Synthesis and fluorescence properties of rare earth (Eu3+ and Gd3+) complexes with α-naphthylacetic acid and 1,10-phenanthroline

Rare earth binary complex Eu(NNA)3 (NNA, α-naphthylacetic acid), ternary complex Eu(NNA)3·phen (phen, 1,10-phenanthroline) and a series of dinuclear complexes with different mole ratios of Eu3+ to Gd3+ were synthesized. Many advanced approaches, such as element analysis, FTIR spectra, TG and DTA analysis, were used to determine the composition and structure of binary and ternary complex. Moreover, their fluorescence properties were studied by fluorescent spectra and lifetimes. The fluorescence spectra and decay curves of dinuclear complexes indicated that the fluorescence emission intensity was enhanced and the fluorescence lifetime was prolonged by Gd3+. The dinuclear complexes show the best properties when the mole ratio of Eu3+ to Gd3+ is 6:4. A new parameter Y, which was used to evaluate the effect of Gd3+, was introduced. In addition, the relationship of Y value and mole fraction of Gd3+ was analyzed by mathematical software. The results showed that Y value decreased by single exponential mode when the content of Gd3+ decreased.