Evaluation of the intramolecular energy transfer rate constants in crystalline Eu(hfaa)4ButNH3
Abstract
The relative fluorescence output and Eu3+ 5D0 level lifetime, τ, of crystalline Eu(hfaa)4ButNH3(hfaa = hexafluoroacetylacetonate anion) have been measured over the temperature range 90–300 K. The observed decrease in τ with increasing temperature is attributed to a back donation of energy from the 5D0 level to the ligand triplet, TEu. These data in conjunction with data from crystalline Gd(hfaa)4ButNH3 and a 1 % europium doped mixed complex have been used to evaluate the TEu[graphic omitted]→5D0 transfer rate, k2, as ca. 1.1 × 106 s–1 from 170 to 270 K. This value is considerably lower than those previously reported for Eu3+ complexes in solution i.e. ca. 1010 s–1. Possible causes of the apparent decrease in k2 at higher and lower temperatures are discussed. The rate of deactivation of TEuby routes other than via the 5D0 level has been calculated and shown to closely follow an Arrhenius function. The results indicate that two ligand triplet levels occur only one of which is involved in intermolecular energy transfer.