Influence of Charge Compensation on Uv-Excitation of Rare-Earth Fluorescence

摘要

Excitation spectra for the fluorescence transitions of Tb(3+), Eu(3+), and Dy(3+) were obtained at room temperature on single crystals of the tungstates and molybdates of Ca, Sr, Pb, and Cd, having the Scheelite structure, and on terbium-doped crystals of CaF2 and SrF2. Rare-earth concentrations were nominally one atomic percent and charge compensation was provided by vacancy formation or interstitials, by substitution in cation-sites or by anionic substitutions. Strong UV-excitation bands were found for Tb- and Eu-doped crystals and weaker bands for Dy-doped matrices. The bands generally occur near the host-lattice absorption-edge but their intensities and energy positions are strongly influenced by the charge-compensating defects near the active ion. The long wavelength peaks of the bands occur at energies coinciding with 4f-level positions of the rare-earth ions, suggesting a strong perturbation of 4f-levels by charge transfer states. The short-wavelength regions of the excitation bands are ascribed to exchange transfer from UV-absorbing groups. (Author)