Study on the Intermixing of Core and Shell in NaEuF₄/NaGdF₄ Core/Shell Nanocrystals

We have studied the intermixing of core and shell material for NaEuF 4 /NaGdF 4 core/shell nanoparticles prepared with two different synthesis procedures. Both methods yield core/shell nanoparticles of high quality showing almost identical TEM images and X-ray powder diffraction data. The luminescence of the core/shell particles is affected by energy transfer processes taking place between Gd 3+ and Eu 3+ ions, between adjacent Eu 3+ ions, and between the FRET ligand 2-naphthoic acid and Eu 3+ ions on the particle surface. Luminescence spectroscopy clearly shows that a significant amount of Eu 3+ ions of the NaEuF 4 particle core are incorporated into NaGdF 4 during shell formation. The degree of intermixing of core and shell material is found to be slightly different in the two synthesis procedures. Our results indicate that the combination of a sensitizing ligand and the NaEuF 4 /NaGdF 4 core/shell system provides a suitable tool for optimizing the synthesis procedures for core/shell nanocrystals of sodium rare earth fluorides.