Faraday Rotation and Spin-Orbit Splitting of theFCenter in Alkali Halides

Abstract

The energy-level structure of the $F$ center in alkali-halide crystals was investigated by means of the Faraday effect. It was found that the Faraday angle is composed of two parts, a small high-temperature contribution and a "paramagnetic" rotation which can be quite large at low temperatures. The results for a number of alkali halides can be consistently interpreted in terms of an energy-level diagram for the $F$ center which includes unequal population of the ground state and a negative spin-orbit splitting of the unrelaxed excited state. The magnitudes of spin-orbit splitting are generally less than the F-band width but increase with atomic number of both the alkali and the halide ion. A comparison is made with theory. Certain additional observations are reported, for example, on the spin-lattice relaxation time of the ground state up to 50 kG.