Interplay between iridium doping and oxygen vacancies in ceria: Experimental and theoretical investigation of optical and electronic properties

Cerium oxide (CeO2) films doped with iridium (Ir) were synthesized using a sol-gel spin-coating technique and systematically characterized by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) to investigate changes in their optical and electronic properties. Complementary first-principles calculations based on the DFT + U + V approach were employed to elucidate the role of Ir doping and oxygen vacancies in CeO2's structural and electronic behavior. Theoretical and experimental findings show that Ir atoms preserve localized electronic states without significantly disturbing the surrounding charge distribution, even in the presence of oxygen vacancies. In contrast, oxygen vacancies strongly affect nearby Ce atoms, promoting their reduction to Ce3+ states while increasing the formation of additional vacancies. The combined effect of Ir doping and oxygen vacancies results in a reduced crystallite size, lattice expansion, and substantial band gap narrowing, thereby enhancing visible-light absorption and refractive index modulation. Photocatalytic activity in the UV region is diminished when Ir or oxygen vacancies are introduced individually; however, their combined presence improves performance at longer wavelengths within the visible spectrum. This study highlights how the interaction between Ir doping and oxygen vacancies can be used to tailor the redox and optical behavior of ceriabased systems, while also demonstrating the importance of accurate beyond-DFT modeling in describing correlated oxides.