Fig. 6: Simplified energy level diagram for Tb³⁺-Eu³⁺ dyads of singlets (S) and triplets (T) of ligand, and lower levels of Tb³⁺ and Eu³⁺ ions.

The J-multiplet energy levels given for Tb³⁺ and Eu³⁺ may not be exact (and are split by the crystal field) but are illustrative of relative energies. The green and red vertical arrows mark emission from Tb³⁺ and Eu³⁺, respectively. The blue horizontal arrow denotes the 355 nm excitation energy