130,462 research outputs found
Luminescent inks based on Eu:PO4 nanoparticles and polyvinyl alcohol for anti-counterfeiting
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Spectroscopic investigations of nanostructured LiNbO3 doped with Eu3+
No full textStructural and optical properties of the sol-gel derived nanocrystalline lithium niobate (LiNbO3) powders doped with Eu3+ ions have been studied. In particular, the influence of the sizes of nanoparticles controlled by temperature on the structural and luminescence properties has been investigated. Emission bands corresponding to 5D0 emission became more resolved with increasing nanocrystal size and changed to a typical Eu3+:LiNbO3 single crystal spectrum for nanocrystals having an average size of more than 40 nm. Nonlinear optical properties of nanostructured LiNbO3 have been confirmed by simple observation of second harmonic generation effect (SHG). The possibility of using nanostructured LiNbO3 doped with rare-earth ions as self-doubling elements in integrated optoelectronic devices has been discussed
The f-f Emission of Pr3+ Ion as an Optical Probe for the Structural Properties of YAG Nanoceramics
No full textTransparent Pr-doped YAG nanocerainics composed of grains with an average size of 42 nm, were fabricated with the Low Temperature Hight Pressure (LTHP) sintering technique using the corresponding nanopowders as the starting materials. The structure of the nanoceramics was analyed by X-ray diffraction (XRD). The effect of the sintering conditions on the structural properties is discussed on the basis of the changes of the spectroscopic properties of Pr3+. In particular, the intensities and decays of the emission transitions originating from the P-3(0) and D-1(2) levels are investigated and correlated with structural properties of the material, such as microstrains produced by the high-pressure process
Effect of Ce3+ concentration on persistent luminescence of YAGG:Ce3+,Cr3+,Nd3+ nanophosphors obtained by the co-precipitation method
No full textSynthesis of Y3Al2Ga3O12 garnet (YAGG) nanophosphors co-doped with Ce3+, Cr3+, and Nd3+ ions by co-precipitation is reported. The effect of Ce3+ concentration on the structure of garnet and on optical properties including persistent luminescence was investigated. The X-ray diffraction measurements showed that single garnet phase was obtained. The contraction of the crystallites size was observed with increasing the cerium concentration. The combined emission of three used co-dopants together allows to extend persistent luminescence spectral range. The photoluminescence, excitation and persistent luminescence spectra were collected and the optimal Ce3+ concentration for the highest efficiency conversion of UV and blue light into the red and the near infrared emission was determined. Based on thermoluminescence data, the effect of Ce3+ concentration on the traps redistribution was also investigated
Luminescent YPO4:Eu@PVA dispersions for anti-counterfeiting ink applications
No full textA method was developed to obtain YPO4:Eu dispersions of PVA as a luminescent inks. YPO4:Eu nanoparticles were prepared by precipitation followed by hydrothermal treatment. The dispersion preparation included systematic studies to prepare a stable colloidal system and to investigate the role of parameters affecting its stability and UV-excited YPO4:Eu emission intensity. The effect of PVA concentration was studied in detail for two different PVAs to determine the optimal parameters for its use as ink with specific luminescent properties. The type of interactions responsible for the dispersion stability was also investigated
Controlling a defect structure of the ZnGa2O4:Cr3+ spinel through synthesis parameters for persistent luminescence optimization
No full textZnGa2O4:Cr3+ (ZGO:Cr) is one of the most promising red persistent phosphors for in-vivo imaging due to its
650–750 nm emission band in the range of the so-called first biological window. In this paper, we report on how
to control the high brightness persistent luminescence of the smallest ZGO:Cr nanoparticles by optimization of
hydrothermal synthesis parameters. The influence of pH solution, the temperature of synthesis, and calcination
on the degree of inversion, lattice parameters, morphology, and crystallite size were systematically investigated.
The results have shown that different synthesis conditions modify the trap depths distribution, by mixing the
occupancy of Zn2+ and Ga3+ sites in the spinel structure, which affects the duration and intensity of persistent
luminescence. The correlation between structural changes and optical properties is established and it is possible
to control them by selecting the appropriate hydrothermal synthesis parameters
Multimodal anti-counterfeiting inks: modern use of an ancient pigment in synergy with a persistent phosphor
No full textMulti-level luminescent, transparent and non-permanent inks for anti-counterfeiting systems and security were developed. The inks emit radiation at different wavelengths based on the type of radiation used to illuminate them, providing multiple layers of safety. The red persistent phosphor Y2O2S:Eu3+,Mg2+,Ti4+ (YOS) was mixed with Egyptian Blue (EB) and dispersed in an aqueous solution of arabic gum. Imaging techniques, excitation and emission spectra, the study of luminescence over time and the duration time were used to verify that the obtained systems showed the desired optical characteristic both in the infrared and in the visible spectral ranges. The two luminescent materials act synergistically: when illuminated with UV light, YOS emits red photons over time and EB, absorbing this energy, emits infrared photons. The resulting emission characteristics are non-obvious and can be designed at the ink developing stage. The tests performed on several substrates showed that the developed luminescent inks are well suited for use in the field of security and anti-counterfeiting
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Structural and luminescence properties of Eu3+ doped BaxSr1−xTiO3 (BST) nanocrystalline powders prepared by different methods
No full textEu3+ doped BaxSr1-xTiO3 (BST) nanocrystalline powders have been prepared using molten salts, sol-gel and hydrothermal techniques in order to compare their structural and luminescence properties. The sizes of the particles are around 50 nm for the BST powders obtained by the sol-gel and hydrothermal methods while they are around 400 nm for the samples prepared by the molten salts method. The Eu3+ doped BST samples show strong emission in the visible range. The luminescence spectra of the Eu3+ ions for the investigated samples depend strongly upon the preparation method. The luminescence bands are affected by a notable amount of inhomogeneous broadening. The broadening of the emission bands and the non-exponential behavior of the emission decay curves point to the presence of significant structural disorder
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