A PICOSECOND STUDY OF THE PHOTOPHYSICS OF CDS CLUSTERS GROWN IN-SITU IN REVERSED MICELLES

A study of the dynamics of the electronic states of CdS semiconductor clusters grown in situ in reversed micelles via picosecond pump-probe technique reveals efficient transient bleaching of the excitonic absor ption. This effect is attributable mainly to hole localization near th e trapped electron, with no evidence of electron ejection (forming a s olvated electron) detectable despite the apparent proximity of the clu ster to the included water pool. Bleaching efficiency is cluster-size dependent, and recovery kinetics are governed by the nature of the par ticle surface. Similar decay behavior is observed in cluster fluoresce nce. Generally, the decay is characterized by two components, the fast er attributed to recombination of a mobile, detrapped electron with a trapped hole, and the slower to an exchange interaction between trappe d carriers. The observed strong multiexponentionality of the decay res ults from a distribution in trap energy levels, as well as from a dist ribution of distances between traps on the cluster surface. By varying preparation conditions, particles of different sizes with different s urface defects can be grown in reversed micelles in a reproducible way so that their electronic properties can be controlled.