Temperature dependence of laser-induced fluorescence of in molten LiCl–KCl eutectic

Fluorescence spectra and lifetimes originated from both 5 D 3 → 7 F J and 5 D 4 → 7 F J transitions of Tb 3 + were measured using time-resolved laser fluorescence spectroscopy in order to investigate the excited state relaxation in a molten salt medium. A cross-relaxation energy transfer of 5 D 3 → 5 D 4 resulted in rise and decay behaviors in fluorescence signal waveforms of 5 D 4 → 7 F J transitions. The fluorescence intensity ratios of 5 D 4 → 7 F 5 to 5 D 3 → 7 F 4 decreased drastically when the temperature of molten salt increased. This result suggests that the cross-relaxation effect becomes weakened with increasing temperature. In addition, a strong increase of the 5 D 4 emission over the 5 D 3 emission was observed at high Tb 3 + concentration.