[en] We have designed and developed novel luminescent lanthanide complexes based on a coumarin derivative, using a new promising synthetic method developed in our laboratory. The unsaturated 6-coordinated complexes coordinated with three H₂O molecules were formed. The present Er(III)- and Eu(III)-chelated complexes showed an intra 4f shell electronic transition from its first excited state to the ground state taking place at 1530 and 614 nm, respectively. The stronger emission intensity was obtained by the photoexcitation of the coumarin-based ligand with the wavelength of 325 nm rather than by the direct photoexcitation of the lanthanide ions. It could be explained by the fact that the effective energy transfer between the coumarin ligand and the lanthanide ions takes place.