Formation of M Centers from ``Stored'' Photoelectrons

Abstract
A process for producing M centers in additively colored KCl, by alternately bleaching F centers at − 120°C and warming up to about 0°C, is described. In undeformed crystals, M centers were formed only in samples in which an absorption at 600 mμ was observed as an intermediate. Plastic deformation enhanced the formation, in both KCl and KBr. M centers did not appear until temperatures well above the temperature of disappearance of F′ centers. A mechanism is proposed involving the migration of α centers to F centers; the F2+ centers thus formed are then neutralized by electrons released from the centers absorbing at 600 mμ.

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