Electronic absorption spectra of praseodymium in molten chlorides

Electronic absorption spectra of trivalent praseodymium in various alkali chloride melts were precisely measured. The oscillator strength of the hypersensitive transition, 3F(2) <- H-3(4), showed a clear decrease with increasing temperature. This temperature dependence was the inverse of reported cases for other trivalent lanthanoides. The Judd-Ofelt parameter was analysed, and the calculated oscillator strength showed quite good agreement with the experimentally obtained oscillator strength. However, the Omega(2) parameter, which is sensitive to the ligand environment change, showed a clear decrease with increasing temperature and negative values at high temperature. We found that the P-3(o) <- H-3(4) transition and its shoulder peak are quite sensitive to the coordination circumstance change of the [PrCl6](3-) complex in molten chlorides. These intensities could be correlated with the octahedral symmetry of [PrC6](3-).