[Na2PbI][Ga7S12]: Combining Diamond-Like Anionic Framework with Polycationic Chain toward Achieving Remarkable Nonlinear Optical Response

The diamond-like structure is characterized by the well-arranged parallel tetrahedral units, which hold significant importance for infrared nonlinear optical (NLO) applications. By employing an unconventional substitution strategy, a diamond-like ZnS (sphalerite) template was utilized to replace the several Zn_xS_y tetrahedra with one-dimensional [Na₂PbI] infinite chains, resulting in the successful design and synthesis of a salt-inclusion sulfide, [Na₂PbI][Ga₇S₁₂] (1). Remarkably, the highly parallel-oriented [Ga₇S₁₆] double T₂-supertetrahedron units and the presence of Pb²⁺-centered polyhedra contribute to its exceptional second-harmonic generation (SHG) intensity (2.6 × AgGaS₂@1800 nm), belonging to the top-performing in salt-inclusion chalcogenides. Furthermore, compound 1 possesses an appropriate band gap (E_g = 2.53 eV) and exceeds the two-photon absorption of 1064 nm, mainly resulting in a high laser-induced damage threshold (LIDT, 3.6 × AgGaS₂). Particularly, phase 1 achieves a phase-matching ability (birefringence: 0.069) that template α-ZnS cannot possess. These characteristics indicate that this unconventional substitution strategy provides insights into the design of excellent diamond-like NLO compounds.