E. Coetsee

Cathodoluminescent properties and surface characterization of bluish-white LiAl5O8:Tb phosphor

Cathodoluminescence (CL) characteristics and electron-beam induced surface chemical changes in nanocrystalline Tb3+ doped LiAl5O8 powder phosphors are presented. Bluish-white CL with a maximum at ∼543 nm was observed when the powders were irradiated with a 2 keV electron beam. The emissions in the green and the blue regions arise from the magnetic dipole D54-F7J (J=6–0) and D53-F7J transitions of the Tb3+ ion. The appearance of the line emissions in the blue region are discussed in terms of Tb oxidation states and their corresponding interconversion. Auger electron spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to probe the chemical changes on the surface of the LiAl5O8 phosphor under electron bombardment. The XPS data suggest that the Tb ions exist both in trivalent and tetravalent oxidation states which could be the reason for the observed green as well as blue CL emissions. A thermodynamically stable Al2O3 layer formed on the surface as a result of the electron stimulated surface che...

Cathodoluminescence degradation of Y2SiO5:Ce thin films

Cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y2SiO5:Ce) phosphor thin films grown by pulsed laser deposition were investigated for possible application in low voltage field emission displays (FEDs). A thin layer of tin oxide (SnO2) was ablated on some of the films in order to investigate the effect of the coated layer on the degradation of the CL intensity. Auger electron spectroscopy (AES) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of the thin films. AES and CL spectroscopy were done with 2keV energy electrons and with beam current densities of 26 and 52mAcm−2. Measurements were done in high vacuum and in oxygen pressures of 1×10−8, 1×10−7, and 1×10−6Torr. Residual gas mass analysis showed that the adventitious carbon (C) was removed from the surface as volatile gas species, which is consistent with the electron stimulated surface chemical reaction model. The SnO2 coated thin films resulted in a lower but more stabl...

Review on electron stimulated surface chemical reaction mechanism for phosphor degradation

Standard cathodoluminescent phosphors normally lose brightness upon bombardment with electron beams. A combination of techniques such as x-ray photoelectron spectroscopy, Auger electron spectroscopy, and cathodoluminescence (CL) spectroscopy was used to show that the main reason for the degradation in CL intensity is the formation of a nonluminescent “dead layer” on the surface due to an electron stimulated surface chemical reaction. The decrease in luminance was found to be a result of the growth of the dead layer. Different phosphors which include sulfide-based as well as oxide-based phosphors reacted similarly under electron bombardment. When ZnS phosphor powder was exposed to the electron beam in a water-rich O2 ambient, a chemically limited ZnO layer was formed on the surface. A layer of ZnSO4 was formed on the surface during the electron beam degradation of the ZnS phosphor powder in a dry O2 ambient. The electron stimulated reaction led to the formation of a luminescent SiO2 layer on the surface of...

Surface Characterization and Photoluminescence Properties of Ce3+,Eu Co-Doped SrF2 Nanophosphor

SrF2:Eu,Ce3+ nanophosphors were successfully synthesized by the hydrothermal method during down-shifting investigations for solar cell applications. The phosphors were characterized by X-ray diffraction (XRD), scanning Auger nanoprobe, time of flight-secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. XRD showed that the crystallite size calculated with Scherrer’s equation was in the nanometre scale. XPS confirmed the formation of the matrix and the presence of the dopants in the SrF2 host. The PL of the nanophosphor samples were studied using different excitation sources. The phenomenon of energy transfer from Ce3+ to Eu2+ has been demonstrated.

Ultra-broadband luminescent from a Bi doped CaO matrix

CaO:Bi phosphor powders were successfully synthesized by the sol–gel combustion method. Post heat treatment led to the enrichment of the Ca2+ site with multiple Bi centers. These centers were responsible for the change in the ultra-broadband cathodoluminescence (CL) emission as a function of different electron beam currents/beam voltages. The CaO phase formation and the presence of the enrichment of Bi was confirmed by using the X-ray diffraction and X-ray photoelectron spectroscopy techniques. The thermoluminescence afterglow spectra for the samples annealed at 800 °C and 1200 °C were strongly modified for the CaO and the presence of the multiple Bi centers. Of particular interest was that the ultra-broadband CL may have potential applications in inorganic single-emitting components that produce various colours under different beam currents/beam voltages or in a variety of optical devices if it can be better controlled.

Gas bubble formation in the cytoplasm of a fermenting yeast.

Abstract Current paradigms assume that gas bubbles cannot be formed within yeasts although these workhorses of the baking and brewing industries vigorously produce and release CO2 gas. We show that yeasts produce gas bubbles that fill a significant part of the cell. The missing link between intracellular CO2 production by glycolysis and eventual CO2 release from cells has therefore been resolved. Yeasts may serve as model to study CO2 behavior under pressurized conditions that may impact on fermentation biotechnology.

Photoluminescence properties of SrAl2O4:Eu2+,Dy3+ thin phosphor films grown by pulsed laser deposition

Thin films of SrAl2O4:Eu2+,Dy3+ phosphor were deposited on silicon [Si (100)] substrates using a 248 nm KrF pulsed laser. Deposition parameters, such as substrate temperature, pulse repetition rate, number of laser pulses, and base pressure, were varied during the film deposition process. Based on the x-ray diffraction data, all the films were amorphous but were emitting visible light when excited by a monochromatic xenon lamp. The chemical composition and the stoichiometry of the films determined by the Rutherford backscattering spectroscopy were consistent with the commercial SrAl2O4:Eu2+,Dy3+ powder used to prepare the films. Photoluminescence (PL) emission spectra of the films were characterized by major green emission with a maximum at ∼520 nm and minor red emission with a maximum at 630 nm. The green and red photoluminescence at 520 and 630 nm are associated with the 4f65d→4f7(S87/2) and D50-F72 transitions of Eu2+ and residual Eu3+ ions, respectively. Brighter films were shown to have relatively hi...

Role of deposition time on the properties of ZnO:Tb3+ thin films prepared by pulsed laser deposition

Terbium (Tb(3+)) doped zinc oxide (ZnO:Tb(3+)) thin films were grown on silicon (100) substrates by the pulsed laser deposition technique at different deposition times that varied from 15 to 55min. The effects of deposition time on the structural and optical properties of the ZnO:Tb(3+) films were investigated by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. As expected, the thickness of the ZnO:Tb(3+) film has increased with an increase in the deposition time. The photoluminescence intensity of the band to band emission has also increased with deposition time, while the deep level defect emission has decreased. The blue emission was observed from all the ZnO:Tb(3+) thin films deposited at the different deposition times excited by 325nm He-Cd laser, while a green emission was observed when excited by 228nm.

Yeast sensors for novel drugs: chloroquine and others revealed.

In this study the mitochondrion is regarded as a target to reveal compounds that may be used to combat various diseases. Consequently, the sexual structures of yeasts (with high mitochondrial activity) were identified as sensors to screen for various anti-mitochondrial drugs that may be toxic to humans and that are directed, amongst others, against fungal diseases and cancer. Strikingly, these sensors indicated that chloroquine is a potent pro-mitochondrial drug which stimulated yeast sexual reproduction. In addition, these sensors also showed that some Non-Steroidal Anti-Inflammatory drugs (NSAIDs), anti-malarial drugs, antifungal and anticancer drugs are anti-mitochondrial. These yeast sensor bio-assays may fast track studies aimed at discovering new drugs as well as their mechanisms and should now be further evaluated for selectivity towards anti-/ pro-mitochondrials, fertility drugs and contraceptives, using in vitro, in vivo, in silico and omics research.

The Potential Use of Bacteriophage Therapy as a Treatment Option in a Post-Antibiotic Era

The impending postantibiotic era creates an urgent requirement for alternative treatments of infectious diseases in humans and animals. Bacteriophages are viruses that infect and kill bacteria. The application of bacteriophages as a treatment option was investigated before the development of antibiotics. However, the initial success of antibiotic therapy soon shifted the focus from bacteriophage research. The revitalization of phage therapy has received increased global attention since the appearance of multidrug-resistant bacteria. Bacteriophages replicate via either the lytic or lysogenic cycle. While both life cycles have potential applications in bacteriophage therapy, the lytic cycle seems most suited to antibacterial therapy. The most striking advantage of bacteriophage therapy is the high degree of host specificity exhibited by these viruses, which enables the formulation of tailored treatments that kill only pathogenic bacteria. However, the high specificity of such treatments requires highly accurate diagnostic procedures in order to succeed. Other restrictions of bacteriophage therapy, such as limitations with the registration of phage therapy options, may possibly be overcome by the expression and engineering of phage lytic enzymes, which break the bacterial cell wall. The problem of bacterial immunity to phage infection also cannot be ignored, although it is more solvable than resistance to antibiotics. Considering the available information, phage therapy holds promise as an alternative treatment option, although the road ahead is not without obstacles.