The Nature of Radiative Transitions in TiO2-Based Nanosheets

Abstract

Because of rapid progress in the synthesis methods, TiO2-based nanomaterials are nowadays the object of strong research interest for their promising performances in photocatalysis and photovoltaics applications. In particular, large quantities of two-dimensional (2D) nanosheets (NSs) can be produced and used for further assembling of new nanostructured materials with different morphologies and functionalities. Investigating the microscopic nature of their opto-electronic properties is a fundamental prerequisite for rationalizing experimental data and improving devices performances. By means of first-principles excited-state simulations, we reveal here the excitonic nature of radiative transitions (in the vis–UV spectral range) of TiO2-based NSs. Furthermore these calculations on top of finite temperature molecular dynamics (MD) simulations explain the large Stokes shifts experimentally observed and confirm how the nature of optical transitions in these two-dimensional oxide materials is due to strongly bound excitons. Our study shows that the inclusion of many-body effects plays a fundamental role for a correct interpretation of the experimental data regarding photoexcited processes in low-dimensional titanium dioxide materials.