Magnetic resonance investigation of the dynamics of F centers in LiF

Damage caused in lithium fluoride crystals by gamma -rays and electrons includes, besides other point defects, F centers and their agglomerates. We have studied the paramagnetic F centers created by radiation doses that vary by several orders of magnitude. We measured the electronic spin relaxation time T-le, of the F centers at low temperatures by the recovery of the magnetic circular dichroism. of absorption (MCDA) as well as the temperature dependence of the F-19 and Li-7 nuclear spin relaxation (NSR) times, T-in. Our results indicate that the nuclear spin relaxation is dominated by spin-diffusion limited paramagnetic relaxation. The electron spin correlation function is determined by the electronic spin-lattice relaxation. In the studied temperature range from 4 to 300 K, the electron spin-lattice relaxation time T-le is long compared to the nuclear Larmor period, omega T-L(le) >> 1 (omega (L): nuclear Larmor frequency). The temperature variation of T-ln indicates that the electron spin-lattice relaxation is dominated by phonon-F center interactions. At temperatures T greater than 360 K, an annealing process takes place that eliminates the F centers and their agglomerates. (C) 2001 Elsevier Science Ltd. All rights reserved.