A review of functional rare earth metal oxides: synthesis strategies, properties, and emerging applications

Rare-earth metal oxide nanomaterials have emerged as versatile multifunctional platforms owing to their unique electronic configurations, defect tolerance, and remarkable optical, magnetic, and electrical properties. Unlike conventional single-function nanomaterials, rare-earth oxides offer integrated structural and electronic tunability, where nanoscale parameters such as particle size, morphology, exposed crystal facets, and A- and B-site rare-earth doping systematically influence defect chemistry, lattice strain, and the local electronic environment. Controlled synthesis approaches encompassing chemical, electrochemical, biological, and other advanced methods play a decisive role in tailoring structure–property relationships and optimizing functional performance. These coordinated structural and electronic characteristics enable broad multifunctional applications across diverse technological sectors. In biomedicine, rare-earth oxides enable drug and gene delivery, cancer therapy, tissue engineering, antimicrobial activity, and high-contrast bioimaging due to their chemical stability, surface functionality, and tunable luminescence. In environmental remediation, they support efficient catalysis, selective adsorption, and sensitive gas sensing for pollution control and environmental monitoring. In energy technologies, their redox flexibility, oxygen vacancy dynamics, and coupled ionic–electronic transport properties enhance performance in supercapacitors, batteries, fuel cells, electrocatalysis, and electrochemical sensors. Furthermore, their structural robustness and radiation-resistant characteristics make them promising candidates for nano-shield systems designed for radiation protection and electromagnetic interference shielding under extreme conditions. Despite substantial progress, key challenges remain in achieving precise atomic-level structural control, scalable and sustainable synthesis, comprehensive mechanistic understanding of defect-mediated processes, and long-term operational stability, all of which are essential for translating rare-earth oxide nanomaterials into reliable, high-performance multifunctional technologies. • Synthesis strategies of rare earth metal oxide nanomaterials are systematically summarized. • Structure–property–function relationships in REMO nanoparticles are critically analyzed. • Applications of REMO nanomaterials in biomedical, energy and environmental fields are highlighted. • Nano-shield concepts for radiation-resistant and extreme-environment uses are discussed. • Key challenges and future perspectives for rational and scalable REMO development are outlined.