Spin-polarized physical properties of Eu-doped CaSiO₃: A first-principles study

Rare-earth-doped silicates have emerged as robust multifunctional materials owing to their structural stability and tunable electronic properties. In this work, a comprehensive spin-polarized first-principles investigation of Eu-doped CaSiO₃ is carried out within the GGA + U framework to elucidate its electronic, optical, mechanical, thermodynamic, and thermoelectric behavior. Substitutional incorporation of Eu at Ca sites is found to be energetically favorable and dynamically stable, consistent with experimentally reported single-phase Eu-activated CaSiO₃ phosphors. The electronic structure reveals pronounced spin asymmetry: the spin-up channel exhibits a finite band gap characteristic of a semiconductor, whereas the spin-down channel remains metallic. This spin-resolved electronic structure corresponds to half-metallic behavior, where semiconducting character appears only in one spin channel, leading to near-complete spin polarization at the Fermi level. Optical calculations show strong ultraviolet absorption and spin-dependent dielectric response originating from transitions involving localized Eu-derived states, in agreement with experimentally observed host-to-dopant energy transfer and red Eu³⁺ luminescence in CaSiO₃-based phosphors. Mechanical and thermodynamic analyses confirm elastic stability, moderate ductility, and excellent thermal robustness, providing a microscopic explanation for the experimentally observed resistance to thermal quenching. The calculated transport coefficients indicate trends that may be favorable for thermoelectric behavior; however, a full evaluation of the thermoelectric figure of merit (ZT) is beyond the scope of the present study. The theoretical predictions are critically discussed in light of available experimental structural, optical, and spectroscopic data, demonstrating strong consistency with reported synthesis and luminescence behavior. These results indicate that Eu-doped CaSiO₃ exhibits properties that may be relevant for optoelectronic, thermoelectric, and spin-dependent materials, although further experimental and device-level studies are required.