Temperature-dependent optical bandgap of TiO2 under the Anatase and Rutile phases

A crucial step in developing new and/or more efficient devices relies on the detailed knowledge of the properties of their main (elemental or combined) parts. The same applies to titanium dioxide TiO2 that forms the basis of today numerous applications whose performances are determined by the presence or relative amount of the Anatase (A-) and Rutile (R-) most common phases of TiO2. Whereas the basic structural characteristics of these two polymorphs are very well-established, some of their optical aspects still deserve attention. With these ideas in mind this work presents a comprehensive investigation of the optical bandgap Egap of TiO2 under the Anatase and Rutile phases. The study considered pure A-TiO2 and R-TiO2 samples in the form of powder, and optical reflectance and Raman spectroscopy in the 83–823 K temperature range. In addition to reliable Egap values the study explores their temperature-dependent Egap(T) behavior that is expected to assist future advancements in the field of TiO2-based materials and devices (thin films, interfaces, low-dimensional systems, and photocatalytic and solar cells, for example).