Temperature dependence of the Eu3+ D-5(0) lifetime in europium tris(2,2,6,6-tetramethyl-3,5-heptanedionato)

The temperature dependence of the Eu3+ D-5(0) relaxation rate in solid europium tris(2,2,6,6-tetramethyl-3,5-heptaaedionato) is presented. Eu3+ emission is strongly quenched in the region of room temperature. It is proposed that thermal quenching of D-5(0) emission is via crossover from the D-5(0) to a ligand-to-lanthanide charge transfer state. Activation energies for the crossover process were determined using the models of Mott and of Englman and Jortner, yielding values of 4120 +/- and 5700 +/- 300 cm(-1), respectively. The crossover process is less efficient in media in which Eu(thd)(3) exists as a monomer.