A METHOD TO COLOR ELECTROLYTICALLY OXYGEN-DOPED ALKALI-HALIDE CRYSTALS

A method for electrolytic coloration of alkali halide crystals contain ing electron-trapping impurities is described. At first the crystal bu lk is doped partially during the growth. In the coloration procedure t he electron injection is started using a matrix-cathode technique in t he undoped part of the crystal. The coloration process is completed by forcing the colour centre cloud to proceed through the doped part usi ng a higher electric field. The method proved successful to produce la ser-active (F2+)H -centres in KNO3 -doped KCl. It can be applied to co lour alkali halides containing other electron trap impurities as dopan ts.