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