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A series of Al2O3 nanoparticles with the sizes ranging from ~ 2 to 21 nm, according to XRD, HRTEM and BET, was obtained by vaporization of α-Al2O3 in flowing helium and argon at different pressures under the action of a cw CO2 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 Al2O3 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-Al2O3 occurs at a lower temperature. In nominally pure Al2O3 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+(Oh) and Fe3+(Td)), surface hydroxyl groups, and point defects represented mostly by F-type centers. The acquired experimental data indicate that manifestation of the size effect for Al2O3 nanoparticles has a boundary corresponding to 6–7 nm. Al2O3 nanoparticles with the dominant γ-Al2O3 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.

Nanostructured powders xFe/nano-Al2O3 with the Fe loading of x = 0,0–5,0 wt% were obtained using laser vaporization by a cw 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 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 involved in the dehydrogenation reaction are present predominantly on the surface of the nanopowders.

This paper presents the results of study of titanium–magnesium catalysts often used in polymerization processes, by photoluminescence spectroscopy (PL) in combination with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interaction of dibutyl phthalate (DBP) with MgCl2was studied at DBPadded/Mg = 0–1 (mol/mol). The luminescence spectra with excitation at 278 nm and the excitation spectra for main emission bands were recorded. It was shown that DBP adsorbed on magnesium chloride, both in the form of donor–acceptor complexes (D+A–) and in the form of molecular complexes. At DBPadded/Mg +A–complexes occur predominantly; with an increase in DBPadded/Mg, the fraction of molecular complexes increases. Molecular complexes are destroyed during the treatment of the support by TiCl4. In this case, the structure of magnesium chloride is disordered and new coordination–unsaturated sites are formed. This work is a first attempt to apply PL spectroscopy in combination with DRIFTS spectroscopy to study titanium–magnesium Ziegler–Natta catalysts. The application of PL spectroscopy to such systems made it possible to detect interactions within and between donor molecules, which would be particularly challenging to achieve using other spectroscopic methods. Both spectroscopic methods provided crucial information about the existence of two types of complexes on the sample surface which is important for tuning the synthesis procedure of the titanium–magnesium catalysts for olefin polymerization.

A comprehensive study of optical and catalytic properties of highly dispersed single-phase η-, γ- and γ*-Al2O3 ([Cr3+] ∼ 10–4 wt.%) powders and the related model chromia-alumina catalysts with different chromium content ([Cr3+] = 0.25, 0.5 and 1 wt%) was carried out. The catalytic characteristics (product yield, conversion and selectivity) in isobutane dehydrogenation to isobutylene were measured for all the samples under consideration. The surface Cr3+S luminescence centers were detected by photoluminescence spectroscopy in all the samples. The content of Cr3+S centers in the samples was estimated before and after isobutane dehydrogenation. It was shown that the amount of surface Cr3+S centers correlates with isobutylene yields of the reaction. Among the studied samples, the maximum amount of Cr3+S luminescence centers was found for the model 1% Cr/γ-Al2O3 catalyst. This sample has the highest values of isobutane conversion and isobutylene yield. The comprehensive study of the Cr/Al2O3 systems made it possible to propose a method for predicting the catalytic activity of nanostructured materials using the photoluminescence detection of surface luminescence centers and their quantitative evaluation.

This paper is devoted to a determination of the 0% probability laser-induced damage threshold of the BaGa4Se7 and BaGa2GeSe6 nonlinear elements by the R-on-1 procedure. A Ho:YAG laser radiation at 2091 nm with pulse duration 13-17 ns and varied pulse repetition rate, 2 kHz, 5 kHz and 10 kHz, was used for testing.

Laser induced damage in dark yellow phase of BaGa 4 Se 7 (BGSe) crystal has been investigated at the wavelengths of 1053 nm. Damage by multiple pulse irradiation (500 pulses) has been studied and the probabilistic behavior of the damage is discussed.

The structural properties of η-, γB-, γPb-, χ-, θ- and α-Al2O3 polymorphs were studied by X-ray diffraction and photoluminescence spectroscopy using Cr3+ ion as a luminescent probe in its natural concentration (

Polyethylene m-Y2O3:Eu3+ composites (PECs) containing 0.32, 0.77, and 1.79 wt% of well-dispersed sphere-like m-Y2O3:Eu3+ nanoparticles were obtained by in situ polymerization in the presence of a titanium-magnesium catalyst (TMC). TMC was synthesized by sequential deposition of organic magnesium and TiCl4 on m-Y2O3:Eu3+ that had been previously dehydroxylated at 650 °C. Detailed photoluminescence properties of the obtained composites as a function of m-Y2O3:Eu3+ content were investigated in combination with UV–Vis and IR spectroscopy data. It was shown that Eu3+ ions in monoclinic Y2O3 lattice are responsible for the high red emission of the composites. The effect of the РЕС host on the luminescence properties of m-Y2O3:Eu3+ was revealed. The obtained chromaticity coordinates with improved red color (0.653, 0.347) and high absolute luminescence quantum yield up to 23% make РЕСs potential promising materials for luminescent applications.

A series of Eu doped ZrO2 micropowders with different concentration of Eu (0.04–6.85 wt%) was obtained by incipient wetness impregnation followed by annealing at 1200 °C. X-ray diffraction analysis revealed that the phase composition of samples with the minimum Eu concentrations in the series is represented predominantly by the monoclinic phase. An increase in the Eu content leads to proportional stabilization of the tetragonal phase, and at concentrations above 2.00 wt% the cubic ZrO2 phase is also stabilized. It was shown that red luminescence of the samples is responsible for the radiation transitions 5D0 → 7FJ (J = 0–4) in Eu3+ ions. It was shown that shaping the photoluminescence spectrum of monoclinic ZrO2:Eu3+ phosphor depending on Eu concentration is related to the stabilization of ZrO2 tetragonal and cubic structure by Eu3+. The local symmetry of Eu3+ in each of the detected phases was identified. The lifetime of Eu3+ in the monoclinic phase of ZrO2 does not depend on the dopant concentration and is in the range of 0.73–0.81 ms, whereas in the tetragonal phase it first increases from 1.7 to 1.85 ms and then reaches a maximum at a concentration of 2.00 wt%. The absolute quantum yield increases from 1.6 to 4.8% over the entire range of Eu concentration.

Oxygen vacancies represented by F and F2 centers were detected in faceted Al2O3 nanoparticles with the size less than 10 nm by a photoluminescence method. Al2O3 nanoparticles with such intrinsic defects were synthesized by evaporation of α-Al2O3 in flowing helium using a continuous wave CO2 laser. The XRD analysis showed that the crystal structure of Al2O3 nanoparticles is represented mostly by the low-temperature γ- and/or η-Al2O3 phases. The luminescence maxima of F and F2 centers in the Al2O3 nanoparticles were found to be 3.07 and 2.47 eV. These values are close to the luminescence maxima of F and F2 centers in bulk α-Al2O3.

Europium doped Gd2O3 sphere-like nanoparticles with dm = 9.3 ± 3.5 nm were synthesized by cw CO2 laser vaporization technique in a flowing mixture of argon and oxygen. According to XRD data, the Eu:Gd2O3 nanoparticles crystallize in the monoclinic symmetry class (C2/m space group). High-resolution luminescence spectroscopy study showed that the ultra-narrow 5D0 → 7F0 transition of Eu3+ demonstrates only two peaks corresponding to two inequivalent Cs positions of Eu3+ ion in monoclinic Gd2O3 lattice that is explained by the peculiarities of local environment of Eu3+ ion at these sites. The hypersensitive transition 5D0 → 7F2 dominates in the spectrum and is expanded to the red part of the spectrum in comparison with cubic Eu:Gd2O3 due to intense transitions terminating at higher-lying components of the crystal-field-split 7F2 state. In the luminescence spectrum, an additional weak band with the maximum at 407 nm corresponding to the electronic transitions 4f65 d1(7FJ) → 4f7(8S7/2) of Eu2+ was detected. The obtained values of chromaticity coordinates and absolute quantum yield are (0.644; 0.325) and ca. 1%, respectively. The phase transformations have been investigated using differential scanning calorimetry and thermogravimetry (50–1400 °C). After annealing in air at 700 °C, the monoclinic symmetry class of the Eu:Gd2O3 nanoparticles is preserved and the particle size increases to dm = 17.8 ± 6.1 nm. After annealing, the chromaticity coordinates (0.659; 0.334) and absolute quantum yield (ca. 4%) can be obtained using red phosphor based on monoclinic Gd2O3:Eu3+. The lifetime of the excited 5D0 state of Eu3+ in the annealed nanoparticles is longer than that in the as-synthesized nanoparticles, due to the suppression of nonradiative decay after annealing.

Spectroscopic features of the local structure of high purity (with the content of impurities −3 wt.%) spinel-like γ- and γ ∗ -Al 2 O 3 phases differing in the unit cell parameters were studied. Samples of these phases were synthesized from crystalline boehmite and nanodispersed pseudoboehmite, respectively. For each of the phases, photoluminescence of transition metal ions and oxygen vacancies – F- and F 2 -centers – was detected, and Raman scattering spectra were recorded. The photoluminescence study of γ ∗ -Al 2 O 3 revealed octahedrally coordinated ions Mn 4+ . Values of the crystal field strength and Racah parameters for Mn 4+ ions in γ ∗ -Al 2 O 3 were determined. Manifestation of PL of Mn 4+ ions in γ ∗ -Al 2 O 3 and its absence in γ-Al 2 O 3 can serve as the indicator for distinguishing between these phases. It was found that γ- and γ ∗ -Al 2 O 3 samples have individual Raman spectra. The revealed spectroscopic features in the local structure of γ- and γ ∗ -Al 2 O 3 phases confirm the differences between these spinel-like structures.

The synthesis of Al2O3:Tb3+ (0.019–0.62 mol%) nanoparticles by laser vaporization of α-Al2O3:Tb3+ ceramic targets using a cw CO2 laser in flowing helium at a pressure of 0.1 bar is reported. HRTEM, XRD and BET studies revealed that under the indicated conditions the produced Al2O3:Tb3+ nanoparticles have faceted and nearly a spherical shape with the average size below 10 nm. As shown by XRD, the phase composition of the synthesized nanoparticles is represented mostly by the low-temperature γ-Al2O3. Photoluminescence (PL) spectra were obtained for Tb3+ ions in γ-Al2O3 nanoparticles upon excitation to the 4f8 → 4f75d (λex = 230 nm), 7F6 → 5H7 (λex = 315 nm) and 5D3 → 7F3 (λex = 458 nm) transitions, and PL excitation spectra – for the most intense 5D4 → 7F5 (λmax = 543 nm) transition. The lifetime of the excited 5D4 state was found to be ca. 2.9 ms. The obtained values of the chromaticity coordinate and absolute quantum yield were (0.299, 0.509) and 12.6% at λex = 315 nm, respectively.

Laser vaporized xCr/Al2O3 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-Al2O3 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/Al2O3 nanoparticles. Such sites are in a weak crystal field. It was shown that catalytic activity of the nanostructured xCr/Al2O3 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.

The surface laser-induced damage threshold (LIDT) of B a G a 4 S e 7 and B a G a 2 G e S e 6 nonlinear crystals was studied at 2091 nm. Both yellow and dark yellow phases of B a G a 4 S e 7 were investigated. The Ho:YAG laser generating nanosecond pulses at 2 kHz, 5 kHz, and 10 kHz was used as a radiation source. The R-on-1 procedure was applied to determine the 0% probability damage threshold. The LIDT of the dark yellow phase of B a G a 4 S e 7 without cleavage planes is very close to the B a G a 2 G e S e 6 LIDT and exceeds by ca. 30% the LIDT of the yellow phase of B a G a 4 S e 7 at 2 and 5 kHz.

Europium doped Y2O3spherical nanoparticles with the diameter ~10 nmobtained via cw laser vaporization are shown to crystallize in monoclinic symmetry class (C2/m space group). The size of nanoparticles established via HRTEM coincides with coherent scattering region established by XRD. Luminescence spectrum in the vicinity of ultranarrow transition demonstrates three peaks consistent with three inequivalent positions of Eu3+ ion in monoclinic Y2O3 lattice. Hypersensitive transition dominates in the spectrum, admitting the lack of inversion symmetry at Cs sites occupied by Eu3+. The spectrum of hypersensitive transition is expanded to the red part of spectrum due intense transitions terminating at higher-lying components of crystal-field-split 7F2 energy level. Obtaining chromaticity coordinates (0.669, 0.331)and absolute quantum yield (~21%) is possible using red phosphor based on monoclinic Y2O3:Eu3+.

Laser evaporation of an Al2O3 target by a continuous wave CO2 laser was used to obtain nanostructured Al2O3 condensates with a mean crystallite size of 6 nm, one nominally pure and another doped with chromium at a concentration of 0.2 wt%. Photoluminescence of Cr3+ was observed in all the samples of the Al2O3 condensate. In all the Al2O3 condensates the α-Al2O3 phase, undetectable by XRD and HRTEM, was revealed by Cr3+ probing. Photoluminescence studies with the use of Cr3+ as a probe also revealed the θ- and (γ + δ)-crystal phases of Al2O3; this finding was supported by XRD and HRTEM data.

The γ and γ* phases of alumina synthesized from crystalline boehmite and pseudoboehmite were shown to strongly differ in some physicochemical characteristics. Photoluminescence of Cr3+ and Fe3+ as luminescent probes with their natural impurity concentrations was detected in the tested alumina samples and the local structure of the samples was examined. The crystal field strength and Racah parameters in γ-Al2O3 phases were determined. The ratio of octahedral and tetrahedral cationic positions was equal to 1 for γ-Al2O3 synthesized from crystalline boehmite, and 0.3 for that obtained from pseudoboehmite. The effect of residual OH groups and weakly bound molecular water on the local structure of γ-Al2O3 phases was revealed. The luminescence of Cr3+ was detected in subsurface structures of each alumina; defects produced by nanocrystallites were shown to affect the luminescence.

Nanosized Eu/γ- and/or η-Al2O3 ([Eu2О3] = 0.00, 0.02, 0.45 and 0.92 wt%) powders with the particle size from

We investigated the laser-induced damage threshold of two barium chalcogenides crystals, BaGa4Se7 and BaGa2GeSe6, at 1.053 μm radiation with a pulse duration of 7–10 ns at different pulse repetition rates, namely, 100 Hz, 500 Hz, and 1 kHz. The R-on-1 procedure was applied to determine the 0% probability damage threshold. Both crystals have close values of surface damage threshold at 0.1 kHz, 299 MW/cm2 (2.28 J/cm2) for BaGa2GeSe6, and 319 MW/cm2 (2.30 J/cm2) for BaGa4Se7.

International audience; Luminescent spectroscopy combined with the technique of luminescent probing with rare earth ions (europium, gadolinium, terbium) and an actinide ion (uranyl) was used to differentiate enantiopure and racemic alanine, the simplest chiral proteinogenic amino acid. Using the achiral luminescent probes, small differences between pure L and DL alanine in the solid state were strongly amplified. Based on the observed electronic transitions of the probes, the position of the triplet level of the coordinated alanine was estimated. Formation of homo- and heterochiral complexes between enantiomers of alanine and the metal ions is discussed as a possible mechanism of chiral self-discrimination.