Decay process of the Mg 2p core exciton in magnesium halides studied by photoelectron spectroscopy.

Abstract

The decay of the Mg 2p core exciton in ${\mathrm{MgF}}_{2}$, ${\mathrm{MgCl}}_{2}$, and ${\mathrm{MgBr}}_{2}$ was investigated by use of the technique of resonant photoemission. The constant-initial-state (CIS) spectrum with the initial state at the peak of the valence band and the constant-final-state (CFS) spectrum with the final state corresponding to the kinetic energy of the Auger electron were measured at photon energies around the Mg 2p core-exciton excitation in these substances. The resonant enhancements were observed in the CIS and CFS spectra of ${\mathrm{MgCl}}_{2}$ and ${\mathrm{MgBr}}_{2}$, whereas in ${\mathrm{MgF}}_{2}$ only the Auger-electron peak shows resonant behavior. These resonant enhancements are interpreted in terms of the nonradiative decay of the Mg 2p core exciton through the ${L}_{2}$,3(exciton)-V and the ${L}_{2}$,3(exciton)-VV processes, respectively, where L(exciton) denotes the initial state with the L hole accompanied by a bound electron (L core exciton) and V denotes the final state with a hole in the valence band. The shapes of the valence-band energy distribution curves obtained at the photon energies of the ${L}_{2}$ and the ${L}_{3}$ core-exciton excitations are different in ${\mathrm{MgCl}}_{2}$ and ${\mathrm{MgBr}}_{2}$. This is attributed to the difference in the relaxation of the ${L}_{2}$ and the ${L}_{3}$ core excitons.