Structural, optical, and electronic properties of europium orthophosphate: a combination of experimental and theoretical studies

Abstract

We report a combined experimental and first-principles DFT study of the electronic and optical properties of EuPO₄. A solid-state synthesis method was used to prepare europium orthophosphate powder. Structural characterization of the prepared phase was carried out using X-ray diffraction, confirming the purity of the compound. Rietveld refinement analysis confirmed that the monazite structure EuPO₄ crystallizes in the monoclinic space group P2₁/n. Optical properties were investigated through UV-visible diffuse reflectance measurements, and the absorption coefficient was analyzed using the Kubelka–Munk formalism and Tauc plots to extract the optical band gap. Additionally, UV-visible diffuse reflectance measurements revealed three distinct absorption features at 2.36 eV, 3.14–3.42 eV, and 3.91–4.17 eV, assigned to the ⁷F₀ → ⁵D₁, ⁷F₀ → ⁸L₆, and ⁷F₀ → ⁵H₄ intraconfigurational 4f–4f transitions, respectively. On the theoretical side, DFT calculations using the mBJ potential with spin–orbit coupling were performed to compute the band structure, density of states, and absorbance. The simulations yield a wide electronic band gap of 7.6 eV for the monazite EuPO₄ phase. The used framework enabled successful and accurate reproduction both intraconfigurational 4f–4f and interconfigurational 4f–5d transitions. The adapted framework and analysis represent an inaugural study towards the comprehension and design of new luminescent materials.