d6versus d10, Which Is Better for Second Harmonic Generation Susceptibility? A Case Study of K2TGe3Ch8 (T = Fe, Cd; Ch = S, Se)

Two acentric chalcogenide compounds, K₂CdGe₃S₈ and K₂CdGe₃Se₈, were synthesized via conventional high-temperature solid-state reactions. The crystal structures of K₂CdGe₃S₈ and K₂CdGe₃Se₈ were accurately determined by single-crystal X-ray diffraction and crystallize in the K₂FeGe₃S₈ structure type. K₂CdGe₃S₈ is isostructural to K₂FeGe₃S₈ with superior nonlinear optical properties. For the second harmonic generation (SHG) response, K₂CdGe₃S₈ is 18× K₂FeGe₃S₈ for samples of particle size of 38-55 μm. The superior nonlinear optical properties of K₂CdGe₃S₈ over K₂FeGe₃S₈ are mainly contributed by the chemical characteristics of Cd compared with Fe, which are elucidated by nonlinear optical property measurements, electronic structure calculations, and density functional theory calculations. The [CdS₄] tetrahedra within K₂CdGe₃S₈ exhibit a higher degree of distortion and larger volume compared to the [FeS₄] tetrahedra in K₂FeGe₃S₈. This study possesses a good platform to investigate how d-block elements contribute to the SHG response. The fully occupied d¹⁰-elements are better for SHG susceptibility than d⁶-elements in this study. K₂CdGe₃S₈ is a good candidate as an infrared nonlinear optical material of high SHG response (2.1× AgGaS₂, samples of particle size of 200-250 μm), type-I phase-matching capability, high laser damage threshold (6.2× AgGaS₂), and good stability.

Highly selective cesium(I) capture under acidic conditions by a layered sulfide

Radiocesium remediation is desirable for ecological protection, human health and sustainable development of nuclear energy. Effective capture of Cs+ from acidic solutions is still challenging, mainly due to the low stability of the adsorbing materials and the competitive adsorption of protons. Herein, the rapid and highly selective capture of Cs+ from strongly acidic solutions is achieved by a robust K+-directed layered metal sulfide KInSnS4 (InSnS-1) that exhibits excellent acid and radiation resistance. InSnS-1 possesses high adsorption capacity for Cs+ and can serve as the stationary phase in ion exchange columns to effectively remove Cs+ from neutral and acidic solutions. The adsorption of Cs+ and H3O+ is monitored by single-crystal structure analysis, and thus the underlying mechanism of selective Cs+ capture from acidic solutions is elucidated at the molecular level.

Na2GaS2Cl: a new sodium-rich chalcohalide with two-dimensional [GaS2]∞ layers and wide interlayer space

By introducing halogens to the A/Ga/Q (A = Na, K; Q = S, Se) system, one new chalcohalide namely Na₂GaS₂Cl was successfully obtained. It crystallizes in the orthorhombic space group Cmcm (63). Na₂GaS₂Cl has a layered structure consisting of two dimensional [GaS₂]_∞ layers which are stacked in "face to face" and "back to back" arrays and separated by Na⁺ and Cl^- ions. Interestingly, supertetrahedral building units [Ga₄S₁₀] (T2) which are rarely found in metal chalcogenides and metal chalcohalides are formed in this structure. Moreover, the distances of two adjacent layers are around four times larger than the ionic radius of the Na⁺ ion, which is very likely to provide a perfect environment for the storage and migration of Na⁺ ions. In particular, the volume concentration of the Na⁺ cations in this compound is as high as 1.54 × 10²² cm^-3. The UV-vis-NIR spectroscopy measurement reveals that the optical band gap of this title compound is 3.06 eV. The electronic structural calculations on Na₂GaS₂Cl show that the band gap is mainly determined by the [GaS₄] groups and Na-Cl ionic bonding.

Four alkali metal molybdates with two types of Mo–O chains, ABMo3O10 (A = Li, B = Rb; A = Li, Na, K, B = Cs): synthesis, structure comparison and optical properties

The effects of cation size on the framework structures of four stoichiometrically equivalent alkali metal molybdates were discussed in detail.

Tailored synthesis of nonlinear optical quaternary chalcohalides: Ba4Ge3S9Cl2, Ba4Si3Se9Cl2 and Ba4Ge3Se9Cl2

Three nonlinear optical chalcohalides, Ba₄Ge₃S₉Cl₂, Ba₄Si₃Se₉Cl₂ and Ba₄Ge₃Se₉Cl₂, have been synthesized by a tailored synthetic approach based on [M₃Q₉]⁶⁻ (M = Ge, Q = S; M = Si/Ge, Q = Se) building units.