Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

Efficiency enhancement by aluminum addition to CaTiO3:Pr phosphor thin films

The mechanism of enhancement of the red emission efficiency from CaTiO₃:Pr³⁺ thin film by Al addition has been investigated. Al-ions have been attracting interest as a sensitizer to improve the luminescent efficiency of phosphors. Also, influence of Al-doping on the crystallization, surface morphology and luminescent properties of CaTiO₃:Pr³⁺ thin films have been discussed. CaTiO₃:Pr³⁺ and Al-doped CaTiO₃:Pr³⁺ films were grown using pulsed laser deposition technique on Al₂O₃ (0001) substrates under different substrate temperatures and oxygen pressures. The crystalline phase and surface morphology of the films were very dependent on the oxygen pressure and substrate temperature and they affected the luminescent brightness of the films. The crystalline structure and microstructure of these films have been characterized by X-ray diffraction and electron microscopy and their luminescent properties have been evaluated at room temperature using a luminescence spectrometer and excitation by a broadband incoherent ultraviolet light source with a dominant excitation wavelength of 325 nm. In particular, the incorporation of Al³⁺ ions into CaTiO₃ lattice could induce a remarkable increase of photoluminescence. The enhancement of luminescence for Al-doped films may result not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces. Also, the luminescent intensity and surface roughness of the films exhibited similar behavior as a function of oxygen pressure.     

Safety climate practice in Korean manufacturing industry

Safety climate survey was sent to 642 plants in 2003 to explore safety climate practices in the Korean manufacturing plants, especially in hazardous chemical treating plants. Out of 642 plants contacted 195 (30.4%) participated in the surveys. Data were collected by e-mail using SQL-server and mail. The main objective of this study was to explore safety climate practices (level of safety climate and the underlying problems). In addition, the variables that may influence the level of safety climate among managers and workers were explored. The questionnaires developed by health and safety executive (HSE) in the UK were modified to incorporate differences in Korean culture. Eleven important factors were summarized. Internal reliability of these factors was validated. Number of employees in the company varied from less than 30 employees (9.2%) to over 1000 employees (37.4%). Both managers and workers showed generally high level of safety climate awareness. The major underlying problems identified were inadequate health and safety procedures/rules, pressure for production, and rule breaking. The length of employment was a significant contributing factor to the level of safety climate. In this study, participants showed generally high level of safety climate, and length of employment affected the differences in the level of safety climate. Managers' commitment to comply safety rules, procedures, and effective safety education and training are recommended.     

Effect of CO2 in the feed stream on the deactivation of Co/γ-Al2O3 Fischer–Tropsch catalyst

The influence of CO₂ on the deactivation of Co/γ-Al₂O₃ Fischer–Tropsch (FT) catalyst in CO hydrogenation has been investigated. The presence of CO₂ in the feed stream reveals a negative effect on catalyst stability and in the formation of heavy hydrocarbons. The CO₂ acts as a mild oxidizing agent on cobalt metal during Fischer–Tropsch synthesis. During FT synthesis on Co/γ-Al₂O₃ of 70 h, the CO conversion and C₅₊ selectivity in the presence of CO₂ decreased more significantly than in the absence of CO₂. CO₂ is found to be responsible for the partial oxidation of surface cobalt metal at FT synthesis environment with the co-existence of generated water.     

The micro-reactor testing of catalysts and fuel delivery apparatuses for diesel autothermal reforming

This study investigated two factors affecting the performance of diesel autothermal reforming (ATR): the reforming activity of selected catalysts and the effect of devised fuel delivery apparatuses. When fluorite and perovskite-structured ceramic materials were used as substrates, H₂ yields were higher than when an inert Al₂O₃ substrate was used at 700–800 °C. Gadolinium (Gd)-doped CeO₂ (CGO) had the highest H₂ production rate in the selected substrates. Platinum (Pt) showed better performance than rhodium (Rh) and ruthenium (Ru) when CGO was used as the substrate. Although the nickel (Ni)-added Pt catalyst (Pt–Ni) showed high H₂ yield, carbon deposition over this catalyst was more severe than with Pt. Oxygen ion (O²⁻) vacancies generated by Gd dopants can enhance the reforming activity of CeO₂. When using a microchannel catalyst bed, the performance degradation at high gas flowrates can be compared to a packed catalyst bed of pellet type. For effective fuel delivery, we have introduced an ultrasonic injector (UI) and a plasma injector (PI). The UI-reforming showed greater long-term stability than non-UI reforming because the generation of carbon precursors was suppressed. On the other hand, the PI-reformer had low conversion efficiency, although it had high H₂ selectivity.     

Sonochemical reaction of fullerene[C60] with several 2'-azidoethyl per-O-acetyl glycosides

Cycloadditive reaction of fullerene[C60] with various 2'-azidoethyl per-O-acetyl glycopyranoside of D-mannose, D-galactose, D-glucose, D-xylose and D-maltose, respectively gave the glycosyl fullerene[C60] derivatives 2a-2e such as alpha-D-mannosyl fullerene[C60] under ultrasonication. Based on analyses using 1H- and 13C-NMR, UV-vis, FT-IR, and FAB-MS spectroscopies of the glycosyl fullerene[C60] derivatives, the products were composed of a mixture of [5,6]- and [6,6]-junction isomers which were predominantly the closed [5,6]-junction isomer.     

In situ EC-STM studies of n-Si(1 1 1):H in 40% NH4F solution at pH 10

In situ electrochemical-scanning tunneling microcopy (EC-STM) was employed to investigate the etching dynamics of the moderately doped n-Si(1 1 1) electrode during cyclic voltammetric perturbation and at the seven different potentials including the open circuit potential (OCP) in 40% NH₄F solution at pH 10, which was prepared from 40% NH₄F and concentrated NH₄OH solution. The etching rate was significant at OCP and showed an exponential dependence on the potential applied to the silicon substrate electrode. Although some triangular pits were generated at the Si(1 1 1) surface, at the potentials more negative than OCP the site dependence in the removal of surface silicon atoms prevailed and led to the atomically flat Si(1 1 1):H surfaces with sharply defined steps of the step height 3.1 Å, where the interatomic distance of 3.8 Å was observed with a three-fold symmetry. At the potentials sufficiently more positive than OCP, macroporous hole was formed to limit further in situ EC-STM study. The results were compared with in situ EC-STM studies of the etching reaction of n-Si(1 1 1):H in the aqueous solution of dilute ammonium fluoride at pH 5, 40% NH₄F at pH 8, and 1 M NaOH reported in the literature.     

Effect of pressure fluctuations on the heat transfer characteristics in a pressurized slurry bubble column

The hydrodynamics and heat transfer characteristics were investigated in a slurry bubble column reactor whose diameter was 0.0508 m (ID) and 1.5 m in height. Effects of gas velocity (0.025–0.1 m/s), pressure (0.1–0.7MPa), solid concentration (0–20 vol%) and liquid viscosity (1.0–38.0 mPa s) on the hydrodynamics and heat transfer characteristics were examined. The pressure difference fluctuations were analyzed by means of attractor trajectories and correlation dimension to characterize the hydrodynamic behavior in the column. The gas holdup increased with increasing gas velocity or pressure, but decreased with increasing solid concentration or liquid viscosity. It was found that the attractor trajectories and correlation dimension of pressure fluctuations were effective tools to describe the hydrodynamic behaviors in the slurry bubble column. The heat transfer coefficient increased with increasing pressure or gas velocity, but decreased with increasing solid concentration or viscosity of slurry phase in the slurry bubble column. The heat transfer coefficient value was well correlated in terms of operating variables and correlation dimension of pressure fluctuations in the slurry bubble column.