The copper europium oxide \(({\text{Eu}}_{2}{\text{CuO}}_{4})\) cuprate was synthesized by the solid-state reaction method and investigated in terms of its structural as well as linear and nonlinear optical properties. X-ray diffraction, combined with Rietveld refinement, Rietveld refinement confirmed that the XRD pattern corresponds to the \({\text{Eu}}_{2}{\text{CuO}}_{4}\) phase. The lattice parameters for \({\text{Eu}}_{2}{\text{CuO}}_{4}\) were determined to be a = 3.902(2) Å and c = 11.905(6) Å, in accordance with reported data for T′-type cuprates, while revealing slight lattice distortions associated with oxygen stoichiometry. Raman spectroscopy further confirms the stabilization of T′-phase through the identification of the characteristic A1g and B1g vibrational modes. The direct optical bandgap was evaluated to be 1.55 ± 6.4 × 10–4 eV, consistent with the 1.45–1.70 eV range reported for \({\text{Eu}}_{2}{\text{CuO}}_{4}\) and other T′-type cuprates, while showing enhanced absorption near the band edge. The refractive index (n), dielectric function (ε), as well as the real and imaginary parts of the optical conductivity ( \({\upsigma }_{1}\) and \({\upsigma }_{2}\) ) were determined. Furthermore, optical dispersion was analyzed using the Wemple–DiDomenico model to extract oscillator parameters and to evaluate the third-order nonlinear optical susceptibility (χ3). The χ3 value obtained, previously scarcely investigated, represents an original contribution of this work and highlights the good potential of Eu₂CuO₄ for advanced optoelectronic applications.
