Reorientation and Motion of the Self-Trapped Hole in KMgF3

The thermal motion of the self-trapped hole in KMg${\mathrm{F}}_3$ has been investigated by observing the decay of [${\mathrm{F}}_2^{-}$]-center aligment as a function of time and temperature. Electron-paramagnetic-resonance [EPR] and polarized-optical-absorption techniques were used. The results show that reorientation through an angle of $\frac{\pi }{2}$ takes place in the range 90-100 K with an activation energy of 0.260 eV. Reorientation through an angle of $\frac{\pi }{3}$ takes place, but at a temperature about 10 K higher, and with an activation energy of 0.29 eV. Annealing of the self-trapped holes occurs between 100 and 110 K. The kinetics are not simple first or second order, but are what would be expected if the self-trapped holes could either annihilate with their complementary electrons or be retrapped at other trapping sites. Consideration of all possible ways in which holes can migrate or reorient suggests that the annealing occurs via a linear motion along [110] rows of ${\mathrm{F}}^{-}$ ions and does not involve any reorientation of the [${\mathrm{F}}_2^{-}$] centers.