Infrared Nonlinear Optical Materials Research Articles

Sr2HgGe2OS6: A Hg-Based Oxychalcogenide Infrared Nonlinear Optical Material Exhibiting Favorable Balance between a Large Band Gap and Strong Second Harmonic Generation Response.

Currently, oxychalcogenides with mixed-anion groups that integrate the property advantages of oxides (wide optical band gap) and chalcogenides [strong second harmonic generation (SHG) response] through chemical substitution engineering have attracted widespread interest and are considered to be important candidates for infrared (IR) nonlinear optical (NLO) materials. Herein, the first Hg-based oxychalcogenide Sr2HgGe2OS6 with mixed anion [GeOS3] units has been successfully synthesized through a spontaneous crystallization method, which exhibits a favorable balance between the strong SHG response (0.7 × AgGaS2) and large optical band gap (2.9 eV). In addition, Sr2HgGe2OS6 shows high laser-induced damage threshold (LIDT, 2.1 × AgGaS2) as well as phase-matching (PM) performance. Theoretical calculations indicate that the Sr2HgGe2OS6 encompasses large birefringence of 0.128@2090 nm (3.3 × AgGaS2) and its SHG density mainly comes from [HgS4] tetrahedra and [GeOS3] units. This work not only demonstrates that Sr2HgGe2OS6 is a promising IR NLO material but also provides new ideas for the exploration of Hg-based oxychalcogenide IR NLO materials.

Infrared nonlinear optical materials with multiple strongly ionic cations

Infrared nonlinear optical (IR-NLO) crystals with excellent properties are in extensive demand due to their important role in IR laser technology. Currently, it remains a great challenge to obtain IR-NLO materials with both high second harmonic generation (SHG) response and large laser-induced damage thresholds (LIDTs). Some structural design strategies such as ‘structural/functional regions’ have been adopted to develop new high-performance NLO materials. The covalent structural region producing SHG signals has been extensively investigated, whereas the hard cations (alkali, alkaline-earth, and rare-earth metal ions) which are responsible for improving LIDTs, have been relatively neglected. Utilizing the concept of structural/functional regions, we focus on the relation between structural regions and SHG properties in chalcogenides. Combining different kinds of hard cations can change the dimension of structures and affect the stacking of NLO-active groups. Introducing more hard cations and constructing more complex ion regions help to increase the laser damage threshold. Based on the mentioned structural strategies, guidance will be provided for developing high-performance multiple-cation materials for IR NLO applications.

Polysubstitution Induced Centrosymmetric-to-Noncentrosymmetric Structural Transformation and Nonlinear-Optical Behavior: The Case of Na0.45Ag0.55Ga3Se5.

Obtaining compounds with large nonlinear-optical (NLO) coefficients and wide band gaps is challenging due to their competitive requirements for chemical bonds. Herein, the first member with mixed cations on the A site in the A-M3-Q5 or A-Ag-M6-Q10 (A = alkali metal; M = Ga, In; Q = S, Se, Te) family, viz. Na0.45Ag0.55Ga3Se5 (NAGSe), was obtained by a solid-state reaction. Its structure features [GaSe4] tetrahedra built three-dimensional {[Ga3Se5]-}∞ network, with Na and Na/Ag cations located at the octahedral cavities. Noncentrosymmetric (R32) NAGSe can also be transformed from centrosymmetric RbGa3S5 (P21/c) via multiple-site cosubstitution. NAGSe exhibits the highest NLO response (1.9 × AGS) in the A-Ag-M-Q family. Crystal structure analysis and theoretical calculations suggest that the NLO response is mainly contributed by the regularly arranged [GaSe4] units. This work enriches the exploration of the undeveloped A-M3-Q5 or A-Ag-M6-Q10 family as potential infrared NLO materials.

Cs3In(In4Se7)(P2Se6): A Multi‐Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting

AbstractNon‐centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro‐optical technologies, yet their rational structural design remains a significant challenge. Here, we report a “group grafting” strategy for designing the first multi‐chromophore selenophosphate, Cs3In(In4Se7)(P2Se6), that crystallizes in a NCS and polar space group of Cm. The structure features a unique basic building unit (BBU) [In(In4Se10)(P2Se6)], formed through “grafting [In4Se10] supertetrahedra on the root of [In(P2Se6)2] groups”. Theoretical calculations confirm that this [In(In4Se10)(P2Se6)] BBU can achieve a “1+1>2” combination of properties from two chromophores, [In4Se10] supertetrahedron and ethane‐like [P2Se6] dimer. That makes Cs3In(In4Se7)(P2Se6) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS2), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 μm), a significant birefringence (0.26 @1064 nm) as well as the congruently‐melting property at ~700 °C. Therefore, Cs3In(In4Se7)(P2Se6) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that “group grafting” will be an effective strategy for constructing novel polar BBUs with multi‐chromophore to design NCS structures and high‐performance IR NLO materials.

Cs3In(In4Se7)(P2Se6): A Multi-Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting.

Non-centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro-optical technologies, yet their rational structural design remains a significant challenge. Here, we report a "group grafting" strategy for designing the first multi-chromophore selenophosphate, Cs3In(In4Se7)(P2Se6), that crystallizes in a NCS and polar space group of Cm. The structure features a unique basic building unit (BBU) [In(In4Se10)(P2Se6)], formed through "grafting [In4Se10] supertetrahedra on the root of [In(P2Se6)2] groups". Theoretical calculations confirm that this [In(In4Se10)(P2Se6)] BBU can achieve a "1+1>2" combination of properties from two chromophores, [In4Se10] supertetrahedron and ethane-like [P2Se6] dimer. That makes Cs3In(In4Se7)(P2Se6) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS2), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 μm), a significant birefringence (0.26 @1064 nm) as well as the congruently-melting property at ~700 °C. Therefore, Cs3In(In4Se7)(P2Se6) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that "group grafting" will be an effective strategy for constructing novel polar BBUs with multi-chromophore to design NCS structures and high-performance IR NLO materials.

Molecular Crystals Constructed by Polar Molecular Cages: A Promising System for Exploring High-performance Infrared Nonlinear Optical Crystals.

Polar molecular crystals, with their densely stacked polar nonlinear optical (NLO) active units, are favored for their large second harmonic generation (SHG) responses and birefringence. However, their potential for practical applications as Infrared (IR) NLO materials has historically been underappreciated due to the weak inter-molecular interaction forces that may compromise their physicochemical properties. In this study, we propose molecular crystals with polar molecular cages as a treasure-house for the development of superior IR NLO materials and a representative system, binary chalcogenide molecular crystals, composed of [P4 Sn ] (n=3-9) polar molecular cages, is introduced. These crystals may not only achieve wide band gap, large SHG response, and birefringence in a single structure, but also exhibit favorable physicochemical properties. We subsequently obtained a polar molecular crystal, α-P4 S5 , which demonstrated exceptional IR optical properties, including a strong SHG response (1.1×AGS), wide band gap (3.02 eV), large birefringence (0.134@2050 nm), and a broad transmission range (0.41-14.7 μm). Moreover, it showed excellent water resistance and hardness. These findings highlight the potential of polar molecular crystals as a promising platform for the development of high-performance IR NLO materials.

Molecular Crystals Constructed by Polar Molecular Cages: A Promising System for Exploring High‐performance Infrared Nonlinear Optical Crystals

AbstractPolar molecular crystals, with their densely stacked polar nonlinear optical (NLO) active units, are favored for their large second harmonic generation (SHG) responses and birefringence. However, their potential for practical applications as Infrared (IR) NLO materials has historically been underappreciated due to the weak inter‐molecular interaction forces that may compromise their physicochemical properties. In this study, we propose molecular crystals with polar molecular cages as a treasure‐house for the development of superior IR NLO materials and a representative system, binary chalcogenide molecular crystals, composed of [P4Sn] (n=3–9) polar molecular cages, is introduced. These crystals may not only achieve wide band gap, large SHG response, and birefringence in a single structure, but also exhibit favorable physicochemical properties. We subsequently obtained a polar molecular crystal, α‐P4S5, which demonstrated exceptional IR optical properties, including a strong SHG response (1.1×AGS), wide band gap (3.02 eV), large birefringence (0.134@2050 nm), and a broad transmission range (0.41–14.7 μm). Moreover, it showed excellent water resistance and hardness. These findings highlight the potential of polar molecular crystals as a promising platform for the development of high‐performance IR NLO materials.

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.

Wide band gap selenide infrared nonlinear optical materials AIIMg6Ga6Se16 with strong SHG responses and high laser-induced damage thresholds.

Infrared (IR) nonlinear optical (NLO) materials with strong NLO response, wide band gap and high laser-induced damage threshold (LIDT) are highly expected in current laser technologies. Herein, by introducing double alkaline-earth metal (AEM) atoms, three wide band gap selenide IR NLO materials AIIMg6Ga6Se16 (AII = Ca, Sr, Ba) with excellent linear and NLO optical properties have been rationally designed and fabricated. AIIMg6Ga6Se16 (AII = Ca, Sr, Ba) are composed of unique [AIISe6] triangular prisms, [MgSe6] octahedra and [GaSe4] tetrahedra. The introduction of double AEMs effectively broadens the band gaps of selenide-based IR NLO materials. Among them, CaMg6Ga6Se16, achieving the best balance between the second-harmonic generation response (∼1.5 × AgGaS2), wide band gap (2.71 eV), high LIDT (∼9 × AgGaS2), and moderate birefringence of 0.052 @ 1064 nm, is a promising NLO candidate for high power IR laser. Theoretical calculations indicate that the NLO responses and band gaps among the three compounds are mainly determined by the NLO-active [GaSe4] units. The results enrich the chemical diversity of chalcogenides, and give some insight into the design of new functional materials based on the rare [AIISe6] prismatic units.

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.

ACu4AsS4 (A = K, Rb): Two infrared nonlinear optical crystals with strong second-harmonic generation responses originating from multiple chromophores

Infrared (IR) nonlinear optical (NLO) crystals are of great significance in modern laser technology, and metal chalcogenides are receiving increasing interest as promising IR NLO candidates. To explore new IR NLO materials with enhanced properties, two quaternary chalcogenides with multiple chromophores, KCu4AsS4 and RbCu4AsS4, were synthesized using the solvothermal method. KCu4AsS4 and RbCu4AsS4 feature 2D [Cu6As2S6]∞ anionic layers with multiple chromophores, and exhibit strong phase-matched second-harmonic generation (SHG) responses (1.8–2.0 × AgGaS2), wide band gaps, suitable birefringence (0.083 and 0.074 @ 2050 nm) and wide infrared transparency. The theoretical calculation results suggest that the strong SHG responses are ascribed to the 2D [Cu6As2S6]∞ anionic layers.

AIB3 IIC2 IIIQ6 VIXVII: A Thioborate Halide Family for Developing Wide Bandgap Infrared Nonlinear Materials by Coupling Planar [BS3] and Polycations.

Developing high-performance infrared (IR) nonlinear optical (NLO) materials is urgent but challenging due to the competition between NLO coefficient and bandgap in one compound. Herein, by coupling NLO-active [BS3] planar units and halide-centered polycations, six new metal thioborate halides ABa3B2S6X (A = Rb, Cs; X = Cl, Br, I) composed of zero-dimensional [XBamRbn/Csn] polycations and [BS3] units, belonging to a new family, are rationally designed and fabricated. The compounds show an interesting structural transition from Pbcn (ABa3B2S6Cl) to Cmc21 (ABa3B2S6Br and ABa3B2S6I) driven by the clamping effect of polycationic frameworks. ABa3B2S6Br and ABa3B2S6I are the first series metal thioborate halide IR NLO materials, and the introduction of [BS3] unit effectively widens the bandgap of planar unit-constructed chalcogenides. ABa3B2S6Br and ABa3B2S6I, exhibiting wide bandgaps (3.55-3.60 eV), high laser-induced damage thresholds (≈ 6 × AgGaS2), and strong SHG effects (0.5-0.6 × AgGaS2) with phase-matching behaviors, are the promising IR NLO candidates for high-power laser applications. The results enrich the chemical and structural diversity of boron chemistry and give some insights into the design of new IR NLO materials with planar units.

Double alkaline earth metals sulfide SrMgGeS4 with high laser-induced damage threshold and strong second-harmonic generation

The exploration of anti-laser damage wide band gap infrared (IR) nonlinear optical (NLO) materials is urgently needed but challenging due to the contradiction between wide band gap and large NLO coefficient. Herein, by introducing [MQ4] (Q = S, Se) tetrahedral units into the AIIBIICIVD4VI family, three double alkaline earth metals chalcogenides SrMgGeS4, BaMgSiSe4 and SrMgSiSe4 with unprecedented [MgGeS6] or [MgSiSe6] dimers are rationally designed and fabricated. The compounds display an interesting structural change from centrosymmetric (CS) I41/acd (BaMgSiSe4, the first CS compound in this family) to non-centrosymmetric Ama2 (SrMgSiSe4) and Fdd2 (SrMgGeS4). Importantly, SrMgGeS4 shows a wide band gap (3.58 eV), a high laser-induced damage threshold (∼6 × AGS), a moderate birefringence (∼0.11@1064 nm), and a strong second-harmonic generation (SHG) response (∼1.1 × AGS), achieving a good balance between wide band gap (Eg ≥ 3.5 eV) and large SHG response (≥1.0 × AGS) for an excellent IR NLO material. The results enrich the chemical and structural diversity of chalcogenides and give insights into the design of high-performance IR NLO materials.

Theoretical investigations on ternary defective diamond-like infrared nonlinear optical materials in Be-Ga-Se system

Beryllium (Be) has made great success in developing Be-based oxide deep-ultraviolet (DUV) nonlinear optical (NLO) materials, but the development of Be-based chalcogenide infrared (IR) NLO materials is still tardy because of the lack of rational material design strategy and in-depth understanding on the composition-structure-propertiy relationships in the compounds. In this work, by coupling [BeSe4] with NLO-active [GaSe4] tetrahedral groups, one thermodynamically stable and three metastable defective diamond-like (DL) BeGa2Se4 (BeGSe) compounds, BeGSe-I (I4¯ 2 m), BeGSe-II (I4¯), BeGSe-III (Pc) and BeGSe-IV (P4¯ 2 m), have been predicted by Universal Structure Predictor: Evolutionary Xtallography (USPEX) code and phonon dispersion spectra. Notably, BeGSe-II and BeGSe-III show high thermal conductivities (6.520 W/m/K for BeGSe-II, 3.835 W/m/K for BeGSe-III), and achieve a good balance between wide band gap (Eg ≥ 3.0 eV) and large NLO effect (≥ 1.0 × AGS) for an excellent IR NLO material. Meanwhile, the charge transfer enhanced band gap mechanism, and covalent radius, bulk modulus effected lattice thermal conductivity in the defective DL-AGa2Se4 (A = Be, Mg, Zn, Cd, Hg) were also uncovered. The results give insights into the design of new defective DL compounds with wide band gap and high thermal conductivity based on [BeSe4] tetrahedron.

Mixed Anionic Tetrahedra Guided Design of New Infrared Nonlinear Optical Material Cs3Ga8S13Cl with High Laser‐Induced Damage Threshold

AbstractThe development of anti‐laser damage infrared (IR) nonlinear optical (NLO) materials is an urgent need but challenging due to the contradiction between wide bandgap and large NLO coefficient. Herein, by introducing a halogen into the NLO‐active tetrahedral unit, two halogenated metal chalcogenides Cs3Ga8S13Cl and Cs9Ga8Se12Cl9 with unprecedented [GaQ3Cl] (Q = S/Se) tetrahedral units are rationally designed and fabricated in experiments by the flux method, enriching the chemical and structural diversity of chalcogenides. Cs3Ga8S13Cl shows a wide bandgap of ≈3.76 eV, resulting in a high laser‐induced damage threshold of ≈8 × AgGaS2 (AGS) and a moderate NLO response (≈0.6 × AGS) with phase‐matching behavior. The results imply that Cs3Ga8S13Cl is a promising IR NLO material for the high powder laser application and demonstrate the feasibility of the halogenated tetrahedron strategy in regulating the optical properties of chalcogenides.

Three-in-One Tetrahedral Functional Units Constructing Diamondlike Ag2In2SiS3.06Se2.94 with High-Performance Nonlinear-Optical Activity.

Exploration of new functional materials with enhanced performance from known ones is always an attractive strategy. A new infrared (IR) nonlinear-optical (NLO) mixed chalcogenide Ag2In2SiS3.06Se2.94 (1), was obtained through partial congener substitution originated from Ag2In2SiS6 (0). 1 crystallizes in the monoclinic space group Cc, and its three-dimensional (3D) polyanionic network is composed of {[In4Si2Se5(S/Se)11]12-}∞ helical chains sharing S/Se(5) corner atoms with cavities embedded with counterion Ag+ ions. It exhibits a much enhanced NLO response compared to that of 0, reaching 1.1 × AgGaS2. Further theoretical analysis results indicate that the large NLO response can be attributed to the synergistic effect of AgQ4 and InQ4 tetrahedral functional motifs. This work not only reports a new high-performance IR NLO material but also enriches the partial ion substitution strategy to obtain new functional materials.

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 , @1.3µm) and a wide band gap (3.75eV) toward a high laser-induced damage threshold (16.7×AgGaS2 , @1.06µm), satisfying the rigorous requirements for a prominent infrared NLO material with concurrent SHG intensity (≥0.5×AGS) and band gap (≥3.5eV). Moreover, to the best of the knowledge, the experimental result shows that phase 1 has the largest birefringence (0.108, @546nm) 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.

Recent advances in IR nonlinear optical chalcogenides with well-balanced comprehensive performance

Infrared nonlinear optical (IR-NLO) crystals have attracted many attentions due to the frequency-conversion capability to generate coherent tunable IR laser output for military and civil applications. Chalcogenides as a most popular branch of IR-NLO materials are the competitive candidates owing to their large second-harmonic generation (SHG) coefficient (deff) and broad transmission regions. Currently, how to obtain the non-centrosymmetric (NCS) structure and realize the coexistence of wide energy gap (Eg ≥ 3.0 eV), sufficient deff (≥ 1.0 × AgGaS2), and beneficial phase-matching (PM) feature are the two major challenges faced in this field. The former can be effectively solved through the combination of local asymmetric units and chemical substitution strategy, while for the latter, there is no systematic survey and lack of universally applicable methodology. In this review, 40 IR-NLO chalcogendides are selected based on the aforementioned two challenges and divided into 7 types according to the different chemical components. The composition-structure-performance relationships and the theoretical origin of their IR-NLO properties are summarized systematically. At length, some useful information and development prospects were briefly discussed, which may offer new ideas and promote the discovery of IR-NLO materials with the ideal comprehensive performance.

Three-in-One Strategy Constructing the First High-Performance Nonlinear Optical Sulfide Crystallizing with the P43 Space Group.

The balance between large nonlinear optical (NLO) effect and wide bandgap is the key scientific issue for the exploration of infrared NLO materials. Targeting this issue, two new pentanary chalcogenides KGaGe1.37 Sn0.63 S6 (1) and KGaGe1.37 Sn0.63 Se6 (2) are obtained by the three-in-one strategy, viz. three types of fourfold-coordinated metal elements co-occupying the same site. They crystallize in the tetragonal P43 (1) and monoclinic Cc (2) space group. Their structures can be evolved from benchmark AgGaS2 (AGS) by suitable substitution. Remarkably, 1 is the first NLO sulfide crystallizing with the P43 space group, representing a new structure-type NLO material. The structural relationship between 1 and 2 and the evolution from 1, 2 to AGS are also analyzed. Both 1 and 2 show balanced NLO properties. Specifically, 1 exhibits phase-matchable SHG response of 0.6 × AGS, a wide bandgap of 3.50eV, and a high laser damage threshold of 6.24 × AGS. Theoretical calculation results suggest that the Ga/Ge/Sn element ratios of the co-occupied sites of 1 and 2 are the most appropriate for stabilizing the structures. The strategy adopted here will provide some inspiration for exploring new high-performance NLO materials.

Na3SiS3F: A Wide Bandgap Fluorothiosilicate with Unique [SiS3F] Unit and High Laser‐Induced Damage Threshold

AbstractThe exploration of antilaser damage wide bandgap infrared (IR) nonlinear optical (NLO) materials is urgent but challenging. Herein, by introducing the idea of fluorination into chalcogenides, a wide bandgap IR NLO material Na3SiS3F with unprecedented [SiS3F] tetrahedra is designed and synthesized. Na3SiS3F shows a wide bandgap of 4.75 eV (the largest one in the reported quaternary metal chalcogenides), resulting in a high laser damage induced threshold of ≈5 × AgGaS2(AGS). Meanwhile, the compound has a moderate NLO response (≈0.3 ×AGS) with phase‐matching behavior, large birefringence (0.15@1064 nm), and wide IR transparent region. The introduction of fluorine breaks the structural symmetry and broadens the highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) gap, polarizability anisotropy, and hyperpolarizability of the Si–S tetrahedral unit. The results indicate that Na3SiS3F is a promising IR NLO material for the high‐power laser application and open an avenue for the design of new wide bandgap IR NLO materials based on NLO‐active [SiSxF4−x] (x = 1, 2, 3) mixed anionic tetrahedral group.