Preparation and Luminescence Properties of Rare Earth(Eu~(3+),Tb~(3+)) Complexes with Citric Acid and 1,10-phenanthroline

Great interest arises from rare earth complexes because the emissions of some rare earth ions exhibit high color purity, strong fluorescent intensity and efficient energy transfer from organic ligands to the central ions through the triple states. When europium ion chelates with some organic ligands, such as βdiketone, carboxylic acid and heterocylic acid, it always exhibits high red color purity and strong fluorescence intensity. In the investigation of europium complexes with carboxylic acids, most attentions were focused on the carboxylic acids containing bezene ring and pyridine ring, such as benzoic acid, phthalic acid, nicotinic acid and 2,6pyridine dicarboxylic acid etc, but less was concerned with tricarboxylic acid.In this paper, rare earth (Eu3+,Tb3+) complexes with citric acid and 1,10phenanthroline were prepared. Their compositions were characterized by elemental analysis and FTIR spectra. Their fluorescent properties were studied by fluorescence spectra and fluorescence lifetimes. The results showed that the europium(Ⅲ) fluorescence was greatly enhanced in the complexes of (EuTb)Cit·phen while the fluorescence of terbium(Ⅲ) was greatly quenched. The data of terbium's fluorescence intensity was fitted and the results showed that the intensity was decayed by exponential mode. The fluorescence of europium(Ⅲ) was changed by europium's mole content, a minimal intensity was appeared when Eu3+∶Tb3+=4∶6 and a maximal intensity was appeared when Eu3+∶Tb3+=6∶4. According to the intensity of Eu3+ and Tb3+, it could be found that the europium's characteristic fluorescence could be largely enhanced when the terbium's characteristic fluorescence was greatly quenched. The fluorescence lifetimes were also measured with N2 laser. The results showed that the lifetime of the Eu(Ⅲ) complex could be prolonged when Tb3+ ion partly replaces the Eu3+ in the Eu(Cit)·phen·2H2O complex and its variation accorded with the fluorescence intensity.