| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1515646 | Journal of Physics and Chemistry of Solids | 2014 | 7 Pages |
•EPR provides g and hyperfine matrices for two radiation-induced Ag2+ ions in Li2B4O7.•The two Ag2+ ions have different ground-state distributions of unpaired spin density.•These Ag2+ ions are the recombination site for a thermoluminescence peak near 152 °C.
Electron paramagnetic resonance (EPR) is used to investigate the effects of ionizing radiation on Ag-doped lithium tetraborate (Li2B4O7) crystals. Two similar, yet distinct, trapped-hole centers (Ag2+ ions substituting for Li+ ions) are produced by 60 kV x rays. One Ag2+ ion, labeled Center A, has no nearby defects and the other Ag2+ ion, labeled Center B, has a neighboring impurity which is most likely a Ag+ ion substituting for a Li+ ion. The production and thermal decay properties of the two Ag2+ ions are described and their g matrices and 107Ag and 109Ag hyperfine matrices are obtained from the EPR angular dependences. The principal values of the g matrices are similar for the two centers, but the hyperfine principal values differ significantly (Center B has smaller values than Center A). There are also differences in the directions of the principal axes for the two centers. Together, these results imply (1) that the unpaired spin is less localized for Center B and (2) that the ground-state positions of the neighboring oxygen ions are different for Centers A and B. This explains why the peaks of the Ag2+ charge-transfer photoluminescence bands associated with Centers A and B occur at different wavelengths (502 and 725 nm, respectively). An isochronal pulsed thermal anneal shows that these radiation-induced Ag2+ ions serve as the recombination site for the intense thermoluminescence peak observed near 152 °C.
