The Eu(NTA)3 · p-tolyl-DAB complex (DAB = 1,4-diaza-1,3-butadienes of the type RNdouble bondCHCHdouble bondNR, R = p-tolyl) is the clearest example reported in the literature until now that provides the experimental validation of the theoretical predictions recently developed for the influence of the intramolecular energy transfer processes involving the ligand-to-metal charge transfer state on the emission quantum yield of Eu3+.