DYNAMICS OF OPTICAL NONLINEARITIES INDUCED BY STRONG LIGHT ILLUMINATION IN CDS NANOCRYSTALLITES

Light induced grating experiments have been performed at room temperat ure in CdS nanocrystallites of 2.5 nm radius embedded in sol-gel glass films of different semiconductor volume concentration. The dynamics o f tile photogenerated carriers at the lowest transition peak has been shown to depend on the excitation intensity, No spatial diffusion is o bserved up to a nanocrystallite volume concentration of 35%. Below a f ew MW/cm(2) the carriers relax in each nanocrystallite, either radiati vely in similar to 150 ps or by trapping the electrons 15 meV below th eir excitation transition. For higher intensities of excitation, a sat uration of the excited stales occurs which allows the electrons to be trapped in the glass matrix, inducing a permanent grating by the creat ion of a static electric field. (C) 1997 American Institute of Physics .