Single crystal growth and the electronic structure of orthorhombic Tl_3PbBr_5: A novel material for non-linear optics

摘要

The X-ray photoelectron core-level and valence-band spectra for pristine and Ar~+-ion irradiated surfaces of a Tl_3PbBr_5 single crystal grown by the Bridgman-Stockbarger method have been measured. The present X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of Tl_3PbBr_5 single crystal surface. Total and partial densities of states of constituent atoms of low-temperature (LT) orthorhombic Tl_3PbBr_5 phase (space group P2_12_12) have been calculated using the full potential linearized augmented plane wave (FP-LAPW) method. The FP-LAPW data reveal that contributions of the Br 4p-like states dominate in the valence band of LT-Tl_3PbBr_5; they contribute mainly into the top and the central portion of the valence band with also significant contributions throughout the whole valence-band region. The bottom of the valence band of LT-Tl_3PbBr_5 is composed mainly of the Tl 6s-like states, whilst the unoccupied Pb 6p- and Tl 6p-like states dominate at the bottom of the conduction band. We have explored the crystallochemistry and origin of the chemical bonds in Tl_3PbBr_5 with respect to the use as mid-IR non-linear optical crystals. Comparison of the spectral dependence to the second order susceptibilities for the titled crystals is performed with respect to the 3.39 μm illuminated crystals. Possibility of the use of TI_3PbBr_5 crystals as IR operated non-linear optical crystals is discussed.