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— The current status of AC powder electroluminescent (ACPEL) displays is reviewed with particular emphasis given to color and lifetime. The printing of the displays in forward and reverse architectures is also discussed, in addition to the fabrication of ACPEL displays with interdigitated electrodes, and different types of ACPEL phosphors and materials for back electrodes, transparent conducting electrodes, binders, and dielectrics are considered. Furthermore, shape conformable and highly flexible ACPEL displays are surveyed.

— A method is required for creating a graphics display, or pixel array, from printed electroluminescent (PEL) display technology and driving it efficiently and cost effectively. The display is made up of a matrix of capacitive light-emitting display elements which are to be driven by a passive multiplexing method. A four-level drive system is required in order to produce the best possible contrast ratio on the display. A four-level drive system is costly to implement at the high voltages at which PEL displays operate, but a system is presented here which is able to make a significant reduction in the amount of electronics required to control the display. By selectively switching the output from a fly-back power supply to different parts of the matrix display, the optimum voltages can be obtained across all segments from a single high-voltage power supply. This provides potential for using passive-matrix PEL displays in a wide variety of applications, as well as having possible applications for other display technologies such as PDLCs (see demonstration in Fig. 1).

Anew method for achieving full-color capability for inorganic EL displays was developed, which combines electroluminescence with photoluminescence phenomena in the same device structure. In this display panel, the blue emission was obtained from the EL device by using the Eu-doped barium thioaluminate phosphor material system, which was then used to generate green and red emission by the use of down-conversion materials. The major advantages of the Color-by-Blue method (CBB) are the elimination of color-balance control issues associated with the use of different electroluminescent phosphor materials for red, green, and blue with potentially different threshold voltages for the onset of luminance and the achievement of a low-cost high-yield manufacturing process.

Defect-free large-area inorganic thick-dielectric EL (TDEL) displays using Color by Blue (CBB) technology have been successfully developed. We have achieved the world's highest blue-phosphor luminance of 900 cd/m 2 for a single-pixel device by using CBB and by optimizing the e-beam gun configuration and the flow rate of H 2 S in the vacuum chamber. By analyzing the defects on panels with triple-pattern phosphors and CBB panels, we also found that the number of defects on CBB panels can be drastically reduced compared with those on triple-pattern panels. The defect-free 17-in. VGA CBB panels show better characteristics, a high peak luminance of 600 cd/m 2 and a high contrast ratio of 1000:1, compared with those of triple-pattern panels.

Organic light-emitting device research focuses on the use of small-molecule and polymer materials to make organic electroluminescent displays, with both passive- and active-matrix technologies. This paper will focus on the characteristics of red, green, and blue electroluminescent polymers suitable for fabricating monochrome and full-color passive-matrix displays. The stability of polymer OLEDs, and the use of ink-jet printing for direct high-resolution patterning of the light-emitting polymers will also be discussed. It will be shown that the performance of light-emitting polymers is at the brink of being acceptable for practical applications.

Excellent organic electroluminescent materials are needed in order to obtain color EL devices with high performance. We have succeeded in realizing bright and efficient devices with long lifetime in various color regions, based on styryl and amine derivatives.

— A new high-resolution electroluminescent display with a luminance of 100 cd/m2 (30 fL) and 6-bit gray scale to support real-time video up to a bandwidth of 45 MHz has been developed under the Defense Advanced Research Projects Agency's Technology Reinvestment Project. Production units are now installed in the M1A2 Abrams Main Battle Tank upgrade program and are used to display the tank commander's new infrared “second-generation FLIR” imagery.

New blue-emitting thin-film-electroluminescent (TFEL) devices that satisfy the requirements for full-color TFEL displays were developed. Eu 2+ -doped BaAl 2 S 4 thin films were used for the emission layer. BaAl 2 S 4 :Eu thin films were prepared by two-target pulsed-electron-beam evaporation suitable for the deposition of multinary compounds that have difficulty in obtaining stoichiometoric thin films. The EL spectrum only had a peak at around 470 nm. The Commission Interantionale de l'Eclairge (CIE) color coordinates were x = 0.12 and y = 0.10. The luminance level from a 50-Hz pulses voltage was 65 cd/m 2 .

With transient measurements it is possible to investigate the electrical and optical characteristics of a thin-film-electroluminescent device for both polarities. With additional UV illumination the charge transfer and luminescence due to electrons and holes can be measured separately. The additional charges generated by the UV illumination make it possible to investigate electroluminescence at electric fields below the threshold in conventional thin-film-electroluminescent devices. The method and the results presented here are of great value for the fundamental understanding of charge-transport and excitation processes in electroluminescent devices.

In thin-film electroluminescent displays the electrical properties of the phosphor material are very important for the device performance. The electric field and the current in the phosphor layer may be quite inhomogeneous due to multiplication and space charge, even in devices without filamentary behavior. Measuring the ratio of luminance to current provides information about the mechanism of the light-generation process. The currents and the efficiencies for SrS:Ce devices with different thicknesses and different bottom layers are discussed and compared with numerical simulations.

A comprehensive study is reported of the chemical-beam epitaxy (CBE) and metalorganic molecular-beam epitaxy (MOMBE) growth of undoped and Mn-doped ZnS on (100) silicon and GaAs substrates for applications in advanced electroluminescent displays and optoelectronic device integration. Low-temperature photoluminescence studies on undoped ZnS at 10K show highly pronounced excitonic and band-edge emission bands with several orders of associated longitudinal optical phonon replicas. The homogeneously Mn-doped ZnS layers showed the characteristic orange luminescence which depended on the concentration of Mn. However, Mn delta-doped ZnS exhibited much brighter luminescence than the ZnS homogeneously doped with a comparable number of Mn ions. The temperature dependence of the Mn luminescence was investigated in detail. Different temperature dependences were observed from the homogeneously and delta-doped ZnS layers. A single-parameter configuration model was applied and found to explain the luminescence properties of homogeneously doped ZnS. For delta-doped ZnS, the configuration coordinate model failed and the antiferromagnetic interaction between the Mn ions must be considered to explain the observed results.

The development of emissive displays is briefly outlined and the types of phosphors they utilize are enumerated. The history of phosphor invention and development is briefly outlined up until the modern era starting in the 1930s. The first practical phosphors for CRTs and fluorescent lamps are enumerated and then the rapid developments starting after World War II and advancing through the commercial realization of rare-earth-based phosphors are presented. The present electronic, emissive display technologies are then presented together with the phosphor properties that they require; namely, cathodoluminescence-based displays, photoluminescent displays, i.e., plasma and LCD backlights, and electroluminescent displays. The presently used phosphors for these displays are mentioned and then the properties of these phosphors that need further improvement are outlined. In conclusion, it pointed out that the understanding of some phosphor properties or types has reached a considerable state of maturity, but the understanding of other phosphor types, e.g., electroluminescent phosphors, is still quite rudimentary.

— The variation of luminance with transferred charge in ZnS:Mn ac thin-film electroluminescent (ACTFEL) display devices was analyzed to determine the roles played by the preferred current paths (filamentary conduction) and manganese clustering in limiting the phosphor efficiency. Luminance-charge (L-Q) characteristics were measured in ZnS:Mn ACTFEL devices of varying Mn concentrations. L-Q characteristics showed a reduction in slope at higher values of Q. Also, the value of Q where the slope changed varied with the Mn/Zn ratio. These effects were attributed to the existence of preferred current paths in the phosphor layer where hot-electron flow clustered.

— Analysis of a ZnS:Mn-type ac thin-film electroluminescent device with a deep level in the bulk of the phosphor layer was performed. Both donor- and acceptor-type levels were considered. Calculations of field, current, and luminescence as a function of the interface-state-level energy (ECD) showed that a trailing-edge peak in the luminescence waveform appears when ECD is less than 0.5 eV. It was found that an acceptor-type bulk level can, under certain conditions, lead to oscillations in the electron flux and the device current. A reasonable match between theoretical and experimental luminescence waveforms could be obtained for ECD = 0.8 eV. However, theory and experiment could not be matched simultaneously at three different drive conditions consisting of three different slew rates for the drive pulses. Further refinement of the model is necessary for predicting the ACTFEL drive response for all drive conditions. These refinements include the energy distribution of hot electrons, probability of impact excitation, and carrier multiplication in the phosphor layer.