Excellent Nonlinear Optical M[M 4 Cl][Ga 11 S 20 ] (M = A/Ba, A = K, Rb) Achieved by Unusual Cationic Substitution Strategy.

The typical chalcopyrite AgGaQ 2 (Q = S, Se) are commercial infrared (IR) second-order nonlinear optical (NLO) materials; however, they suffer from unexpected laser-induced damage thresholds (LIDTs) primairy due to their narrow band gaps. Herein, what sets this apart from previously reported chemical substitutions is the utilization of an unusual cationic substitution strategy, represented by [[SZn 4 ]S 12 + [S 4 Zn 13 ]S 24 + 11ZnS 4 ⇒ MS 12 + [M 4 Cl]S 24 + 11GaS 4 ], in which the covalent S x Zn y units in the diamond-like sphalerite ZnS are synergistically replaced by cationic M x Cl y units, resulting in two novel salt-inclusion sulfides, M[M 4 Cl][Ga 11 S 20 ] (M = A/Ba, A = K, 1; Rb, 2). As expected, the introduction of mixed cations in the GaS 4 anionic frameworks of 1 and 2 leads to wide band gaps (3.04 and 3.01 eV), which exceeds the value of AgGaS 2 , facilitating the improvement of high LIDTs (9.4 and 10.3 × AgGaS 2 @1.06 µm, respectively). Furthermore, compounds 1 and 2 exhibit moderate second-harmonic generation intensities (0.84 and 0.78 × AgGaS 2 @2.9 µm, respectively), mainly originating from the orderly packing tetrahedral GaS 4 units. Importantly, this study demonstrates the successful application of the cationic substitution strategy based on diamond-like structures to provide a feasible chemical design insight for constructing high-performance NLO materials.