Denysyuk N. Electronic structure and optical properties of APb2X5 and Tl3PbX5 (A = K, Rb, Tl; X = Cl, Br, I) compounds, prospective materials for non-linear optics

Thesis for the candidate degree in physics and mathematics according in specialty 01.04.07 - solid state physics. - Frantsevich Institute for the Problem of Materials Science of NASU, Kyiv, 2016. Studies of the electronic structure and optical properties of the APb2X5 and Tl3PbX5 (A = Tl, K, Rb; X = Cl, Br, I) halides, prospective materials for non-linear optics, have been made in the thesis. In particular, based on density functional theory (DFT), the calculations have been performed using the full potential linearized augmented plane wave (FP-LAPW) and augmented plane wave -local orbitals (APW-LO) methods in order to obtain total and partial densities of states of the atoms constituting the APb2X5 and Tl3PbX5 compounds. The calculations indicate that the investigated halides are indirect-gap semiconductors and the Х p-like states are the principal contributors to the valence band (in its upper and central parts) of the TlPb2X5 and Tl3PbX5 compounds. The bottom of the valence band is formed mainly from contributions of the Pb 6s- and Tl 6s-states while the unoccupied states Pb 6р-states are the principal contributors to the bottom of the conduction band of the TlPb2X5 i Tl3PbX5 compounds, with significant contributions of the Х р*-states as well. In the present thesis the X-ray photoelectron core-level and valence-band spectra of the APb2X5 and Tl3PbX5 halides have been measured as well as the X-ray emission bands representing the energy distributions of the Br 4p- and K 4s states has been recorded for the KPb2Br5 and RbPb2Br5 bromides. The XPS results indicate the low hygroscopicity and high chemical stability of the АPb2X5 і Tl3PbX5 surfaces.