Rare earth doped TiO2 thin film: A review on structural, optical, photocatalytic, magnetic, and electrical properties

Rare earth (RE) doping become an effective strategy for enhancing the multifunctional properties of TiO₂ thin films, making them highly suitable for diverse advanced applications. This review explores how different RE dopants, including Cerium (Ce), Europium (Eu), Neodymium (Nd), Lanthanum (La), Erbium (Er), Lutetium (Lu), Yttrium (Y), and Terbium (Tb), affect the optical, structural, photocatalytic, morphological, and electrical behaviors of TiO₂ thin film. At lower doping concentrations and moderate annealing temperatures, TiO₂ typically maintains its anatase phase. However, specific dopants and higher concentrations can lead to phase transitions or a reduction in crystalline size. RE doping enhances photocatalytic activity by narrowing the band gap, improving charge separation, and increasing surface reactivity. Additionally, dopants influence the film's morphology, promoting porosity, refined grain sizes, and the formation of surface defects. The electrical and magnetic properties of TiO₂ thin films are also significantly modified, with improvements in conductivity, dielectric performance, and ferromagnetic behavior attributed to defect engineering and orbital interactions. RE doping is a powerful strategy for modifying the optical landscape of TiO₂ thin films, unlocking new functionalities through atomic-scale modifications. In this review, we discuss how specific dopants affect optical transmittance, shifts in the absorption edge, and the evolution of the band gap through systematic UV-Vis analysis. For instance, dopants like Eu and Lu significantly enhance optical transparency by reducing light scattering and utilizing Burstein–Moss-driven band filling, while Yb and Er lower the band gap, improving visible-light absorption through defect-mediated electronic restructuring. These dopant-induced phenomena not only redefine photon–semiconductor interactions but also establish design principles for next-generation optoelectronic and photocatalytic, spintronic, and sensing platforms based on TiO₂.