Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-09-21
2003-11-25
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S110000, C313S504000
Reexamination Certificate
active
06653778
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a fluorescent color conversion film that converts light emitted in near ultraviolet to visible region by a light-emitting element to light with different wavelength in the visible region. The invention also relates to a fluorescent color conversion filter employing such a fluorescent color conversion film. The invention further relates to an organic light-emitting device equipped with such a fluorescent color conversion filter. The fluorescent color conversion filter and the organic light-emitting device are suitably applied to both consumer-oriented and industry-used display apparatuses, such as a self-emitting multi-colored- or full colored-display, a display panel and a backlight.
With increasing demand for a flat panel display to replace a conventional CRT, development and practical application of various display devices are being actively conducted. An electroluminescent device (hereinafter referred to as a light-emitting device) is one of the devices to meet these needs. The light-emitting device has received great attention, as it is a self light-emitting device of full solid-state exhibiting such high resolution and high visibility that are not attained by other display devices.
In a conventional method for multi-colored or full-colored display of a light-emitting device for use in a flat panel display, light-emitting elements corresponding to three primary colors of red, blue and green are separately arranged in a matrix form and each of them is caused to emit each color of light, as disclosed by Japanese Unexamined Patent Application Publication Nos. S57-157487, S58-147989 and H3-214593. However, the color display using an organic light-emitting device requires precise arrangement of three kinds of light-emitting material for red, blue and green in a matrix form. The technology for the arrangement is difficult and the manufacture of such an arrangement is costly. In addition, the method has a problem that chromaticity gradually deviates because the lifetimes of the three light-emitting materials differ from each other.
In another known method for color display, white light emitted from a backlight is passed through color filters to obtain three primary colors, as disclosed by Japanese Unexamined Patent Application Publication Nos. H1-315988, H2-273496 and H3-194895. However, an organic white-light-emitting device exhibiting a long life and high brightness that are necessary to attain red, green and blue light of high brightness has not yet been obtained.
In another known method for color display, fluorescent elements separately arranged in a plane absorb light from a light-emitting element. Each of the fluorescent elements emits fluorescent light of different colors, as disclosed by Japanese Unexamined Patent Application Publication No. H3-152897. The method in which multi-colored fluorescent light is emitted from a light-emitting element using fluorescent elements is also applied to CRT and plasma display.
In recent years, a color conversion method has been developed in which fluorescent material is used as a filter. The material absorbs light in the region of an organic light-emitting element and emits fluorescent light in a visible light region, as disclosed by Japanese Unexamined Patent Application Publication Nos. H3-152897 and H5-258860. In this method, color of the light emitted from the organic light-emitting element is not limited to white light, which allows use of a brighter organic light-emitting element as a light source. In an example of a color conversion method using an organic light-emitting element emitting blue light, wave length conversion is performed from blue light to green or red light, as disclosed by Japanese Unexamined Patent Application Publication Nos. H3-152897, H8-286033 and H9-208944. A full-colored self-emitting display device could be constructed by precisely patterning a fluorescent color conversion film containing such an organic fluorescent dye, even when low energy rays such as radiation in a near ultraviolet to visible light region from an organic light-emitting element is utilized. The following two methods are among known methods for patterning a fluorescent color conversion film.
(1) Similar to the case of inorganic fluorescent material, organic fluorescent dye is dispersed in a liquid photoresist, which is a photo-reactive polymer, then, the resulting material is laminated by spin-coating, followed by patterning by means of photolithography, as disclosed by Japanese Unexamined Patent Application Publication Nos. H5-198921 and H5-258860.
(2) Fluorescent dye or fluorescent pigment is dispersed in a basic binder, then the resulting article is etched by acidic aqueous solution, as disclosed by Japanese Unexamined Patent Application Publication No. H9-208944.
It is commonly known that a dielectric constant of a material decreases with solidification of matrix of the material. For example, methyl methacrylate, which is a monomer, has a dielectric constant of 4.0, while poly(methyl methacrylate), in which solidification has progressed by polymerization, exhibits a lowered dielectric constant down to2.9. Decrease in the dielectric constant due to solidification of the matrix alters the environmental condition of the organic fluorescent dye, and increases ion pair interaction of the organic fluorescent dye in a ground state or an excited state, resulting in a lower value of fluorescence quantum yield of the dye. When an organic solvent of high polarity, for example, ethyl alcohol, is added to this system, the dielectric constant of the system increases, and as a result, ion pair interaction of the organic fluorescent dye is suppressed. D. A. Gromov reported in
J. Opt. Soc
. Am. B/Vol. 2, No. 7, p. 1028 (1985). Addition of ethanol in Rhodamine 6G, a xanthene dye, makes an ion pair apart, which means that ion pair interaction decreases, resulting in improvement of the fluorescence quantum yield.
[Problem to Be Solved by the Invention]
In forming a fluorescent color conversion film using organic fluorescent dye dispersed in a liquid photoresist by means of photolithography process, there has been a problem that proportion of monomer decreases by polymerization due to optical or thermal curing of the resist. Furthermore, the organic solvent used evaporates. As a result, the dielectric constant of the system decreases, causing deterioration of color conversion characteristics (fluorescence quantum yield, in particular) of the fluorescent color conversion film.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a fluorescent color conversion film formed by a photolithography process that overcomes the foregoing problems.
It is a further object of the present invention to provide a fluorescent color conversion film formed by a photolithography process that suppresses degradation in color conversion characteristic by compensating for decrease in dielectric constant due to solidification of the system.
It is another object to provide a fluorescent color conversion filter employing such a fluorescent color conversion film.
It is still another object of the invention to provide an organic light-emitting device equipped with the fluorescent color conversion filter.
The first embodiment of the present invention is a fluorescent color conversion film comprising an organic fluorescent dye which absorbs light, emitted from a light-emitting element, in a near ultraviolet to visible light region, and emits visible light of different wavelength, a matrix resin bearing the organic fluorescent dye, and a high boiling point solvent having a boiling point of 150° C. or higher and a vapor pressure of 5 mmHg or lower at temperature of 20° C.
The second embodiment of the present invention is a fluorescent color conversion film as the first embodiment, wherein the high boiling point solvent is contained in an amount of 0.00001 to 50 weight % with respect to the weight of the fluorescent color conversion film.
The third aspect of embodiment of the pres
Shiraishi Yotaro
Tomiuchi Yoshimasa
Fuji Electric Co., LTD.
Patel Ashok
Zimmerman Glenn
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