BaGa4Se7: A New Congruent-Melting IR Nonlinear Optical Material

The new compound BaGa4Se7 has been synthesized for the first time. It crystallizes in the monoclinic space group Pc with a = 7.6252 (15) Å, b = 6.5114 (13) Å, c = 14.702 (4) Å, β = 121.24 (2)°, and Z = 2. In the structure, GaSe4 tetrahedra share corners to form a three-dimensional framework with cavities occupied by Ba2+ cations. The material is a wide-band gap semiconductor with the visible and IR optical absorption edges being 0.47 and 18.0 μm, respectively. BaGa4Se7 melts congruently at 968 °C and exhibits a second harmonic generation response at 1 μm that is approximately 2−3 times that of the benchmark material AgGaS2. A first-principles calculation of the electronic structure, linear and nonlinear optical properties of BaGa4Se7 was performed. The calculated birefractive indexΔn = 0.08 at 1 μm and the major SHG tensor elements are: d11 = 18.2 pm/V and d13 = −20.6 pm/V. This new material is a very promising NLO crystal for practical application in the IR region.