IR Nonlinear Optical Research Articles

ACuGa6S10 (A = Rb, Cs): Design and Synthesis of Two New Cavity-Chalcopyrite Chalcogenides Based on "Iterative Substitution" Strategy.

Two new non-centrosymmetric chalcogenides, ACuGa6S10 (A = Rb, Cs) have been successfully synthesized by an "iterative substitution" strategy based on chalcopyrite CuFeS2 structural template. Benefiting from the substitution of Fe3+ cations by Ga3+ cations, ACuGa6S10 (A = Rb, Cs) exhibit wide suitable band gap of 2.48 and 2.40 eV, respectively, which is about five times higher than their structure template CuFeS2, and the large second harmonic generation response (1.5 and 1.8 × AgGaS2). Combining theoretical calculation and structural analysis confirm that the [GaS4] tetrahedra make the main contribution on their good liner and nonlinear optical (NLO) performances. The "iterative substitution" strategy expands the design idea of materials and can lead to the discovery of a large number of IR NLO compounds.

Phase-Matching Second-Harmonic Generation and Enhanced Laser-Induced Damage Threshold Induced by Cs Substitution: Cu3PSe4 vs Cs2CuP3S9.

Chalcophosphates are an important type of infrared nonlinear optical (NLO) candidates in view of their rich anionic motifs. Here, two copper chalcophosphates Cu3PSe4 (CPSe) and Cs2CuP3S9 (CCPS) were synthesized and studied as IR NLO materials. They both feature three-dimensional polyanionic frameworks constructed by similar T2-supertetrahedra, and the structure of CCPS can be derived from CPSe via introducing Cs and substituting Se with S. This structural evolution results in phase-matchable NLO behavior, enlarged optical band gap, and enhanced laser-induced damage threshold for CCPS. These results are elucidated by structure analysis and theoretical calculations, and the increased structural anisotropy contributes to the phase matchable behavior of CCPS. This work presents a case on how to adjust NLO properties via certain structure considerations, which may be extended to more systems for obtaining high-performance NLO materials.

“Three‐in‐One”: A New Hg‐Based Selenide Hg7P2Se12 Exhibiting Wide Infrared Transparency Range and Strong Nonlinear Optical Effect

AbstractThe exploration of high‐performance mid‐ and far‐infrared (IR) nonlinear optical (NLO) crystals is an urgent need. Herein, a new Hg‐based selenide Hg7P2Se12 (HPSe) is designed and synthesized by a rigid and flexible units coupled strategy. It is interesting that in the compound, three types of NLO‐active units, including linear [HgSe2], triangular [HgSe3], and tetrahedral (MSe4) (M = Hg/P) groups, simultaneously exist. It shows a wide transparency range (0.84–22.8 µm), large SHG response (1 × AGS), high laser‐induced damage threshold (≈2 × AGS), and a large birefringence (0.102 @ 2090 nm). Moreover, the compound melts congruently along with good crystal growth habits, and single crystals with a maximum size of ≈7 × 5 × 2 mm3 are obtained. Theoretical analyses confirm that the large NLO response originates from the synergistic effects of Hg–Se units, (PSe4) and nonbonding electrons. The results indicate that HPSe is a promising mid‐ and far‐IR NLO material, and inspire a path to finding new classes of IR NLO materials that are different from traditional chalcopyrite materials by grouping the linear, planar, and tetrahedral units.

K4ZnV5O15Cl: A Congruent‐Melting Mid‐Infrared Nonlinear Optical Crystal Combined with Strong Second‐Harmonic Generation and High Laser‐Induced Damage Threshold

AbstractIt is extremely challenging to accomplish second‐harmonic generation (SHG) in the whole mid‐infrared (MIR) region for oxide crystals due to their short IR absorption cutoff wavelengths. Herein, a new MIR nonlinear optical (NLO) crystal of K4ZnV5O15Cl (KZVC) is designed and synthesized by the aliovalent substitution of [VIIIO5] with [ZnIIO4Cl] based on the K2(VO)(V2O7) matrix. KZVC features an ordered 2D [ZnV5O15Cl]∞ layered structure comprising [ZnO4Cl] / [VO5] square pyramids and [VO4] tetrahedron as functional units. Importantly, KZVC shows excellently balanced performances of strong SHG responses (12 × KDP @ 1064 nm, 1.1 × AgGaS2 @ 2.05 µm), broad IR transparency range (0.52‒10 µm), congruent‐melting behavior, and highest laser‐induced damage threshold (LIDT) (60 × AgGaS2 @ 1064 nm) among the reported vanadates. Most remarkably, KZVC represents the first example in the oxide‐based IR NLO crystals that can achieve phase matching in a wide wavelength range extending from 1.8 to 10 µm, fully covering the important MIR atmospheric windows (3‒5 µm).

AllHgMIVS4 (All = Sr, Ba, MIV = Si, Ge): A Series of Materials with Large Second Harmonic Generation Response and Wide Band Gaps

AbstractWide band gaps and large second harmonic generation (SHG) response are two crucial yet contradictory parameters for nonlinear optical (NLO) crystals. Herein, through exploring the influence of anion groups on structural crystallization dimension and space group, a series of new NLO Hg‐based chalcogenides AIIHgMIVS4 (AII = Sr, Ba, MIV = Si, Ge) with wide band gaps and large SHG responses have been successfully designed and synthesized. The structures of these compounds consist of 2D [HgMS4]2− (M = Si and Ge) layers composed of distorted (HgS4 and MS4) tetrahedra arranged alternately, and the layers are separated by eight‐coordinated A2+ (A = Sr and Ba) cations. Their band gaps and SHG responses meet the basic requirements (SHG > 1 × AgGaS2; Eg > 2.33 eV). Especially, SrHgSiS4 and SrHgGeS4 exhibit both large SHG effects (2 and 2.4 × AgGaS2) and wide band gaps (3.06 and 2.97 eV), respectively, indicating they are promising IR NLO crystals. This work opens a new avenue for new NLO material design to achieve the balance between strong SHG response and large band gaps.

The compatibly large nonlinear optical effect and high laser-induced damage threshold in a thiophosphate CsInP2S7 constructed with [P2S7]4- and [InS6]9-

It is challenging to cooperatively improve the nonlinear optical (NLO) efficiency and the laser-induced damage threshold (LIDT). This work reports a novel IR NLO materials CsInP2S7 (CIPS) designed by combination the strategies of alkali metals substitution and microscopic NLO units PS4 introduction based on AgGaS2. CIPS was composed of strongly distorted [InS6]9- octahedra and [P2S7]4- dimers constructed by corner-sharing [PS4]3-, which increase the NLO efficiency and decrease thermal expansion anisotropy simultaneously. Compared with AgGaS2, CIPS exhibited strong phase matchable NLO response ca. 1.1 × AGS@2.1 µm, high LIDT ca. 20.8 × AgGaS2, and IR transparency up to 15.3 µm. Structural analysis and theoretical investigation confirmed that large SHG effect and ultrahigh LIDT of CIPS originated from the synergistic contribution of [InS6]9- octahedra and [P2S7]4- dimers. These results indicate that CIPS is a promising NLO candidate in the mid-IR region, and this study provides a new approach for developing potential NLO-LIDT compatible materials.

Ba4 (S2 )][ZnGa4 S10 ]: Design of an Unprecedented Infrared Nonlinear Salt-Inclusion Chalcogenide with Disulfide-Bonds.

Salt-inclusion chalcogenides (SICs) have been receiving widespread attention due to their large second harmonic generation (SHG) responses and wide bandgaps, however most of them suffer from small birefringence limiting their technical application. Herein, by introducing the π-conjugated (S2 )2- units in the ionic guest of salt-inclusion structure, the first disulfide-bond-containing SIC, [Ba4 (S2 )][ZnGa4 S10 ] has been synthesized. It exhibits the widest bandgap up to 3.39eV among polychalcogenides and strong SHG response as large as that of AgGaS2 (AGS). Importantly, its birefringence reaches a max value of 0.053@1064nm among AGS-like SICs, indicating it is a promising IR nonlinear optical (NLO) material. Theoretical calculations reveal that the π-conjugated (S2 )2- units and covalent GaS layers favor the enhanced birefringence and large SHG response. This work provides not only a new type of SIC for the first time, but also new lights on the design of IR NLO materials.

Honeycomb layered topology construction for exceptional long-wave infrared nonlinear optical crystals.

Nonlinear optical (NLO) crystals capable of efficient long-wave infrared (8-14 μm) laser output remain scarce, and the exploration of long-wave IR NLO materials with superior comprehensive optical performances is a momentous challenge. Herein, we develop two selenide-halide NLO crystals, Hg3AsSe4Br and Hg3AsSe4I, which are derived from the honeycomb layered topology of prototype GaSe. Remarkably, they exhibit not only strong SHG effects, suitable band gap, large birefringence, broad IR transparency range and low two-photon absorption coefficients but reinforced interlayer interaction and more benign crystal growth habit, compared to those of GaSe, indicating that they are promising long-wave IR NLO materials. Moreover, Hg3AsSe4I achieved better comprehensive optical properties than conventional IR crystals, GaSe, ZnGeP2, CdSe and AgGaSe2. The idea of honeycomb layered topology construction provides a material design heuristic to explore cutting-edge IR NLO materials.

Eu2P2S6: The First Rare‐Earth Chalcogenophosphate Exhibiting Large Second‐Harmonic Generation Response and High Laser‐Induced Damage Threshold

AbstractMetal chalcogenophosphates are receiving increasing interest, specifically as promising infrared nonlinear optical (NLO) candidates. Here, a rare‐earth chalcogenophosphate Eu2P2S6 crystallizing in the monoclinic noncentrosymmetric space group Pn was synthesized using a high‐temperature solid‐state method. Its structure features isolated [P2S6]4− dimer, and two types of EuS8 bicapped triangular prisms. Eu2P2S6 exhibits a phase‐matchable second‐harmonic generation (SHG) response ≈0.9×AgGaS2@2.1 μm, and high laser‐induced damage threshold of 3.4×AgGaS2, representing the first rare‐earth NLO chalcogenophosphate. The theoretical calculation result suggests that the SHG response is ascribed to the synergetic contribution of [P2S6]4− dimers and EuS8 bicapped triangular prisms. This work provides not only a promising high‐performance infrared NLO material, but also opens the avenue for exploring rare‐earth chalcogenophosphates as potential IR NLO materials.

Eu2 P2 S6 : The First Rare-Earth Chalcogenophosphate Exhibiting Large Second-Harmonic Generation Response and High Laser-Induced Damage Threshold.

Metal chalcogenophosphates are receiving increasing interest, specifically as promising infrared nonlinear optical (NLO) candidates. Here, a rare-earth chalcogenophosphate Eu2 P2 S6 crystallizing in the monoclinic noncentrosymmetric space group Pn was synthesized using a high-temperature solid-state method. Its structure features isolated [P2 S6 ]4- dimer, and two types of EuS8 bicapped triangular prisms. Eu2 P2 S6 exhibits a phase-matchable second-harmonic generation (SHG) response ≈0.9×AgGaS2 @2.1 μm, and high laser-induced damage threshold of 3.4×AgGaS2 , representing the first rare-earth NLO chalcogenophosphate. The theoretical calculation result suggests that the SHG response is ascribed to the synergetic contribution of [P2 S6 ]4- dimers and EuS8 bicapped triangular prisms. This work provides not only a promising high-performance infrared NLO material, but also opens the avenue for exploring rare-earth chalcogenophosphates as potential IR NLO materials.

BaSi7P10 and SrSi7P10: Two Infrared Nonlinear Optical Phosphides with T2 Supertetrahedra Exhibiting Strong Second‐Harmonic Generation Effects

AbstractBecause mid‐ and far‐infrared (IR) nonlinear optical (NLO) materials play an important role in military and civil fields, plenty of excellent IR NLO materials have been discovered in recent decades, such as chalcogenides with T2 supertetrahedra. Pnictides with T2 supertetrahedra instead of MQ4 (M = IIB, IIIA, IVA metals; Q = P, As) tetrahedra, may favor high second‐harmonic generation (SHG) efficiency due to their large hyperpolarizability, but they have been rarely reported. Therefore, in this study, two pnictides with T2 supertetrahedra, BaSi7P10 and SrSi7P10, are synthesized and studied. With three‐dimensional (3D) framework structures assembled from 1D zigzag chains of [Si7P16] dual‐T2 supertetrahedra, both BaSi7P10 and SrSi7P10 exhibit strong phase‐matching (PM) SHG responses (3.2‐ and 3.0‐times that of AgGaS2), large birefringences (0.077 and 0.112), and wide infrared transparency. In addition, theoretical calculation also reveals that the two‐coordinated P atom can enhance the SHG effects. This study provides a new strategy for exploring new IR NLO materials.

NaGa3Se5: An Infrared Nonlinear Optical Material with Balanced Performance Contributed by Complex {[Ga3Se5]−}∞ Anionic Network

Second-order nonlinear optical (NLO) materials are extensively applied in laser-related techniques. For developing IR NLO materials, chalcogenides are the main candidates. Here, NaGa3Se5 was explored as inspired by its unique anionic structure. It crystallizes with the orthorhombic chiral P212121 structure, featuring 12 types of GaSe4 tetrahedra built into a three-dimensional {[Ga3Se5]-}∞ anionic network, representing a new NLO-functional motif. NaGa3Se5 exhibits large and phase-matchable NLO response 1.37 × AgGaS2. It has the largest band gap among the noncentrosymmetric A-MIII-Se (A = alkali metal; M = Ga, In) compounds. The NLO properties' origin is explored via theoretical analysis. The success of NaGa3Se5 contributes a practical case for exploring new NLO materials.

Toward the Rational Design of Mid‐Infrared Nonlinear Optical Materials with Targeted Properties via a Multi‐Level Data‐Driven Approach

AbstractDesign and exploratory synthesis of new mid‐infrared (mid‐IR) nonlinear optical (NLO) materials are urgently needed for modern laser science and technology because the widely used IR NLO crystals still suffer from their inextricable drawbacks. Herein, a multi‐level data‐driven approach to realize fast and efficient structure prediction for the exploration of promising mid‐IR NLO materials is proposed. Techniques based on machine learning, crystal structure prediction, high‐throughput calculation and screening, database building, and experimental verification are tightly combined for creating pathways from chemical compositions, crystal structures to rational synthesis. Through this data‐driven approach, not only are all known structures successfully predicted but also five thermodynamically stable and 50 metastable new selenides in AIBIIISe2 systems (AI = Li, Na, K, Rb, and Cs; BIII = Al and Ga) are found, among which eight outstanding compounds with wide bandgaps (> 2.70 eV) and large SHG responses (>10 pm V−1) are suggested. Moreover, the predicted compounds I2d‐LiGaSe2 and I4/mcm‐KAlSe2 are successfully obtained experimentally. In particular, LiGaSe2 exhibits a robust SHG response (≈2 × AGS) and long IR absorption edge that can cover two atmospheric windows (3–5, 8–12 µm). Simultaneously, this new research paradigm is also applicative for discovering new materials in other fields.

Cd7SiAs6, a Nonchalcopyrite Arsenide with a Strong Nonlinear-Optical Response.

A new arsenide, Cd7SiAs6, has been successfully synthesized and characterized. It is the first arsenide that adopts a nonchalcopyrite structure and possesses a strong nonlinear-optical (NLO) response. In the structure, the CdAs3 trigonal planar unit, a kind of π-conjugated planar NLO-active group, was identified for the first time. Furthermore, theoretical calculations reveal that the CdAs3 planar unit contributes more to the NLO effect than the CdAs4 tetrahedron does. The result may provide valuable insights for the future exploration of IR NLO materials, especially for application above 10 μm.

Superior Infrared Nonlinear Optical Performance Achieved by Synergetic Functional Motif and Vacancy Site Modulations

Achieving large phase-matchable (PM) nonlinear optical (NLO) efficiency and high laser-induced damage threshold (LIDT) in an infrared second-order NLO (IR NLO) material is the most crucial technica...

Helical {[HgS]}n Chain-Induced Balanced Nonlinear-Optical Performance for Trigonal Mercury Sulfide.

Large second-harmonic-generation (SHG) response and enhanced laser-induced damage threshold (LIDT) compared with benchmark AgGaS2 (AGS), together with a simple chemical composition and exclusion of the light-sensitive Ag element, are vital for exploration of superior IR nonlinear-optical (NLO) materials beyond AGS. Herein, we report trigonal HgS as a highly promising IR NLO material. It was obtained by a facile one-pot hydrothermal reaction, and its noncentrosymmetric P3221 structure features a unique dumbbell-shaped HgS2 group and a neutral helical {[HgS]}n chain, which first served as a SHG functional motif. Its polycrystalline powder sample exhibits a phase-matchable SHG response comparable to that of AGS and a LIDT value of 1.2 × AGS. Structural analysis and theoretical calculation suggest that the {[HgS]}n chain plays an important role for excellent NLO performance. This work not only provides a strong candidate for IR NLO application but also introduces a new SHG functional motif for the design of future NLO materials.

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, Cu5Zn0.5P2S8, 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, Cu5Zn0.5P2S8 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.

Na6 MQ4 (M=Zn, Cd; Q=S, Se): Promising New Ternary Infrared Nonlinear Optical Materials.

Four sodium-based ternary IR nonlinear optical (NLO) materials, Na6 MQ4 (M=Zn, Cd; Q=S, Se), were prepared through a high-temperature flux method. The crystal structure of the compounds is built up of isolated [MQ4 ] tetrahedra and a 3D framework formed by the NaQn (n=4, 5) units. The two selenides, Na6 MSe4 (M=Zn, Cd), as promising IR NLO materials, show moderate second-harmonic generation (SHG) responses (0.9 and 0.5×AgGaS2 ) with good phase-matching behavior, as well as high laser damage thresholds (2 and 1.9×AgGaS2 ). The two sulfides, Na6 MS4 (M=Zn, Cd), exhibit higher laser damage thresholds (13 and 4×AgGaS2 ), but smaller SHG responses (0.3 and 0.2×AgGaS2 ). Theoretical calculations and statistical analyses indicate that the SHG effect and band gap in the compounds originate mainly from the distorted NaQ4 NLO-active units with a short Na-S bond length, which provides a new insight into the design of novel IR NLO materials.

Synthesis, crystal structure, and electronic structure of Li2PbSiS4: a quaternary thiosilicate with a compressed chalcopyrite-like structure.

The new quaternary thiosilicate, Li2PbSiS4 (dilithium lead silicon tetrasulfide), was prepared in an evacuated fused-silica tube via high-temperature, solid-state synthesis at 800 °C, followed by slow cooling. The crystal structure was solved and refined using single-crystal X-ray diffraction data. By strict definition, the title compound crystallizes in the stannite structure type; however, this type of structure can also be described as a compressed chalcopyrite-like structure. The Li+ cation lies on a crystallographic fourfold rotoinversion axis, while the Pb2+ and Si4+ cations reside at the intersection of the fourfold rotoinversion axis with a twofold axis and a mirror plane. The Li+ and Si4+ cations in this structure are tetrahedrally coordinated, while the larger Pb2+ cation adopts a distorted eight-coordinate dodecahedral coordination. These units join together via corner- and edge-sharing to create a dense, three-dimensional structure. Powder X-ray diffraction indicates that the title compound is the major phase of the reaction product. Electronic structure calculations, performed using the full potential linearized augmented plane wave method within density functional theory (DFT), indicate that Li2PbSiS4 is a semiconductor with an indirect bandgap of 2.22 eV, which compares well with the measured optical bandgap of 2.51 eV. The noncentrosymmetric crystal structure and relatively wide bandgap designate this compound to be of interest for IR nonlinear optics.

Phase Matching Achieved by Bandgap Widening in Infrared Nonlinear Optical Materials [ABa 3 Cl 2 ][Ga 5 S 10 ] (A= K, Rb, and Cs)

Large nonlinear optical (NLO) coefficient (dij), high laser damage threshold (LDT), and phase matching (PM) are crucial for the practical applications of IR NLO crystals. A great number of IR NLO m...