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Carbon nitride (CN) compounds have attracted significant attention as new photocatalysts capable of decomposing water and producing hydrogen upon irradiation using visible light. To date, many studies have focused on their applications as photocatalysts. Melon, a typical CN polymer, is a semiconductor with a direct energy gap, because of which it cannot exhibit high photocatalytic activity without a cocatalyst. However, melon shows high potential as a blue-light-emitting material with high color purity, and the basic physical characteristics of melon are worth clarifying. Additionally, the synthesis of melon during thermal polymerization remains unclear. In this study, the polymerization of melon is investigated by varying the thermal polymerization conditions, and new CN compounds with optical properties similar to those of melon are examined. Characterization of the products prepared under different conditions allowed the identification of a new CN compound, a likely precursor of melon, at temperatures slightly below the calcination temperature of melon. This new compound, which consists of oligomers with four melem units, is very stable in air and shows improved optical properties compared to those of melon.

In this study, the Nd x Fe1− x N y materials are applied for the magnetic core of the series resonance circuit of GaN wireless power transmission (WPT) for the first time. At over 10 MHz, the inductance of the fabricated Nd2Fe17N3 coil is stable at $1.15~\mu \text{H}$ and the effective magnetic permeability of the Nd2Fe17N3 is estimated to be 2.6. At the same inductance, the number of turns of the Nd2Fe17N3 coil can be decreased as compared with that of the air-core coil, and the coil size can be reduced by 0.7 times by using the Nd2Fe17N3 material. At the 13.56 MHz GaN-WPT operation, the successful WPT waveforms can be obtained, and the drastic reduction of the energy loss at the coil is achieved due to the low imaginary part of the magnetic permeability. The Nd-Fe-N materials are considered indispensable to GaN high-frequency switching circuits.

Cooling heat loss is one of the most dominant losses among the various engine losses to be reduced. Although many attempts to reduce it by insulating the combustion chamber wall have been carried out, most of them have not been successful. Charge air heating by the constantly high temperature insulating wall is a significant issue, because it deteriorates charging efficiency, increases the emissions of soot and NOx in diesel engines, and promotes the knock occurrence tendency in gasoline engines. A new concept heat insulation methodology which can reduce cooling heat loss without heating the charging air has been developed. Surface temperature of insulation coating on the combustion chamber wall changes rapidly, according to the quickly changing in-cylinder gas temperature in each engine stroke. During the compression and expansion stroke, the surface temperature of the insulation coating goes up rapidly, and consequently, the heat transfer becomes lower by the reduced temperature difference between the surface and the gas. During the intake stroke, the surface temperature goes down rapidly, and it prevents intake air heating from the wall. To realize the above-mentioned functionality, a thin coating layer with low thermal conductivity and low heat capacity was developed. It was applied on the pistons of diesel engines, and showed improvement in thermal efficiency. It also showed a reduction of unburnt fuel emission in low temperature engine starting condition. The energy balance analysis showed reduction of cooling heat loss and, on the contrary, increase in the brake power and the exhaust loss.

We establish the method for estimating the stray elements of the GaN-WPT circuit by measuring the radiated emission around the GaN switching device. By controlling the circuit supply voltage, the spectrum peak shift due to the output capacitance of the GaN-HEMT is observed. It is found that these peak shift characteristics include the influence of both the stray wire inductance and stray capacitance. By fitting using the series resonance model, the value of the stray inductance and stray capacitance can be estimated in the non-destructive measurement in the GaN-WPT circuit.

We propose a promising preparation technique to construct optically high-quality Langmuir-Blodgett (LB) films of lead bromide-based layered perovskites having an organic-inorganic quantum-well structure called "squeezed-out technique." Using this technique, we successfully prepared PbBr-based layered perovskite LB films whose average roughness is small enough to apply them for cavity polariton devices. The small roughness reveals that one can prepare microcavities having a high quality factor by using the technique. In addition, optical simulation of a cavity using the LB film demonstrated that the cavity polariton device has a large Rabi splitting of 116 meV, suggesting a stable polariton formation in the cavity even at room temperature.

An accelerated test method for evaluating the long-term lifetime and color shift of white OLED panels based on device-degradation models was proposed. We successfully estimated the lifetime and color shift of white OLED panels at standard drive conditions with a short test period.

The dynamic characteristics of GaN-based vertical-cavity surface-emitting laser (VCSEL) with an AlInN/GaN semiconductor distributed Bragg reflector has been reported for the first time. The max dynamic lasing frequency of 1.1 GHz with a wavelength of 415 nm and a threshold current of 7 mA has been demonstrated. Moreover, at the pulse lasing operation, both the steep lasing waveforms and the tailing spontaneous emission waveforms were observed in driven with the square pulse waveforms. The dynamic lasing frequency driven by the sine waveform seems to be related to this steep lasing waveform at the square pulse operation. During these dynamic measurements, the lasing characteristics of the VCSEL were gradually degraded, and the lasing power is decreased by −7 dB at the same bias condition after several hours.

Trifluoromethylphenyl-substituted phthalimide derivatives favorably form triboluminescence (TL) active noncentrosymmetric crystals. Oligothienyl-, oligophenyl-, and naphthyl-substituted phthalimide derivatives were successfully developed as a series of metal free TL compounds. X-ray crystal structure analyses of bithienyl and naphthyl derivatives revealed noncentrosymmetric layer structures in the same direction. Introduction of suitable electron rich π-units such as thienyl groups enhances their photoluminescence and TL characteristics, and the colors can be also controlled in the visible region. A rigid naphthyl-substituted imide derivative exhibits extremely high TL performance.

Non-destructive analyses are conducted on the intrinsic degradation of organic light-emitting diodes (OLEDs). After longterm operation, sum-frequency spectroscopy reveals changes in the molecular orientation. Furthermore, change in the mobility of the OLEDs can be evaluated from impedance spectroscopy. Carrier trap behavior is also investigated via thermally stimulated current spectroscopy.

Diagenetic alteration of aragonite coral skeletons causes changes in their chemical and isotopic compositions. Such altered coral samples are unsuitable for age dating or paleoclimate reconstructions. Recently developed microanalysis techniques have elucidated secondary aragonite precipitation and calcite overgrowth on primary aragonitic coral skeletons, but an effective screening method for bulk samples is still desirable. Although powder X-ray diffraction (XRD) analysis is widely used for this purpose, its detection limit for calcite (1–2% at best) is not sufficient to detect very small amounts of diagenetic calcite. Here, we propose that thermoluminescence (TL) spectra can be used to detect the presence of tiny amounts of secondary calcite in coral skeletons. We used a TL spectrometer with a Fourier-transform detector to detect the calcite component in TL spectra of powdered skeletons of modern and fossil corals (from 127 ka and 3.5 Ma) in which calcite was not detectable by XRD. The key element is manganese, because the TL emission efficiency and the partition coefficient of Mn are greater for calcite than for aragonite. As a result, the calcite spectral component becomes evident. Thus, the TL spectroscopic technique is a highly sensitive tool for screening fossil corals for diagenetic alteration.

Sum frequency generation (SFG) spectroscopy has been used to study the operational degradation of 4, 4′-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (α-NPD)/tris(8-hydroxylquinoline) aluminum (Alq3) organic light-emitting diodes (OLEDs). A reduction in the SFG peak strengths of Alq3 was found in aged OLEDs, indicating that the permanent dipole orientation in the Alq3 layer was randomized as a result of long-term continuous operation. In contrast, the SFG signals derived from the α-NPD in aged samples were enhanced as compared to those of pristine OLEDs, and it can be attributed to an increase of the internal electric field near the interface by the long-term operation.

We have fabricated dispersions of ethyl-intercalated germanane (GeEt) by a liquid exfoliation approach in chlorobenzene, with sufficient concentration for thin-film fabrication. Monolayers and a few layers of GeEt with lateral dimensions of a few micrometers were deposited from its dispersion onto a solid substrate and characterized with a scanning electron microscope. The physical properties and structures of the GeEt dispersions were investigated by UV–visible, FT-IR and Raman spectroscopies. The sonication power for the dispersion process affected the interlayer distance between germanium sheets, as well as the photoluminescence of GeEt dispersions. Electroluminescence was observed with a peak at 835 nm from a device with a cast film from the chlorobenzene dispersion of GeEt.

The thermoluminescence (TL) exhibited by crystalline tris(2-phenylpyridine) iridium (Ir(ppy)3) microrods was investigated over temperatures of 29–160 °C using a multichannel Fourier transform spectrometer. The glow curves and TL spectra were analyzed to elucidate the origins of the emission. Four peaks were observed at different temperatures in the glow curves. Furthermore, by analyzing the TL spectra, we found that various types of charge-carrier trap sites exist in Ir(ppy)3; these sites become active or remain inactive, depending on the presence of oxygen or light or both. Thus, charge-carrier trapping within crystalline Ir(ppy)3 depends on the environment to which the sample has been exposed.

We studied chemiluminescence spectroscopy to develop an evaluation method for organic material degradation. The thermal oxidation of oleic acid as a monounsaturated fatty acid was investigated using chemiluminescence measurements. The obtained spectra indicated that the luminescence consisted of several peaks, including peaks for singlet oxygen and excited carbonyls. A detailed analysis of the nuclear magnetic resonance and infrared absorption spectra allowed us to determine the probable structures of the oxidative products. The relationship between the spectrum and the analyzed structure implied that the wavelength of the carbonyl group emission peak shifted as a result of the structure.

Silicon carbide (SiC) and gallium nitride (GaN) devices have been found to withstand high voltages without showing degradation and can be switched at high frequencies, making them attractive for high-power drives. Although Sic/GaN devices can be operated at high temperature and high frequencies, it is important to develop gate-drive circuits to efficiently turn on and off these devices at high speeds. This paper proposes a resonant gate-drive circuit that aims at reducing the power loss associated with high-frequency switching of power insulated gate bipolar transistors/metal–oxide–semiconductor field-effect transistors. The main thrust of the circuit is its application to the motor-drive industry. The proposed circuit is compared with traditional gate-drive circuits from the points of view of power consumption and switching speed. Experimental results are given to illustrate the concept. Test results show that the power consumption using the proposed circuit reduces by a factor of greater than 5 compared with a traditional gate-drive circuit.

A series of asymmetric N-phenyl imides with trifluoromethyl and pentafluorosulfanyl substituents at the terminal phenyl position have been prepared. They are colorless both in solution and the solid state, and they show blue emission in the solid state. X-ray crystal structure analysis of trifluoromethyl and pentafluorosulfanyl substituted derivatives revealed highly ordered noncentrosymmetric molecular arrangements with large net-dipole moments related to the piezoelectric behavior. XRD measurements of the powders afforded intense sharp reflection peaks, indicating formation of the lamellar ordering. By grinding with a spatula, their solids showed vivid blue triboluminescence.

Organic light emitting diodes are extremely sensitive to dopant concentrations in emitting layers. We developed a sensor that could simultaneously monitor the composition and thickness of co-deposited films. This sensor enables more precise control of the composition of the emitting layers compared to quartz crystal oscillator thickness monitors.

We previously reported that dipoles on the surface of the gate insulator layer in organic transistors cause time decay of the drain current on time scales of less than 0.1 s from the application of the gate voltage. In this study, we investigated the relationship between the time decay and magnitude of the gate voltage. We found that this time decay can be attributed to threshold voltage shifts unaccompanied by mobility changes. When the insulator surface has dipoles that can move somewhat, the threshold voltage shift has two components: one with a time scale of approximately 0.1 s and the other with a time scale of tens of minutes.

Diode rectifiers with large dc-bus capacitors, used in the front ends of variable-frequency drives (VFDs) and other ac-to-dc converters, draw discontinuous current from the power system, resulting in current distortion and, hence, voltage distortion. Typically, the power system can handle current distortion without showing signs of voltage distortion. However, when the majority of the load on a distribution feeder is made up of VFDs, current distortion becomes an important issue since it can cause voltage distortion. Multipulse techniques to reduce input current harmonics are popular because they do not interfere with the existing power system either from higher conducted electromagnetic interference, when active techniques are used, or from possible resonance, when capacitor-based filters are employed. In this paper, a new 18-pulse topology is proposed that has two six-pulse rectifiers powered via a phase-shifting isolation transformer, while the third six-pulse rectifier is fed directly from the ac source via a matching inductor. This idea relies on harmonic current cancellation strategy rather than flux cancellation method and results in lower overall harmonics. It is also seen to be smaller in size and weight and lower in cost compared to an isolation transformer. Experimental results are given to validate the concept.

Variable-frequency drives (VFDs) with diode front-end rectifiers are typically equipped with a resistor-contactor arrangement to limit the inrush current into the dc-bus capacitors, thereby providing a means for soft charging the dc-bus capacitors. Because of the mechanical nature of the magnetic contactor typically used in VFDs, there exists a concern for fatigue. In addition, during a brownout condition, typically, the contactor remains closed, and when the voltage recovers, the ensuing transient is often large enough to possibly cause unfavorable influence to surrounding components in the VFD. Many researchers and application engineers have thought about this issue, and many are actively seeking nonmechanical solutions in a cost-effective manner. In this paper, a new topology to soft charge the dc-bus capacitor is proposed. Other techniques that have been evaluated are also introduced. The relative advantages and disadvantages are discussed. Experimental tests to show the feasibility of the proposed idea are also provided.

The spectral emission from thermographic phosphors in free flow and its dependence of laser energy per cross section area (laser fluence [J/cm2]) has been investigated. Temperature measurements in gaseous flows using thermographic phosphors require higher laser energy than measurements performed on surfaces, due to lower particle density. A troublesome systematic error associated with high fluences would be introduced if the excitation laser heats the particles. In the presented work, three different types of the thermographic phosphor BaMg2Al10O17:Eu (BAM) are investigated. Spectra of the phosphorescence are achieved for a range of laser fluences. The results show no indications of the laser heating the particles, making further development of phosphor thermography in free-flow applications feasible.

We investigated a field-effect transistor (FET) based on a poly(3-n-hexylthiophene) (P3HT) to determine the influence of moisture on device characteristics and thus gain a deep understanding of the mechanism underlying the susceptibility to air of the operation of FETs of this kind. The fundamental output characteristics, which include effective field-effect modulation and saturation behavior in the output current, remained almost the same for every current–voltage profile in a vacuum, N2 and O2. By contrast, operation in N2 humidified with water resulted in enlarged off-state conduction and deterioration in the saturation behavior, in the same manner as that experienced with exposure to room air. We concluded that atmospheric water had a greater effect on the susceptibility of the device operation to air than O2, whose p-type doping activity as regards P3HT caused only a small increase in the conductivity of the active layer and a slight decrease in the field-effect mobility with exposure at ambient pres...

We have proposed novel photoresponsive green- and blue-emitting organic electroluminescent (EL) devices combining organic EL diodes with titanyl phthalocyanine as a photoconductive layer. By irradiating red and near-infrared (IR) lights to these devices, green and blue emissions were generated, respectively, well below the turn-on voltage. The results indicate that the devices act as an optical switch and up-converter. The EL response time using a laser pulse was about 300 μs. Above the turn-on voltage, enhancement of the EL intensities was observed with the light irradiation with the ratio of up to 10 4 .

Time-resolved electric-field-induced sum-frequency generation (EFI-SFG) spectroscopy was employed to study the charge behavior of multilayer organic light-emitting diodes (OLEDs). Through application of the square wave pulse bias to the OLEDs, compensation for the polarization charges in the electron transport layer and the generation of 4,4'-bis[N-(1-naphthyl-N-phenylamino)-biphenyl] (α-NPD) cations were observed. When the pulse voltage was turned off, the α-NPD cations immediately disappeared, confirming that charge recombination occurs at the interfaces. We therefore concluded that time-resolved EFI-SFG is useful for directly probing the carrier behavior in OLEDs in addition to identifying the origin of the charge carriers present in OLEDs.

Time variation of the source-drain current for organic field-effect transistors (OFETs) with aminopropyl and octadecyl groups on the insulator layer was examined. The source-drain current of both OFETs decreased with time immediately after the application of the gate voltage. The decrease in the source-drain current was very little in the OFET with an octadecyl group while it was very large in the OFET with an aminopropyl group. The origin of the decrease in the source-drain current was attributed to the dipole of the aminopropyl and octadecyl groups. The decrease in the source-drain current was observed in the OFET with the octadecyl group (that has a small dipole), indicating that the time variation of the source-drain current is very sensitive to the dipole of the insulator surface. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A novel polysilane, poly[(p-butoxyphenyl)phenylsilane] (PBPPS) has been synthesized and employed as an emissive layer of an organic electroluminescence (EL) device. PBPPS was spin-coated onto a uniaxially oriented poly(diethylsilane) (PDES) ultrathin film prepared by the friction-transfer method. We observed polarized, near-ultraviolet (UV) EL with its dichroic ratio of 2 from the polysilane-based multilayered EL device. Polarization direction was found to be identical with the drawing direction of the friction-transfer process for the PDES film, indicating that PBPPS in the emissive layer was aligned parallel to the uniaxial orientation of PDES. A depolarized, broad visible band appeared in the EL spectrum, which was absent in photoluminescence of PBPPS or PDES films. Origins of near-UV and visible EL components are discussed.

In order to understand the relationship between the molecular orientation and optical properties of oligophenylenevinylene film, oriented thin films of 1,4-di(p-methoxystyryl)benzene (DSB-1) and 1,4-di(p-methoxystyryl)-2,5-dimethoxybenzene (DSB-2) were fabricated on a potassium bromide (KBr) (001) surface by the vacuum-evaporation method. The structures and optical properties of DSB films have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and polarized photoluminescence (PL) spectroscopy, respectively. DSB-1 molecules orient obliquely and/or parallel to the substrate surface depending on the substrate temperature. On the other hand, DSB-2 molecules tend to grow epitaxially with the molecular plane parallel to the substrate surface. The anisotropic molecular orientations represent the polarized PL. The epitaxial growth and molecular orientations observed by TEM and AFM at the local and microscopic scale are confirmed by polarized PL measurement on a macroscopic scale. (C) 1999 American Institute of Physics. [S0021-8979(99)01523-6].

Dispersion of silver nanoparticles was prepared from silver n-tetradecanoate via thermal decomposition. The absorption spectrum of the dispersion showed a broad band at ca. 420 nm, characteristic of plasmon in the silver nanoparticles. On the other hand, the nanoparticle monolayers both on water and on quartz had an absorption band at 470 nm, which coincided with the position of the reflection bands. Surface reflectance of the dispersion in toluene also had a broad band with a peak wavelength of 470 nm.

A comparison of the transient electroluminescence (EL) between a microcavity organic light-emitting diode (MC-OLED) and a conventional OLED was performed and their carrier dynamics were discussed. We found that the behavior of transient EL in a MC-OLED can be accurately described using rate equations without exciton-carrier interaction for a conventional OLED, suggesting that carrier dynamics is not modified using a MC structure.

Under high current density, lots of organic electroluminescent devices (OELDs) exhibit a substantial decrease in an external quantum coefficient (ηext). Understanding the operating principles of the device is necessary to control the ηext roll off and achieve good performance of OELDs. In this study, we mainly discuss the possible dynamics of charge carrier in our device according to the transient behaviors of electroluminescence (EL) and current after voltage pulse was turn off. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of back-channel electronic state on device characteristics was investigated for pentacene-based thin-film transistors (TFTs), where top surface of the semiconductor layer was covered with an LiF thin film. We observed higher field-effect hole mobility in the TFTs with the LiF-covered back channel than in the corresponding uncovered counterparts. In addition, the LiF-covered TFTs exhibited a decrease in turn-on voltages and an increase in off-state current depending on the thickness of the LiF layer and top- or bottom-contact configuration of the source and drain electrodes. We attributed the electronic effect brought about by the LiF coating to a downward band bending in the back channel originating from a rearrangement of the electronic energy-level alignment at the pentacene/LiF interface. The difference in the device characteristics from those of the uncovered TFTs was successfully explained by such electronic processes in the pentacene layer induced by the downward band bending in the back channel as a pseudo -back gate effect and generation of offsetting holes against the surface electronegativity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Distyryl benzene derivatives (DSB-1 and DSB-2) were deposited on a KBr (001) surface. DSB-1 molecules took two kinds of orientations depending on the substrate temperature. On the other hand, DSB-2 grew epitaxially. The longitudinal axes of DSB-2 molecules were oriented parallel to the substrate surface.

Transient properties of mechanoluminescence (ML) from europium complex in powder and in polymer-dispersed film were investigated. In polymer-dispersed film, its decay curve was found to be composed of two components corresponding to the emission from ambient nitrogen molecules and europium ion. On the other hand, the decay curve of powder was composed of a single component corresponding to the emission from europium ion. From these results and supplemental experiments, the difference in ML excitation mechanism between polymer-dispersed film and powder is discussed.

Mechanoluminescence (ML) from polymer-dispersed films of europium complexes was investigated for the first time. We synthesized four new kinds of europium complexes and examined their mechanoluminescent properties in different sample forms: powder and polymer-dispersed film. While only two complexes exhibited ML in powder form, all the four became mechanoluminescent when dispersed in polymer matrix. The excitation mechanism of ML of the complexes is studied by the measurement of the spectral and transient behavior.

Four new kinds of europium complexes were synthesized and their mechanoluminescent properties were investigated. Out of the four, only europium tris(2-thenoyltrifluoroacetone) phenanthroline (Eu(TTA)3(phen)) exhibited intense mechanoluminescence. Its spectra were measured and found to be essentially the same as that of the photoluminescence, indicating an identical emitting species. The excitation mechanisms of mechanoluminescence are also discussed.

To fabricate “polarized” electroluminescence (EL) devices as a next generation, the growth mechanism of dye materials on several substrates, KBr, KCl, indium tin oxide (ITO) and quartz plate (fusued silica glass) was characterized by TEM and SEM to control the molecular orientations in films. The qualitative analysis of photo-luminescence (PL) from Tris(8-hydroxyqunoline) aluminum (Alq3) films epitaxially grown on KCl was done to confirm successively the anisotropic emission.

We report the observation of strong coupling between exciton and photon modes in a conjugated polymer-based semiconductor microcavity. Thin films of the σ-conjugated poly[bis(p-butylphenyl)silane] (PBPS) were inserted between metal and dielectric mirrors to form the microcavity structures. Variation of the PBPS film thickness between 80 and 140 nm allowed the cavity photon resonance to be tuned in the vicinity of the free exciton energy. The expected anticrossing behavior, with intensity and linewidth averaging, was observed at room temperature in the cavity reflection spectra and the vacuum Rabi splitting was found to be ⩽430 meV. This large value is consistent with the expectations of transfer matrix reflectivity calculations performed with optical constants data derived from a Kramers–Kronig analysis of the PBPS absorption spectrum. Angle-dependent photoluminescence measurements were performed for the microcavity with a 120 nm thickness PBPS layer. Unlike the emission from a standard, weakly coupled, c...