2016/01/31 by E. Baldini, Edoardo Baldini, L. Chiodo +25 · 184 citations
Energy · Materials Science · Physics and Astronomy · #Ab initio #Absorption spectroscopy #Anatase #Electronic and Structural Properties of Oxides #Ellipsometry #Exciton #Nanoparticle #Photoemission spectroscopy #Spectroscopy #TiO2 Photocatalysis and Solar Cells #Wave function #ZnO doping and properties #cond-mat.mtrl-sci
paper · pdf · doi:10.1038/s41467-017-00016-6
published in Nature Communications 8(1), 13 (Nature Portfolio)
openalex publication_date 2017/04/06 · openalex created_date 2017/04/14 · arxiv created 2017/08/17 · arxiv updated 2017/08/18 · openalex updated_date 2026/08/05
Abstract Anatase TiO 2 is among the most studied materials for light-energy conversion applications, but the nature of its fundamental charge excitations is still unknown. Yet it is crucial to establish whether light absorption creates uncorrelated electron–hole pairs or bound excitons and, in the latter case, to determine their character. Here, by combining steady-state angle-resolved photoemission spectroscopy and spectroscopic ellipsometry with state-of-the-art ab initio calculations, we demonstrate that the direct optical gap of single crystals is dominated by a strongly bound exciton rising over the continuum of indirect interband transitions. This exciton possesses an intermediate character between the Wannier–Mott and Frenkel regimes and displays a peculiar two-dimensional wavefunction in the three-dimensional lattice. The nature of the higher-energy excitations is also identified. The universal validity of our results is confirmed up to room temperature by observing the same elementary excitations in defect-rich samples (doped single crystals and nanoparticles) via ultrafast two-dimensional deep-ultraviolet spectroscopy.