Abstract

Rare earth nanomaterials, derived from the unique f-block elements of the periodic table, have developed as a transformative class of functional nanomaterials with exceptional optical, magnetic, catalytic, and electronic properties. The partially filled 4f orbitals endow these elements with sharp emission spectra, long fluorescence lifetimes, high magnetic anisotropy, and remarkable redox versatility, making them attractive for diverse applications in nanotechnology. This review presents a comprehensive overview of the strategies for synthesizing rare earth-based nanostructures, including doped nanocrystals, upconversion nanoparticles, and rare earth oxide or hydroxide nanomaterials. We examine the underlying structure–property relationships, highlighting how nanoscale engineering can modulate luminescence efficiency, magnetic performance, and catalytic activity. Particular emphasis is placed on their role in bioimaging, photodynamic therapy, sensing, photocatalysis, and energy conversion technologies. The challenges of controlling size, morphology, surface chemistry, and biocompatibility are critically discussed alongside emerging solutions such as ligand engineering and hybrid nanocomposite design. Finally, we outline current trends and future prospects, emphasizing the potential of rare earth nanomaterials to bridge fundamental f-block chemistry with cutting-edge technological applications.