A Dual-Mode Magnetic–Luminescent Hybrid: Fe3O4 + Y2O3:Yb3+,Tm3+ Decorated with a Eu3+ β-Diketonate Complex

We report the fabrication of multifunctional core@shell nanostructures integrating photonic and magnetic properties via a stepwise synthetic approach. The Fe₃O₄ + Y₂O₃:Yb,Tm@SiO₂ hybrid was prepared through co-precipitation, homogeneous precipitation with urea, and silica coating, followed by functionalization with isocyanate groups. Subsequent coupling with 4-(aminomethyl)benzoic acid (pamba) enabled Eu³⁺ coordination through carboxylate moieties. Finally, the β-diketonate ligand 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione (4-Cl-btfa) was coordinated to Eu³⁺, promoting efficient ligand-to-metal energy transfer. The resulting nanostructure exhibited a saturation magnetization of 0.58 emu g⁻¹ with negligible coercivity, consistent with related systems. Under 980 nm excitation (1500 mW), bright blue upconversion emission from Yb³⁺/Tm³⁺ in the Y₂O₃ matrix was observed. In contrast, ultraviolet excitation (335 nm) produced intense red emission with an absolute quantum yield of 12.7 %, arising from Eu³⁺ β-diketonate complexes on the surface. These findings demonstrate tunable emission behavior depending on excitation wavelength and highlight the potential of rational core@shell assembly for multifunctional nanoplatforms.