Two Nonlinear Optical Thiophosphates Cu 5 Hg 0.5 P 2 S 8 and AgHg 3 PS 6 Activated by Their Tetrahedra-Stacking Architecture.

Infrared (IR) lasers are very critical in military and civil affairs, but it is also challenging and difficult to develop new infrared nonlinear optical (NLO) crystals. Herein, two new mixed-metal thiophosphates, Cu 5 Hg 0.5 P 2 S 8 and AgHg 3 PS 6 were discovered with the noncentrosymmetric (NCS) space group Pmn 2 1 (No. 31) and Cc (No. 9). Cu 5 Hg 0.5 P 2 S 8 displays a three-dimensional (3D) defective diamond-like structure stacked by ∞ 2 [Cu 2.5 Hg 0.25 PS 8 ] 8- layers. AgHg 3 PS 6 is characterized by a 3D framework consisting of distorted tetrahedrons. Moreover, the optical spectra show the band gaps of Cu 5 Hg 0.5 P 2 S 8 and AgHg 3 PS 6 are 2.12 and 1.85 eV, respectively, with a broad transparent range of 0.7-16.0 μm. In these two compounds, the dipole moments of nonlinear active units are strengthened due to the high-valence element P and the Hg-S bonds with large susceptibility. Therefore, AgHg 3 PS 6 exhibits a moderate second harmonic generation (SHG) response that is half that of AgGaS 2 (AGS) at 30-45 μm, while Cu 5 Hg 0.5 P 2 S 8 performs a phase-matching (PM) behavior with a good SHG signal of 0.8 × AGS at 150-200 μm. The origin of NLO performance and electronic structures were revealed by the calculated dipole moments of distorted tetrahedra and theoretical calculations on the basis of density functional theory.