UV Absorption Bands of Semiconductor Oxides

two adsorption coefficients must be considered [53], one (tta) for the process with phonon absorption  

Since both phonon and emission absorption are possible when hv Eg + Bp, the absorphon coefficient is then 

For each type/family of semiconductor oxide the value of Eg is related to significant dimensional, structural and/or functional properties, and so the features of the ophcal absorption edge is a source of relevant insight into such materials. 

As for the funchonal properties directly dependent on the optical absorption edge, a special place is held by the photocatalytic behavior of titania [49, 50]. In this respect, the determination of Eg of Ti02 materials by electronic spectroscopy data is of great interest. This allows assessment of the effectiveness of treatment/ preparation methods intended to decrease the wide Eg (3.2 eV for the anatase form, usually the most active photocatalyticaUy). This is of interest in the quest for visible 

Figu re 2.8 Plot of a against E hv) panel (A) as from equations and panel (B) forTi02 colloidal particles (three samples 2.1, 13.3 or26.7nm) suspended in an aqueous medium (15gL ). Panel (A) adapted from ref [26] panel (B) reprinted with permission from ref [54]. Copyright 1995 American Chemical Society. 

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