Spin Relaxation ofF-Center Electrons

Several possible mechanisms leading to spin transitions in the electron-nuclear spin system of an $F$-center electron and its neighboring nuclei have been examined. Calculations show that the most probable transition is one in which the electron spin changes, but the nuclear spin does not change, and which results from the second-order perturbation of the spin-orbit coupling of the electron due to lattice vibrations. The spin-lattice relaxation time of the $F$-center electrons in NaCl at 300°K has been measured at 70, 2950, and 8300 gauss. The relaxation time is 2×${10}^{-6\mathrm{}}$ second, independent of the magnetic field, in approximate agreement with the theory.