Up-conversion luminescence of GdVO4:Nd3+/Er3+ and GdVO4:Nd3+/Ho3+ T phosphors under 808 nm excitation

All authors acknowledge to the COST Action CM1403: The European upconversion network - from the design of photon-upconverting nanomaterials to biomedical applications (2014–2018). The authors from the University of Belgrade acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ). K. S. acknowledges the Latvian National Research Program IMIS2 (Grant No. 302/2012 ). T. G. acknowledges the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ).In recent years, there exists a tendency in research of up-conversion materials to shift excitation from 980 nm to shorter wavelengths. Here, in order to produce up-conversion luminescence emission of GdVO4-based materials under 808 nm excitation, polycrystalline powders of GdVO4:Er3+/Nd3+ and GdVO4:Ho3+/Nd3+ were successfully prepared by a high-temperature solid-state reaction technique. The prepared powders were highly crystalline with a single-phase zircon-type GdVO4 structure and consisted of micrometer-sized irregular spherical particles (2–6 μm in diameter). In all studied samples, visible up-conversion luminescence was successfully achieved under 808 nm illumination. Near-infrared pumping produced emission bands in the green, yellow-orange and green regions of the visible spectrum. The bands in the green and red regions of GdVO4: Er3+/Nd3+ as well as GdVO4:Ho3+/Nd3+ were, respectively, characteristic of Er3+ and Ho3+ ions. The dominant band originating from the 4G7/2 → 4I11/2 transition in Nd3+ ions was observed around 597 nm in all samples.COST Action CM1403 (2014–2018); Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ); Latvian National Research Program IMIS2 (Grant No. 302/2012 ); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

A comparative study of photocatalytically active nanocrystalline tetragonal T zyrcon- type and monoclinic scheelite-type bismuth vanadate

The authors from Vinča Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ). The work of K. Smits was supported by Latvian National Research Program IMIS2 (Grant no. 302/2012 ).Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (∼34 m2/g) were ∼7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties.Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Multicolor-tunable emissions of YOF: Ln 3+ /Yb 3+ (Ln 3+ = Ho 3+ , Er 3+ , Tm 3+ ) nanophosphors

Color tuning of down-shifting and up-conversion emissions of YOF:Ln(3+)/Yb3+ (Ln(3+) = Er3+, Tm3+) nanophosphors is demonstrated. Nanophosphors were prepared by the modified sol-gel Pechini method and characterized by the X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. Samples consist of 20 nm particles crystallized in the rhombohedral crystal structure. Depending on the Ln(3+) / Yb3+ concentration ratio and the type of excitation (UV/VIS or NIR) color of the particles emission varied from the blue to red. Commission Internationale de L'Eclairage chromaticity coordinates of emission colors are given for the range of Ln(3+)/Yb3+ concentration ratios for both down-shifting and up-conversion luminescence. We showed that the emission color of these nanophosphors may be additional tuned by simultaneous excitation with UV-VIS and NIR radiation (in different proportion) which yields unique color labels for the anti-counterfeit and security applications

Improved coloristic properties and high NIR reflectance of environment-friendly yellow pigments based on bismuth vanadate

Herein, fine powders of yellow pigments based on BiVO4 were successfully prepared in two crystalline forms, tetragonal zircon-structured and monoclinic scheelite-structured, through a ethylene glycol-assisted method subjected to a thermal treatment at two different temperatures. The obtained materials were brightly colored with different hues of yellow, exhibited high reflection in the near-infrared region and showed visible luminescence under excitation by UV light. The new preparation method had a considerable effect on chromatic properties of the prepared scheelite-structured BiVO4 pigments. The sample with the most vivid and bright shade of yellow was found to have the L*a*b* and L*C* ab h* ab color coordinates of (87.28, 0.37, 91.53) and (87.28, 91.53, 89.79), which are indicative of exceptionally good chromatic properties superior and/or comparable to those of other inorganic yellow pigments, both commercially available and recently described. In addition, the NIR reflectance of this powder was very high (≥ 80%). © 2018 Elsevier Ltd and Techna Group S.r.l

Intra- and inter-configurational luminescence spectroscopy of Pr 3+ -doped YPO 4 nanophosphors

Nanopowders of YPO4 phosphors with different Pr3+ doping were successfully prepared by a sol gel method under different synthesis conditions. The crystallite size and strain show a strong dependence on the Pr3+ doping concentration and on the annealing temperature. By annealing at 300 degrees C one can obtain the xenotime structure of the pure YPO4. The crystallite size can be controlled by controlling the annealing temperature and it increases with increasing the annealing temperature. The room temperature inter-configurational 4f(2) 4f5d and intra-configurational 4f(2) 4f(2) emission-excitation transitions spectra are measured and investigated. Upon 4f(2) 4f(2) emission transitions and peaks in red region assigned to D-1(2) -> H-3(4) transition as photon cascade emission phenomena (PCE). The presence of only D-1(2) -> H-3(4) transition is discussed. In addition, the D-1(2) energy level lifetimes as well as the refractive indexes were determined and discussed

Sol gel synthesis and pH effect on the luminescent and structural properties of YPO4: Pr3+ nanophosphors

Pr3+-doped YPO4 nanophosphors prepared by simple sol gel method with different pH values (2, 4, 7 and 11) were obtained. The nanopowders samples were characterized by X-ray diffraction (XRD), room temperature steady and time resolved photoluminescence spectroscopy. The thorough study of pH influence on particles structure and luminescence of YPO4: 1 at. Pr3+ is presented. It was found that the grain size of samples increases with increases in pH value and obtained particles crystallize in a tetragonal phase with xenotime structure. Under 4f5d excitation (230 nm), all emission spectra show the inter -configurational 4f(2)- GT 4f5d and under (3)P2 excitation (449 nm), only the intra-configurational D-1(2)- GT H-3(4) red emission transition between 580 nm and 620 nm are observed. The highest luminescent intensity was obtained for samples prepared at pH = 4. Furthermore, it was found that the pH of solution has no effect of D-1(2) lifetime. (C) 2017 Elsevier B.V. All rights reserved

Europium-doped GdVO4 nanocrystals as a luminescent probe for hydrogen peroxide and for enzymatic sensing of glucose

The authors describe the preparation of Eu3+-doped GdVO4 nanocrystals (NCs) by precipitation of the Cd3+(Eu3+)-citrate complex which was then converted to the respective vanadate by dialysis. The fractions of Eu3+ ranged from 5 to 100 mol%. The NCs were characterized by XRD, TEM, ICP-OES and dynamic light scattering which revealed that they possess superior colloidal stability in aqueous solutions in that no precipitation can be observed even after several months. The NCs display red and largely red shifted fluorescence (peaking at 618 nm) on photoexcitation at around 300 nm. Fluorescence is strongly quenched by hydrogen peroxide. It is also shown that the fraction of doping with Eu3+ strongly affects quenchability. Most efficient quenching by H2O2 is observed if the NCs are doped with 50% of Eu3+. The findings were exploited to develop a fluorometric assay for H2O2 that works in the 5 to 250 mu M concentration range, with a limit of detection as low as 1.6 mu M (at a signal-to-noise ratio of 3). The probe was further employed to design a highly sensitive enzymatic assay for glucose via measurement of the quantity of H2O2 formed as a result of the catalytic action of glucose oxidase. (C) 2016 Elsevier B.V. All rights reserved

Degradation of anionic surfactants using the reactor based on dielectric barrier discharge

Two anionic surfactants (sodium lauryl sulfate - SDS and sodium dodecylbenzenesulfonate - SDBS) were treated with dielectric barrier discharge. Loss of surfactant activity, decrease of chemical oxygen demand and total organic carbon as well as lower toxicity of degradation products were determined. Effects of catalysts - hydrogen peroxide and iron (II), on parameters mentioned above, were determined. Catalysts affect the degradation of SDBS and in the case of SDS catalysts have no effect on degradation. Both catalysts induce the decrease of COD and TOC values. Toxicity of solutions after the plasma treatment is lower in all the systems tested. [Projekat Ministarstva nauke Republike Srbije, br. OI 172030