Relaxation between Excited Levels of Tb^3 Ion Due to Resonance Energy Transfer

The probability of relaxation between two excited levels, 5 D 3 and 5 D 4 , of Tb 3+ ion is obtained experimentally in glassy calcium meta-phosphate. Effects of coexisting other rare earth ions on this relaxation process are studied. It is clarified that energy transfer due to resonance between Tb 3+ ions or to other rare earth ions strongly accelerates this relaxation process, and that the mechanism governing this energy transfer is electric multipole interaction.