We demonstrated an improved durability of Eu(HFA)3(TPPO)2 [tris(hexafluoroacetylacetonato)- europium(III) 1,2-phenylenebis(diphenylphosphine oxide)] encapsulated by a sol-gel derived silica glass film. The film was constructed using phenyltrimethoxysilane and diethoxy- dimethylsilane as a starting solution. Unlike cases in which conventional tetramethoxysilane is used, no decrease in internal quantum efficiency was observed at room temperature. We further improved the thermal and long-term stability of Eu(HFA)3(TPPO)2 inside the transparent glass film at elevated annealing temperatures when compared to the Eu(HFA)3(TPPO)2 powder itself: The photoluminescence quantum efficiency of the transparent film was 60% at 160°C and 32% at 20°C. Properly prepared glass networks protect the Eu chelate from free oxygen and water in the transparent glass film, which is promising for future practical applications.
Organic-inorganic hybrids based on the layered perovskite framework ([CH3(CH2)17NH2]2PbI4 and [CH3(CH2)17NH2]2PbCl4) have been naturally formed by intercalating lead hallide into organic (alkylammine) Langmuir-Blodgett films. Only diffraction peaks corresponding to (0 0 n) of the layered perovskite were observed in the X-ray diffraction pattern of the deposited film. X-ray diffraction measurement demonstrated that the layer structure is oriented parallel to the film plane. The deposited film showed sharp and strong UV-Vis absorption at 390 nm, which is charactristic of Wannier exciton in lead halide-alkylammonium multi-layered perovskites, thus demonstrating the formation of the layered perovskite structure.
Bi-activated SrGa2S4 (SrGa2S4:Bi) phosphor exhibits green luminescence with a peak wavelength of 533 nm and a full width half maximum of 58 nm. This luminescence is attributed to the 6p-6s transition in the 6s2 configuration of Bi3+. As SrGa2S4 is co-activated by the Bi3+ and Mn2+ ions, the excitation band around 400 nm is enhanced relative to that around 300 nm. Since the PL properties of SrGa2S4:Bi were similar to those of SrGa2S4:Eu, the SrGa2S4:Bi phosphors are potential alternatives to SrGa2S4:Eu phosphors.
White light emitting diodes (LEDs) are expected to be used as lighting of the next generation for, for example, headlights, back lighting of liquid crystal displays (LCDs), illuminations, and so on. However, red emitting phosphors used for white LEDs have lower luminance efficiency than other emitting color phosphors because of larger stokes shift. La2O2S:Eu is known as red emitting phosphor; it shows good luminescence under near-ultraviolet excitation. In this study, synthesis of La2O2S:Eu using the citric acid gel method has been investigated. The results show that the particle size can be controlled by changing pre-firing conditions.
Using a 135-kHz induction-coil-type electrodeless lamp system offers several advantages including high efficiency, long life, and low resource consumption. To optimize the lamp dimensions, electron density was analyzed by the complex finite element method for magnetic fields and plasma. Magnetic flux density, current density, and electric field distribution were derived from magnetic analysis. The electron temperature and ionizing frequency were then calculated on the basis of the electric field. The distributions of electron density were subsequently deduced by solving diffusion equations. The maximum value of electron density for a 150-W bulbous electrodeless lamp was 1.5×1018m-3 near the induction coil. The analyzed distributions are in agreement with the experimental ones.
One of the key elements in improving lamp efficiency is understanding and controlling the halogen transport process. Therefore, it is worthwhile to build a model that depicts this process and can be applied to the study of various types of lamps. We examined the halogen transport process in a lamp by using a hybrid simulation model based on fluid dynamics and chemical equilibrium.
Tungsten transport in halogen lamp operation was examined by fluid dynamics and thermo-chemical simulation. Partial pressures of almost all species dramatically increased around the coil leads. The cause appears to be a stagnant flow of filling gases. Results of a life test showed that tungsten was slightly deposited at the coil leads. Such a tungsten deposit can be attributed to a high concentration of tungsten compounds during the gas phase.
The authors have constructed a simultaneous multi-point illuminance measurement system to measure illuminance. The functions of this system include environment measurement, signal transmission via wired and wireless networks, and data analysis. The system contains a control PC and a control module. The control module is made up of the voltage supply, the communication part, and the measuring module, which includes the illuminance meters. Measured values are converted from analogue to digital signals, and they are transmitted to the control PC through both the wired and wireless LAN systems. The operating system of the control PC is Wmdows 2000 and the controlling software is Visual Basic 6.0. The authors will discuss the measurement results (which are now applicable) of the following illuminances: continuing long time and maximum and simultaneous multi-points.