Dye-doped nanoparticles of Eu³⁺ chelate complexes with naphtoyltrifluoroacetone and 1,10-phenanthroline were synthesized using two different reprecipitation techniques. The nanoparticles were characterized by atomic force microscopy, absorption spectroscopy, steady-state, and time-resolved fluorescence spectroscopy. Fluorescent spectroscopy of chelate nanoparticles doped with Oxazine 170 and Nile blue dyes indicates that a single dye molecule efficiently quenches luminescence of more than a hundred chelates. The Eu³⁺ chelates have a significantly longer luminescence lifetime than organic dyes, which leads to the appearance of delayed dyes fluorescence with microsecond lifetimes. The fluorescence brightness of dye-doped chelate nanoparticles was determined to be 50 times higher than that of a single Rhodamine 6G molecule. The combination of high fluorescence brightness and long fluorescence lifetime of the dye-doped chelate nanoparticles is promising for time-gated applications. (Graph Presented).