Optical absorption study on the conversion and restoration of color centers in pure KCl crystals

The conversion and restoration processes of colour centers in pure KCl crystals were studied by optical absorption measurements. When the sample is heated the aggregative centers in it begin to dissolve to F centers, and the opposite process will take place, i.e. F centers will aggregate to form F-2, F-3, F-4 centers if the samples are cooled down. It was found that the conversion and restoration processes are dependent on the the annealing temperature and time. In our experiment, the samples were treated at various temperatures and time. In addition the restoration process for the 350 degrees C treated sample was studied five. We found that the higher the annealing temperature is the slower the restoration in the samples proceed, and the conversion process maintained for a few minutes even after annealing treatment.