Foszforeszcens stroncium-aluminátok előállítása és fejlesztése

Light is one of the central factors in the life of mankind, which is why the various natural light phenomena and the materials that display them have been of interest to mankind since the beginning of history. Numerous attempts have been and are still being made to understand and reproduce these phenomena and materials. Today, it is possible to imitate, study and model almost any natural phenomenon or substance, and thus to increase our knowledge of light phenomena and substances exhibiting light phenomena. Nevertheless, the functioning of some phenomena is still only partially understood and their understanding is still ongoing. New properties of new materials, which are constantly being developed, are gradually shedding light on analogies, thus also helping to deepen our understanding of the phenomena we experience. Among the different types of luminescence, phosphorescence is one of the most complex phenomena, in which the individual sub-processes and their roles are still only partially understood. With our current knowledge, we can therefore design in advance the luminescent materials that best meet our needs. These needs can vary widely depending on the application, so it may be necessary to manipulate the wavelengths emitted and absorbed for materials with extremely long or even short afterglow times. With the advance of the green approach, new demands have been made on luminescent materials such as long lifetime, reusability, extreme chemical and physical stability, safer use or simply cheap and large-scale production. To meet these needs, new materials can be developed or old materials can be improved, and new applications can be associated with known materials. Today, a large number of activated photoluminescent inorganic oxides are known, just to mention a few examples: MAl2O4, M4Al14O25 M2ZnSiO7, MAlSiN3, MBPO5, M3PO4 (M = Mg, Ca, Sr, Ba). The presence of impurity (activating/co-activating) ions is usually required; these can be one or more rare earth metals, depending on the host crystal structure, but also transition metals. One of the main advantages of these materials, besides their durability, is that they do not contain any radioactive component. However, of the hundreds of known phosphorescent materials, only a few can be charged in sunlight and then emit light for hours, so materials that can do this together are of particular interest

Photocatalytic performance of Sr4Al14O25: Eu,Dy phosphor assisted ZnO:Co+Ag nanocomposite under continuous and pulsed illumination

We report on the photocatalytic performance of the ZnO:Co+Ag nanocomposite photocatalyst coupled with the commercial cyanic blue Sr4Al14O25:Eu,Dy long afterglow phosphor. In this composition the phosphor can harvest and recover light as persistent phosphorescence. The contribution of the phosphor to the photocatalytic model reaction of methyl orange dye decomposition in aqueous solution was experimentally verified under power-saving illumination conditions. The two most important findings of this work are that the cobalt doped and silver nanoparticle decorated ZnO nanocomposite catalyst can outperform bulk ZnO under certain conditions and that rare earth metal doped strontium aluminate phosphor assistance allows running photocatalytic experiments with short on/long off illumination pulses. Power savings over one order of magnitude are possible this way while maintaining a photocatalytic performance comparable with that achieved using continuous illumination. This suggests a strategy to design new arrangements of more sustainable photocatalytic reactors and catalyst compositions for effective treatment of wastewaters or air pollutants. © 2016 Elsevier B.V

Cross-Calibration of an α-Source Used for Luminescence Dating by Applying Different Samples and Procedures

In terms of fine-grain luminescence dating applications, the efficiency of a-radiation in producing luminescence is an important issue when determining environmental dose rates. Efficiency is usually assessed by measuring the ratio of luminescence intensities induced by known a and b laboratory doses. Consequently, most thermoluminescence (TL)/optically stimulated luminescence (OSL) readers besides the standard 90Sr/90Y b-source can also be equipped with a 241Am a-source. A crucial point is, however, the calibration of these sources. The calibration of b-sources is routinely performed using standard quartz samples previously irradiated by a known g-dose, though, in the case of a-sources, the procedure is less standardised, partly because there are no calibration materials with a known a-efficiency value. In this study, we aimed to cross-calibrate the built-in a-source of a RISØ TL/OSL DA-20 luminescence reader by testing and comparing five procedures, applying different samples (quartz and polymineral), different protocols multiple aliquot regeneration (MAR) and single aliquot regeneration (SAR) and different calibration sources. Throughout the tests, the performance of the fine-grain RISØ calibration quartz was also assessed. Regardless of the applied procedure, the calculated a-dose rates with one exception gave similar results. On the one hand, the applied polymineral sample due to potential fading, fairly high residuals after bleaching and relatively low infrared stimulated luminescence (IRSL) sensitivity proved to be the least optimal choice for cross-calibration. On the other hand, the tested natural fine grain quartz gave almost identical results when using different types of bleaching and different calibration a-sources. The mean dose rate determined for the source was 0.080 ± 0.004 Gy/s. The cross-calibration by using the RISØ fine grain quartz yielded somewhat higher but at the apparent uncertainty of luminescence dating still not significantly different dose rate for the source under calibration. Tests showed that the calibration quartz saturates at a relatively low a-dose, and the shape of a- and b-dose-response curves also depart from each other quite early, suggesting that cross-calibration with this material seems to be reliable only at low doses. For the first time, the a-value of the fine-grain calibration quartz was also determined using the freshly calibrated a-source, and the measurement yielded a 0.054 ± 0.003 value. We propose that after further validation of this result, the RISØ calibration quartz can ease the dose rate assessment of uncalibrated a-sources in the future

Pulse electrodeposition and characterization of non-continuous, multi-element-doped hydroxyapatite bioceramic coatings

Multi-element-modified bioactive hydroxyapatite (mHAp) coatings were developed onto commercial titanium alloy material (Ti6Al4V) in clusters. The coatings were prepared by applying pulse current deposition technique. The pure HAp layer was doped and co-deposited with Ag+, Zn2+, Mg2+, and Sr2+ ions. Potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) were performed in simulated body fluid (SBF) using three-electrode open cell over a long time period to assess the corrosion properties of bioceramic coatings. The biocompatible characteristics of layers were investigated by seeding osteoblast-like MG-63 cells onto the samples’ surface. The morphology and structure of coatings were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) while cross-sectional analyses were carried out by focused ion beam (FIB). The elemental composition of coatings was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The biocompatible measurements revealed enhanced bioactivity of modified HAp compared to uncoated implant materials and pure HAp bioceramic coating. The corrosion tests confirmed that the coatings were biodegradable