IR Nonlinear Optical Materials Research Articles

Rare-earth-based chalcogenides and their derivatives: an encouraging IR nonlinear optical material candidate

Non-centrosymmetric rare-earth-based chalcogenides and their derivatives could offer novel insights into the targeted design and exploratory synthesis of new IR nonlinear optical candidates.

“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.

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.

An overview of Mg-based IR nonlinear optical materials

This review article provides an overview of Mg-based IR nonlinear optical materials including synthetic methods, structural chemistry, structure–activity relationships, current problems and future development.

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.

RbBiP2S6: A Promising IR Nonlinear Optical Material with a Giant Second-Harmonic Generation Response Designed by Aliovalent Substitution

RbBiP₂S₆: A Promising IR Nonlinear Optical Material with a Giant Second-Harmonic Generation Response Designed by Aliovalent Substitution

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.

Rational design via dual-site aliovalent substitution leads to an outstanding IR nonlinear optical material with well-balanced comprehensive properties.

The acquisition of a non-centrosymmetric (NCS) structure and achieving a nice trade-off between a large energy gap (E g > 3.5 eV) and a strong second-harmonic generation (SHG) response (d eff > 1.0 × benchmark AgGaS2) are two formidable challenges in the design and development of infrared nonlinear optical (IR-NLO) candidates. In this work, a new quaternary NCS sulfide, SrCdSiS4, has been rationally designed using the centrosymmetric SrGa2S4 as the template via a dual-site aliovalent substitution strategy. SrCdSiS4 crystallizes in the orthorhombic space group Ama2 (no. 40) and features a unique two-dimensional [CdSiS4]2- layer constructed from corner- and edge-sharing [CdS4] and [SiS4] basic building units (BBUs). Remarkably, SrCdSiS4 displays superior IR-NLO comprehensive performances, and this is the first report on an alkaline-earth metal-based IR-NLO material that breaks through the incompatibility between a large E g (>3.5 eV) and a strong phase-matching d eff (>1.0 × AgGaS2). In-depth mechanism explorations strongly demonstrate that the synergistic effect of distorted tetrahedral [CdS4] and [SiS4] BBUs is the main origin of the strong SHG effect and large birefringence. This work not only provides a high-performance IR-NLO candidate, but also offers a feasible chemical design strategy for constructing NCS structures.

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.

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 < Eg < 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.

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.

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.

Recent progress in oxychalcogenides as IR nonlinear optical materials

Currently, non-centrosymmetric oxychalcogenides, a class of newly developed heteroanionic compounds, have emerged as promising candidates for IR nonlinear optical (NLO) materials due to the fact that they can combine the impressive second-harmonic generation (SHG) responses of chalcogenides with the wide energy gaps of oxides. Moreover, multiple combinations of chalcogens and the oxygen element would, in principle, lead to more new frequency-doubling building units, enabling the extensive seeking and design of new NLO-active oxychalcogenides. In this Frontiers article, the recent developments of oxychalcogenides as IR-NLO candidates are summarized. These materials can be grouped into three types in terms of their structural dimensions: (i) two-dimensional layered CaZnOS, SrZn2OS2, Sr8Ga8O3S14, Sr6Cd2Sb6O7S10 and Sr4Pb1.5Sb5O5Se8; (ii) one-dimensional chain-typed AEGeOQ2 (AE = Sr and Ba; Q = S and Se); and (iii) zero-dimensional molecular Sr3Ge2O4Se3 and α-Na3PO3S. We discuss the rich coordination environment of mixed-anion frequency-doubling building units focusing on the correlations between their non-centrosymmetric structures and NLO properties, as well as their synthetic methods. Finally, the present challenges and future perspectives in this field are also proposed.

Aliovalent-cation-substitution-induced structure transformation: a new path toward high-performance IR nonlinear optical materials

A quaternary IR-NLO thioantimonate, K2Ag3Sb3S7, designed using an aliovalent-cation-substitution-induced (ACSI) strategy based on the centrosymmetric K2Sb4S7 is reported.

LiGa0.54In0.46S2: A new infrared nonlinear optical material with large laser damage threshold designed by gallium substitution in LiInS2

Larger second-order harmonic generation (SHG) efficiency and high laser damage threshold (LDT) are two crucial requirements for the practical applications of IR nonlinear optical (NLO) materials. Li-(Ga, In)-Q2 (Q = S, Se) is a well-known IR NLO materials system, in which InQ bonds are more covalent than GaQ bonds and benefit larger SHG efficiency. However, the incompatibility between LDT and SHG leads to a smaller LDT of LiInS2 than that of LiGaS2. A new IR NLO compound LiGa0.54In0.46S2 was successfully synthesized by the introduction of gallium in LiInS2, where mixing Ga3+ in In3+ sites result in a wider band-gap of 3.86 eV and a smaller thermal expansion anisotropy value (0.26) compared with LiInS2, leading to the large LDT of 12 times that of commercial AgGaS2 under 1064 nm at room temperature. Meanwhile, the title compound had a relatively strong SHG efficiency of about 0.6 times that of AgGaS2 under a 1910 nm laser radiation. This work highlights the strategy of pursuing IR NLO materials with high LDTs by atom doping in classic material systems.

Synthesis, crystal structures and nonlinear optical properties of β-RbCdI3·H2O and CsCdI3·H2O.

Searching for new IR nonlinear optical (NLO) crystals with a high laser damage threshold (LDT) is still a challenge. In this paper, two new halides, β-RbCdI3·H2O and CsCdI3·H2O, have been synthesized by a conventional solution reaction. Both of them crystallize in the monoclinic space group Pc (no. 7). In their crystal structures, all the corner-sharing [CdI4] tetrahedra connect with each other to form 1D chains, which further connect with [Rb(H2O)]+/[Cs(H2O)]+ complexes to form three-dimensional (3D) frameworks. All the polar [CdI4]2- groups align in such a way that results in a favorable net polarization. Powder second-harmonic generation (SHG) measurements indicate that β-RbCdI3·H2O and CsCdI3·H2O show phase-matchable SHG responses of 2.7 and 2.6 times that of KH2PO4 (KDP). The infrared transmission range can reach 21 μm. The UV-vis diffuse reflectance spectra indicate that the band gaps of β-RbCdI3·H2O and CsCdI3·H2O are about 3.26 and 3.54 eV, respectively. A preliminary measurement indicates that the LDT of their powders is about 90 and 100 MW cm-2, respectively, suggesting that β-RbCdI3·H2O and CsCdI3·H2O are two new promising IR NLO materials. Their band structure and optical property calculations based on DFT methods are carried out.