Abstract
Cerium-concentration-dependence studies of the optical spectra of doubly doped Sr with 0.1-mole% for eight concentrations ranging from 0.001 to 1.0 mole% were carried out. A new four-line pattern was observed in the fluorescence spectra of these samples. In addition, an unusual single-line spectrum was found in the 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 ( mole%) and other data, energy transfer from the Ce ion to the Gd ion in these clusters by exchange is proposed. The fluorescence excitation and decay scheme of the usual site was found to be the usual three-level scheme. The lifetime of the pump state was observed to be 13.5 msec ± 9% while for the 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 , , and sites of Gd. We observed an anomalous increase in the 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 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.
- Received 29 July 1974
DOI:https://doi.org/10.1103/PhysRevB.11.2460
©1975 American Physical Society