MECHANISMS OF ENERGY TRANSFER INVOLVING TRIVALENT Tb AND Eu

Excitation can move from Tb to Eu at 4.2°K by processes involving exchange even though the electronic transitions concerned are not matched in energy. At 295°K, thermal effects cause an overlap permitting dipole-dipole transfer to occur. Transfer to Eu may be enhanced by excitation migration from more remote Tb ions to those closer to Eu at 295°K. This migration is not effective at 4.2°K, and hence appears to require thermal activation.