Porous magnetic-luminescent Fe₃O₄@Y₂O₃:Ln (Ln = Eu, Yb/Er) nanoparticles (NPs) have been fabricated using carbonized ferrocene as templates. Through hydrothermal carbonization of ferrocene, carbon-coated Fe₃O₄ NPs were obtained, providing both a magnetic core and a good depositing surface to establish a uniform layer of Ln(OH)CO₃:Ln. After annealing the pre-synthesized Fe₃O₄@C@Y(OH)CO₃:Ln NPs in air, core–shell Fe₃O₄@Y₂O₃:Ln NPs with a porous morphology were synthesized. The as-synthesized NPs are uniform in size with a core diameter of 140 nm and a shell thickness of 20 nm. N₂ adsorption–desorption isotherms reveal that these porous NPs possess a large surface area of 32 m² g⁻¹. After being doped with different lanthanide ions, these NPs can exhibit various down- and up-conversion emissions. Magnetic measurements also indicate that these NPs display superparamagnetic behavior and high magnetization at room temperature.