A dinuclear manganese(II) complex with 2,6-pyridinedicarboxylate: Preparation,crystal structure and oxygen evolution activity in the presence of oxone

A dinuclear complex of Mn(II) with 2,6-pyridinedicarboxylate, [Mn₂(dipic)₂(H₂O)₆].2H₂dipic, where dipic = 2,6-pyridinedicarboxylate, has been synthesized and characterized by elemental analysis, IR, EPR, electronic absorption spectroscopy, electrochemistry and single-crystal X-ray diffraction. The complex acts as an oxygen evolving complex with oxone (2KHSO₅.KHSO₄ .K₂SO₄) as primary oxidant in aqueous solution with a turnover number of ∼ 5 (mol of O₂/mol of the complex).     

Effects of physical growth conditions on the structural and optical properties of sputtered grown thin HfO2 films

HfO₂ thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O₂/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO₂ grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiO_x suboxide layer at the HfO₂/Si interface is unavoidable. The HfO₂ thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O₂/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO₂, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO₂ to form HfO₂, leaving Si-Si bonds behind.     

Spectroscopic properties of red Bi4Ge3O12 by vertical Bridgman method

Red Bi₄Ge₃O₁₂ (BGO) single crystals had been grown by vertical Bridgman (VB) method. The structure of this crystal was determined by XRD. The absorption and emission spectra of the red BGO in visible and near infrared region (NIR) were measured at room temperature. The emission intensity of the red BGO is weaker than that of ordinary BGO at about 500 nm. Interestingly, the red BGO shows a significant emission band centered at about 1495 nm. The red BGO faded and its properties recovered after ultraviolet (UV) irradiation or annealing.     

Determination of the local site occupancy of Eu ions in ZnAl2O4 nanocrystalline powders

Once lanthanides-doped ZnAl₂O₄ have attracted attention for highly efficient phosphors and due to the complexity of this system, this work is focused in the understanding of the local site occupancy of the doped ions in the spinel structure by using Eu³⁺ as a spectroscopic probe. Europium(III)-doped ZnAl₂O₄ nanocrystalline powder samples were prepared by the Pechini method. Different heat treatment temperatures and doping levels were investigated. No impurities of residual Eu₂O₃ were observed for the samples with Eu³⁺ doping levels up to 10 at.%, indicating that the doping ions are diluted into the host. The luminescence spectroscopy from the Eu³⁺ ions revealed the Eu³⁺ ions might occupy at least two non-centro-symmetric sites and that the occupation ratio might be dependent on the heat treatment or doping level. It is observed that one site is related to a high covalent environment while at the other the ionic character prevails. This behavior is in agreement with the luminescence lifetime results. The decay curves were fitted according to double first-order decay model and it was confirmed the covalence difference between the two sites and also the population variation with the doping level. There are strong evidences that the europium ions substitute for the aluminum ones in the normal spinel structure. It cannot be disregarded that the dopant ions may be present on the surface of the particles.     

Spectroscopic studies of the Eu(III) and Gd(III) tris(3-aminopyridine-2-carboxylic acid) complexes

The synthesis and spectroscopic studies of the complexes of Eu(III) and Gd(III) with 3-aminopyridine-2-carboxylic acid (3-NH₂pic) are described. An experimental and theoretical analysis of the intensities of the ⁵D₀→⁷F_0,1,2,4 transitions of the Eu(III) ion is presented. An approximate structure for the Eu(III) complex is assumed and the theoretical calculations are based on a model, previously described, which takes into account the forced electric dipole and dynamic coupling mechanisms.     

An ellipsometric study of polymer film curing: 2,6-Bis(3-aminophenoxy) benzonitrile/4,4′oxidiphthalic anhydride poly(amic acid)

The curing of 2,6-bis(3-aminophenoxy)benzonitrile/4,4′oxidiphthalic anhydride ((β-CN) APB/ODPA) has been investigated using spectroscopic ellipsometry on films with various degrees of imidization. Results indicate that much of the film imidization is accomplished at 200 °C and above. Three absorption peaks have been observed (4.1, 5, and 6 eV) which correspond to intra- and inter-molecular optical transitions. A comparison of the film optical constants for the pristine poly(amic acid) and the fully cured polyimide shows film densification upon imidization. A curing timeline has been obtained using in situ real-time spectroscopic ellipsometry, and ellipsometry is shown to serve as a general technique for studying organic film curing.     

Spectroscopic,stability and radical-scavenging properties of a novel pigment from gardenia

A novel pigment, named gardecin, has been isolated from gardenia fruits, together with another five known crocins. The pigment, which possessed a structure which is unique among crocins, was characterised using spectrometric techniques, particularly 1D and 2D NMR. The NMR assignments were based on data from ¹H NMR, ¹³C NMR, DEPT, ¹H–¹H COSY, NOESY, HMQC and HMBC measurements. The five known crocins were identified on the basis of MS, UV/visible and 1D NMR data. Chemical stability and antioxidant ability of gardecin in comparison with the other five crocins were studied. The stronger DPPH free radical-scavenging ability of gardecin compared, with the other crocins, was observed. Kinetic studies have shown that all crocins were unstable under various conditions, but surprisingly gardecin was fairly stable.     

Light intensity analysis of plasma jet constriction with applied magnetic field

Light intensity analysis was carried out to consider the constriction of plasma jet with the application of a strong magnetic field. Argon was employed as working gas. Plasma jet was generated in a vacuum chamber by a plasma torch and went into a magnet bore. The magnet composed of a pair of superconducting coils imposes a strong axial magnetic field on the jet. The jet between the coils was taken with  a digital single-lens reflex camera through viewing window. The light intensity is determined from the RAW image files of the camera with the software for analyzing the RAW format. The jet constriction with applied magnetic field was evaluated quantitatively on the basis of the obtained results. The distributions of the light intensity were also compared with those of the typical spectral lines from excited argon that were measured at the same time as shooting the images. The results suggest that the light intensity analysis of the RAW image files could be utilized for the quantitative evaluation of the constriction of plasma jet due to the magnetic field.     

Structural and optical properties of sintered ZnSxSe1−x films

Sintered ZnS_xSe_1−x films have been prepared in the entire composition range from ZnSe to ZnS by using the screen printing method. To deposit good quality films, optimum conditions have been determined. Wide band gap ternary films have wide applications in solar cells. The band gap of these films are determined by reflection spectra in the wavelength range of 325–600 nm using the Tauc relation. These films have a direct band gap, which varies from 3.50 eV for ZnS to 2.66 eV for ZnSe films. The wurtzite structure of ZnSSe films was confirmed by X-ray diffraction analysis of these films.     

Synthesis, luminescence and quantum yields of Eu(III) mixed complexes with 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline-N-oxide

The new complex tris(4,4,4-trifluoro-1-phenyl-1,3-butanedionate)(1,10-phenanthroline-N-oxide)europium(III) has been synthesized, characterized, and its photophysical properties (excitation and luminescence spectra, and quantum yields) investigated down to 4.2 K. A similar complex containing H₂O instead of phenNO molecules was also investigated for comparison. The more pronounced temperature dependence of the quantum yield q and the larger difference between the q values upon ligand and direct Eu³⁺ excitation for the hydrated compound show that there are other quenching processes operative, besides the expected multiphonon relaxation via the H₂O vibrations. The results clearly show that the substitution of the water molecules by phenNO leads to greatly enhanced quantum yields (i.e. 30% vs. 66%, upon ligand excitation at 300 K) and longer ⁵D₀ lifetimes (380 μs vs. 670 μs respectively). This can be ascribed to a more efficient ligand-to-metal energy transfer and to less efficient non-radiative ⁵D₀ relaxation processes.