Magnetism and Afterglow United: Synthesis of Novel Double Core-Shell Eu²⁺ -Doped Bifunctional Nanoparticles

Afterglow-magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core-shell strategy is presented, uniting co-precipitation with combustion synthesis routes to combine an Fe₃ O₄ magnetic core (≈15 nm) with an afterglow SrAl₂ O₄ :Eu²⁺ ,Dy³⁺ outer coat (≈10 nm), and applying a SiO₂ protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe₃ O₄ @SiO₂ @SrAl₂ O₄ :Eu²⁺ ,Dy³⁺ NPs emit green light attributed to the 4f⁶ 5d¹ →4f⁷ (⁸ S_7/2 ) transition of Eu²⁺ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules.