Characterizations and Nonlinear-Optical Properties of Pentanary Transition-Metal Oxysulfide Sr2CoGe2OS6.

As one type of material containing multiple anions, oxysulfides can combine the advantages of oxides and sulfides and are deeply studied as nonlinear-optical (NLO) materials. Herein, a new melilite-type pentanary oxysulfide Sr2CoGe2OS6 is studied. It crystallizes in the noncentrosymmetric tetragonal space group P4̅21m, and its structure features GeOS3 and CoS4 tetrahedra-built {[CoGe2OS6]4-}∞ layers. Its powder sample exhibits a moderate phase-matchable NLO response and a high laser-induced damage threshold. The NLO response is mainly determined by CoS4 tetrahedra according to the theoretical calculation results. This work indicates that transition-metal oxysulfides can also be considered as potential infrared NLO materials.

KEu2In3B12S13: a novel type of thioborate featuring B12S12 cluster and unique In6S6 12-membered ring.

Both borates and sulfides are important inorganic multifunctional materials. Encouraged by this background, thioborates attract considerable interest. However, their investigations are highly hindered by the scarcity of the available ones and the synthetic difficulty of the new ones. Here, we report a new thioborate KEu2In3B12S13 (1), which was obtained via a facile solid-state reaction in KI flux. It crystallizes in the trigonal R3̄m structure, and the three-dimensional structure features a six InS6 octahedron consolidated B12 icosahedron built {[In3B12S12]5-}∞ polyanionic framework and a unique In6S6 12-membered ring, representing a new type of compound. The B12S12 cluster is also different from the other known thioborates. The structural chemistry, optical and magnetic properties, as well as theoretical calculations of 1 were systematically studied. This study not only provides a new type of thioborate but also makes a breakthrough in the synthesis of thioborates.

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.

Structural Chemistry and Excellent Nonlinear Optical Properties of a Series of Ternary Selenides GaxIn2-xSe3.

Novel nonlinear optical (NLO) materials possessing simple chemical compositions and facile syntheses are competitive when considering their practical application. Here, a series of ternary selenides GaxIn2-xSe3 (x = 0.07, 0.38, 0.45, and 0.81) that crystallize in a chiral P65 structure are obtained by melting Ga, In, and Se elements. Their three-dimensional structures are built by (Ga/In)Se4 tetrahedra and InSe5 trigonal bipyramids. The hexagonal modification's phase stability is analyzed by energy calculation, and their optical band gaps are determined to be 1.72-1.99 eV. They exhibit large NLO responses that are 1.41-1.64 times that of the benchmark AgGaS2. The results of density functional theory calculations suggest that introduction of Ga onto the In site in (InSe4)5- units can form a deformed tetrahedron with more distortion in the structure, and the (InSe5)7- units contribute a large amount of birefringence to the structure. This work is the first to investigate the ternary chalcogenides M2Q3 (M = Ga or In; Q = S or Se) as new types of infrared NLO crystals with excellent performances, which will stimulate more interest in those possessing simple compositions and outstanding performances.

Hexagonal In2Se3: A Defect Wurtzite-Type Infrared Nonlinear Optical Material with Moderate Birefringence Contributed by Unique InSe5 Unit.

The balance between second harmonic generation (SHG) intensity and laser-induced damage threshold (LIDT), together with phase-matchable behavior, is the key point for exploration of novel nonlinear optical (NLO) materials. In this work, the NLO property of defect wurtzite-type hexagonal-In2Se3 (γ) is extensively explored first. It exhibits a strong SHG intensity of 2.6 × AgGaS2 (AGS) at 2.1 µm, and a high powder LIDT of 7.3 × AGS. From wurtzite to γ-In2Se3, the birefringence changes from 0.003 to 0.075, resulting in the phase-matchable phenomenon of γ-In2Se3. This is well ascribed to the contribution of the unique InSe5 unit in γ-In2Se3 from the result of birefringence calculation and analysis.