[en] In order to promote the development of technologies related to spent fuel reprocessing and radioactive waste processing/disposal, it is essential to enhance basic research on the solution chemistry of actinides, and time-resolved laser-induced fluorescence spectroscopy (TRFLS) is one of the important research tools. Although as the most effective research target for determining the internal hydration number of trivalent ions, the direct comparison of the ion configuration environment in the separation of actinides and lanthanides using ion exchange or solvent extraction is named, TRFLS is an effective means for exploring the configuration state and separation mechanisms of trivalent ions with similar chemical behaviors. Since U(VI), which has a relaxation process different from actinide(III), has the emission lifetime and emission spectra unique to its dissolved state, TRFLS has been proven to be useful for the state analysis of chemical species. In addition, since hydration and solvation studies have been extended to lanthanide ion Nd (III) etc., comparative studies between actinides and lanthanides have become possible. One of the advantages of TLFLS is that it can be applied to all conditions of samples, such as solution, solid, solid-liquid or liquid-liquid interfaces, extremely low temperatures to high temperature, and high pressure, and it is particularly essential for studies on solid-liquid interface whose analytical methods are limited. (A.O.)