Photo- and Radiation-Induced Charge Transfer Processes in Nanoscopic Materials

摘要

Semiconductor nanoclusters undergo charge separation when subjected to bandgap excitation. The benchtop chemical approach employed for the synthesis of semiconductor colloids results in a high density of defect sites, usually at the semiconductor surface. The nature of these defect sites depends strongly on the experimental conditions of chemical synthesis and controls the charge trapping and recombination of photogenerated charge carriers. The majority of the free carriers get trapped at the defect sites, and these trapped charge carriers then undergo radiative and radiationless recombination. A small fraction of the free charge carriers that escape the recombination process induce electron transfer at the interface. For example, photogenerated holes reaching the interface can directly oxidise the adsorbed substrate or react with surface-bound hydroxyl groups to generate hydroxyl radicals. The hydroxyl radicals in turn can induce secondary oxidations. This photocatalytic aspect of semiconductor nanoparticles has been widely used for the degradation of harmful organic compounds in air and water.