AgGa 2 PS 6 : A New Mid‐Infrared Nonlinear Optical Material with a High Laser Damage Threshold and a Large Second Harmonic Generation Response

To develop new mid‐infrared (MIR) nonlinear optical (NLO) materials, which can overcome the low laser damage threshold (LDT) of the commercial MIR‐NLO crystals (AgGaS 2 , AgGaSe 2 and ZnGeP 2 ) and simultaneously keep the large NLO susceptibility, is necessary for high‐power MIR laser frequency conversion technology. To improve the LDT, a new strategy of increasing lattice stability was adopted. Here, the strongly covalent structural unit of the PS 4 tetrahedron was introduced into AgGaS 2 (AGS), and that led to the isolation of the first compound in Ag I ‐Ga III ‐P V ‐S system, namely, AgGa 2 PS 6 ( Cc ). It retains a large SHG efficiency (1.0×AGS) with phase‐matchable ability, and also exhibits an improved LDT (5.1×AGS), indicating AgGa 2 PS 6 is a new promising MIR‐NLO crystal. Moreover, a novel 3D framework of [Ga 2 PS 6 ] − , with triangular‐shaped channels, as well as interesting single triangular geometry of AgS 3 —both of which are very rare in reported sulfides—was discovered in AgGa 2 PS 6 . Furthermore, theoretical calculations, and lattice energy and thermal expansions analyses suggest that the PS 4 group makes a large contribution to the large SHG efficiency and high LDT.