Peculiar temperature-dependent fluorescence of EuCl3 in LiCl molten salt as a result of phase changes

Fluorescence spectra were obtained in situ as a function of temperature (ranging from room temperature to 956 K) from a melt of EuCl₃ and LiCl. Three different characteristic Eu²⁺ fluorescence bands, associated with phase changes, were observed. The critical fluorescence dependence on temperature appearing in the blue fluorescence were resulted from the radiative relaxation from 4f⁶5d¹ excited state to 4f⁷ (⁸S_7/2) ground state of Eu²⁺, which was reduced from Eu³⁺ of EuCl₃ at high temperature. The fluorescence studies could provide information regarding the phase changes estimated as the stable dihalide, aggregation, and precipitation states of Eu²⁺ in alkali halide not only crystallic but also fluidic melting matrix.