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In this study, the effect of a dual microcavity on the luminescent characteristics and light extraction efficiency of organic red light-emitting devices with a multi-cathode structure was investigated. It was clarified that surface plasmon loss on a metal cathode was reduced to about one-fifth and can be efficiently extracted from the outside with the help of the dual-microcavity effect. About half of the radiant energy in dipole emission was successfully utilized as external and substrate modes. The luminous efficiency increased by about 1.52 times, and a narrow-band emission spectrum was observed with a forward directional red emission. The relationship between the luminescence characteristics and the dual-microcavity effect will be discussed from the viewpoint of the optical design of multi-stacked thin film devices.

Light extraction efficiency of organic light-emitting devices has improved by using a nano-sized multi-cathode structure consisting of semi-transparent metal and an optical compensation layer. From the detail optical calculation based on the multi-scale analysis including near-field optics, it was found that surface plasmon loss in the metal cathode is suppressed to less than 10% due to long range and short range surface plasmon coupling between both sides of metal cathode. Not less than 90% of optical power in the dipole emission can be successfully utilized as propagation light. Light extraction efficiency in a phosphorescent device has improved about twice by using the multi-cathode structure.

Angular dependence of the emission intensity can be successfully controlled by using back-cavity effect in a multi-cathode structure. It is useful for this technique to optimize optical properties, without sacrificing electrical properties. In addition, surface plasmon loss in the cathode is significantly suppressed as a result of optical coupling between waveguide mode and long-range surface plasmon mode. Approximately 60% of optical power can be utilized as external mode.

We have developed green phosphorescent organic light-emitting diodes (OLEDs) with high external quantum efficiency of 59.7% and power efficiency of 243 lm/W at 2.73 V at 0.053 mA/cm2. A double emission layer and a thick n-doped electron transport layer were adopted to improve the exciton recombination factor. A high refractive index hemispherical lens was attached to a high refractive index substrate for extracting light trapped inside the substrate and the multiple-layers of OLEDs to air. Additionally, we analyzed an energy loss mechanism to clarify room for the improvement of our OLEDs including the charge balance factor.

Light extraction of transparent OLED can be improved by using an optical compensation layer on the back-side of semi-transparent metal cathode. From the results of detail optical calculation based on the multi-scale analysis including near-field optics, surface plasmon loss in semi-transparent metal cathode was drastically suppressed to less than 10% due to the increase of wave-vector caused by phase control of reflective coefficient of evanescent wave on the cathode interface. Not less than 90% of optical power in the dipole emission can be successfully utilized as the propagation light. The phosphorescent green light emitting device exhibits higher light extraction by a factor of about 1.5.

The light extraction of OLED has been successfully enhanced by employing high refractive index intermediate layer in the anode side and back-cavity structure in the cathode side Back-cavity structure consisting of semi-transparent cathode, optical buffer layer and high reflection mirror was newly introduced to reduce surface plasmon loss in the metal cathode. The high index inter-layer plays the role in the energy transfer from the waveguide mode to the substrate propagation mode by refractive matching between high refractive index ITO anode and the normal index glass substrate. From the results of detail optical calculation based on the multi-scale analysis including near-field optics, approximately 70∼80% of electromagnetic energy in the dipole emission was effectively converted to the glass and air modes by suppressing both surface plasmon and waveguide losses. The phosphorescent green light emitting device exhibits higher light extraction by a factor of 1.6∼1.7.

Light extraction efficiency has been successfully enhanced by using high refractive index substrate coupled with micro-lens array and weak micro-cavity structure. Optical energy intensity including waveguide, substrate and external modes was analyzed based on wave optics. It was shown that most of the waveguide mode is turned to the substrate mode by the effect of high index refraction substrate. About a half of the light can be extracted from the substrate by the assistance of surface textured structure. An external quantum efficiency of 57% and a power efficiency of over 200-lm/W were obtained in a green phosphorescent device. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

For the improvement of emission efficiency, ZnS-doped Mg0.8Ca0.2S:Eu phosphor film was made using rf-magnetron sputtering method. When the concentration of ZnS in the film is 4%, the photoluminescence intensity is about three times higher than that of ZnS-non-doped Mg0.8Ca0.2S:Eu film with keeping pure red emission (∼650 nm). The crystal planes are oriented in (2 0 0) direction and make a solid solution with ZnS. Enhancement in photoluminescence (PL) intensity is closely related to the change of the crystal quality.

This paper investigates the availability of aerostatic journal bearings to a high vacuum chamber, theoretically and experimentally. This bearing has several steps of a viscous seal, and vacuum pumps are connected to the space between viscous seals in order to achieve the vacuum degree of less than 10-3 Pa in a vacuum chamber. The vacuum degree of a chamber is affected by many design parameters such as the number of steps of a viscous seal, seal length, seal gap, the pumping speed of vacuum pumps and the conductance of exhaust tubes. Influences of these design parameters on the vacuum degree are theoretically discussed and the theoretical predictions are compared with the experimental data. It is found that the aero-static journal bearing with viscous seals can achieve the vacuum degree of the order of 10-4 Pa in a vacuum chamber by properly designing the seal regions.

By Mg doping of ZnS, the lattice constants and the band gap of Zn1−XMgXS host material were increased. The emission spectrum of Mn in Zn1−XMgXS shifted to shorter wavelengths than that of ZnS:Mn. The electroluminescent (EL) devices fabricated with the source of X=0.32 show 552 nm peak yellowish–green emission. Deposition conditions for the Zn1−XMgXS:Mn phosphor layer were optimized to obtain bright emission. As a result, the Zn1−XMgXS:Mn EL devices have a luminance of 282–333 cd/m2 which is as high as that of the conventional ZnS:Mn EL devices.

Light extraction efficiency has been enhanced by using weak micro-cavity structure and high refractive index substrate coupled with micro-lens array. Phosphorescent green light emitting device designed by wave optics showed external quantum efficiencies more than 50% and power efficiencies of 200-lm/W.

The stability of luminance‐voltage characteristics (L‐V) has been investigated on ZnS:Mn electroluminescent films grown by chemical vapor deposition. It is found that the aging pattern varies between the positive shift (P shift) and the negative shift (N shift) with the growth temperature. In both cases the L‐V curve, the current‐voltage relationship, and the symmetry of the light emission with respect to the voltage polarity are strictly cooperative during the aging process. The N shift appears to be dominant when the current is limited by electron injection from the interface, whereas the P shift becomes dominant under the bulk limited conduction, accompanying an excellent symmetry of the emission. A high‐field‐conduction characteristic in the ZnS layer, which is a decisive factor to determine the aging pattern, is significantly affected by its stoichiometry, grain size, and impurity content. It has been further clarified that the N shift consists of the combination of a softening and a shifting in the ...

Green-emitting ZnS : Tb electroluminescent films have been successfully grown by low-pressure chemical vapor deposition, in which a Tb source is transported as gaseous halide by using a HCl carrier gas. A secondary HCl flow, bypassing the source material, is additionally supplied to the growth ambience. It is shown that the ZnS : Tb film changes from the cubic structure to the hexagonal structure with increasing the bypass-HCl flow rate, whereas the Tb concentration is basically determined by the mass transfer of the Tb-halide. The film growth rate decreases significantly in the presence of the HCl flow, and simultaneously the crystal quality is much improved by the incorporation of the Tb-dopant. Such growth behaviors are explained by supposing two kinds of competetive relations; one is a surface migration process competing between ZnCl2 and an isolated Zn atom, the other is a hexagonal nucleation process competing between TbCl3 and ZnCl2. The critical HCl flow rates to control the crystal structure are completely determined. The growth kinetics and the roles of Tb3+ and Cl- ions are discussed on the basis of the competitive adsorption model.

A new technique to produce a manganese-doped zinc-sulfide (ZnS) electroluminescent (EL) film has been developed using a low-pressure chemical vapor deposition system. The Mn 2+ ions are doped in the ZnS layer by controlling the flow rate of the hydrogen-chloride (HCl) carrier gas. Undoped ZnS films show 〈111〉-oriented cubic structure, whereas the Mn-doped ZnS films have hexagonal structure with 〈00·1〉 preferred orientation. The crystal structure changes from cubic to hexagonal with incorporation of the Mn-dopant. The single crystal layers are epitaxially grown on a silicon substrate at 500°C. A strong blue-light emission originating from a self-activated center is observed in the photoluminescence spectra. This blue band, however, is rapidly quenched with increasing the Mn concentration. It is clarified that a competitive adsorption phenomenon between Zn-Cl 2 and Mn-Cl 2 species on the growing surface plays an important role in the growth process and the film characteristics. A high efficiency of 4 lm/W and a steep luminance-voltage curve with a saturation luminance exceeding 3500 cd/m 2 are obtained in a device with double insulator structure under 1 kHz excitation. The crystalline properties and luminescence characteristics are discussed in terms of the effect of the Mn-doping and the growth temperature.

Light extraction of organic light-emitting device has been successfully enhanced by preparing on a plastics substrate. We describe optical design method of mode conversion for reducing optical losses in waveguide and evanescent modes by introducing a new cathode and a plastic substrate. The phosphorescent green light emitting device exhibits higher light extraction by a factor of 2–3.

In this paper, we propose a high efficiency white OLED structure based on the color conversion technique named "side-coupling color-conversion method (SC3M)", in which the blue emission from organic layer is laterally transferred to the adjacent orange color-conversion material. Two times higher efficiency is possible compared with an original blue-OLED. The objective of this work is to demonstrate the possibility and high performance of the white-OLED with SC3M structure

The total flux of the emitted light has been successfully enhanced by employing high refractive index (n=2.0) glass substrate coated with a light extraction layer. The normal CBP:Ir(ppy)3 based small molecule multilayer device exhibits a maximum external quantum efficiency of 56.9% and a power efficiency of 210-lm/W with a threshold voltage of 2.7V. Optical mode analysis by original computer software identified the importance of the control of refractive index of substrate for total improvement of out-coupling efficiency.

A high efficiency UV-OLED was developed and applied to a white light source by using red, green and blue color conversion materials. UV-OLED showed high external quantum efficiency of 3.1 % with a peak wavelength at 380nm. “White by UV” showed 5,000cd/m2 in luminance and stable white color (x=0.33, y=0.31) against driving current and operation time.

A high efficiency phosphorescent light-emitting organic device has been developed based on a Side-Coupling-Color-Conversion-Method, in which the color-conversion layer was excited by the propagating light laterally transferred from the organic light emitting layer. The device showed an external quantum efficiency (EQE) of 24.2% by using a phosphorescent excitation light with 19.4% of EQE.

Blue, green and white organic light-emitting devices doped with fluorescent dyes have been successfully fabricated on high-refractive-index plastic substrates and characterized in terms of their electrical and optical properties. The devices consist of a wide-band-gap polymer emissive layer stacked with several small-molecule layers and were designed considering carrier balance, carrier confinement, dye-guest doping and optical characteristics. It was demonstrated that dye-doped polymer devices are effective for the improvement of color and emission efficiency. We demonstrated deep-blue-, bright-green- and pure-white light-emitting devices having external quantum efficiencies and color coordinates (x,y) of 6.0% (0.15,0.07), 5.5% (0.20,0.60) and 4.0% (0.33,0.33), respectively.

In this paper, we describe that fluorescent guest doped polymer light-emitting devices have been successfully fabricated on high index of refraction plastic substrate and characterized in terms of electrical and optical viewpoints. Deep blue, bright green and pure white OLEDs showed external quantum efficiencies and color coordinates (x,y) of 5.1% (0.15,0.09), 5.5% (0.20,0.60) and 4.0% (0.33,0.33), respectively.

The excitation spectrum for terbium (Tb) emission in a ZnS:Tb,F film varies sensitively with Tb concentration, the amount of fluorine (F) relative to Tb, post‐deposition annealing, and the temperature of measurement. There are at least three kinds of channels for the excitation of Tb3+ ions; namely, resonant energy transfer from the recombination of an electron‐hole pair, direct transitions between the 4f 8 configuration states of a Tb3+ ion, and the indirect excitation via lattice defects. A rapid quenching of photoluminescence (PL) is observed above 0.2 at. % of the Tb concentration in the case of indirect excitation of energy transfer. The PL intensity additionally reduced in the presence of F− ions, even at the same Tb concentration. In contrast, when the Tb3+ ions are directly excited to the 5D3 energy state, the PL intensity increases proportionally up to a maximum of about 2 at. %. The luminance of the electroluminescent device behaves in the same way. Another excitation band is found in an energy ...

Thin-film ZnS:TbF3 was deposited by sputtering and a thin-film electroluminescent panel having a display area of 34 mm × 34 mm was fabricated. The brightness distribution was investigated and film thickness variation and distribution of Tb luminescence centers were studied in conjunction with the brightness. It was found that uniformity of the brightness increases as the applied voltage increases and frequency decreases. Relative brightness deviation (Bmax -Bmin,)/Ba, where Bmax, Bmin and Ba indicate maximum, minimum and average brightness, respectively, of the film was 13 to 23% when it was driven by 5 kHz, 40-V voltage. It was observed that brightness distribution depends on film thickness of the ZnS:TbF3 layer and that the thinner part has higher brightness. Based on the consideration that thickness variation causes irregular field intensity as well as the conduction charge distribution, and results in brightness variation, we calculated the brightness deviation and found that it agreed well with the experimental results. It was also demonstrated that Tb ions were scattered uniformly in the sputtered ZnS film, which was proved to have uniform luminescence center distribution.

Five-layered electroluminescent (EL) devices having an active ZnS:TbF3 layer sand-wiched by an insulating layer and a low-resistive Ta2O5 layer were produced, and luminous characteristics were investigated. It was found that these devices provide high brightness and luminous efficiency compared with the conventional three-layered El devices, as well as low driving voltage. This is because the low-resistive layer between the active layer and the insulating layer is important in improvement of crystallinity of the active layer, increase of conduction carriers in the active layer, and improvement of device breakdown voltage which enables a thinner insulating layer compared to the three-layered structure. Bright green electroluminescence exceeding 1000 cd/m2 at 90 V and threshold voltage of 68 V have been obtained under 5-kHz sinusoidal voltage excitation.

Excitation spectrum varies with Tb concentration, relative amount of F to Tb, post-deposition annealing and measurement temperature. From a comparison of EL with PL properties obtained with three kinds of excitation channels, it is concluded that direct impact excitation is a reasonable process.