F center/OH^- defect pairs (“F_H(OH^-) centers”) in KBr and KI exhibit a novel and unpredicted twofold optical absorption behavior, which at low temperatures can be optically converted and reconverted in a stable and reversible way. Obviously this effect is caused by the bistability of two different orientational configurations of the OH^- impurity ion relative to the F center. The temperature dependence of the two absorption bands and their magnetic circular dichroism have been determined.