Laporte Selection Rule Induced the Suppression of d ‐ d Transitions and Vacancies Enhanced the Second Harmonic Generation in I 4¯‐MnGa 2 S 4

The d ‐ d transitions lead to strong orbital hybridization near the band edge, decreasing the band gap ( E g ) for magnetic transition metal chalcogenides. The small E g seriously limits the high laser‐induced damage threshold (LIDT) of the mid‐infrared (IR) nonlinear optical (NLO) crystal. Herein, a quasi‐centrosymmetric (quasi‐CS) [MnS 4 ] tetrahedron is proposed to suppress the d ‐ d transitions by the Laporte selection rule in I ‐MnGa 2 S 4 for the first time, leading to the largest E g of 3.43 eV in magnetic transition metal NLO sulfides. The partial density of states calculations indicate that the Mn‐3 d orbital hardly contributes to the optical transitions in [MnS 4 ] tetrahedron. Meanwhile, the consistent arrangement of tetrahedral motifs and cation vacancies in defect chalcopyrite I ‐MnGa 2 S 4 improve the second harmonic generation (SHG) response. As a result, the I ‐MnGa 2 S 4 possesses a large SHG response of 2.1 × AgGaS 2 (AGS) and a high polycrystalline LIDT of 8.15 × AGS. In addition, the isomorphic solid‐solution I ‐MnGa 2 Se x S 4− x ( x = 1, 2, 2.8, and 4) exhibit an enhanced SHG response of 4.6 × AGS for I ‐MnGa 2 Se 4 .