A comprehensive review on metal chalcogenides with three-dimensional frameworks for infrared nonlinear optical applications

Second-order infrared nonlinear optical (IR-NLO) crystals are of great scientific and technological significance because of the ability to produce coherent tunable laser irradiation in the IR regions. Nowadays, the intrinsic problems in these traditional commercial IR-NLO crystals include AgGaS2, AgGaSe2, and ZnGeP2 have severely limited their further applications in modern laser technology, especially in the high-power and high-efficiency laser fields. Therefore, exploring novel IR-NLO candidates with excellent overall performance is the frontier and focus of related research fields. Notably, metal chalcogenides with three-dimensional (3D) frameworks have drawn extensive concern as a family of important IR-NLO candidates owing to their intriguing architectures and attractive optical properties. However, a comprehensive review on this IR-NLO family is absent to date. In this review, the reported metal chalcogenides are divided into six categories according to different types of filled cations, including (i) alkali-metal-based IR-NLO chalcogenides; (ii) alkaline-earth-metal-based IR-NLO chalcogenides; (iii) rare-earth-metal-based IR-NLO chalcogenides; (iv) lone-pair-cation-based IR-NLO chalcogenides; (v) polycation-based IR-NLO chalcogenides; and (vi) mixed-cation-based IR-NLO chalcogenides. The syntheses, crystal structures and the intrinsic structure-activity relationships for >200 non-centrosymmetric chalcogenides (including 7 crystal systems, 32 space groups and 51 representative compositions) have been systematically summarized and analyzed. Finally, some helpful guidance for the further exploration and design of novel IR-NLO 3D chalcogenide frameworks in the future is also provided.