Here, we report the synthesis and characterization of multifunctional Fe3O4-ZrO2:Yb3+/Er3+hybrid nanoparticles, which simultaneously exhibit magnetic responsiveness, upconversion luminescence, white-light emission, and near-infrared NIR-activated photothermal behavior. The Fe3O4 cores were synthesized by thermal decomposition and subsequently coated with a ZrO2 doped with 2 mol% Yb3+and 0.8 mol% Er3+via a modified Stöber process, using varied concentrations of zirconium butoxide precursors to modulate the photoactivated response. Structural analyses confirmed the presence of both types of oxides, while spectroscopic and elemental mapping demonstrated successful incorporation of Yb3+/Er3+ions within the ZrO2 lattice. Magnetic measurements revealed superparamagnetic behavior, characterized by reduced saturation magnetization upon hybrid formation, yet with a preserved magnetothermal response under alternating magnetic fields. Under 975 nm excitation, the nanoparticles initially exhibited green and red upconversion emissions, followed by the emergence of white-light luminescence arising from a multiphoton-driven interconversion mechanism associated with an increase in temperature. Photothermal experiments revealed strong wavelength-dependent heating. Indeed, Fe3O4 cores dominated under 808 nm excitation, whereas Yb3+dopants enhanced photothermal efficiency at 975 nm, enabling rapid temperature increases up to 212.6 °C after 3 min of irradiation. These results underscore the synergistic interface between magnetic and lanthanide-doped upconverting nanomaterials, which allows tuning of optical and thermal outputs by synthesis parameters. Overall, Fe3O4-ZrO2:Yb3+/Er3+hybrid nanoparticles represent a versatile multifunctional platform with potential for integrated bioimaging, sensing, and therapeutic applications.
