Ga-based IR nonlinear optical materials: Synthesis, structures, and properties

Infrared nonlinear optical (IR-NLO) crystals play a crucial role in the field of all-solid state lasers. They enable the generation of tunable coherent radiations through frequency conversion technology, which is urgently required for the advancement of numerous advanced sciences and technologies. Currently, the chalcopyrite-type AgGaS2, AgGaSe2, and ZnGeP2 are leading IR-NLO materials, but their applications are significantly restricted due to their inherent drawbacks. Therefore, exploring new promising IR-NLO crystals with excellent comprehensive performance is an urgent task that remains challenging. Benefiting from their diverse structure, wide IR transmission range, and adjustable optical performance, non-centrosymmetric Ga-based materials have garnered significant attention. Research on the IR-NLO properties of Ga-based chalcogenides began in 1971, resulting in the discovery of many Ga-based materials that exhibit exceptional IR-NLO performance. However, a comprehensive review of this field is currently lacking. In this review, Ga-based IR-NLO materials, which comprise over 200 reported chalcogenides and their derivatives, with 7 crystal systems and 34 space groups, are classified based on the assembly method of their Ga-based tetrahedral asymmetric units into five categories: (1) zero-dimensional (0D) molecular structures, (2) one-dimensional (1D) chain structures, (3) two-dimensional (2D) layer structures, (4) three-dimensional (3D) framework structures, and (5) mixed-dimensional (MD) structures. Furthermore, this review systematically summarizes and discusses the synthesis, crystal structures, and structure–property relationships of Ga-based materials. Additionally, valuable suggestions and opportunities for further exploration and development of novel Ga-based IR-NLO materials are addressed. This comprehensive review not only consolidates the existing knowledge but also lays the groundwork for broader research opportunities in the field of high-performance IR-NLO candidates.