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The introduction of fluorine (F) into the borate crystals is proven to be an effective approach in designing novel non-centrosymmetric crystals, which is a requirement for nonlinear optical (NLO) materials. In this contribution, the electronic structure and optical properties of borate fluoride crystals are determined by the first-principles method. First-principles calculations indicate that the key second-harmonic generation (SHG) factor is attributed not only to borate groups but also to the bonding of the F anions with cations where F coordinates to cations (Sr, Ba). The electron withdrawing effect of the F atom leads to the higher values for anisotropy of the polarizability around cation-centered polyhedra, ultimately making it easy for the external electric field of incident light to effect the dielectric susceptibility. The direct contribution of anion on the NLO properties is observed as fluorine-induced variation of electronic structure. [ABSTRACT FROM AUTHOR]

Investigating ultraviolet (UV) birefringent crystals is a focal point of research in recent years. The development of superior birefringent materials faces substantial challenges, primarily due to the need to pinpoint optimal fundamental building blocks and to perfect their geometric arrangement within the crystal lattice. By selecting a planar π-conjugated [C(NH 2 ) 3 ] group and a staggered [S 2 O 6 ] group, we have successfully synthesized an organic-inorganic hybrid crystal, [C(NH 2 ) 3 ] 2 S 2 O 6 . Similar to the famous inorganic crystal Sr 2 Be 2 B 2 O 7 (SBBO), [C(NH 2 ) 3 ] 2 S 2 O 6 exhibits a two-dimensional double-layered crystal structure connected by N-H···O hydrogen bonding. Due to the ideal spatial arrangements of the planar π-conjugated [C(NH 2 ) 3 ] group, this crystal displays a large birefringence (0.150 at 546 nm) among sulfate derivatives in the short-wave UV region. Meanwhile, [C(NH 2 ) 3 ] 2 S 2 O 6 has a large band gap of 5.23 eV. This work indicates that the [S 2 O 6 ] unit, acting as a direct structural motif, is beneficial for the discovery of UV birefringent crystals.

The S( 1 D) + D 2 → SD + D reaction is a prototype insertion chemical reaction that involves spin-orbit interactions in the exit channel. In this work, we report spin-orbit state-resolved differential cross sections (DCSs) of this reaction obtained by crossed beam experiments at collision energies of 266.2 and 206.5 cm -1 . The DCSs of specific rovibrational states exhibit a slight preference for forward scattering. When integrated over all rotational quantum states within each spin-orbit manifold, the total angular distributions of the two manifolds show nearly forward-backward symmetry, indicating that the deep well responsible for the long-living complex-forming mechanism predominates the entire reaction dynamics. Moreover, significant spin-orbit preference was observed at rotational quantum number N > 9 in the vibrationally ground state of SD products. It was also observed that SD products in the vibrationally excited state v ' = 1 prefer to populate in the 2 Π 3/2 manifold, with the 2 Π 3/2 / 2 Π 1/2 ratio of 15.8 and 25.2 at collision energies of 266.2 and 206.5 cm -1 , respectively. The experimental spin-orbit state-resolved DCSs obtained in this work will be of great importance for developing an accurate diabatic theory that includes spin-orbit interactions for this title reaction.

Investigating novel nonlinear optical (NLO) active units serves as a valuable method for broadening the research landscape of NLO materials. This study showcases the potential of the cytosinium cation (C 4 H 6 N 3 O) + as a novel NLO-active motif through theoretical calculations. The title compound exhibited a wide band gap of 3.85 eV, along with a moderate second harmonic generation (SHG) response of 1.65 times that of KH 2 PO 4 (KDP) and significant birefringence of 0.47. Its exceptional optical properties are primarily attributed to the synergy interaction between cations and anionic groups in the asymmetric unit.

We herein report an unprecedented organic-inorganic hybrid borate incorporating a novel nonlinear-optical (NLO) active unit, namely, [C(NH 2 ) 3 ][B(C 2 O 2 H 4 ) 2 ]. The novel NLO active unit was derived from the condensation reaction between two glycol molecules and one (BO 4 ) 5- group. The title compound exhibits a moderate second-harmonic-generation effect (0.7 × KDP), a significant band gap (5.76 eV), and a suitable birefringence (0.078 at 550 nm). The optical properties are determined by the synergistic interaction between the C(NH 2 ) 3 + cation and the [B(C 2 O 2 H 4 ) 2 ] - group, as indicated by theoretical calculations.

The key to searching novel nonlinear optical (NLO) crystals was effectively combining the NLO-active units to obtain a noncentrosymmetric structure. Nevertheless, the present predicament lies in the growing challenge of discovering novel crystals within conventional inorganic frameworks that surpass the properties of the current NLO materials. In view of this, researchers expanded their research focus to the organic-inorganic hybridization system; it is foreseeable to concentrate the advantages from several kinds of NLO-active units to acquire novel NLO crystals with superior properties. We herein report an organic-inorganic hybrid molybdate crystal, namely, [C(NH 2 ) 3 ] 6 Mo 7 O 24 (GMO). It was successfully obtained via combining inorganic NLO-active MoO 6 octahedra and organic π-conjugated [C(NH 2 ) 3 ] + groups. GMO demonstrates a moderate second-harmonic-generation response, specifically measuring about 1.3 times the value of KDP. Additionally, it exhibits a significant birefringence value of 0.203 at the wavelength of 550 nm and possesses a wide band gap of 3.31 eV. Theoretical calculations suggest that the optical properties of the GMO are primarily influenced by the synergy effect of [C(NH 2 ) 3 ] + groups between MoO 6 octahedra.

Three thiophosphates including noncentrosymmetric Na 6 Pb 3 P 4 S 16 and centrosymmetric K 2 M II P 2 S 6 (M II = Mg and Zn) were successfully synthesized in vacuum-sealed silica tubes. Note that interesting multiple six membered-rings (6-MRs) including 6-NaS 6 -MRs and 6-KS n -MRs ( n = 6 and 7) formed by A + -centered polyhedra were discovered in the structures of title thiophosphates and these MR-composed three-dimensional (3D) tunnels show great possibility to facilitate the filling of various structural blocks (such as zero-dimensional (0D) Pb 3 S 10 trimers or one-dimensional (1D) (M II S n ) n chains). Na 6 Pb 3 P 4 S 16 exhibits the strongest nonlinear optical (NLO) response (5.4 × AgGaS 2 ) with phase-matching (PM) behavior among the known Pb-based PM NLO sulfides, which is much larger than that of Pb 3 P 2 S 8 (3.5 × AgGaS 2 ); it was verified that such large second harmonic generation (SHG) response in Na 6 Pb 3 P 4 S 16 can be attributed to the huge contribution of stereochemically active PbS 4 units based on the SHG-density and dipole-moment calculations. Moreover, title thiophosphates show large birefringences (Δ n = 0.102-0.21), which indicates that incorporation of [P 2 S 6 ] dimers or polarized PbS 4 units into structures provides positive benefits for the onset of strong optical anisotropy.

Atoms in special lattice sites can play a crucial role in realizing materials properties, which is long pursued but difficult to control. Herein, by adopting a stereochemically active lone-pair-containing metal substitution strategy, a nonlinear-optical (NLO) silicate crystal Li 3 (OH)PbSiO 4 was successfully synthesized, featuring [PbSiO 4 ] ∞ layers with the perfect orientation of the stereochemically active lone-pair Pb(II) cation in the polar-axis lattice. Li 3 (OH)PbSiO 4 overcomes the long-standing problem of silicates, that is, poor nonlinear properties because it exhibits both the largest birefringence of 0.082 and the largest phase-matchable second-harmonic-generation (SHG) efficiency of 21 × KDP among the known silicates. The successful polar-axis lattice substitution could offer a new direction for realizing the rational control of materials structures and properties.

Fluorine-containing borate crystal materials are particularly attractive due to their rich structural chemistry and excellent properties for optical applications. In this work, a new compound Ba 3.75 MgB 7 O 14 F 2.5 has been synthesized through the high-temperature solution method. In the crystal structure of Ba 3.75 MgB 7 O 14 F 2.5 , the [B 7 O 14 ] basic building unit and the [MgO 3 F 3 ] octahedra are interconnected to create a complex three-dimensional network. The structural feature of the less commonly observed [B 7 O 14 ] units is discussed, and it has been found that such units in Ba 3.75 MgB 7 O 14 F 2.5 are most conducive to achieving large birefringence. In addition, Ba 3.75 MgB 7 O 14 F 2.5 exhibits good thermal stability, a short ultraviolet cutoff of 203 nm, and large birefringence (0.081@546 nm), indicating its potential as a new UV birefringent crystal.

Ultraviolet (UV) nonlinear optical (NLO) crystals are a vital component in laser systems to modulate frequency. Organic groups have the advantages of easy synthesis, structural diversity, and large hyperpolarizations (β), which can be combined with inorganic groups to form unique organic-inorganic hybrid NLO crystal materials. Herein, a urea-containing crystal NaCl·CH 4 N 2 O·H 2 O is screened out and large-size crystals have been grown by a simple aqueous solution method. Compared with most reported organic-inorganic hybrid NLO materials, it has optimized comprehensive properties including a large SHG effect of 1.53 × KDP, a moderate birefringence (0.084@1064 nm), and a short UV cutoff edge of 209 nm. First-principles studies reveal that the dominant contributor to the linear and nonlinear optical properties is the urea molecule.