Radiation-Induced[K]0Center in CaO and SrO

Abstract

Substitutional monovalent potassium ions in CaO and SrO trap holes when the crystals are exposed to ionizing radiation at 77 K. The resulting neutral, but paramagnetic, ${\mathrm{}\left[\mathrm{K}\right]\mathrm{}}^0$ centers have axial symmetry and their spin-Hamiltonian parameters are reported. Unlike the ${\mathrm{}\left[\mathrm{Li}\right]\mathrm{}}^0$ and ${\mathrm{}\left[\mathrm{Na}\right]\mathrm{}}^0$ centers in these hosts, the hyperfine structures of the ${\mathrm{}\left[\mathrm{K}\right]\mathrm{}}^0$ centers are best resolved when the axis of the defect is aligned with the magnetic field, suggesting that the isotropic and anisotropic parts of the hyperfine tensor have the same sign and are roughly equal in value. Optical-absorption bands for these centers are tentatively assigned at approximately 1.6 and 1.5 eV for CaO and SrO, respectively.