In Ukrainian

Abstract

This paper presents the results of studying by spectral methods (IR transmittance spectroscopy, diffuse reflectance (DR) spectroscopy, luminesce spectroscopy) of solidified solutions-melts of LaF3 and EuF3 in the saline system NaCl-KCl. A preliminary assessment of fluoride solubility on the basis of thermodynamic calculations of exchange reactions in the melt gave values of about 0.74 and 0.29% by weight, respectively, for LaF3 and EuF3 at 700°C. IR spectra of solidified solutions-melts contain a clear band in the range of 250-260 cm-1, corresponding to NaCl, and a less expressive band at 206-210 cm-1 (KCl). At the same time, the IR spectra of the undissolved residues also contain bands in the range of 360-390 cm-1, corresponding to the Ln – F bonds. The DR spectra of LaF3 in NaCl-KCl contain a deep band in the negative region at 245 nm, which corresponds to the intrinsic luminescence of NaCl, in the absence of its own absorption bands of La3+ ions. An analogous band is observed in the EuF3 DR spectra in NaCl-KCl, while it overlaps with the luminescence excitation band of Eu2+ at 350 nm. These bands are also contained in the DR spectra of the undissolved residue, while their intensity is much lower. In the range of 1800-2200 nm, in this case, the absorption band characteristic of Eu3+, consisting of several peaks of different intensities, also manifests itself. The possibility of a redox reaction between Eu3+ and Cl- ions is shown. The luminescence spectrum of LaF3 in saline melt is a broad band of middle intensity with a maximum at 460 nm. In the case of salt melt with EuF3, the luminescence band has the form of a rather narrow peak of high intensity with a maximum at 430-440 nm. In addition, a low-intensity emission band is detected, consisting of several peaks in the range of 500–700 nm, which is due to its appearance to 4f - 4f electronic transition in Eu3+. A similar absorption band takes place in the undissolved residue, while its intensity is much higher.