Electroluminescence from single layer devices comprised of a solid state solution of an electron transport small molecule and an emitter molecule dispersed in poly(N-vinylcarbazole) is described. The use of molecularly doped polymers as the materials package and the single layer nature of these devices simplifies their fabrication by enabling spin coating techniques to be used. The color of the electroluminescence from these devices can be tuned across the visible spectrum by appropriate selection of the emitter molecule. In addition the use of molecularly doped polymers allows one to tailor the transport properties of the device. Incorporation of a hole transport small molecule in the polymer based film enables one to tune the mobility of the carriers injected into the device from the indium tin oxide anode. Evidence will be presented showing that whereas the luminance from any given device increase linearly with the injected current density, the luminance observed from different devices is independent of the hole mobility. The critical determinant for the level of light output is the number of carriers injected into the device; how fast they move is unimportant.

High-field electroluminescence (EL) of inorganic materials are of basic and practical interest. There are two types of the high field EL; one is a thin film EL (TFEL) and the other is a powder type. Recent researches are mainly on TFEL. In this paper, recent progress on TFEL will be discussed and reviewed. Features of high field TFEL are as follows: (1) Strength of electric field is as high as 10⁶V/cm. This is quite different from light emitting diode (LED) of p-n junction. (2) EL phosphor materials are composed of host and luminescent centers; the host materials are wide gap semiconductors of ZnS and IIa-VIb (CaS, SrS) etc. The luminescent centers are ions which show intra-shell transitions for f-f or f-d transitions (rare-earth ions; Tb³⁺, Tm³⁺, Ce³⁺ etc.) and of d-d transitions (Mn²⁺ etc.). (3) Excitation mechanisms are not yet well understood and should be clarified, of (a) carrier generation and injection, (b) hot electron transport and distribution function, and (c) excitation mechanism of luminescent centers. Problems to be solved is color, especially blue EL materials. To solve this, a new material should be developed, and in addition, a new structure of multi-layer of quantum-well structure should be investigated.

Electroluminescent devices with double organic layers were fabricated using polymeric materials as the hole transport layer and tris(8-quinolinolato)aluminum(III) complex (Alq) as the emitting layer, respectively. The polymeric materials used are poly(methylphenylsilane), plasma-polymerized carbon disulfide, and polycarbonate (TPD). A cell structure of glass substrate/indium-tin-oxide (ITO)/polymer layer/Alq/Mg:Ag (10:1) or Mg/Ag was employed. Among the polymeric systems, the doped PC system affords efficient electroluminescence from the Alq layer. In this cell, bright green emission with luminance of 7,700 cd/m² was observed at a drive voltage of 16 V. Single-layer-type EL devices were also fabricated using poly(methyl methacrylate) (PMMA) molecularly doped with both TPD and Alq. A cell structure of glass substrate/ITO/doped PMMA/Mg:Ag (10:1) was employed. Green emission with luminance of 920 cd/m² was achieved for a cell with a TPD/Alq ratio of 0.67 at a drive voltage of 17 V, and the EL color was tuned to blue-green and yellow-orange by further doping the PMMA layer with suitable organic dyes.

We have studied organic electroluminescence (EL) characteristics for a multilayer thin film cell with distyryl arylene derivatives (DSA) as emitting materials. We found that it is very important for an emitting layer not to form exciplex or charge transfer complex (ECT) with the hole transporting layer (diamine derivatives) in addition to an ability to form a good thin film. In this paper, we report a new series of DSA not to form the ECT with the hole transporting layer owing to the molecular conformation. We substituted two hydrogen atoms for two phenyl rings and designed some new DSA which are not planar. These DSA are intense blue fluorescent materials and have good film-forming ability. A cell with ITO/hole transporting layer/emitting layer/Mg:Ag was fabricated by vacuum evaporation technique. We obtained bright emission more than 1000 cd/m² with dc voltage of less than 12 V and high luminous efficiency about 0.6 lm/W at 1000 cd/m² for several kinds of DSA as emitting materials. In these cells we successfully avoid ECT formation at the interface between the hole transporting layer and the emitting layer.

After the establishment of a reasonably detailed understanding of thin film electroluminescence (TFEL) of ZnS:Mn sandwiched between dielectric films, which is commonly addressed as the 'Simple Model' of TFEL, research activities concentrate now on multi- or full-color displays in thin film technology. This interest is not only a scientific one, but of course augmented by the commercial success of the monochrome devices, which have reached sizes up to 18" diagonal and super-VGA resolution, with their main customers in niche markets, but nevertheless sales of almost 200 million $ in 1992.

Conjugated polymers are promising materials for electro-luminescence devices. We have shown recently that blue light emission can be achieved, when poly(paraphenylene) is used as the active material in a Schottky-like device. The maximum of the electroluminescence emission is observed around 470 nm. Poly(paraphenylene), PPP is stable up to high temperatures and its electronic structure can be tailored by influencing the conjugation length and the tilt angle of consecutive phenyl rings. PPP was synthesized by soluble precursor polymers and as a soluble PPP ladder type polymer. Via the tailoring of the electronic structure, electroluminescence devices with different colors can be fabricated. In contrast to the blue emission of the PPP prepared by a precursor route, the PPP ladder polymer, which has planar structure exhibits a strong yellow-green emission. We report on the physical properties of the different devices, concerning the device structure and the active materials.

Novel characteristics of visible electroluminescent (EL) diodes utilizing poly(3- alkylthiophene)s and organic molecules with superlattice structure have been presented. The diodes with poly(3-alkylthiophene)s emit red-orange light with a broad band emission of 640 nm. The EL diode has unique characteristics in temperature dependence of emission intensity. Superlattice (SL) structure which consists of thin films of organic i-hydroxyquinoline aluminum (Alq₃) and aromatic diamine (TPD) has been grown by organic molecular beam deposition. The SL structure was determined by X-ray diffraction, optical absorption and photoluminescence. Photoluminescence peak of Alq₃ shifts to higher energy with decreasing layer thickness, suggesting a quantum size effect. The EL diodes with SL structure emit green light at around 520 nm. Quantum size effect in the organic SL structure has been discussed.

In this paper we discuss the principles of operation of polymer electroluminescent devices, and identify the factors which limit device efficiency. We identify how efficiencies can be improved by careful control of the polymer system, and by the use of multilayer structures to confine holes within the device. Using these techniques we can achieve efficiencies of better than 1% photons per electron in devices based on poly(p-phenylenevinylene). We also describe the use of induced absorption techniques to identify the excited states present within an electroluminescent device and to estimate their concentrations.

Lithographic patterns of electrically conducting polymers are obtained starting from films of insulating precursor polymers or from appropriate composites via laser irradiation. The precursor polymers yield conducting patterns directly, whereas in the composites the initially formed latent images have to be developed in a subsequent step. Vapors of pyrrole, thiophene, or aniline derivatives are used as gaseous developers. Laser ablation of the materials may be combined with the laser induced generation of electrical conductivity using the same exposure apparatus.

A study of poly(p-phenyleneacetylene) (PPA)-based light-emitting diodes (LEDs) is described and discussed. The LEDs were fabricated by spin-coating the indium tin oxide (ITO) coated glass substrate with the 2,5-dibutoxy or 2,5-dihexoxy derivative of PPA dissolved in toluene, followed by evaporation of a layer of Ca and Al or Al only on the polymer. As the spin- coating, drying, and operation of the diodes was performed in air with no heat sink, the Ca/Al devices degraded within a few minutes at room temperature, but were stable in a He ambient at low temperatures. However, it was noted that baking the diodes coated with an Al layer for 2 - 6 hours at 150 degree(s)C in a flow of dry N₂ markedly increased their performance. However, no improvement was achieved by baking the polymer laser prior to metallization. It is therefore believed that the baking process removes significant defects from the polymer/metal interface. The nature of these results is discussed in terms of bulk defects as well as defects at the ITO/polymer and polymer/metal interfaces.

We have constructed electroluminescent diodes using several layers of conjugated polymers with differing energy gaps; these provide a range of different color light-emitting layers and can be used to control charge injection and transport. Poly(1,4-phenylenevinylene), PPV, and derivatives have been used, with indium tin oxide as hole-injecting electrode and calcium as electron-injecting electrode. For this selection of materials, we show that the sequence of the polymer layers allows control of the color of device emission. Emission from more than one layer can be produced simultaneously. The position and breadth of the light-emitting region of the device provides information about the mechanisms of charge transport and of exciton motion. Various models for multilayer emission are discussed in the paper.

Transient photoluminescence, photoluminescence excitation and picosecond photoinduced absorption studies on stretch oriented phenylenevinylene polymer films are presented. A coherent picture of the processes occurring after light absorption emerges which can account for the data. The implications of this picture for photoconductivity and electroluminescence are considered.

The elucidation of spatial distribution of emitting states in electroluminescent (EL) cells is a challenge to both a refined scientific probe of materials and to design a variety of EL devices. In molecular organic crystals important aspects of this distribution can be mapped onto a trap- dependent electron-hole recombination process involving exciton-charge carrier interaction. We use this process to describe the space-resolved EL in single crystals of anthracene and tetracene as a function of applied electric field. The emphasis of the paper will be on the importance of EL spatial pattern of the charge injection ability of electrodes and distributions of electron and hole traps. Detailed features of the spatial EL intensity patterns in these crystals will be illustrated as a function of electric field and type of injecting contacts. They differ essentially for these two model crystals. In particular, it will be shown that a splitting of the anode EL zone, proceeding regularly with increasing voltage in tetracene, disappears in anthracene crystals.

The X-band photoluminescence (PL)-, electroluminescence (EL)-, conductivity ((sigma) )-, and photoconductivity ((sigma) _ph)-detected magnetic resonance of poly(p- phenylenevinylene) (PPV) and poly(p-phenyleneacetylene) (PPA)-based LEDs is described and discussed. A strong narrow PL-enhancing and EL-quenching resonance is observed at g approximately equals 2.0023 in all cases. However, while the (sigma) - and (sigma) _ph-detected resonances are also quenching in the PPV-based diodes, the (sigma) -detected resonance of the PPA-based diodes is enhancing. The g-values and lineshapes of all of the resonances are identical in each type of diode, and they are attributed to polaron-polaron fusion to singlet excitons or bipolarons. The implications of this picture to the issues of polaron and bipolaron mobility in these diodes and a potential upper limit of their efficiency is discussed. In addition to the narrow resonance, half-field PL-, EL-, (sigma) - and (sigma) _ph-detected resonances due to the (Delta) m_s equals 2 transitions of triplet excitons are also observed. These resonances are believed to result from singlet exciton generation via triplet-triplet fusion.

Theory predicts that a charge added to a conjugated polymer chain forms a polaron Recent calculations of the three-dimensional band structure of trans-polyacetylene, t-PA, and poly(phenylene vinylene), PPV, have obtained values for the interchain coupling that are large enough to destabilize the polaron. Nevertheless, there is experimental evidence that polarons exist in these materials. We show that the existence of chain endings and other conjugation breaks can stabilize the polaron in actual samples.

The effect of weak magnetic fields on the photoconductivity of poly(p-phenylene vinylene) (PPV) was observed within the temperature range 130 - 350 K. This effect is attributed to the formation of interchain pairs involving a negative polaron and a positive polaron. A polaron pair is formed as a result of interchain electron transfer from a molecular exciton. The lifetime of a pair is estimated to be within the range of 10^-8 - 10^-9 s. Thermal dissociation of a polaron pair produces free charge carriers, and recombination of the pair regenerates a singlet or triplet exciton on a single conjugated segment of a chain.

Using three 9,10-bis-styrylanthracene derivatives (BSA's) with different substituents for emission layer materials, various types of electroluminescent (EL) devices were fabricated. Combining with a triphenylamine derivative as a hole transport layer material and an oxadiazole derivative as an electron transport layer material, two-layer type and three-layer type devices were fabricated. We found that the performances of two- and three-layer type devices were largely dependent on the electronic nature of emission layer materials. We found that the BSA's attached with electron-donating groups have the specific electronic nature which allowed the transport of both electrons and holes. A single layer device with about 100 nm-thick BSA layer showed high luminance comparable with conventional two-layer type devices. Two-layer type devices which consisted of two different BSA layers were prepared in order to confirm that BSA layers surely behave as both electron and hole transporting materials. BSA with an electron-accepting substituent surely behaved as an electron transport material. In contrast, BSA's with electron-donating groups showed the bipolar charge transporting characteristics, which means the capability of transport of both electrons and holes.

Narrow beamed light emission was successfully obtained in a new type of organic electroluminescent (EL) diode whose organic layer was sandwiched between two metal layers acting as charge injecting electrodes and mirrors. EL from the organic film edge showed much sharper spectrum with a peak depending on the thickness of the organic layer and about 100 times larger emission density compared with that from the film surface of a conventional EL diode.

The progress of thermal conversion of the thin films of poly(p-xylylene-(alpha) - tetrahydrosulfonium chloride) to poly(phenylene vinylene) (PPV) was investigated in situ under ultra-high vacuum by x-ray photoelectron spectroscopy (XPS). We found that at 150 - 200 degree(s)C chlorine was completely eliminated, sulfur was less than 1%, oxygen was 10 - 15% and carbon was about 85 - 90%. One could reduce the oxygen content to 3 - 5% by heating the samples at 320 degree(s)C. The interfaces of Ca or Al with the PPV films were then investigated using XPS. The interaction between Ca and PPV was very weak. Band bending of the Ca/PPV interface was very slow indicating the formation of Schottky barrier was a slow process. In contrast, Schottky barrier formation of Al/PPV was much faster. The slow barrier formation at the metal-PPV interface may be due to the shielding by the surface oxygen impurities, part of which underwent metal oxide formation at the interface. Our results may be highly relevant to the application of sulfonium precursor derived PPVs in optoelectronic layer devices where the interface chemistry is likely to govern the device performance.

The field of displays is still evolving. New principles and technological breakthroughs overcome earlier limitations. Electroluminescence appears on the threshold of significant changes, hence it is too early to set standards. The driving voltage is coming down, brightness and efficiency are increasing, and the color range is expanding. In this paper we review several developments that may lead to new EL devices: excitation by tunneling hot carriers, recombination of electron-hole pairs injected by pn junctions into wide bandgap materials, and the use of quantum wells to increase brightness and efficiency and to adjust the color by mechanical design rather than by chemical strategy (e.g. doping).

Survey of dye materials for the emission layer in the multilayer organic electroluminescent (EL) device is discussed in terms of emission color and fluorescent efficiency. Organic semiconductors for the electron or the hole transport layer in the EL device are proposed for preparing stable homogeneous thin layer. Requirement of accomplishing the confinement of the singlet excitons generated by the recombinations of injected electrons and holes is discussed by using three layer EL devices with extremely thin bimolecular emission layer. Then the emphasis is laid on the size effects in three layer EL device with double heterojunctions on the spontaneous emission. Variations of the intensity and pattern of outer emission through semitransparent ITO glass substrate with the spacing between the emission layer and the metallic electrode are discussed theoretically and experimentally. And variation of the fluorescent lifetime or the radiative decay rate with the spacing is also discussed theoretically and experimentally.

A new type of light transducer consisting of an organic electroluminescent (EL) diode on a photoconductive amorphous silicon carbide (a-SiC:H) film has been successfully designed, which performs efficient light up-conversion from red to green with quantum conversion of 1% with the assistance of newly observed photocurrent multiplication in a-SiC:H film. EL output under red light irradiation can be modulated by superimposing UV light.

We have synthesized and characterized several poly(ferrocenyl dialkylsilane) polymers. The solutions and films of these polymers showed two reversible and stable redox reactions when cycled in organic electrolytes between 0.0 and 1.0 V (vs Ag/AgCl reference electrode). Their electrochemical behavior depends on the size of the alkyl substituents and the silane bridge between the ferrocene units for the (alpha) , (beta) diferrocenyl oligosilane. In addition, these newly synthesized polymers are thermally stable up to 400 degree(s)C. These poly(ferrocenyl dialkylsilane) polymers are potential candidates for use as the counter electrode or in the electrolyte component in electrochromic and electroluminescence display devices.

Large screen displays are typically viewed from distances which are proportionally greater than smaller CRT displays. In specifying large screen displays, conventional performance standards such as HFS-88-100 must be augmented to consider the effects of visual acuity limitations in the user. Using an expression for the viewer's modulation threshold as a function of angular frequency and luminance presented by Barten, we derive a requirement for screen modulation as a function of observer position. We define a parametric relationship between display contrast ratio and display modulation transfer function which bounds the set of usable values for these parameters. This analysis predicts luminance and resolution requirements often unobtainable from current systems. This analysis is presented in the context of a case study derived from the installation of a large screen display at the Gaston Steam Plant control room of Alabama Power Company. The use of front or rear projection, as well as the implications of the color usage in the displayed images is discussed.

There has been a trend during the 1980s in commercial airliner cockpits of replacing many of the round-faced, analog instruments with CRT displays. However, the computer graphics technology that is utilized in these CRT displays is more than ten years old and frequently simply mimics the appearance of the older, analog displays. We will explore some of the possible uses of state of the art, three dimensional computer graphics as an integrator and as a visualizer of flight information. Using computer models of primary navigational features and the ray-tracing rendering technique, three-dimensional, symbolic representations of flight information are explored. Flight tasks investigated include enroute navigation, collision avoidance, weather, and the instrument approach.

This paper is concerned with the development of a new high-definition, high-contrast membrane-mirror light valve for use in high-brightness, three-color, flickerless, large-screen projection display system. The membrane-mirror light valve is an electron-beam-addressed unit that achieves high resolution, high contrast and flickerless operation through the use of charge-transfer-plate technology, and grid-stabilized flickerless operation. The paper focuses on the physics of the light valve and presents preliminary experimental results for a flickerless light valve framing at 30 Hz with 256 X 256 pixels in a 20 mm active area.

Optics design for acquisition of image positional information suitable for geometry correction in a single projection lens, full-color light-valve projector. All signal acquisition and control is internal to the projector. Correction light path is separate, coaxial and color complementary to the projection light path. Design parameters for precision signal acquisition are discussed.

High definition color projection systems require substantial geometric precision in the co- projection of the red, green and blue images. A system for providing precise automatic geometry correction (automatic convergence) has been designed for the single lens light-valve projector. The correction system is independent of the main deflection, providing high precision with flexible scan capability. The hardware and software system, and methods for high resolution measurement, correction and control are described.

The presently reported development of a simultaneous raster and calligraphic projection system with a reliable, maintainable and cost-effective solution to current demand for ultrahigh resolution flight-simulator system displays, enhancing scene content over existing sequential raster/calligraphic systems while meeting all design requirements. The additional time available in this simultaneous raster system can be used for additional raster/polygon computation time or reduced clock speeds, as well as to support larger fields of view and reduced visual anomalies due to aliasing.

A development status evaluation is presented for gas plasma display technology, noting how tradeoffs among the parameters of size, resolution, speed, portability, color, and image quality can yield cost-effective solutions for medical imaging, CAD, teleconferencing, multimedia, and both civil and military applications. Attention is given to plasma-based large-area displays' suitability for radar, sonar, and IR, due to their lack of EM susceptibility. Both monochrome and color displays are available.

A technique of constructing picture elements for a large screen display with improved color quality is described. Existing large screen displays generally make use of a cluster of lamps to form a single pixel. Such a pixel usually consists of four lamps corresponding to the red, green, blue and white colors. Most of these displays have limited color palette as the individual lamp can only be turned on or off and is unable to adjust its intensity. Even if the intensities of each of the color lamps can be adjusted independently, it will not produce a uniformly colored pixel especially when viewed at close distance. We have developed a true- color display device that can be used as a picture element in a large screen display unit. The true-color display device is constructed by mixing the three primary color lights optically before they are transmitted. With this method, a pre-mixed uniform color can be seen even at close range. Using the color mixing theory, an almost infinite range of colors can be simulated.

Software generated gratings, which have the ability to be readily manipulated, are used for measurement applications. To be adapted to a particular measurement involves appropriate displays to be used. The use of these computer gratings on different displays are demonstrated for topographic contouring, slope and curvature measurement in static as well as dynamic applications.

The M3i MOSAIC System provides the technology to project high resolution large area screen (LASD) information displays. This system is particularly suited to the display of information in 'Command and Control' room applications. Simultaneous viewing of the information by multiple persons enhanced group decisions. The platform for the M3i MOSAIC System is the IBM PS/2, IBM AT, or compatible microcomputer supporting MCA, ISA, or EISA bus architecture. The microcomputers can operate in a stand alone or LAN configuration. The information displayed takes the form of a single image spread across multiple projected images. Each projected image is controlled by a M3i/3980 graphics card with a resolution of 1280 X 1024. A host of existing and emerging large area screen display technologies can be employed (CRT, LCD, LV, LCDLV). This system is the processor of the graphical information displays, receiving data from external control system and transforming it into the best medium for easy comprehension--visual graphics.

The advances in the technology of high performance polygonal scanners, both for laser beam typesetting and the projection of computer generated images, meet the requirements for laser beam projection of high definition television (HDTV) onto large screens; screen widths in the order of 30 meters (approx. 100 feet). This paper illustrates the interrelationship between the scanned image quality resolution for laser beam projected TV and HDTV, and the scanner design and manufacturing tolerances-- spatial and temporal. It provides a guideline for systems' designers to calculate and trade-off the specification tolerances for a polygonal scanning subsystem.

Photophysical properties of poly (3-hexylthiophenes) (P3HT) possessing various degrees of regioregularity have been investigated. Wavelengths of emission are blue-shifted for polymers possessing twisted head-to-head (HH) dyads. Quantum yields of luminescence from polymer solutions decreases with increasing head-to-head dyad content of the polymer whereas the reverse is true in thin solid films. The latter can be explained by classical concentration quenching effects which arise from non-emissive excimer complexes. This constitutes an intermolecular decay of excitation.

Dimension Technologies Inc. (DTI) has devised and experimentally tested a new photonics system which will allow the display of images on LCDs with resolutions greatly exceeding the pixel resolution of the LCD. The technique involves use of special lenses to successively image light from an array of sources into different subregions of pixels on a fast operating LCD, creating a high resolution image made up of the light points. The technique was successfully used to create 308 dpi images on an experimental 154 dpi ferroelectric LCD. Field sequential color illumination can be combined with this technique to create high resolution color images. Using this technique, it is possible to create very high resolution images without using a correspondingly large number of pixels on an LCD, thus avoiding manufacturing and yield problems associated with high resolution LCDs.