Turku Center for Materials and Surfaces MatSurf

Finland

Turku Center for Materials and Surfaces MatSurf

Finland
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Kale V.,University of Turku | Lastusaari M.,University of Turku | Lastusaari M.,Turku Center for Materials and Surfaces MatSurf | Holsa J.,University of Turku | And 3 more authors.
RSC Advances | Year: 2015

Photon upconverting luminescent hexagonal NaRF4:Tm (0.5 mol%) (R:Y3+,Yb3+) crystals with Yb3+ concentrations between 20 and 99.5 mol% were synthesized by a modified thermal coprecipitation method. The effects of the Yb3+ sensitizer concentration on the shape, size, structure, upconversion luminescence intensities and dynamic luminescence lifetimes were studied in detail. The intensity of ultraviolet upconversion luminescence at 340-365 nm upon 980 nm excitation increased up to 20 times with increasing Yb3+ concentration. The mechanisms for the changes in morphology, size and UV upconversion emission are discussed. In addition, the effect of the Tm3+ concentration on the UV emission of NaYbF4 crystals was investigated. The results demonstrate that the NaYbF4 with Tm3+ concentration between 0.4 to 0.8 mol% produce the most intense UV upconversion luminescence. These crystals may find applications in e.g. UV-visible solid state lasers or as an internal UV radiation source for many photochemical reactions. © The Royal Society of Chemistry 2015.


Salomaki M.,University of Turku | Salomaki M.,Turku Center for Materials and Surfaces MatSurf | Myllymaki O.,University of Turku | Hatonen M.,University of Turku | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2014

Fabrication of precisely tailored layers of conductive polymers in thin film assemblies is an attractive extension of the layer-by-layer technique. This approach provides tools for fabricating thin films with customized optical and electrical properties. In this paper, we study inorganic layer-by-layer assembled films prepared using polyphosphate and cerium(IV). It is shown that these multilayers can oxidize certain monomers from the adjacent aqueous solution to produce conducting polymer layers. We studied the thermodynamic factors that allow the aforementioned autopolymerization. A five bilayer polyphosphate/cerium(IV) film was shown to possess high oxidative power in acidic solutions. It was found that the polymerization of pyrrole, aniline and 3,4-ethylenedioxythiophene in contact with the redox active multilayer is thermodynamically favored. The rate of polymer formation and the thickness of the conducting film could be controlled by the concentration of the monomer in solution and the number of cerium/polyphosphate bilayers in the oxidative film. The oxidative polymerization of pyrrole was unambiguously recognized on UV-vis spectra with characteristic reduction and oxidation bands. The film formation was not restricted by charge diffusion and the reaction formally followed first-order kinetics. The results suggest that the reaction takes place effectively within the whole pre-existing polypyrrole film and it continues until all oxidant in the film was used. The spectral changes that are characteristic for conducting polypyrrole are shown on spectroelectrochemical analysis of the films indicating that cationic (polaron) and dicationic (bipolaron) species are involved in the redox processes of the film. The functional polymer films formed are found to be electroactive and conducting. Therefore, they fully resemble of conducting polymer films prepared using traditional electropolymerization. © 2014 American Chemical Society.


Lastusaari M.,University of Turku | Lastusaari M.,Turku Center for Materials and Surfaces MatSurf | Brito H.F.,University of Sao Paulo | Carlson S.,Lund University | And 8 more authors.
Physica Scripta | Year: 2014

The existence and effect of different rare earth (R2+/3+/IV) ions in SrAl2O4:Eu2+,R3+ and M 2MgSi2O7:Eu2+,R3+ (M: Sr, Ba) persistent luminescence materials was studied with XANES (x-ray absorption near edge structure) measurements at HASYLAB/DESY (Hamburg, Germany) and MAX-lab (Lund, Sweden). The experiments were carried out at 298 K for selected rare earth (co-)dopants (Eu2+; Ce3+, Nd3+, Sm 3+, Dy3+ and Yb3+). The co-existence of Eu 2+ and Eu3+ was observed in all materials. The co-dopants were always in the trivalent form. © 2014 The Royal Swedish Academy of Sciences.


Norrbo I.,University of Turku | Gluchowski P.,Institute of Low Temperature And Structure Research | Paturi P.,University of Turku | Sinkkonen J.,University of Turku | And 2 more authors.
Inorganic Chemistry | Year: 2015

Na8Al6Si6O24(Cl,S)2 materials were prepared with a solid state reaction. The products were studied using X-ray powder diffraction, reflectance measurements as well as X-ray fluorescence, conventional and persistent luminescence, nuclear magnetic resonance, and electron paramagnetic resonance spectroscopies. All materials containing sulfur showed purple tenebrescence, which persisted 2 days in a lit room at room temperature. Considerable blue persistent luminescence peaking at 460 nm and lasting for 1 h was obtained, as well. Persistent luminescence was obtained with irradiation at 365 nm, while tenebrescence required 254 nm. The materials show great promise as low-cost multifunctional optical markers. (Figure Presented) © 2015 American Chemical Society.


Kale V.,University of Turku | Soukka T.,University of Turku | Holsa J.,University of Turku | Holsa J.,Turku Center for Materials and Surfaces MatSurf | And 2 more authors.
Journal of Nanoparticle Research | Year: 2013

Hexagonal (β)-NaYF4 is recognized as one of the most efficient hosts for NIR to blue and green upconversion (UC). A new method to tune the blue UC emission in β-NaYF4:Yb,Tm nanocrystals through the possible substitution of the host material with different concentrations of K+ and Sc3+ ions was investigated in detail. In this work, Na1-x K x YF4:Yb,Tm and NaY1-x Sc x F4:Yb,Tm nanocrystals were synthesized with varying Na:K and Y:Sc ratios. X-ray diffraction, transmission electron microscopy, and UC luminescence spectroscopy showed that size, morphology, and UC luminescence intensity were affected by the addition of K+ and Sc3+ ions. Substituted ions disturbed the local symmetry and also resulted in changes in the crystal field. The distance between Yb3+ and Tm3+ was affected by different concentration of K+ and Sc3+ ions, and those differences in the distance are responsible for tuning UC luminescence. This study revealed that when the concentration of K+ and Sc3+ ions were nominally increased from 20 to 100 mol% during synthesis, hexagonal NaYF4 changed to structurally different KYF 4 and Na3ScF6 so that the solid solubility became difficult. We also demonstrate that the added K+ does not enter into the NaYF4 lattice, but it still plays an important role by controlling the Na/R ratio. K+ and Sc3+ ion concentration of 20 mol% during the synthesis was found to result in materials with size 30-35 nm, and shows ca. four times brighter UC emission than the previously reported lanthanide based nanocrystals. The enhancement in UC luminescence intensity makes upconversion nanophosphors versatile imaging tools for diagnosis. Graphical Abstract: [Figure not available: see fulltext.] © 2013 Springer Science+Business Media Dordrecht.

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