Optical excitation of semiconductors

3 Formation and Decay of the Excited States of Semiconductors 7.3.1 Optical Excitation of Semiconductors 

Out of various nanoassemblies, nano- and microcrystalline solid semiconductors deserve a particular attention due to their specific spectroscopic, photochemical, and photocatalytic properties. These properties derive from the nature of the semiconductor s excited states. 

There are several optical absorption processes associated with semiconductors and their contribution depends on semiconductor properties and incident light energy. These processes include  

For most photocatalytic (electron transfer) and analytical (photoluminescence) applications only the fundamental absorption plays an important role. 

The envelope of the semiconductor absorption spectrum is described by a simple power function  

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Niemeyer et al. have reported the design of quantum dot/enzyme nanohybrids that are capable of catalyzing an organic transformation upon optical excitation of semiconductor quantum dots (QDs) [31]. The hybrid device was composed of semiconductor CdS nanoparticles and cytochrome p450BSp enzyme. It has been proposed that irradiation of QDs leads to formation of excitons (h+-e pairs) that on dissociation generate superoxide and hydroxyl radicals in interfacial electron transfer process (see Chapter 7). These radicals in turn activate the enzyme adsorbed at the QD surface. The activated enzyme is able to catalyze mono-oxygenation of fatty acids, but has a lower activity than the native enzyme [31]. 

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