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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]

• Single crystal structure of a novel ultraviolet NLO tourmaline was solved. • Sellmeier equations were obtained by fitting the measured refractive indices. • Phase matching range of the title crystal is obtained from the Sellmeier equations. • The linear and NLO properties were investigated by the experimental and theory calculation. Transparent tourmaline NaAl 9 (BO 3) 3 Si 6 O 21 OH is first reported by combining experimental and theory calculation methods, which exhibits potential ultraviolet nonlinear optical properties. [Display omitted] Tourmaline, as an important mineral, has received intensive interest, since it is not only a valuable gemstone, but also is a piezoelectric or pyroelectric material, due to the polar structural configuration. However, its nonlinear optical (NLO) properties were not explored so far, because a transparent crystal with high transmittance is scarce, being essential to optical functional materials. Here, we report a novel ultraviolet (UV) NLO tourmaline crystal with chemical composition NaAl 9 (BO 3) 3 Si 6 O 21 OH for the first time by combining first-principles analysis and experimental measurements. It exhibits a short UV absorption edge, considerable second harmonic generation effect and moderate birefringence, thereby facilitating its phase-matching coherent beam output in the range from visible to UV regions. [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]

[Display omitted] • Recent developments in mid-IR NLO materials utilizing f 0 rare earth chalcogenides (RE = Sc, Y, La) are reviewed. • The advantages of utilizing f 0 rare earth chalcogenides as mid-IR NLO materials are thoroughly analyzed. • Several useful conclusions and considerations for future research are presented. Mid-infrared (mid-IR) nonlinear optical (NLO) materials are extensively researched as a vital optoelectronic material family with widespread applications ranging from civil to military fields. Metal chalcogenides possess a wide range of IR transparency and vast structural diversity, making them ideal system for exploration of novel mid-IR NLO materials. Incorporating rare earth elements with 4 f 0 and 5 f 0 electrons, including Sc, Y, and La, into chalcogenide structures in mid-IR NLO materials has been actively studied in the recent years. In this review, we categorize all typical f 0 rare earth (RE = Sc, Y, La) chalcogenides in the inorganic crystal structure database based on their NLO functional groups. We then assess their energy band gaps, NLO coefficients, birefringence, IR cut-offs, and mechanical properties using available experimental data and first-principles results and investigate the correlation between structural features and mid-IR NLO performance. It is showed that the f 0 rare earth chalcogenides can possess suitable birefringence and NLO response for mid-IR NLO applications, while not compromising energy band gap, thus may have a well-balanced mid-IR NLO performance. The prospects of novel f 0 rare earth chalcogenides with favorable mid-IR NLO performance are also discussed. [ABSTRACT FROM AUTHOR]