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 NaEuF4/NaGdF4 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 Gd3+ and Eu3+ ions, between adjacent Eu3+ ions, and between the FRET ligand 2-naphthoic acid and Eu3+ ions on the particle surface. Luminescence spectroscopy clearly shows that a significant amount of Eu3+ ions of the NaEuF4 particle core are incorporated into NaGdF4 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 NaEuF4/NaGdF4 core/shell system provides a suitable tool for optimizing the synthesis procedures for core/shell nanocrystals of sodium rare earth fluorides.