Thermal Bleaching of Color Centers in KCl Crystals Containing U Centers

From the study of thermal bleaching of the F , M and R 2 bands in KCl crystals containing U centers, the behavior of the hydrogen molecules produced from U centers was examined. The hydrogen molecules do not react with F centers but with M centers by bimolecular reaction and make M centers convert to U centers. Furthermore, thermal bleaching of the Z 1 and Z 2 bands in KCl crystals containing divalent cations was also investigated. The Z 1 and Z 2 bands are thermally unstable at temperature above 80°C, while they are stable up to 110°C and 250°C, respectively, in the crystal containing no U centers. From these results, in KCl:Sr crystals it is supposed that Z 1 centers do not return to U centers but form unknown centers by combining with the hydrogen molecules.