Host emission from BaMgAl10O17 and SrMgAl10O17 phosphor: Effects of temperature and defect level

Abstract— Understanding the mechanism of blue‐light emission in Eu‐doped BAM phosphor as well as its sensitive degradation is required because this is a very important material in fluorescent lamps and plasma‐display panels. In this study, both theoretical and experimental investigations on the host emissions in BaMgAl¹⁰O¹⁷ and SrMgAl¹⁰O¹⁷ were performed. Host emissions from BaMgAl¹⁰O¹⁷ and SrMgAl¹⁰O¹⁷ by photoluminescence and thermoluminescence spectra were observed. Photoluminescence spectra suggested that the host emission from SrMgAl¹⁰O¹⁷ was easily quenched by thermal vibrations. The thermoluminescence spectra showed the existence of shallow and deep defect levels in BaMgAl¹⁰O¹⁷ and SrMgAl¹⁰O¹⁷ phosphors. It was shown that SrMgAl¹⁰O¹⁷ and its conduction plane could undergo degradation during irradiation of vacuum‐ultra‐violet (VUV) lights based on the calculated energy of formation of an oxygen vacancy. Moreover, the structural defects, such as oxygen vacancies, would cause localizing levels in the upper level in the valence band and in theconduction band. The results suggest the contribution of the host emission to the energy transfer to the Eu atoms would not be significant and the oxygen vacancies would act as the traps for excited carriers.     

Quantum chemistry and QSPR study on relationship between crystal structure and emission wavelength of Eu2+‐doped phosphors

Abstract— The relationship between crystal structures and emission properties has been computationally investigated for Eu²⁺‐doped phosphors. The electronic structure of the Eu²⁺‐doped BaMgAl¹⁰O¹⁷ phosphor was analyzed by using the quantum chemistry method. The different effects of O and Ba atoms on the Eu 5d states were determined. The presence of O and Ba atoms increases and decreases the energy level of the Eu 5d orbital by forming anti‐bonding and bonding interactions, respectively. According to the electronic‐structure analysis, the structure index that represents the local geometrical information of the Eu atom was defined. The relationship between the crystal structures and the emission wavelengths of the 1 6 Eu²⁺‐doped oxide phosphors were studied by using the quantitative structure‐property relationship (QSPR). The QSPR model suggested that the both O and alkaline‐earth atoms around the Eu atom are of importance in the determination of the emission wavelength. The interaction between the Eu and the nearest O atoms make the Eu²⁺ emission wavelength short. On the other hand, the interaction from the alkaline‐earth atoms around the Eu atom lengthens the Eu²⁺emission wavelength. This evaluation method is useful in selecting the host material that indicates a desirable emission wavelength of the Eu²⁺‐doped phosphors.     

Low refractive index silicon oxide coatings at room temperature using atmospheric-pressure very high-frequency plasma

Low refractive index silicon oxide films were deposited using atmospheric-pressure He/SiH₄/CO₂ plasma excited by a 150-MHz very high-frequency power. Significant increase in deposition rate at room temperature could prevent the formation of dense SiO₂ network, decreasing refractive index of the resulting film effectively. As a result, a silicon oxide film with the lowest refractive index, n = 1.24 at 632.8 nm, was obtained with a very high deposition rate of 235 nm/s. The reflectance and transmittance spectra showed that the low refractive index film functioned as a quarter-wave anti-reflection coating of a glass substrate.     

Two-Mode Behavior in Complex Perovskite Materials

Infrared reflection and Raman spectra have been measured for two complex perovskite ceramic materials, Ba(Mn_1/3Ta_2/3)O₃ and Ba(Ni_1/3Ta_2/3)O₃. Two-mode behavior was observed for both of the compounds in the inner vibrations of the BO₆-type octahedrons, where B indicates Mn, Ta, and Ni ions. This behavior indicates that the local symmetry about Mn, Ni, and Ta ions is octahedral (O_h), although the superlattice structure of the compounds (D_3d) is observed by XRD analysis.     

An 81‐in. 8 K OLED Kawara‐type multidisplay with flexible displays that provides a seamless image

We fabricated a Kawara‐type multidisplay, providing a seamless image by precisely arranging 13.5‐in. organic light‐emitting diode flexible panels with transparent edges on two adjacent sides. To make overlapping portions less visible, the transparent regions were adjusted optically and corrected in luminance and chromaticity. We used 36 panels to fabricate an 81‐in. 8 K organic light‐emitting diode Kawara‐type multidisplay.     

Screening of lipase inhibitors from marine algae

The possible presence of an inhibitor of pancreatic lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) was screened in 54 marine algae. An active inhibitor, caulerpenyne, was purified from an extract of Caulerpa taxifolia, using ethyl acetate extraction, followed by successive chromatographies on ODS and silica gel columns. The purified inhibitor was identified by thin-layer chromatography, infrared and nuclear magnetic resonance spectroscopy. Caulerpenyne competitively inhibited lipase activities using emulsified triolein and dispersed 4-methylumbelliferyl oleate (4-MU oleate) as substrates. The concentrations producing 50% inhibition against triolein and 4-MU oleate hydrolysis were 2 mM and 13 μM, respectively. In vivo, oral administration of corn oil with or without caulerpenyne to rats demonstrated a reduced and delayed peak plasma triacylglycerol concentration with caulerpenyne.     

Effect of Moisture on the Structure and Fracture Strength of Ceramic Green Bodies

To study independently the effects of moisture on the structure and the mechanical strength of the binder in green bodies, specimens of the system alumina/PVA were formed with spray-dried granules of various moisture contents. The structure and fracture strength of these specimens then were examined after their moisture contents had been adjusted to specified values. As moisture content increased in the granules during compaction, the density and strength of the green body also increased. The accompanying change in the fracture mode, from intergranular to transgranular, showed that the strength of the green bodies was affected more significantly by bonding between granules than by bonding between powder particles.     

The parameters evaluation and optimization of polycrystalline diamond micro-electrodischarge machining assisted by electrode tool vibration

The objective of this research is to evaluate and optimize machining parameter of tool electrode vibration on micro-electric discharge machining of polycrystalline diamond. The machining parameters evaluated are charge voltage, capacitance, and vibration of the tool electrode. An orthogonal array, signal-to-noise ratio, and analysis of variance are employed to analyze the effect of these machining parameters. The results show that by application of vibration on tool electrode in machining of polycrystalline diamond, it has significant effect up to 66.48% in increasing material removal rate without increasing surface roughness and tool electrode wear. Using Taguchi method for design of experiment, other significant effects on surface quality and tool electrode wear are also investigated. The results also show that surface roughness is mostly affected by the amount of capacitance (52.24%), and the tool electrode wear is also affected by the amount of capacitance (92.82%).