Hot electron-induced electrogenerated chemiluminescence of rare earth(III)chelates at oxide-covered aluminum electrodes

Aromatic Gd(III) and Y(III) chelates produce ligand-centered emissions duri ng cathodic pulse polarization of oxide-covered aluminum electrodes, while the corresponding Tb(III) chelates produce metal-centered D-5(4) --> F-7(J) emissions. It was observed that a redox-inert paramagnetic heavy lanthanoi d ion, Gd(III), seems to enhance strongly intersystem crossing in the excit ed ligand and direct the deexcitation toward a triplet-state emission, whil e a lighter diamagnetic Y(III) ion directs the photophysical processes towa rd a singlet-state emission of the ligand. The luminescence lifetime of Y(I II) chelates was too short to be measured with our apparatus, but the lumin escence lifetime of Gd(III) chelates was between 20 and 70 mu s. The mechan isms of the ECL processes are discussed in detail.