Papers by Keyword: Photoluminescence Spectroscopy

Abstract: Multifunctional Si-Fe nanocomposites with varying atom percent of Fe were prepared by the high energy ball milling technique. Presence of pristine Fe and Si as separate entities in the nanocomposites was confirmed through the analyses of their Mössbauer spectrum and, x-ray diffraction patterns. The average grain size of Si has been found to be 40nm and the superparamagnetic Fe particles in the nanocomposite systems has been found to increase with increase in milling time. Transmission electron microscopic images revealed discontinuous distribution of Fe in the Si matrix. The Si-Fe nanocomposites exhibit both magnetic and photoluminescence properties at room temperature. The photoluminescence intensity was found to decrease with increase in Fe content in the nanocomposite samples, however, saturation magnetization and retentivity increases. Thus it is imperative that by adjusting the composition of Si-Fe nanocomposites their properties can be tailored to suit the desired requirements for applications in electronic devices.

Abstract: In this research, a new approach is used to identify the products of electrochemical oxidation of UV visible substances over solid electrodes. In order to determine the product of phenol electrooxidation over glassy carbon electrode, the results obtained using voltammetric method and photoluminescence spectroscopy have been compared. It was proved that in an alkaline solution phenol is present in form of phenolate-ion, adsorbing on the surface of glassy carbon electrode, and oxidized to hydroquinone with transfer of two electrons.

Abstract: Photoluminescence (PL) spectroscopy has been used to characterize neutron-irradiated cubic silicon carbide crystals. The effects of thermal annealing (600-1100^OC) on the PL bands have been studied. Several PL bands consisting of a sharp line and its phonon replicas have been observed in the 9-80 K temperature range. Certain of them like the D₁ spectrum doublet with 1.975 eV and 1.977 eV zero-phonon lines (ZPL) at 9 K and the L2 spectrum with ZPL at 1.121 eV were reported previously for ion-implanted and electron irradiated 3C-SiC crystals, respectively. Besides, some new bands with ZPL at 2.027, 1.594, 0.989 and 0.844 eV and a broad band at 1.360 eV have been found. A correlation of PL and EPR spectra intensities of these neutron-irradiated and annealed cubic SiC crystals is briefly discussed.

Abstract: Positron annihilation lifetime (PALS) and photoluminescence spectroscopies measurements were performed in Tb(III) and Eu(III) dipivaloylmethanates, Tb(dpm)₃ and Eu(dpm)₃, and also on their binary solid solutions of general formula Tb_1-xEu_x(dpm)₃. A correlation between the ⁵D₄ Tb(III) energy level lifetime and the positronium formation probability was observed, indicating that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition. From these results, a new model is proposed, showing that excited electronic states have a relevant role in the positronium formation mechanism.

Abstract: Spindle-like bis (8-hydroxyquinoline) iron (FeQ₃) complex has been synthesized with a facile method in a mixed solvent system at room temperature for 12 h. The molecular formula of the products is speculated by the C, H and N element analysis and thermal gravimetric analysis, and Fourier-transformation infrared spectroscopy was also utilized to measure its structure, which further confirm the molecular formula of the products. The observation of field emission scanning electron microscopy and transmission electron microscopy shows that the morphology of tris (8-hydroxyquinoline) iron complex is spindle-like structure. The photoluminescence of the products were also investigated. The results indicate that the photoluminescence emission of FeQ₃ spindles shows obvious blue shift contrasted with that of 8-hydroxyquinoline.

Abstract: With use of electron-assisted chemical vapor deposition technology, nanocrystalline diamond films were deposited on SiC ceramics substrates at various gas pressure ( 0.5 ~ 2 kPa ). Effect of the gas pressure on optical properties of the nanocrystalline diamond films was studied. Raman scattering spectra were measured. Photoluminescence spectra were investigated in the range of 420 ~ 680 nm. Spectroscopic ellipsometry were analyzed from the near IR to the UV region ( 1.5 ~ 5.0 eV ). Results show that, when the gas pressure increased from 0.5 to 2 kPa, Raman scattering intensity of diamond increase and D/G ratio decrease; when the gas pressure was 0.5kPa and 2kPa, there is not any PL peak, however, there is a stronger PL peak at 485 nm when the gas pressure was 1kPa; extinctive coefficient k for the nanocrystalline diamond films deposited at 1kPa increase obviously with increase of photo energy.

Abstract: Hierarchical bis(8-hydroxyquinoline) nickel(NiQ₂) complex has been synthesized with a facile method in a mixed solvent system at 120 °C for 12 h. The molecular formula of the products is speculated by the C, H and N element analysis and thermal gravimetric analysis, and Fourier-transformation infrared spectroscopy was also utilized to measure its structure, which further confirm the molecular formula of the products. The observation of field emission scanning electron microscopy shows that the morphology of bis(8-hydroxyquinoline) nickel complex is flower-like structure. According to the result, it is found that the photoluminescence of bis(8-hydroxyquinoline) nickel complex is stronger than that of 8-hydroxyquinoline, which indicate that inorganic elements played key roles in their luminescence properties.

Abstract: Zn and Cu were separately incorporated to the diamond powder and then the compacts were prepared under 5GPa, 1273K. The results showed that Zn was a good additive to prepare polycrystalline diamond by high-pressure and high-temperature (HPHT) because it could inhibit the graphitization of diamond. The element Zn left in the polycrystalline was in the form of ZnO. The photoluminescence spectroscopy showed that there were a series of sharp bands between 310 and 390nm when the excitation was above 200nm. However, the full width at half maximum of the diamond peaks mostly was below 0.5nm. The intensity of sharp band decreased with the decrease of excitation energy and then disappeared at last.

Abstract: In this paper the challenges associated with the determination of within section macrostresses in the non-metallic materials porous reactor core graphites, glasses and thermally grown oxides, will be considered, with respect to the length-scale over which such measurements are required. Examples are briefly presented to demonstrate the capability of the methods selected, which include deep hole drilling and photoluminescence and Raman spectroscopy. These techniques span the length-scale from micro-metres to tens of millimetres. The measured values will be discussed with respect to the confidence with which these techniques may be applied and hence benefits for life/integrity evaluation.

Abstract: Residual macro-stresses have to be evaluated using trial samples that comprise a CMSX4 superalloy coated with either a RT22 or a CN91 bond-coat. The samples were exposed in air to a matrix of temperatures, in the range 850°C to 1050°C, and times extending upto 4000hrs to produce thermally grown oxide. This oxide is essentially Al2O3 which allows stresses to be measured by photoluminescence spectroscopy. In addition, Raman spectroscopy and X-ray diffraction have been used to characterise the oxides formed. The results are discussed with respect to confidence in the measurements, changes in stress with temperature and exposure time and the potential for photoluminescence spectroscopy to be used to measure stresses for service components.