Influence of Solvent Effects on the Photophysical Properties of Europium Amino Acid Complexes

Concentration quenching is mainly caused by energy transfer and cross relaxation between luminescent centers. As the concentration of luminescent centers increases, the distance between them decreases, making it easier for energy to be transferred or consumed, resulting in a reduction in luminescence intensity. In this paper, to reveal the influence of solvent effects on the luminescence properties of rare earth complexes, firstly, low-toxicity rare earth amino acid complex luminescent matrix materials such as europium octanoyl alaninate Eu(oct-ala) ₃ , europium octanoyl phenylalaninate Eu(oct-phe) ₃ , and europium octanoyl serine Eu(oct-ser) ₃ were prepared through in-solution chemical reactions. Subsequently, ethanol solutions of rare earth complexes with different concentrations were prepared, and their photophysical properties such as infrared absorption spectra, ultraviolet-visible absorption spectra, and fluorescence spectra were tested. The study found that as the concentration increases, a red shift occurs in the ultraviolet-visible absorption peaks of the rare earth complex solutions. In addition, further research on fluorescence spectra, fluorescence lifetimes, and CIE diagrams revealed that as the concentration increases, the luminescence intensities of the three complex solutions first increase and then all exhibit concentration quenching. After concentration quenching, phenomena such as a decrease in fluorescence lifetime, luminous efficiency, color purity, and color temperature were observed. Through the study of solvent effects, the "antenna effect" of energy transfer between ligands and rare earth ions in the solution can be discovered, thus determining the optimal luminescence concentrations of these luminescent matrix materials.