Ag[SC(NH₂)₂]₂F: A Laser Damage-Tolerant Infrared Nonlinear Optical Material

Mild hydrothermal reactions of π-conjugated SC(NH2)2, Ag(NO3), and NaF afforded a new prospective infrared (IR) nonlinear optical (NLO) crystal, namely, Ag[SC(NH2)2]2F. It shows a 3D open framework consisting of corner-sharing AgS4 tetrahedra with six-member ring tunnels that are filled by organic groups of the SC(NH2)2 molecules. Ag[SC(NH2)2]2F maintains 80% transmittance in the spectral region of 0.32–5.91 μm and features large second harmonic generation (SHG) responses with phase-matching at both 1064 nm (15.8 × KH2PO4) and 2.05 μm (0.7 × AgGaS2). It also exhibits a large band gap of 4.19 eV, resulting in a high laser-induced damage threshold (LIDT) of 9.3 times that of AgGaS2. Theoretical calculation revealed that SC(NH2)2, AgS4 tetrahedra, and F– anions all give the positive contribution to SHG effects. Ag[SC(NH2)2]2F overcomes the small band gap and low LIDT of tetrahedral-based chalcogenides while maintaining a large SHG response. This work gives a promising facile design strategy for IR NLO materials.