Relations between Intramolecular Energy Transfer Efficiencies and Triplet State Energies in Rare Earth β-diketone Chelates

Abstract The fluorescence yield of europium chelates in several solutions varies, through its maximum value, with the increase in the energy difference between the triplet state of a ligand and the emitting level of an europium ion. The time-resolved spectroscopic measurements show that the excitation energy is transferred from the triplet state to the lower and nearest resonance level of the europium ion. The intramolecular energy transfer mechanisms for europium chelates and terbium chelates are proposed, taking the resonance exchange interaction and the thermal deactivation processes from the emitting levels of rare earth ions into consideration. Steady-state rate equations are made, and the equation of the fluorescence yield is obtained. Thus, the relations between the fluorescence yield and the triplet state energy are estimated and the fluorescence properties of rare earth β-diketone chelates may be qualitatively described.