Dear colleagues. As rule, anatase is considered as an indirect band gap semiconductor - in contrast to rutile. But acc. to some papers (Daude & Serpone), direct transitions between VB and CB of anatase are possible, if TiO2 particles are nano-sized. OK.
Since two types of transitions occur at such conditions, a question naturally arises, what the type of Eg exists and should be approved. The values of two Eg-s are different and their dependences on composition are absolutely diverse. Please, suggest your ideas. Let's discuss it. Thank you!
Thanks. And if the Eg vs. composition (concentration of a dopant in TiO2) is discussed, which result must be used as right one - direct or indirect Eg? The question's not to establish the Eg of TiO2. Please, read it thoroughly
The optical bandgap is narrowed in smaller crystals due to the surface defects (like oxygen vacancies). These defects create states within the gap that lead to optical transition. Truely speaking you need to differentiate between Band gap and optical gap. For your calculation of energy gap you should consider TiO2 as indirect bandgap material
OK, thank you very much. What are the cases when the band gap of titania (anatase) has to be considered as direct, i.e. characterized by direct transitions?
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