were successfully synthesized for the first time.

An alkali metal phosphate RbPbBi2(PO4)3 with three kinds of disorder: the effect of isolated soft cation units on the crystal structure

We have reported a new phosphate, RbPbBi₂(PO₄)₃ with three kinds of disorder, and a concept of isolated soft units has been firstly put forward to study the origin of structural distortions and disorder.

K2[B4O5(OH)4]·H2O and K2[B4O5(OH)4]: two new hydrated potassium borates with isolated [B4O5(OH)4]2− units and different structural frameworks

Two new hydrated potassium tetraborates with isolated [B₄O₅(OH)₄]²⁻ units were obtained via a mild hydrothermal method.

Metal-cation substitutions induced the enhancement of second harmonic generation in A8BS6 (A = Cu, and Ag; B = Si, Ge, and Sn)

The substitution from Ag to Cu with isostructural compounds induces the apparent enhancement of the SHG responses, which is mainly attributed to the different intensity of dp hybridization between the metal cation and S.

A new barium fluorooxoborate BaB5O8F·xH2O with large birefringence and a wide UV transparency window

By a cation substitution strategy, a new barium fluorooxoborate BaB₅O₈F was synthesized, which exhibits two interesting interpenetrating three-dimensional B–O/F frameworks and improved optical properties.

Mg(H2O)6B4O5(OH)4(H2O)3: a new hydrated borate with a short DUV cutoff edge

[B₄O₅(OH)₄] groups are linked together by hydrogen bonds forming undulating pseudo layers, leading to a short cutoff edge.

Pb7F12Cl2: a promising infrared nonlinear optical material with high laser damage threshold

This study reports, for the first time, the second-harmonic generation (SHG) property of Pb₇F₁₂Cl₂ as a promising infrared nonlinear optical (NLO) material.

Fluoroborophosphates: a family of potential deep ultraviolet NLO materials

A series of new fluoroborophosphates obtained by combining BO₃F or BO₂F₂ with a PO₄ tetrahedron exhibit short UV absorption edges and display second-harmonic generation signals.

Three new phosphates, Cs8Pb4(P2O7)4, CsLi7(P2O7)2 and LiCa(PO3)3: structural comparison, characterization and theoretical calculation

Three new phosphates with a short cutoff edge were obtained, and the structural comparisons were discussed in detail.

K2SrP4O12: a deep-UV transparent cyclophosphate as a nonlinear optical crystal

Benefiting from high transmittance of PO4 tetrahedra in the deep-ultraviolet (deep-UV) region, phosphates have been investigated as deep-UV nonlinear optical (NLO) candidates for years. So far, reported deep-UV NLO phosphates are orthophosphates and polyphosphates while cyclophosphates, important members of the phosphates family, have usually been neglected for use as deep-UV NLO crystals. Here, we first report a novel cyclotetraphosphate K2SrP4O12 (KSPO) as a deep-UV transparent NLO crystal. In its structure, the fundamental building groups are ring [P4O12]4- groups. KSPO exhibits a moderate second-harmonic generation (SHG) response that is 0.5 times that of KH2PO4 (KDP) and a short deep-ultraviolet absorption edge smaller than 200 nm.

M2(SeO3)F2 (M = Zn, Cd): understanding the structure directing effect of [SeO3]2− groups on constructing ordered oxyfluorides

The structure directing effect of [SeO₃]²⁻ anionic groups play a crucial role in the configuration of ordered [MO₃F₃] octahedral and its large anisotropy.

LiGeBO4: a nonlinear optical material with a balance between deep-ultraviolet cut-off edge and large SHG response induced by hand-in-hand tetrahedra

LiGeBO₄ is found to be a material that can balance a large band gap (>6.2 eV) and strong SHG coefficient (2 × KDP), which is rarely seen in tetrahedral-based crystals.

Two new tin(iv)-containing phosphate fluorides with two types of Sn(iv)–P–O–F frameworks and short cutoff edges

Two new [SnOF] groups connect with the [P–O] group to form interesting structures.

Experimental characterization and first principles calculations of linear and nonlinear optical properties of two orthophosphates A3Al2(PO4)3 (A = Rb, K)

We report the experimental characterization and first principles calculation of linear and nonlinear optical properties of two orthophosphates A₃Al₂(PO₄)₃ (A = Rb, K).

Modulation of perovskite-related frameworks induced by alkaline earth metals in phosphate fluorides A2MPO4F (A = K, Rb; M = Ba, Ca)

A₂CaPO₄F (A = K, Rb) are isomorphs. The 1D zig-zag [FA₄Ca₂]_∞ chains in the two compounds belong to the 1D perovskite-related structure.

Ba3Ca4(BO3)3(SiO4)Cl: a new non-centrosymmetric complex alkaline-earth metal borosilicate chloride with a deep-ultraviolet cut-off edge

The first complex alkaline-earth metal borosilicate chloride, Ba₃Ca₄(BO₃)₃(SiO₄)Cl, as a potential ultraviolet nonlinear optical material.

BaB8O12F2: a promising deep-UV birefringent material

A new alkaline-earth fluorooxoborate, BaB8O12F2, has been discovered through chemical substitution of a cation. It exhibits a short cutoff edge and a large birefringence.

Co-crystal LiCl·(H3C3N3O3): a promising solar-blind nonlinear optical crystal with giant nonlinearity from coplanar π-conjugated groups

Co-crystal LiCl·(H₃C₃N₃O₃) with the largest SHG coefficient among all solar-blind nonlinear optical crystals was studied by first principles calculations.

Structural modulation induced by MIIIA metals in Ba3MQ4X (M = Al, Ga, In; Q = S, Se; X = Cl, Br): an experimental and computational analysis

The optical properties of Ba₃MQ₄X (M = Al, Ga, In; Q = S, Se; X = Cl, Br) have been studied and their structures have been compared.

Adjustable optical nonlinearity in d10 cations containing chalcogenides via dp hybridization interaction

The role of d¹⁰-cations on band gap and nonlinearity in Cd/Hg-containing metal chalcogenides was investigated using DFT.

“Two in one”: an unprecedented mixed anion, Ba2(C3N3O3)(CNO), with the coexistence of isolated sp and sp2 π-conjugated groups

The first mixed cyanate–cyanurate double salt Ba₂(C₃N₃O₃)(CNO) containing two types of π-conjugated groups was successfully synthesized and systematically characterized.

Multifunctional property exploration: Bi4O5I2 with high visible light photocatalytic performance and a large nonlinear optical effect

Exploration of the versatility of materials is very important for increasing the utilization of materials. Herein, we successfully prepared Bi₄O₅I₂ powders via a facile solvothermal method. The Bi₄O₅I₂ photocatalyst exhibited significantly higher photocatalytic activity as compared to the common BiOI photocatalyst in the degradation of methyl orange, methylene blue and rhodamine B under visible light irradiation. Especially, for the degradation of methyl orange, the photocatalytic activity of Bi₄O₅I₂ is about 10 times that of BiOI. Moreover, Bi₄O₅I₂ exhibits an extremely high second harmonic generation response of about 20 × KDP (the benchmark) estimated by the unbiased ab initio calculations. The coexisting multifunction of Bi₄O₅I₂ is mainly because of the increased dipole moment due to the stereochemical activity of lone pairs that promotes separation and transfer of photogenerated carriers, then enhances the photocatalytic activity and results in a high second harmonic generation response. This indicates that Bi₄O₅I₂ may have good potential applications in photocatalytic and nonlinear optical fields.

Bi₄O₅I₂ exhibits an extremely high second harmonic generation response and enhanced photocatalytic activity. The multifunction of Bi₄O₅I₂ is mainly resulting from the dipole moment of the stereochemical activity of Bi 6s lone pairs.

Prediction of MCO [M = S, (Cl2B)3B] Systems with Giant Optical Birefringence and Nonlinearity in the Deep-Ultraviolet Region

Deep-ultraviolet (DUV) materials with giant optical birefringence and nonlinearity are scarce, and their discovery is very challenging. In this Communication, we predict that the MCO [M = S, (Cl₂B)₃B] compounds containing the polar C-O motif, which have been synthesized in the experiments, could be the first material systems to achieve this rare capability. First-principles calculations demonstrate that (Cl₂B)₃BCO and SCO exhibit the largest second-harmonic-generation effect (∼4.4 pm/V) and the largest birefringence (∼0.6) in all known DUV nonlinear-optical (NLO) crystals. In addition, SCO might be a DUV NLO material for the practical 193.7 nm laser output. Our discovery could enrich the structural chemistry of NLO crystals and advance the development of functional DUV optical materials.

Pb2GaF2(SeO3)2Cl: Band Engineering Strategy by Aliovalent Substitution for Enlarging Bandgap while Keeping Strong Second Harmonic Generation Response

Wide bandgap and strong second-order generation (SHG) effect are two crucial but contradictory conditions for practical nonlinear optical (NLO) materials. Herein, a new NLO crystal Pb₂GaF₂(SeO₃)₂Cl (I) containing novel functional (GaO₃F₃)^6- octahedra is designed and synthesized by a rational band engineering strategy with aliovalent substitution. Benefiting from the removal of transition metal cations and the introduction of bridged F anions, I exhibits the widest bandgap among all reported phase-matchable NLO selenites. Meanwhile, a strong SHG response more than 4.5 times of KH₂PO₄ (KDP) is maintained. The dominate role of the (GaO₃F₃)^6- groups to the enlarged bandgap in I are elucidated by first-principles studies.

A Langbeinite-Type Yttrium Phosphate LiCs2Y2(PO4)3

Langbeinite-type inorganic compounds have a wide range of applications, but nonlinear-optical properties are rarely mentioned in this series. Here, we report a new orthophosphate, LiCs₂Y₂(PO₄)₃, with a langbeinite-type structure, which is the first example in the system of mixed alkali-metal yttrium phosphates. Notably, LiCs₂Y₂(PO₄)₃ exhibits a moderate second-harmonic-generation efficiency of 0.9KH₂PO₄ and is transparent down to 200 nm. In addition, the thermal stability and theory calculations, including the electronic band structure, second-order nonlinear-optical coefficients, and dipole moment analysis, are also reported. This work not only expands the langbeinite-type system but also inspires a study on their nonlinear-optical properties.

Na4Yb(CO3)3F: A New UV Nonlinear Optical Material with a Large Second Harmonic Generation Response

A new nonlinear optical crystals fluoride carbonate, Na4Yb(CO3)3F, has been synthesized by mild hydrothermal method. The Na4Yb(CO3)3F crystallizes in the noncentrosymmetric space group Cc (no. 9) with the lattice parameters a = 8.018(3), b = 15.929(5), c = 13.950(5) Å and β = 101.425(6)°. The compound Na4Yb(CO3)3F has a high density of [CO3] groups. The structure can be described as one-dimensional [Na5Yb(CO3)2F2] chains connected by [CO3] groups, forming an intricate three-dimensional (3D) framework. Other Na+ and Yb3+ cations are located in the cavities of 3D network. The powder second harmonic generation (SHG) measurement shows that Na4Yb(CO3)3F features a large SHG response, about 4.3 times that of KH2PO4 (KDP), and is a phase-matchable material. In addition, its UV-Vis-NIR diffuse reflectance spectral data indicate that Na4Yb(CO3)3F has a large optical gap about 4.72 eV, which corresponds to the UV cut-off edge of 263 nm.

Cs3VO(O2)2CO3: an exceptionally thermostable carbonatoperoxovanadate with an extremely large second-harmonic generation response

A highly thermostable carbonatoperoxovanadate, Cs₃VO(O₂)₂CO₃, exhibits a remarkably strong SHG response of approximately 23.0 times that of KDP, which is the largest among those of the reported NLO carbonate materials.

A novel nonlinear optical (NLO) carbonatoperoxovanadate, Cs₃VO(O₂)₂CO₃, with an exceptionally high thermostability was successfully synthesized by introducing highly polarizable Cs⁺ cations and inorganic polydentate carbonate anions into asymmetric peroxovanadates. The structure of Cs₃VO(O₂)₂CO₃ is composed of distorted [VO(O₂)₂CO₃]^3– units and charge balancing Cs⁺ cations. The title compound exhibits the largest NLO intensity ever found in the current carbonate NLO materials, i.e., 23.0 times that of KH₂PO₄ (KDP). The remarkably strong second-harmonic generation (SHG) response originates from the synergistic effect of the exceedingly polarizable Cs⁺ cations, distortive polyhedra of the V⁵⁺ cation, delocalized π orbitals in CO₃ groups, and distorted localized π orbitals in O₂ groups. First-principles calculations indicated that introducing the polarizable cations into peroxovanadates not only induces the enhancement of the SHG response but also improves the thermal stability of the framework.

Why Some Noncentrosymmetric Borates Do Not Make Good Nonlinear Optical Materials: A Case Study with K3B5O8(OH)2

Synthesis of deep-ultraviolet (DUV) transparent materials, especially those with noncentrosymmetric structures, remains a great challenge in the solid-state chemistry community. A new DUV transparent borate, K₃B₅O₈(OH)₂, was discovered with a short absorption edge below 200 nm. The title compound crystallizes in a noncentrosymmetric, polar space group, Fdd2 (point group mm2), with the following cell parameters: a = 13.736(9) Å, b = 19.317(12) Å, c = 7.606(5) Å. The structure of K₃B₅O₈(OH)₂ features a 3D framework composed of [B₅O₈(OH)₂]^3- basic building units that are linked by contacts with K⁺ cations and O-H···O hydrogen bonds. Second harmonic generation (SHG) measurements were performed, and an SHG efficiency of 0.5 × SiO₂ was observed. Symmetry dictates that the χ₁₄ component of the macroscopic NLO susceptibility is equal to zero in mm2, which prevents the maximal component of the microscopic NLO susceptibility for [B₅O₈(OH)₂]^3- units (χ₁₄) from contributing to the macroscopic NLO susceptibility of the crystal and therefore limits the SHG efficiency. In contrast, large SHG effects can be observed from compounds containing [B₅O₁₀] units that crystallize in point groups with nonzero χ₁₄, such as 222. These findings provide insight into understanding the relationship between crystal structure and SHG efficiency in [B₅O₁₀]-based compounds and discovering other borate-based DUV materials.

Removal of A-Site Alkali and Alkaline Earth Metal Cations in KBe2BO3F2-Type Layered Structures To Enhance the Deep-Ultraviolet Nonlinear Optical Capability

In order to generate deep-ultraviolet (DUV, λ < 200 nm) coherent light, many DUV-transparent nonlinear optical (NLO) compounds have been synthesized experimentally over the past few decades, most of which contain alkali or/and alkaline earth metal cations. However, to date, practical DUV NLO materials beyond KBe₂BO₃F₂ (KBBF) are still very scarce. In this work, based on analysis of the DUV NLO effect induced by the A-site alkali and alkaline earth metal cations, we attempt to expand the options for DUV NLO compounds from a molecular engineering point of view. Accordingly, a useful strategy is proposed to design densely stacked layered structures without A-site cations as new and promising DUV NLO materials. Along with the available experimental and first-principles calculation results, it is demonstrated that layered structures in which the A-site cations are removed, such as Be₂BO₃F, Be₂CO₃F₂, AlCO₃F, SiCO₃F₂, AlNO₃F₂, PBO₃F₂, and PB₃O₆F₂, whether real or hypothetical, exhibit excellent DUV NLO performances. Based on the findings, our strategy may open up new opportunities for the design and exploration of high-performance DUV NLO materials beyond KBBF.

Advantageous Units in Antimony Sulfides: Exploration and Design of Infrared Nonlinear Optical Materials

The exploration of infrared (IR) nonlinear optical (NLO) materials remains attractive because of the urgent requirements in the laser field. Meanwhile, the deepened cognition of structure-property relationships is necessary to help guide the exploration of IR NLO materials. So far, the family of antimony sulfides is an important system with a lot of attention, and a series of antimony sulfides are reported. However, it is urgent to reveal how different Sb-S units, like SbS₃, SbS₄, and more complex combinations, affect apparent properties. Here, taking ternary metal antimony sulfides as examples, the sources of some essential optical properties, such as second harmonic generation (SHG) and birefringence, are systematically analyzed through first-principles calculations, and the mechanisms of the performances with various magnitudes are also presented to clarify the structure-property relationships. The results indicate that the SbS₄ unit among antimony sulfides is an advantageous NLO-active unit, which can balance the contradiction between the band gap and SHG response. Introduction of transition metals in the Sb-S anionic frameworks can tune the magnitude of birefringence. Besides, the substitution of a cation from a transition metal to an alkali metal can notably enlarge the band gap and maintain a large SHG response. These design strategies are beneficial to explore potential IR NLO materials with Sb-S units.

Ba3Mg3(BO3)3F3 polymorphs with reversible phase transition and high performances as ultraviolet nonlinear optical materials

Nonlinear optical (NLO) materials are the vital components of future photoelectric technologies as they can broaden the tunable wavelength range supplied by common laser sources. However, the necessary prerequisites for a practical NLO material are rather strict. Accordingly, considerable efforts have been focused on finding potential NLO materials. Here we report two asymmetric beryllium-free borates Pna2₁- and P\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\bar 6$$\end{document}6¯2m-Ba₃Mg₃(BO₃)₃F₃ featuring NLO-favorable ²_∞[Mg₃O₂F₃(BO₃)₂] layered structures. The reversible phase transition among two polymorphs was demonstrated by multiple experimental tests. The optical measurements reveal that Pna2₁-Ba₃Mg₃(BO₃)₃F₃ possesses the optical properties required for ultraviolet NLO applications. Remarkably, Pna2₁-Ba₃Mg₃(BO₃)₃F₃ has a large laser damage threshold, a deep-ultraviolet cutoff edge, a favorable anisotropic thermal expansion as well as the capacity of insolubility in water. These optical properties can be comparable or superior to that of commercial NLO material β-BaB₂O₄, which make Pna2₁-Ba₃Mg₃(BO₃)₃F₃ a promising ultraviolet NLO material.

Nonlinear optical crystals suitable for the UV spectral region could simplify short-wavelength generation and make it more efficient. Here, the authors design and demonstrate that one of two asymmetric borate polymorphs exhibits promising optical and mechanical properties for generating UV light.

Synthesis, Crystal Structure, and Optical Gap of Two-Dimensional Halide Solid Solutions CsPb2(Cl1- xBr x)5

Exploring new perovskite-related solid-state materials and the investigating composition-dependent structural and physical properties are highly important for advanced functional material development. Herein, we present the successful hydrothermal synthesis of tetragonal CsPb₂Cl₅ and the anion-exchange phase formation of CsPb₂(Cl_{1- x}Br _x)₅ ( x = 0-1) solid solutions. The CsPb₂(Cl_{1- x}Br _x)₅ crystal structures, which crystallize in the tetragonal system, space group I4/ mcm, with parameters similar to those of CsPb₂Cl₅, have been determined by Rietveld analysis. The optical band gap was obtained by UV-vis spectroscopy, and the band structure was further calculated by the full-potential method within the generalized gradient approximation. It was revealed that the band gap in CsPb₂(Cl_{1- x}Br _x)₅ solid solutions can be tuned over the range of 4.5-3.8 eV by anion substitution.

From LiB3 O5 to NaRbB6 O9 F2 : Fluorine-Directed Evolution of Structural Chemistry

Introducing fluorine into borates indicates the direction for structural evolution. A new fluorooxoborate, NaRbB₆ O₉ F₂ featuring a unique [B₆ O₉ F₂ ]_∞ layered structure and excellent optical properties has been synthesized. It is further demonstrated that incorporation of fluorine can enrich the structural chemistry of borates.