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(Y_1.5Na _0.5)F₆: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.