The design of novel photocatalytic and photovoltaic devices requires an in-depth understanding of the microscopic physical mechanisms governing the light-matter interaction.
In reduced TiO2, electronic transitions originating from polaronic excess electrons in localized band-gap states are known to contribute to the photoabsorption and to the photocatalytic response of TiO2 in the visible region. However, despite the broad interest raised in the past years and the efforts made in the experimental characterizations, due to the complexity of the photoexcitation mechanisms an accurate theoretical description and a general understanding of the role played by the band-gap states is still lacking and strongly needed.
It has been shown experimentally that doping rutile with Nb brings a new optical characteristic to the material, with intense optical absorption in the visible region.
In a recent work based on a Many-Body Perturbation Theory (MBPT) study, the authors have shown that when Nb is inserted as a substitutional single impurity it introduces a level in the upper half of the gap, which provides the basis for the optical absorption.
However, the MBPT approach employed fails in reproducing the intense optical absorption of Nb-doped TiO2 rutile in the visible spectrum. To rationalize the experimental results one needs a realistic description of the doping procedure, where disorder is an intrinsic property.
Analyzing different combinations of neighboring Nb defects and polaron localization sites within the MBPT formalism the approach proposed in this project will shed light on the microscopic mechanisms that introduce deeper/shallower band-gap states or bright new excitations, thus providing a wider optical absorption band in the visible spectrum.
Italian Research Council, Italy