Magnetism and Afterglow United: Synthesis of Novel Double Core‐Shell Eu$^{2+}$‐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 Fe$_{3}$O$_{4}$ magnetic core (≈15 nm) with an afterglow SrAl$_{2}$O$_{4}$:Eu$^{2+}$,Dy$^{3+}$ outer coat (≈10 nm), and applying a SiO$_{2}$ protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe$_{3}$O$_{4}$@SiO$_{2}$@SrAl$_{2}$O$_{4}$:Eu$^{2+}$,Dy$^{3+}$ NPs emit green light attributed to the 4f$^{6}$5d$^{1}$→4f$^{7}$ ($^{8}$S$_{7/2}$) transition of Eu$^{2+}$ 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.