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Nanostructured powders xFe/nano-Al2O3 with the Fe loading of x = 0.0 – 5.0 wt% were obtained using laser vaporization by CO2 laser. XRF, XRD, HRTEM, PL and UV–Vis DRS techniques were employed to investigate physicochemical, structural and optical properties of the synthesized nanopowders with the average particle size of 9 nm. Nanopowders xFe/nano-Al2O3 as model catalysts were tested in isobutane dehydrogenation reaction. The results obtained were compared with similar data for the xFe/γPb-Al2O3 systems synthesized by the conventional sol–gel method. According to XRD and UV–Vis DRS data, in the series of xFe/nano-Al2O3 samples a great part of Fe3+ ions is in the disordered environment of subsurface layers of Al2O3 nanocrystallites, predominantly in the tetrahedral coordination. In distinction to samples of the xFe/γPb-Al2O3 series, in the case of nanostructured xFe/nano-Al2O3 powders the formation of Fe2O3 phase does not occur at any concentrations of iron or conditions of testing. The analysis of the PL spectra of xFe/nano-Al2O3 powders also showed the presence of surface sites of Fe3+ ions, which were not detected for xFe/γPb-Al2O3. Catalytic testing of the xFe/nano-Al2O3 series samples in isobutane dehydrogenation revealed the formation of the iron active sites that ensure catalytic activity of the samples. Differences in the catalytic properties of FeOx/Al2O3 samples obtained by the sol–gel method and laser vaporization are related to different states of Fe3+ ions. Thus, the xFe/nano-Al2O3 nanopowders, in contrast to xFe/γPb-Al2O3, contain a large amount of active Fe3+ sites. These sites, being involved in the dehydrogenation reaction, are present predominantly on the surface of the nanopowders. [ABSTRACT FROM AUTHOR]

In the present article we report on the laser synthesis of Eu3+ doped nanophosphor with improved red color based on single-phase monoclinic Y 2 O 3 and an experimentally measured quantum yield as high as 60% at λ = 395 nm excitation. HRTEM and SEM studies evidence the formation of nanoparticles with a spherical morphology, the average diameter of ca. 20 nm, and high crystallinity. We demonstrate that such a high quantum yield can be achieved by adding oxygen during laser synthesis in a combination with post-synthesis treatments in air at T = 750 °C. The thermal annealing effects in air and vacuum in the range of 250–750 °C on the morphology, structure, optical and photoluminescence properties of as-synthesized m -Y 2 O 3 :Eu3+ have been discussed. The obtained chromaticity coordinates (0.659, 0.332), high color purity (96%) and high absolute quantum yield indicate the possibility of using red nanophosphor based on monoclinic Y 2 O 3 :Eu3+ in numerous luminescence applications. [ABSTRACT FROM AUTHOR]

Nanosized zirconia doped with europium (ZrO 2 :xEu3+, x = 0.07–9.95 wt%) and represented by weakly agglomerated spherical particles with the size of 9.7 ± 4.3 nm was synthesized by laser vaporization in an argon atmosphere using a cw CO 2 laser. The specific surface area of the obtained nanoparticles is 92 ± 4 m2/g. The XRD study with Rietveld refinement revealed that the phase composition of the samples is represented predominantly by the tetragonal phase with a small content of monoclinic phase. At the concentrations above 4.57 wt%, stabilization of the cubic phase also occurs. The dependence of the PL intensity, PL lifetime, absolute quantum yield, and color coordinates of ZrO 2 :Eu3+ on the Eu concentration was studied. It was shown that the maximum PL intensity is observed at the concentration of 8.39 wt%. The Eu3+ lifetime decreases from 5.60 to 3.21 ms with a growth of the Eu content. Aging of the samples due to the adsorption of OH groups was revealed. The absolute quantum yield QY was measured for the 575–725 nm region corresponding to the luminescence of europium, and for the 410–725 nm region, which also includes the emission of oxygen vacancies. The QY was found to increase with the growth of Eu concentration, reaching the highest values for ZrO 2 :8.39Eu3+; it is equal to 1.6 and 17.6% for 575–725 and 410–725 nm regions, respectively. It was shown that variation of the Eu3+ concentration and excitation wavelength makes it possible to obtain color coordinates with red and close to white light. Along with the high QY for the region of 410–725 nm, this indicates that it is more promising to use ZrO 2 :Eu3+ as the white phosphor rather than the red one. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al 2 O 3 NPs with the particle size from 2 to 21 nm were synthesized by CO 2 laser vaporization. • The structure, morphology, thermal, and optical properties of Al 2 O 3 NPs were studied. • Photoluminescence is determined by 3d elements, surface hydroxyl groups, and F-type centers. • The size effect for Al 2 O 3 NPs has a boundary corresponding to 6–7 nm. A series of Al 2 O 3 nanoparticles with the sizes ranging from ~ 2 to 21 nm, according to XRD, HRTEM and BET, was obtained by vaporization of α-Al 2 O 3 in flowing helium and argon at different pressures under the action of a cw CO 2 laser. The particle size was changed by varying the composition of ambient gas (He, Ar) and its pressure in a vaporization chamber from 0.034 to 0.9 bar. The effect of the synthesis conditions on the properties of Al 2 O 3 nanopowders is presented and discussed. Particles with the size smaller than 6–7 nm have a faceted shape, whereas the shape of larger particles is close to spherical. It was found that the resulting nanopowders consist of a mixture of transition aluminas, among which the γ -polymorph is dominant. Thermal analysis showed that for smaller nanoparticles the phase transition to α-Al 2 O 3 occurs at a lower temperature. In nominally pure Al 2 O 3 nanoparticles with different sizes, photoluminescence at RT and 80 K is determined by trace level concentrations (≤10–3 wt%) of uncontrolled impurities of 3d elements (Cr3+(O h) and Fe3+(T d)), surface hydroxyl groups, and point defects represented mostly by F-type centers. The acquired experimental data indicate that manifestation of the size effect for Al 2 O 3 nanoparticles has a boundary corresponding to 6–7 nm. Al 2 O 3 nanoparticles with the dominant γ-Al 2 O 3 structure obtained by the laser method can be promising in many chemical reactions, particularly as the supports of catalysts and sorbents, for which the high specific surface area is of special importance. [ABSTRACT FROM AUTHOR]

Laser vaporized xCr/Al 2 O 3 nanopowders with the particle size of ca. 15 nm were studied by XRF, EDX, HRTEM, XRD, DD, BET, TGA, UV–Vis DRS, Raman and PL spectroscopy methods as a catalytic system in dehydrogenation of isobutane. The nanopowders were found to contain not only the Cr6+ ions located on the surface of nanoparticles, but also two different types of Cr3+ sites as components of the γ-Al 2 O 3 solid solution. One type consists of the bulk Cr3+ b sites in a strong crystal field. Another type is represented by the Cr3+ s sites residing near the surface of xCr/Al 2 O 3 nanoparticles. Such sites are in a weak crystal field. It was shown that catalytic activity of the nanostructured xCr/Al 2 O 3 system is provided by the high content of surface Cr3+ s sites. The results obtained make it possible to propose the nanopowders obtained by laser synthesis as a promising catalytic system that can be used in the development of highly active catalysts for dehydrogenation of alkanes with the decreased chromium content. Unlabelled Image • Model CrO x /Al 2 O 3 nanoparticle catalysts were obtained by laser vaporization • Structure, morphology and optical properties of CrO x /Al 2 O 3 nanopowders were studied • Cr3+ s sites are located near the surface of CrO x /Al 2 O 3 nanoparticles • Cr3+ s sites play the key role in the isobutane dehydrogenation reaction • CrO x /Al 2 O 3 nanoparticles are highly active catalysts with the decreased Cr content [ABSTRACT FROM AUTHOR]