Production of Divalent Thulium in CaO and SrCl2

Abstract

Sr${\mathrm{Cl}}_2$ crystals doped with 0.5% Tm${\mathrm{Cl}}_3$ were irradiated with either ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ $\gamma$ rays or 1.7-meV electrons at room temperature. At 20 and 4.2°K and at 10 Gc/sec, the electron spin resonance of divalent thulium was observed in sites of cubic symmetry. The ground state is a ${\Gamma }_7$ doublet with $g=3.428\mathrm{}\pm 0.001$ and $A^{169}=370.0\mathrm{}\pm 0.3\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The thulium appeared to remain in the divalent state for long periods of time at room temperature. Irradiation at either room temperature or 77°K did not produce divalent thulium in Sr${\mathrm{Cl}}_2$ crystals doped with ${\mathrm{Tm}}_2$ ${\mathrm{O}}_3$. CaO doped with 0.5% ${\mathrm{Tm}}_2$ ${\mathrm{O}}_3$ was irradiated at 77°K with ${}_{}{}^{60}{}_{}{}^{}\mathrm{Co}$ $\gamma$ rays or 1.7-meV electrons. The ESR of divalent thulium in sites with cubic symmetry was observed at 20 and 4.2°K and at 10 Gc/sec without an intervening warmup. The ground state is a ${\Gamma }_6$ doublet with $g=2.6155\mathrm{}\pm 0.0005$ and $A^{169}=285.8\mathrm{}\pm 0.3\times {10}^{-4\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$. After warming to room temperature and returning to 4.2°K, the thulium resonance signals were no longer observable, indicating that the thulium had reverted to the trivalent state between 77°K and room temperature. In both Sr${\mathrm{Cl}}_2$ and CaO, the ${\mathrm{Tm}}^{2+}$ resonance was not observable at 77°K.