Second Harmonic Generation and Hyperpolarizabilities of the Double-Cubane Compound [Sb7S8Br2](AlCl4)3: Chalcogenide in Ionic Liquids

Because noncentrosymmetric [Sb7S8Br2](AlCl4)(3) single crystals possess a wide optical transparency region, it is a promising material for nonlinear optical applications. We have calculated the dispersion of linear and nonlinear optical susceptibilities including optical second harmonic generation (SHG) using a relaxed geometry. We find that the fundamental optical absorption edge situated at about 2.03 eV is in excellent agreement with the experimental data. Calculations of epsilon(xx)(2)(omega), epsilon(yy)(2)(omega), and epsilon(zz)(2)(omega) tensor components of the frequency-dependent dielectric function are presented. The single crystal possesses a considerable anisotropy of linear optical susceptibilities, which usually favors an enhanced phase matching conditions necessary to observe SHG and optical parametric oscillator (OPO) effects. Our calculations show that, in [Sb7S8Br2](AlCl4)3, vertical bar chi((2))(123)(omega)vertical bar is the principal tensor component having the highest value of SHG at zero frequency limit as well as at 1.165 eV (lambda = 1064 nm) laser wavelength generation. The microscopic second-order hyperpolarizability, beta(123), of the dominant SHG component is calculated at the static limit and at lambda = 1064 nm.