Transition-metal-based chalcogenides: A rich source of infrared nonlinear optical materials

The developments of new infrared nonlinear optical (IR-NLO) crystals with excellent comprehensive performance are urgently needed owing to the current commercially available materials (e.g., AgGaS2, AgGaSe2, and ZnGeP2) possess their inevitable disadvantages which limited significantly their high-power laser applications. The class of transition-metal-based chalcogenides is the most favorable source of promising IR-NLO candidates with rich structural diversity and broad IR transparent windows. Moreover, most of them can intrinsically meet many vital requirements for ideal IR-NLO crystals, such as phase-matching (PM) features, strong second harmonic generation (SHG) responses, high laser induced damage thresholds (LIDTs), low melting points and wide energy gaps. However, there has not been a comprehensive survey on this attractive family. In this review, these existing transition-metal-based chalcogenides are divided into three groups according to their chemical compositions, and the dimensionality–bandgap–NLO property relationship for the 36 representative series (including 6 crystal systems, 34 space groups and >500 non-centrosymmetric chalcogenides) has been compared and summarized in detail. In addition, current problems and future development of this field are also proposed. Finally, we hope this review could provide some inspirations and help to the chemists and material scientists to design and synthesis high-performance transition-metal-based chalcogenides for IR-NLO applications.