Soluble Direct-Band-Gap Semiconductors LiAsS2and NaAsS2: Large Electronic Structure Effects from Weak As⋅⋅⋅S Interactions and Strong Nonlinear Optical Response

Na3Ge2P3: A Zintl Phase Featuring [P3Ge-GeP3] Dimers as Building Blocks

Recently, ternary lithium phosphidotetrelates have attracted interest particularly due to their high ionic conductivities, while corresponding sodium and heavier alkali metal compounds have been less investigated. Hence, we report the synthesis and characterization of the novel ternary sodium phosphidogermanate Na3Ge2P3, which is readily accessible via ball milling of the elements and subsequent annealing. According to single crystal X-ray structure determination, Na3Ge2P3 crystallizes in the monoclinic space group P21/c (no. 14.) with unit cell parameters of a = 7.2894(6) Å, b = 14.7725(8) Å, c = 7.0528(6) Å, β = 106.331(6)° and forms an unprecedented two-dimensional polyanionic network in the b/c plane of interconnected [P3Ge-GeP3] building units. The system can also be interpreted as differently sized ring structures that interconnect and form a two-dimensional network. A comparison with related ternary compounds from the corresponding phase system as well as with the binary compound GeP shows that the polyanionic network of Na3Ge2P3 resembles an intermediate step between highly condensed cages and discrete polyanions, which highlights the structural variety of phosphidogermanates. The structure is confirmed by 23Na- and 31P-MAS NMR measurements and Raman spectroscopy. Computational investigation of the electronic structure reveals that Na3Ge2P3 is an indirect band gap semiconductor with a band gap of 2.9 eV.

Two Electrocatalytic Selenoarsenates with Manganese Complex Cations as Counterions

The discovery of new organic hybrid chalcogenidometalates is of great importance for structural chemistry and functional material. Here, new types of organic hybrid selenoarsenates [Mn(dien)2]2[AsII4Se6] (1, dien = diethylenetriamine) and [Mn(dien)2]2[Mn(AsIIISe3)2] (2) have been solvothermally synthesized by the reaction of K3AsO3, Se, and MnCl2·xH2O (x = 0, 2) in dien solution at 120 °C. 1 presents a hitherto unknown [AsII4Se6]4- anion with low-valent As2+ ion, which comprises a centrosymmetric six-membered [AsII4Se2] ring in chair-like conformation, while 2 contains a new type of heterometallic selenoarsenate(III) [Mn(AsIIISe3)2]4- constructed by the connection of one tetrahedral [MnSe4] and two rare noncondensed [AsIIISe3]3- anions. 1 and 2 were first combined with nickel nanoparticle (Ni) and the nickel foam (NF) for fabricating the 1/Ni/NF and 2/Ni/NF electrodes, which exhibited excellent oxygen evolution reaction electrocatalytic property with a low overpotential of 248 mV for 1 and 219 mV for 2 at 10 mA cm-2 in alkaline media.

Ca2 Ln(BS3 )(SiS4 ) (Ln = La, Ce, and Gd): Mixed Metal Thioborate-Thiosilicates as Well-Performed Infrared Nonlinear Optical Materials

The first examples of thioborate-thiosilicates, namely Ca2 Ln(BS3 )(SiS4 ) (Ln = La, Ce, and Gd), are synthesized by rationally designed high-temperature solid-state reactions. They crystalize in the polar space group P63 mc and feature a novel three-dimensional crystal structure in which the discrete [BS3 ]3- and [SiS4 ]4- anionic groups are linked by Ca2+ and Ln3+ cations occupying the same atomic site. Remarkably, all three compounds show comprehensive properties required as promising infrared nonlinear optical materials, including phase-matchable strong second harmonic generation (SHG) responses at 2.05 µm (1.1-1.2 times that of AgGaS2 ), high laser-induced damage thresholds (7-10 times that of AgGaS2 ), wide light transmission range (0.45-11 µm), high thermal stabilities (>800 °C), and large calculated birefringence (0.126-0.149 @1064 nm), which justify the material design strategy of combining [BS3 ]3- and [SiS4 ]4- active units. Theoretical calculations suggest that their large SHG effects originate mainly from the synergy effects of the LnS6 , BS3 , and SiS4 groups. This work not only broadens the scope of research on metal chalcogenides but also provides a new synthetic route for mixed anionic thioborates.

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.

A novel bifunctional thioarsenate based on unprecedented molecular [Cd4As8Se16(Se2)2]8- cluster anions

Exploring and developing new functional inorganic chalcogenides with unique structures is always one of the most important missions in solid-state chemistry, especially those with molecular structures. Herein, a novel quaternary thioarsenate, Cs2CdAsSe5, is found to be based on an unprecedented molecular (poly)chalcogenide cluster architecture, which has never been discovered in inorganic chalcogenide systems. This rare windmill-like [Cd4As8Se16(Se2)2]8- cluster is made of four [CdSe4] and [As(V)Se4] tetrahedra via corner-sharing Se atoms and Se-Se bonds. Specifically, Cs2CdAsSe5 exhibits a remarkable photocurrent response and a large computationally predicted birefringence, and the origin of the optoelectronic performance and optical anisotropy is confirmed by detailed theoretical investigation.

AgMAsS3 (M = Cd, Hg): Double d10 Cation-Containing Thioarsenites(III) Exhibiting High Photocurrent Response and Moderate Second Harmonic Generation

Thioarsenites(III) are an advanced functional material platform owing to the stereochemically active lone pair cations. In this paper, two novel quaternary thioarsenites(III), AgMAsS3 (M = Cd, Hg), are successfully obtained by introducing double d10 cations. In the compounds, d10 cations show a variety of different coordination modes ([AgS4] and [HgS4] in AgHgAsS3 vs [AgS5] and [CdS6] in AgCdAsS3). As a result, AgHgAsS3 and AgCdAsS3 crystallize in the noncentrosymmetric Cc space group and centrosymmetric C2/c space group, respectively. The band gaps of AgHgAsS3 and AgCdAsS3 are determined experimentally as 1.90 and 2.20 eV, respectively. Meanwhile, title compounds exhibit strong photocurrent responses. Specifically, AgHgAsS3 has a large birefringence of 0.18 at 2100 nm and a moderate second harmonic generation of (0.5 × AgGaS2). Moreover, the origin of linear and nonlinear optical responses is investigated based on first-principles calculations. This study enriches the family of MI-MII-As-Q (M = Ag, Cu; MII = Zn, Cd, Hg; Q = chalcogen) chalcogenides and helps to understand and design other multifunctional optical materials.

[K2 PbX][Ga7 S12 ] (X = Cl, Br, I): The First Lead-Containing Cationic Moieties with Ultrahigh Second-Harmonic Generation and Band Gaps Exceeding the Criterion of 2.33 eV

In contrast to anionic group theory of nonlinear optical (NLO) materials that second-harmonic generation (SHG) responses mainly originate from anionic groups, structural regulation on the cationic groups of salt-inclusion chalcogenides (SICs) is performed to make them also contribute to the NLO effects. Herein, the stereochemically active lone-electron-pair Pb2+ cation is first introduced to the cationic groups of NLO SICs, and the resultant [K2 PbX][Ga7 S12 ] (X = Cl, Br, I) are isolated via solid-state method. The features of their three-dimensional structures comprise highly oriented [Ga7 S12 ]3- and [K2 PbX]3+ frameworks derived from AgGaS2 , which display the largest phase-matching SHG intensities (2.5-2.7 × AgGaS2 @1800 nm) among all SICs. Concurrently, three compounds manifest band gap values of 2.54, 2.49, and 2.41 eV (exceeding the criterion of 2.33 eV), which can avoid two-photon absorption under the fundamental laser of 1064 nm, along with the relatively low anisotropy of thermal expansion coefficients, leading to improved laser-induced damage thresholds (LIDTs) values of 2.3, 3.8, and 4.0 times that of AgGaS2 . In addition, the density of states and SHG coefficient calculations demonstrate that the Pb2+ cations narrow the band gaps and benefit SHG responses.

Heteroanionic Control of Exemplary Second-Harmonic Generation and Phase Matchability in 1D LiAsS2-xSex

The isostructural heteroanionic compounds β-LiAsS_2-xSe_x (x = 0, 0.25, 1, 1.75, 2) show a positive correlation between selenium content and second-harmonic response and greatly outperform the industry standard AgGaSe₂. These materials crystallize in the noncentrosymmetric space group Cc as one-dimensional ¹/_∞ [AsQ₂]^- (Q = S, Se, S/Se) chains consisting of corner-sharing AsQ₃ trigonal pyramids with charge-balancing Li⁺ atoms interspersed between the chains. LiAsS_2-xSe_x melts congruently for 0 ≤ x ≤ 1.75, but when the Se content exceeds x = 1.75, crystallization is complicated by a phase transition. This behavior is attributed to the β- to α-phase transition present in LiAsSe₂, which is observed in the Se-rich compositions. The band gap decreases with increasing Se content, starting at 1.63 eV (LiAsS₂) and reaching 1.06 eV (β-LiAsSe₂). Second-harmonic generation measurements as a function of wavelength on powder samples of β-LiAsS_2-xSe_x show that these materials exhibit significantly higher nonlinearity than AgGaSe₂ (d₃₆ = 33 pm/V), reaching a maximum of 61.2 pm/V for LiAsS₂. In comparison, single-crystal measurements for LiAsSSe yielded a d_eff = 410 pm/V. LiAsSSe, LiAsS_0.25Se_1.75, and β-LiAsSe₂ show phase-matching behavior for incident wavelengths exceeding 3 μm. The laser-induced damage thresholds from two-photon absorption processes are on the same order of magnitude as AgGaSe₂, with S-rich materials slightly outperforming AgGaSe₂ and Se-rich materials slightly underperforming AgGaSe₂.

The rare example of hybrid chalcogenoarsenates(III) incorporating trivalent vanadium complexes

A series of new hybrid vanadium chalcogenoarsenates(III) [VIII(en)2AsIIIS3] (1, en = ethylenediamine), [VIII(dap)2AsIIISe3] (2, dap = 1,2-diaminopropane), [VIII(teta)AsIIIQ3] {Q = S (3), Se (4), teta = triethylene-tetramine}, and [VIII2(en)6(μ2-O)][As2Se5] (5)...

KEu2In3B12S13: A Novel Type of Thioborate Featuring B12S12 Cluster and Unique In6S6 12-membered Ring

Both borates and sulfides are important inorganic multifunctional materials. Encouraged by this background, thioborates attract broad interest. However, their investigations are highly hindered by the available ones’ scarcity and new...

Ba3Zr2Cu4S9: the first quaternary phase of the Ba–Zr–Cu–S system

We report the synthesis of red-colored crystals of Ba3Zr2Cu4S9 via a high-temperature reaction of elements at 1223 K. The title compound is the first quaternary phase of the Ba–Zr–Cu–S system....

Two Organic Hybrid Manganese Selenoarsenates: The Discovery of One-Dimensional Low-Valent Selenoarsenate(II)

Two organic hybrid manganese selenoarsenates, [Mn(en)₃][MnAs^II₂Se₄] (1; en = ethanediamine) and {[Mn(atep)]₂[Mn(tepa)](As^VSe₄)₂} [2; atep = 4-(2-aminoethyl)triethylenetetramine], were made under mild solvothermal conditions. 1 is a new type of one-dimensional low-valent selenoarsenate(II) constructed by the linkages of tetrahedral [MnSe₄] units and two manners of bridging of [As^II₂Se₄]^4- anions. 2 comprises a neutral {[Mn(atep)]₂[Mn(tepa)](As^VSe₄)₂} molecule with a rare seven-coordinated manganese center, which represents the sole example of an organic hybrid selenoarsenate with the [Mn(tepa)]²⁺ complex as the bridging group. Both 1 and 2 exhibit special photocurrent responses upon visible-light illumination and magnetic properties.

Investigation into Structural Variation from 3D to 1D and Strong Second Harmonic Generation of the AHgPS4 (A+ = Na+, K+, Rb+, Cs+) Family

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, P4̅n2; 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 < E_g < 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.

Structure Tuning, Strong Second Harmonic Generation Response, and High Optical Stability of the Polar Semiconductors Na1-xKxAsQ2

The mixed cation compounds Na_1-xK_xAsSe₂ (x = 0.8, 0.65, 0.5) and Na_0.1K_0.9AsS₂ crystallize in the polar noncentrosymmetric space group Cc. The AAsQ₂ (A = alkali metals, Q = S, Se) family features one-dimensional (1D) ¹/_∞[AQ₂^-] chains comprising corner-sharing pyramidal AQ₃ units in which the packing of these chains is dependent on the alkali metals. The parallel ¹/_∞[AQ₂^-] chains interact via short As···Se contacts, which increase in length when the fraction of K atoms is increased. The increase in the As···Se interchain distance increases the band gap from 1.75 eV in γ-NaAsSe₂ to 2.01 eV in Na_0.35K_0.65AsSe₂, 2.07 eV in Na_0.2K_0.8AsSe₂, and 2.18 eV in Na_0.1K_0.9AsS₂. The Na_1-xK_xAsSe₂ (x = 0.8, 0.65) compounds melt congruently at approximately 316 °C. Wavelength-dependent second harmonic generation (SHG) measurements on powder samples of Na_1-xK_xAsSe₂ (x = 0.8, 0.65, 0.5) and Na_0.1K_0.9AsS₂ suggest that Na_0.2K_0.8AsSe₂ and Na_0.1K_0.9AsS₂ have the highest SHG response and exhibit significantly higher laser-induced damage thresholds (LIDTs). Theoretical SHG calculations on Na_0.5K_0.5AsSe₂ confirm its SHG response with the highest value of d₃₃ = 22.5 pm/V (χ₃₃₃⁽²⁾ = 45.0 pm/V). The effective nonlinearity for a randomly oriented powder is calculated to be d_eff = 18.9 pm/V (χ_eff⁽²⁾ = 37.8 pm/V), which is consistent with the experimentally obtained value of d_eff = 16.5 pm/V (χ_eff⁽²⁾ = 33.0 pm/V). Three-photon absorption is the dominant mechanism for the optical breakdown of the compounds under intense excitation at 1580 nm, with Na_0.2K_0.8AsSe₂ exhibiting the highest stability.

AZn4Ga5Se12 (A = K, Rb, or Cs): Infrared Nonlinear Optical Materials with Simultaneous Large Second Harmonic Generation Responses and High Laser-Induced Damage Thresholds

Despite the fact that nonlinear optical (NLO) crystals such as AgGaS₂ and AgGaSe₂ have been widely used in the infrared (IR) range due to their large second harmonic generation (SHG) coefficients and wide range of IR transparency windows, the small laser-induced damage threshold (LIDT) remains a great issue hindering their high-power applications. Herein, three noncentrosymmetric (NCS) chalcogenides AZn₄Ga₅Se₁₂ (A = K, Rb, or Cs) are successfully obtained through an appropriate flux method after the extensive design and synthesis of the A/Zn/Ga/Q system. Single-crystal X-ray diffraction data demonstrate that they adopt trigonal space group R3 (No. 146) with three-dimensional diamond-like frameworks composed of [M₉Se₂₄] layers (M = Zn or Ga) stacking in the same direction and filled by charge-balancing A⁺ cations. Noticeably, they all exhibit strong powder SHG responses (2.8-3.7 × AgGaS₂) and amazing LIDTs (19.2-23.4 × AgGaS₂). In addition, theoretical calculations are performed to further determine the relationship between NCS structures and NLO properties. This work provides effective solutions for overcoming the trade-off between strong SHG and high LIDT in IR-NLO materials.

A Copper(I)-Thioarsenate(III) Inorganic Framework Directed by [Ni(en)3]2

One novel three-dimensional (3-D) copper(I)-thioarsenate(III) [Ni(en)₃]Cu₄As₄S₉ (1, en = ethylenediamine) has been solvothermally prepared with the utilization of the in situ formation of [Ni(en)₃]²⁺ complex as structure-directing agent (SDA). 1 contains cubane-like [Cu₈S₁₂]^16- clusters and rare tetrameric [As₄S₉]^6- units, which are interconnected to generate the first example of a 3-D anionic framework [Cu₄As₄S₉]_n^2n-, topologically identical to pyrite, and having large channels filled by [Ni(en)₃]²⁺ complex cations. 1 is a potential wide-band-gap semiconductor with an energy gap of 1.91 eV that exhibits selectively photocatalytic degradation of methylene blue under visible-light irradiation. The density functional theory calculation, photocurrent response, and magnetic properties of 1 were also investigated.

Structural Modulation from Cu3PS4 to Cu5Zn0.5P2S8: Single-Site Aliovalent-Substitution-Driven Second-Harmonic-Generation Enhancement

Diamond-like (DL) chalcophosphates, which possess the merits of impressive second-harmonic-generation (SHG) responses, strong laser-induced damage thresholds, and low melting points, are highly desirable for IR nonlinear-optical (NLO) applications. Herein, a new quaternary DL chalcophosphate, Cu₅Zn_0.5P₂S₈, is successfully discovered, taking known Cu₃PS₄ as the template via a single-site aliovalent-substitution strategy. It crystallizes in the orthorhombic system with noncentrosymmetric space group Pmn2₁, and the 3D DL structure is built by corner-shared [(Cu/Zn)S₄], [CuS₄], and [PS₄] tetrahedra. Compared with its parent Cu₃PS₄, Cu₅Zn_0.5P₂S₈ exhibits a good phase-matching capability and a sharply enhanced SHG effect (10Cu₃PS₄) benefiting from partial Zn substitution. Moreover, the structure-performance relationships have been illustrated by means of theoretical investigations. Such an aliovalent-substitution strategy based on known DL semiconductors might be widely applied for the discovery of high-performance IR NLO crystals.

Structural diversities in centrosymmetric La8S4Cl8La12S8Cl4[SbS3]8 and non-centrosymmetric Ln12S8Cl8[SbS3]4 (Ln = La and Ce): syntheses, crystal and electronic structures, and optical properties

Three thioantimonides charge compensated by Ln/S/Cl cationic layers, namely, La8S4Cl8La12S8Cl4[SbS3]8 and Ln12S8Cl8[SbS3]4 (Ln = La and Ce), have been discovered by conventional solid-state reactions. The former crystallizes in the centrosymmetric space group Pbcm (no. 57), while the latter adopts the polar non-centrosymmetric space group Cc (no. 9). Both of them contain isolated SbS3 trigonal-pyramidal units, which are connected either with the alternating centric [La8S4Cl8]8+ and mirror-symmetric [La12S8Cl4]16+ cationic layers perpendicular to the [001] direction in La8S4Cl8La12S8Cl4[SbS3]8 or with the acentric [Ln12S8Cl8]12+ cationic layers perpendicular to the [100] direction in Ln12S8Cl8[SbS3]4. Interestingly, the discrete SbS3 trigonal pyramids pack in a centrosymmetric and non-centrosymmetric fashion in La8S4Cl8La12S8Cl4[SbS3]8 and La12S8Cl8[SbS3]4, respectively, which can be ascribed to the different compositions and packing fashions in Ln/S/Cl cationic layers. In addition, optical gaps of 2.31 and 2.60 eV for La12S8Cl8[SbS3]4 and La8S4Cl8La12S8Cl4[SbS3]8, respectively, were determined by UV/vis reflectance spectroscopy, showing a blue shift with respect to La7Sb9S24, which can be attributed to the greater contributions of La to the bottom of the CB as confirmed by the DFT study.

Direct synthesis of nanostructured silver antimony sulfide powders from metal xanthate precursors

Silver(I) ethylxanthate [AgS2COEt] (1) and antimony(III) ethylxanthate [Sb(S2COEt)3] (2) have been synthesised, characterised and used as precursors for the preparation of AgSbS2 powders and thin films using a solvent-free melt method and spin coating technique, respectively. The as-synthesized AgSbS2 powders were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The crystalline AgSbS2 powder was investigated using XRD, which shows that AgSbS2 has cuboargyrite as the dominant phase, which was also confirmed by Raman spectroscopy. SEM was also used to study the morphology of the resulting material which is potentially nanostructured. EDX spectra gives a clear indication of the presence of silver (Ag), antimony (Sb) and sulfur (S) in material, suggesting that decomposition is clean and produces high quality AgSbS2 crystalline powder, which is consistent with the XRD and Raman data. Electronic properties of AgSbS2 thin films deposited by spin coating show a p-type conductivity with measured carrier mobility of 81 cm2 V-1 s-1 and carrier concentration of 1.9 × 1015 cm-3. The findings of this study reveal a new bottom-up route to these compounds, which have potential application as absorber layers in solar cells.

Ba2BS3Cl and Ba5B2S8Cl2: first alkaline-earth metal thioborate halides with [BS3] units

Ba2BS3Cl and Ba5B2S8Cl2 have been synthesized by using PbCl2 as the flux and source of halogen. The two compounds show 3D network structures built by isolated [BS3] units with different Ba-S-Cl groups. This work enriches the structural diversity of boron chemistry and provides an insight into the synthesis of thioborates.

Role of lone-pair electrons in determining the thermal transport behavior of LiAsS2: first-principles investigation

As³⁺ cations possessing stereochemically active lone pairs (SALPs) lead to high SHG coefficients of nonlinear-optical crystal LiAsS₂, but the role of SALPs in determining the thermal transport behavior of LiAsS₂ is still unknown.

AMnAs3S6 (A = Cs, Rb): Phase-Matchable Infrared Nonlinear Optical Functional Motif [As3S6]3- Obtained via Surfactant-Thermal Method

Exploration of a new nonlinear optical (NLO)-active functional motif is important in the rational design of promising infrared (IR) NLO materials. Compared with typical tetrahedral MQ₄ (M = IIB, III, IV metals; Q = S, Se) motifs, MQ₃ (M = As, Sb) pyramids favor high second-harmonic generation (SHG) efficiency while frequently hindering phase matching (PM) because of excessively large optical anisotropy. The surfactant-thermal method was first adopted to achieve PM in MQ₃-containing systems and synthesize mixed covalent-ionic IR NLO materials. Two new thioarsenates of AMnAs₃S₆ (A = Cs, Rb) exhibiting strong PM SHG efficiencies comparable to commercial AGS and laser-induced damage thresholds of one order higher than AGS were obtained. The [As₃S₆]^3- unit in their structures is an unprecedented NLO-active functional motif, which can be useful in designing new IR NLO compounds with large SHG efficiency. In addition, the surfactant-thermal method provides a new general strategy for synthesizing new IR NLO materials.

Two new members in the quaternary Cs-Ag-As-S family with different arrangements of Ag-S and As-S asymmetric building units: syntheses, structures, and theoretical studies

New functional materials of As-based multinary chalcogenidometalates have received special attention due to their different oxidation states and flexible building blocks. In this work, two new quaternary thioarsenates(iii), namely Cs2Ag2As2S5 (I) and Cs3AgAs4S8 (II), have been obtained by a simple surfactant-thermal technique. Their structures were determined on the basis of single-crystal X-ray diffraction; compound I belongs to the triclinic space group P1[combining macron] (no. 2) [a = 7.49(2) Å, b = 9.30(2) Å, c = 9.94(2) Å, α = 63.28(3)°, β = 82.11(3)°, γ = 87.78(3)°, V = 612.4(2) Å3 and Z = 2], whereas compound II crystallizes in the monoclinic space group C2/c (no. 12) [a = 27.76(6) Å, b = 6.98(2) Å, c = 19.68(4) Å, β = 109.85(3)°, V = 3586.7(2) Å3 and Z = 8]. Both structures are shown to feature two-dimensional (2D) layers with different arrangements of Ag-S and As-S asymmetric building units (ABUs). In compound I, the layer is constructed from vertex-sharing dimeric [As2S5] units linked by tetrameric [Ag4S8] moieties. The layered structure in compound II is formed by 21 helical chains based on [As4S9] groups which are further interconnected by tetrahedral [AgS4] chains. The analysis of the quaternary X-Ag-As-S (X = cations) system shows that various combination ways of Ag-S and As-S ABUs in these sulfides can be attributed to the cation-cation repulsion and stereochemically active lone-pair effect. The UV-vis/NIR absorption spectrum indicates that the optical band energy (Eg) of compounds I and II is 2.48 eV and 2.24 eV, respectively. Moreover, theoretical calculations indicate that the As-S and Ag-S bonding states determine the optical properties of the title compounds. This work not only enriches the structural chemistry of thioarsenates, but also opens up a new avenue for exploring novel multinary chalcogenidometalates.

Synthesizing Crystalline Chalcogenidoarsenates in Thiol-Amine Solvent Mixtures

Thiol-amine solvent mixtures have been widely applied in the solution processing of binary chalcogenide thin films due to their excellent ability to dissolve various bulk binary chalcogenides. However, application of this solvent system in preparing new crystalline chalcogenidometalates has not been explored. In this work, by using a thiol-amine solvent mixture of n-butylamine (BA) and 1,2-ethanedithiol (EDT) as the reaction medium and protonated piperazine (pip) cation as the template, we synthesized a series of new chalcogenidoarsenates with structures ranging from discrete clusters to two-dimensional layers, namely, [pipH₂][pipH][AsS₄] (1), [pipH₂][pipH][As(Se_0.4S_0.6)₄] (2), [pipH₂]₂[pipH]₂[In₂As^III₂As^V₂S_13.3(S₂)_0.7] (3), [pipH₂]₂[pipH]₂[In₂As^III₂As^V₂S_10.2Se_3.1(Se₂)_0.7] (4), [pipH₂]_0.5[AsS(S₂)] (5), [pipH₂]_0.5[AsS₂] (6), [pipH]₂[AgAsS₄] (7), [pipH₂]_1.5[GaAs^IIIAs^VS₇] (8), and Cs₂[pipH]₂[InAs₆S₁₂]Cl (9). Particularly, compounds 3, 4, and 8 contain mixed-valent As^III and As^V ions in their discrete clusters and one-dimensional chain. In addition, compound 5 could thermodynamically transform to compound 6 with increasing reaction temperature, which may be attributed to the thermodynamically unstable S-S species in the chains of 5. The BA-EDT solvent mixture was crucial to the synthesis of these compounds, since no title crystals can be prepared by replacing the BA-EDT solvent mixture with other conventional solvents or removing one component of the BA-EDT solvent mixture from the reaction system. Our research demonstrates that thiol-amine solvent systems could be promising reaction media for growing novel crystalline chalcogenidometalates.

From CuFeS2 to Ba6Cu2FeGe4S16: rational band gap engineering achieves large second-harmonic-generation together with high laser damage threshold

From CuFeS₂, the introduction of Ge leads to an increase in band gap. The ordered arrangement of NLO active units [GeS₄] results in a strong SHG response. Finally, Ba₆Cu₂FeGe₄S₁₆ exhibits good NLO performance (SHG, 1.5 × AgGaSe₂; LDT, 2 × AgGaSe₂).

Intrinsic defects and their effects on the optical properties in the nonlinear optical crystal CdSiP2: a first-principles study

In view of their high nonlinear optical coefficients and good phase-matching properties, CdSiP₂ (CSP) crystals are considered as one of the most promising materials in the field of nonlinear optical applications. However, the slight absorption losses around 1.34 μm and 1.78 μm under e-polarized light have been affecting its performance. In this study, first-principles calculations were performed to identify the effects of various charge defects on the absorption properties. Different intrinsic defects in the CSP crystal were calculated using the HSE method and compared according to the specific chemical environments in the experiments. The results show that the point defects of V, Si, and V, which can be spontaneously formed, are dominant in the Cd-poor environment. The combination of Si and V defects is the most favorable cluster in the Cd-poor case because of its relatively low formation energy. Furthermore, the antisite defect Si_Cd was found to be responsible for the main absorption peaks at 1.34 and 1.78 μm in the experimental spectra, whereas other defects and clusters, such as the defects Si and V, also contribute to these red shifted absorptions. Our results intend to provide a guideline for adjusting the optical absorption in CSP by modifying its defects.

Na2CdGe2Q6(Q = S, Se): two metal-mixed chalcogenides with phase-matching abilities and large second-harmonic generation responses

Two metal-mixed chalcogenides with phase-matching abilities and large SHG responseshave been systematically reported.

Facile Hydrazine-Hydrothermal Syntheses and Characterizations of Two Quaternary Thioarsenates(III): Two-Dimensional SrAg4 As2 S6 ⋅2 H2 O and One-Dimensional BaAgAsS3

Two new quaternary thioarsenates(III), SrAg4 As2 S6 ⋅2 H2 O (1) and BaAgAsS3 (2), have been prepared through a hydrazine-hydrothermal method at low temperature. Compound 1 possesses a two-dimensional (2D) layer network, while compound 2 features a one-dimensional (1D) column structure. The detailed structure analysis indicates that Sr(2+) and Ba(2+) cations have different directing effects on the structures of thioarsenates(III). Both experimental and theoretical studies demonstrate that compounds 1 and 2 are narrow-gap semiconductors. Our success in synthesizing these two quaternary thioarsenates(III) proves that the hydrazine-hydrothermal technique is a powerful yet facile synthetic method for exploring new complex chalcogenides with diverse crystal structures and interesting physical properties.