The absorption spectra of natural, colored fluorites (CaF2) are analyzed and compared with the presence of chemical impurities such as rare‐earth elements, yttrium, and sodium located within the fluorite structure. Mechanisms for charge compensation of monovalent and trivalent ions are shown to be provided by color centers and related substitutional or interstitial arrangements either remote or proximate to the ions. It is shown that the color‐center concentration of the 3050 Å absorption band of natural fluorites is directly related to rare‐earth element concentrations. In the visible‐region spectra, the color‐center concentration of the 5600 to 5900 Å absorption band of natural fluorites is shown to be a direct function of monovalent (Na+) ion concentration. The presence of bands along the boundary between the ultraviolet and visible regions is a function of the total concentrations of rare‐earth elements, yttrium, and sodium, with some contribution from F‐center aggregates. This indicates that natural radioactivity is important in the generation of coloration of the natural fluorites. These findings raise serious doubts in the use of absorption bands in natural fluorites in geological age determinations because these bands originate mainly from impurity‐related color centers.
A synthetic fluorite of the Harshaw Chemical Company is analyzed for rare earth elements, yttrium, and sodium. Samples of this fluorite are irradiated with X-rays, y-rays, neutrons, electrons, protons, and %-particles at different energies, and their absorption spectra are analyzed. Analyzing the thermal bleaching of these radiation-coloured fluorites shows that both, impurities and radiation play a part in the coloration of synthetic fluorite. However, the main contribution comes from the radiation induced lattice defects. In the visible region spectra, the colour centre of the 5800 to 5900 A absorption band is probably mainly related with large aggregates of F-centres. The 6450 and the 5300 A absorption bands are mainly related to monovalent and divalent ion impurities and their association with lattice defects. The 3800 A absorption band seems to be related with F-centre aggregates. However, the contribution from the rare earth elements related complex color centres also plays some part for the production of this absorption band. These results indicate that the color centres of different origin can absorb light a t the same wavelength.Eia synthetischer Fluorit der Harshaw-Chemical Company wird auf Seltene Erden, Yttrium und Natrium hin analysiert. Proben dieses Kristalls werden mit Rontgenstrahlen, y-Strahlen, Neutronen, Elektronen, Protonen und a-Teilchen mit unterschiedlichen Energien bestrahlt und ihre Absorptionsspektren analysiert. Die Analyse des thermischen Bleichens dieser strahlungsverfarbten Fluorite zeigt, daB sowohl die Vernnreinigungen als auch die Bestrahlung eine Rolle bei der Verfarbung des synthetischen Fluorits spielt. Jedoch stamint der Hauptbeitrag von den strahlungsinduzierte? Gitterdefekten. Im sichtbaren Bereich des Spektrums ist das Farbzentrum der 6800 bis 5900 A Ahsorptionsbande wahrscheinlich mit groden Aggregaten von F-Zentren verkniipft. Die 5450 und die 5300 A Absorptionsbande sind hanptslchlich mit den monovalenten und divalenten Storstellenionen und deren Assoziation mit Gitterdefekten verbunden. Die 3800 A Absorptionsbande scheint rnit F-Zentrenaggregaten verkniipft zu sein. Jedoch spielt auch der Beitrag von den mit Seltenen Erdelementen verkniipften komplesen Farbzentren eine Rolle bei der Entstehung dieser Absorptionsbande. Die Ergebnisse zeigen, daB die Farbzentren mit unterschiedlichem Ursprung Licht derselben Wellenlange absorbieren konnen.
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