AIP Digital Archive
In this work we study CaF2:Ce,Mn and use optical absorption, photoluminescence (excitation and emission), and x-ray-induced luminescence to characterize the role played by Ce in various lattice sites during these processes. The data indicate that energy transfer takes place from Ce to Mn, predominantly from Ce3+ in tetragonal sites (i.e., Ce3+-F−int centers with C4v symmetry). There is also some evidence of transfer from higher-order clusters of these defects. In contrast, however, we note that there is no evidence of energy transfer in x-ray-excited luminescence; an increase in the Ce concentration causes a decrease in the Mn2+ emission. It appears from the present investigations that, during x-ray excitation, nonlocally compensated Ce3+ ions of cubic symmetry compete with Mn2+ ions for free electrons released during irradiation. Thus, the data indicate that tetragonal Ce3+ sites are dominant during UV excitation and give rise to energy transfer to Mn2+, whereas cubic Ce3+ sites are dominant during irradiation with high-energy ionizing radiations and no energy transfer takes place.
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