ENHANCED REDOX CHEMISTRY IN QUANTIZED SEMICONDUCTOR COLLOIDS

Optical properties of extremely small metal chalcogenide particles tha t exhibit quantization effects have been examined. For extremely small semiconductor clusters with low effective carrier mass, optical absor ption edges are shifted by several volts as a result of quantization e ffects that increase the effective bandgap of particles. Injection of electrons or holes into quantized semiconductor colloidal particles wa s studied by the pulse radiolysis technique. The reducing potential of photogenerated carriers was found to be greatly enhanced in quantized semiconductor particles, compared to the corresponding bulk material. Excess electrons trapped on the surface lead to a blue-shift in the a bsorption edge of colloids. The appearance of this shift depends criti cally on the method of colloid preparation. The presence of OH- ions i n PbS, CdS, and CdTe colloidal solutions blocks the sites where electr ons are trapped and shortens the lifetime of bleaching, whereas in a s lightly acidic solution long-lived bleaching was observed. Different s pectroscopic properties were found for hole excess and OH adducts of h ydrous titanium oxides as a consequence of the existence of different environmental conditions of Ti(IV) atoms at the surface. The position where bole injection occurs lies in the mid-gap level of 25-angstrom T iO2.