Optical Absorption and Fluorescence Intensities in Several Rare-Earth-Doped Y2O3 and LaF3 Single Crystals
The absolute intensities of transitions occurring in the optical spectra of single crystals of Y2O3 doped with small amounts of Pr, Nd, Eu, Er, and Tm; single crystals of LaF3 doped with small amounts of Pr and Nd; and single crystals of Er2O3, Tm2O3, and Yb2O3 have been measured at room temperature. All observed transitions occur within the ground configurations of the trivalent rare-earth ions, and their intensities are accounted for using three phenomenological parameters for each system, whose values are determined by a a least-squares fitting calculation. A calculation of the relevant crystal-field terms is made, and theoretical values for the intensity parameters are calculated using free-ion radial wave functions and certain closure approximations. It is concluded that excited 4fn-1 g configurations contribute to observed intensities more than is indicated by free-ion calculations, and that the excited 4fn-15d configuration contributes to the observed intensities an order of magnitude less than indicated by free-ion calculations. A hypersensitive transition in the neodymium systems is observed and its sensitivity is traced to a simple change in point symmetry of the host.