Colloidal synthesis of rare earth-based nanoparticles

Colloidal nanocrystals (NCs) are free-standing nano-sized objects, coordinated by a layer of organic amphiphilic molecules which allows their dispersion in solvents, making easy the manipulation. The organic molecules play a central role in all the synthesis steps by controlling the NC surface during the growth, allowing to obtain a fine control over the size and the shape of NCs. In addition, organic ligands prevent the occurrence of aggregation phenomena. Luminescent NCs, presenting intense emission in the visible and NIR region of the spectra, are of great interest for application in several fields, as optoelectronics and bio-imaging. On the other hand, rare-earth elements, generally in form of trivalent cation, emit sharp-fluorescence peaks which allow their application in bio-imaging and therapeutics. Here, we focused on the synthesis of Gd-based NCs by the thermal decomposition of organometallic precursor in hot coordinating solvents using exclusively natural products for each synthetic phase, with the exception for the organometallic NC precursor. In particular, seed oil was used as high-boiling and coordinating solvent and ethanol was used as non-solvent in purification processes. The optical properties of synthesized NCs were monitored by UV-vis absorption and photoluminescence spectroscopy during the NC growth. The morphology of NCs has been monitored by SEM microscopy. Experimental measurement highlighted the formation of Gd-based NCs, 30-40 nm in diameter, characterized by a strong absorption in the UV region of the spectrum and an intense photoluminescence in the green.