DFT-investigation on anisotropy degree of electronic, optical, and mechanical properties of olivine ZnRE₂S₄ (RE = Er, Tm) compounds

Using PP-APW method the electronic, optical and mechanical anisotropy of ZnRE₂S₄ (RE=Er, Tm) olivine compounds was investigated. The calculated unit cell parameters are in good agreement compared to the experimental ones. In addition, the study of electronic properties reveals that ZnEr₂S₄ and ZnTm₂S₄ are semiconductors with a direct bandgap of about 2.37 eV and 2.35 eV, respectively. The optical constants such as refractive index, reflectivity, and absorption coefficient have been calculated and analyzed. These constants show a clear anisotropy in the UV region for both compounds caused by the different electron polarizability in x−, y− and z−direction. Moreover, the elastic constants are estimated for the first time for ZnEr₂S₄ and ZnTm₂S₄ indicating that the compounds are mechanically stable and reveal ductility behavior. The direct bandgap, optical absorption, and mechanical stability make ZnEr₂S₄ and ZnTm₂S₄ promising candidates for optoelectronic application. (paper)