Study on Fabrication and UV Photoelectric Property of TiO2 Nanotube Array Electrodes.

Highly ordered TiO2 nanotube array electrodes were successfully fabricated by a two-step anodization method on Ti sheet substrates in an electrolyte composed of ammonium fluoride, deionized water, and glycol. The tube wall was smooth, and the average internal and external diameters, wall thickness, and tube length achieved were 80 nm, 90 nm, 10 nm, and 9 µm, respectively. X-ray diffraction and field emission scanning electron microscopy results revealed that the TiO2 nanotube arrays presented an amorphous structure. When calcined at 300 °C, the arrays crystallized into the anatase phase, and the crystallization degree of the oxide layer increased as the temperature rose. Calcinating at 400 °C did not obviously disrupt the porous structure of the highly ordered arrays. However, higher temperature enlarged the diameter of the nanotube array and roughened the tube wall. When the temperature reached 600 °C, the nanotube mouth broke because of the excessive stress, causing the oxide layer's thinness and nanotube mouth clogging. The photoelectric test showed that the electrode presented obvious photoresponse under 300-400 nm UV excitation (maximized at 360 nm). The degree of crystallization and the micro-structure of the oxide layer can significantly affect the photoelectric properties of the electrode. After calcination at 400 °C, the TiO2 nanotube arrays, with highly ordered tubular structure directly connected to the Ti substrate, can ensure the rapid transportation of photo-induced electrons to the Ti substrate, while the high crystallinity of the arrays can help reduce the defect density of the nanotube and extend the lifetime of the photo-induced carriers. The electrode showed the best photoelectric property, and the photocurrent intensity was maximized (29.6 µA). However, the calcination process with over-temperature resulted in substantial loss of the TiO2 oxide layer, mouth clogging, and a severe decline in the photoelectric properties.

Preparation of Highly Crystallized Yttrium Oxysulfide Suspension via a Novel Colloidal Processing.

High-crystallized Y2O2S suspension was synthesized by a novel two-step method of high temperature solid-state reaction and subsequent colloidal processing. The synthesis method proposed in this study retains all advantages of the high temperature solid-state reaction method. The obtained data agrees with that of the PDF card, which indicates the product is pure Y2O2S crystals. The results show that the prepared Y2O2S particles are highly crystallized without any significant defects. The fine smooth particles were almost regular, exhibiting an approximately subspherical shape. Quantitative image analysis of particles suggests a mean particle size of 120±34 nm. That is to say, the yttrium oxysulfide colloid prepared by this method have a very narrow size distribution. The obtained ethanol suspension shows Tyndall effect when irradiated with laser of wavelength 532 nm. In addition, the particles exhibit excellent dispersibility in ethanol solution. This is rarely observed for the covalent compounds, which generally present poor dispersibility in solution. As is known to all, the state of the dispersion depends on the acid leaching process. The acid leaching process facilitates the adsorption of ethanol molecules on the surface of the particles. The electrostatic repulsive force among colloidal particles will improve their rheological properties and dispersibility in solution. In this study, the particles can be dispersed well in ethanol after acid leaching. The method'proposed in this study can be extended for the preparation of mono-dispersed oxysulfide nanophosphors and may provide an efficient way for the preparation of stable covalent compound dispersions.

[Hydrothermal synthesis and optical properties of full-color-emission ZnS:Cu, Al nanocrystals].

ZnS:Cu, Al nanocrystals were synthesized by a hydrothermal method at 200 degrees C and their optical properties were studied. The analysis of XRD and TEM show that the spherical-like nanocrystals had a grain size of approximately 15 nm and were well dispersed, with a zinc blende structure. The energy dispersive X-ray spectroscopy (EDX) and atomic absorption spectrometry were applied to the analysis of S, Zn and Cu content in the sample. The results proved that a large number of zinc vacancies exist and Cu is incorporated into the sample lattice. The photoluminescence (PL) spectra were investigated. The PL mechanism is discussed. The excitation spectrum is broad. Under 337 nm excitation the sample emits bright green light. Under 370-410 nm excitation the sample emits white light. The broad emission spectra are almost coincident with any excitation wavelength of between 370 and 410 nm making them attractive as conversion phosphors for LED applications and full-color fluorescence display devices. The emitted white light under 375 nm excitation was found to be the result of blue, green, and orange emission bands. For Cu/Zn, Cu/Al and S/Zn molar ratios of 3 x 10(-4), 2 and 3, respectively, the near blue white light can be observed with the naked eye in daylight.

[Broad excitation band alkaline-earth silicate luminescent materials activated by rare earth and its applications].

Series of novel broad excitation band phosphors M2 MgSis O7 : Eu, Dy(M = Ca, Sr) were prepared by a high temperature solid-state reaction method. The crystal structure of compound was characterized. And the effects of part substitution of alkaline-earth on crystal structure, photoluminescence spectra and luminescence properties were also investigated. It is found that the excitation band of silicate luminescent materials extend to visible region and they exhibit yellow, green and blue long after-glow luminescence after excited by ultraviolet or visible light. Ca MgSi O7 : Eu, Dy luminescent materials can be excited effectively under the 450-480 nm range and exhibit a strong emission at 536 nm, nicely combining with blue light emitted by InGaN chips to produce white light. This promises the silicate luminescent materials a potential yellow phosphor for white LED.