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

K2HgGe3Se8: A Quaternary Hg-Based Selenide with Nonlinear Optical Properties

A new quaternary Hg-based selenide K2HgGe3Se8 was successfully synthesized and characterized as an engaging infrared (IR) nonlinear optical (NLO) material, which crystallizes in the P21 space group of the noncentrosymmetric monoclinic crystal system. The crystal structure of K2HgGe3Se8 is characterized by the stacking of countless [ H g G e 3 S e 8 ] 2 - ∞ 2 layers with K+ cations filling the interlayers. The UV-vis-NIR diffuse reflectance spectrum shows that K2HgGe3Se8 possesses an indirect band gap of 2.13 eV. The second harmonic generation (SHG) response of K2HgGe3Se8 is approximately 1.1 times that of AgGaS2 (AGS) within the particle size of 20-50 μm along with a nonphase-matching (NPM) behavior at 2090 nm, as indicated by the SHG test. K2HgGe3Se8 also has a large powder laser-induced damage threshold (∼ 2.3 × AGS). As revealed by theoretical calculations, the optical properties of K2HgGe3Se8 are predominantly determined by [HgSe4] and [GeSe4] tetrahedra, and K2HgGe3Se8 possesses a calculated optical band gap of 1.44 eV together with a maximum SHG coefficient d22 of -7.70 pm V-1.

A Congruent-Melt Infrared Nonlinear Optical Crystal Na4SrAs2S8

A quaternary metal thioarsenate infrared (IR) nonlinear optical (NLO) compound Na4SrAs2S8 was successfully prepared by a high-temperature reaction method from stoichiometric agents. It crystallizes in the tetragonal P4n2 with the unit cell parameters a = 10.0393(3) Å, c = 6.9638(3) Å, and Z = 2, with the basic structural groups of isolated AsS4 tetrahedra. Compared with benchmark IR NLO crystal AgGaS2 (AGS), the title compound exhibits balanced optical properties of large band gap (3.05 eV vs. 2.60 eV) and considerable second harmonic generation response (0.95 × AGS). Moreover, the combined powder X-ray diffraction and differential scanning calorimetry analyses demonstrate that Na4SrAs2S8 is a congruent-melting compound with a low melting point of 668 °C, which is benefical for bulk single crystal growth. Experimental and theoretical calculation results indicate that Na4SrAs2S8 is a practically usable IR NLO crystal, also motivating the exploration of thioarsenates as high-performance IR NLO candidates.

Ba10In2Mn11Si3O12S18: First Hexanary Oxychalcogenide Containing an Infrequent Three-Dimensional Noncentrosysmmetric Framework

Noncentrosymmetric (NCS) oxychalcogenides have attracted great attention in recent years due to their immense potential as candidates for IR nonlinear-optical (NLO) applications. Despite notable advancements in this field, the discovery of oxychalcogenides with three-dimensional (3D) framework structures remains a formidable challenge. In this study, we report the discovery of the first hexanary oxychalcogenide, Ba10In2Mn11Si3O12S18, exhibiting second-order NLO activity, using a high-temperature solid-phase method. This compound showcases a novel structure type, featuring an uncommon NCS 3D [In2Mn11Si3O12S18]20- framework formed by vertex-sharing [(Mn/In)S6] octahedra, [(Mn/In)OS3] tetrahedra, and [SiO4] tetrahedra, with charge-balanced Ba2+ cations occupying the channels. Our study serves as a source of inspiration for researchers to further investigate the synthesis of novel NLO-active oxychalcogenides with 3D frameworks.

KHg4Ga3S9: A Hg-Based Sulfide with Nonlinear-Optical Activity in the A-MII-MIII-Q (A = Alkali Metal; MII = d10 Metal; MIII = Ga, In; Q = S, Se) System

The search for new high-performance infrared (IR) nonlinear-optical (NLO) materials is a hot topic in the fields of laser chemistry and inorganic solid-state chemistry. Here, a new Hg-based sulfide KHg4Ga3S9 in the family of A-MII-MIII-Q (A = alkali metal; MII = d10 metal; MIII = Ga, In; Q = S, Se) was synthesized. It crystallizes in the orthogonal system of the C2221 structure, which is rare for IR NLO chalcogenides. Its anionic framework {[Hg4Ga3S9]-}∞ is constructed by two types of interconnected helical chains, viz., the inner layer ({[Hg6Ga2S29/3]4/3-}∞) and the outer layer ({[Hg2Ga4S25/3]2/3-}∞). It exhibits a moderate NLO response and a high laser-induced damage threshold. Theoretical calculations indicate that the HgS4 unit accounts for its much larger NLO response compared to RbCd4Ga3S9. The influence of alkali metals and d10 metals on the initial phase-matching wavelength is also discussed. This work provides inspiration for improving the properties of NLO materials' properties.

Open honeycomb frameworks of sulphides AHg4Ga5S12 (A = Rb, Cs) exhibiting infrared nonlinear optical properties

A crystal structure with a diamond-like anionic framework belongs to a non-centrosymmetric macrostructure due to the aligned arrangement of tetrahedral units, meeting the premise of second-order nonlinear optical (NLO) materials. Herein, two new Hg-based sulphides, namely RbHg₄Ga₅S₁₂ (1) and CsHg₄Ga₅S₁₂ (2), which are isostructural and crystallise in the trigonal space group R3, are successfully isolated in sealed silica tubes by a solid-state reaction. The features of their three-dimensional open honeycomb frameworks are attributed to the parallel alignment of tetrahedral MS₄ (M is disordered by 0.444 Hg and 0.555 Ga) building motifs, accompanied by Rb⁺ (or Cs⁺) reseating in the cavities. Notably, although the band gap values of 1 and 2 are 2.30 and 2.36 eV, separately, their thermal expansion anisotropies (0.15 and 0.41, respectively) are favourable for achieving laser-induced damage thresholds (5.6 and 5.8 times that of AgGaS₂ for 1 and 2, respectively). In addition, the strong polarisability of tetrahedral MS₄ building motifs in the diamond-like anionic structures is responsible for the promising second-harmonic generation (SHG) intensities (1.1 and 1.8 times that of AgGaS₂ for 1 and 2, respectively) in the particle size range of 50-75 μm with non-phase-matchable behaviour at 1910 nm. Furthermore, theoretical investigation elaborates that electron transitions in compounds 1 and 2 mainly occur from valence band S-3p to conduction band Hg-6s and Ga-4s states, demonstrating that the linear and nonlinear optical properties originate primarily from the synergy of tetrahedral MS₄ units.

K2CdGe3S8: A New Infrared Nonlinear Optical Sulfide

A quaternary metal chalcogenide, namely K2CdGe3S8 (I), is obtained through a high-temperature solid-state approach. Compound I crystallizes with the non-centrosymmetric space group P212121. It features a 2D layer structure with [CdGe3S8] layers consisting of tetrahedral GeS4 and CdS4 units, and counter K+ embedded between the layers. The compound exhibits a powder second-harmonic generation (SHG) response of ~0.1 times that of KH2PO4 (KDP) with phase-matchable character at the laser wavelength of 1064 nm. Remarkably, it has a wide band gap (3.20 eV), which corresponds to a favorable high laser-induced damage threshold of 6.7 times that of AgGaS2. In addition, the calculated birefringence (Δn) is 0.039 at the wavelength of 1064 nm, which satisfies the Δn criteria for a promising infrared NLO material.

Organic Cation Modulation Triggered Second Harmonic Response in Manganese Halides with Bright Fluorescence

Zero-dimensional (0D) hybrid manganese halides have been recently synthesized and exhibited rich functional properties including fluorescence, ferroelectrics, and ferromagnetism. However, few studies on second-harmonic generation (SHG) behaviors of manganese halide crystals have been reported, presumably owing to the d-d transitions. Here, we report three manganese bromides, [TEA]₂MnBr₄ (TEA⁺ = tetraethylammonium; 1), [BTEA]₂MnBr₄ (BTEA⁺ = benzyltriethylammonium; 2), and [BTMA]₂MnBr₄ (BTMA⁺= benzyltrimethylammonium; 3), with linear and nonlinear optical properties via benzyl or ethyl/methyl substitution strategies. They feature 0D structures containing isolated [MnBr₄]^2- anions and quaternary ammonium cations with different sizes inserted for charge balance. They all show green phosphorescence, and 2 possesses good luminescence efficiency with a quantum yield of 97.8%, which is larger than those of 1 (79%) and 3 (72%). Specifically, acentric 1 and 3 present effective SHG responses about 0.48 and 0.59 times that of KDP, respectively. The result throws light on the new properties of the hybrid manganese halides and provides a new way to develop novel nonlinear optical-active organic-inorganic hybrid metal halides.

Alkali metal partial substitution-induced improved second-harmonic generation and enhanced laser-induced damage threshold for Ag-based sulfides

Two new pentanary sulfides LiAgIn2GeS6 and NaAgIn2GeS6 were derived from parent Ag2In2GeS6via Li and Na partial substitution of Ag element, and their SHG efficiencies and LIDT intensities enhanced concurrently.