Parametrization of 5f-5f Transition Probabilities Between Stark Levels of U ³⁺ in LiYF ₄

(Received 21 December 1994, received in final form 21 February 1995, accepted 1 March 1995)

Abstract
In order to simulate intensities of the 5f-5f transitions of U ³⁺ in LiYF ₄, 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 is introduced to describe the transition probabilities between the crystal-field sublevels of U ³⁺. 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 are calculated and the corresponding radiative lifetime is compared to the experimental one. Moreover, a comparison between the actinide ion U ³⁺ (5f ³) and the lanthanide ions Nd ³⁺ (4f ³) and Er ³⁺ (4f ¹¹) in LiYF ₄ is made.