Aliovalent-cation-substitution-induced structure transformation: a new path toward high-performance IR nonlinear optical materials

Non-centrosymmetric (NCS) structure is the precondition and foundation for the development of high-performance nonlinear optical (NLO) crystals. In this research, a quaternary NCS thioantimonate, K 2 Ag 3 Sb 3 S 7 , is designed through an aliovalent-cation-substitution-induced strategy based on the centrosymmetric (CS) parent compound K 2 Sb 4 S 7 and successfully obtained through a facile surfactant-thermal technology. The unique crystal structure of K 2 Ag 3 Sb 3 S 7 belongs to the orthorhombic space group Cmc 2 1 (no. 36) and is made of charge-balanced K + cations and two-dimensional (2D) anionic layers [Ag 3 Sb 3 S 7 ] 2− constructed by the vertex-sharing of ∞ [Ag 3 SbS 5 ] 4− and ∞ [SbS 2 ] − chains. Remarkably, K 2 Ag 3 Sb 3 S 7 not only possesses a phase-matching (PM) ability in the IR region, but also displays a perfect balance between a high second-harmonic-generation (SHG) coefficient (1.5 × commercial AgGaS 2 ) and a large laser-induced damage threshold (3.2 × commercial AgGaS 2 ). Moreover, theoretical studies uncover that the synergistic effects of three types of asymmetric building motifs ( i.e. , [SbS 3 ], [Sb 2 S 5 ] and [Ag 3 S 6 ]) contribute to the large SHG effect and birefringence (Δ n ). This study not only demonstrates that aliovalent cation substitution can be a robust means of obtaining the NCS thioantimonates but also provides a deeper insight into the structure-property relationship of IR-NLO chalcogenides. A quaternary IR-NLO thioantimonate, K 2 Ag 3 Sb 3 S 7 , designed using an aliovalent-cation-substitution-induced (ACSI) strategy based on the centrosymmetric K 2 Sb 4 S 7 is reported.