Magnetic circular dichroic effects in the luminescence ofFcenters in KI, KBr, and KCl

We have measured magnetic-field-induced circular polarization of the $F$-center emission in Kl, KBr, and KCl at 1.9 K in fields up to 80 kG. Both diamagnetic (field-dependent) and paramagnetic (spin-dependent) effects have been observed. The latter requires a special technique in which the pump beam is modulated between right and left circular polarization. The expected behavior as a function of the frequency of the modulation has been observed. We have also measured the spin-lattice relaxation time in the relaxed excited state in KI and KBr for $B\ge 50$ kG. All the previous measurements indicate a value of the spin-orbit splitting, $\left|\lambda \right|$, of the order of 1 meV, which is considered a surprisingly small value from purely theoretical grounds.