Effects of pressure on theVKcenter in KCl

Abstract

The effects of isotropic pressure on the relaxation and optical-absorption spectra of ${\mathrm{Cl}}_2$ ${\mathrm{}}^{\mathrm{-}}$ in KCl are presented. This study is based on an extended Mott-Littleton relaxation calculation for KCl:${\mathrm{Cl}}_2$ ${\mathrm{}}^{\mathrm{-}}$ as a function of lattice constant using the h a d e s program. The calculations show relatively little effect of pressure on the properties of the $V_K$ center (${\mathrm{Cl}}_2$ ${\mathrm{}}^{\mathrm{-}}$) until the lattice constant drops below ∼3.0 Å. Below this value of the lattice constant, there are substantial changes in the relaxation effects and optical spectrum predicted. Comparisons with normal MCl:${\mathrm{Cl}}_2$ ${\mathrm{}}^{\mathrm{-}}$ $V_K$ centers and hybrid KX:${\mathrm{Cl}}_2$ ${\mathrm{}}^{\mathrm{-}}$ $V_2$ centers are also presented. We conclude that in KCl, the optical and spin-resonance spectra should show a clear change in their pressure dependence beyond a threshold. This threshold is not related to the phase transition in crystal structure.