AI2Mg3Ga12S22 (AI = K, Rb): T2-type supertetrahedra coupled with [MgS6] octahedra for designing wide-band gap infrared nonlinear optical materials with well-balanced properties

The simultaneous achievement of wide band gap and strong nonlinear optical (NLO) effect poses a challenging task in the development of infrared (IR) NLO materials. The coupling strategy of polyhedral building blocks has been demonstrated to be one of the effective approaches for constructing superior optical materials with well-balanced performance. Here, a new family of IR NLO materials A^I₂Mg₃Ga₁₂S₂₂ (A^I = K, Rb) that first contain [MgS₆] octahedra and T2-type supertetrahedra was designed and synthesized. K₂Mg₃Ga₁₂S₂₂ exhibits a wide band gap of 3.34 eV, and a moderate second-harmonic generation response intensity of 0.4 times that of AgGaS₂ under 2 µm Q-switched laser radiation. Furthermore, the birefringence of K₂Mg₃Ga₁₂S₂₂ is calculated to be 0.028@1064 nm, resulting in favorable phase-matching behavior in IR region. These characteristics suggest that K₂Mg₃Ga₁₂S₂₂ could be a promising material for nonlinear frequency conversion applications and it provides new ideas into the design of novel compounds with outstanding IR NLO performances.