Binary activated iron oxide/SiO2/NaGdF4:RE (RE = Ce, and Eu; Yb, and Er) nanoparticles: synthesis, characterization and their potential for dual T1-T2 weighted imaging

We report the microwave-assisted synthesis of binary doped optical-magnetic up/downconverting NaGdF4:RE and iron oxide/SiO2/NaGdF4:RE nanoparticles. The morphological characteristics were finely tuned from elongated rod-shaped to ovoidal nanoparticles. The (Yb, and Er) activated particles provided an excellent up/down conversion luminescence emission in the green and mid-infrared region under excitation of 980 nm, whereas the (Ce, and Eu) activated systems exhibited a strong red emission via the Gd3+ sublattice upon excitation in the UV region. The magnetic hysteresis at 300 K for beta-NaGdF4:RE showed typical signatures of a paramagnetic system, whereas iron oxide/SiO2/beta-NaGdF4:RE exhibited superparamagnetic behavior along with a Curie-like component. The luminescence quenching effects induced by the presence of iron oxide phase have been validated through comparing the emission/lifetime decay curves. In addition to the excellent optical and magnetic properties, these materials show remarkably high longitudal and transverse relaxivity values (for Fe and Gd) and thus are potential candidates for T-1 and T-2-weighted bioimaging.