An Exceptional Peroxide Birefringent Material Resulting from d–π Interactions

High-Performance Sulfate Optical Materials Exhibiting Giant Second Harmonic Generation and Large Birefringence

Discovering novel sulfate optical materials with strong second-harmonic generation (SHG) and large birefringence is confronted by a great challenge attributed to the intrinsically weak polarizability and optical anisotropy of tetrahedral SO₄ groups. Herein, two superior-performing sulfate optical materials, namely, noncentrosymmetric Hg₃ O₂ SO₄ and centrosymmetric CsHgClSO₄  ⋅ H₂ O, have been successfully synthesized through the introduction of a highly polarizable d¹⁰ metal cation, Hg²⁺ . The unique component layers in the reported compounds, [Hg₃ O₂ SO₄ ]_∞ layers in Hg₃ O₂ SO₄ and [HgClSO₄ (H₂ O)] ∞ - layers in CsHgClSO₄  ⋅ H₂ O, induce enlarged birefringence in each sulfate. Remarkably, Hg₃ O₂ SO₄ exhibits a very large SHG response (14 times that of KH₂ PO₄ ), which is the strongest efficiency among all the reported nonlinear optical sulfates. Detailed theoretical calculations confirm that the employment of highly polarizable Hg²⁺ is an effective strategy to design superior optical materials with large birefringence and strong SHG response.

A New Nonlinear Optical Material with N(CN)2 - Anion

Discovering new functional genes and developing high-performance materials are the goals being pursued by scientists. In this work, we successfully obtained a second-order nonlinear optical (NLO) material via the aqueous solution method, Y[N(CN)₂ ]₄ [NH(C₂ H₅ )₃ ] ⋅ 3H₂ O, which is the first NLO material with the anionic group N(CN)₂ ^- . Remarkably, this material is not only strongly NLO-active at 1064 nm with a response of about 2.8 × KH₂ PO₄ , but also possesses a short UV absorption edge of 250 nm. In-depth first-principles calculations illustrate well that the optical properties are mainly from the strong interaction of N, C and Y atoms. This result indicates that the N(CN)₂ ^- anion may be a new NLO functional gene. This work enriches the diversity of NLO functional genes and materials.

Li2 MTeO6 (M=Ti, Sn): Mid-Infrared Nonlinear Optical Crystal with Strong Second Harmonic Generation Response and Wide Transparency Range

Oxide crystals have been widely used in nonlinear optics (NLO) in the ultraviolet-visible and near-infrared regions. Most traditional oxide crystals are restricted to the mid-infrared region due to their narrow transmission window. Hence, attempting to extend infrared cutoff wavelength of oxides has attracted much attention. Herein, we report two new tellurates Li₂ TiTeO₆ (LTT) and Li₂ SnTeO₆ (LST) with broad transparent regions of 0.38-6.72 and 0.38-6.86 μm, respectively, as excellent candidates for mid-infrared NLO applications. Both LTT and LST crystallize in the orthorhombic space group Pnn2. The LTT crystal exhibits intense powder second-order generation efficiency (26×KDP) under the fundamental wavelength of 1064 nm. First-principles calculations and dipole moments were used to illustrate the results of the powder second-harmonic generations based on the crystal structures. Our results provide a novel oxide NLO crystal with a strong SHG and wide transparency range. They also pave a way for the design of new oxide mid-IR NLO crystals.

Li4 MgGe2 S7 : The First Alkali and Alkaline-Earth Diamond-Like Infrared Nonlinear Optical Material with Exceptional Large Band Gap

Large band gap and strong nonlinear optical (NLO) effect are two valuable but contradictory parameters, which are difficult to balance in one infrared (IR) NLO material. Herein, the first alkali and alkaline-earth metal diamond-like (DL) IR NLO material Li₄ MgGe₂ S₇ , presenting a honeycomb-like 3D framework constructed by 6-membered LiS₄ rings and GeMgS₆ zigzag chains, was rationally designed and synthesized. The introduction of rigid alkali metal and alkaline-earth metal LiS₄ and MgS₄ tetrahedra effectively broadens the band gap of DL compound to 4.12 eV (the largest one in the reported quaternary metal chalcogenides), generating a high laser damage threshold of 7 × AgGaS₂ at 1064 nm. Furthermore, Li₄ MgGe₂ S₇ displays a suitable SHG response (0.7 × AgGaS₂ ) with a type I phase-matching behavior. The results indicate that Li₄ MgGe₂ S₇ is a promising IR NLO material for the high-power laser application and it provides an insight into the design of new DL compound with outstanding IR NLO performances.

Cs2ZnSn3S8: A Sulfide Compound Realizes a Large Birefringence by Modulating the Dimensional Structure

Birefringence, an important optical performance parameter for optoelectronic functional materials, is mainly influenced by the types of anion groups and their spatial arrangement. Inspired by the relationship between the structure and properties of chalcogenides, combined with the dimensional transformation, we successfully synthesized a sulfide compound (Cs₂ZnSn₃S₈) with a two-dimensional layered structure and a large birefringence. The experimental results showed that, compared with Rb₁₀Zn₄Sn₄S₁₇, Cs₂ZnSn₃S₈ achieved the structural transition from a zero-dimensional arrangement to a two-dimensional lamellar arrangement and achieved a breakthrough of birefringence from 0 to 0.12, which was determined by both experiments and first-principles calculations. These findings demonstrated that Cs₂ZnSn₃S₈ was a potential birefringent material and provided instructions for the study of the synthesis of birefringent materials.