AgGa₂PS₆: A New Mid‐Infrared Nonlinear Optical Material with a High Laser Damage Threshold and a Large Second Harmonic Generation Response

Abstract

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, AgGa₂ PS₆ (Cc). It retains a large SHG efficiency (1.0×AGS) with phase-matchable ability, and also exhibits an improved LDT (5.1×AGS), indicating AgGa₂ PS₆ is a new promising MIR-NLO crystal. Moreover, a novel 3D framework of [Ga₂ PS₆ ]^- , with triangular-shaped channels, as well as interesting single triangular geometry of AgS₃ -both of which are very rare in reported sulfides-was discovered in AgGa₂ PS₆ . 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.