Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-03-21
2001-11-20
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S112000, C349S071000
Reexamination Certificate
active
06320633
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a display device comprising a first substrate with pixels, provided with a layer of luminescent material patterned in areas, and means for exciting the luminescent material during use. Such patterned layers may be activated by means of ultraviolet radiation which is modulated by a suitable switch, for example, an LCD switch. The separate areas may alternatively form pixels of a display device based on electroluminescence, such as a polymer (O)LED.
The invention also relates to a method of manufacturing such a display device.
BACKGROUND OF THE INVENTION
A display device of the type described above is known from U.S. Pat. No. 4,822,144. In one of the examples shown in this patent, a pattern of phosphors is excited by UV radiation via an LCD switch. Notably when the luminescent layers in said example are transparent (organic) phosphors, waveguiding may occur in these layers due to reflection on the interfaces with, for example, the substrate or a transparent protective coating in such a layer. The same applies to layers of electroluminescent material forming, for example, an (O)LED or (Organic)Light-Emitting Device. Due to said waveguiding, much of the light generated in the layers is lost. Another consequence is that the light leaves the layers at undesired areas in the viewing direction, so that, for example, colors are mixed. Moreover, the layer of luminescent material is often coated with a transparent protective coating. Daylight is reflected on each of the layers (the substrate, the layer of luminescent material and the transparent protective coating), which is at the expense of the contrast.
SUMMARY OF THE INVENTION
It is, inter alia, an object of the present invention to obviate one or more of said drawbacks. To this end, a display device according to the invention is characterized in that at least an area of the layer of luminescent material is situated between a light-absorbing layer present at the viewer's side of the display device and a dielectric layer, and, in plan view, is provided with light-reflecting or light-scattering means at least along a part of its edge. In this application, a dielectric layer is understood to mean a layer having a low refractive index as compared with the refractive index of the layer of luminescent material. This may be an underlying substrate but is preferably a stack of layers having mutually different refractive indices (a sub-layer may have a higher refractive index than the layer of luminescent material).
By providing light-reflecting or light-scattering means along the edge, it is achieved that light at the area of the edge (in the direction of the viewer) is reflected or scattered. This raises the light output. Moreover, it is avoided that light reaches an adjacent area of the layer of luminescent material via said waveguiding; this largely prevents said color mixing. The light-absorbing layer absorbs ambient light so that no troublesome reflections occur any longer and the contrast is enhanced.
A preferred embodiment of a display device according to the invention is characterized in that a layer reflecting light in the direction of the layer of luminescent material is situated between the light-absorbing layer and the layer of luminescent material. Said waveguiding is, as it were, intensified thereby and used to advantage.
The light-reflecting or light-scattering means may not only be provided along the edge of the separate areas of the patterned layer of luminescent material but may also be situated within apertures in these areas.
When using light-reflecting means, reflective surfaces at an angle of approximately 45° with respect to the substrate are preferably chosen. A further preferred embodiment of a display device according to the invention is characterized in that at least one head end of an area of the layer of luminescent material is provided with semi-transparent mirrors. In this case, an optically intensified effect (laser effect) occurs under well-chosen conditions. Advantages are a higher light output and the fact that saturated colors are obtained because of the narrow emission band (single line emission).
A first method of manufacturing such a display device is characterized in that a layer of luminescent material patterned in areas is provided on a substrate, whereafter a layer of light-reflecting material is deposited in a first direction at an angle of between 10 and 30 degrees with respect to the normal on the surface, reflecting or light-scattering material is provided between the separate areas, and the areas are coated with a light-absorbing material.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 3998526 (1976-12-01), Katz
patent: 4394068 (1983-07-01), Page et al.
patent: 4822144 (1989-04-01), Vriens
patent: 4830469 (1989-05-01), Breddels et al.
patent: 4882617 (1989-11-01), Vriens
patent: 5146355 (1992-09-01), Prince et al.
Broer Dirk J.
De Witz Christianne M. R.
Ton Toan
U.S. Philips Corporation
Waxler Aaron
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