O2 adsorption dependent photoluminescence emission from metal oxide nanoparticles

Optical properties of metal oxide nanoparticles are subject to synthesis related defects and impurities. Using photoluminescence spectroscopy and UV diffuse reflectance in conjunction with Auger electron spectroscopic surface analysis we investigated the effect of surface composition and oxygen adsorption on the photoluminescence properties of vapor phase grown ZnO and MgO nanoparticles. On hydroxylated MgO nanoparticles as a reference system, intense photoluminescence features exclusively originate from surface excitons, the radiative deactivation of which results in collisional quenching in an O2 atmosphere. Conversely, on as-prepared ZnO nanoparticles a broad yellow emission feature centered at hνEm = 2.1 eV exhibits an O2 induced intensity increase. Attributed to oxygen interstitials as recombination centers this enhancement effect originates from adsorbate-induced band bending, which is pertinent to the photoluminescence active region of the nanoparticles. Annealing induced trends in the optical properties of the two prototypical metal oxide nanoparticle systems, ZnO and MgO, are explained by changes in the surface composition and underline that particle surface and interface changes that result from handling and processing of nanoparticles critically affect luminescence

Tunable Nanostructures and Crystal Structures in Titanium Oxide Films

Controllable nanostructures in spin coated titanium oxide (TiO2) films have been achieved by a very simple means, through change of post deposition annealing temperature. Electron beam imaging and reciprocal space analysis revealed as-deposited TiO2films to be characterized by a dominant anatase phase which converts to the rutile form at 600 °C and reverts to the anatase modification at 1,200 °C. The phase changes are also accompanied by changes in the film microstructure: from regular nanoparticles (as-deposited) to nanowires (600 °C) and finally to dendrite like shapes at 1,200 °C. Photoluminescence studies, Raman spectral results, and X-ray diffraction data also furnish evidence in support of the observed solid state phase transformations in TiO2

O2 adsorption dependent photoluminescence emission from metal oxide nanoparticles

Optical properties of metal oxide nanoparticles are subject to synthesis related defects and impurities. Using photoluminescence spectroscopy and UV diffuse reflectance in conjunction with Auger electron spectroscopic surface analysis we investigated the effect of surface composition and oxygen adsorption on the photoluminescence properties of vapor phase grown ZnO and MgO nanoparticles. On hydroxylated MgO nanoparticles as a reference system, intense photoluminescence features exclusively originate from surface excitons, the radiative deactivation of which results in collisional quenching in an O2 atmosphere. Conversely, on as-prepared ZnO nanoparticles a broad yellow emission feature centered at hνEm = 2.1 eV exhibits an O2 induced intensity increase. Attributed to oxygen interstitials as recombination centers this enhancement effect originates from adsorbate-induced band bending, which is pertinent to the photoluminescence active region of the nanoparticles. Annealing induced trends in the optical properties of the two prototypical metal oxide nanoparticle systems, ZnO and MgO, are explained by changes in the surface composition and underline that particle surface and interface changes that result from handling and processing of nanoparticles critically affect luminescence

Visible Light Absorption of N-Doped TiO 2

We have performed detailed ground- and excited-state calculations of pure and N-doped TiO2 rutile to model and analyze the experimentally observed UV/vis spectrum. Using our embedding model, we have performed both linear response (LR) and real-time (RT) TDDFT calculations of the excited states of the pure and N-doped systems. We have also studied the lowest excitations using high-level active space equation-of-motion coupled cluster (EOMCC) approaches involving all single and interband double excitations. We compare and contrast the nature of the excitations in detail for the pure and doped systems and also provide an analysis of the excited-state density using our RT-TDDFT calculations. Our calculations indicate a lowering of the band gap and verify the role of the N3- states on the observed spectrum of N-doped TiO2 rutile as suggested by experimental findings. Both RT-TDDFT and EOMCC calculations show that the excitations in pure TiO2 are more delocalized compared with the N-doped system. © 2011 American Chemical Society