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Fluorescence and absorption studies of Sr0.999-xGd0.001CexF2.001+x

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Physical Review B





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Cerium-concentration-dependence studies of the optical spectra of doubly doped SrF2 with 0.1-mole% Gd3+ for eight Ce3+ concentrations ranging from 0.001 to 1.0 mole% were carried out. A new four-line pattern was observed in the P726 fluorescence spectra of these samples. In addition, an unusual single-line spectrum was found in the P726 region. These and other new features studied using intensity and lifetime measurements were tentatively identified as arising from various Gd-Ce mixed double and triple clusters. From the enhancement of the Gd fluorescence due to Ce at low Ce concentrations (0.1 mole%) and other data, energy transfer from the Ce ion to the Gd ion in these clusters by exchange is proposed. The P726 fluorescence excitation and decay scheme of the usual C4 site was found to be the usual three-level scheme. The lifetime of the I6 pump state was observed to be 13.5 msec 9% while for the P726 decay we observed radiation trapping giving lifetimes as much as four times the radiative value of 10 msec. Analysis of the absorption spectra gave a self-consistent set of site concentrations vs Ce concentration for the Oh, C4, and C3 sites of Gd. We observed an anomalous increase in the Oh site concentration with a corresponding decrease in the axial site concentration with increasing Ce concentration starting at about 0.1-mole% Ce. An ad hoc gettering model is proposed which assumes that the Ce ions extract extra interstitial F- ions from the Gd population producing the observed site-concentration changes. The calculations based on this model provide a satisfactory fit to the observed data. © 1975 The American Physical Society.

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