Design and application of ZnO/rGO nanocomposite opto-catalyst as wide-bandgap optical material for solar-driven dye degradation

Synthesis and enhancement of photocatalytic activities of ZnO by silver nanoparticles

Exposure of solar optical materials to use environments results in degradation of the materials. Degradation effects can be evaluated by measurements of the appropriate optical properties. In situ environmental exposure tests were conducted at two locations. Both reflecting and transmitting materials were evaluated for changes in optical properties due to environmental effects. These results were computerized along with information obtained from the literature survey summarized in Volume 1 of this report. The computerized data base was used for an analysis and correlation of degradation in optical properties' values with selected environmental test site parameters. Optical properties for reflecting and transmitting materials were investigated as well as differing exposure test techniques and optical properties measurement methods. Modeling of optical properties degradation was studied for various materials in the soiled condition and following a cleaning procedure.

The 3rd International Conference on the Physics of Optical Materials and Devices (ICOM2012) was held in Belgrade (Serbia) from 2 to 6 September 2012 (figure 1). The conference was organized by the Vinča Institute of Nuclear Sciences, University of Belgrade (Serbia) and the Laboratoire de Chimie de la Matière Condensée de Paris (France), and supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia and Optical Society of America. ICOM2012 was a follow-up to the two previous, successful ICOM conferences held in Herceg Novi in 2006 and 2009.The conference aimed at providing a forum for scientists in optical materials to debate on: • Luminescent materials and nanomaterials• Hybrid optical materials (organic/inorganic)• Characterization techniques of optical materials• Luminescence mechanisms and energy transfers• Theory and modeling of optical processes• Ultrafast-laser processing of materials• Optical sensors• Medical imaging• Advanced optical materials in photovoltaics and biophotonics• Photothermal and photoacoustic spectroscopy and phenomena The conference stressed the value of a fundamental scientific understanding of optical materials. A particular accent was put on wide band-gap materials in crystalline, glass and nanocrystalline forms. The applications mainly involved lasers, scintillators and phosphors. Rare earth and transition metal ions introduced as dopants in various hosts were considered, and their impact on the optical properties were detailed in several presentations. This volume contains selected contributions of speakers and participants of the ICOM2012 conference.The conference provided a unique opportunity for about 200 scientists from 32 countries to discuss recent progress in the field of optical materials. During the three and half days, 21 invited talks and 52 contributed lectures were given, with a special event in memory of our dear colleague Professor Dr Tsoltan Basiev (Russia). In addition, 183 posters were presented and the two Young Scientist Awards were announced at the closing ceremony.AcknowledgmentsWe thank all the authors for their valuable research contribution presented in this volume. We express our acknowledgements to all reviewers with a special thanks to Dr G Watt, then Publisher of the journal, for accepting the publication of these papers in a special issue of Physica Scripta . We wish to express our gratitude to the members of the ICOM scientific advisory committee and organizing committee for their excellent work and commitment for the success of ICOM2012.

Understanding the dynamics of excited carriers in wide band gap materials is a requirement to describe a broad range of physical mechanisms such as scintillator response, radiation induced damage of crystals, or laser-induced breakdown in optical materials and coatings. The difficulty arises from the competition between all the different relaxation channels: electron-phonon collisions, impact ionization, exciton and transient or permanent defects formation. Ultrashort laser pulses are ideal tool to investigate transparent materials since they allow to induce a large excitation density, and provide a temporal resolution high enough to track in real time the carrier relaxation. Two results concerning material which are extremely important for numerous application, namely silica (SiO2) and sapphire (Al2O3), and using different techniques, will be presented. First, in Al2O3, we have measured in a broad temporal range – from 30fs to 8 ns - the absorption induced by photo-excited carriers using time revolved absorption spectroscopy. By changing the intensity of the pump pulse, and thus the initial excitation density, we could measure the induced absorption on more than two orders of magnitude and demonstrate that the carrier relaxation dynamics exhibit a complex decay, and strongly depends on the initial density of excited carriers. We have developed a two steps model based on rate equations and taking into account the laser damping, which allows to fully reproduce the decay and the amplitude of the measured absorption. We demonstrate that in sapphire the electrons are mobile and can recombine with any hole. With this experiment and our modelling we can explain for instance the complex decay of luminescence observed when sapphire is irradiated with heavy ions or VUV photons. In SiO2, an important problem related to optical breakdown is the impact ionization which can lead to avalanche: electron excited by an intense laser can gain high kinetic energy in the conduction band and collide with valence electron (impact ionization) thus multiplying the excited carrier density. By using a sequence of double pump pulse we could control independently the two key parameters: plasma density and temperature. Under appropriate conditions, using time resolved interferometry as a probe, we could directly observe for the first time an electronic avalanche induced by a laser pulse. Again a complete modeling, using multiple rate equation and taking into account the laser propagation,; allow to completely describe the experimental results.

Cadmium selenide nanoparticle [CdSe] is an important chemical substance gaining great importance and widely used as an additive in the production of various, industrial products like rubber, cosmetics, catalyst, optical materials solar cells etc. CdSe being a wide band gap material and with better lattice matching properties made it suitable option for solar cell applications, the CdSe nano rods are synthesized by a simple solvothermal method at the morphology, phase and the optical properties of Cdse nano particles are studied using powder X-ray diffraction [XRD], High resolution transmission electron microscope [HRTEM], UV-visible absorption spectroscopy, and Photoluminescence [PL] Spectroscopy, the HRTEM images confirm the formation of CdSe nano rods. The presence of elements was confirmed by Fourier transform infrared spectroscopy [FTIR], energy dispersive X-ray spectroscopy [EDAX], SEM images showed the morphology of the samples.

A kind of amorphous/nanocrytalline Si (a-Si:H/nc-Si:H) PIN type tandem solar cell of TCO/a-SiC:H(p1)/buffer/a-Si:H(i1)/nc-Si:H(n1)/tunnel junction (TJ)/nc-Si:H(p2)/ nc-Si:H(i2)/ a-Si:H(n2)/Al was optimized with numerical method. The high conductivity, high optical transmittance and wider band-gap material was selected as window layer in the cell. The buffer layer between p1 and i1 layers and the tunnel junction were designed, respectively. The thickness and band-gap of intrinsic layers in sub-cells were adjusted separately. The simulation results indicate that absorption solar spectrum by the designed cell can be expanded towards the long wave direction. The light-induced recession of present cell was restrained while the stability was improved.

Three different clay-supported nanoscale zero-valent iron materials for industrial azo dye degradation: A comparative study

Green ZnO nanorod material for dye degradation and detoxification of pharmaceutical wastes in water

ABSTRACTIn this paper, degradation mechanisms of optical materials, used in the light emitting diode (LED)-based products, are reviewed. The LED lighting is one of the fastest technology shifts in human history. Lighting accounts for almost 20% of the global electrical energy use, inferring that replacement of traditional lighting sources with LEDs with higher efficiencies will have major positive implications for the global energy consumption. Organic optical materials are key components in LEDs in the sense that they control the functionality of the device and they have decisive effects on the durability and reliability of LEDs. This paper aims at describing the influences of chemical structure and service conditions on the degradation mechanisms of organic optical materials in LEDs which lead to the lumen depreciation, discolouration, and colour shift of the LED light output. The contributions of different degradation mechanisms of optical and package materials in LED-based products to the lumen depreciation and colour shift are methodically reviewed.

Background:We synthesized cerium oxide (CeO2) nanoparticles (NPs) via green synthesis method mediated with Rajma seeds powder as a fuel and cerium nitrate as an oxidizer.Objective:The obtained cerium oxide nanoparticles are used to study the various environ mental appilications.Methods:The achieved CeO2 nanoparticles are tested using PXRD (Powder X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), electron microscopic studies including SEM, Raman spectroscopy, UV-Visible spectroscopy. Formation of agglomerated cubic phased CeO2 nanoparticles were confirmed from both PXRD and SEM.Results:The average crystallite size of CeO2 nanoparticles was found to be 38 nm calculated from highly intense peak using Debye-Scherer’s formula. The characteristic Ce-O stretching was confirmed by FTIR and Raman studies. CeO2 nanoparticles are promising material for the organic dye degradation. Photocatalytic activities evaluation under various parameters like sunlight, UV light and variation of PH, catalytic dosage etc. CeO2 nanoparticles exhibit highly enhanced photo degradation of Methylene Blue dye. Kinetics and isotherm models of Photocatalysis were studied.Conclusion:We have prepared CeO2 nanoparticles by low-temperature combustion technique using Rajma germinated and Rajma non- germinated seeds as fuel. The XRD pattern confirms the formation of cubicphase CeO2 nanoparticles. The existence of Ce-O vibration is confirmed by FTIR and Raman spectra of the CeO2 nanoparticles. The UV-Visible spectra of CeO2 nanoparticles reveal the absorbance band range at 350-390 nm. SEM images of CeO2 nanoparticles indicates the agglomerated with irregular morphology. CeO2 nanoparticles are favorable material for the organic Methylene blue dye degradation. The different amount of the Rajma influences improved Photodegradation of cerium oxide nanoparticles was characteristics of slight crystal dimension, new superficial deficiencies, more band hole and ability to make smaller the electron-hole pair rearrangement. Adsorption kinetics results show that adsorption of MB over cerium oxide follows pseudo-first-order and second-order kinetics. Using the Langmuir isotherm, Freundlich isotherm, maximum adsorption capacity is calculated. Thus it can be used as attractively recoverable nano adsorbent for the removal of MB dye by adsorption technique from effluent water.

Bi2WO6 as a high visible-light-driven catalyst has been aroused broad interest. However, it can only be excitated by the light with λ < 450 nm and the solar energy utilization need to be improved. Here, the wide–range–visible photoresponse Bi2WO6−x nanoplates were fabricated by introducing surface oxygen vacancies through the controllable hydrogen reduction method. The visible photoresponse wavelength range is extended from 450 nm to more than 600 nm. In addition, the photocatalytic activity of Bi2WO6−x is also increased and is 2.1 times as high as that of pristine Bi2WO6. The extending of the photoresponse range and the enhancement of the photoactivity both can be attributed to the surface-oxygen-vacancy states. This is because surface-oxygen–vacancy states generated above and partly overlapping of with the valence band (VB) will result in the rising of valence band maximum (VBM), thus broadening the VB width. This approach is proposed to develop many types of wide–range–visible optical materials and to be applicable to many narrow and wide bandgap materials.

Oxygen‐deficient BaAl2O4, with strong optical absorption in the spectra range from 200 to 2500 nm, was prepared by a simple and economic thermal treatment of BaAl2O4 in a H2 gas flow. Further studies found that a molar ratio of oxygen vacancies of about 0.4 % existed in the prepared oxygen‐deficient BaAl2O4 sample. The influence of oxygen vacancies on the electronic band structures and optical absorption of BaAl2O4 are elucidated via first principle calculations. Oxygen vacancies introduce impurity states above the valence band; these impurities expand and enhance the optical absorption of BaAl2O4. This approach is proposed to develop a new type of optical materials and to be applicable to many wide bandgap materials.

Luminescence quenching via nonradiative recombination channels limits the efficiency of optical materials such as phosphors and scintillators and therefore has implications for conversion efficiency and device lifetimes. In materials such as Ce-doped yttrium aluminum garnet (YAG:Ce), quenching shows strong dependence on both temperature and activator concentration, limiting the fabrication of high-intensity white-light emitting diodes with high operating temperatures. Here, we reveal by means of first-principles calculations an efficient recombination mechanism in YAG:Ce that involves oxygen vacancies and gives rise to thermally activated concentration quenching. We demonstrate that the key requirements for this mechanism to be active are localized states with strong electron-phonon coupling. These conditions are commonly found for intrinsic defects such as anion vacancies in wide band gap materials. The present findings are therefore relevant to a broad class of optical materials and shine light on thermal quenching mechanisms in general.

Comprehensive calorimetric absorption measurements were performed for CaF₂ crystals at irradiation wavelengths 193 nm and 157 nm. By using samples with different thickness a separation of surface and bulk absorptance could be achieved and thus, single- and two-photon absorption coefficients could be determined. For the surface absorptance, a dependence of the polishing grade of the sample was observed at 193 nm. The presented results support earlier proposed models of the absorption mechanisms in wide band-gap materials. For an assessment of the optical quality of DUV optics, a high-sensitivity wavefront analyzer system based on the Hartmann-Shack principle is employed. The device accomplishes precise online monitoring of wavefront deformations of a collimated test beam transmitted through the laser-irradiated site of a sample. Due to the achieved sub-nm resolution, it can be used as an alternative to interferometric measurements for 'at wavelength' testing of optics, e.g. for on-line registration of thermal lensing effects or compaction in fused silica.

The degradation of optical materials exposed to the near earth orbit space environment is of primary interest for spacecraft designers and must be accurately predicted. Optical materials generally have highly polished and accurately formed surfaces so that even low levels of degradation may have a significant effect on the long-term performance of the component. This paper describes the design and testing of a miniature spectrometer system which will be used to actively monitor the on-orbit degradation of optical materials placed on the exterior of the International Space Station.