The time-resolved emission spectra and lifetimes of a series of lanthanide acylpyrazolones complexes were measured under 266 nm laser excitation. The phosphorescence spectra of the triplet states of the Gd(III) complexes were observed at room temperature. The relative efficiencies of intramolecular energy transfer from the triplet state of different ligands to the D-5(4) level of Tb3+ ion have been quantitatively calculated on the basis of the exchange-interaction theory. The properties and functions of ligand-localized excited singlet and triplet states have been discussed; the triplet energy level is one of the key parameters in intramolecular energy transfer. The illumination efficiency of the Tb(III) complex is associated with two factors : one is the lifetimes of the singlet and triplet states of the ligand and the D-5(4) level of terbium ion, and the other is the intersystem-crossing rate of the ligand and the energy transfer rate from triplet state to the D-5(4) level.