Core-level excitation in polymorph of AS2S3 and β-In2S3

X-ray absorption near-edge structure (XANES) is one of the most widespread spectroscopies for studying the chemical properties of materials. It is a sensitive probe of the atomic environment, because it can be used to effectively measure the transition probability between core electrons and unoccupied states. In this paper, single level excitonic effects on the core state of the polymorph of As2S3 and tetragonal In2S3 were studied using X-ray absorption spectroscopy. Our results for the first time show striking similarities in Arsenic L3 (s, d)-edges peaks for the two phases of As2S3 orpiment and anorpiment crystals. Optical absorption increases mostly due to core-hole for S K (p) and As L3-edges in orpiment as compared to the other structures. The core-level calculations for these orbitals show good agreement with the experimental ones thus validating the approach used in this study. In orpiment and anorpiment, an indirect energy band gap which has been improved by the mBJ potential to about 1.03 eV and 0.65 eV respectively was observed. We have calculated the imaginary dielectric function and the absorption coefficient with the mBJ potential and core-hole, the optical excitations, is observe to be enhance by core level spectroscopy for all the crystals. Furthermore, the bond length and angles of monoclinic and triclinic As2S3 as well as the beta-phase In2S3 compared well with the experimental results. Structural optimization and total energies of all structures are computed using the all electrons full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) within the framework of DFT.