Large Color Gamut Research Articles

Structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN 2 and ZnGeN 2:Mn 2+ for field emission displays

Yellowish-orange-emitting ZnGeN 2 and orange-red-emitting ZnGeN 2:Mn were synthesized by a facile and mild gas-reduction–nitridation reaction at 1153 K under NH 3 flow with air-stable raw materials ZnO, GeO 2 and MnCO 3. The structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN 2 doped with or without Mn 2+ were systematically investigated. Rietveld refinements show that the as-synthesized samples are obtained as single-phase compounds and crystallize as an orthorhombic structure with a space group of Pna2 1. The actual chemical composition of the as-prepared ZnGeN 2 determined by energy dispersive X-ray spectroscopy suggests that the Ge vacancy defects probably exist in the host. The SEM image reveals that the Zn 0.99Mn 0.01GeN 2 particles form aggregates ∼500–600 nm in size. The diffuse reflection spectrum and photoluminescence excitation spectrum confirm that the band edge absorption of ZnGeN 2 at low energy is 3.3 eV (∼376 nm). Upon UV light excitation and electron beam excitation, ZnGeN 2 gives an intense yellowish-orange emission around 580–600 nm, associated with a deep defect level due to the Ge vacancy defects, and ZnGeN 2:Mn shows an intense red emission at 610 nm due to the 4T 1g( 4G) → 6A 1g( 6S) of Mn 2+. The unusual red emission of Mn 2+ in tetrahedral Zn 2+ sites is attributed to the strong nephelauxetic effect between Mn 2+ and the surrounding tetrahedrally coordinated nitrogen. The photoluminescence and cathodoluminescence emission colors of ZnGeN 2:Mn have a high color purity of ∼93–98%. These results demonstrate that ZnGeN 2:Mn is a novel, promising red-emitting nitride, potentially applicable to field emission displays with brilliant color-rendering properties and a large color gamut.

Chromaticity-Tunable Emission of Sr3AlO4F : Ce3 + Phosphor: Correlation with Matrix Structure and Application in LEDs

phosphors were synthesized by a high temperature solid-state reaction method, and their luminescence properties were investigated. ions occupy two different sites in these phosphors, and the different emissions derived from the two luminescent centers are discussed in terms of the matrix structure. The site occupancy and energy-transfer process give rise to the concentration-dependent luminescence behaviors, and the emission color may be tuned in a large color gamut from blue-green to yellow-green by controlling the concentration. Because the phosphors exhibit a strong absorption in the range of near-UV to blue spectral region, the phosphors were utilized to fabricate the phosphor-converted light emitting diodes. The results show that the phosphors have potential applications in light emitting diode (LED) devices.

Stereoscopic projector for polarized viewing with extended color gamut

Stereoscopic projectors show left and right eye information to induce a sense of depth. The viewer wears eyeglasses that separate the left and right eye images using color, shutters or polarization mechanisms. Polarization-based systems can use two identical projectors with passive polarizers at the output of their projection lens. We have designed and built a prototype of a stereoscopic projection system that incorporates the functionality of both projectors and polarizers into one optical engine. Furthermore, the system is adapted to incorporate large color gamut visualization with up to six primary colors. Light emitting diodes with different colors are used as light sources. The optical engine uses two liquid crystal on silicon light modulators to simultaneously modulate one s- and one p-polarized image. Both modulation light paths in the optical engine have a throughput of 10% yielding a total throughput of 20%. In red, green and blue color operation we demonstrate stereoscopic vision wearing polarization sensitive eyeglasses with a 40% increase of the ITU-R BT.709 color space. The images are shown at a frame rate of 120 Hz, producing a total light output of 25 lm, a contrast of 1000:1 and 0.5% crosstalk. We also demonstrate that cyan-colored information can be modulated by the system, which results in a 50% increase of the ITU-R BT.709 color space.

Color separation system with angularly positioned light source module for pixelized backlighting

A color-separation system that angularly positions color LEDs to produce color separation and a lens array to focus this light onto the pixels is proposed. The LED rays from different incident angles are mapped into corresponding sub-pixel positions to efficiently display color image, which can be used to replace the absorbing color filter in the conventional liquid crystal layer. In this paper, the prototype backlight has been designed, fabricated and characterized. The measurement results of this module showed that a gain factor of transmission efficiency three times more than that of conventional color filters efficiency improvement and a larger color gamut are expected.

New collection systems for multi LED light engines

Light emitting diodes (LEDs) have numerous advantages as light sources in projectors. LEDs are more compact, exhibit a larger color gamut, have a longer lifetime, and need a lower supply voltage. However, there is still one important disadvantage: the optical power per unit of etendue (luminance) of an LED is significantly low. As a result of the etendue limitations of LEDs, the projected flux on the screen will not be high. Despite this shortcoming, LED’s are still of great interest for low power applications because of their other superior properties. Thus we collect the available light flux optimally and combine multiple high luminance LEDs within the system. In this study we discuss three collection systems designed to collect the LED flux with high optical efficiency while retaining small device size. The best collection efficiency attained with our collection systems is 96%. The fabrication tolerance and cost of our collection systems are also analyzed.

Additive colour mixing by surface relief gratings utilizing the power spectrum of a fluorescent lamp

Additive colour mixing produced by diffractive grating structures is studied. The gratings produce almost monochromatic primary colours to a selected viewing angle, providing thus a very large colour gamut. The colours inside the gamut are obtained by additive colour mixing in the reflected diffraction order. The amount of a single primary in the additive colour mixing within one colour pixel is determined by the area fraction of the corresponding grating. We demonstrated the concept by fabricating samples which appear white at 30° viewing angle when illuminated by 4000 K fluorescent lamp.

Increased lumens per étendue by combining pulsed light-emitting diodes

LED-based projectors have numerous advantages compared to traditional projectors, such as compactness, larger color gamut, longer lifetime, and lower supply voltage. As LEDs can switch rapidly, there is the possibility to pulse. However, there is also an important disadvantage. The optical power per unit of étendue of an LED is significantly lower than, e.g., an ultra-high-performance (UHP) lamp. This problem can be remedied partly by pulsing the LEDs. If one drives an LED with a pulsed current source, the peak luminance can be higher, albeit the average luminance will not increase. By pulsing two LEDs alternately (50% duty cycle), their increased flux can be added up in time and will generate a higher average flux within the same étendue. We combine the LEDs with a polarizing beam splitter (PBS) and change the polarization of one LED with a switchable retarder. The achieved substantial net gain after all losses is 36%.

Design of relative primary luminances for four-primary displays

Multi-primary displays have the advantage of large color gamut. The relative primary luminances of a conventional three-primary display are uniquely determined by its white point. There are N−3 degrees of freedom for choosing the relative primary luminances of an N-primary display with a given white point. This paper presents the methods designing the relative primary luminances of four-primary displays. A four-primary LED display is taken as an example for showing the methods. The maximum display luminance and color gamut are, respectively, taken as an additional requirement for determining the relative primary luminances of the display. The requirement of the maximum display luminance is taken for a set of available primary luminances. The gamut volume in CIELAB color space is defined for maximizing the display gamut. In practice, the design of the relative primary luminances may be a compromised result of the two additional requirements.

25.2: A Wide Gamut, High Aperture Mobile Spectrum Sequential Liquid Crystal Display

The spectrum sequential LCD has fewer columns than the equivalent conventional RGB LCD, a large aperture ratio, a very large colour gamut and it transmits more light. We demonstrate a 1.9″ QVGA spectrum sequential LCD and discuss its implementation, including array, addressing, colour filter, backlight and processing.

Océ's Mono Component, Magnetic, Conductive Colour Toner

Océ's Direct Imaging (DI) technology is a unique 7 colour dry-toner based printing process. The printing process is controlled by a subtle interplay between a magnetic force and an electrical force exerted on the inductively charged toner particles. Océ's DI technology therefore requires magnetizable and conductive colour toners.A major challenge was to develop colour toners that yield a sufficiently large colour gamut. Carbonyl iron has been chosen as a magnetic pigment. For a conductive coating on the toner particles fluorine doped tinoxide (FTO) is used.The FTO coating on the toner particles is completely transparent and colourless. The carbonyl iron pigment in the toner however still absorbs a significant fraction of the incident light. By using fluorescent mixtures of dyes, in addition to colour pigments, we have succeeded in attaining vivid colours and a large colour gamut.

25.3: Spectrum Sequential Liquid Crystal Display

Conventional displays cannot show all real-world colours. We have made a 30-inch Spectrum Sequential LCD that uses two different types of fluorescent lamps that alternately illuminate the panel. In this way, a 6 primary display is obtained with a 22% larger colour gamut, without modifying the panel itself.

12.1: Digital Cinema Projection with R‐LCOS Displays

AbstractA digital cinema projector developed by Eastman Kodak Company, utilizing three JVC QXGA liquid crystal displays (LCDs), and providing 12,000 lumens, 2,000:1 contrast, and 3 Mpixel resolution, is described. This system, which has a novel optical configuration, wire grid polarizers and polarization compensators, provides high contrast at low F#, a large color gamut, and minimal stress birefringence at high power.

Fluorescent Nanocolorants Based on Dye-Packaging Technology for Ink Jet Application

The emerging markets and evolving safety regulations for color ink jet printing have placed more rigorous and at times new and specific requirements on ink jet ink designs. A short list of these requirements may include: 1. Larger color gamut (clear color); 2. Archival prints with enhanced image quality; 3. Any substrate or media printing; 4. Rapid throughput (approaching engine limits); 5. All-safe properties.Colorants available today do not enable the ink design chemists and engineers to meet existing market needs much less the requirements of emerging ink jet markets. This paper provides an example of a dye-packaging technology (DPT) that addresses in-part these same topics. Two disadvantages of DPT materials relative to pigmented materials which include dye-loading and light fastness will be discussed. Both of these parameters are active areas of DPT research and will be greatly improved upon in the near future. We have developed new DPT colorants of fluorescent pigments having uniform particle size, excellent solvent resistance and satisfactory light fastness in aqueous solutions. The DPT colorants containing fluorescent dyes encapsulated within spherical, solvent resistant, polymer particles having a mean particle size below 140 nm show excellent dispersion stability.Also discussed will be the light fading stability of images made with DPT materials containing fluorescent dyes and images made with water solutions containing the same dyes. Results are quoted as color difference (ΔE) units in CIEL*a*b* color space. Four different DPT fluorescent colorants (yellow, orange, red and magenta) were studied. All investigated colorants are more photostable systems than corresponding dyes.

Novel Colorants for Jet Inks Based on Dye-Packaging Technology

The emerging markets and evolving safety regulations for color ink jet printing have placed more rigorous and at times new and specific requirements on ink jet ink designs. A short list of these requirements may include: 1. Larger color gamut (clear color); 2. Archival prints with enhanced image quality; 3. Any substrate or media printing; 4. Rapid throughput (approaching engine limits); 5. All-safe properties.Colorants available today do not enable the ink design chemists and engineers to meet existing market needs much less the requirements of emerging ink jet markets. This paper addresses the issues biased from a colorant design perspective. In addition, we provide an example of a dye-packaging technology (DPT) that addresses in-part these same topics.Two major varieties of ink colorants are embodied in conventional ink jet ink systems. One is water- or alcohol-soluble dye based inks and the other is pigmented inks. Dye-based inks have clear color and high reliability, however they are suffering from inadequate water fastness and light fastness properties. Pigmented inks have advantages in both of the latter properties, but they have limitations based on complex dispersion designs, and clear color. The dye-packaging technology is one of the new approaches that can be used to minimize and in some cases, overcome these problems.The bodacious design goal of DPT systems is to separate the color science issues from the printability issues. In so doing, color science design teams may meet market requirements without a dramatic impact on the print engine design. Similarly, the print engine design team is able to optimize for printability without dramatic impact on the color science. Through the separation of these two highly interactive design constraints, less technologically oriented OEM's are empowered to identify and develop new markets for all digital printing technologies. This is particularly viable for the needs of the emerging textile or decorative and applied fine arts markets. Dye packaging promises to provide vehicle blindness over a wide range of ink vehicles and also offers a type of dye receptor for optimal image formation on a wide variety of print media. As packaged dyes, the DPT materials depict color gamut's that are identical to the dyestuff that they are derived. Most importantly, the DPT materials permit the use of otherwise unsafe dyestuff such as Rhodamines thereby providing a kind of all-safe packaging of dyes. As particles, these pseudo-pigments provide holdout and other rheological properties that are similar to their pigment counter-parts. As free polymeric surfaces that may be modified, the DPT materials offer the potential to make systems that are sensitive to the media environment thereby providing a “pre-receptor” component to the colorant.In this presentation, the two disadvantages of DPT materials relative to pigmented materials which include dye-loading and light fastness will be discussed. Both of these parameters are active areas of DPT research and will be greatly improved upon in the near future. We have developed new DPT colorants based on the stable suspension of cross-linked aminoformaldehyde resin having relatively uniform particle size, excellent solvent resistance and satisfactory light fastness in aqueous solutions. The DPT colorants containing conventional or fluorescent dyes encapsulated within spherical, solvent resistant, polymer particles having a mean particle size below 250 nm show excellent dispersion stability.Also discussed will be the light fading stability of images made with DPT materials containing fluorescent dyes and images made with water solutions containing the same dyes. Results are quoted as color difference (ΔE) units in CIEL*a*b* color space. Four different DPT fluorescent colorants (yellow, orange, red and magenta) were studied. All investigated colorants are more photostable systems that corresponding dyes. Yellow and orange colorants have almost identical fading rates whereas the red is less stable and magenta is the least stable.

Retinal scanning display: light sources moving over the retina.

A retinal scanning display is a new kind of display that directly uses the retina as a projection screen. This differs from, for example, a TV which first creates an image on a screen outside the eye. Although a retinal scanning display needs no screen, the principle of creating an image is similar to that of a TV. Where the TV uses an electron beam to create (scan) a raster pattern on a screen, a retinal scanning display uses a beam of light to scan a raster pattern on the retina. The way to get from an equally illuminated raster pattern to an image is to modulate the intensity of the beam as it scans. Since the eye does not look at a physical screen, people often wonder what the image of a retinal scanning display will look like. Upon seeing the image, the general response is: 'It looks just like a normal display'. In fact it is a normal display, but one that has many advantages compared to other kind of displays, such as: possibility of high brightness, large color gamut, possibility of high-resolution and good image quality.

Solid‐State Laser‐Based Displays

AbstractRecent advances in compact visible microlasers have enabled the development of portable laser display systems. The benefits of large color gamut, invariant color accuracy, image uniformity, high contrast, large depth of focus and reliability inherent in the microlaser design make them attractive for display applications. Lasers are under development for both “backlit” and “direct‐write” displays. Advantages of the microlaser technology will enable applications such as command/control centers, simulators, HMDs/HUDs, CAD workstations, and electronic cinema.

Optical coatings for document security

Optical coatings that shift color with viewing angle have been adapted into optically variable foils, pigments, and inks to prevent color copying by color copiers, printers, cameras, or lithographic reproduction. Metal-dielectric multilayer thin-film structures have large color shifts with angle, high chroma, a large color gamut, and light fastness that make them uniquely suited for security inks. World currencies are now protected by these structures.

Various chromatic‐adaptation transformations tested using new colour appearance data in textiles

AbstractA new set of colour appearance data was obtained from a series of experiments in which 240 wool samples having a large size of 3 x 3 in. square that subtends 10° at the observer's eye, and covering a large colour gamut were used. Each colour was assessed by a panel of five observers using a magnitude estimation method under three light sources, D65, TL84, and A. In total, 10,770 estimations were made, and these form a set of new colour appearance data in textiles. Data analysis was carried out and shows that the accuracy of the visual results for different observers is quite good. the colour appearance data were used to test the performance of seven chromatic‐adaptation transformations, i.e., BFD, Bartleson, von Kries, CIE, Hunt, CIEL*a*b*, and Fairchild. the results show that the BFD transformation gives the most accurate prediction to the visual results between all transformations studied. All transformations can have a better fit to the experimental grid under TL84 than that under A. However, the results given by the best chromatic‐adaptation transformation are still unsatisfied in colour industries, especially in the textile industry. the two sets of experimental grids respectively derived from this work and by Luo et al. (1991) were also studied. an expected difference between the two sets of experimental grids was found. the difference may mainly result from two factors: the experimental method in assessment and the size of the samples. © 1995 John Wiley & Sons, Inc.

Optimum Absorption Bands of Subtractive Dyes for Colour Photography

THREE dyes—cyan, magenta and yellow—are used in modern subtractive colour photography and many articles have been published on the synthesis and photographic characteristics of couplers which yield them. The colour gamut produced by these dyes has, however, not yet been fully evaluated. Although most naturally occurring colours are comparatively unsaturated (with the exception of the colours of certain flowers) there are now many highly saturated artificial colours in existence. A large colour gamut is thus desirable for the satisfactory reproduction of these highly saturated colours.