LUMINESCENT DETERMINATION OF EUROPIUM AND CERIUM IN THE JOINT PRESENCE IN SOLUTIONS – MELTS OF EQUIMOLAR MIXTURES NaCl–KCl

Abstract

Europium and Cerium belong to lanthanides of variable valency and have similar chemical properties. Luminescent method was proposed for the analytical determination of Eu(III) and Ce(III) with the simultaneous presence in the sample of [EuF3–CeF3 (1:1)]–[NaCl–KCl] (2:8), which is a promising material for detecting UV-solar radiation. Determination of Eu(III) was carried out by the method of sensitized 4f-4f luminescence in a complex with nalidixic acid at an emission wavelength of 613 nm, λex =351 nm. During complexation, a standard ratio of Stark components to Europium is observed in the luminescence spectra, in contrast to the spectrum of the sample solution without the reagent. This fact indicates that the formation of complexes not only increases the intensity of Eu(III) luminescence, but also reduces the effect of Cerium present in the solution. To determine Ce(III), its own luminescence caused by 5d-4f electronic transitions was used at an emission wavelength of 351 nm, λex =263 nm. The presence of Europium ions in the solution does not affect the nature of the luminescence excitation spectra and Ce(III) luminescence spectra. For the quantitative determination of these lanthanides, the additive method was used, which allows to level the mutual influence of ions, as well as the influence of Ce(IV) on the determination of Ce(III). It was found that the content of Eu(III) in the melt is 2.44–2.53% weight, which is in good agreement with the data obtained earlier when studying the EuF3 – [NaCl–KCl](1:9) system. Compared to EuF3, the solubility of CeF3 ((0.028–0.032)% weight) is significantly lower than that predicted by previous thermodynamic calculations. The obtained data allow us to conclude that the solubility of fluoride systems containing Eu in the NaCl–KCl melt is almost the same, and the presence of Ce(III) does not significantly affect the EuF3 dissolution process, and therefore does not affect the properties of the systems [EuF3 – CeF3] – [NaCl–KCl] as detectors of ultraviolet solar radiation.