Material research from the viewpoint of functional motifs

Ordered Perovskite Structure with Functional Units for High Performance and Stable Solar Cells

Ion migration is one of the most critical challenges that affects the stability of metal-halide perovskite solar cells (PSCs). However, the current arsenal of available strategies for solving this issue is limited. Here, novel perovskite active layers following the concept of ordered structures with functional units (OSFU) to intrinsically suppress ion migration, in which a three-dimensional (3D) perovskite layer is deposited by vapor deposition for light absorption and a 2D layer is deposited by solution process for ion inhibition, are constructed. As a promising result, the activation energy of ion migration increases from 0.36 eV for the conventional perovskite to 0.54 eV for the OSFU perovskite. These devices exhibit substantially enhanced operational stability in comparison with the conventional ones, retaining >85% of their initial efficiencies after 1200 h under ISOS-L-1. Moreover, the OSFU devices show negligible fatigue behavior with a robust performance under light/dark cycling aging test (ISOS-LC-1 protocol), which demonstrates the promising application of functional motif theory in this field.

Intelligent Biomaterialomics: Molecular Design, Manufacturing, and Biomedical Applications

Materialomics integrates experiment, theory, and computation in a high-throughput manner, and has changed the paradigm for the research and development of new functional materials. Recently, with the rapid development of high-throughput characterization and machine-learning technologies, the establishment of biomaterialomics that tackles complex physiological behaviors has become accessible. Breakthroughs in the clinical translation of nanoparticle-based therapeutics and vaccines have been observed. Herein, recent advances in biomaterials, including polymers, lipid-like materials, and peptides/proteins, discovered through high-throughput screening or machine learning-assisted methods, are summarized. The molecular design of structure-diversified libraries; high-throughput characterization, screening, and preparation; and, their applications in drug delivery and clinical translation are discussed in detail. Furthermore, the prospects and main challenges in future biomaterialomics and high-throughput screening development are highlighted.

A Noncentrosymmetric Metal-Free Borophosphate: Achieving a Large Birefringence and Excellent Stability by Covalent-Linkage

Organic-inorganic hybrid linear and nonlinear optical (NLO) materials have received increasingly wide spread attention in recent years. Herein, the first hybrid noncentrosymmetric (NCS) borophosphate, (C5H6N)2B2O(HPO4)2 (4PBP), is rationally designed and synthesized by a covalent-linkage strategy. 4-pyridyl-boronic acid (4 PB) is considered as a bifunctional unit, which may effectively improve the optical properties and stability of the resultant material. On the one hand, 4 PB units are covalently linked with PO3(OH) groups via strong B-O-P connections, which significantly enhances the thermal stability of 4PBP (decomposition at 321, vs lower 200 °C of most of hybrid materials). On the other hand, the planar π-conjugated C5H6N units and their uniform layered arrangements represent large structural anisotropy and hyperpolarizability, achieving the largest birefringence (0.156 @ 546 nm) in the reported borophosphates and a second-harmonic generation response (0.7 × KDP). 4PBP also exhibits a wide transparency range (0.27-1.50 µm). This work not only provides a promising birefringent material, but also offers a practical covalent-attachment strategy for the rational design of new high-performance optical materials.

Pore engineering of micro/mesoporous nanomaterials for encapsulation, controlled release and variegated applications of essential oils

Essential oils have become increasingly popular in fields of medical, food and agriculture, owing to their strongly antimicrobial, anti-inflammation and antioxidant effects, greatly meeting demand from consumers for healthy and safe natural products. However, the easy volatility and/or chemical instability of active ingredients of essential oils (EAIs) can result in the loss of activity before realizing their functions, which have greatly hindered the widely applications of EAIs. As an emerging trend, micro/mesoporous nanomaterials (MNs) have drawn great attention for encapsulation and controlled release of EAIs, owing to their tunable pore structural characteristics. In this review, we briefly discuss the recent advances of MNs that widely used in the controlled release of EAIs, including zeolites, metal-organic frameworks (MOFs), mesoporous silica nanomaterials (MSNs), and provide a comprehensive summary focusing on the pore engineering strategies of MNs that affect their controlled-release or triggered-release for EAIs, including tailorable pore structure properties (e.g., pore size, pore surface area, pore volume, pore geometry, and framework compositions) and surface properties (surface modification and surface functionalization). Finally, the variegated applications and potential challenges are also given for MNs based delivery strategies for EAIs in the fields of healthcare, food and agriculture. These will provide considerable instructions for the rational design of MNs for controlled release of EAIs.

Li13YGe4O16: A Mid-infrared Rare-Earth Germanate Nonlinear Optical Crystal Featuring a Broad Transmission Range and an Enlarged Band Gap

Germanate is garnering increasing attention in the field of optoelectronics owing to its competitive optical transparency and robust stability. Herein, a novel lithium-rich rare-earth germanate, Li13YGe4O16, was fabricated for the first time using a high-temperature solution approach. This compound adopts the asymmetric space group Cmc21 (no. 36), characterized by isolated [YO6] and [GeO4] structural motifs with Li+ cations located in the channel. Notably, Li13YGe4O16 presents a short ultraviolet cutoff edge at 240 nm, indicative of an enlarged band gap of 4.96 eV and showcases a wide mid-infrared transmission region exceeding 6.0 μm. Moreover, Li13YGe4O16 features exceptional thermal stability and moderate second harmonic generation (SHG) intensity. Additionally, a theoretical analysis suggests that the distorted [YO6] octahedra. [GeO4] and [LiO4] tetrahedra play a significant role in the optical activities of Li13YGe4O16. These attributes endow Li13YGe4O16 with the potential to serve as a new mid-IR nonlinear optical (NLO) crystal and enrich the structural chemistry of germanates.

Thermally Activated Delayed Fluorescence (TADF)-active Coinage-metal Sulfide Clusters for High-resolution X-ray Imaging

The study of facile-synthesis and low-cost X-ray scintillators with high light yield, low detection limit and high X-ray imaging resolution plays a vital role in medical and industrial imaging fields. However, the optimal balance between X-ray absorption, decay lifetime and excitonic utilization efficiency of scintillators to achieve high-resolution imaging is extremely difficult due to the inherent contradiction. Here two thermally activated delayed fluorescence (TADF)-actived coinage-metal clusters M6 S6 L6 (M=Ag or Cu) were synthesized by simple solvothermal reaction, where the cooperation of heavy atom-rich character and TADF mechanism supports strong X-ray absorption and rapid luminescent collection of excitons. Excitingly, Ag6 S6 L6 (SC-Ag) displays a high photoluminescence quantum yield of 91.6 % and scintillating light yield of 17420 photons MeV-1 , as well as a low detection limit of 208.65 nGy s-1 that is 26 times lower than the medical standard (5.5 μGy s-1 ). More importantly, a high X-ray imaging resolution of 16 lp/mm based on SC-Ag screen is demonstrated. Besides, rigid core skeleton reinforced by metallophilicity endows clusters M6 S6 L6 strong resistance to humidity and radiation. This work provides a new view for the design of efficient scintillators and opens the research door for silver clusters in scintillation application.

Rational Design of Novel Promising Infrared Nonlinear Optical Materials: Structural Chemistry and Balanced Performances

ConspectusSecond-order nonlinear optical (NLO) materials are currently a hot topic in modern solid-state chemistry and optics because they can produce coherent light by frequency conversion. Noncentrosymmetric (NCS) structure is not only the prerequisite for NLO materials but also a challengeable issue because materials tend to be centrosymmetric (CS) in terms of thermodynamical stability. Among NLO materials, an excellent infrared (IR) candidate should simultaneously meet several strict key conditions including a large NLO coefficient, high laser-induced damage threshold (LIDT), phase-matchable (PM) behavior, and so on. Achieving a balance between the large NLO effect and high LIDT is difficult, as they have contradictory requirements for chemical bonds. Considering the urgent need of the high-power IR laser market and the drawbacks of the available ones, exploring new high-performance IR NLO crystals is necessary while challenging. In this Account, we first briefly introduce the status and advancement of IR NLO crystals and emphasize the criteria of an excellent candidate. Then, we will introduce five simple methods developed by us to discover practical NLO candidates through understanding of the chemical composition-structure-NLO performance relationship. (1) A rarely investigated system with simple chemical compositions as new-type NLO crystals, namely, adducts containing S8 molecules, are developed. Combining a chairlike S8 unit with other units through van der Waals forces has successfully obtained several high-performance NLO adducts. (2) The main trend in exploring new NLO crystals is that the chemical composition is more and more diversified and the structure is more and more complex, and expensive and chemically active alkaline and alkaline earth metals are usually introduced as counter cations. In contrast, the research on systems with simple chemical compositions, simple structures, and low costs has been continuously ignored. The binary M2Q3 (M = Ga, In; Q = S, Se) family with rich acentric modifications has been systematically investigated, and they all exhibit strong SHG effects and high LIDTs. (3) We first proposed the concept of inducing CS structures transformed to NCS ones by partial cation substitution to design novel NLO crystals. Considering the huge number of CS structures in the database compared to the number of NCS structures, it is an attractive method to apply CS structures as the parents to obtain potential NLO materials via partial-substitution-induced symmetry breaking. A series of chalcogenides with high NLO performances have been successfully obtained by us in this way. (4) We investigated the first NLO-active rare earth (RE) chalcophosphates and developed this family systematically, and they demonstrate wonderful comprehensive NLO properties. (5) We created a novel mixed-anion system for NLO applications, namely, chalcogenide borates. Usually, mixed-anion compounds can engender a synergistic effect to obtain desired IR NLO properties. Our recent progress on this system suggests that chalcogenide borates are potential candidates for IR NLO applications, although the study is still in its infancy. Finally, we state the current problems of IR NLO materials and give some perspectives for their future development.

Nonlinear Optical Phosphide CuInSi2P4: The Inaugural Member of Diamond-Like Family I-III-IV2-V4 Inspired by ZnGeP2

Noncentrosymmetric phosphides have garnered significant attention as promising systems of infrared (IR) nonlinear optical (NLO) materials. Herein, a new quaternary diamond-like phosphide family I-III-IV2-V4 and its inaugural member, namely, CuInSi2P4 (CISP), were successfully fabricated by isovalent and aliovalent substitution based on ZnGeP2. First-principles calculations revealed that CISP has a large NLO coefficient (d14 = 110.8 pm/V), which can be attributed to the well-aligned tetrahedral [CuP4], [InP4], and [SiP4] units. Remarkably, the extremely small thermal expansion anisotropy (0.09) of CISP enables it to exhibit a considerable laser-induced damage threshold (LIDT, 5.0 × AgGaS2@1.06 μm) despite the relatively narrow band gap (0.81 eV). This work improves the chemical diversity of inorganic phosphide and promotes the development of phosphide systems, which may provide valuable perspectives for future exploration of IR NLO materials.

Excellent Nonlinear Optical M[M4 Cl][Ga11 S20 ] (M = A/Ba, A = K, Rb) Achieved by Unusual Cationic Substitution Strategy

The typical chalcopyrite AgGaQ2 (Q = S, Se) are commercial infrared (IR) second-order nonlinear optical (NLO) materials; however, they suffer from unexpected laser-induced damage thresholds (LIDTs) primairy due to their narrow band gaps. Herein, what sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, represented by [[SZn4 ]S12 + [S4 Zn13 ]S24 + 11ZnS4 ⇒ MS12 + [M4 Cl]S24 + 11GaS4 ], in which the covalent Sx Zny units in the diamond-like sphalerite ZnS are synergistically replaced by cationic Mx Cly units, resulting in two novel salt-inclusion sulfides, M[M4 Cl][Ga11 S20 ] (M = A/Ba, A = K, 1; Rb, 2). As expected, the introduction of mixed cations in the GaS4 anionic frameworks of 1 and 2 leads to wide band gaps (3.04 and 3.01 eV), which exceeds the value of AgGaS2 , facilitating the improvement of high LIDTs (9.4 and 10.3 × AgGaS2 @1.06 µm, respectively). Furthermore, compounds 1 and 2 exhibit moderate second-harmonic generation intensities (0.84 and 0.78 × AgGaS2 @2.9 µm, respectively), mainly originating from the orderly packing tetrahedral GaS4 units. Importantly, this study demonstrates the successful application of the cationic substitution strategy based on diamond-like structures to provide a feasible chemical design insight for constructing high-performance NLO materials.

Organic metal chalcogenide-assisted metabolic molecular diagnosis of central precocious puberty

Metabolic analysis in biofluids based on laser desorption/ionization mass spectrometry (LDI-MS), featuring rapidity, simplicity, small sample volume and high throughput, is expected to be a powerful diagnostic tool. Nevertheless, the signals of most metabolic biomarkers obtained by matrix-assisted LDI-MS are too limited to achieve a highly accurate diagnosis due to serious background interference. To address this issue, nanomaterials have been frequently adopted in LDI-MS as substrates. However, the "trial and error" approach still dominates the development of new substrates. Therefore, rational design of novel LDI-MS substrates showing high desorption/ionization efficiency and no background interference is extremely desired. Herein, four few-layered organic metal chalcogenides (OMCs) were precisely designed and for the first time investigated as substrates in LDI-MS, which allowed a favorable internal energy and charge transfer by changing the functional groups of organic ligands and metal nodes. As a result, the optimized OMC-assisted platform satisfyingly enhanced the mass signal by ≈10 000 fold in detecting typical metabolites and successfully detected different saccharides. In addition, a high accuracy diagnosis of central precocious puberty (CPP) with potential biomarkers of 12 metabolites was realized. This work is not only expected to provide a universal detection tool for large-scale clinical diagnosis, but also provides an idea for the design and selection of LDI-MS substrates.

The first polyanion-substitution-driven centrosymmetric-to-noncentrosymmetric structural transformation realizing an excellent nonlinear optical supramolecule [Cd4P2][CdBr4]

Crystallographically, noncentrosymmetricity (NCS) is an essential precondition and foundation of achieving nonlinear optical (NLO), pyroelectric, ferroelectric, and piezoelectric materials. Herein, structurally, octahedral [SmCl6]3- is substituted by the acentric tetrahedral polyanion [CdBr4]2-, which is employed as a templating agent to induce centrosymmetric (CS)-to-NCS transformation based on the new CS supramolecule [Cd5P2][SmCl6]Cl (1), thereby providing the NCS supramolecule [Cd4P2][CdBr4] (2). Meanwhile, this replacement further results in the host 2D ∞2[Cd5P2]4+ layers converting to yield the twisted 3D ∞3[Cd4P2]2+ framework, which promotes the growth of bulk crystals. Additionally, phase 2 possesses well-balanced NLO properties, enabling considerable second-harmonic generation (SHG) responses (0.8-2.7 × AgGaS2) in broadband spectra, the thermal expansion anisotropy (2.30) together with suitable band gap (2.37 eV) primarily leading to the favorable laser-induced damage threshold (3.33 × AgGaS2), broad transparent window, and sufficient calculated birefringence (0.0433) for phase-matching ability. Furthermore, the first polyanion substitution of the supramolecule plays the role of templating agent to realize the CS-to-NCS transformation, which offers an effective method to rationally design promising NCS-based functional materials.

Design Strategy for Improving Detection Sensitivity in a Bromoplumbate Photochromic Semiconductor

Reducing the dark current of photodetectors is an important strategy for enhancing the detection sensitivity, but hampered by the manufacturing cost due to the need for controlling the complex material composition and processing intricate interface. This study reports a new single-component photochromic semiconductor, [(HDMA)4 (Pb3 Br10 )(PhSQ)2 ]n (1, HDMA = dimethylamine cation, PhSQ = 1-(4-sulfophenyl)-4,4'-bipyridinium), by introducing a redox-active monosubstituted viologen zwitterion into inorganic semiconducting skeleton. It features yellow to green coloration after UV irradiation with the sharply dropping intrinsic conductivity of 14.6-fold, and the photodetection detection sensitivity gain successfully doubles. The reason of decreasing conductivity originates from the increasing the band gap of the inorganic semiconducting component and formation of Frenkel excitons with strong Coulomb interactions, thereby decreasing the concentration of thermally excited intrinsic carriers.

New Functional Groups Design toward High Performance Ultraviolet Nonlinear Optical Materials

ConspectusThe invention of the laser is a pivotal milestone in the evolution of modern science and technology. Second-order nonlinear optical (NLO) crystals, which possess the ability to convert frequencies, have found widespread applications in laser science, information transmission, industrial Internet, and other cutting-edge fields within materials and optics. As modern science and technology continue to advance at a rapid pace, existing ultraviolet (UV) and deep ultraviolet (DUV) NLO crystals struggle to meet the ever-growing demands of various applications. Consequently, the development of novel UV and DUV NLO crystals has become an urgent necessity. For a UV NLO crystal to be considered outstanding in the UV/DUV range, it must exhibit three fundamental yet crucial properties: large second-order NLO coefficients, suitable birefringence, and short UV cutoff edge corresponding to a wide band gap. However, these key factors often conflict with one another, making it challenging to achieve a harmonious balance within a single crystal. It is widely believed that these mutually constrained optical properties are codetermined by microscopic NLO-active units and macroscopic structure features. Therefore, how to design high performance UV NLO-active groups to balance these three key properties is an essential scientifically question and serious challenge. In this Account, we present three strategies for designing high-performance UV NLO-active groups: (1) The "tetrahedron partial substitution" strategy by employing various substituents to replace one or more atoms in the traditional nonpolar tetrahedral groups, might achieve the aim of increasing the polarizability anisotropy and hyperpolarizability of the newly formed polar tetrahedral functional groups, such as from SO4 to SO3NH2 or SO3CH3 groups. (2) The "structure-analogue" strategy to develop a range of organic functional groups exhibiting more strong polarizability anisotropy and hyperpolarizability by using inorganic π-conjugated groups, such as BO3 and B3O6 groups, as templates. (3) The "two in one" strategy for integrating groups featuring planar triangle configurations and tetrahedrons to create NLO-active functional groups possessing large band gaps, strong hyperpolarizability, and moderate polarizability anisotropy. These three strategies successfully guide us to design and explore various kinds of organic-inorganic composite NLO crystal materials with excellent performances, like Ba(SO3CH3)2, M(SO3NH2)2 (M = Sr, Ba), C(NH2)3SO3F, KLi(HC3N3O3)·2H2O, KLi(C3H2O4)·H2O, and so on. Finally, we briefly conclude these strategies and propose some prospects for exploring new excellent UV/DUV NLO materials with practical applications. These findings could inspire novel thoughts for researchers designing new UV/DUV NLO materials and providing abundant materials used in UV/DUV regions.

Cs4 Zn5 P6 S18 I2 : the Largest Birefringence in Chalcohalide Achieved by Highly Polarizable Nonlinear Optical Functional Motifs

Chalcohalides not only keep the balance between the nonlinear optical (NLO) coefficient and wide band gap, but also provide a promising solution to achieve sufficient birefringence for phase-matching ability in NLO crystals. In this study, a novel chalcohalide, Cs4 Zn5 P6 S18 I2 (1) is successfully synthesized, by incorporating the highly electropositive Cs and the large electronegative I element into the zinc thiophosphate. Its 3D open framework features an edge-shared by distorted [ZnS4 ], ethanol-like [P2 S6 ], and unusual [ZnS2 I2 ] polyhedrons, which is inconsistent with the soft-hard-acids-bases theory. Remarkably, compound 1 simultaneously exhibits the large second-harmonic generation (SHG, 1.1×AgGaS2 , @1.3 µm) and a wide band gap (3.75 eV) toward a high laser-induced damage threshold (16.7×AgGaS2 , @1.06 µm), satisfying the rigorous requirements for a prominent infrared NLO material with concurrent SHG intensity (≥0.5×AGS) and band gap (≥3.5 eV). Moreover, to the best of the knowledge, the experimental result shows that phase 1 has the largest birefringence (0.108, @546 nm) in chalcohalide and meets phase-matching behavior demand originating from the polarizable anisotropy of NLO-functional motifs. This finding may provide great opportunities for designing birefringent chalcohalides.

Highly Sensitive Direct X-Ray Detector Based on Copper(II) Coordination Polymer Single Crystal with Anisotropic Charge Transport

Anisotropic charge transport plays a pivotal role in clarifying the conductivity mechanism in direct X-ray detection to improve the detection sensitivity. However, the anisotropic photoelectric effect of semiconductive single crystal responsive to X-ray is still lacking of theoretical and experimental proof. The semiconductive coordination polymers (CPs) with designable structures, adjustable functions, and high crystallinity provide a suitable platform for exploring the anisotropic conductive mechanism. Here,the study first reveals a 1D conductive transmission path for direct X-ray detection from the perspective of structural chemistry. The semiconductive copper(II)-based CP 1 single crystal detector exhibits unique anisotropic X-ray detection performance. Along the 1D π-π stacking direction, the single crystal device (1-SC-a) shows a superior sensitivity of 2697.15 µCGyair -1  cm-2 and a low detection limit of 1.02 µGyair  s-1 among CPs-based X-ray detectors. This study provides beneficial guidance and deep insight for designing high-performance CP-based X-ray detectors.

Nonlinear Optical Sulfides LiMGa8 S14 (M = Rb/Ba, Cs/Ba) Created by Li+ Driven 2D Centrosymmetric to 3D Noncentrosymmetric Transformation

Cations that can regulate the configuration of anion group are greatly important but regularly unheeded. Herein, the structural transformation from 2D CS to 3D noncentrosymmetric (NCS, which is the prerequisite for second-order NLO effect) is rationally designed to newly afford two sulfides LiMGa8 S14 (M = Rb/Ba, 1; Cs/Ba, 2) by introducing the smallest alkali metal Li+ cation into the interlamination of 2D centrosymmetric (CS) RbGaS2 . The unusual frameworks of 1 and 2 are constructed from C2 -type [Ga4 S11 ] supertetrahedrons in a highly parallel arrangement. 1 and 2 display distinguished NLO performances, including strong phase-matchable second-harmonic generation (SHG) intensities (0.8 and 0.9 × AgGaS2 at 1910 nm), wide optical band gaps (3.24 and 3.32 eV), and low coefficient of thermal expansion for favorable laser-induced damage thresholds (LIDTs, 4.7, and 7.6 × AgGaS2 at 1064 nm), which fulfill the criteria of superior NLO candidates (SHG intensity >0.5 × AGS and band gap >3.0 eV). Remarkably, 1 and 2 melt congruently at 873.8 and 870.5 °C, respectively, which endows them with the potential of growing bulk crystals by the Bridgeman-Stockbarge method. This investigated system provides a new avenue for the structural evolution from layered CS to 3D NCS of NLO materials.

Improved Birefringence Activated by Tetrahedra Decorated with a Single Linear Unit

Performance enhancement induced by structural modification has long been the target in materials science fields. Direct evidence to witness the effectivity of one strategy is challenging and necessary. In this work, a tetrahedra-decoration strategy was proposed to improve the birefringent performance sharply, namely decorating the tetrahedra with a single linear [S2 ] unit. The strategy was verified by comprehensive characterization of two thiogermanates K2 BaGeS4 and K2 BaGeS5 , which crystallize in the same space group, have similar unit cells and the same units arrangements. Theoretical characterization verified that the [GeS5 ] group has much larger polarization anisotropy than [GeS4 ], further demonstrated that the linear [S2 ] led to the sharp birefringence enlargement of K2 BaGeS5 (0.19 vs 0.03 of K2 BaGeS4 ). This work provides a new guiding thought to improve the birefringence performance.

TiO2@COF Nanowire Arrays: A "Filter Amplifier" Heterojunction Strategy to Reverse the Redox Nature

Surface modification is a promising method to change the surface properties of nanomaterials, but it is limited in enhancing their intrinsic redox nature. In this work, a "filter amplifier" strategy is proposed for the first time to reverse the intrinsic redox nature of materials. This is demonstrated by coating a COF-316 layer with controlled thickness on TiO₂ to form core-sheath nanowire arrays. This unique structure forms a Z-scheme heterojunction to function as "a filter amplifier" which can conceal the intrinsic oxidative sites and increase the extrinsic reductive sites. Consequently, the selective response of TiO₂ is dramatically reversed from reductive ethanol and methanol to oxidative NO₂. Moreover, TiO₂@COF-316 provides remarkably improved sensitivity, response, and recovery speed, as well as unusual anti-humidity properties as compared with TiO₂. This work not only provides a new strategy to rationally modulate the surface chemistry properties of nanomaterials but also opens an avenue to design high-performance electronic devices with a Z-scheme heterojunction.

Open honeycomb frameworks of sulphides AHg4Ga5S12 (A = Rb, Cs) exhibiting infrared nonlinear optical properties

A crystal structure with a diamond-like anionic framework belongs to a non-centrosymmetric macrostructure due to the aligned arrangement of tetrahedral units, meeting the premise of second-order nonlinear optical (NLO) materials. Herein, two new Hg-based sulphides, namely RbHg₄Ga₅S₁₂ (1) and CsHg₄Ga₅S₁₂ (2), which are isostructural and crystallise in the trigonal space group R3, are successfully isolated in sealed silica tubes by a solid-state reaction. The features of their three-dimensional open honeycomb frameworks are attributed to the parallel alignment of tetrahedral MS₄ (M is disordered by 0.444 Hg and 0.555 Ga) building motifs, accompanied by Rb⁺ (or Cs⁺) reseating in the cavities. Notably, although the band gap values of 1 and 2 are 2.30 and 2.36 eV, separately, their thermal expansion anisotropies (0.15 and 0.41, respectively) are favourable for achieving laser-induced damage thresholds (5.6 and 5.8 times that of AgGaS₂ for 1 and 2, respectively). In addition, the strong polarisability of tetrahedral MS₄ building motifs in the diamond-like anionic structures is responsible for the promising second-harmonic generation (SHG) intensities (1.1 and 1.8 times that of AgGaS₂ for 1 and 2, respectively) in the particle size range of 50-75 μm with non-phase-matchable behaviour at 1910 nm. Furthermore, theoretical investigation elaborates that electron transitions in compounds 1 and 2 mainly occur from valence band S-3p to conduction band Hg-6s and Ga-4s states, demonstrating that the linear and nonlinear optical properties originate primarily from the synergy of tetrahedral MS₄ units.

KREP2 Se6 (RE = Sm, Gd, Tb): The First Rare-Earth Selenophosphates with Remarkable Nonlinear Optical Activities Realized by Synergistic Effect of RE- and P-Based Motifs

Rare-earth (RE) chalcogenides have been extensively studied as infrared nonlinear optical (NLO) materials because of their nice integrated performances; however, very few RE chalcophosphates are involved for this topic. Here, three quaternary RE selenophosphates, KSmP₂ Se₆ (1), KGdP₂ Se₆ (2), and KTbP₂ Se₆ (3), are profoundly studied for their NLO potentials. Their noncentrosymmetric P21 structures feature RESe8-bicapped trigonal prisms and ethane-like [P₂ Se₆ ]₄ - dimers built {[REP₂ Se₆ ]-}∞ layers. As the first studied NLO-active RE selenophosphates, 1-3 exhibit second harmonic generation (SHG)responses ≈0.34-1.08 × AgGaS₂ at 2.10 µm and laser-induced damage thresholds (LIDTs) ≈1.43-4.33 × AgGaS₂ , and they all show phase-matchable behaviors, indicating their wonderful balanced NLO properties. Theoretical calculations demonstrate that the synergistic effect between RESe₈ and P₂ Se₆ units makes the major contribution to the SHG responses.

Sn(II)-doped one-dimensional hybrid metal halide [C5H14NO]CdCl3 single crystals with broadband greenish-yellow light emission

Low-dimensional organic-inorganic hybrid halides, as an important branch of metal halide materials, have attracted much attention due to their excellent photoelectric properties. Herein, we designed one new hybrid cadmium chloride [C₅H₁₄NO]CdCl₃ based on combinations of the d¹⁰ metal cation (Cd²⁺) and choline chloride molecules. [C₅H₁₄NO]CdCl₃ single crystals belong to the orthorhombic Pna2₁ space group and show a one-dimensional (1D) structure with distorted [CdCl₅O]^5- octahedra. The second harmonic generation (SHG) response of [C₅H₁₄NO]CdCl₃ exhibits an intensity of approximately 0.4 × KDP. Moreover, the photoluminescence properties of the [C₅H₁₄NO]CdCl₃ crystal are activated by doping with Sn²⁺ ions having stereochemically active lone pair 5s² electrons. Under UV excitation conditions, bright greenish-yellow light emission can be observed, and the quantum efficiency (PLQY) is as high as 91.27%. The luminescence mechanism is revealed by combining the results of temperature dependent luminescence and density functional theory (DFT) calculation. This work can serve as a guide for the design and synthesis of emerging optical materials.

K2CdGe3S8: A New Infrared Nonlinear Optical Sulfide

A quaternary metal chalcogenide, namely K2CdGe3S8 (I), is obtained through a high-temperature solid-state approach. Compound I crystallizes with the non-centrosymmetric space group P212121. It features a 2D layer structure with [CdGe3S8] layers consisting of tetrahedral GeS4 and CdS4 units, and counter K+ embedded between the layers. The compound exhibits a powder second-harmonic generation (SHG) response of ~0.1 times that of KH2PO4 (KDP) with phase-matchable character at the laser wavelength of 1064 nm. Remarkably, it has a wide band gap (3.20 eV), which corresponds to a favorable high laser-induced damage threshold of 6.7 times that of AgGaS2. In addition, the calculated birefringence (Δn) is 0.039 at the wavelength of 1064 nm, which satisfies the Δn criteria for a promising infrared NLO material.

Broad transparency and wide band gap achieved in a magnetic infrared nonlinear optical chalcogenide by suppressing d-d transitions

Magnetic infrared (IR) nonlinear optical (NLO) materials, particularly those containing d-block metals, have attracted considerable attention due to the contributions of d-orbitals to large NLO efficiency. However, the d-d transitions from the d-block metals lead to strong optical absorption and narrow band gap, seriously hindering their practical applications. The structural flexibility of salt-inclusion systems provides a good opportunity for modulating the crystal field of magnetic ions to suppress the d-d transitions but allowing the NLO-active d-s and d-p transitions. These ideas afford a new salt-inclusion sulfide [K₃Cl][Mn₂Ga₆S₁₂], which features a rare nanoporous [MnGa₃S₆]^- framework with tunnels of inner diameter of 9.0 Å and possesses a broad transparency (0.39-25.0 μm) and the widest band gap (3.17 eV) among all magnetic IR NLO chalcogenides. Remarkably, it exhibits a strong phase-matchable second-harmonic generation intensity (0.8 × AgGaS₂ at 1910 nm and 3.1 × AgGaS₂ at 1064 nm) and a high laser-induced damage threshold (12.5 × AgGaS₂ at 1064 nm), achieving the important criteria of an advanced IR NLO material.

AAg3Ga8Se14 (A = Rb, Cs): Second-Harmonic Generation Responses Realized through the Parallel Arrangement of AgSe4 and GaSe4 Tetrahedrons

Two new quaternary selenides AAg3Ga8Se14, (A = Rb, 1; Cs, 2) were synthesised via sold-state reaction in sealed silica tubes. Compounds 1 and 2 crystallised in the monoclinic space group...

Li-free Ternary Sulphide Cs5Ga9S16 with Excellent Nonlinear Optical Performance Similar to Classic LiGaS2

The element with the strongest electropositivity, Cs, was introduced into an anionic framework [Ga9S16]5− constructed from GaS4 tetrahedrons, which are functional nonlinear optical motifs, to acquire the ternary noncentrosymmetric sulphide...

Achieving a strong second harmonic generation response and a wide band gap in a Hg-based material

The property-oriented structural design strategy is employed in Hg-based chalcogenide to synthesize a new IR NLO crystal, [Ba4Cl2][HgGa4S10], which exhibits well-balanced NLO properties, including large SHG response and wide band gap.