Strong Infrared NLO Tellurides with Multifunction: CsXII4In5Te12 (XII = Mn, Zn, Cd)

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

With the continuous development of laser technology and the increasing demand for lasers of different frequencies in the infrared (IR) spectrum, research on infrared nonlinear optical (NLO) crystals has garnered growing attention. Currently, the three main commercially available types of borate materials each have their drawbacks, which limit their applications in various areas. Rare-earth (RE)-based chalcogenide compounds, characterized by the unique f-electron configuration, strong positive charges, and high coordination numbers of RE cations, often exhibit distinctive optical responses. In the field of IR-NLO crystals, they have a research history spanning several decades, with increasing interest. However, there is currently no comprehensive review summarizing and analyzing these promising compounds. In this review, we categorize 85 representative examples out of more than 400 non-centrosymmetric (NCS) compounds into four classes based on the connection of different asymmetric building motifs: (1) RE-based chalcogenides containing tetrahedral motifs; (2) RE-based chalcogenides containing lone-pair-electron motifs; (3) RE-based chalcogenides containing [BS3] and [P2Q6] motifs; and (4) RE-based chalcohalides and oxychalcogenides. We provide detailed discussions on their synthesis methods, structures, optical properties, and structure-performance relationships. Finally, we present several favorable suggestions to further explore RE-based chalcogenide compounds. These suggestions aim to approach these compounds from a new perspective in the field of structural chemistry and potentially uncover hidden treasures within the extensive accumulation of previous research.

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.

Bridging oxygen atoms in trigonal prism units driven strong second-harmonic-generation efficiency in Sr3Ge2O4Te3

Herein, a novel IR NLO oxytelluride Sr₃Ge₂O₄Te₃ was successfully designed and synthesized through a "partial O-to-Te substitution" strategy. Compared with the parent oxide, Sr₃Ge₂O₄Te₃ not only successfully achieves a phase-matchability transition (from NPM to PM), but also greatly improves the linear and NLO performances, including a wide band gap (2.26 eV), strong SHG response (1.3 × AgGaSe₂) and large optical anisotropy (Δn = 0.152@2090 nm). The analyses of the structure-property relationship and SHG-density indicate that the bridging oxygen in the [O₃Ge-O-GeTe₃] prism unit plays the most important role in the multiplication SHG effect. This work provides some insights into the design and exploration of novel IR NLO materials.

Design of Infrared Nonlinear Optical Compounds with Diamond-like Structures and Balanced Optical Performance

Infrared (IR) nonlinear optical (NLO) crystals are the major materials to widen the output range of solid-state lasers to mid-infrared regions, but they are still inadequate for application due to the difficulties in balancing the large band gaps and strong NLO response. The diamond-like structure is a potential structural template to explore IR NLO materials. Herein, a computational workflow is proposed for exploring compounds with diamond-like structures, a series of LiMgGaSe₃ structures were predicted successfully through this workflow, and LiMgGaSe₃-I-III exhibited good optical performances in a large band gap (2.75-2.92 eV), strong SHG response (1.2-1.3 × AGS), and suitable birefringence (0.0470-0.0783 at 1064 nm). The in-depth mechanism explorations strongly demonstrate that the synergistic effect of alkaline earth metal tetrahedral [MgSe₄] and [GaSe₄] units is the main origin of large SHG response. The foregoing results suggest that our workflow can accelerate the discovery of new mid-IR NLO materials with diamond-like structures.

Band Gap Modulation and Properties of Quaternary Tellurates Li2GeTeO6

Tellurate crystals are attractive for developing new () materials in the mid-infrared region due to their wide transmission window. In this work, we report a quaternary tellurate oxide crystal, Li2GeTeO6,...

Ba2HgTe5: a Hg-based telluride with giant birefringence induced by linear [HgTe2] units

Ba2HgTe5, the first Hg-based telluride birefringent material, was successfully synthesized. The analysis of the response electron distribution anisotropy illustrates that the large birefringence of Ba2HgTe5 originates from the linear [HgTe2] unit.

Triclinic Layered A2ZnSi3S8 (A = Rb and Cs) with Large Optical Anisotropy and Systematic Research on the Inherent Structure-Performance Relationship in the A2MIIBMIV3Q8 Family

Two triclinic A₂ZnSi₃S₈ (A = Rb and Cs) with layered structures were successfully synthesized, and their physicochemical performances including optical bandgap, thermal behavior, and optical anisotropy were investigated. A₂ZnSi₃S₈ could be viewed as the first discovered Si-based examples in the known A₂M^IIM^IV₃Q₈ family (2-1-3-8 system; A = monovalent alkali metal; M^II = divalent transition metal; M^IV = group 14 metal; Q = chalcogen). The A₂M^IIM^IV₃Q₈ family members crystallize in five different space groups (P1̅, P2₁, P2₁/n, P2₁2₁2₁, and Pa3̅), and their structural transformation and optical performances (bandgap, NLO coefficient, and birefringence) were systematically studied based on the first-principles calculation among 13 A₂M^IIBM^IV₃Q₈ (M^IIB = Zn, Cd, and Hg) compounds without cubic β-K₂ZnSn₃S₈. Research result shows that the above 13 compounds exhibit the layered structures, but diverse wavelike layers and their optical anisotropy (Δn) undergo an increasing trend range from the triclinic to orthorhombic systems. Moreover, P2₁2₁2₁ compounds have very weak NLO effects compared with those of the P2₁ compounds since the polarization directions of anionic groups (M^IIBQ₄ and M^IVQ₄) in P2₁2₁2₁ compounds are directing oppositely and almost completely canceled out by the dipole moment calculation, which further indicates that P2₁ compounds exhibiting the relatively strong NLO effect and large optical anisotropy could be expected as potential IR NLO candidates.

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

Despite the fact that nonlinear optical (NLO) crystals such as AgGaS₂ and AgGaSe₂ have been widely used in the infrared (IR) range due to their large second harmonic generation (SHG) coefficients and wide range of IR transparency windows, the small laser-induced damage threshold (LIDT) remains a great issue hindering their high-power applications. Herein, three noncentrosymmetric (NCS) chalcogenides AZn₄Ga₅Se₁₂ (A = K, Rb, or Cs) are successfully obtained through an appropriate flux method after the extensive design and synthesis of the A/Zn/Ga/Q system. Single-crystal X-ray diffraction data demonstrate that they adopt trigonal space group R3 (No. 146) with three-dimensional diamond-like frameworks composed of [M₉Se₂₄] layers (M = Zn or Ga) stacking in the same direction and filled by charge-balancing A⁺ cations. Noticeably, they all exhibit strong powder SHG responses (2.8-3.7 × AgGaS₂) and amazing LIDTs (19.2-23.4 × AgGaS₂). In addition, theoretical calculations are performed to further determine the relationship between NCS structures and NLO properties. This work provides effective solutions for overcoming the trade-off between strong SHG and high LIDT in IR-NLO materials.

Applying band gap engineering to tune the linear optical and nonlinear optical properties of noncentrosymmetric chalcogenides La4Ge3SexS12−x (x = 0, 2, 4, 6, 8, 10)

Band gap engineering was applied to tune the properties of a phase-matchable La4Ge3S12 by replacing S with Se, which uncovered five new compounds: La4Ge3SexS12−x (x = 2, 4, 6, 8, 10).

A3Mn2Sb3S8 (A = K and Rb): a new type of multifunctional infrared nonlinear optical material based on unique three-dimensional open frameworks

A new type of multifunctional IR-NLO material, A₃Mn₂Sb₃S₈ (A = K and Rb), with unique 3D open frameworks has been developed using a facile surfactant–thermal method.

Ba2Ge2Te5: a ternary NLO-active telluride with unusual one-dimensional helical chains and giant second harmonic-generation tensors

The linear-optical and NLO properties of a ternary NLO-active telluride, Ba2Ge2Te5, were investigated systematically at the experimental and theoretical levels for the first time.

Ultralow thermal conductivity in the quaternary semiconducting chalcogenide Cs4[Ho26Cd7Se48] with an unprecedented closed cavity architecture

A quaternary semiconducting chalcogenide, Cs₄[Ho₂₆Cd₇Se₄₈], with an unprecedented closed cavity architecture exhibits ultralow thermal conductivity.

A new type of novel salt-inclusion chalcogenide with ultralow thermal conductivity

The design and development of novel chalcogenides with ultralow thermal conductivity is extremely important but very challenging for promoting the efficiencies of thermoelectric (TE) materials. Herein, a new type of salt-inclusion chalcogenide (SIC), [Rb6Cl][RE23Mn7Se44] (RE = Ho-Yb), was discovered via a modified flux method. They possessed [RESe6] and [MSe6] (M = RE/Mn) octahedra as basic building units, which interlinked to form a three-dimensional quasi-NaCl-type [RE23Mn7Se44]5- host framework, where the [Rb6Cl]5+ guest ions resided. Interestingly, these isomorphic compounds showed ultralow thermal conductivities (0.28-0.37 W m-1 K-1) at 673 K, which are reported for the first time in SICs. This work not only enriches SIC chemistry but also broadens the application of SICs in the TE field.

Functional Chalcogenide Na2HgSn2Se6 and K2MnGe2Se6 Exhibiting Flexible Chain Structure and Intriguing Birefringence Tunability

The two functional chalcogenides K₂MnGe₂Se₆ and Na₂HgSn₂Se₆, featuring a straight-chain structure, have been successfully prepared and fully characterized. K₂MnGe₂Se₆ shows paramagnetic behavior. The birefringence of Na₂HgSn₂Se₆ is as large as 0.3107 and derives from the superposition of the polarizabilities of its fundamental building blocks, on the basis of first-principles calculations. Moreover, the flexible framework of the A₂M^IIM^IV₂Se₆ family enables a variety of heterogeneous substitutions and thus offers possible birefringence tunability, which may inspire the design and exploratory synthesis of IR birefringent materials.

ABaSbQ3 (A = Li, Na; Q = S, Se): diverse arrangement modes of isolated SbQ3 ligands regulating the magnitudes of birefringences

The interrelation of arrangement modes of isolated SbQ₃ ligands on structures and birefringences has been systematically studied in series of chalcogenides.

Cs2Ge3In6Se14: A Structure Transformation Driven by the Size Preference and Its Properties

The new selenide Cs₂Ge₃In₆Se₁₄, featuring its own structure type with germanium in mixed-valence states, is discovered via a solid-state reaction at 1173 K. The compound crystallizes in the R3̅ m space group with a = 7.9951(6) Å and c = 41.726(4) Å. Two adjacent condensed layers of InSe₄ tetrahedra are linked by a [Ge²⁺Se₆] octahedron into a double slice that is further stacked along the c direction with a packing sequence of ··· abca··· through the [Ge³⁺₂Se₆] dimer via its Ge-Ge metallic bond. The coexistence of Ge²⁺/Ge³⁺ and Ge-Ge metallic bonding has been confirmed by XPS and ELF analyses, respectively. More interestingly, although sharing many structure similarities, Cs₂Ge₃In₆Se₁₄ and our previously reported Cs₂Ge₃In₆Te₁₄ reveal a R3̅ m to P3̅ m1 structure transformation with a tripled c parameter. Single-crystal diffraction data and a thorough structure survey of related compounds point out that such a transformation is driven by the size preference of the [Ge₂Q₆] dimer. The title compound possesses a band gap of 2.08 eV and shows photodegradation of RhB under visible light that is more efficient than that for the commercial P25.

Negative thermal expansion and electronic structure variation of chalcopyrite type LiGaTe2

The LiGaTe₂ crystals were grown by the Bridgman–Stockbarger technique and the cell parameter dependence on temperature in the range of 303–563 K was evaluated by the X-ray diffraction analysis and first principles calculations.

Remarkable multimember-ring configurations in a new family of Na7MIISb5S12 (MII = Zn, Cd, Hg) exhibiting various three-dimensional tunnel structures

A new series of thioantimonates featuring the newly discovered trimer (M^II/Sb)₃S₉ and 12 + 12-MR configurations are verified as potential IR birefringent materials.

Experimental and theoretical studies on the NLO properties of two quaternary non-centrosymmetric chalcogenides: BaAg2GeS4and BaAg2SnS4

Two new phase-matchable MFIR NLO materials, BaAg₂MS₄(M = Ge, Sn), with a compressed chalcopyrite-like structure are reported. Remarkably, they exhibit a good balance between strong SHG responses and high LIDTs.

Two excellent phase-matchable infrared nonlinear optical materials based on 3D diamond-like frameworks: RbGaSn2Se6 and RbInSn2Se6

Two new excellent phase-matchable MFIR NLO materials RbXSn₂Se₆ (X = Ga, In) with 3D diamond-like framework structures are reported.

Syntheses and characterization of three new sulfides with large band gaps: acentric Ba4Ga4SnS12, centric Ba12Sn4S23 and Ba7Sn3S13

Three new sulfides with large band gaps, NCS Ba₄Ga₄SnS₁₂, CS Ba₁₂Sn₄S₂₃ and Ba₇Sn₃S₁₃ were synthesized for the first time. Ba₄Ga₄SnS₁₂ exhibits a desired balance between the band gap (2.90 eV) and the SHG intensity (34 × KDP).

AXII4XIII5Te12 (A = Rb, Cs; XII = Mn, Zn, Cd; XIII = Ga, In): quaternary semiconducting tellurides with very low thermal conductivities

Three-dimensional diamond-like framework tellurides AXII4XIII5Te₁₂ with very low thermal conductivities are reported for the first time.