AgGa2PS6: 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 (AgGaS2, AgGaSe2 and ZnGeP2) 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 PS4 tetrahedron was introduced into AgGaS2 (AGS), and that led to the isolation of the first compound in Ag-I-Ga-III-P-V-S system, namely, AgGa2PS6 (Cc). It retains a large SHG efficiency (1.0xAGS) with phase-matchable ability, and also exhibits an improved LDT (5.1xAGS), indicating AgGa2PS6 is a new promising MIR-NLO crystal. Moreover, a novel 3D framework of [Ga2PS6](-), with triangular-shaped channels, as well as interesting single triangular geometry of AgS(3)both of which are very rare in reported sulfideswas discovered in AgGa2PS6. Furthermore, theoretical calculations, and lattice energy and thermal expansions analyses suggest that the PS4 group makes a large contribution to the large SHG efficiency and high LDT.