Solidified Salt Melts of the NaCl-KCl-CeF₃-EuF₃ System as Promising Luminescent Materials

This study presents the results of investigating the interaction between the CeF₃-EuF₃ system and the NaCl-KCl salt melt using spectroscopic methods. It was found that CeF₃ ions undergo no significant changes upon dissolution in the NaCl-KCl melt. In contrast, the dissolution of EuF₃, both individually and within the CeF₃-EuF₃ system, is accompanied by redox reactions leading to the formation of Eu²⁺. The diffuse reflectance spectra of both the bottom (insoluble sediment) and upper parts of the solidified salt melt in the UV range indirectly indicate photoluminescence excitation from Ce³⁺ and Eu²⁺ ions. In addition, absorption bands in the near-IR region (1900-2300 cm⁻¹) confirm the retention of some Eu³⁺ ions in the salt melt. The study explored the effects of various factors-including sample composition, excitation wavelength, prior and subsequent heat treatment, and medium composition-on the excitation and emission spectra of the samples. Intense 5d-4f luminescence of Ce³⁺ and Eu²⁺ ions (at 330 and 430 nm, respectively) was observed predominantly in the upper part of the salt melts, along with much weaker 4f-4f luminescence from Eu³⁺ ions. Certain parameters were optimized to reduce the luminescence contribution from Ce³⁺ and especially Eu³⁺ ions while enhancing the luminescence of Eu²⁺ ions. Solidified salt solution-melts of the NaCl-KCl-CeF₃-EuF₃ system show promise as materials for developing solar ultraviolet radiation detectors.