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.

A new flux system, Li2O–MoO3, has been applied to growing BPO4 single crystals. Transparent BPO4 single crystals with sizes up to 31×18×16 mm3 have been successfully grown from the new flux by the top-seeded solution growth method. The viscosity of solution using this new flux decreased significantly compared with that of previously utilized Li4P2O7–Li2O flux. The solubility was measured and favorable concentration for BPO4 crystal growth was in the range of 55–64%. The powder SHG effect of as-grown BPO4 crystal was observed and its intensity was about twice as large as that of KDP. The laser damage threshold of BPO4 crystal at λ=1.064 nm and τ=8.0 ns is about 10.3 GW/cm2.