Although aluminate phosphors have attracted great interest for applications in lamps, cathode ray tubes and plasma display panels, there still remain issues affecting operational parameters such as luminescence efficiency, stability against temperature, high color purity and perfect decay time. In addition, issues involving important aspects of the monoclinic↔hexagonal phase transition temperature still exist. In this work, SrAlxOy:Eu2+,Dy3+ phosphor powders were prepared by the sol–gel method. X-ray diffraction (XRD) has shown that both crystallinity and crystallite sizes increased as the temperature increased. Both SrAl2O4 and Sr2Al3O6 phases were observed. Photoluminescence (PL) characterization shows temperature-dependence, which indicates emission at low and high annealing temperatures originating from Eu2+ and Eu3+ ions. Thermoluminescence glow and decay measurements provided useful insight on the influence of traps on luminescence behavior. Differential scanning calorimetry (DSC) and thermogravimetric studies (TGA) on composites of the phosphor in low density polyethylene (LDPE) demonstrated the varied influence of annealing temperature on some luminescence and thermal properties. 相似文献
Silica-PMMA nanocomposites with different silica quantities were prepared by a melt compounding method. The effect of silica amount, in the range 1-5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics of PMMA was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), 13C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (13C{1H} CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame (T1ρ(H)), in the laboratory frame (T1(H)) and cross-polarization times (TCH). Results showed that silica nanoparticles are well dispersed in the polymeric matrix whose structure remains amorphous. The degradation of the polymer occurs at higher temperature in the presence of silica because of the interaction between the two components. 相似文献
In this work, the adhesion strength between poly(ethylene terephthalate) (PET) fibres and styrene-butadiene rubber (SBR) was studied. The effects of atmospheric plasma treatment, used to increase adhesion strength between PET fibres and the rubber matrix, were investigated and compared. It was confirmed that lubricants on the fibres caused a decrease in adhesion strength between the plasma treated reinforcing PET fibres and the SBR rubber matrix. These lubricants can be removed by acetone. When washed and treated in plasma, a substantial improvement in adhesion strength was observed. No ageing in air before combination with the rubber matrix was observed. This confirmed that the plasma streamers caused the creation of a new, relatively stable chemical species on the polymer surface. It suggests that the surface modification of PET fibres by plasma treatment at atmospheric gas pressure is a suitable and technologically applicable method for the improvement of adhesion strength of polyester reinforcing materials to rubber. 相似文献
A variety of poly(lactic acid) (PLA)-poly(ε-caprolactone) (PCL) samples with different PLA:PCL ratios, containing different contents of graphite nanoplatelets (GrP), were analysed in a thermogravimetric analyser (TG) under, respectively, nitrogen and oxygen atmospheres, and in a differential scanning calorimeter (DSC) in a nitrogen atmosphere. Their respective morphologies were determined through scanning electron microscopy. The TG analyses in nitrogen gave fairly predictable results, but the analyses in oxygen gave complex results that seemed to be dependent on the respective morphologies of the blend samples and on the presence and amount of GrP in the respective samples. It was observed that, depending on the blend or nanocomposite morphologies, the GrP could have played the role of catalysing the degradation process, or inhibiting the onset of degradation by immobilizing the polymer or free radical chains and by delaying the evolution of the degradation products from the respective samples. The DSC results clearly showed the influence of the respective components in the blends and composites on the crystallization behaviour and crystallinities of the two polymers.
Evaluation of three subclasses of boron difluoride formazanate complexes bearing o‐, m‐, and p‐anisole N‐aryl substituents (Ar) as readily accessible alternatives to boron dipyrromethene (BODIPY) dyes for cell imaging applications is described. While the wavelengths of maximum absorption (λmax) and emission (λem) observed for each subclass of complexes, which differed by their carbon‐bound substituents (R), were similar, the emission quantum yields for 7 a – c (R=cyano) were enhanced relative to 8 a – c (R=nitro) and 9 a – c (R=phenyl). Complexes 7 a – c and 8 a – c were also significantly easier to reduce electrochemically to their radical anion and dianion forms compared to 9 a – c . Within each subclass, the o‐substituted derivatives were more difficult to reduce, had shorter λmax and λem, and lower emission quantum yields than the p‐substituted analogues as a result of sterically driven twisting of the N‐aryl substituents and a decrease in the degree of π‐conjugation. The m‐substituted complexes were the least difficult to reduce and possessed intermediate λmax, λem, and quantum yields. The complexes studied also exhibited large Stokes shifts (82–152 nm, 2143–5483 cm?1). Finally, the utility of complex 7 c (Ar=p‐anisole, R=cyano), which can be prepared for just a few dollars per gram, for fluorescence cell imaging was demonstrated. The use of 7 c and 4′,6‐diamino‐2‐phenylindole (DAPI) allowed for simultaneous imaging of the cytoplasm and nucleus of mouse fibroblast cells. 相似文献
Blue–green emitting BaAlxOy:Eu2+,Dy3+ phosphor was synthesized by the combustion method. The influence of various parameters on the structural, photoluminescence (PL) and thermoluminescence (TL) properties of the phosphor were investigated by various techniques. Phosphor nanocrystallites with high brightness were obtained without significantly changing the crystalline structure of the host. In the PL studies, broad-band excitation and emission spectra were observed with major peaks at 340 and 505 nm, respectively. The observed afterglow is ascribed to the generation of suitable traps due to the presence of the co-doped Dy3+ ions. Though generally broad, the peak structure of the TL glow curves obtained after irradiation with UV light was non-uniform with suggesting the contribution to afterglow from multiple events at the luminescent centers. Further insight on the afterglow behavior of the phosphor was deduced from TL decay results. 相似文献
Differential scanning calorimetry, thermogravimetry, thermogravimetry/mass spectrometry and infrared spectroscopy were used to study the thermal behaviour of high polyphenylacetylene obtained through the Mo(CO)6 catalyzed metathesis polymerization of phenylacetylene. The exothermic peaks observed in nitrogen are explained by crystallization or a solid state transition, initiation and decomposition to aromatic compounds, and the endothermic peaks by volatilization. In oxygen the exothermic peaks are explained by crystallization or a solid state transition, initiation, oxidation, cross-linking and decomposition. The TG and MS results indicate that the polymer is stable to ca. 250°C with solvent molecules trapped in the polymer matrix evolving below this temperature. 相似文献