PREPARATION AND PHOTOLUMINESCENT PROPERTIES OF COMPLEXES OF TERBIUM, EUROPIUM AND THEIR COPRECIPITATES WITH METHYL ETHER 2-HYDROXYBENZOIC ACID

Abstract

The amorphous coordination compounds of terbium (III) and europium (III) with methyl ester of 2-hydroxybenzoic acid, as well as their mixtures (coprecipitate), in the composition of TbxEu(1-x)L2OH·H2O, are isolated in a solid state by the method of coprecipitation from a weakly basic aqueous-ethanolic medium. According to elemental analysis and pH potentiometric studies, neutralization of cations’ charges is carried out by two molecules of dissociating ligand and one hydroxyl group. The method of thermogravimetric analysis has established that the water molecule that is part of the complexes is coordinated. According to the IR spectroscopy, the coordination of the ligand is carried out with the help of the oxygen atoms of the dissociating hydroxyl and the carbonyl group of the ester fragment. The obtained compounds are not volatile and when the mass spectra are registered in the BBA mode, they are completely destroyed. The complex of terbium (x = 1) in solid state exhibits an effective sensitized luminescence of green color, which is due to the intramolecular transfer of excitation energy from the ligand to the Tb3+ ion. The europium containing complex (x =0), which is isomorphic to terbium one, when excited by UV light, practically does not radiate due to the discrepancy between the energies of the triplet level of the ligand and the emission level of the Eu3+ ion. Sensitized f-f luminescence of the Eu3+ of red color be realized in solid precipitates of the complex mixture (x <1) due to the intermolecular transfer of the excitation energy from the terbium complex (III) to the compound of europium (III) (columinescence). The intensity of the glow of europium (III) depends on the ratio of ion emitters and reaches the maximum value at the values of Tb: Eu = 7: 3. At the same time there is a corresponding decrease in the intensity of the glow of terbium (III).