Structural and mophological control of luminescent rare earth tetrafluoride nanoparticles by colloidal conversion of sacrificial templates

Abstract

Rare earth sodium tetrafluorides (NaREF4) are highly important materials for several academic and technological applications, with emerging uses in nanoscale thermal sensing and cellular imaging. Such applications arise from the luminescent properties of this matrix, in which low phonon energies result in high intensities and efficiencies of upconversion luminescence. The preparation of NaREF4 nanoparticles is of paramount importance in the Chemistry of luminescent nanomaterials. Generally, the synthesis of monodisperse NaREF4 nanoparticles comprises complex procedures using high boiling point coordinating solvents or long lasting hydro-solvothermal treatments, which require a fine regulation of heating/cooling ramps for structural control (cubic or hexagonal), also demanding the growth of epitaxial layers to generate core@shell particles. In addition, such procedures normally result in nanoparticles, which are not readily dispersible in water due to the presence organic stabilizing ligands at the surface. In this sense, the use of techniques based on the colloidal conversion of templates may enable simple and mild methodologies for the controlled preparation of NaREF4-based nanomaterials. Hence, the aim of this proposal is to develop new methodologies to synthesize NaREF4 nanoparticles in aqueous medium with structural and morphological control of the products in the absence of surface amphiphilic ligands. We propose the use of rare earth hydroxycarbonates (RECO3OH.xH2O) as colloidal sacrificial templates. This may enable the control of structure (cubic/hexagonal) and morphology (size/porosity) of the final NaREF4 nanoparticles by varying the size of hydroxycarbonate templates and the conditions of colloidal conversion (solvent and temperature). The kinetics of colloidal conversion will be evaluated via in situ monitoring of luminescence signals under near infrared or ultraviolet excitation. The products will be characterised with respect to structural purity and surface area. Finally, methodologies for the epitaxial growth of passivating layers at the surface of the particles will be evaluated, which is crucial for the enhancement of the luminescence properties and to verify the applicability of these particles in optical thermal sensing and biolabeling.