Second-Harmonic Generation and Crystal Structure of the Diamond-like Semiconductors Li2CdGeS4 and Li2CdSnS4

Recent advances in rational structure design for nonlinear optical crystals: leveraging advantageous templates

Nonlinear optical (NLO) crystals that can expand the spectral range of laser outputs have attracted significant attention for their optoelectronic applications. The research progress from the discovery of new single crystal structures to the realization of final device applications involves many key steps and is very time consuming and challenging. Consequently, exploring efficient design strategies to shorten the research period and accelerate the rational design of novel NLO materials has become imperative to address the pressing demand for advanced materials. The recent shift in paradigm toward exploring new NLO crystals involves significant progress from extensive "trial and error" methodologies to strategic approaches. This review proposes the concept of rational structure design for nonlinear optical crystals leveraging advantageous templates. It further discusses their optical characteristics, promising applications as second-order NLO materials, and the relationship between their structure and performance, and highlights urgent issues that need to be addressed in the field of NLO crystals in the future. The review aims to provide ideas and driving impetus to encourage researchers to achieve new breakthroughs in the next generation of NLO materials.

Hydrazine-Assisted Synthesis, Structures, Photoelectricity, and Photocatalysis of Ternary Mercury-Tellurostannate Hybrids with Transition-Metal Complexes

Tellurostannates are traditionally prepared by multistep reactions using the tellurides SnTe, SnTe2, K4SnTe4, or A6SnTe6 (A = K, Rb, or Cs) as precursors, which are usually prepared by the molten reaction of alkali metals Sn and Te under harsh synthetic conditions. Differently, ternary Hg-tellurostannate hybrids [Mn(en)3]HgSnTe3(Te2) (1) (en = ethylenediamine), [Mn(dien)2]HgSnTe3(Te2) (2), and [Fe(dien)2]HgSnTe3(Te2) (3) (dien = diethylenetriamine) were synthesized by one-pot reactions using Sn and Te powders as starting materials in the presence of hydrazine under mild solvothermal conditions. In 1, HgTe3 and SnTe4 units are joined via Te-sharing to form a 1-D polymeric chain [HgSnTe3(Te2)]n2n-, while the [HgSnTe3(Te2)]n2n- chains in 2 and 3 are composed of HgTe4 and SnTe4 units. The common feature of the [HgSnTe3(Te2)2-]n chains in 1-3 is that they are constructed by both the telluride anion Te2- and the polytelluride anion Te22-. 1-3 exhibited strong photocurrent responses with current densities of 5.26, 3.38, and 3.94 μA cm-2, respectively. They showed effective photocatalytic activities for methylene blue degradation with degradation ratios in the range of 85.3-94.6% after light irradiation for 80 min. Investigation of the photocatalytic mechanism showed that •O2- radicals and h+ holes were the main active substances in the photodegradation.

Crystal structure, phase width, and physical properties of the barium tetrel selenides Ba6Si2-xGexSe12 (x = 0, 0.5, 1, and 1.5) with ultralow thermal conductivity

The new compound Ba6Si2Se12 was synthesized, and the crystal structure and physical properties are reported here. Ba6Si2Se12 adopts a new structure type in the triclinic P1̄ space group with the lattice parameters a = 9.1822(7) Å, b = 12.2633(14) Å, c = 12.3636(18) Å, α = 109.277(3)°, β = 104.734(2)°, and γ = 100.4067(16)°. Notably, the structure features disordered Se22- dumbbells that have also been observed in the germanium selenide with the analogous stoichiometry (Ba6Ge2Se12). Density functional theory calculations revealed that Ba6Si2Se12 is a semiconductor with a calculated band gap of 1.74 eV. UV/vis/NIR absorption spectra indicated that the experimental band gap of Ba6Si2Se12 is 1.89 eV. While exploring this compound's phase width, it was discovered that up to 75% of the Si could be substituted with Ge while retaining the structure type. Rietveld refinements were performed on the phase-pure samples of Ba6Si2-xGexSe12 (x = 0, 0.5, 1, and 1.5) using data collected at the Canadian Light Source's High Energy Wiggler Beamline. The cell parameters, Si/Ge occupancies, and disordered Se22- occupancies were studied. Raman spectra displayed the expected Si-Se and Ge-Se stretching modes from 215 cm-1 to 280 cm-1. The samples were also hot-pressed into pellets to determine their thermal conductivity values ranging from 0.5 to 0.4 W m-1 K-1 for the x = 0, 0.5, and 1.5 samples. The x = 1 sample stood out with a remarkably low thermal conductivity of 0.3 W m-1 K-1, consistent from room temperature up to 573 K.

Boron Chalcogen Mixture Method-Assisted Alkali Halide Flux Crystal Growth of an Extensive Family of Quaternary Rare Earth Transition-Metal Thiosilicates: Investigation of Their Structures and Magnetic Properties

A series of transition-metal-containing rare earth thiosilicates, RE3TM0.5SiS7 (RE = Gd-Yb; TM = Fe, Co, Ni), was obtained via flux crystal growth utilizing the boron chalcogen mixture (BCM) method. The series includes the first reported ytterbium-containing thiosilicates crystallizing in this structure type. The thiosilicates crystallize in the hexagonal crystal system in space group P63. The use of the BCM method to synthesize phase-pure samples of the title compounds for magnetic measurements is discussed, highlighting how the approach avoids some of the difficulties that plague typical chalcogenide syntheses. Magnetic measurements demonstrate that some of the compounds order antiferromagnetically and exhibit transition temperatures below 15 K.

Zn2 HgP2 S8 : A Wide Bandgap Hg-Based Infrared Nonlinear Optical Material with Large Second-Harmonic Generation Response

Hg-based chalcogenides, as good candidates for the exploration of high-performance infrared (IR) nonlinear optical (NLO) materials, usually exhibit strong NLO effects, but narrow bandgaps. Herein, an unprecedented wide bandgap Hg-based IR NLO material Zn2 HgP2 S8 (ZHPS) with diamond-like structure is rationally designed and fabricated by a tetrahedron re-organization strategy with the aid of structure and property predictions. ZHPS exhibits a wide bandgap of 3.37 eV, which is the largest one among the reported Hg-based chalcogenide IR NLO materials and first breaks the 3.0 eV bandgap "wall" in this system, resulting in a high laser-induced damage threshold (LIDT) of ≈2.2 × AgGaS2 (AGS). Meanwhile, it shows a large NLO response (1.1 × AGS), achieving a good balance between bandgap (≥3.0 eV) and NLO effect (≥1 × AGS) for an excellent IR NLO material. DFT calculations uncover that, compared to normal [HgS4 ]n , highly distorted [HgS4 ]d tetrahedral units are conducive to generating wide bandgap, and the wide bandgap in ZHPS can be attributed to the strong s-p hybridization between Hg─S bonding in distorted [HgS4 ]d , which gives some insights into the design of Hg-based chalcogenides with excellent properties based on distorted [HgS4 ]d tetrahedra.

Accurate X-ray diffraction data required for proper evaluation of bond valence sums and global instability indexes: redetermination of the crystal structures of diamond-like Cu2CdSiS4 and Cu2HgSnS4 as a case study

Our calculations of the global instability index (G) values for some diamond-like materials with the general formula I2-II-IV-VI4 have indicated that the structures may be unstable or incorrectly determined. To compute the G value of a given compound, the bond valence sums (BVSs) must first be calculated using a crystal structure. Two examples of compounds with high G values, based on data from the literature, are the wurtz-stannite-type dicopper cadmium silicon tetrasulfide (Cu2CdSiS4) and the stannite-type dicopper mercury tin tetrasulfide (Cu2HgSnS4), which were first reported in 1967 and 1965, respectively. In the present study, Cu2CdSiS4 and Cu2HgSnS4 were prepared by solid-state synthesis at 1000 and 900 °C, respectively. The phase purity was assessed by powder X-ray diffraction. Optical diffuse reflectance UV/Vis/NIR spectroscopy was used to estimate the optical bandgaps of 2.52 and 0.83 eV for Cu2CdSiS4 and Cu2HgSnS4, respectively. The structures were solved and refined using single-crystal X-ray diffraction data. The structure type of Cu2CdSiS4 was confirmed, where Cd2+, Si4+ and two of the three crystallographically unique S2- ions lie on a mirror plane. The structure type of Cu2HgSnS4 was also verified, where all ions lie on special positions. The S2- ion resides on a mirror plane, the Cu+ ion is situated on a fourfold rotary inversion axis and both the Hg2+ and the Sn4+ ions are located on the intersection of a fourfold rotary inversion axis, a mirror plane and a twofold rotation axis. Using the crystal structures solved and refined here, the G values were reassessed and found to be in the range that indicates reasonable strain for a stable crystal structure. This work, together with some examples gathered from the literature, shows that accurate data collected on modern instrumentation should be used to reliably calculate BVSs and G values.

d6versus d10, Which Is Better for Second Harmonic Generation Susceptibility? A Case Study of K2TGe3Ch8 (T = Fe, Cd; Ch = S, Se)

Two acentric chalcogenide compounds, K₂CdGe₃S₈ and K₂CdGe₃Se₈, were synthesized via conventional high-temperature solid-state reactions. The crystal structures of K₂CdGe₃S₈ and K₂CdGe₃Se₈ were accurately determined by single-crystal X-ray diffraction and crystallize in the K₂FeGe₃S₈ structure type. K₂CdGe₃S₈ is isostructural to K₂FeGe₃S₈ with superior nonlinear optical properties. For the second harmonic generation (SHG) response, K₂CdGe₃S₈ is 18× K₂FeGe₃S₈ for samples of particle size of 38-55 μm. The superior nonlinear optical properties of K₂CdGe₃S₈ over K₂FeGe₃S₈ are mainly contributed by the chemical characteristics of Cd compared with Fe, which are elucidated by nonlinear optical property measurements, electronic structure calculations, and density functional theory calculations. The [CdS₄] tetrahedra within K₂CdGe₃S₈ exhibit a higher degree of distortion and larger volume compared to the [FeS₄] tetrahedra in K₂FeGe₃S₈. This study possesses a good platform to investigate how d-block elements contribute to the SHG response. The fully occupied d¹⁰-elements are better for SHG susceptibility than d⁶-elements in this study. K₂CdGe₃S₈ is a good candidate as an infrared nonlinear optical material of high SHG response (2.1× AgGaS₂, samples of particle size of 200-250 μm), type-I phase-matching capability, high laser damage threshold (6.2× AgGaS₂), and good stability.

Crystal structure, electronic structure, and optical properties of the novel Li4CdGe2S7, a wide-bandgap quaternary sulfide with a polar structure derived from lonsdaleite

The novel quaternary thiogermanate Li4CdGe2S7 (tetralithium cadmium digermanium heptasulfide) was discovered from a solid-state reaction at 750 °C. Single-crystal X-ray diffraction data were collected and used to solve and refine the structure. Li4CdGe2S7 is a member of the small, but growing, class of I4–II–IV2–VI7 diamond-like materials. The compound adopts the Cu5Si2S7 structure type, which is a derivative of lonsdaleite. Crystallizing in the polar space group Cc, Li4CdGe2S7 contains 14 crystallographically unique ions, all residing on general positions. Like all diamond-like structures, the compound is built of corner-sharing tetrahedral units that create a relatively dense three-dimensional assembly. The title compound is the major phase of the reaction product, as evidenced by powder X-ray diffraction and optical diffuse reflectance spectroscopy. While the compound exhibits a second-harmonic generation (SHG) response comparable to that of the AgGaS2 (AGS) reference material in the IR region, its laser-induced damage threshold (LIDT) is over an order of magnitude greater than AGS for λ = 1.064 µm and τ = 30 ps. Bond valence sums, global instability index, minimum bounding ellipsoid (MBE) analysis, and electronic structure calculations using density functional theory (DFT) were used to further evaluate the crystal structure and electronic structure of the compound and provide a comparison with the analogous I2–II–IV–VI4 diamond-like compound Li2CdGeS4. Li4CdGe2S7 appears to be a better IR nonlinear optical (NLO) candidate than Li2CdGeS4 and one of the most promising contenders to date. The exceptional LIDT is likely due, at least in part, to the wider optical bandgap of ∼3.6 eV.

Remarkable Infrared Nonlinear Optical, Dielectric, and Strong Diamagnetic Characteristics of Semiconducting K3[BiS3]

The ternary sulfido bismuthate K₃[BiS₃] is synthesized in quantitative yields. The material exhibits nonlinear optical properties with strong second harmonic generation properties at arbitrary wavelengths in the infrared spectral range and a notable laser-induced damage threshold of 5.22 GW cm^-2 for pulsed laser radiation at a wavelength of 1040 nm, a pulse duration of 180 fs, and a repetition rate of 12.5 kHz. K₃[BiS₃] indicates semiconductivity with a direct optical band gap of 2.51 eV. Dielectric and impedance characterizations demonstrate κ values in the range of 6-13 at 1 kHz and a high electrical resistivity. A strong diamagnetic behavior with a susceptibility of -2.73 × 10^-4 m³ kg^-1 at room temperature is observed. These results suggest it is a promising nonlinear optical candidate for the infrared region. The synergic physical characteristics of K₃[BiS₃] provide insight into the correlation of optical, electrical, and magnetic properties.

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.

Designing A New Infrared Nonlinear Optical Material, β-BaGa2 Se4 Inspired by the Phase Transition of the BaB2 O4 (BBO) Crystal

Infrared nonlinear optical (IR NLO) crystals play a significant role in the development of IR laser technology. But rationally designing a new IR NLO crystal remains a huge challenge because of the unpredictability of inorganic structures. Herein, inspired by phase transformation of the famous BaB₂ O₄ (BBO) crystal, a temperature-induced centrosymmetric (CS) to noncentrosymmetric (NCS) transformation approach is employed in CS BaGa₂ Se₄ to uncover a new NCS ternary chalcogenide, β-BaGa₂ Se₄ which can exhibit the well-balanced NLO properties, including moderate phase-matching SHG response (≈0.6×AgGaS₂ ), high LDT (10×AgGaS₂ ), and large birefringence (Δn=0.18 in the visible region). Therefore, β-BaGa₂ Se₄ will be a promising IR NLO crystal. The analysis for the structure-property relationship shows that the excellent NLO properties of β-BaGa₂ Se₄ mainly originate from edge-sharing GaSe₄ tetrahedral chains, which are different from B₃ O₆ groups in β-BBO and respect a new direction for the design of IR NLO crystals. So, we believe that the current research provides not only a new IR NLO crystal but also some insights for the design of new IR NLO crystals.

Syntheses, Structures and Properties of Alkali and Alkaline Earth Metal Diamond-Like Compounds Li2MgMSe4 (M = Ge, Sn)

Two new diamond-like (DL) chalcogenides, Li2MgGeSe4 and Li2MgSnSe4, have been successfully synthesized using a conventional high-temperature solid-state method. The two compounds crystallize in the non-centrosymmetric space group Pmn21 with a = 8.402 (14) Å, b = 7.181 (12) Å, c = 6.728 (11) Å, Z = 2 for Li2MgSnSe4, and a = 8.2961 (7) Å, b = 7.0069 (5) Å, c = 6.6116 (6) Å, Z = 2 for Li2MgGeSe4. The calculated results show that the second harmonic generation (SHG) coefficients of Li2MgSnSe4 (d33 = 12.19 pm/v) and Li2MgGeSe4 (d33 = -14.77 pm/v), mainly deriving from the [MSe4] (M = Ge, Sn) tetrahedral units, are close to the one in the benchmark AgGaS2 (d14 = 13.7 pm/V). The calculated band gaps for Li2MgSnSe4 and Li2MgGeSe4 are 2.42 and 2.44 eV, respectively. Moreover, the two compounds are the first series of alkali and alkaline-earth metal DL compounds in the I2-II-IV-VI4 family, enriching the structural diversity of DL compounds.

Highly Distorted [HgS4] Motif-Driven Structural Symmetry Degradation and Strengthened Second-Harmonic Generation Response in the Defect Diamond-Like Chalcogenide Hg3P2S8

Chalcogenides with diamond-like (DL) structures are a treasury of infrared nonlinear optical (NLO) materials. Here, a ternary Hg-based chalcogenide with a defect DL structure, Hg₃P₂S₈, is synthesized by solid-state reaction. Driven by the highly distorted [HgS₄] tetrahedra, this compound displays an interesting structural symmetry degradation from tetragonal to orthorhombic compared with its analogue Zn₃P₂S₈. Meanwhile, the overall performances of Hg₃P₂S₈ are quite remarkable, including a very strong phase-matchable second-harmonic generation (SHG) response (4.2 × AgGaS₂), large band gap (2.77 eV), wide IR transparent range (0.45-16.7 μm), and high laser-induced damage threshold (4 × AGS). Furthermore, the theoretical analysis and local dipole moment calculations elucidate that the highly distorted [HgS₄] tetrahedra contribute a lot to the enhancement of the SHG effect. This discovery will motivate the exploration of other DL Hg-based chalcogenides serving as high-performing mid-IR NLO materials.

Stepwise Li Substitution Induced Structure Evolution and Improved Nonlinear Optical Performance for Diamond-like Sulfides

One of the key scientific issues for exploration of novel infrared nonlinear optical (NLO) crystals is to obtain ones with good hybrid NLO behaviors. Herein, we report four diamond-like Ag-based sulfides via stepwise Li substitution of Ag in Ag₂ZnSnS₄, including Ag₂ZnSnS₄ (1), (Li_1.22Ag_0.78)ZnSnS₄ (2), (Li_1.58Ag_0.42)ZnSnS₄ (3), and Li₂ZnSnS₄ (4). With the increase of Li content, the sulfide's noncentrosymmetric crystal structure changes from tetragonal I42m for 1, to orthorhombic Pmn2₁ for 2 and 3, and to monoclinic Pn for 4. Accordingly, their NLO responses are improved along with the increase of Li content, viz. from non-NLO-active for 1, to non-phase-matchable for 2 and 3, and to phase-matchable for 4. Their optical band gaps also increase regularly. The relationship between their chemical compositions, crystal structures, and NLO activities is investigated by means of chemical structural analysis and theoretical calculation. This work offers a new systematic case for designing promising NLO-active compounds via rarely adopted cation's stepwise partial substitution and understanding the chemical composition-structure-NLO property relationship.

Li4 MgGe2 S7 : The First Alkali and Alkaline-Earth Diamond-Like Infrared Nonlinear Optical Material with Exceptional Large Band Gap

Large band gap and strong nonlinear optical (NLO) effect are two valuable but contradictory parameters, which are difficult to balance in one infrared (IR) NLO material. Herein, the first alkali and alkaline-earth metal diamond-like (DL) IR NLO material Li₄ MgGe₂ S₇ , presenting a honeycomb-like 3D framework constructed by 6-membered LiS₄ rings and GeMgS₆ zigzag chains, was rationally designed and synthesized. The introduction of rigid alkali metal and alkaline-earth metal LiS₄ and MgS₄ tetrahedra effectively broadens the band gap of DL compound to 4.12 eV (the largest one in the reported quaternary metal chalcogenides), generating a high laser damage threshold of 7 × AgGaS₂ at 1064 nm. Furthermore, Li₄ MgGe₂ S₇ displays a suitable SHG response (0.7 × AgGaS₂ ) with a type I phase-matching behavior. The results indicate that Li₄ MgGe₂ S₇ is a promising IR NLO material for the high-power laser application and it provides an insight into the design of new DL compound with outstanding IR NLO performances.

α-Ca2CdP2 and β-Ca2CdP2: Two Polymorphic Phosphide-Based Infrared Nonlinear Crystals with Distorted NLO-Active Tetrahedral Motifs Realizing Large Second Harmonic Generation Effects and Suitable Band Gaps

Two polymorphic phosphide-based infrared (IR) nonlinear optical (NLO) crystals, α-Ca₂CdP₂ and β-Ca₂CdP₂, were obtained by combining alkaline-earth metals and d¹⁰ transition metals using metal flux and metal salt flux methods, respectively. The crystal structure of α-Ca₂CdP₂ is orthorhombic in the space group Cmc2₁ (no. 36), while the structure of β-Ca₂CdP₂ is monoclinic in the space group Cm (no. 8). Both are two-dimensional layered structures that are composed of CdP₄ tetrahedra layers via sharing vertices, which stack along the b-axis and the c-axis, respectively. The second harmonic generation (SHG) measurements manifest that α-Ca₂CdP₂ and β-Ca₂CdP₂ exhibit strong SHG intensities (1.41 and 3.28× that of AgGaS₂ at a 2050 nm laser, respectively). Other optical measurements indicate that α-Ca₂CdP₂ and β-Ca₂CdP₂ have suitable band gaps (1.98 and 1.55 eV, respectively), high laser-induced damage thresholds (4.5 and 3.1× that of AgGaS₂ at 1064 nm laser, respectively) and appropriate birefringence (0.12 and 0.20 at 2050 nm, respectively) in addition to covering wide infrared transparent regions. The research on α-Ca₂CdP₂ and β-Ca₂CdP₂ demonstrates that they are potential IR NLO candidates. Theoretical calculations uncover that their SHG effects are from distorted CdP₄ tetrahedra, highlighting that tetrahedral motifs, including d¹⁰ transition metals, would be ideal NLO-active building blocks.

Cu2ZnSbS4: A Thioantimonate(V) with Remarkably Strong Covalent Sb-S Bonding

A new member to the A₂^IB^IIC^IVX₄ compound family, Cu₂ZnSbS₄, was synthesized successfully using ball milling and postannealing in H₂S-atmosphere. For comparative purposes, Cu₃SbS₄ was additionally prepared using the same synthetic approach. As is common for A₂^IB^IIC^IVX₄ compounds, Cu₂ZnSbS₄ crystallizes isostructural to Cu₃SbS₄ in the stannite-type structure in space group I42m. Both antimony sulfides contain monovalent diamagnetic copper and are characterized by substantial covalent bonding. This is consistent with the ¹²¹Sb isomer shifts occurring for the Mössbauer spectra of Cu₂ZnSbS₄ (-7.71 mm s^-1) and Cu₃SbS₄ (-7.68 mm s^-1) which fall in the region of covalently bonded Sb(V) compounds. These spectroscopic results are supported by electronic structure calculations.

Na2MgSnS4 – a new member of the A 2 I B II C IV X 4 family of compounds

A new member of the A 2 I B II C IV X 4 compound family, Na2MgSnS4, has been synthesized by ball milling of the binary sulfides SnS, Na2S, and MgS with elemental sulfur in a high-energy planetary mill, followed by annealing in an atmosphere of H2S (T = 600 °C/3 h). Na2MgSnS4 adopts the NaCrS2-type structure (rhombohedral, space group R 3 ¯ $\overline{3}$ m) with a = 3.7496(11) and c = 19.9130(6) Å. The Na atoms occupy Wyckoff position 3b, whereas the Mg and Sn atoms are statistically distributed on the cation sites 3a; all cations are surrounded by six sulfur atoms.

Syntheses and crystal structures of the quaternary thio-germanates Cu4FeGe2S7 and Cu4CoGe2S7

The quaternary thio-germanates Cu4FeGe2S7 (tetra-copper iron digermanium hepta-sulfide) and Cu4CoGe2S7 (tetra-copper cobalt digermanium hepta-sulfide) were prepared in evacuated fused-silica ampoules via high-temperature, solid-state synthesis using stoichiometric amounts of the elements at 1273 K. These isostructural compounds crystallize in the Cu4NiSi2S7 structure type, which can be considered as a superstructure of cubic diamond or sphalerite. The monovalent (Cu+), divalent (Fe2+ or Co2+) and tetra-valent (Ge4+) cations adopt tetra-hedral geometries, each being surrounded by four S2- anions. The divalent cation and one of the sulfide ions lie on crystallographic twofold axes. These tetra-hedra share corners to create a three-dimensional framework structure. All of the tetra-hedra align along the same crystallographic direction, rendering the structure non-centrosymmetric and polar (space group C2). Analysis of X-ray powder diffraction data revealed that the structures are the major phase of the reaction products. Thermal analysis indicated relatively high melting temperatures, near 1273 K.

Effects of oxygen variation on the improved structural stability, electronic and optical properties of ZnTeO compounds

Crystalline ZnTeO thin films are promising materials for next generation photovoltaics. However, their structural stability and optical nonlinearity potential in bulk form have not been reported. Here, structural, electronic and optical properties of ZnTeO composites have been thoroughly studied using genetic algorithm and density functional theory (DFT). Energetically, mechanically and dynamically stable O-rich phases, namely Zn₂Te₂O₆ and ZnTeO₄, were obtained. Ground-state properties such as lattice constants and simulated XRD were analyzed and compared to the experimental literature wherever possible. With a G ₀ W ₀ corrected band gap, these semiconducting phases display several desirable features, namely, Jahn-Teller distorted cations, hardness and shear anisotropy-induced optical nonlinearity that increase monotonically as O concentration elevates. Such trends appear to be consistent with that seen in the experimental study of ZnTeO thin film. It is observed that Zn-d, Te-p  and O-p  states have immense influence towards the electronic properties of these structures. Both phases exhibit steep elevation of absorption throughout the ultraviolet (UV) range, hitting peak value of ~5.0  ×  10⁵ cm^-1. Of particular interest, the non-centrosymmetric ZnTeO₄ has second harmonic generation coefficients (9.84 pm V^-1 and 2.33 pm V^-1 at static limit) greater than borates crystal and large birefringence that exceeds 0.08 in deep UV region, thus highlighting its potential pedigree as new optical materials in UV range.

Crystal structure of mechanochemically synthesized Ag2CdSnS4

Ag2CdSnS4 was synthesized by a two step mechanochemical synthesis route. From a detailed analysis of the observed reflections in the X-ray powder diffraction pattern, the crystal structure proposed in the literature (space group Cmc21 [E. Parthé, K. Yvon, R. H. Deitch, Acta Crystallogr. 1969, B25, 1164–1174; O. V. Parasyuk, I. D. Olekseyuk, L. V. Piskach, S. V. Volkov, V. I. Pekhnyo, J. Alloys Compd. 2005, 399, 173–177]) is questionable. Our structural investigations presented in this contribution point to the fact that Ag2CdSnS4 crystallizes in the monoclinic wurtzkesterite-type structure (space group Pn). At around T = 200°C, a phase transition to the orthorhombic wurtzstannite-type structure (space group Pmn21) is observed.

Li2CdSiS4, a promising IR NLO material with a balanced Eg and SHG response originating from the effect of Cd with d10 configuration

A new promising infrared nonlinear optical crystal Li₂CdSiS₄ with millimeter size was obtained and systematically characterized.

A review of the AI2BIICIVDVI4 family as infrared nonlinear optical materials: the effect of each site on the structure and optical properties

The AI2B^IIC^IVDVI4 family as promising infrared NLO materials is summarized. The influence of each site substitutions on the structures and properties is systematically analyzed.

New quaternary chalcogenide Ba4HgAs2S10 originating from the combination of linear [HgS2]2− and tetrahedral [AsS4]3− modules

A new quaternary chalcogenide Ba₄HgAs₂S₁₀ is constructed by combining linear HgS₂²⁻ and tetrahedral AsS₄³⁻ modules.

Ba10In6Zn7S26- nZnS: An Inorganic Composite System with Interface Phase-Matching Tuned for High-Performance Infrared Nonlinear Optical Materials

Mid- and far-infrared nonlinear optical (MFIR NLO) materials are important in modern laser technologies. However, it is very challenging to develop materials that can achieve a subtle balance between the key requirements, such as large NLO response, high laser-induced damage threshold (LIDT), wide IR transparency, and phase-matching. In this work, a new wide IR transparency (0.38-15.3 μm) NLO crystal Ba₁₀In₆Zn₇S₂₆ (SS26) is synthesized. Further, its composite system Ba₁₀In₆Zn₇S₂₆- nZnS is synthesized by eutectic reaction. In particular, Ba₁₀In₆Zn₇S₂₆-14ZnS (SS40) shows excellent balanced NLO performance that includes a large band gap of 3.05 eV, high LIDT (13.3 × AgGaS₂), large second harmonic generation (SHG) response (2.1 × AgGaS₂ at 2050 nm, 5.2 × KDP at 1064 nm), and wide optical transmission window (0.37-15.4 μm). Importantly, the phase-matching condition is realized for SS40 by interfaces formed between the crystal face (112) of matrix SS26 and the crystal face (111) of reinforcement cubic ZnS by topological chemical reaction, and the NLO performance can be tuned by different concentrations of ZnS. First-principles simulations are employed to study NLO properties of SS26 and the interfaces. This work demonstrates that SS40 is a promising MFIR NLO material, and tuning components of the composite material system is a useful way to develop new MFIR NLO materials with excellent comprehensive performance.

Ba4(BS3S)2S4: a new thioborate with unprecedented [BS3-S] and [S4] fundamental building blocks

The first BS-S group, BS₃S, with π-conjugation composed of planar BS₃ and a non-polar covalent S–S bond.

Li2ZnGeS4: a promising diamond-like infrared nonlinear optical material with high laser damage threshold and outstanding second-harmonic generation response

A promising IR nonlinear optical material Li₂ZnGeS₄ with a diamond-like configuration and high optical performance is reported.

New strategy for designing promising mid-infrared nonlinear optical materials: narrowing the band gap for large nonlinear optical efficiencies and reducing the thermal effect for a high laser-induced damage threshold

To circumvent the incompatibility between large nonlinear optical (NLO) efficiencies and high laser-induced damage thresholds (LIDTs) in mid-infrared NLO materials, a new strategy for designing materials with both excellent properties is proposed. This strategy involves narrowing the band gap for large NLO efficiencies and reducing the thermal effect for a high LIDT. To support these proposals, a series of isostructural chalcogenides with various tetrahedral center cations, Na2Ga2MQ6 (M = Ge, Sn; Q = S, Se), were synthesized and studied in detail. Compared with the benchmark AGS, these chalcogenides exhibit significantly narrower band gaps (1.56-1.73 eV, AGS: 2.62 eV) and high NLO efficiencies (1.6-3.9 times that of AGS at 1910 nm), and also outstanding LIDTs of 8.5-13.3 × those of AGS for potential high-power applications, which are contrary to the conventional band gap view but can be attributed to their small thermal expansion anisotropy, surmounting the NLO-LIDT incompatibility. These results shed light on the search for practical IR NLO materials with excellent performance not restricted by NLO-LIDT incompatibility.