Optical Intensities of Rare-Earth Ions in Yttrium Orthoaluminate

Optical absorption and emission intensities are investigated for trivalent rare earths in YAl${\mathrm{O}}_3$. Ions examined included Pr, Nd, Eu, Tb, Ho, Er, Tm, and Yb. Oscillation strengths of $f\to f$ transitions between $J$ manifolds were measured at room temperature and compared with calculated electric and magnetic dipole oscillator strengths. The Judd-Ofelt approach and phenomenological parameters for each ion were used to derive the electric dipole intensities. The intensity parameters, which were obtained for a least-square-fitting procedure, exhibited a general decrease with increasing number of $4f$ electrons throughout most of the series. The intensities for Pr and Tb were not satisfactorily accounted for in the present theory; some reasons for this are presented.