Electron spin resonance investigation of F65-centres in LiF:Co and LiF:Ni

Two types of tetragonal centre have been discovered in LiF:Co. One centre produced by X-irradiation at 77 K is converted by heating into another centre. The latter is stable up to 180 degrees C. A large splitting with two equivalent fluorine atoms and a small splitting with four equivalent fluorine atoms are observed in both centres. HFS caused by the Co nucleus is absent. These defects are molecular ions F65- bonded with an impurity. The broad line of Co+ is observed too.