SUBPICOSECOND DEACTIVATION OF F-CENTER EXCITATION BY MOLECULAR DEFECTS IN ALKALI-HALIDES

An extremely rapid deactivation process of F center excitation has been observed in OH- or CN- doped alkali halide crystals. This superfast bleach recovery time of F center at 10.5 K is as short as similar to 0.5 ps in CN- doped CsBr and similar to 3 ps in OH- or OD- doped KCl and in OH- doped RbCl. The excitation of F-H center is deactivated mainly by this superfast process which is due to energy transfer from the excited electronic F center into the stretching vibrational mode of the associated molecular defect via vibronic tunneling near the curve crossover point.