Ag-based chalcogenides and derivatives as promising infrared nonlinear optical materials

Abstract

Infrared (IR) nonlinear optical (NLO) crystals with outstanding properties are crucial for extending the laser wavelengths through frequency conversion technology and have been employed in many fields such as civil industry, medicine, and military affairs. Among the studied IR NLO crystals, Ag-based chalcogenides are one of the most favorable candidates, not only owing to their compositional or structural relationship with the benchmark IR NLO materials AgGaS2 and AgGaSe2, but also due to their diverse structures, large NLO intensities, wide IR transparent regions, and suitable birefringences for phase matching. So far, many Ag-based chalcogenides and derivatives (AChDs) with prominent NLO properties have been reported; however, a systematic summary of them is absent, which is significantly needed to facilitate the ever-increasing research on IR NLO materials. Herein, we summarized AChDs by classifying the investigated materials into three groups, based on their chemical composition and expounding the chemical composition-NCS structure-NLO performance relationship. In this review, the following features of AChDs with IR NLO properties were summarized. (1) Quaternary Ag-based chalcogenides were much more abundant compared to the ternary ones. (2) Although Ag possessed various coordination modes (linear or V-shaped, triangular, and tetrahedral), AgQ4 tetrahedra were much more common than the AgQ2 and AgQ3 (Q = S, Se) units. (3) The cations of AChDs tended to construct one type of conventional IR NLO structural unit, namely, MQ4 tetrahedra (M = Zn, Cd, Hg, Ga, In, Si, Ge, Sn, P; Q = S, Se), making great contributions to the microscopic NLO responses. Finally, the exploration directions and development prospects of AChDs as promising IR NLO candidates were discussed from the deduced structure–property relationship.