DIFFUSE REFLECTION SPECTRA OF FROZEN SALT MELTS OF THE CeF3-EuF3-NaCl-KCl SYSTEMS

Abstract

The nature of the interaction was determined by the method of diffuse reflection (DR) spectroscopy and conclusions were made about the possible composition of the reaction products in the CeF3-EuF3-NaCl-KCl system. As a result of high-temperature (800 and 1100 °C) heat treatment of a mixture of CeF3 with EuF3 in the ratios 1: 1 and 1: 2, a significant change in the nature of the spectral curves of DR in UV and near IR-spectral ranges is observed. In the first of them, intense absorption was found in the entire spectral range, and more pronounced at higher EuF3 content. On the other hand, significant deformation and a sharp decrease in the intensity of the absorption band are observed on the spectral curves of the DR in the near IR range of the spectrum. The DR spectra of sintered samples in the UV range indicate the emergence of various valent states of Ce (III, IV) and Eu (II, III) with a predominance of Ce4+ and Eu2+ ions compared to Ce3+ and Eu3+. The decrease in the absorption intensity of Eu3+ ions due to 4f‑4f electronic transitions in the near-IR spectra is a direct confirmation of the oxidation-reduction processes occurring in the solid state system. These processes become even more pronounced when processing samples of systems in NaCl-KCl melt, even without pre-sintering. Thus, in the sample, which is a mechanical mixture of CeF3-EuF3 after treatment in the salt melt, the absorption in the near IR range on the DR spectra either disappears altogether (ratio 1: 1), or is a slight residue of F(R) at about 10–3 a. u.). The spectra of DR in the UV range also change dramatically, indicating a predominant content of Eu (II) compared to Eu (III). A similar effect on the nature of the DR spectrum is exerted by the processing of pre-sintered samples in the salt melt, namely, there is a change in the nature of the DR spectral curves both in the UV and in the near IR ranges of the spectrum. This indicates the deepening of the oxidation-reduction processes in the samples of the CeF3-EuF3-NaCl-KCl system with the participation of the salt melt. The increase in the ratio of CeF3-EuF3 from 1: 1 to 1: 2 contributes to above mentioned processes.