First-Principles Study of Novel BaLnAgSe₃ (Ln = Er, Gd) Active UV-reflecting Materials for Optoelectronic and Thermoelectric Applications

Chalcogenides exhibit exceptional thermal performance and tunable optoelectronic characteristics. The structural, electronic, optical, and thermoelectric properties of novel BaLnAgSe₃ (Ln = Er, Gd) quaternary chalcogenides are studied by employing density functional theory. The predicted cohesive and formation energies of these materials confirm stability. Based on the band structure investigation, it was predicted that these materials possess a direct band gap nature. Results demonstrated that direct energy losses in both materials were caused by the hybridization of the Er-f, Ag-d, Se-p, and Gd-f orbitals. Because of its electronic structure and Er interactions, BaErAgSe₃ has a larger bandgap for the spin-up case. The constituents of the complex dielectric function and the other significant optical characteristics were investigated for their potential use in optoelectronic applications. Both UV and visible light are more strongly absorbed by these materials. These materials could also be principally useful UV-reflecting materials, as observed from the peaks in the reflection spectrum. In the complete temperature range, both materials exhibit p-type conductivity due to their positive Seebeck coefficient values.