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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]

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]

Two UV inorganic yttrium selenite optical materials, namely, Y(HSeO 3)(SeO 3)(H 2 O)·(H 2 O) (1) and Y 2 (SeO 3) 2 (SeO 4)(H 2 O) 2 ·(H 2 O) 0.75 (2), have been synthesized successfully by hydrothermal reactions. Of these, Y 2 (SeO 3) 2 (SeO 4)(H 2 O) 2 ·(H 2 O) 0.75 (2) is a new mixed valent selenium oxide containing Se(IV) and Se(VI) cations simultaneously. Y(HSeO 3)(SeO 3)(H 2 O)·(H 2 O) (1) shows a 3D structure composed of 2D yttrium selenite layers linked by O−H···O bonds. Y 2 (SeO 3) 2 (SeO 4)(H 2 O) 2 ·(H 2 O) 0.75 (2) exhibits a 3D structure composed of 2D yttrium selenite layers connected by SeO 4 tetrahedron. Y(HSeO 3)(SeO 3)(H 2 O)·(H 2 O) (1) crystallized in a chiral space group P 2 1 2 1 2 1 and could display a moderate SHG intensity about 0.7 times of the commercial KH 2 PO 4 (KDP). Its powder laser damage threshold quantity was estimated to be 120.2 MW/cm2, which is about 46.2 times that of AGS (2.6 MW/cm2). UV–vis–NIR spectra reflectance spectra showed that these solids are wide band gap compounds with Eg of 5.5 and 5.1 eV respectively. Theoretical calculations disclosed that Y(HSeO 3)(SeO 3)(H 2 O)·(H 2 O) (1) is an indirect band gap structures and its bandgaps is determined by O and Se atoms. [Display omitted] • Y(HSeO 3)(SeO 3)(H 2 O)•(H 2 O) is a UV NLO material in pure selenite compounds with balanced properties. • Y(HSeO 3)(SeO 3)(H 2 O)•(H 2 O) exhibits a moderate SHG intensity, wide band gap, large LIDT and moderate birefringence. • Y 2 (SeO 3) 2 (SeO 4)(H 2 O) 2 •(H 2 O) 0.75 is a new mixed valent selenium oxide containing Se(IV) and Se(VI) cations simultaneously. [ABSTRACT FROM AUTHOR]