Detection ofAl2O3:Fe2+by EPR Relaxation-Time Measurements ofCr3+Ions in Corundum
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Abstract
Angular-dependence experiments of relaxation times ${T}_{1}$ for the ${\mathrm{Cr}}^{3+}$ ion have already been reported in a ruby sample doped with silicon. They showed minima in ${T}_{1}$ which could not be interpreted in terms of harmonic cross relaxation. The presence of ${\mathrm{Fe}}^{2+}$ ions in the specimen may explain these minima. Ruby samples doped with both iron and silicon have been made to increase the ${\mathrm{Fe}}^{2+}$ concentration by charge compensation with ${\mathrm{Si}}^{4+}$ ions. The minima in relaxation time for ${\mathrm{Cr}}^{3+}$ are enhanced in these crystals and they occur at all the crossing points of the ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Fe}}^{2+}$ lines. The variation of ${T}_{1}$ vs angle for ${\mathrm{Cr}}^{3+}$ is studied and the temperature dependence of ${T}_{1}$ is investigated from 4.2 to 1.2\ifmmode^\circ\else\textdegree\fi{}K. Further work is in progress to see if our results are in agreement with the sign of the zero-field splitting parameter $D$ found by Lewiner et al. or with the one obtained by Ganapol'skii. Theoretical work by Stevens and Walsh and the acoustical-paramagnetic-resonance experiments by Lewiner et al. and Ganapol'skii on ${\mathrm{Fe}}^{2+}$ in corundum are inconsistent.
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