Inherent laws between tetrahedral arrangement pattern and optical performance in tetrahedron-based mid-infrared nonlinear optical materials

Abstract Mid-infrared (MIR) nonlinear optical (NLO) crystals are commonly used as the core devices for all-solid-state MIR lasers which play a key role in many military and civilian areas. The discovery of new MIR NLO crystals with great performance is vital for the development of relevant scientific and technology fields. In this work, we focus on the tetrahedron-based MIR NLO compounds with the chemical formula of A-M-Q (A = alkali or alkaline earth metal cations except Li; M = tetra-coordinated cations; Q = S, Se, Te, P, F, Cl, Br, I), whose structural frameworks are constructed by [MQ4] tetrahedral units. These materials have attracted great attention since almost all existing MIR NLO materials with the practical application prospects belong to this category. Systematic understanding of these tetrahedron-based compounds will contribute a lot to the design and preparation of novel well-performed MIR NLO crystals. We comprehensively reviewed the reported tetrahedron-based compounds A-M-Q for the first time and revealed the inherent laws among A/M ratio, arrangement pattern of tetrahedral units and NLO performance in these compounds.