Parametrization of 5f-5f transition probabilities between Stark levels of U3+ in LiYF4

In order to simulate intensities of the 5f-5f transitions of U3+ in LiYF4, we applied the Judd-Ofelt theory. Because of the large crystal-field splitting of the J-multiplets in the actinides, a set of phenomenological intensity parameters Bλkq is introduced to describe the transition probabilities between the crystal-field sublevels of U3+. The intensities of the absorption transitions between the crystal field levels calculated and a set of six phenomenological intensity parameters give a rather good simulation of the experimental intensities, and the applicability of the Judd-Ofelt theory is discussed for the 5f → 5f transitions of the actinides. From these values, the oscillator strengths between the excited states involved in the laser transition 4I11/2 → 4I9/2 are calculated and the corresponding radiative lifetime is compared to the experimental one. Moreover, a comparison between the actinide ion U3+ (5f3) and the lanthanide ions Nd3+ (4f3) and Er3+ (4f11) in LiYF4 is made. (orig.)