Characterization of multifunctional beta-NaEnuF(4)/NaGdF4 core-shell nanoparticles with narrow size distribution

The properties of beta-NaEuF4/NaGdF4 core-shell nanocrystals have been thoroughly investigated. Nano-particles with narrow size distribution and an overall diameter of similar to 22 nm have been produced with either small beta-NaEuF4 cores (similar to 3 nm diameter) or large beta-NaEuF4 cores (similar to 18 nm diameter). The structural properties and core-shell formation are investigated by X-ray diffraction, transmission electron microscopy and electron paramagnetic resonance, respectively. Optical luminescence measurements and X-ray photoelectron spectroscopy are employed to gain information about the optical emission bands and valence states of the rare earth constituents. Magnetic characterization is performed by SQUID and X-ray magnetic circular dichroism measurements at the rare earth M-4.5 edges. The characterization of the core-shell nanoparticles by means of these complementary techniques demonstrates that partial intermixing of core and shell materials takes place, and a significant fraction of europium is present in the divalent state which has significant influence on the magnetic properties. Hence, we obtained a combination of red emitting Eu3+ ions and paramagnetic Gd3+ ions, which may be highly valuable for potential future applications.