Electron-spin-resonance and optical study of the Bi0(6p3) center in KCl.

Abstract

An electron-spin-resonance study of a tetragonal ${\mathrm{Bi}}^{0}$(6${\mathit{p}}^{3}$) center in KCl:${\mathrm{Bi}}^{3+}$ crystals is presented. The defect is produced either after x irradiation above 220 K, or after a warmup above this temperature consecutive to low-temperature irradiation, demonstrating that the release and/or capture of anion or cation vacanices is involved in the defect production. The g values, the quadrupole parameter, and the dipolar contribution to the magnetic hyperfine parameters have been calculated in a crystal-field model, yielding good quantitative agreement with the experimental electron-spin-resonance results and permitting the determination of the signs of the hyperfine and the quadrupole parameters. To this end, Coulomb, spin-orbit, and crystal-field interactions were diagonalized between the states of the 6${\mathit{p}}^{3}$ configuration. The hf analysis points to a small delocalization of the valence electrons and to a crystal field, either without or with only a small odd component. Preliminary optical-absorption measurements are presented, and absorption bands at 629 and 725 nm are tentatively correlated with weakly allowed transitions between the calculated energy levels arising from the ground manifold of the ${\mathrm{Bi}}^{0}$ center.