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 (8S7/2) 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.