In this paper we propose the study of nanocomposites for white light emission in a semiconductor device, by incorporating the yttrium aluminum garnet doped with cerium ions (YAG:Ce3+), into a polymeric matrix of poly methyl methacrylate. The co-precipitation method was used for the synthesis of YAG:Ce yellow phosphor. The transition from the amorphous state to the crystalline was observed at a temperature of 1200°C. In order to obtain a better dispersion of the nanoparticles in the polymeric matrix has been chosen a capping agent. The structural analysis of the nanocomposite and the phosphor were studied by Fourier transform infrared spectroscopy and x-ray diffraction, morphological properties were investigated by scanning electron microscope, and photoluminescence spectrometry has highlighted the applicability of phosphors and, implicitly, of the nanocomposite for application in emitting optoelectronics.
In this paper we aim to develop a summer garment with improved ultraviolet (UV) protection. Due to its lightweight and breathability, cellulose-based viscose rayon was selected to be covered with inorganic ZnO film. Atomic layer deposition (ALD) is a modern technique that delivers uniform coatings with controlled thickness. Viscose fragments were evenly covered with ZnO at 120°C in high vacuum, and their properties were tested against UV exposure and wettability. Morphological examination conducted by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) elemental analysis demonstrated the uniform deposition of ZnO onto the porous semi-synthetic material. The bond structure of cellulose-ZnO composite was assessed by Fourier-transform infrared spectroscopy (FTIR). High wettability of viscose was restrained by the ZnO superficial layer, as revealed by contact angle measurements. Optical absorbance and transmittance evaluated by diffuse reflectance spectroscopy (DRS) displayed the increase of the absorption peak below the 400 nm wavelength in dry and wet conditions, after the ZnO functionalization.
Due to the honeycomb arrangement of carbon atoms, graphene exhibits unique properties, such as superior thermal conductivity, exceptionally large surface area and zero bandgap, and has become one of the fastest growing domains of scientific research. Many processes have been developed to obtain single layer graphene by chemical vapour deposition, but the main drawback of using graphene in large area industrial manufacturing processes is the transfer procedure from the transition metal to the target substrate. In the present paper we study the possibility to obtain single layer graphene by chemical vapour deposition (CVD) on copper catalyst and transfer it to different substrates. The quality of CVD graphene on copper catalyst and on substrate target after transfer was evaluated from the structural (by Raman spectroscopy), morphological (by SEM) and optical properties (UV-VIS) point of view. The transfer process proposed in this paper enable the use of this type of material in applications such as pressure sensors and field effect transistors, when proper control of the graphene/substrate interface is very important.
The present paper focuses on the obtaining of ZnO in powder form with a limited distribution of the nanoparticle size using different types of surface-active agents and optimizing the synthesis conditions. The coprecipitation process was chosen for the ZnO powder synthesis in the absence and in the presence of surface-active agents, being considered one of the most common synthesis and processing methods for producing nanostructured materials. The use of agents consists in preventing the nanoparticle size growth, but also in stabilizing the aggregation trend effectively by controlling structural features and by reducing the oxygen bridge bonds between particles. The anionic surfactant (SDS sodium dodecyl sulfate) and the cationic surfactant (CTAB cetyltrimethylammonium bromide) were used to modify the size, morphology and surface properties of the precipitated nanoparticles. Based on the structural characterization by FTIR, XRD, morphology by SEM, as well as UV absorption and PL analyses of ZnO in various versions, the significant influence of agents on ZnO particles, as well as the correlation of optical systems properties with particles morphology and size was revealed. The development of this type of material encourages the uses in many applications in nanotechnology, electronics, optics and other areas of modern science and technology.
In this paper we aim to perform a cross section morphological characterization of an acrylic polymer used for dental prostheses subjected to microwave disinfection. The method was largely investigated and the microbiological effectiveness is well established, but there are some issues regarding the in-depth alteration of the material. In our research, the surface roughness is insignificant and the samples were not polished or refined by any means. Two groups of 7 acrylic discs (20 mm diameter, 2 mm thickness) were prepared from a heat-cured powder. Half of the samples embedded a stainless steel reinforcement, in order to observe the changes at the interfaces between the polymer and metallic wire. After the gradual wet microwave treatment, the specimens - including the controls - were frozen in liquid nitrogen and broken into pieces. Fragments were selected for gold metallization to ensure a good contrast for SEM imaging. We examined the samples in cross section employing a high resolution SEM. We have observed the alterations occurred at the surface of the acrylic sample and at the interface with the metallic wire along with the increase of the power and exposure time. The bond configuration of acrylate samples was analysed by FTIR spectrometry.
Semiconductor oxides such as SnO2, TiO2, WO3, ZnO2 etc. have been shown to be useful as gas sensor materials for monitoring various pollutant gases like H2S, NOx, NH3 etc. In this work, we would like to present the preparation of titanium dioxide films for gas sensor application, via the sol-gel technique. The coating solution was prepared by using titanium isopropoxide precursor, which was hydrolyzed with distilled water under the catalytic effect of different acids (HNO3, HCl or CH3COOH). Titanium dioxide films have been deposited using spin coating method and then synthesized at different temperatures. Fourier transform infrared spectroscopy observation has been used to analyze the sol-gel process. The morphology and the structure of the thin films were analyzed.
Interaction between polymers and nanoparticles are known to influence structure and properties of polymer materials containing dispersed nanomaterials. Titanium oxide was prepared by sol-gel method and used as inorganic materials; polyvinyl alcohol was used as polymer matrix. The objectives of this paper are to synthesize and characterized TiO2 - polymer composite. TiO2 nanoparticles were dispersed in polymer solution with the aid of ultrasonic vibration to obtained polymer composite materials.
The properties of TiO2 - polymer composite films were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and optical microscopy. FT-IR showed that there existed a strong interaction at the interface of TiO2 and polymer, which implied that the polymer chains were grafted onto the surface of TiO2 nanoparticles. It can be also be seen from SEM images that the TiO2 nanoparticles were perfect dispersed in polymer matrix.
Future electric lights will be composed of white LEDs (Light Emitting Diodes) and for this reason the development of
new luminescence materials has become a great challenge to researchers. In the present paper it is presented a sol-gel
method, simple and with superior potential for synthesis of nanoparticles of yttrimn aluminium garnet doped with
cerium luminescent powders. This method has a big potential for application in new generation luminescent lighting
devices. The gels were prepared using stoichiometric amounts of reagent-grade Y203 and A1203 as the starting
materials. The XRD pattern of the powder calcinated al 1100°C shows the formation of single-phase nano-crystal garnet
materials. The XRD measurements and AFM measurements show that we obtained a phosphorus with grain size of 24
nm. The emission spectra of white LED demonstrate that acquired phosphor has good applicability in optoelectronics.
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