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.