Vacuum‐deposited and spin‐coated color changing media (CCM) films for use in color microdisplays with blue OLED emitters have been demonstrated with optical density 5.0 and 2.8 per micron at the maximum of absorption, respectively. CCM efficiency has been studied as a function of film thickness, dopant concentration and excitation wavelength.

AbstractVarious approaches to color changing media (CCM) for color microdisplays using blue pixelated OLED display with blue‐to‐green and blue‐to‐red CCM have been studied. Vacuum‐deposited CCM films have been demonstrated with optical density 3.75/micron at the maximum of absorption and absolute quantum efficiency of photoluminescence of 82% and 67% for B/G and B/R CCM, respectively.

This paper reports the fabrication of a high efficiency and high brightness white Organic Light Emitting Device (OLED) based on evaporated small molecules. The luminous efficiency of the device is approximately 1.5 lumens/watt, which, to the best of our knowledge, is the highest reported efficiency in the literature. Brightness in excess of 1000 cd/m2 is achieved at a voltage of 10V. The emitted white light, with CIE coordinates of x=0.33 and y=0.33, can be converted to red, green and blue sub-pixels using color filters. The OLED device comprises an emission layer made of DPV type host with a single fluorescent dopant. The emission layer is sandwiched between a hole transport layer and an electron transport layer (Alq3).

SummaryRelationships of permeability to porosity are shown from analyses of more than 2, 100 core plugs from nine wells in the Travis Peak, a low-permeability, tight-gas sandstone formation in northeast Texas. Effects of reservoir vs. ambient stress are shown for permeability, porosity, and the Klinkenberg factor. The relationship of brine permeability to gas permeability is also shown.

Summary A study was conducted to verify or to improve the routine laboratory procedures normally used to measure porosities of cores from tight gas sands. After routine analysis of 242 core plugs from the Travis Peak formation in east Texas, 20 of the plugs were analyzed for porosity by two additional laboratories. Each of the three laboratories had problems with their results that normally would have gone unnoticed but were recognized because of disagreement with results from the other laboratories. After reruns, agreement was excellent, with a standard deviation of about 0.25 porosity units (p.u.) when comparing one laboratory against another. To improve reliability of routine porosity measurements, recommended practices and quality-control procedures are presented.

A model is proposed for the observed hysteretic behavior of ac-coupled ZnS:Mn thin-film electroluminescent devices. The following mechanisms are invoked: (1) tunnel injection from ZnS-dielectric interfaces (ℰ4106 V/cm), (2) electron-hole pair generation, (3) deep trapping of holes, leading to space-charge formation, (4) charge storage at the ZnS-dielectric interfaces, and (5) direct recombination of injected electrons and trapped holes. When these mechanisms are combined in a self-consistent numerical simulation model, a bistability of charge transfer versus applied voltage is obtained which exhibits many of the characteristics of the observed device behavior. Experimental evidence in support of the individual assumptions is also discussed.

The characteristics of thin-film electroluminescent devices made from ZnS:Mn and exhibiting hysteretic behavior are reviewed. The nature of the hysteresis (which leads to display devices with inherent memory), the switching characteristics, and some of the empirical requirements for observing the phenomenon are described and discussed. This background is used as a basis for a discussion of device operation, leading to a description of a phenomenological model which has been developed to explain the hysteretic behavior. Some technological difficulties associated with the phenomenon are also described.

Quantitative data is presented concerning the optical process of writing and erasing of memory electroluminescent (EL) devices. The switching process is dependent on the energy of the exciting photons and the energy required varies from approximately 10 µJ/cm2at 325 nm (associated with bandgap photoconductivity)to about 75 mJ/cm2at 515 nm (associated with impurity photoconductivity). Experimental evidence is presented to show that necessary and sufficient conditions for EL cell erasure are the photoconductive discharging of the insulator-ZnS charge and the decay of the bulk excitation of the ZnS:Mn film. The technique of photoinduced detrapping of the stored space charge is shown to lead to the determination of midgap as the approximate location in energy of the deep traps in one of our sample films.

The concept of a storage CRT display using a thin-film electroluminescent (EL) faceplate is discussed. The storage is based on the hysteretic behavior of some thin-film EL devices made from ZnS:Mn. Results are presented of experiments in which the writing and erasing of such devices with electron beams were investigated in detail. Since realization of the concept involves large-area hysteretic thin-film devices having stable characteristics, the constraints and problems arising from these requirements and the current status of efforts to meet them are discussed.

AC-coupled thin-film electroluminescent devices employ insulating layers to limit the current density through the active layers. The requirements and limitations in driving such devices are then dependent upon the properties of the dielectric layers. We define an external efficiency for an ac thin-film electroluminescent device and consider two limiting cases, current response 1) fast, and 2) slow, compared to an applied voltage change. Relationships are then derived among external efficiency, relative luminance, and the two principal characteristics of the insulating layer, specifically charge density at breakdown and thickness. It is shown, for example, that charge density at breakdown for the insulators should be at least three times the corresponding quantity for the active layer.

An electron beam of moderate current density (∼10−5 A/cm2) and energy (10–16 keV) has been used to change the luminance state of a thin-film ZnS : Mn electroluminescent device having hysteretic or memory-type behavior with respect to applied voltage. The dwell time of the beam required for writing is of the order of 0.05–1 ms, depending upon applied voltage and beam current density. The change in luminance is confined to the area bombarded and persists for hours, decaying approximately as erf(αt−1/2) for 50

At low temperatures and for moderate surface charge densities, electrons in inversion layers on (100) $p$-type Si are two-dimensional in character; i.e., they occupy only one electric quantum level, or sub-band. For electron densities greater than about 6 \ifmmode\times\else\texttimes\fi{} ${10}^{12}$ per ${\mathrm{cm}}^{2}$, depending upon substrate doping, we have observed deviations from two-dimensional behavior in oscillatory magnetoconductance (Shubnikov-de Haas) measurements, which are interpreted as evidence of the onset of occupation of a higher sub-band. The effects of such occupation of higher sub-bands have been calculated for the four different resistivities used in the experiments. The observed change in effective density of states [(10-20)%] and its dependence upon substrate resistivity are in good agreement with theory. The experimental values for the threshold charge densities for higher sub-band occupation are higher than the theoretical values by a factor of about 1.5.

Several different types of electrochromic display devices are discussed. Their electrooptical properties and device characteristics are investigated and compared. Performance parameters for these devices are discussed in terms of their applicability to information display. It is concluded that electrochromism is best suited for direct-addressed displays.

Unlike crystalline GeTe, amorphous GeTe has a relatively wide energy gap of 0.7 eV at 295°K, and 0.77 eV at 77°K. Its resistivity is about 103 ohm-cm at room temperature, and increases exponentially with T−1, giving an activation energy of 0.35 eV. The crystallization temperature for the amorphous GeTe films is about 390°K. The measured absorption coefficient is used to calculate a density of states which behaves very much as one would expect on the basis of the Mott model. The photocurrent for low photon energies has a long lifetime of tens of milliseconds, however, at higher photon energies, above 1 eV, the lifetime is less than 30 nsec. At low temperatures the fast lifetime is slowed to a few μsec. Near room temperatures where the thermally generated carrier density is approximately 3 × 1016 cm−3, obtained from our density of states, the dependence of the photocurrent on the light intensity is linear; below 150°K, the intensity dependence is a square root law, indicating bimolecular recombination.