BaAl4Se7: A new infrared nonlinear optical material with a large band gap

摘要

The new compound BaAl4Se7 has been synthesized by solid-state reaction. It crystallizes in the non-centrosymmetric space group Pc and adopts a three-dimensional framework built from AlSe4 tetrahedra and with Ba2+ cations in the cavities. The material has a large band gap of 3.40(2) eV. It melts congruently at 901 °C and exhibits a second harmonic generation (SHG) response at 1 μm that is about half that of AgGaS2. From a band structure calculation, BaAl4Se 7 is a direct-gap semiconductor with strong hybridization of the Al 3s, Al 3p, and Se 4p orbitals near the Fermi level. The calculated birefractive index is about 0.05 for wavelength longer than 1 μm and major SHG tensor elements are: d15 = 5.2 pm V-1 and d13 = 4.2 pm V-1.