Masakazu Ohashi

Warm-white light-emitting diode with yellowish orange SiAlON ceramic phosphor

A warm-white light-emitting diode (LED) without blending of different kinds of phosphors is demonstrated. An approach that consists of a blue LED chip and a wavelength-conversion phosphor is carried out. The phosphor is a newly developed yellowish orange CaEuSiAlON ceramic phosphor with high efficiency. The CIE1931 chromaticity coordinates (x, y) are (0.458, 0.414), the color temperature is 2750 K, and the luminous efficacy of this LED is 25.9 lm/W at room temperature and with a forward-bias current of 20 mA. The chromaticity of the assembled LED is more thermally stable than that of a LED with a conventional oxide phosphor (YAG:Ce) because of the better thermal stability of the oxynitride phosphor.

White Light-Emitting Diode Lamps Using Oxynitride and Nitride Phosphor Materials

White-light emitting diode lamps for general illumination can be realized by a combination of a blue light-emitting diode semiconductor die and phosphors. Newly developed oxynitride and nitride phosphors are promising candidates for this application because they have suitable excitation and emission wavelengths and stable optical properties in a high temperature environment. High brightness warm-white LED lamps have been realized using a yellowish-orange α-SiAlON oxynitride phosphor. High color-rendering index white LED lamps have been also realized using three color oxynitride/nitride phosphors.

High Coupling Efficiency of Microcavity Organic Light-Emitting Diode with Optical Fiber for as Light Source for Optical Interconnects

A scaling relation of the anomalous Hall effect recently found in a ferromagnetic semiconductor (Ti,Co)O_2_ is compared with those of various ferromagnetic semiconductors and metals. Many of these compounds with relatively low conductivity sigma_xx_<10^4 ohm^-1 cm^-1 are also found to exhibit similar relation: anomalous Hall conductivity sigma_AH_ approximately scales as sigma_AH_ proportional to sigma_xx_^1.6, that is coincident with a recent theory. This relation is valid over five decades of sigma_xx_ irrespective of metallic or hopping conduction.We investigated directional characteristics of the electroluminescence (EL) from microcavity organic light-emitting diodes (MOLEDs) to examine applicability of these diodes as a light source for optical interconnects. By measuring the angular dependence of a EL emission, we estimated the coupling efficiency between a MOLED and an optical fiber. The coupling efficiency was enhanced by 1.4-fold compared with that of a non cavity organic light-emitting diode (OLED), and reached 85% for an optical fiber with a numerical aperture (NA) of 0.5. The current efficiency of the MOLED also increased optimizing the device structure, and its maximum was 18.4 cd/A.

Development of 1kW DMFC system with waste heat recovery for improving energy efficiency

Direct methanol fuel cells (DMFCs) are electrochemical devices that convert chemical energy of liquid methanol directly to electricity. DMFC can provide electricity and heat continuously as long as methanol and oxygen are provided. Therefore, DMFC is expected as power source for emergency, mobile and so on. The system maintains the fuel cell stack working at constant temperature and optimized methanol concentration. Moisture from the cathode is captured at the condenser, and the condensed water is sent to the liquid/gas separator for compensating the water loss. The dilute methanol solution is circulated through the stack and radiator. A novel concept of recovery waste heat is verified in real DMFC system working conditions. This DMFC system is completely self-maintained with the capability of providing 1 kW electricity and 3 kW heat. The total energy efficiency of the system is greater than 80%. This paper shows the fundamental research approaches for evaluating the performance of 1 kW DMFC system and optimizing the system working conditions. It shows that the higher system energy efficiency could be achieved based on the optimization of the system thermal management.

Development of Large Scale DMFC System for Aviation Applications

Due to the trend of an increased electrical energy usage on board of aircraft and more restricted environment concern for reducing the pollutant and CO 2 emission, fuel cell technology becomes attractive for aviation application. Thanks to the inherent advantages of using liquid fuel and system simplicity, direct methanol fuel cells (DMFCs) present a great potential application for replacement of APU in aircraft. In present work, we will focus on finding out the optimum working conditions for the large scale DMFCs. Electrochemical impedance spectroscopy (EIS) is used as a powerful diagnostic tool for achieving the goal. It was found that humidification is necessary for obtaining the ideal fuel cell performance as working temperature is higher than 70 o C. VIATION plays a key role in the economic prosperity and is growing by 5.9% per year. However, according to the concern of the environment issues and global warming, aviation accounts for about 13% of all transportation related CO 2 emissions. In order to reduce the pollution from the ever increasing numbers of aircrafts, it is expected to reduce the aircraft fuel consumption and emissions in the future. Fuel cells provide an attractive option, which are inherently cleaner power sources and higher efficiency than auxiliary power units. Fuel cells will not replace jet engines on commercial transports, but they could replace gas turbine auxiliary power unit as the technology becoming more mature. For this application, fuel cells can be used to power non-critical loads like galleys and in-flight entertainment. Waste heat and waste water from the fuel cell can be used to improve the overall efficiency. Direct methanol fuel cells are electrochemical devices that convert chemical energy of liquid methanol directly to electricity in an environmentally friendly way for various applications. DMFC can provide electricity (and heat) continuously as long as methanol and oxygen are provided. As methanol is easy to store and transport and has a very high energy density, DMFC presents an inherent advantage on producing a lot of electric power with liquid fuel stored in a fixed volume. Since space and weight are at a premium in most aircraft, DMFC is attractive for aviation applications (1). We initialed a project for developing a complete 1 kW DMFC system with the potential to be scaled-up to tens of kW range in the following projects for replacement of the anxious power unit (APU) in aviations applications. A schematic diagram of the fuel cell system and 3-D sketch overview of the system are shown in Figure 1. The system will maintain the fuel cell stack working at constant temperature, proper methanol concentration and guarantee the water balance. Air is provided to the fuel cell stack by an air pump. Moisture in the cathode exhausting gas is captured at the condenser and the recovered water is sent to the liquid/gas separator for making up the water loss. A methanol supply pump is used to dose methanol into the liquid/gas separator to keep the methanol concentration constant. The dilute methanol solution is circulated through the stack and radiator. The waste heat produced in the stack is absorbed in the anode liquid flow and dissipated to the ambient environment at the radiator. Alternatively, this waste heat can be reused for supply of hot air or water for the galley in a commercial airplane.