Applications of the Judd–Ofelt theory to the praseodymium ion in laser solids

The praseodymium ion in its trivalent state is a very good representative of the entire class of rare earth ions and of the complex spectroscopic properties that they exhibit when placed in solid host lattices. The plethora of its radiative transitions, on one hand, demands the intervention of a theory that could explain their absolute and relative intensities, and, on the other hand, provides a good opportunity for the verification of the validity and of the limits of such a theory. We present our data on the spectral characteristics of trivalent praseodymium in a crystal of barium yttrium fluoride and apply the Judd–Ofelt theory to this system. We then examine the problems presented by the application of the Judd–Ofelt theory to the praseodymium ion and the remedies that have been proposed to ameliorate its performance in the somewhat extreme case provided by the spectra of this ion in solids.