DFT studies on optical properties of Hg3S2Br2 crystals and their possible applications in biomedical engineering

Abstract

The APW–LO technique as implemented in the WIEN2k package was employed to calculate the band structure, total and partial density of states, and the optical constants of Hg₃S₂Br₂.. The analysis of the band energy dispersion for Hg₃S₂Br₂ shows that the optical band gap is estimated to be roundly 2.69 eV. It is in satisfactory agreement with the experimental value of 2.9 eV. The essential contribution to the energy of the Hg-S bond adds to the hybridization of sulfur p orbitals that are oriented along the bond. However, some contribution to the bond between the [SHg₃] trigonal pyramids of the [Hg₃S₂Br₄] octahedra also came from the hybridization of p orbitals of sulfur atoms that form neighbor pyramids. DFT calculations show that four fine-structure particularities are detected in our computation of real and imaginary components of the dielectric function for Hg₃S₂Br₂.. Their energy positions in the case of ε1 (ω) dielectric function at about 5, 6.2, 7.5, and 10.3 eV, respectively. It should be noted, that energy positions in the case of the ε2 (ω) curve differ slightly. The computed real component of the dielectric function ε1 (ω) diminishes beginning from about 5.0 eV up to 6.5 eV. Whereas, the computed imaginary component of the dielectric function ε2 (ω) decreases gradually beginning from 7.2 eV and tends to be about null with enhancing photon energy. Based on studies of optical activity in the Hg₃S₂Br₂, it was found that the optical values and dispersion of rotatory ability are connected with the direct inter-band optical transitions [1-3]. Using the calculated dispersion of the real and the imaginary parts of the complex dielectric function, one can determine other optical properties such as absorption coefficient α(ω), refractive index n(ω), energy loss function L(ω) and reflectivity R(ω). The recent advances in optical devices have opened up new opportunities for sensing and biomedical imaging techniques. One of the main tasks of modern nanophysics is to develop new low-cost semiconductor materials for functional elements of medical devices with much-improved detection properties. This fact is very important for the qualitative formation of medical imaging. Hg₃S₂B r2 crystals are expected to contribute to the development of nanophysics and personalized medicine for health monitoring and prevention.