Nonlinear optical properties of a new polar bismuth tellurium oxide fluoride, Bi3F(TeO3)(TeO2F2)3

Abstract

A novel noncentrosymmetric polar bismuth tellurium oxide fluoride, Bi3F(TeO3)(TeO2F2)3, has been hydrothermally synthesized by using Bi2O3, TeO2, and HF solution at 230 °C. The structural backbone of Bi3F(TeO3)(TeO2F2)3 is composed of several polyhedra with lone pair cations, such as BiO6F3, TeO2F2, and TeO3. The asymmetric geometric features found from the polyhedra of Bi3+ and Te4+ should be attributed to the lone pairs on the cations. The overall framework of Bi3F(TeO3)(TeO2F2)3 can be considered as a three-dimensional hexagonal tungsten oxide-like topology. The UV–vis diffuse reflectance spectral data suggest that the title compound has a wide band gap of ca. 3.85 eV due to the distortions of the asymmetric units, as well as the electronegative fluoride anions. Second-harmonic generation (SHG) measurements using a 1064 nm radiation indicate that Bi3F(TeO3)(TeO2F2)3 reveals a nonphase-matching behavior and ca. 9 times larger SHG counts than that of α-SiO2. The near-static value of the second-order nonlinear optical susceptibility, χS(2), of the reported compound is calculated to be ca. 5.1 ± 0.6 pm/V. The wavelength-dependent SHG measurements indicate that the SHG counts of Bi3F(TeO3)(TeO2F2)3 decrease as the excitation wavelength increases from 1064 to 1600 nm.