Excellent Nonlinear Optical M[M₄Cl][Ga₁₁S₂₀] (M = A/Ba, A = K, Rb) Achieved by Unusual Cationic Substitution Strategy

Abstract The typical chalcopyrite AgGaQ₂ (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 [[SZn₄]S₁₂ + [S₄Zn₁₃]S₂₄ + 11ZnS₄ ⇒ MS₁₂+ [M₄Cl]S₂₄ + 11GaS₄], in which the covalent S_xZn_y units in the diamond‐like sphalerite ZnS are synergistically replaced by cationic M_xCl_y units, resulting in two novel salt‐inclusion sulfides, M[M₄Cl][Ga₁₁S₂₀] (M = A/Ba, A = K, 1; Rb, 2). As expected, the introduction of mixed cations in the GaS₄ anionic frameworks of 1 and 2 leads to wide band gaps (3.04 and 3.01 eV), which exceeds the value of AgGaS₂, facilitating the improvement of high LIDTs (9.4 and 10.3 × AgGaS₂@1.06 µm, respectively). Furthermore, compounds 1 and 2 exhibit moderate second‐harmonic generation intensities (0.84 and 0.78 × AgGaS₂@2.9 µm, respectively), mainly originating from the orderly packing tetrahedral GaS₄ 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.