Ab initio and experimental investigations of the electronic and optical properties of pure and p-Aminopyridine-intercalated In1.2Ga0.8S3

The electronic and optical properties of pure and p-Aminopyridine-intercalated In_1.2Ga_0.8S₃ crystals were investigated using absorption and photoluminescence spectroscopy, and density functional theory. From the first principles calculation, we determined the band gap energy, nature of the chemical bonds, and dielectric functions of In_1.2Ga_0.8S₃. Band structure calculations reveal that the valence band maximum (VBM) and conduction band minimum (CBM) are both located at the high-symmetry point Γ, indicating that In_1.2Ga_0.8S₃ is a direct-gap semiconductor with a band gap of approximately 2.35 eV. From the projected density of states analysis, it is evident that the VBM primarily originates from the p-states of the S atom, while the CBM is mainly derived from the s-states of the Ga, In1, and In2 atoms. Furthermore, there is strong hybridization between the s- and p-states of the Ga atom and the s- and p-states of the In1 atom, respectively. The optical absorption and photoluminescence spectra of pure (unintercalated) and intercalated crystals were investigated experimentally at various temperatures. A significant increase in luminescence intensity was observed in the intercalated crystals. The absorption spectra indicate that intercalation with p-Aminopyridine increases the band gap by 0.14 eV compared to the pure crystal. Additionally, photoluminescence measurements show that the luminescence intensity of the intercalated compound is higher than that of the pure compound.