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8 results on '"Kränzlin N"'

1. Size-Dependent Luminescence in HfO2 Nanocrystals: Toward White Emission from Intrinsic Surface Defects

Author

Villa, I, Vedda, A, Fasoli, M, Lorenzi, R, Kränzlin, N, Rechberger, F, Ilari, G, Primc, D, Hattendorf, B, Heiligtag, F, Niederberger, M, Lauria, A, VILLA, IRENE, VEDDA, ANNA GRAZIELLA, FASOLI, MAURO, LORENZI, ROBERTO, LAURIA, ALESSANDRO, Villa, I, Vedda, A, Fasoli, M, Lorenzi, R, Kränzlin, N, Rechberger, F, Ilari, G, Primc, D, Hattendorf, B, Heiligtag, F, Niederberger, M, Lauria, A, VILLA, IRENE, VEDDA, ANNA GRAZIELLA, FASOLI, MAURO, LORENZI, ROBERTO, and LAURIA, ALESSANDRO

Abstract

Defect engineering operated on metal oxides by chemical and structural modifications may strongly affect properties suitable for various applications such as photoelectrochemical behavior, charge transport, and luminescence. In this work, we report the tunable optical features observed in undoped monoclinic HfO2 nanocrystals and their dependence on the structural properties of the material at the nanoscale. Transmission electron microscopy together with X-ray diffraction and surface area measurements were used to determine the fine structural modifications, in terms of crystal growth and coalescence of crystalline domains, occurring during a calcination process in the temperature range from 400 to 1000 °C. The fit of the broad optical emission into spectral components, together with time-resolved photoluminescence, allowed us to identify the dual nature of the emission at 2.5 eV, where an ultrafast defect-related intrinsic luminescence (with a decay time of a few nanoseconds) overlaps with a slower emission (decay of several microseconds) due to extrinsic Ti-impurity centers. Moreover, the evolution of intrinsic visible bands during the material transformation was monitored. The relationship between structural parameters uniquely occurring in nanosized materials and the optical properties was investigated and tentatively modeled. The blue emissions at 2.5 and 2.9 eV are clearly related to defects lying at crystal boundaries, while an unprecedented emission at 2.1 eV enables, at relatively low calcination temperatures, the white luminescence of HfO2 under near-UV excitation.

Published
2016

4. Size-Dependent Luminescence in HfO2 Nanocrystals: Toward White Emission from Intrinsic Surface Defects

Author

Anna Vedda, Florian J. Heiligtag, I Villa, Roberto Lorenzi, Felix Rechberger, Mauro Fasoli, Niklaus Kränzlin, Bodo Hattendorf, Gabriele Ilari, Darinka Primc, Alessandro Lauria, Markus Niederberger, Villa, I, Vedda, A, Fasoli, M, Lorenzi, R, Kränzlin, N, Rechberger, F, Ilari, G, Primc, D, Hattendorf, B, Heiligtag, F, Niederberger, M, and Lauria, A

Subjects
Diffraction, Photoluminescence, Materials science, General Chemical Engineering, Crystal growth, 02 engineering and technology, General Chemistry, Atmospheric temperature range, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, 0104 chemical sciences, nanocrystal, Crystallography, Nanocrystal, Transmission electron microscopy, Chemical physics, luminescence, Materials Chemistry, Hafnia, 0210 nano-technology, Luminescence, Monoclinic crystal system
Abstract

Defect engineering operated on metal oxides by chemical and structural modifications may strongly affect properties suitable for various applications such as photoelectrochemical behavior, charge transport, and luminescence. In this work, we report the tunable optical features observed in undoped monoclinic HfO2 nanocrystals and their dependence on the structural properties of the material at the nanoscale. Transmission electron microscopy together with X-ray diffraction and surface area measurements were used to determine the fine structural modifications, in terms of crystal growth and coalescence of crystalline domains, occurring during a calcination process in the temperature range from 400 to 1000 °C. The fit of the broad optical emission into spectral components, together with time-resolved photoluminescence, allowed us to identify the dual nature of the emission at 2.5 eV, where an ultrafast defect-related intrinsic luminescence (with a decay time of a few nanoseconds) overlaps with a slower emission (decay of several microseconds) due to extrinsic Ti-impurity centers. Moreover, the evolution of intrinsic visible bands during the material transformation was monitored. The relationship between structural parameters uniquely occurring in nanosized materials and the optical properties was investigated and tentatively modeled. The blue emissions at 2.5 and 2.9 eV are clearly related to defects lying at crystal boundaries, while an unprecedented emission at 2.1 eV enables, at relatively low calcination temperatures, the white luminescence of HfO2 under near-UV excitation.

Published
2016
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6. Wet-chemical preparation of copper foam monoliths with tunable densities and complex macroscopic shapes.

Author

Kränzlin N and Niederberger M

Abstract

Macroscopic monoliths of copper foams have been prepared by a template-assisted wet-chemical process. The method offers subtle control over the pore size and size distribution, density and macroscopic size and shape of the metal foam. Uniaxial compression tests revealed different deformation behavior depending on the relative density. Non-vacuum-based and low-temperature routes are attractive for the cost-effective production of metal foams., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Published
2013
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8. Nonaqueous TiO2 nanoparticle synthesis: a versatile basis for the fabrication of self-supporting, transparent, and UV-absorbing composite films.

Author

Koziej D, Fischer F, Kränzlin N, Caseri WR, and Niederberger M

Subjects
Crystallization methods, Materials Testing, Particle Size, Refractometry, Scattering, Radiation, Surface Properties, Ultraviolet Rays, Water chemistry, Biocompatible Materials chemistry, Membranes, Artificial, Nanoparticles chemistry, Nanoparticles ultrastructure, Titanium chemistry
Abstract

A successful strategy to obtain self-supporting (100 microm), UV-absorbing, and, in the visible region, highly transparent TiO2-poly(methyl methacrylate) (PMMA) films was developed. The 15 nm large anatase TiO2 nanocrystals were prepared in a nonaqueous sol-gel approach involving the mixing of Ti(O(i)Pr)4 and benzyl alcohol. The surfaces of the resulting particles were modified with minute amounts of organic ligands in order to make the particles easily dispersible in nonpolar media like xylene and dichloromethane and compatible with PMMA, a polymer of high optical transparency and considerable technical importance. The empirical optimization process of composite fabrication was supplemented by fundamental studies of the crystallization and growth mechanism of anatase particles in a nonaqueous medium. After the preparation of corresponding nanocomposites, the materials were investigated with respect to their UV absorption capability, optical transparency in the visible-wavelength region, and photodegradation.

Published
2009
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