Achieving excellent nonlinear optical performance via “dimensionality elevation”-driven transformation from centrosymmetric to non-centrosymmetric structures

Achieving the second-order nonlinear optical (NLO) effect necessitates a non-centrosymmetric (NCS) structure, which is a prerequisite, but obtaining it effectively remains greatly challenging. In pursuit of this, a strategy known as “dimensionality elevation” has been operated to create a high-dimensional NCS framework based on a low-dimensional centrosymmetric (CS) structure. Concretely, the acentric [CdS 4 ] tetrahedral unit serves as a linkage point in the zero-dimensional (0D) [Si 4 S 10 ] T2-supertetrahedra, leading to the formation of the 3D NCS rigid sulfide, Cs 2 CdSi 4 S 10 ( 1 ), which exhibits moderate second-harmonic generation (SHG) effect (0.5 × AgGaS 2 @1.91 μm). To enhance the SHG coefficient, a structural modification has been made by replacing the Si-based framework with a Ga-based one and re-employing the “dimensionality elevation” strategy. This alteration prompted the tetrahedral [CdS 4 ] units to connect with 0D T2-supertetrahedral [Ga 4 S 10 ] motifs, creating the 3D NCS salt-inclusion chalcogenide [Ba 4 Cl 2 ][CdGa 4 S 10 ] ( 2 ). Notably, compared with 1 , compound 2 not only demonstrates an increased SHG response (1.3 × AgGaS 2 @1.91 μm) but also retains a broad band gap (3.74 eV for 1 and 3.50 eV for 2 ) for exceptional laser-induced damage thresholds (LIDTs, 9.3 × and 7.3 × AgGaS 2 @1.06 μm for 1 and 2 , respectively), suggesting that compound 2 is an advanced infrared NLO material. This research pioneers new pathways for discovering NCS NLO materials through the “dimensionality elevation” strategy.