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Metal sulfides with diamond-like (DL) structures are systematically investigated in this study for nonlinear optical (NLO) applications in the mid-infrared (mid-IR) spectral region. All the selected materials are characterized by a 3D framework connected by various sulfide tetrahedral units, such as [PS 4 ], [SiS 4 ], [GeS 4 ], [GaS 4 ], [InS 4 ], [CdS 4 ], [ZnS 4 ], [LiS 4 ], and [AgS 4 ]. The linear and nonlinear optical properties of these materials are analyzed on the basis of first-principles calculations. It is concluded that it is relatively easy to achieve good balance between the bandgap and the NLO effect. Additionally, moderate birefringence Δn (∼0.03–0.10) is required for practical mid-IR NLO applications. In particular, several metal sulfides with normal DL and defect DL structures, exhibiting superior mid-IR NLO properties, are highlighted. These provide an instructive guide for the design and discovery of new materials with good mid-IR NLO performance. [ABSTRACT FROM AUTHOR]

Highlights • This is the first systematic review for NLO metal halides. • The relationships between microscopic structures and NLO performances in NLO metal halides are summarized and analyzed. • The development prospects for NLO metal halides are discussed. Abstract Infrared (IR) nonlinear optical (NLO) materials are of current interest owing to their technological applications in many military and civil fields. Metal halides are among the most favorable candidates for IR laser frequency conversion owing to their relatively large NLO effects, wide IR transparency and high laser damage thresholds (LDT). However, the comprehensive review for metal halides NLO materials is absent. Herein, we focus on the relationship between the structural features and NLO performances in the reported metal halide NLO materials. In particular, metal halides are classified according to the NLO-active [ MX k ] anionic units and NLO-active cations, i.e. , they are sorted into traditional metal halides containing linear units, triangle pyramidal units, tetrahedral units, rectangular pyramidal units, five-coordinated pseudo-octahedra, six- and more-coordinated polyhedral units, organic-inorganic and supramolecular metal halides. The determination rules of these microscopic structures on NLO properties in metal halides are summarized and analyzed on the basis of the combination of available experimental data and first-principles results. From the deduced structure-property relationship, the development prospects for NLO metal halides are discussed. [ABSTRACT FROM AUTHOR]

Abstract: KBe2BO3F2 (KBBF) is still the only practically usable crystal that can generate deep‐ultraviolet (DUV) coherent light by direct second harmonic generation (SHG). However, applications are hindered by layering, leading to difficulty in the growth of thick crystals and compromised mechanical integrity. Despite efforts, it is still a great challenge to discover new nonlinear optical (NLO) materials that overcome the layering while keeping the DUV SHG available. Now, two new DUV NLO beryllium borates have been successfully designed and synthesized, NH4Be2BO3F2 (ABBF) and γ‐Be2BO3F (γ‐BBF), which not only overcome the layering but also can be used as next‐generation DUV NLO materials with the shortest type I phase‐matching second‐harmonic wavelength down to 173.9 nm and 146 nm, respectively. Significantly, γ‐BBF is superior to KBBF in all metrics and would be the most outstanding DUV NLO crystal. [ABSTRACT FROM AUTHOR]