Fluorescence, photochemistry and size quantization effects of colloidal semiconductor particles

The electrons and positive holes, which are generated upon the absorption of light in colloidal semiconductor particles, can initiate redox reactions. Fluorescence light often is emitted upon the recombination of the charge carriers. Typical examples are described, which illustrate that unusual effects are encountered in the kinetics of microheterogeneous reactions. They include the photo-dissolution of CdS, two-electron and two-hole transfer reactions on ZnS, and reactions of positive holes in TiO2.Very small particles experience a transition from semiconductor properties to molecular properties (Q-particles). The optical and photocatalytic properties change in this transition range