SPECTROSCOPIC STUDY OF SALT MELTS OF THE SmF3-CeF3-NaCl-KCl SYSTEM

Abstract

Redox interactions between the components of the SmF3-CeF3 and SmF3-CeF3-NaCl-KCl systems have been established by IR transmission spectroscopy, diffuse reflectance electron spectroscopy and luminescence spectroscopy. A significant decrease in the transparency in the IR range of the spectrum was found when passing from the first of the systems to the second, which is explained by an increase in scattering by ultramicrodispersed particles of fluorides in the salt melt. In both systems, the formation of a significant amount of Sm (II) and a decrease in the content of Sm (III) are observed. The change in the valence state of Samarium both during solid-phase heat treatment (1100 °C) and during holding in a salt melt at 700 °C is manifested in the disappearance of some absorption bands, the appearance of new bands, and a gypsochromic shift of the remaining bands. The luminescence spectra exhibit high-intensity emission bands in the 640–740 nm range, which correspond to 5d‑4f electronic transitions in Sm2+ ions. At the same time, the highest intensity is observed in the band corresponding to intracenter 5d‑4f electronic transitions in Ce3+ ions. Apparently, the Ce(IV) compound, formed as a result of the exchange reaction of complex fluoride with a salt melt, volatilizes with subsequent decomposition and does not affect the character of luminescence. On the whole, the luminescence intensity after treatment in the molten salt increases by several tens of times, which indicates a significant change in the radiation mechanism. The mechanism of redox reactions in the solid-phase state, as well as exchange processes in the salt melt and after its crystallization, is discussed. A significant role of solvation shells around particles of lanthanide fluorides in luminescence processes is assumed.