Exploring the Structural, Optoelectronic, Transport, and Radiation Shielding Capabilities of Al-based Chalcogenides for Energy Technologies: Spin Polarized Approach

Abstract

Chalcogenides represent a versatile class of materials with diverse properties, enabling their application in a broad range of technologies, including solar cells, LEDs, superconductors, magneto-resistive devices, and topological insulators. In this study, the structural, electronic, optical, phononic, and radiation-related properties of XAl₂S₄ (X = Eu, Fe, Rh) compounds were investigated using first-principles density functional theory (DFT). The electronic properties reveal a semiconducting nature with bandgaps in the range of 1.2–3.4 eV. The computed negative formation energy and phonon calculations confirm phase stability. Analysis of the density of states highlights the specific electronic states contributing to the band structure. The density of states (DOS) analysis for XAl₂S₄ (X = Eu, Fe, Rh) compounds identifies the electronic states contributing to the band structure. The valence band is mainly influenced by S-3p orbitals and X-d states, while the conduction band is predominantly shaped by Al-3p and X-d orbitals. The interaction between X-d and S-3p states plays a significant role in defining the bandgap and electronic transitions. These findings highlight the key contributions of localized and hybridized states in determining the semiconducting nature of these materials, with bandgaps ranging from 1.2 to 3.4 eV. Optically, the reflectivity remains around 30% below 12.0 eV and reaches a maximum of 32% at approximately 13.0 eV. The compounds demonstrate strong potential for radiation shielding, attributed to their high-density elements and effective absorption properties. Notably, the strong optical anisotropy of these materials suggests their potential for polarization-sensitive photodetector applications. The Seebeck coefficient is positive, indicating the properties of a p-type semiconductor with the highest power factor is approximately 2.0 × 10¹¹ W m⁻¹ K⁻². At 600 K, the thermoelectric figure of merit ZT reaches its maximum value of 1.2. These findings indicate that XAl₂S₄ compounds are promising candidates for optoelectronic devices and LED technologies, particularly as green phosphors for energy applications. Radiation shielding analysis reveals that the EuAl₂S₄ compound achieves a mass attenuation coefficient of 0.145 cm²/g at 1 MeV, surpassing conventional materials like lead-based shields in low-energy regimes.