Frequency dependent linear and nonlinear optical properties of compositionally tuned inorganic CsSnX (X = Br, I) composites

Abstract

Structural, electronic and optical properties of CsSnX (X = Br, I) system have been thoroughly investigated by means of an unbiased crystal structure screening, density functional theory and perturbation approach. Crystallography of known parent structures, CsI and CsBr were well replicated compared to experimental observations. Experimentally verified cubic Cs2SnI6 phase was operatively reproduced. Its computed crystal class and simulated XRD pattern match the available experimental data, hence signifying the robustness of methodology applied. Other energetically and dynamically stable structures include cubic Cs2SnBr6, triclinic Cs2Sn2Br6 and Cs2Sn2I6. These phases are direct semiconductors which exhibit non-monotonic association between GW corrected band gap and halogen type or atomic mass. Instead, their energy gap is determined by the structure of CsSn halide compounds, and span an energy range from mid infrared to near ultraviolet region. The GW-raised gap was incorporated as scissor shift to ensure good reliability of optical calculations. Dynamical dielectric function, adsorption coefficient, energy-loss and refractive index spectrum of aforementioned phases were acquired. Both novel Cs2Sn2Br6 and Cs2Sn2I6 phases have impressive zero limit second-order susceptibility ranging from 3.1 p.m. V−1 to 22.8 p.m. V−1.