Enhancement of the Luminescence Efficiency of Europium(III) Tris(β-diketonato) Complex in Organic Media by Quaternary Ammonium Salts with Anionic Ligands

Benzyldimethyltetradecylammonium (BA14+) salts with anionic ligands (X−), such as bis(2-ethylhexyl)sulfosuccinate, bis(2-ethylhexyl)phosphate (BEHP−), and benzotriazole (BTA−) anions, were prepared. These salts were soluble in various organic solvents. The luminescence emission spectra of organic solutions of a red luminescent, tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octadionato)europium(III) complex in the presence of the BA14X’s were recorded. The emission intensity of the Eu(III) complex was increased remarkably by the addition of BA14X (X− = BEHP− and BTA−). This effect can be attributed to the formation of 1:1 X−-adducts of the Eu(III) complex, in which the asymmetry of the ligand field is increased so as to enhance the emission efficiency of the 5D0→5F2 transition. The enhancement effect by BA14X was higher than that of charge-neutral ligands, such as tri-n-octylphosphine oxide and 1,10-phenanthroline, which have been used as second ligands to enhance the emission efficiency of tris(β-diketonato)europium(III) complexes.