Anna Lukowiak

White emission of lithium ytterbium tetraphosphate nanocrystals.

An efficient anti-Stokes white broadband emission induced by 976 nm laser diode in lithium ytterbium tetraphosphate (LiYbP4O12) nanocrystals was investigated. The emission occurs at room temperature and atmospheric pressure. Its intensity demonstrates an evident threshold dependence on the temperature and excitation density characteristic to avalanche process. The white emission is accompanied by very efficient photoconductivity characterized by microampere photocurrent which increases with the fourth order of applied incident light power (~P4). We show that this emission is critically dependent on temperature and increases significantly in vacuum. It is concluded that the anti-Stokes white emission is associated with theYb3+- CT luminescence.

Anti-Stokes bright yellowish emission of NdAlO3 nanocrystals

Infrared laser diode–induced anti-Stokes bright yellowish emission of NdAlO3 nanocrystalline powder was observed at room temperature in ambient atmosphere. The emission intensity was found to be unaltered with lowering temperature and to increase by two orders of magnitude in vacuum. The temperature of bright emission under ambient atmosphere was determined to be 350 °C. It was found that the yellowish emission was accompanied by a giant photocurrent of 0.5 microamperes at relatively low applied voltage. The power dependence of the photocurrent was governed by an avalanche-like mechanism. The origin of the bright emission is discussed in terms of charge transfer luminescence of Nd3+.

Antimicrobial graphene family materials: Progress, advances, hopes and fears.

Graphene-based materials have become very popular bionanotechnological instruments in the last few years. Since 2010, the graphene family materials have been recognized as worthy of attention due to its antimicrobial properties. Functionalization of graphene (or rather graphene oxide) surface creates the possibilities to obtain efficient antimicrobial agents. In this review, progress and advances in this field in the last few years are described and discussed. Special attention is devoted to materials based on graphene oxide in which specifically selected components significantly modify biological activity of this carbon structure. Short introduction concerns the physicochemical properties of the graphene family materials. In the section on antimicrobial properties, proposed mechanisms of activity against microorganisms are given showing enhanced action of nanocomposites also under light irradiation (photoinduced activity). Another important feature, i.e. toxicity against eukaryotic cells, is presented with up-to-date data. Taking into account all the information on the properties of the described materials and usefulness of the graphene family as antimicrobial agents, hopes and fears concerning their application are discussed. Finally, some examples of promising usage in medicine and other fields, e.g. in phytobiology and water remediation, are shown.

Synthesis, structure and luminescence properties of KEu0.01Gd0.19Yb0.8(WO4)2 powder

Abstract The synthesis of co-doped KEu 0.01 Gd 0.19 Yb 0.8 (WO 4 ) 2 was achieved by a modified Pechini method at 750 °C. The structure of obtained compound was confirmed using X-ray diffraction measurement and Raman spectroscopy. The Scherrers formula was used to confirm the grain sizes visualized by TEM technique. The grain sizes of about 100 nm of monoclinic KGW were successfully obtained by this methodology. In order to study spectroscopic properties of the prepared system the emission spectra were measured. The effective down- and up-conversion processes in non-resonant system were investigated.

Synthesis and Optical Properties of Eu3+ Ion Doped Nanocrystalline Hydroxyapatites

ABSTRACT The Ca10(PO4)6(OH)2 hydroxyapatite (HA) nanopowders doped with Eu3+ ions were prepared using a wet synthesis method. Their structure and morphology were investigated. The XRD analysis has proven a single-phase of HA nanocrystallites. The average sizes of HA nanocrystallites calcinated at 400°C and 700°C were determined to be about 20 nm and 30 nm, respectively. The emission and excitation spectra as well as the fluorescence decay rates of Eu3+ ion doped HA nanocrystallites were measured. Particular attention was given to the spectroscopic properties of Eu3+ ions as a luminescent probe of nanocrystalline HA structure as a result of varying annealing temperature and dopant concentration. The Judd-Ofelt analysis of f-f transitions of Eu3+:HA nanocrystallites was performed. The effect of calcination temperatures on grain sizes and luminescence properties is noted and discussed.

Influence of terbium on structure and luminescence of nanocrystalline TiO2 thin films

In this work analysis of the structural and optical properties of TiO2 thin films doped with terbium has been described. Samples were prepared by a high energy reactive magnetron sputtering process under low pressure of oxygen plasma. X-ray diffraction results have shown that different TiO2 crystal forms have been produced, depending on the amount of Tb dopant. The undoped matrix had rutile structure with crystallites with a size of 8.7 nm, while incorporation of 0.4 at. % of Tb into the film during the sputtering process resulted in anatase structure with bigger crystallites (11.7 nm). Increasing the amount of terbium up to 2 at. % and 2.6 at. % gave rutile structure with crystallites with a size of 6.6 nm for both films. However, Raman spectroscopy has revealed that in the case of TiO2:(2 at. % Tb), except for the rutile form, the presence of fine-crystalline anatase was observed. Moreover, the lack of Raman peaks shift attests to the lack of stress in the titania lattice of all of the TiO2:Tb films. This fact indicates localization of Tb3+ ions on the surface of TiO2 nanocrystals. In the case of optical investigation, results have shown that doping with terbium has a significant influence on the properties of TiO2, but it does not decrease the high transparency of the matrix. The observed changes of the transmission characteristics were produced only due to modification of the TiO2:Tb structure. Photoluminescence measurements have shown that emission of light from TiO2:Tb films occurs when the amount of terbium is 2.6 at. %. Based on the obtained results a scheme of direct energy transfer from titanium dioxide matrix (with rutile structure) to Tb3+ ions has been proposed.

Thermo optical coefficient of tin-oxide films measured by ellipsometry

The thermo-optic coefficient of tin-oxide thin films on silicon substrates was measured using fixed wavelength ellipsometry. The applicability of ellipsometry for these measurements is discussed with special considerations to the problem of measurement of the thermo-optic coefficient of materials with very low values of the thermo-optic coefficient (<2 × 10−5). The effect of thermal annealing on the thermo-optic coefficient and on the film-substrate boundary properties of the tin oxide film is also discussed.

Determination of reverse cross-relaxation process constant in Tm-doped glass by 3 H 4 fluorescence decay tail fitting

In this paper, we numerically investigate the fluorescence decay of Tm-doped tellurite glasses with different dopant concentrations. The aim is to find a set of data that allows the prediction of material performance over a wide range of doping concentrations. Among the available data, a deep investigation of the reverse cross-relaxation process (3F4,3F4,→3H6,3H4) was not yet available. The numerical simulation indicates that the reverse cross-relaxation process parameter can be calculated by fitting the slow decaying 3H4 fluorescence tails emitted when the pump level is almost depopulated. We also show that the floor of the 3H4 decay curve is indeed related to a second exponential constant, half the 3F4 lifetime, kicking in once the 3H4 level depopulates. By properly fitting the whole set of decay curves for all samples, the proposed value for the reverse cross-relaxation process is 0.03 times the cross-relaxation parameter. We also comment on the measurement accuracy and best set-up. Excellent agreement was found between the simulated and experimental data, indicating the validity of the approach. This paper therefore proposes a set of parameters validated by fitting experimental fluorescence decay curves of both the 3H4 and 3F4 levels. To the best of our knowledge, this is the first time a numerical simulation has been able to predict the fluorescence behavior of glasses with doping levels ranging from 0.36 mol% to 10 mol%. We also show that appropriate calculations of the reverse cross-relaxation parameter may have a significant effect on the simulation of laser and amplifier devices.

Rare-earth doped optical fibers with nano-phase glass-ceramic structures

In this article we present possibility of obtaining nano-phase structures in glasses and optical fibers doped with RE ions. Effect of phosphate on structural and optical properties of antimony-germanate glasses doped with Eu³⁺ ions have been investigated. Modification of Sb₂O₃ - GeO₂ - SiO₂ - Al₂O₃ - Na₂O glass system by P₂O₅ (up to 10 mol.%) shows possibility of creation of the EuPO₄ phosphate nanophase. Controlled heat-treatment process selected glasses are used as a core of optical fiber. The luminescence spectra of glass, glass-ceramics and optical fibers were compared and discussed in terms of embedding nano-crystalline phase structures in RE - doped optical fiber.

Glass and glass-ceramic photonic systems

The development of optically confined structure is a major topic in both basic and applied physics not solely ICT oriented but also concerning lighting, laser, sensing, energy, environment, biological and medical sciences, and quantum optics. Glasses and glass-ceramics activated by rare earth ions are the bricks of such structures. Glass-ceramics are nanocomposite systems that exhibit specific morphologic, structural and spectroscopic properties allowing developing new physical concepts, for instance the mechanism related to the transparency, as well as novel photonic devices based on the enhancement of the luminescence. The dependence of the final product on the specific parent glass and on the fabrication protocol still remain an important task of the research in material science. Looking to application, the enhanced spectroscopic properties typical of glass ceramic in respect to those of the amorphous structures constitute an important point for the development of integrated optics devices, including optical amplifiers, monolithic waveguide laser, novel sensors, coating of spherical microresonators, and up and down converters. This paper presents some results obtained by our consortium regarding glass-based photonics systems. We will comment the energy transfer mechanism in transparent glass ceramics taking as examples the up and down conversion systems and the role of SnO2 nanocrystals as sensitizers. Coating of spherical resonators by glass ceramics, 1D-Photonic Crystals for luminescence enhancement, laser action and disordered 1-D photonic structures will be also discussed. Finally, RF-Sputtered rare earth doped P2O5- SiO2-Al2O3-Na2O-Er2O3 planar waveguides, will be presented.