Growth, structure and optical properties of Tl sub(4)HgBr sub(6) single crystals

Tl[sub 4]HgBr[sub 6] single crystals were grown using solution-fusion method. The crystal structure of the ternary bromide was refined. Tl[sub 4]HgBr[sub 6] crystallizes in the non-centrosymmetric space group P4nc with the lattice parameters [alpha] = 8.9539(8) A and c = 8.7884(8) A and it is isostructural to the Tl[sub 4]HgBr[sub 6] compound. The non-centrosymmetric structure of the Tl[sub 4]HgBr[sub 6] compound was also confirmed by the existence of a modest second harmonic generation effect and by the value of piezoelectric coefficient. The electronic structure of Tl4HgBr6 was explored using X-ray photo-electron spectroscopy (XPS) and X-ray emission spectroscopy (XES). The measurements of spectral distribution of the absorption coefficient indicate that the Tl[sub 4]HgBr[sub 6] compound is a semiconductor with the band-gap energy value of 2.43 eV at 300 K, and the band-gap energy increases up to 2.48 eV when temperature decreases to 100 K.