Energy transfer study between Ce3+ and Tb3+ ions in doped and core-shell sodium yttrium fluoride nanocrystals

Here, we report the preparation of Ce3+ and Tb3+ co-doped sodium yttrium fluoride nanorods and NaYF4:Ce3(+)/Tb3+ core-shell nanoparticles by the emulsion method. The core-shell nanoparticles are confirmed by X-ray diffraction study and transmission electron microscopy (TEM) analysis. The hexagonal crystal phase of Ce3+-doped sodium yttrium fluoride nanocrystals is converted to the cubic polymorph after surface coating by TbF3. Cell volume, cell parameters and lattice strain have been modified due to core-shell structure. The decay times are found to be 8.4 ms and 5.4 ms for doped nanorods and core-shell nanoparticles, respectively, which reveals that non-radiative decay is higher in the case of core-shell nanoparticles than doped nanorods. Energy transfer efficiencies from Ce3+ to Tb3+ are 65% and 45% for doped Na(Y1.5Na0.5)F-6:Ce:Tb material and NaYF4:Ce/Tb core-shell materials, respectively. Quantum yields are found to be 75% and 42% for doped and core-shell samples, respectively.