CHARGE CONVERSION OF IRRADIATED RARE-EARTH IONS IN CALCIUM FLUORIDE.
HARVARD UNIV CAMBRIDGE MASS CRUFT LAB
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Optical absorption and thermoluminescence measurements are used to study the x-ray induced reduction of trivalent rare-earth ions to the divalent state in CaF2. Thermoluminescent glow curves for the thirteen available lanthanide ions are measured between 80 degrees and 450K. These are found to be remarkably similar, with glow peaks occurring at nearly the same temperatures for each of the ions. The activation energies for each of the glow peaks is estimated. High resolution measurements of the spectra of each glow peak show that the emission is identical to the fluorescence of trivalent rare-earth ions, and determine the site symmetry of the emitting ion. The results of these spectral measurements can be interpreted in a consistent manner. All of the glow emission below room temperature originates from trivalent rare-earth ions in cubic sites, while the glow spectra above room temperature indicates tetragonal symmetry. Vibrational side bands are observed for some of the ions. In the model proposed to explain this data irradiation at 77K produces divalent rare-earth ions and hole centers. Heating allows a hole to diffuse to the site of a divalent rare earth. The hole and extra electron recombine, leaving an excited trivalent rare-earth ion. Decay of this ion to its ground state results in the observed thermoluminescence. Author
- Inorganic Chemistry
- Physical Chemistry