Layered and Cubic Semiconductors AGaM′Q4 (A+ = K+, Rb+, Cs+, Tl+; M′4+ = Ge4+, Sn4+; Q2– = S2–, Se2–) and High Third-Harmonic Generation

Pseudotetrahedral Organotin-Capped Chalcogenidometalate Supermolecules with Optical Limiting Performance

The rational design of crystalline clusters with adjustable compositions and dimensions is highly sought after but quite challenging as it is important to understand their structural evolution processes and to systematically establish structure-property relationships. Herein, a family of organotin-based sulfidometalate supertetrahedral clusters has been prepared via mixed metal and organotin strategies at low temperatures (60-120 °C). By engineering the metal composition, we can effectively control the size of the clusters, which ranges from 8 to 35, accompanied by variable configurations: P1-[(RSn)4M4S13], T3-[(RSn)4In4M2S16] (R = nbutyl-Bu and phenyl-Ph; M = Cd, Zn, and Mn), T4-[(BuSn)4In13Cu3S31], truncated P2, viz. TP2-[(BuSn)6In10Cu6S31], and even T5-[(BuSn)4In22Zn6Cu3S52], all of which are the largest organometallic supertetrahedral clusters known to date. Of note, the arylstannane approach plays a critical role in regulating the peripheral ligands and further enriching geometric structures of the supertetrahedral clusters. This is demonstrated by the formation of tin-oxysulfide clusters, such as T3-[(RSn)4Sn6O4S16] (R = Bu, Ph, and benzyl = Be) and its variants, truncated T3, viz., TT3-[(BuSn)6Sn3O4S13] and augmented T3, viz., T3-[(Bu3SnS)4Sn6O4S16]. Especially, two extraordinary truncated clusters break the tetrahedral symmetry observed in typical supertetrahedral clusters, further substantiating the advantages offered by the arylstannane approach in expanding cluster chemistry. These organometallic supertetrahedral clusters are highly soluble and stable in common solvents. Additionally, they have tunable third-order nonlinear optical behaviors by controlling the size, heterometallic combination, organic modification, and intercluster interaction.

Ba3.5Cu7.55In1.15Se9: A Wide-Bandgap Copper Indium Selenide Reveals Strong Luminescence and Third-Harmonic Generation

A new copper indium selenide, Ba_3.5Cu_7.55In_1.15Se₉, was synthesized by the KBr flux reaction at 800 °C. The compound crystallizes with orthorhombic Pnma, a = 46.1700(12) Å, b = 4.26710(10) Å, c = 19.8125(5) Å, and Z = 8. The structural framework mainly consists of four sites of cubane-type defective M₄Se₃ (M = Cu, Cu/In) units with disordered Cu⁺/In³⁺ ions present at the part corner of each unit. The single crystal emits intense photoluminescence at 657 nm with a relative quantum yield (RQY) 0.2 times that of rhodamine 6G powder. The compound belongs to a direct band gap at 1.91 eV, analyzed by Tauc's plot, and the energy is close to the PL position. The Hall effect measurement on a pressed pellet reveals an n-type conductivity with a carrier concentration of 3.358 × 10¹⁷ cm^-3 and a mobility of 24.331 cm² V^-1 s^-1. Furthermore, the compound produces a strong nonlinear third-harmonic generation (THG), with an χ_S⁽³⁾ value of 1.3 × 10⁵ pm²/V² comparable to 1.6 × 10⁵ pm²/V² for AgGaSe₂ measured at 800 nm.

AInSn2S6 (A = K, Rb, Cs)─Layered Semiconductors Based on the SnS2 Structure

RbInSn₂S₆ and CsInSn₂S₆ are yellow two-dimensional (2D) semiconductors featuring anionic SnS₂-type layers of edge-sharing (In/Sn)S₆ octahedra. These structures are directly derived from the parent structure of SnS₂ by replacement of Sn⁴⁺ atoms with A⁺ and In³⁺ atoms. The compounds crystallize, isotypic to the ion-exchange material KInSn₂S₆. They adopt the triclinic space group R3̅m (no. 166). The compounds have similar indirect optical band gaps of 2.31(5) eV for Rb and 2.47(5) eV Cs. The measured work functions for each material are ∼5.38 eV. The density functional theory-calculated effective mass values exhibit strong anisotropy due to the 2D nature of the crystal structures and in the case of CsInSn₂S₆ for hole carriers along the a, b, and c crystallographic directions are 0.30 m₀, 0.34 m₀, and 2.54 m₀, respectively, while for electrons are 0.06 m₀, 0.07 m₀, and 0.47 m₀, respectively.

Add a Pinch of Tetrel: The Transformation of a Centrosymmetric Metal into a Nonsymmorphic and Chiral Semiconductor

Centrosymmetric skutterudite RhP₃ was converted to a nonsymmorphic and chiral compound RhSi_0.3P_2.7 (space group P2₁2₁2₁) by means of partial replacement of Si for P. The structure, determined by a combination of X‐ray crystallography and solid state ³¹P NMR, exhibits branched polyanionic P/Si chains that are unique among metal phosphides. A driving force to stabilize the locally noncentrosymmetric cis‐RhSi₂P₄ and fac‐RhSi₃P₃ fragments is π‐electron back‐donation between the Rh t_2g‐type orbitals and the unoccupied antibonding Si/P orbitals, which is more effective for Si than for P. In situ studies and total energy calculations revealed the metastable nature of RhSi_0.3P_2.7. Electronic structure calculations predicted centrosymmetric cubic RhP₃ to be metallic which was confirmed by transport properties measurements. In contrast, the electronic structure for chiral orthorhombic RhSi_0.3P_2.7 contained a bandgap, and this compound was shown to be a narrow gap semiconductor.

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 < E_g < 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.