Time-resolved fluorescence spectra of several europium chelates have been measured using the stroboscopic time-resolution technique. For each of the β-diketone chelates, where the ligand triplet levels are in general above the 5D1 level of Eu3+, the spectra provide evidence that the Eu3+5D0 state is populated by nonradiative energy transfer from the higher-lying 5D1 state. The relaxation time for energy decay from the 5D1 state is measured both in the microcrystals and in solution to be of the order of a few microseconds. Since this is shorter than the corresponding relaxation time of Eu3+ in systems where there are no vibrational frequencies near 1760 cm−1, the 5D1—5D0 energy separation, it is suggested that the ligand[Complex chemical formula]stretching vibrations and the bending vibration of coordinated water molecules make important contributions to the relaxation process. On the other hand, complete nonradiative degradation to the molecular environment from the 5D0 and the 5D1 energy levels appears to be more strongly influenced by higher-energy molecular vibrations such as the C–H and O–H stretches. Variations with temperature in the relaxation time from the 5D1 energy level are mainly accounted for by the temperature dependence of the rate of energy degradation from the 5D1 level to the environment, and it is suggested that the [Complex chemical formula] relaxation process is temperature insensitive between 300° and 77°K. In general, the nonradiative energy-transfer processes in Eu3+ appear to be dominated by interactions with molecular vibrations, and to a smaller extent by crystal lattice modes, rather than by other possible relaxation mechanisms.