Designing A New Infrared Nonlinear Optical Material, β-BaGa2 Se4 Inspired by the Phase Transition of the BaB2 O4 (BBO) Crystal.

Infrared nonlinear optical (IR NLO) crystals play a significant role in the development of IR laser technology. But rationally designing a new IR NLO crystal remains a huge challenge because of the unpredictability of inorganic structures. Herein, inspired by phase transformation of the famous BaB2 O4 (BBO) crystal, a temperature-induced centrosymmetric (CS) to noncentrosymmetric (NCS) transformation approach is employed in CS BaGa2 Se4 to uncover a new NCS ternary chalcogenide, β-BaGa2 Se4 which can exhibit the well-balanced NLO properties, including moderate phase-matching SHG response (≈0.6×AgGaS2 ), high LDT (10×AgGaS2 ), and large birefringence (Δn=0.18 in the visible region). Therefore, β-BaGa2 Se4 will be a promising IR NLO crystal. The analysis for the structure-property relationship shows that the excellent NLO properties of β-BaGa2 Se4 mainly originate from edge-sharing GaSe4 tetrahedral chains, which are different from B3 O6 groups in β-BBO and respect a new direction for the design of IR NLO crystals. So, we believe that the current research provides not only a new IR NLO crystal but also some insights for the design of new IR NLO crystals.