Thermally stimulated processes related to photochromism of scandium doped sillenites

The low temperature photochromism of the scandium doped sillenites was inve stigated. The time dependence of the light induced absorption was measured for different conditions of the stimulation process. The optical coloring s pectrum and the optical bleaching spectrum have been established on the bas is of the obtained kinetics. The distinction between short time illuminatio n (< 20 s) and long time illumination (> 1000 s) in the coloring process ha s been noticed. The thermal bleaching curves obtained for the different con ditions of illumination provided information about energy of the shallow tr ap levels responsible for the thermal stability of the photochromic effect. It has been shown that there are five energy levels involved in the therma l bleaching processes but their activity is strongly related to the conditi ons of illumination. Some arguments are presented that the investigation of thermal bleaching could be used as a good tool for the shallow trap spectr oscopy as it is in the conventional thermoluminescence and measurements of thermally stimulated currents. (C) 2000 American Institute of Physics. [S00 21-8979(00)03709-9].