NaBa₄(GaB₄O₉)₂X₃ (X = Cl, Br) with NLO-Active GaO₄ Tetrahedral Unit: Experimental and ab Initio Studies

Two gallium borates, NaBa 4 (GaB 4 O 9 ) 2 X 3 (X = Cl, Br), were synthesized by high temperature solution method. The title compounds crystallize in the same space group P 4 2 nm . Their structures feature a 3D [GaB 4 O 9 ] ∞ framework composed of GaO 4 tetrahedra and B 4 O 9 groups. NaBa 4 (GaB 4 O 9 ) 2 X 3 (X = Cl, Br) compounds show the largest second harmonic generation responses among alkali metal and alkaline-earth metal gallium borates that are 1.5 and 1.1 times that of KH 2 PO 4 (KDP), respectively, and are type I phase-matchable. Combined electronic structure and SHG density calculations as well as local dipole moment analysis have revealed that B–O groups and GaO 4 tetrahedron play major roles in SHG response.