Advanced Materials Research Vols. 652-654

Abstract: Different compositions of blended poly (N-carbazole) (PVK) with polyvinylpyrrolidone (PVP) were prepared. The optical properties such as infinite frequency refractive index (n_∞), average oscillator wavelength (λ₀), oscillator strength (S_o), dispersion energy (E_d), oscillator energy (E_o) and optical dielectric loss have been calculated. The refractive index of polymer blending systems significantly changes with the volume composition of PVP and shows a normal dispersion behavior. Mean while, the values of n_∞, E_d and E_o increase with the increase of PVP composition. Both of the real and imaginary part of the dielectric constant decrease as the wavelength increase. Thus, it reveals that the polymer composition has influenced the optical properties of the polymer blending system.

Abstract: A simple solar-blind ultraviolet (UV) detector was fabricated by using Al0.3Zn0.7O alloy thin films as photocathode and ZnO:Al (AZO) thin film as transparent electrode. Transmission spectra of Al0.3Zn0.7O alloy thin film was characterized through spectrometer and result showed significant enlargement of its optical band gap value. This alloy film only absorbed illumination whose wavelength is below 280nm, and the UV on/off characteristics of this detector presented very clearly. Scanning electron microscope (SEM) image revealed fine structure of both layers and the interface of these two layers performed clear and uniform.

Abstract: Two new three-branched s-triazine derivatives with near-octupolar symmetry have been synthesized. In each of them, two branches have donor groups attaching to their ends, while the other one has none. Their photophysical characteristics, such as UV–vis spectra, fluorescence spectra and two-photon excited fluorescence spectra, are compared with their octuplar analogs in which all the three branches are ended by donor group. The little structural difference results in great decline of single-photon absorptivity and single-photon excited fluorescence, as well as the two-photon excitated fluorescence.

Abstract: The CaMoO₄:Eu³⁺, Li⁺ red phosphors were synthesized by combustion synthesis with urea or urea-thiourea as fuels, and their crystalline phase, morphology and luminescent properties were investigated. The XRD results demonstrated that all the diffraction peaks of the products can be well indexed to the pure tetragonal phase of CaMoO₄. The SEM photographs showed that the particles of sample using urea as fuel are agglomeration, while the particles of sample using urea-thiourea mixture fuels are non-agglomeration. The powder can be effectively excited by ultraviolet with wavelength of 395 nm, and exhibits a strong red emission with maximum wavelength at 615 nm. The luminescent intensity of the phosphor with mixture fuels had 2.2 times stronger than that of the phosphor with single fuel, and its chromaticity coordinates (0.65, 0.35) was closer to NTSC standard values (0.67, 0.33).

Abstract: We present the results concerning the excitation and emissions spectra of Poly (N-carbazole) (PVK) blend with different compositions of polyvinylpyrrolidone (PVP). Doctor blade technique was used to coat the blended polymer on a quartz substrate. The influences of polymer composition to the excitation and emission spectra were observed under UV excitation source of a xenon lamp. The result shows a discrepancy in the maximum excitation, emission and Stokes shift for each samples. The variation of Full Width at Half Maximum (FWHM) for excitation and emission indicate that the variation in composition has affected on the fluorescence properties of the blended thin film polymer system. Fourier Transform Infrared (FTIR) spectroscopy reveals that the discrepancy in the emission and excitation properties of this polymer blending system is due to the discrepancy of infrared absorption peak in the carbazole functional group.

Abstract: The relations between electronic structure and thermoelectric property of misfit layered cobaltite of Ca3Co4O9 and La-doped series are studied from the calculation by density function and discrete variation method (DFT-DVM). The highest valence band (HVB) and the lowest conduction band (LCB) near Fermi level are only mainly from O 2p and Co 3d in Ca2CoO3 layer. Therefore, the semiconductor, or thermoelectric property of Ca3Co4O9 should be mainly from Ca2CoO3 layer, but have no direct relation to the CoO2 layer, which is consistent with that binary oxides hardly have thermoelectric property, but trinary oxide compounds have quite good thermoelectric property. With the amount of La-doped increase, the gap between HVB and LCB firstly decrease, then reaches the minimum, finally increase. The gap affects the thermoelectric property. Therefore, there is a best amount of Na-doped to improve thermoelectric property, which is consistent with the experiment.

Abstract: Er3+/Nd3+ co-doped oxyfluoride tellurite glass was prepared successfully by the conventional melting method. Luminescent properties of Er3+/Nd3+ co-doped oxyfluoride tellurite glass were studied in the NIR spectral range. There existed strong absorption peaks of Nd³⁺ ions at 580 nm, 743 nm, 800 nm and 874 nm and obvious absorption peaks of Er³⁺ ions at 580 nm, 743 nm, 800 nm and 874 nm. Er 3+ /Nd 3+ co-doped glass performed excellent fluorescence properties at 1.53 μm and 1.06 μm. There existed energy transfer between Nd3+ ions and Er3+ ions, that is 4I9/2 (Er 3+ ) + 4I9/2 (Nd3+) → 4I15/2 (Er3+) + 4F5/2 (Nd3+). Owing to the energy transfer from Er3+ ions to Nd3+ ions, multi-phonon relaxation or up-conversion radiations, emission intenisty of Er3+/ Nd3+ co-doped glass was weaker than that of Er3+ single-doped glass at 1.53 μm.

Abstract: Hollow spherical CaMoO₄:Eu³⁺, Li⁺ red phosphors have been successfully synthesized by spray pyrolysis method. The crystalline phase, morphology and luminescent properties of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence emission spectra (PL). The XRD results demonstrated that all the diffraction peaks of the samples can be well indexed to the tetragonal phase of CaMoO₄. The SEM images showed that the particles were composed of hollow spheres, whose diameters are about 1.4 μm. The as-prepared CaMoO₄:Eu³⁺, Li⁺ hollow spheres show a strong red emission corresponding to the ⁵D₀-⁷F₂ transition of the Eu3+ ions under ultraviolet light.

Abstract: In this paper, iron powder with high purity is covered by a Mn-Zn ferrite layer, and the effect of amount of ferrite on the microstructure and magnetic properties are investigated. The morphology of the samples was characterized by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. It was shown that the particle surface layer contains a thin insulating layer of Mn-Zn ferrite, with high particle surface coverage. The magnetic measurements on samples were carried out using a B-H curve analyzer and an AC performance tester at Bm=50mT. The results indicate that the Mn-Zn ferrite coated samples have excellent frequency characteristics compared with uncoated samples. Also, the composites with 4wt% ferrite show a good combination of magnetic permeability and magnetic loss in the range 0.8-150 kHz.

Abstract: SrAl₂O₄:Eu²⁺ was prepared by microwave-combustion method with europium oxide, strontium nitrate and aluminium nitrate as reaction materials under urea solution as reaction medium. The products were characterized by several analytical methods. Fourier transform infrared spectroscopy was used to determine whether the product was SrAl₂O₄:Eu²⁺. X-ray technique was used to study the phase composition. Scanning electron microscopy was used to study micro-structure and surface morphology of powders. X-ray fluorescence spectrometer was used to study the content and impurity of the product. The results show that the prepared SrAl₂O₄:Eu²⁺ luminescent materials belong to monoclinic crystal structure, the prepared SrAl₂O₄:Eu²⁺ presents loose, porous and foamy micro-structure and surface morphology. The product is made of SrAl₂O₄:Eu²⁺ mainly, which concludes W, P, Ni, Fe and Ca elements.