Exciton-Migration Processes in Crystalline Lanthanide Chelates. I. Triplet Exciton Migration in Lanthanide Chelates of 1,10-Phenathroline

Efficient long‐range energy transfer takes place from the ligand 1,10‐phenanthroline to Tb³⁺ and Eu³⁺ in lightly doped crystalline chelates of gadolinium (1,10‐phenanthroline) triacetate, GdPhenAc₃, and from Tb³⁺ to Eu³⁺ in TbPhenAc₃ doped with various concentrations of EuPhenAc₃. A self‐consistent interpretation of the observation is given in terms of a mechanism involving triplet exciton migration. In Eu³⁺‐doped TbPhenAc₃ the measured temperature dependence and the europium concentration dependence of the fluorescence decay time of the ${}^5{D}_4$ level of Tb³⁺ and the buildup time of the Eu³⁺ fluorescence agree rather well with our theoretical prediction. The activation energy of the lifetime of the ${}^5{D}_4$ level of Tb³⁺ can be identified with the difference of the ligand triplet level and the ${}^5{D}_4$ level.