Cadmium Hydroxyl Chloride with Balanced Band Gap and Second-Harmonic-Generation Response

Ultraviolet (UV) nonlinear-optical (NLO) materials are crucial in laser technology due to their ability to modulate light frequency. In this work, when d10 cations, hydroxyl groups, and Cl atoms were combined, a cadmium double salt, Cd(OH)Cl, was synthesized by a simple hydrothermal method. It has a large phase-matched second-harmonic-generation (SHG) response at 1064 nm (2.5 × KDP) with a short UV-cutoff edge (260 nm), which can be applied in a solar-blind UV band. Theoretical calculations suggest that [Cd(OH)3Cl3] groups lead to a large SHG response. Our work may shed light on the exploration of new NLO materials in metal hydroxyl chlorides.

Sb5O7I: Exploration of Ternary Antimony-Based Oxyhalide as a Nonlinear-Optical Material

Metal oxyhalides are attracting extensive interest for their enchanting structures and diverse properties. Herein, a ternary antimony oxyiodide, Sb₅O₇I with the new hexagonal noncentrosymmetric P6₃ structure is systematically surveyed by focusing on its nonlinear-optical (NLO) behavior. Its two-dimensional structure is constructed by {Sb₂[Sb₃O₇]}_∞⁺ layers separated by charge-balanced I^- anions. The second-harmonic-generation measurement result suggests that Sb₅O₇I is NLO-active, and the effect is assigned to the [SbO₃]^3- triangular pyramids' contribution. Sb₅O₇I shows a direct optical energy gap of 3.22 eV, which is the largest among all reported ternary oxyiodides. This work is the first investigation of ternary NLO Sb-based oxyhalides and enriches the study of metal oxyhalides as promising NLO materials.

Metal oxyhalides: an emerging family of nonlinear optical materials

Second-order nonlinear optical (NLO) materials have drawn enormous academic and technological attention attributable to their indispensable role in laser frequency conversion and other greatly facilitated applications. The exploration of new NLO materials with high performances thus has long been an intriguing research field for chemists and material scientists. However, an ideal NLO material should simultaneously satisfy quite a few fundamental yet rigorous criteria including a noncentrosymmetric structure, large NLO coefficients, desired transparent range, large birefringence, high laser damage threshold, and availability of a large-size single crystal. Therefore, the identification of promising compound systems, targeted design, and experience-based syntheses are crucial to discover novel NLO materials working in the spectral region of interest. As an important family of mixed-anion compounds, versatile metal oxyhalides containing metal-centered oxyhalide functional units ([MO m X n ] (X = F, Cl, Br, and I)) are becoming a marvelous branch for interesting NLO materials. Especially, when the central metals are d0/d10 transition metals or heavy post-transition metals, a number of novel NLO materials with superior functionalities are expected. Our thorough review on the recent achievements of metal oxyhalides for NLO materials are divided into the fast-growing NLO metal oxyhalides with single type halogen anions and the newly identified NLO metal oxyhalides with mixed halogen anions. Here we mainly focus on the design strategy, structural chemistry, NLO-related properties, and structure-property correlation of the metal oxyhalides with relatively large NLO responses. We hope this review can provide an insight on the rational design and future development of emerging metal oxyhalides for NLO and other applications.

Second-Harmonic-Generation-Active Oxyhalides: CuSb2O3X (X = Cl, Br)

Metal oxyhalides have attracted broad interest recently because of their diverse structures and versatile properties. Here, two oxyhalides, CuSb₂O₃Cl (1) and CuSb₂O₃Br (2), were studied by focusing on their nonlinear-optical properties. They are crystallized in the noncentrosymmetric monoclinic Cc structure, and the layered structures could be derived from a 1:1 combination of CuX- (X = Cl, Br) and Sb₂O₃-type slabs. Their energy gaps were determined to be 2.76 and 2.64 eV. The second-harmonic-generation (SHG) test suggests that they are nonlinear-optical-active, and the effects are ascribed to the contribution of CuX₃O units. Meanwhile, the SbO₃ units' arrangement has a small contribution to the SHG effects. This work is the pioneer SHG investigation of the M^I-M^III-O-X (M^I = Cu, Ag; M^III = trivalent As, Sb, Bi; X = halogen) family.

A new broad-band infrared window material CdPbOCl2 with excellent comprehensive properties

Herein, a new IR window material CdPbOCl₂ is rationally designed and fabricated by a heavy-metal oxide and halide combined strategy. The millimeter-scale CdPbOCl₂ single crystal exhibits a wide IR transparent region (1.4-18.0 μm) and excellent comprehensive properties. The results provide an insight into the exploration of broad-band IR window materials.

Synthesis and Characterization of Two New Second Harmonic Generation Active Iodates: K3Sc(IO3)6 and KSc(IO3)3Cl

Transparent single crystals of two new iodates K₃Sc(IO₃)₆ and KSc(IO₃)₃Cl have been synthesized hydrothermally. Single-crystal X-ray diffraction was used to determine their crystal structures. Both compounds crystallize in non-centrosymmetric space groups. The compound K₃Sc(IO₃)₆ crystallizes in the orthorhombic space group Fdd2. The crystal structure is made up of [ScO₆] octahedra, [IO₃] trigonal pyramids, and [KO₈] distorted cubes. The compound KSc(IO₃)₃Cl crystallizes in the trigonal space group R3. The building blocks are [ScO₆] octahedra, [KO₁₂] polyhedra, and [IO₃] trigonal pyramids. The Cl^- ions act as counter ions and reside in tunnels in the crystal structure. The second harmonic generation (SHG) measurements at room temperature, using 1064 nm radiation, on polycrystalline samples show that the SHG intensities of K₃Sc(IO₃)₆ and KSc(IO₃)₃Cl are around 2.8 and 2.5 times that of KH₂PO₄ (KDP), respectively. In addition, K₃Sc(IO₃)₆ and KSc(IO₃)₃Cl are phase-matchable at the fundamental wavelength of 1064 nm. The large anharmonicity in the optical response of both compounds is further supported by an anomalous temperature dependence of optical phonon frequencies as well as their enlarged intensities in Raman scattering. The latter corresponds to a very large electronic polarizability.

Imidazole-directed fabrication of three polyoxovanadate-based copper frameworks as efficient catalysts for constructing C–N bonds

Three polyoxovanadate-based copper frameworks with 3D, 2D and 1D networks have been developed and they displayed efficient heterogeneous catalytic activities in the Chan-Lam reaction.