Cw laser action of Ti:Al2O3 under argon-ion laser pumping is presented. We analyze the free-running characteristics and the effective emission cross section of the laser. The temperature dependence of the 2E lifetime was measured from 4 to 650 K and is explained in a single-phonon model. The quantum efficiency of Ti:Al2O3 at room temperature is 80%.

Continuous-wave laser operation and quantum efficiency of titanium-doped sapphire

Luminescent properties and X-ray photoelectron spectroscopy study of ZnAl2O4:Ce3+,Tb3+ phosphor

Simplistic synthesis of ultrafine CoMnO3 nanosheets: An excellent electrocatalyst for highly sensitive detection of toxic 4-nitrophenol in environmental water samples.

ZnAl2O4 spinel powders were prepared using the Pechini or co-precipitation synthetic route and were then treated at different temperatures (600–1350 °C). These powders were characterised by X-ray diffraction, scanning electron microscopy (SEM), diffuse reflectance and luminescence measurements. SEM investigations and the X-ray patterns showed that the spinel crystallite size was dependent on the synthetic route and the treatment temperature. In addition, the structural evolution was investigated by Rietveld refinements. The inversion rate decrease was correlated with the temperature, leading to a direct spinel phase for the sample treated at high temperature. Furthermore, luminescence measurements showed various emissions linked to the presence of defects in the matrix structure. The two main emissions observed were attributed to oxygen vacancy and Zn in the interstitial positions (as revealed by differential Fourier maps). The luminescence spectra exhibited strong differences between 1200 °C and 1350 °C. At the higher temperature, the characteristic emission spectra can be attributed to the direct spinel phase. The indirect–direct spinel transformation can be monitored through the change in the optical properties and correlated to the thermal history of the sample.

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ZnAl2O4 as a potential sensor: variation of luminescence with thermal history

The 3d transition-metal oxides are a class of promising catalysts for the oxygen evolution reaction (OER) in alkaline media. Manganese-based spinel oxides usually do not show impressive OER perform...

Switch of the Rate-Determining Step of Water Oxidation by Spin-Selected Electron Transfer in Spinel Oxides

Microwave-assisted hydrothermal synthesis is a simple, reproducible, rapid, and effective method, and therefore, has attracted considerable interest among scientists in the field of synthesis not only of iron oxide but also of other metal oxides. This method has been used for the synthesis of iron oxide nanoparticles, hematite (α-Fe2O3), and goethite (α-FeOOH) in strongly alkaline media with iron(III) chloride (FeCl3) as precursor under microwave emission of 850 W. In this work, the effect on the size, shape, and composition of the final product was investigated by changing the conditions, such as shortening the synthesis time, increasing the synthesis temperature, and adding various substances to the synthesis pathway. Samples synthesized at 200 °C for 20 min by increasing the added percentage of polyethylene glycol (PEG), sodium dodecyl sulfate (SDS), rosemary essential oil and lavender essential oil promote goethite-to-hematite transformation, while N-guanylurea sulfate (NGS) and sage essential oil behave differently. The aforementioned substances added at 260 °C resulted in a decrease in particle size, but pure hematite was obtained, regardless of the type of the substances added or the decrease in synthesis time from 20 min to 5 min. Furthermore, the use of essential oils rather than surfactants in this study was presented as a novel, environmentally friendly method of iron oxide synthesis.

https://www.mdpi.com/2073-4352/12/11/1567/pdf?version=1667723006

The Effects of Surfactants and Essential Oils on Microwave−Assisted Hydrothermal Synthesis of Iron Oxides

Pure and Co3+-doped BaAl2O4 [Ba(Al1-xCox)2O4, x = 0, 0.0077, 0.0379] powder samples were prepared by a facile hydrothermal route. Elemental analyses by static secondary ion mass spectrometry (SIMS), X-ray absorption spectroscopy (XAS) measurements at the Co K-edge, and X-ray diffraction studies were fully correlated, thus addressing a complete description of the structural complexity of Co3+-doped BaAl2O4 powder. Powder X-ray diffraction (PXRD) patterns indicated that prepared samples were nanocrystalline with a hexagonal P63 symmetry. The X-ray absorption near-edge structure (XANES) measurements revealed the presence of cobalt in a +3 oxidation state, while the rarely documented, tetrahedral symmetry around Co3+ was extracted from the extended X-ray absorption fine structure (EXAFS) oscillation patterns. Rietveld structure refinements showed that Co3+ preferentially substitutes Al3+ at tetrahedral Al3 sites of the BaAl2O4 host lattice, whereas the (Al3)O4 tetrahedra remain rather regular with Co3+-O distances ranging from 1.73(9) to 1.74(9) A. The underlying magneto-structural features were unraveled through axial and rhombic zero-field splitting (ZFS) terms. The increased substitution of Al3+ by Co3+ at Al3 sites leads to an increase of the axial ZFS terms in Co3+-doped BaAl2O4 powder from 10.8 to 26.3 K, whereas the rhombic ZFS parameters across the series change in the range from 2.7 to 10.4 K, showing a considerable increase of anisotropy together with the values of the anisotropic g-tensor components flowing from 1.7 to 2.5. We defined the line between the Co3+ doping limit and influenced magneto-structural characteristics, thus enabling the design of strategy to control the ZFS terms' contributions to magnetic anisotropy within Co3+-doped BaAl2O4 powder.

Structural Behavior and Spin-State Features of BaAl2O4 Scaled through Tuned Co3+ Doping.

The formation of ZnO nanomaterials from different Zn acetylacetonate precursor solutions was studied in situ by employing simultaneous, time-resolved X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS) at the Zn K-edge. The precursor solutions were heated from room temperature to the desired reaction temperatures in a hermetically sealed cell dedicated to X-ray experiments. In general, the first indications for the formation of hexagonal ZnO were found for elevated temperatures of about 80 °C both by XRD and EXAFS, and the contributions increase with temperature and time. However, no reaction intermediates could be proved in addition to the Zn precursors and the formed hexagonal ZnO materials. Furthermore, the results show that the efficiency of the reaction, i.e., the conversion of the precursor material to the ZnO product, strongly depends on the solvent used and the reaction temperature. ZnO formation is accelerated by an increased temperature of 165 °C and the use of 1-octanol, with a conversion to ZnO of more than 80% after only a ca. 35 min reaction time according to a detailed analysis of the EXAFS data. For comparison, an identical concentration of Zn acetylacetonate in water or dilute alkaline NaOH solutions and a reaction temperature of around 90 °C leads to a smaller conversion of approximately 50% only, even after several hours of reaction. The particle size determined from XRD for different orientations shows a preferred orientation along the c-direction of the hexagonal crystal system, as well in accordance with scanning electron microscopy. The LaMer model explained this highly non-uniform growth of needle-like ZnO crystallites.

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Martina Vrankić

Papers

The Effects of Surfactants and Essential Oils on Microwave−Assisted Hydrothermal Synthesis of Iron Oxides

Structural Behavior and Spin-State Features of BaAl2O4 Scaled through Tuned Co3+ Doping.

In Situ Observation of ZnO Nanoparticle Formation by a Combination of Time-Resolved X-ray Absorption Spectroscopy and X-ray Diffraction

Piezochromic Luminescence of Dicoronylene: Key for Revealing Hidden Raman Modes at High Pressure

Pressure-induced valence fluctuation in CsEuF3: From divalent Eu valence to trivalent Eu valence state