Trapped Hole Center Containing Fluorine in Magnesium Oxide

Abstract

An intrinsic defect center readily induced in MgO by ionizing radiation is the positive hole localized on an oxygen atom adjacent to a positive ion vacancy ($V_1$ center). This has a tetragonal symmetry axis along [001] or equivalent directions. A similar ESR spectrum but with each line a hyperfine doublet was identified earlier as arising from the center ${\mathrm{O}}^{+}$-[=]-${\mathrm{H}}^{+}$O ($V_{\mathrm{OH}}$ center). This paper describes a similar ESR spectrum of a trapped hole center ($V_{\mathrm{F}}$) with smaller (anisotropic) hyperfine splitting than $V_{\mathrm{OH}}$. It is best observed in single crystals, but it may be induced in powdered MgO by fluorine doping and heating. It thus appears that fluorine is the nucleus responsible for hyperfine splitting. The contact and dipolar splitting constants are, respectively: $a=0.08\mathrm{}$ G, $b=0.33\mathrm{}$ G. The proposed model for the $V_{\mathrm{F}}$ center is ${\mathrm{O}}^{+}$-[=]-${\mathrm{F}}^{+}$ (only deviations from normal site symmetry are shown).