Binary Activated iron-oxide/SiO2/NaGdF4:RE (RE = Ce, Eu; Yb, 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,Er) activated particles provided an excellent up/down conversion luminescence emission in green and mid-infrared region under excitation of 980 nm whereas the (Ce, Eu) activated systems exhibited a strong red emission via Gd3+ sublattice upon excitation in the UV region. The magnetic hysteresis at 300 K for β-NaGdF4:RE showed typical signatures of a paramagnetic system whereas iron-oxide/SiO2/β-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 display potential candidates for T1 and T2-weighted bioimaging.