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Trigonal planar units with large polarizability anisotropy and high physicochemical stability are ideal structural units for exploring nonlinear optical (NLO) materials. Integrating the merits of two types of triangular‐like moieties, a family of second‐order NLO‐active hybrid halides, MATX (X = Cl (1), Br (2), and I (3)), are achieved. MATX crystallizes in a nonpolar space group of P6¯$P\overline 6 $2c but exhibits the optimal spatial arrangement and superior NLO performance. The low coordination planar trigonal AgX3 units enable segregation in layers of the three‐winged propeller‐like Me3TPA units. All of the layers are packed in a perfect parallel fashion, making the functional materials exhibit superior NLO performances, including the phase matchable behavior with strong SHG responses (6.2/1, 6.5/2, and 7.6/3 times that of potassium dihydrogen phosphate), large birefringence (0.232/1, 0.252/2 and 0.260/3 at 1064 nm), high laser damage threshold, wide transparent window, and easiness of crystal growth. The first‐principles calculations reveal that the coexistence of strong linear and nonlinear optical properties are ascribed to the synergistic effect of the trigonal moieties. This study points out a useful path for the rational design of excellent NLO materials. [ABSTRACT FROM AUTHOR]

Through systematic experiments, two novel mercury iodate sulfates, namely, Hg2(IO3)2(SO4)(H2O) and Hg2(IO3)2(SO4) were obtained. They crystallize in monoclinic space group C2 and C2/c, respectively. Hg2(IO3)2(SO4)(H2O) exhibits the [Hg(IO3)]+ polar cationic layer inherited from Hg(IO3)2 and the three‐dimensional (3D) framework inherited from HgSO4. This enables Hg2(IO3)2(SO4)(H2O) to generate a strong second harmonic generation (SHG) response of 6 times that of KH2PO4 (KDP). The structure of Hg2(IO3)2(SO4) is very similar to that of Hg2(IO3)2(SO4)(H2O), and they can be transformed into each other. Hg2(IO3)2(SO4)(H2O) shows a large optical band gap of 3.98 eV and a high dehydration temperature of 250 °C. This study indicates that by reasonable design, the introduction of multiple functional groups into a compound may combine their advantages to achieve good overall optical performance. [ABSTRACT FROM AUTHOR]

A large nonlinear optical (NLO) coefficient and a wide band gap are two crucial but contradictory parameters that are difficult to achieve simultaneously in a single infrared (IR) NLO compound. A salt‐inclusion chalcogenide (SIC), Li[LiCs2Cl][Ga3S6] (1), was prepared that presents a nanosized tunnel framework constructed from monotype chalcogenide tetrahedra. Highly oriented covalent GaS4 tetrahedra in the host lead to a moderate second harmonic generation response (0.7 AgGaS2), and ionic guests effectively broaden the band gap to the widest value (4.18 eV) among all IR NLO chalcogenides, thereby achieving a remarkable balance between NLO efficiency and band gap. [ABSTRACT FROM AUTHOR]

New middle and far-infrared (MFIR) nonlinear optical (NLO) chalcogenides have been receiving increasing attention for their great importance in military and civil fields. In addition, the current challenge in the efforts for identifying a promising MFIR NLO material lies in achieving simultaneously large second-harmonic generation (SHG) intensity and high laser-induced damage threshold (LIDT) in the same material. In this study, two quaternary non-centrosymmetric (NCS) sulfides, BaAg2GeS4 (1) and BaAg2SnS4 (2), were synthesized from a high-temperature solid-state reaction using BaCl2 flux in evacuated closed silica tubes. Although 1 and 2 show identical stoichiometry, they crystallize in different NCS space groups, tetragonal I4̅2m (no. 121) and orthorhombic I222 (no. 23), respectively, based on the results of crystal structure solution. In their structures, highly distorted AgS4 tetrahedra interconnect together via corner-sharing to form two-dimensional (2D) layers, which are further bridged with isolated GeS4 or SnS4 units to produce a three-dimensional (3D) framework structure with Ba cations lying in the tunnels. Remarkably, they not only possess phase-matchable (PM) abilities but also exhibit a good balance between strong SHG responses (1.7× and 0.4× AgGaS2) and high LIDTs (3.2× and 1.5× AgGaS2). Moreover, theoretical calculations based on density functional theory (DFT) methods have aided the understanding of energy bands, electronic structures, and linear and NLO properties. [ABSTRACT FROM AUTHOR]

To develop new mid-infrared (MIR) nonlinear optical (NLO) materials, which can overcome the low laser damage threshold (LDT) of the commercial MIR-NLO crystals (AgGaS2, AgGaSe2 and ZnGeP2) and simultaneously keep the large NLO susceptibility, is necessary for high-power MIR laser frequency conversion technology. To improve the LDT, a new strategy of increasing lattice stability was adopted. Here, the strongly covalent structural unit of the PS4 tetrahedron was introduced into AgGaS2 (AGS), and that led to the isolation of the first compound in AgI-GaIII-PV-S system, namely, AgGa2PS6 ( Cc). It retains a large SHG efficiency (1.0×AGS) with phase-matchable ability, and also exhibits an improved LDT (5.1×AGS), indicating AgGa2PS6 is a new promising MIR-NLO crystal. Moreover, a novel 3D framework of [Ga2PS6]−, with triangular-shaped channels, as well as interesting single triangular geometry of AgS3-both of which are very rare in reported sulfides-was discovered in AgGa2PS6. Furthermore, theoretical calculations, and lattice energy and thermal expansions analyses suggest that the PS4 group makes a large contribution to the large SHG efficiency and high LDT. [ABSTRACT FROM AUTHOR]

New middle and far-infrared (MFIR) nonlinear optical (NLO) chalcogenides have been receiving increasing attention for their great importance in military and civil fields. In addition, the current challenge in the efforts for identifying a promising MFIR NLO material lies in achieving simultaneously large second-harmonic generation (SHG) intensity and high laser-induced damage threshold (LIDT) in the same material. In this study, two quaternary non-centrosymmetric (NCS) sulfides, BaAg2GeS4 (1) and BaAg2SnS4 (2), were synthesized from a high-temperature solid-state reaction using BaCl2 flux in evacuated closed silica tubes. Although 1 and 2 show identical stoichiometry, they crystallize in different NCS space groups, tetragonal I4̅2m (no. 121) and orthorhombic I222 (no. 23), respectively, based on the results of crystal structure solution. In their structures, highly distorted AgS4 tetrahedra interconnect together via corner-sharing to form two-dimensional (2D) layers, which are further bridged with isolated GeS4 or SnS4 units to produce a three-dimensional (3D) framework structure with Ba cations lying in the tunnels. Remarkably, they not only possess phase-matchable (PM) abilities but also exhibit a good balance between strong SHG responses (1.7× and 0.4× AgGaS2) and high LIDTs (3.2× and 1.5× AgGaS2). Moreover, theoretical calculations based on density functional theory (DFT) methods have aided the understanding of energy bands, electronic structures, and linear and NLO properties. [ABSTRACT FROM AUTHOR]