Li₄MgGe₂S₇: The First Alkali and Alkaline‐Earth Diamond‐Like Infrared Nonlinear Optical Material with Exceptional Large Band Gap

Abstract

Abstract Large band gap and strong nonlinear optical (NLO) effect are two valuable but contradictory parameters, which are difficult to balance in one infrared (IR) NLO material. Herein, the first alkali and alkaline‐earth metal diamond‐like (DL) IR NLO material Li 4 MgGe 2 S 7 , presenting a honeycomb‐like 3D framework constructed by 6‐membered LiS 4 rings and GeMgS 6 zigzag chains, was rationally designed and synthesized. The introduction of rigid alkali metal and alkaline‐earth metal LiS 4 and MgS 4 tetrahedra effectively broadens the band gap of DL compound to 4.12 eV (the largest one in the reported quaternary metal chalcogenides), generating a high laser damage threshold of 7 × AgGaS 2 at 1064 nm. Furthermore, Li 4 MgGe 2 S 7 displays a suitable SHG response (0.7 × AgGaS 2 ) with a type I phase‐matching behavior. The results indicate that Li 4 MgGe 2 S 7 is a promising IR NLO material for the high‐power laser application and it provides an insight into the design of new DL compound with outstanding IR NLO performances.