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The formation of excitons in organic molecules by charge injection is an essential process in organic light-emitting diodes (OLEDs).sup.1-7. According to a simple model based on spin statistics, the injected charges form spin-singlet (S.sub.1) excitons and spin-triplet (T.sub.1) excitons in a 1:3 ratio.sup.2-4. After the first report of a highly efficient OLED.sup.2 based on phosphorescence, which is produced by the decay of T.sub.1 excitons, more effective use of these excitons has been the primary strategy for increasing the energy efficiency of OLEDs. Another route to improving OLED energy efficiency is reduction of the operating voltage.sup.2-6. Because T.sub.1 excitons have lower energy than S.sub.1 excitons (owing to the exchange interaction), use of the energy difference could--in principle--enable exclusive production of T.sub.1 excitons at low OLED operating voltages. However, a way to achieve such selective and direct formation of these excitons has not yet been established. Here we report a single-molecule investigation of electroluminescence using a scanning tunnelling microscope.sup.8-20 and demonstrate a simple method of selective formation of T.sub.1 excitons that utilizes a charged molecule. A 3,4,9,10-perylenetetracarboxylicdianhydride (PTCDA) molecule.sup.21-25 adsorbed on a three-monolayer NaCl film atop Ag(111) shows both phosphorescence and fluorescence signals at high applied voltage. In contrast, only phosphorescence occurs at low applied voltage, indicating selective formation of T.sub.1 excitons without creating their S.sub.1 counterparts. The bias voltage dependence of the phosphorescence, combined with differential conductance measurements, reveals that spin-selective electron removal from a negatively charged PTCDA molecule is the dominant formation mechanism of T.sub.1 excitons in this system, which can be explained by considering the exchange interaction in the charged molecule. Our findings show that the electron transport process accompanying exciton formation can be controlled by manipulating an electron spin inside a molecule. We anticipate that designing a device taking into account the exchange interaction could realize an OLED with a lower operating voltage. Recombination of excitons to produce molecular light emission is made more efficient by controlling electron spin within the molecule to produce spin-triplet excitons only, without the usual accompanying spin-singlet excitons., Author(s): Kensuke Kimura [sup.1] [sup.2] , Kuniyuki Miwa [sup.1] [sup.3] [sup.5] , Hiroshi Imada [sup.1] , Miyabi Imai-Imada [sup.1] [sup.2] , Shota Kawahara [sup.1] , Jun Takeya [sup.2] , Maki [...]

4H-SiC Junction Barrier Schottky (JBS) diodes are processed by using the same technology with two different layouts. Electroluminescence measurements have displayed the expansion of stacking faults in 3.5 kV diodes unlike in 1.2-kV diodes.

The results of an investigation of the thermoluminescence and electroluminescence of arylated methylenecyclopropanes 1 are described. The mechanistic features of this reaction system have the potential of overcoming significant problems associated with organic light emitting diodes.

The properties of nominally undoped ZnO films, which are deposited by reactive sputtering on the lightly boron-doped([p.sup.-]) and heavily boron-doped([p.sup.+]) silicon substrates, are studied. The analysis reveals that the ZnO/[p.sup.+]-Si hetereojunctions are electroluminescent to a certain extent in the visible region, whereas the ZnO/[p.sup.-]-Si heterojunctions does not exhibit this property.

The synthesis and structural, photophysical, electrochemical and electroluminescent properties of a novel class of trifunctional Pt(II) cyclometalated complexes are described in which the hole-transporting triarylamine, electron-transporting oxadiazole and electroluminescent metal components are integrated into a single molecule. The management of the relative electroluminescent (EL) intensities of the singlet and triplet excitons is shown to be a good tool for making efficient single-dopant white organic light-emitting devices (WOLEDs).

A sensitive electrochemiluminescent detection scheme by solid-phase extraction at Ru[(bpy).sub.3.sup.2+]-modified ceramic carbon electrodes (CCEs) was developed. The as-prepared Ru[(bpy).sub.3.sup.2+]-modified CCEs show much better long-term stability than other Nation-based Ru[(bpy).sub.3.sup.2+]-modified electrodes and enjoy the inherent advantages of CCEs. The log-log calibration plot for dioxopromethazine is linear from 1.0 x [10.sup.-9] to 1.0 x [10.sup.-4] mol [L.sup.-1] using the new detection scheme. The detection limit is 6.6 x [10.sup.-10] mol [L.sup.-1] at a signal-to-noise ratio of 3. The new scheme improves the sensitivity by ~3 orders of magnitude, which is the most sensitive Ru[(bpy).sub.3.sup.2+] ECL method. The scheme allows the detection of dioxopromethazine in a urine sample within 3 min. Since Ru[(bpy).sub.3.sup.2+] ECL is a powerful technique for determination of numerous amine-containing substances, the new detection scheme holds great promise in measurement of free concentrations, investigation of protein-drug interactions and DNA-drug interactions, pharmaceutical analysis, and so on.

A study uses microfluidics applicator in the fabrication of a polyfluorene based polymer light emitting diode (PLED). Room temperature analysis of the poly(di-n-octylfluorene) indicates that the combination of high-speed deposition and rapid drying process traps the polymer into a metastable conformational state.

A simple thermal process for the preparation of small Pt nanoparticles is presented, carried out by heating a [H.sub.2]Pt[Cl.sub.6]/3-thiophenemalonic acid aqueous solution. The following treatment of such colloidal Pt solution with Ru[(bpy).sub.3.sup.2+] causes the assembly of Pt nanoparticles into aggregates. Most importantly, directly placing such aggregates on bare solid electrode surfaces can produce very stable films exhibiting excellent electrochemiluminescence behaviors.

The electroluminescence (EL) properties of the [Gd.sup.3+] ultraviolet (UV) luminescent centers in Si[O.sub.2] metal-oxide-semiconductor light emitting devices (MOSLEDs) are investigated. The strong EL quenching related to a negative charge trapping around the optically active [Gd.sup.3+] luminescent centers is observed during excitation by hot electron injection, suggesting different methods for improving the EL stability of rare-earth doped MOSLEDs.

A significant improvement in the external electroluminescence efficiency of red-emitting polymer light emitting diodes (LEDs) by modifying the optical structure of the device is demonstrated. Improvements in the external efficiency of polymer LEDs by a factor of 1.6 times compared to a device using a cathode composed of calcium backed with lower reflectivity aluminum is measured.

Electroluminescence (EL) produced by a commercially available additive free low density polyethylene film has been investigated under a 50Hz ac electrical stress. The spatial distribution, spectral characteristics and the phase angle relationship of EL with respect to the 50Hz applied ac voltage were studied using a sensitive Peltier cooled charge-couple device (CCD) camera. The experimental results from several test samples show that the EL can be divided into two different groups according to the EL spatial distribution: (1) homogeneous EL and (2) inhomogeneous EL. At the same applied voltage, the spectra of the homogenous and inhomogeneous EL were found to be significantly different. Homogeneous EL had maximum emission intensity in the red and near infra-red (> 700nm), whereas the inhomogeneous emission had maximum intensity at shorter wavelengths (550-600 nm). Phase resolved measurements showed that homogeneous EL always produced equal emission intensity in the positive and negative half-cycles (symmetric distribution), whereas, inhomogeneous EL produced an asymmetric intensity distribution. To explain these results, it is suggested that homogeneous emission is associated with charge injection and bipolar recombination in the surface states on both sides of the sample, whereas inhomogeneous emission is associated with field enhancement at defects on one of the two sides of the film which allow charge to be injected into states more representative of the bulk material. Index Terms--Electroluminescence, thin Films, polyethylene, ac electrical stress.

Electroluminescent ZnS:Mn thin films were deposited by the atomic layer deposition (ALD) technique. The results show that a relatively small change in the Zn precursor can have a clear impact on the electro-optical properties of the devices, and that a mixed halide/metalorganic ALD process can produce an electroluminescent device that ages relatively slowly.

The quantum efficiency of negative and positive luminescence in binary type-II InAs-GaSb superlattice photobodies in the midinfrared spectral range around the 5-mum wavelength is investigated. A negative luminescence efficiency of 45% is found for infrared diodes with a 2-mum absorbing layer, processed without anti-reflection coating.

A series of cationic bis-cyclometalated iridium(III) complexes are synthesized and their electrochemical, photophysical, electroluminescent properties are studied. The complexes are found to be luminescent both in a fluid solution and as neat solids at 298 K, while single-layer electroluminescent devices that give blue, green, and red electroluminescence are also fabricated.

Bright electroluminescence (EL) from an organic field-effect transistor (OFET) structure is demonstrated with a 1 wt%-rubrene:tetraphenypyrene (TPPy) codeposited film as an active layer. Results reveal a maximum eta(sub ext) of ~0.8% in a short channel device with MgAl/Au double-layer source and drain (S-D) electrodes.

Electroluminescence (EL) at submicron-sized breakdown sites is identified and studied using metal-insulator-silicon (MIS) tunnel diodes with ITO transparent electrodes. The number of sites grows linearly with the current, consistent with the dielectric breakdown of the insulator.

An easy but effective technique is described here for quick fabrication of low-cost electrochemiluminescence detection cells for capillary electrophoresis. The technique is based on molding of poly(dimethylsiloxane) (PDMS) with a capillary column inserted into a pipet tip. Two access holes are left in the PDMS slab; they provide neat accommodations for the separation capillary and the working electrode made with the same type of tip. Since the access holes are well-aligned, the electrode and the capillary are automatically aligned; thus, end-column detection is easily obtained. Fabrication of the detection cell is straightforward; no micromechanical operation is included. Also the principle for the procedure makes it possible to efficiently batch production detection cells with good reproducibility. Because of the end-column scheme, the cell can be adopted for electrophoresis with electrochemical detection as well.

A new series of Os(II) diimine complexes with the general formula [Os(N^N)(CO)2I2] N^N=2,2'-bipyidine (bpy), 4,4'-di-tert-butyl-2,2'- bipyidine, 4,7-diphenyl-1,10-phenanthroline, 2-(2'-pyridyl)-benzoxazole and 5-tert-butyl-2-(2'-pyridyl)benzoxazole were synthesized and characterized. The potential to serve as a phosphor for organic light emitting diodes were evaluted by examing their electroluminescent performances.

The electroluminescent properties of polyamidoamine dendrimers containing pendant [Ru(bpy)(sub 3)](super +2) are investigated. Indium tin oxide (ITO) and gold electrodes were used to make devices and they were compared to devices made from [Ru(bpy)(sub 3)](super +2) films.

A new driving scheme for the improvement and flexibility of a color temperature without sacrificing a peak white luminance using an independent control of the red, green, and blue luminance in an alternate current plasma display panel (ac-PDP) is presented. PDPs must overcome several serious problems for the complete replacements of the conventional cathode ray tube (CRT).

The generation and evolution of defects in 4H-SiC p-n junctions due to carrier injection under forward bias are investigated by synchrotron white beam x-ray topography, electroluminescence imaging, and KOH etching. Low angle grain boundaries are observed to act as one of a number of possible nucleation sites of stacking faults.

The thick-dielectric electroluminescent (TDEL) approach has been studied and it has been observed that it possesses some clear advantages over the thin-dielectric electroluminescence (TFEL) and I-TDEL structures. In fact, it could replace some of the TFEL applications and could strongly be considered for applications such as flat TVs.

The temperature dependence of visible and infrared (IR) rare-earth-activated electroluminescence of Er-doped GaN has been reported. It is shown that a simple model consisting of two back-to-back Schottky diodes accurately describes the I-V relationship.

The overshoot effect in transient electro luminescence (EL) is attributed to an accumulation and trapping of holes at the polymer/metal interface and this effect is enhanced at large reverse bias. The roughness of the Al(sub 2)O(sub 3) has an important bearing on the electron-hole recombination near the interface and its useful manifestation is the appearance of a large EL-spike upon reversing the driving voltage.

An n-sheet, state-space model is employed for the assessment of insulator issues of relevance to the operation of alternating-current thin-film electroluminescent (ACTFEL) devices. Simulation demonstrates that ACTFEL devices which have large insulator capacitances and no space charge present in the phosphor are optimal in terms of providing maximum luminance and efficiency.

This review discusses spectroscopic probing of the molecular aspects of homogeneous and heterogeneous electron transfer in electrochemical processes emitting light. Application of electrochemical processes to the solution redox reactions, ion- and electron conducting polymer hybrids, and to insulating polymers and thin films are presented.

The electroluminescence mechanisms of the lanthanide complex Eu(TTA)phen doped into CBP are investigated. The results suggest that lanthanide complexes face the same limitations as other metallorganic phosphors via triplet-metal ion transitions.

Results reveal two energy trap states for the behavior of SrS:Ce atomic layer epitaxy devices. The asymmetric emissions are due to the trap energy level in relation to the conduction and interface whereas the sallower are closer to the conduction band at the Al interface with a narrow energy interface.

The rise of electroluminescence from bilayer light-emitting diodes with internal energy barriers can be computed using an analytic theory. Instead of charge carrier transport, it will be observed that the onset of electroluminescence is influenced by the redistribution of electrical field inside the device and the growth of interfacial charge densities. Energy barriers that control hole and electron injection are considered as significant system parameters.

The static space charge density of evaporated ZnS:Mn alternating-current thin-film electroluminescent (ACTFEL) devices is estimated based on trends in the phosphor clamping field. The estimate suggests a cathode clamping field of around 2.2 MV/cm and a clamping interface trap death of some 1.5 eV. While the space charge of the static charge does not alter even during the operation of the ACTFEL device, the dynamic space charge is occasionally created and eliminated during applied voltage waveform.

The effect of annealing on the electroluminescence (EL) was studied by examining the EL from Si+ implanted SiO2 prepared by thermal oxidation. The results were then compared with the photoluminescence to clarify its application in the study of Si-based visible light emitting materials. The results revealed that both EL and PL emanated from the same three luminescence bands around 470, 600 and 730 nm, with the 470 and 730 nm bands dominating the PL spectra in the samples annealed below and above 1000 degrees C, respectively.

EL (electroluminescence) in several polymeric materials was investigated in the electric field range < 90 kV/mm. We used polymeric films with semi-transparent gold electrodes: low-density polyethylene, polypropylene, polytetrafluoroethylene and polyvinylchloride. The EL characteristics were very low EL inception fields (2 to 20 kV/mm) which strongly depend on the material and very low energy photon emission (mainly in the red region of 1.6 to 1.8 eV). These results reveal that EL emission occurs predominantly in the metal-polymer interface region rather than in the bulk of the polymer at the applied field. We present a model of EL emission in the metal-polymer interface region to explain our results qualitatively. In this model, the mechanism of EL emission is the radiative recombination of the electrons and holes trapped at the surface states of the polymer, which causes photon emission in the red region. The EL inception field and EL intensity depend on the density of the surface states of the polymers.

Electroluminescence (EL) of insulating polymers is now recognized as a warning sign for electrical aging. In order to further understand the emission process, we have compared the luminescence spectra of the same material when the emitting states are created by different excitation sources. Additive free and carbonyl containing low density polyethylene films were used. Light emission was stimulated by photon irradiation in the ultraviolet range (photoluminescence), by the interaction between a cold plasma and the polymer surface leading to a post-discharge emission (plasma induced luminescence), and by the electric field in the absence of any gaseous discharge (EL). Plasma induced luminescence and electroluminescence exhibit similar spectral features in the wavelength range between 500 and 650 nm. It is concluded that the same kind of chromophores is involved in both processes. They could be conjugated groups acting as recombination centers because charges are selectively trapped on these groups. This explains why photoluminescence does not show similar emission features since all the material chromophores are excited upon UV irradiation. Moreover, it is shown that the EL-features are sensitive to structural relaxation of the polymer probably through the interaction between emitting species and the surrounding molecules.