Electron Spin Resonance Absorption Spectra of Hole-Trap Centers Associated with Phosphorous in Irradiated Single Crystal Calcite

Abstract

An irradiation-produced defect center associated with phosphorous impurities and corresponding to S = 12, I = 12 has been observed in natural single crystal calcite. Its electron spin resonance absorption spectrum consists of six doublets each exhibiting orthorhombic symmetry with spin-Hamiltonian parameters given by gξξ = 2.0024, gηη = 2.0382, gζζ = 2.0090, Aξξ = − 17.25 MHz, Aηη = 14.27 MHz, and Aζζ = 17.33 MHz, where the coordinates ξ, η, and ζ are canted with respect to the calcite crystal coordinates. In addition to providing the nuclear magnetic moment of 31P, ENDOR data were used to determine the signs of the hyperfine splitting tensor components which in turn yield unambiguous values for the Fermi contact term and the traceless dipole–dipole interaction. On the basis of the small contact term in comparison to the dipole–dipole interaction strength and upon g-value comparisons, it is proposed that the defect center is a CO3− molecule ion in close association with a PO23− molecule ion, probably mutual charge compensators. The ENDOR spectrum of the PO42− molecule ion in calcite was reinvestigated, and the resulting data were used to provide relative signs of the hyperfine structure tensor components. From an analysis of the latter, it is concluded that the unpaired electron spin is localized primarily in an oxygen nonbonding orbital.