Materials Science Forum Vols. 663-665

Abstract: An azobenzene derivative substituted with a 2-bromoisobutyryl group was used as an initiator for the atom transfer radical polymerization of 2-[4-(4-ethoxyphenylazo)phenoxy]ethyl methacrylate) (MAZO). The resulting homopolymers (AZO-PMAZO) possess azobenzene moieties both in the main chain and in the side chain. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) preliminarily revealed the liquid crystalline property of these polymers. The novel liquid crystalline polymers are expected to act as the candidates in some promising areas including optical data storage, optical switch, and molecular devices.

Abstract: High performance aqueous CdSe quantum dots (QDs) have been prepared by combination of Se source as vapor-phase and hydrothermal method. The main advantages of this approach included: one is to utilize H2Se vapor as a higher pure selenium source to make the prepared QDs have little other impurities, another is to obtain the QDs with characteristics of more rapid growth in the hydrothermal reaction. The as-prepared products have been characterized by ultraviolet-visible absorption spectra, photoluminescence spectroscopy (PL), X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive spectroscopy (EDS) analysis etc. The results show the as-synthesized water-soluble CdSe nanoparticles possess higher purity and quantum yields (QY), favorable narrow photoluminescence band with full width of half-maximum (FWHM) down to 40 nm, better photo-stability, and less synthetic time as compared with aqueous CdSe QDs obtained by other methods.

Abstract: The synthesis of hexagonal phase Zn1-xMnxS (x = 0–0.05) nanorods was achieved by hydrothermal treatment of zinc manganese diethyldithiocarbamates (Zn1-xMnx-(DDTC)2, x=0–0.05) in 40 mass % hydrate hydrazine aqueous solution at 180 °C for 12 h. The structure, composition and optical property of the obtained products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and UV-vis diffuse reflectance spectra.

Abstract: A chemical bath deposition method has been proposed for the preparation of SnS2 thin films onto glass slides from the aqueous solutions of tin (IV) chloride pentahydrate, thioacetamide and citric acid at 35 °C. High quality SnS2 thin films were obtained by adjusting the amounts of citric acid, which was used here as a complexing agent. The as-prepared thin films were characterized by Raman spectra, field emission scanning electron microscopy (FESEM), surface profiler and UV-vis absorption spectra. Raman spectra revealed that the as-prepared films were of hexagonal phase SnS2. FESEM images and surface profiler measurements indicated that the SnS2 thin film deposited under the optimum condition was homogeneous and well adhered to the substrate, with a thickness of about 200 nm. Optical absorption measurements disclosed that the SnS2 thin film deposited under the optimum condition had a band gap of about 2.40 eV.

Abstract: Using the coherence theory of non-stationary fields and the method of Fourier transform, the spectral properties of spatially and spectrally partially coherent Gaussian Schell-model pulsed (GSMP) beams in fused-silica glass medium are studied and analyzed numerically. It is shown that the spectral shift takes place, which depends on the position of the field point, spatial correlation length, temporal coherence length and dispersive property of medium, as GSMP beams propagate in fused-silica glass medium. The on-axis spectrum is blue-shifted, and the relative spectral shift increases with increasing propagation distance, and decreases as the spatial correlation length and temporal coherence length increases, and then approaches an asymptotic value. The dispersive property of medium plays an important role in the spectral properties of spatially and spectrally partially coherent beams.

Abstract: An analytical expression for the spectrum of stochastic spatially and temporally partially coherent electromagnetic Gaussian Schell-model pulsed (GSMP) beams is derived, and used to study the spectral changes of electromagnetic GSMP beams in free space. The influence of polarization on the on-axis relative spectral shift is emphasized. It is shown that the on-axis relative spectral shift increases with increasing the degree of polarization of source P0 for the case of δxx≠δyy, i.e. the spatial coherence length δxx of x component of the electric field at the source is not equal to that of y component. For δxx=δyy or δxx→∞ and δyy→∞, the on-axis relative spectral shift is independent of P0.

Abstract: Divalent europium and trivalent dysprosium co-doping in the compounds Sr2.97-xCaxMgSi2O8 (x=0, 0.5, 1.5, 2, 2.5, 2.97) produces phosphors of high luminescence yield. These phosphors were prepared at high temperature and weak reductive atmosphere. The ratio of Eu/Dy is 1/2. The phosphors were characterized for their crystal phases by x-ray powder diffraction. Slight shifts of the peaks in the structure, which indicate a small change of the interplanar crystal spacing, were observed for each different x’s. The interplanar spacing becomes narrow as increasing the value of x. These phosphors respond well to the ultraviolet excitation. The peak of the emission band occurs at progressively longer wavelength and widens as the ratio of alkaline earth Sr/Ca ions is decreased. The emission peaks of the phosphors indicated on the emission spectra range from 463nm to 490nm. It is probably due to the influence of 5d electron states of Eu2+ in the crystal field because of atomic size variation causing crystal defects. Dy3+ ion doping in the phosphor generates deep traps, which results in long afterglow phosphorescence. As the proportion of Ca in the composition increases, the attenuation time of the phosphors becomes short.

Abstract: Cauliflower-like ZnO superstructures composed of nanoparticles in large scale were successfully synthesized only using Zn(CH3COO)2•2H2O and triethanolamine (TEA) aqueous solution mixtures via a template-free sonochemical process at the ambient condition. A number of techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV-visible absorption and photoluminescence (PL) were used to characterize the obtained ZnO products. It has been interestingly found that UV-Vis absorption spectrum shows not only a weak and sharp peak at 367 nm in ultraviolet region but also a strong and broad band centered at 564 nm in visible region. The possible formation mechanism of ZnO cauliflower-like structure is also proposed.

Abstract: A series of Re3+ (Re=Lu, Gd, La) co-doped YAG phosphors were successfully synthesized by a sol-gel combustion method and characterized with XRD and photoluminescent spectrum. The phase composition and luminescent properties of YAG:Ce under different Re co-doped concentrations were investigated. Doping only 50 mol% of La3+ to replace Y3+ sites, the main phase of sample has transformed into LaAlO3. While the concentration of Gd3+ reached 90~99 mol%, it was still cubic YAG. Lu3+ could replace Y3+ ions completely with the garnet structure. The location of the emission peak of Gd-codoped YAG:Ce3+ shifted to red region 21 nm corresponding to the maximum emission intensity before the appearance of GdAlO3. In addition, it had a 24 nm blue shift when Y3+ replaced by Lu3+ completely.

Abstract: CaCO3 was chosen as main raw material and wet chemical method was used to prepare the precursor. The precursor was directly sintered at 1060oC with reducing atmosphere for 3 h to obtain new green CaO:Tb3+ ,Li+ Phosphors. The effects of the content of the doping ions Tb3+ and Li+ on the luminescent properties have been studied. The structure, morphology and luminescent properties of the phosphors were characterized by XRD, laser particle size analyzer, SEM, UV and PL-PLE spectra respectively. The results showed that the CaO:Tb3+,Li+ was a single face-centered cubic crystals, the phosphor particle distributed uniformly, the average size of particle was 2μm. The phosphor has a strong absorptive capacity excited by 282 nm ultraviolet ray, and could emit the strong green light with the wavelength of 543 nm(5D4→7F5). The CaO:Tb3+,Li+ is a new type of green fluorescent material.