nanopowders

Photocatalytic Properties of TiO2 and ZnO Nanopowders

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L. Grigorjeva, J. Rikveilis, J. Grabis, Dz. Jankovica,
C. Monty, D. Millers, K. Smits

Photocatalytic activity of TiO2 and ZnO nanopowders is studied
depending on the morphology, grain sizes and method of synthesizing.
Photocatalysis of the prepared powders was evaluated by degradation of the
methylene blue aqueous solution. Absorbance spectra (190–100 nm) were
measured during exposure of the solution to UV light. The relationships
between the photocatalytic activity and the particle size, crystal polymorph
phases and grain morphology were analyzed. The photocatalytic activity of
prepared TiO2 nanopowders has been found to depend of the anatase-to-rutile
phase ratio. Comparison is given for the photocatalytic activity of ZnO
nanopowders prepared by sol-gel and solar physical vapour deposition
(SPVD) methods

Latvian Journal of Physics and Technical Sciences 2013, N 4

DOI: 10.2478/lpts-2013-0025

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Defect Luminescence of YAG Nanopowders and Crystals

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L. Grigorjeva, D. Jankoviča, K. Smits, D. Millers, S. Zazubovich

Undoped and rare-earth-ion-doped Y3Al5O12 (YAG) nanopowders are prepared by the sol-gel low-temperature combustion method. The luminescence characteristics of the YAG, YAG:Ce, YAG:Pr, and YAG:Ce/Pr nanopowders are compared with those of the single crystals. The luminescence band peaking around 3.1 eV is complex and excited at about 3.6 eV, 3.9 eV and 4.3 eV. The 3.1 eV emission was peculiar to all the samples studied. The Stokes shift of this band is ~0.5 eV. The decay time of the ~3.1 eV emission at 80 K is ~14 ns and the slower decay (afterglow) components are practically absent. The 3.1 eV luminescence was suggested to arise from different intrinsic lattice defects.

Latvian Journal of Physics and Technical Sciences 2012, N 4

DOI: 10.2478/v10047-012-0022-4

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Luminescence Properties of ZnO Nanocrystals and Ceramics

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Larisa Grigorjeva, Donats Millers, Janis Grabis, Claude Monty, Aleksandr Kalinko, Krishjanis Smits,
Vladimir Pankratov, and Witold Łojkowski

Abstract—The luminescence excitation spectra, luminescence
spectra and the nanosecond-scale decay kinetics were studied.
The ZnO and ZnO:Al nanopowders were prepared by vaporization-
condensation in a solar furnace using different raw powders:
commercial, hydrothermal and those obtained by plasma synthesis.
Exciton-phonon as well as exciton-exciton interaction
processes in nanopowders, a bulk crystal and ZnO ceramics were
studied and compared. The fast decay and low afterglow intensity
of ZnO nanopowders and ceramics support these materials for
scintillators.

IEEE Transactions on Nuclear Science, VOL. 55, NO. 3, JUNE 2008

Digital Object Identifier 10.1109/TNS.2008.921931

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The Luminescence Properties of ZnO nanopowders

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Aleksandr Kalinko, Janusz D. Fidelus, Larisa Grigorjeva, Donats Millers, Claude J. Monty, Adam Presz and Krisjanis Smits

Abstract. Pure and Al3+ doped ZnO nanopowders were studied by means of time-resolved
luminescence spectroscopy. The powders were synthesized by hydrothermal and plasma
methods. These powders were used as a raw material for vaporization-condensation process
inside the Solar reactor. The commercially available ZnO nanopowder was studied for a
comparison. Exciton to defect band luminescence intensity ratio was estimated in different
types of ZnO nanopowders. It was found that nanopowders with whiskers morphology show
superlinear luminescence intensity depending on excitation density. The observed effect
depends on the average nanoparticle size and on the powder morphology.

IOP Publishing
Journal of Physics: Conference Series 93 (2007) 012044

doi:10.1088/1742-6596/93/1/012044

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The Luminescence Properties of ZnO:Al Nanopowders Obtained by Sol-gel, Plasma and Vaporization-condensation Methods

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Larisa Grigorjeva, Donats Millers, Krishjanis Smits, Claude Monty, Jules Kouam and Lassad El Mir

Abstract: ZnO nanocrystals were synthesized and characterized by XRD and SEM methods. The
luminescence spectra and decay kinetics were studied under pulsed laser excitation (266 nm, 8 ns).
ZnO and ZnO:Al powders were prepared by sol-gel and plasma chemical synthesis. These powders
were used as a raw material for the SPVD (Solar Physical Vapour Deposition) process. In this way,
the vaporisation-condensation phenomenon (VC) led to the formation of ZnO whiskers and
nanopowders. The luminescence properties of the VC nanopowders were studied and compared to
those displayed by the raw material. The Al dopant, present in the raw powders as a solid solution
and ZnAl2O4 precipitates, was only present as Al ions in the nanopowders after the SPVD. The blue
luminescence intensity increased considerably after SPVD. The whiskers type microstructures
showed nonlinear blue luminescence dependent on the excitation pulse density.

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