Role ofVkcenters in the equilibria among centers created by electron irradiation at 4 K in KBr

The kinetics of the $F$, $F^{+}$, $I$, and 380-nm $H+V_k$ bands have been studied under irradiation up to a very high concentration (∼ 5 × ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$) as well as their behavior when the irradiation is discontinued. The slow evolution of the population of centers, as well as the related emission which takes place after stopping irradiation, is due to the tunneling of the electrons of the $F$ centers to $V_k$ centers, according to the pair reaction $F+V_k\to F^{+}+h{\nu }_e$. The presence of $V_k$ centers under irradiation is due to the charge compensation of the electrons trapped on $F^{+}$ centers. Their number has been studied as a function of various parameters: energy deposition rate $\dot{\epsilon }$, $F^{+}$ center concentration, and $\frac{F^{+}}{F}$ ratio. The results are interpreted theoretically considering the dynamic equilibrium between their creation rate and their destruction rate related to their recombination with either free electrons or $F$-center electrons.