Key Engineering Materials Vols. 368-372

Abstract: ZnS:Cu,Cl phosphors were synthesized by high temperature (1200 °C) solid state reaction, mechanical milling (rotation speed = 0, 75, 150, 250 and 350 r / min) and the final annealing at 750 °C for 1 h in different atmospheres (hydrogen sulfide, sealed evacuated silica tubes and Ar). The as-prepared phosphors were characterized by X-ray powder diffraction and photoluminescence spectra. It was found that mechanical milling led to width increases of diffraction peaks. Both the mechanical milling and atmosphere play important roles in the photoluminescence performance of the phosphors. Some phosphors prepared by the three-step method possess higher photoluminescence performances than the normal one-step method. Particularly, the luminescence intensity of the phosphor milled at the rotation speed of 75 r / min and then treated in Ar atmosphere is about one time higher than that prepared by the normal one-step process.

Abstract: Eu-doped CaS phosphors were prepared from sulfurization of CaCO3 in H2S gas without flux. The doping of Eu activator was conducted in two different modes: synchronous doping during sulfurization of CaCO3 and subsequent doping by vacuumly calcinning pure CaS and Eu2O3. Comparison of the as-prepared samples indicated that subsequent doping led to larger optimum Eu concentration and lower red emission intensity than synchronous doping. The different luminescence properties are ascribed to the different activator distributions in CaS host induced by different doping modes, and the uniform distribution resulted from synchronous doping is beneficial to the luminescence of the phosphor.

Abstract: SiC films were prepared by HFCVD technique on (111) Si substrate. The composition and the structure of the films were investigated using EDX, XRD and transient fluorescence. Results indicated the films deposited were nanocrystalline and the calculation of the grain size gave a further confirmation. PL measurement of the present films showed that there existed a strong ultraviolet emission at room temperature.

Abstract: Pulsed laser deposition (PLD) technique is a very powerful method for fabricating various oxide thin films due to its native merits. In this study, gallium and nitrogen co-doped ZnO thin films (0.1 at.%) were deposited at different temperatures (100-600°C) on sapphire (001) substrates by using PLD. X-ray diffractometer, atomic force microscope, spectrophotometer, and spectrometer were used to characterize the structural, the morphological and the optical properties of the thin films. Hall measurements were also carried out to identify the electrical properties of the thin films.

Abstract: Transparent ZnO and aluminum-doped zinc oxide (AZO) thin films were prepared via the sol-gel process on glass substrates using an alcoholic non-polyol route and spin-coater technique for film deposition. Zinc acetate, zinc chloride, and aluminum salt used as cations source. All the undoped and doped xerogel films were amorphous and converted into zincite structure after firing at 200 oC, irrespective of precursor types and dopant amounts. However, the evolution of morphology, microstructure, and texture of the gel films were strongly depended on the precursors and dopants. The films derived from zinc chloride showed strongly preferential (002) orientation, while acetate-derived films exhibited random orientation. On firing at 500 oC, the visible transmittances of films were 50~92%, depending on the kinds of precursors and dopant contents.

Abstract: ZnO nanorods were prepared by a hydrothermal reaction in the presence or absence of PVP (polyvinyl pyrrolidone). The obtained products were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, UV-Vis absorption (UV) spectroscopy and photoluminescence (PL) spectroscopy. The results suggest that PVP plays an important role in the preparation of ZnO nanorods. The UV absorption spectrum showed PVP increases the UV-shielding ability but doesn’t influence the transparency in the visible light region. A weak UV emission at 353 nm of PL spectra exhibit the surface of ZnO nanorods is passivated and oxygen-related defects is supplied by PVP.

Abstract: Sm2O3 optical thin films were prepared by hydrothermal method using samarium dichloride as source material. The influence of preparation temperature on the crystallinity, morphology and optical properties of Sm2O3 thin film were investigated. The as-fabricated thin films were characterized by X-ray diffraction, atomic force microscopy and spectrophotometer. Results show that the prepared thin film is Sm2O3 crystallites thin film with compact and uniform surface microstructures. Transmittance curve displays that the Sm2O3 crystallites thin films are transparent to visible and infrared light; and possess excellent absorbency of UV light. With the increase of deposition temperature, the crystallinity and optical properties of the prepared Sm2O3 thin film are improved. With the increase of hydrothermal temperature from 170 °C to 185 °C, the bandgap of the thin film increase from 2.88 eV to 2.95 eV.

Abstract: WO3 sol was prepared through the sol-gel process. Ethanol, acetone and SiO2 sol were added to the WO3 sol. The WO3 thin films on glass substrate were obtained with the hybrid sol by the dip-coating technique, and then were heat-treated at different temperatures for a certain time. X-ray diffractometer and scanning electron microscope were used to characterize the crystal structure and surface morphology of these coatings. Visible light transmittance changes of the thin films irradiated under UV light were measured with UV spectrometer. The experimental results demonstrated that photochromic effect, hardness and uniformity of thin films were improved when the thin films are obtained with the hybrid sol.

Abstract: This work studies the effects of microstructure and relative density on the dielectric constant of porous silica prepared by two different techniques: gelcasting of suspension (GCS) and gelcasting of foams (GCF). Both routes are carried out from the preparation of silica suspension containing starch granules. In GCS route, the resultant suspensions were heated for consolidation, while in GCF route, the suspension was foamed before consolidation. The results indicated that the dielectric constant of porous silica was obviously determined by relative density, but scarcely influenced by microstructure. The logarithmic fitting equation lnε = ρ·lnεs was a good model to describe the relationship between the dielectric constant and the relative density of porous silica prepared by both GCS and GCF routes.

Abstract: Porous silica was prepared by selective leaching of metakaolinite with 20 mass% HCl solution. The metakaolinite was derived from the 1:1 layered structure clay mineral kaolinite by firing at 600°C for 24 h. The characteristics of porous silica were studied. The content of Al2O3 in metakaolinite was sharply changed from 45% to less than 2% after 2 h leaching. The maximum specific surface area of the leached sample was about 350 m2/g. The average pore size is about 2 nm. The total pore volume is 0.3 ml/g. The layer structure of kaolinite and metakaolinite is responsible for forming micropores.