High Visible Light Transparency Research Articles

Organic-inorganic hybrid aerogels with high mechanical properties via organotrialkoxysilane-derived sol-gel process

A brief overview of siloxane-based low-density aerogels and aerogels-like xerogels is presented. Aerogels are highly porous solids composed of inorganic oxides, metals, cross-linked polymers and carbons, and are known to possess a number of excellent physical properties such as high visible-light transparency with low refractive index, low dielectric properties, and extremely-low thermal conductivity. Aerogels are therefore regarded as a promising candidate for applications such as superinsulators; however, a mass production and applications of aerogels have been significantly discouraged due to the lack of mechanical properties since the first invention in 1931. This review introduces the substantial effort to improve the mechanical properties of aerogels with particularly highlighting our recent findings on elastic organic–inorganic hybrid aerogel monoliths obtained from methyltrimethoxysilane (MTMS) using the controlled sol–gel chemistry.

Study of the morphology of ultra-thin Pt films as the anode of an organic light emitting display

An ultra-thin Pt layer could be used as a transparent conducting anode to replace the ITO used today in a top-emitting OLED. A proper thickness of Pt thin layer is needed to avoid large leakage current while still keeping the high transparency for visible light. X-ray reflectivity and AFM were used to measure the morphology of e-gun deposition Pt thin films grown on glass substrates. The islands grown on the glass coalesced at the thickness of less than 4 nm. For the sample of 4 nm thickness, the sheet resistance is 800 Ω/□ with a transparency of 65%.

Ga-Doped ZnO Transparent Conductive Oxide Films Applied to GaN-Based Light-Emitting Diodes for Improving Light Extraction Efficiency

In this study, Ga-doped ZnO (GZO) thin films were deposited on a sapphire substrate utilizing a magnetron sputtering approach. ZnO and Ga2O3 targets were employed as the sputtering sources during a cosputtering deposition. After thermal annealing in nitrogen ambient conditions, the electrical resistivity and optical transparency of the GZO films were analyzed in detail. The GZO films exhibited high transparency (~90%) in visible light and low resistivity (~5.3 x 10-4Omega-cm) when they were annealed at a temperature of 600-800deg C. Although the utilization of indium tin oxide (ITO) serving as the transparent contact layer (TCL) in conventional GaN-based light-emitting diodes (LEDs) is a well accepted technology, ZnO-based TCLs with a high refractive index of around 2.0 would render another advantage when a roughening process is performed on the surface. In other words, since packaged LEDs are generally encapsulated using epoxy with a refractive index of around 1.5, surface roughening performed on ITO TCL would thus result in only a minor improvement in light extraction because the typical refractive index of an ITO film prepared by our e-beam evaporator is around 1.7. In this study, GaN-based LEDs that utilized ITO/GZO composite oxide films as a TCL were also demonstrated. The light output power of an LED (LED-C) with a textured ITO/GZO composite TCL is markedly improved by 42 % and 48 % of magnitude as compared to LEDs with a planar GZO TCL (LED-A) and a ITO/GZO composite TCL (LED-B), respectively. This enhancement is due to the fact that a ZnO-based TCL with a higher refractive index (n~2.0) allows further enhancement of light extraction through the creation of a textured structure on the TCL that is deposited on the top surface of LEDs.

Synthesis of Nano‐Sized TiO2 Colloidal Sol and Its Optical Properties

Nano‐sized TiO2 sol was prepared through a wet synthesis process. The synthesis procedure involved hydrolysis of TiCl4, acid treatment, and a SiO2 surface‐modifying process. Before surface modification, the TiO2 suspension was treated with acid to remove Na ions, soluble TiO2, and other impurities. The acid treatment of a TiO2 suspension at a higher temperature was proved to be useful for effective SiO2 modification. The colloidal sol provided high transparency in visible light as well as excellent UV‐shielding properties. Surface modification of TiO2 particles with SiO2 greatly improved both the dispersing stability in neutral pH and the photostability of TiO2 colloidal sol.

Material design using genetic algorithms and preparation of innovative UV‐reflecting composite

Genetic algorithm (GA), which is one of the methods that optimize the combination of factors, was applied to the design of a new cosmetic material. GA effectively gives an adequate solution especially when there are huge factors and infinite combinations among those individual factors. In this work, the UV‐reflecting composite that effectively reflects UV light and has high visible light transparency was chosen as the target material. From GA simulation, a blueprint of the composite was obtained as follows: the multiple layers on the core material (mica) should be 27 nm titanium dioxide, 42 nm silica, 33 nm titanium dioxide, and 115 nm silica (from the inner layer). According to the results, the composite was prepared, and its cosmetic properties were evaluated. This composite showed both high UV reflection effect and good visible light transparency while having a smooth feeling on use, compared with the commercial ultra fine titanium dioxide.

Preparation and characterization of transparent ZnO/epoxy nanocomposites with high-UV shielding efficiency

Transparent ZnO/epoxy nanocomposites with high-UV shielding efficiency were reported in this paper. First, zinc oxide (ZnO) precursor was synthesized via the homogeneous precipitation method and ZnO nanoparticles were then made by calcination of the precursor at different temperature. The structural properties of the as-prepared ZnO nanoparticles were studied in detail using thermogravimetry (TGA), differential thermal analysis (DTA), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and transmission electron microscopy (TEM), respectively. Transparent ZnO/epoxy nanocomposites were subsequently prepared from transparent epoxy (EP-400) and as-prepared ZnO nanoparticles via in situ polymerization. Optical properties of ZnO/epoxy nanocomposites, namely visible light transparency and UV light shielding efficiency, were studied using an ultraviolet–visible (UV–vis) spectrophotometer. The optical properties of the as-obtained nanocomposites were shown to depend on ZnO particle size and content. The nanocomposite containing a very low content (0.07% in weight) of ZnO nanoparticles with an average particle size of 26.7 nm after calcination at 350 °C possessed the most optimal optical properties, namely high-visible light transparency and high-UV light shielding efficiency, that are desirable for many important applications.

Chemical vapor deposition of tin oxide: Fundamentals and applications

Tin oxide thin layers have very beneficial properties such as a high transparency for visible light and electrical conductivity making these coatings suitable for a wide variety of applications, such as solar cells, and low-emissivity coatings for architectural glass windows. Each application requires different properties of the tin oxide layer. These properties can be tuned by adjusting the parameters of the chemical vapor deposition (CVD) process, the main technique used for applying the tin oxide layer to the substrate. This paper discusses the state of the art of the kinetic models for tin oxide CVD. In the case of organometallic precursors the gas-phase chemistry may be initiated by cleavage of the tin–carbon bond, followed by radical-driven chain reactions that enhance the overall decomposition rate. However, in commercial tin oxide CVD reactors the gas-phase temperature may be too low or the residence time too short for these reactions to occur, thereby favoring surface chemistry. Preliminary investigations of the MBTC–H 2O–O 2 chemistry indicate that a mechanism comprising the reaction between gaseous oxygen and an adsorbed MBTC–H 2O complex is a plausible model.

Synthesis and UV-shielding properties of calcia-doped ceria nanoparticles coated with amorphous silica

Nanoparticles of calcia-doped ceria were prepared by adding CeCl 3–CaCl 2 mixed solution and NaOH solution simultaneously in distilled water followed by oxidation with hydrogen peroxide solution at 40 °C and pH 12. After that, amorphous silica was coated by dispersing them in Na 2SiO 3 aqueous solution at pH 10, followed by decreasing the solution pH to 5. Doping with calcia resulted in a considerable decrease in particle size to form nanoparticles of ceria (2–4 nm in diameter) possessing excellent UV ray ( λ<400 nm) absorption ability and high transparency in visible light ( λ>400 nm). Coating calcia-doped ceria nanoparticles with amorphous silica was effective in depressing particle agglomeration. The catalytic activity for the air oxidation of castor oil substantially decreased by both doping with calcia and coating with amorphous silica. The photocatalytic activity of ceria was much smaller than that of titania and zinc oxide. Although as-prepared ceria was yellow, the powders calcined above 700 °C were white. These findings revealed that nanoparticles of calcia-doped ceria coated with amorphous silica can be safely used to provide high UV-shielding ability while maintaining a natural appearance when they are applied to the skin of humans.

Effect of O2Partial Pressure on AlOxThin Films Prepared by Reactive Ion Beam Sputtering Deposition

The barrier and optical properties of AlO x thin films on polycarbonate deposited by Reactive Ion Beam Sputtering (RIBS) were investigated at different oxygen partial pressure. We measured the deposition rate of AlO x thin films. As the oxygen partial pressure increased, the deposition rate increased then decreased. The changes of deposition rate are associated with the properties of deposited films. The properties of deposited AlO x thin films were studied using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). Optimum deposition parameters were found for fabricating aluminum oxide thin films with high optical transparency for visible light and low Oxygen Transmission Rate (OTR). The optical transmittance of AlO x thin film deposited on polycarbonate (PC) showed the same value of bare PC.

Preparation of a UV-attenuating agent using a mechanochemical reaction

This paper describes a mechanical preparation method of an ultraviolet (UV)-attenuating agent with a high transparency for visible light using a high-speed elliptical-rotor-type powder mixer (HEM). Ultra-fine zinc oxide particles are used to attenuate UV radiation. To stabilize homogeneous dispersion of zinc oxide particles in a suspension, they were uniformly immobilized on the surface of silica particles by a mechanochemical reaction between zinc oxide and silica, and the composite particles were incorporated into a polymer medium. The optimum processing time in the immobilization was determined by means of a proposed model considering both the activation energy of the mechanochemical reaction and the mechanical energy applied to the particles in the minimum clearance region of the HEM. The relative change in the number of hydroxyl groups on the surface of the silica particles confirmed that a processing time based on the number of zinc oxide particles was suitable for immobilization. The suspension in which the composite particles were dispersed showed more effective UV attenuation performance and had a higher transparency for visible light in comparison with a suspension containing only a mixture in which the zinc oxide and silica particles were simply blended.

Powder design for UV-attenuating agent with high transparency for visible light

To design high-performance ultraviolet (UV)-attenuating agent for dispersion type of functional paints and/or cosmetic powders, nano-meter size of zinc oxide (ZnO) powder was immobilized onto the surface of 4 μm square size of crystalline sheet (H-ilerite: synthetic polysilicic acid (PSA)). A high-speed elliptical-rotor-type powder mixer (HEM) was applied for exfoliating in a sheet one by one from the PSA agglomerates without breakage of the original shape and for arranging the ZnO in the mono-particle layer on the sheet during dispersing the self-coagulative ultra-fine ZnO. The critical operating conditions of the HEM were determined by an observation of the morphological change of PSA. Optical characteristics of the compounded powder (ZnO-PSA) were evaluated in the form of suspension dispersed into polymer medium. The UV-attenuating effect was confirmed in the UVA region (320–400 nm) and the heat treatment after immobilization was one of the effective methods to get higher transparency for visible light.

Oxidation of methanol to formaldehyde over a silver catalyst: Properties of the process

A novel Ir(ppy)2(bpy) complex-containing mesoporous cellular silica foams (Ir(ppy)2(bpy)-MCFs) was prepared by a facile thiol-ene click reaction between the prefabricated thiol-functionalized mesoporous cellular silica foams and vinyl-tagged [Ir(ppy)2(bpy)]PF6 complex. The elaborate Ir(ppy)2(bpy)-MCFs material possessed the large surface area (355 cm2/g), open foam-like mesoporous structure with 30 nm cell pore size and 3.0 nm window pore size. Importantly, it had the well-defined molecular configuration of Ir(ppy)2(bpy) active species. As expected, it exhibited excellent catalytic reactivity and selectivity in the visible-light-driven reductive depolymerization of oxidized lignin β-O-4 model compounds including p-hydroxyphenyl (H)-, guaiacyl (G)- and syringyl (S)-type units under the mild conditions. Meanwhile, it showed the comparable catalytic efficiency with the corresponding homogeneous [Ir(ppy)2(bpy)]PF6 catalyst. These high catalytic performances could be attributed to aerogel-like three-dimensional pore structure and high visible-light transparency, which efficiently decreased the mass transfer resistance and the photon propagation hindrance. Furthermore, it could be easily recycled and reused at least six times without the remarkable loss of catalytic activity.