Conversion ofF3+Centers and Destruction ofRCenters in LiF withRLight

Abstract

$R_1$ and $R_2$ bleaches of irradiated LiF near 300°K have revealed the existence of a new color center whose main absorption band covers the region of the $R_1$ and $R_2$ bands. The new center is not related to any of the known color centers, and facilitates the conversion of ${F_3}^{+}$ centers into $R$ centers according to the mechanism ${F_3}^{+}+e\to R$, where the electron is provided by the photo-ionization of the new color center by the $R$ bleach. Simultaneously, but at a slower rate, the $R$ bleach also destroys the $R$ centers by two concurrent mechanisms: (a) decomposition of an $R$ center into an $M$ center and an $F$ center, and (b) conversion of an $R$ center into another color center whose absorption band (550 mμ) is in the $N$-band region. If an $N$ band in LiF is to be identified with the 550-mμ band, the present work favors a rearranged $F_3$ model for the $N$ center over the current Pick model of an $F_4$ complex.