A Lead Mixed Halide with Three Different Coordinated Anions and Strong Second-Harmonic Generation Response.

Nonlinear optical (NLO) crystals are widely applied in information technology, micro-manufacturing and medical treatment. Herein, a new lead mixed halide with strong second-harmonic generation (SHG) response, Cs3 Pb2 (CH3 COO)2 Br3 I2 , has been designed and rationally synthesized. Cs3 Pb2 (CH3 COO)2 Br3 I2 represents the rare NLO crystal featuring that three different anions (I- , Br- and O2- ) simultaneously coordinate the Pb(II) atom to form a severely distorted [PbBr2 I2 O2 ] polyhedron with a large polarizability. Remarkably, Cs3 Pb2 (CH3 COO)2 Br3 I2 not only exhibits a very strong phase-matching SHG response of 9×KH2 PO4 (KDP), but also possesses a large birefringence (0.27@1064 nm) and high laser damage threshold (LDT). The strong SHG effect of Cs3 Pb2 (CH3 COO)2 Br3 I2 mainly originates from the oriented arrangement of [Pb2 Br3 I2 ] chains. This study points out an effective strategy to develop new NLO crystals with strong SHG response.

KCs2 [Pb2 Br5 (HCOO)2 ]: A Polar 3D Lead-Bromide Framework Exhibiting Strong Second-Harmonic Generation Response.

The discovery of new nonlinear optical (NLO) crystals with excellent properties is in urgently demand because of their ability to generate coherent light. Herein, we report an unique NLO lead bromide formate, KCs2 [Pb2 Br5 (HCOO)2 ], which has been synthesized by a mix-solvothermal method. KCs2 [Pb2 Br5 (HCOO)2 ] exhibits strong phase-matching second-harmonic generation (SHG) response (6.5×KDP), large birefringence (0.16@ 1064 nm), and a wide transparent window in most visible light and mid-IR region. Interestingly, KCs2 [Pb2 Br5 (HCOO)2 ] features a polar 3D lead-bromide framework in which adjacent Pb-Br layers containing coplanar Pb6 Br6 rings are not only parallel to each other, but also orient in the same direction. These oriented arrangements are responsible for the strong SHG response and large birefringence that are elucidated by both local dipole moment and theoretical calculations. This research provides a new strategy to explore subsequent NLO crystals.

A Potassium Tungsten Oxyfluoride with Strong Second-Harmonic Generation Response Derived from Anion-Ordered Functional Motif.

The unity of structure-property design and practical synthesis is a key to develop nonlinear optical (NLO) materials. However, many designed structures are hard to get because of the incapability of controlling the arrangement of structural motifs. After careful synthesis, we successfully obtained a new NLO crystal with expected properties, KWO3F, which features a long-range anion-ordered while directed parallel arrangement of [WO5F] d0 transition metal fluorooxo-functional (d0 [TMOF]) motifs. This arrangement is vital to achieve a strong second-harmonic generation (SHG) response, which is proved by dipole moment analyses and theoretical calculations. Remarkably, KWO3F possesses a strong phase-matching SHG response (3 × KDP), high thermal stability (stable up to 350 °C in air), a large laser damage threshold (LDT, 129.7 MW/cm2), a wide transparent window (0.5-10 µm), and a suitable birefringence (0.088 @ 1064 nm). Our research demonstrated that the introduction of the NLO-active d0 [TMOF] motif is an effective strategy to design new potential NLO materials.

Titanium Iodates with a Second-Harmonic-Generation Response.

Nonlinear-optical (NLO) crystal is an important photoelectric functional material. In this work, a new NLO titanium iodate, (H3O)2Ti(IO3)6, along with Ti(IO3)4 has been synthesized under facile conditions. The space group of (H3O)2Ti(IO3)6 is the chiral noncentrosymmetric group R3 (No. 146), with an interesting three-dimensional framework, while that of Ti(IO3)4 is the centrosymmetric space group P1̅ (No. 2) containing one-dimensional chains. Thermogravimetric analysis shows that (H3O)2Ti(IO3)6 and Ti(IO3)4 have no weight loss below 220 and 390 °C, respectively. In addition, (H3O)2Ti(IO3)6 not only is thermally stable up to 200 °C in an air atmosphere but also is stable in water. (H3O)2Ti(IO3)6 has a moderate-intensity second-harmonic-generation (SHG) response (1.4×KDP), a large laser-induced damage threshold (46×AgGaS2), and high transmittance in the wavelength ranges of 0.5-1.4 and 2.5-10 µm. Both local dipole moment and systematic theoretical calculations reveal that the SHG response of (H3O)2Ti(IO3)6 is mainly because of the combined effect of [TiO6] octahedra and IO3 and IO4 units. In a word, (H3O)2Ti(IO3)6 exhibits good NLO performances, as well as water resistance and facile growth of a single crystal with high quality, indicating its potential application as NLO materials in the visible and mid-IR regions, especially the visible region.

Cs3 Pb2 (CH3 COO)2 X5 (X=I, Br): Halides with Strong Second-Harmonic Generation Response Induced by Acetate Groups.

Nonlinear optical (NLO) crystals are the key component in solid-state lasers. New second-harmonic generation (SHG) effective halides, Cs3 Pb2 (CH3 COO)2 X5 (X=I, Br), have been rationally synthesized by introducing acetate groups into lead halide perovskites under moderate solvothermal conditions. Cs3 Pb2 (CH3 COO)2 X5 (X=I, Br) feature highly oriented anionic chains constructed by distorted [PbX4 O2 ] (X=I, Br) polyhedrons. Both the theoretical studies and the dipole moment calculations uncover that their SHG effects are mainly originated from the distorted [PbX4 O2 ] (X=I, Br) polyhedrons. Remarkably, Cs3 Pb2 (CH3 COO)2 I5 exhibits strong phase-matching SHG response (8×KDP) and large birefringence (0.26@ 1064 nm). Moreover, Cs3 Pb2 (CH3 COO)2 X5 (X=I, Br) also possess high laser damage threshold (LDT) which are almost 27 and 41 times that of AgGaS2 , respectively.

A Niobium Oxyiodate Sulfate with a Strong Second-Harmonic-Generation Response Built by Rational Multi-Component Design.

A novel niobium oxyiodate sulfate, Nb2 O3 (IO3 )2 (SO4 ), was fabricated by a rational multi-component design under moderate hydrothermal conditions. This multi-component design is inspired by an interesting niobium oxysulfate reaction, which opens a new door for synthetic method to effectively introduce refractory metals such as Nb into crystal structures by hydrothermal synthesis. Nb2 O3 (IO3 )2 (SO4 ) features a cube-like topological structure with a large phase-matching second harmonic generation (SHG) response (6×KDP), a wide transparency window (0.38-8 µm), and a high laser damage threshold (LDT) (20×AgGaS2 ). It has the highest thermostability (stable up to 580 °C under air) among reported non-centrosymmetric (NCS) iodates and sulfates and is stable in water and even concentrated H2 SO4 . Furthermore, Nb2 O3 (IO3 )2 (SO4 ) is a unique nonlinear optical (NLO) material among iodates and sulfates, because its SHG effect is mainly caused by the MO6 units rather than the IO3 or SO4 units, which is demonstrated by density functional theory (DFT) calculations.

A lithium-scandium sulfate with second-harmonic generation response and deep-ultraviolet transparency.

A new beryllium-free deep-UV transparent NLO crystal Li(H2O)2Sc(SO4)2 features a two-dimensional [Sc(SO4)2] framework consisting of twisted [Sc3S4O9] units decorated by [LiO2(H2O)2] groups into a unique layer. Remarkably, Li(H2O)2Sc(SO4)2 exhibits a phase-matching SHG response of 0.7 × KDP and a deep-UV cutoff edge below 190 nm.

[Ni(phen)3]2Sb18S29: a novel three-dimensional framework thioantimonate(III) templated by [Ni(phen)3] complexes.

A novel thioantimonate(III), namely, [Ni(phen)(3)](2)Sb(18)S(29) (1; phen = 1,10-phenanthroline), has been solvothermally synthesized. Its structure features a three-dimensional framework with the largest channels in thioantimonates. The chiral [Ni(phen)(3)](2+) cations and the Sb:S ratio (1:1.611) in 1 are unique among those in the reported thioantimonates. The thermal stability, optical properties, and electric conductivity as well as the theoretical band structure and density of state of 1 have also been studied.

New lead-iodide formates with a strong second-harmonic generation response and suitable birefringence obtained by the substitution strategy.

Nonlinear optical (NLO) crystals featuring a strong second-harmonic generation (SHG) response and suitable birefringence to achieve phase-matching are in urgent demand in industrial and commercial applications. Based on the substitution strategy, two new NLO lead-iodide formates, K2[PbI2(HCOO)2] and Rb2[PbI2(HCOO)2], have been successfully synthesized using a moderate mixed-solvothermal method. K2[PbI2(HCOO)2] and Rb2[PbI2(HCOO)2] exhibit strong phase-matching SHG responses of 8 and 6.8 × KDP, respectively, a suitable birefringence and transparent window covering most of the visible light and mid-IR region. Crystal structures and theoretical calculations unveil that the origins of the strong SHG response and suitable birefringence can be credibly attributed to the oriented arrangement of the highly distorted [PbI2O4] hexa-coordinated polyhedra, which are consistent in their local dipole moments, as well. This research provides a new strategy to explore high-performance NLO crystals.

AxCe9(IO3)36 (A = K, La): the effects of a change in the intermediate valence on the second-harmonic generation response.

Two new isostructural non-centrosymmetric cerium iodates KxCe9(IO3)36 (x≈ 3) and LaxCe9(IO3)36 (x≈ 0.3) were synthesized via a hydrothermal method and systematically characterized. They are intermediate valence compounds with the same band gap, showing similar microscopic net dipole moments per unit volume, but different macroscopic second-harmonic generation (SHG) responses under 1064 nm laser irradiation. This research gives a new view for understanding the effects of electronic structure on the SHG response.

(enH2)(4.5)[In(As(V)S4)3][As2(III)(µ-S2)S3]Cl and (enH2)MnAs(III)As(V)S6: two thioarsenates(III, V) with mixed-valent optical properties.

Two mixed-valent thioarsenates, namely (enH2)(4.5)[In(As(V)S4)3][As2(III)(µ-S2)S3]Cl (1) and (enH2)MnAs(III)As(V)S6 (2) (en = ethylenediamine), have been solvothermally synthesized and characterized. Thermal stability, magnetic and mixed-valent optical properties, as well as theoretical band structures and DOSs, of 1 and 2 have also been studied.