New method of formingF′centers in KI

An $F^{\prime }$ center represents an $F$ center that has acquired an electron from an ionized $F$ center at low temperature. According to Pick, two $F$ centers are destroyed per $F^{\prime }$ center formed, i.e., $2F\leftrightarrows F^{\prime }+\alpha$. If the electron to be trapped by an $F$ center originates from a source other than an ionized $F$ center, one $F$ center would be destroyed per $F^{\prime }$ center formed. The experimental proof would be the absence of $\alpha$ centers formation. The formation of $F^{\prime }$ centers but no $\alpha$ centers was produced by re-x-raying, at 78 K, a pure KI crystal that contained $F_2$ centers in addition to $F$ and $V$ centers. It is believed that $F_2$ centers become ionized, rather than $V_k$ centers being formed, when $F^{\prime }$ centers are produced at 78 K in the absence of $\alpha$ centers.