Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-11-09
2004-07-13
Glick, Edward J. (Department: 2882)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S502000, C313S503000, C313S504000, C313S506000, C313S483000, C313S486000, C313S512000, C313S498000
Reexamination Certificate
active
06762553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate for a light emitting device, a light emitting device, and a process for the production of a light emitting device. Particularly, the present invention relates to a light emitting device which is used for various devices such as a displaying device, an indication devices and a back lighting device for a liquid crystal display, a substrate used for the production of such light emitting device, and a production process for such light emitting device. In the light emitting device as described above, various light emitting mechanisms (such as an electroluminescent (which may be referred to as “EL”) mechanism, a photoluminescent (which may be referred to as “PL”) mechanism, and a light emission mechanism by means of electron radiation) may be used. In addition, the present invention relates to a plane lamp (such as a flat fluorescent lamp) or a plasma display panel in which such light emitting device is used.
2. Description of the Related Art
Hitherto, various displaying devices have been developed with progress of the intelligent society. One of those devices is an EL device (or an electroluminescent device) which is expected to be used for an electronic display of a self-emission type. The EL device makes use of a luminous phenomenon which occurs upon application of an electric field to a material, and has a structure in which an inorganic EL layer or a organic EL layer is sandwiched by electrodes.
FIG. 11
shows a basic structure of one example of such an organic EL device wherein a transparent electrode
12
as an anode which is made of indium-tin oxide (ITO), an organic EL layer
13
and an back metal electrode
14
as a cathode are laminated in the referred order on a glass plate
11
. In such a device, a hole injected from the transparent electrode
12
and an electron injected from the back metal electrode
14
recombines in the organic EL layer
13
, whereby an emission center such as a fluorescent dye is excited to result in the light emission. The light emitted in the organic EL layer
13
ejects from the glass plate
11
directly or after being reflected by the back metal electrode
14
made of for example aluminum.
Upon the ejection of the light as described above, an external efficiency (&eegr;, which is also referred to as a coupling-out efficiency) which is defined by a ratio of a light quantity drawn outside the light emitting device to a light quantity generated inside the light emitting device is determined by the critical angle &thgr;c when the light is totally reflected upon its ejection from a medium of which refractive index is n to the ambient air of which refractive index is 1.0 according to a theory of the classical optics. According to the laws of refraction, the critical angle &thgr;c is given by the following equation (1):
sin &thgr;
c
=1/
n
(1)
The external efficiency (&eegr;) is obtained by the following equation (2) based on a ratio of a quantity of light passing into the ambient air from the medium of which refractive index is n to a quantity of the generated light (i.e. sum of a quantity of light totally reflected at an interface between the air and the medium and a quantity of light passing into the air):
&eegr;=1−(
n
2
−1)
1/2
(2)
It is noted that when the refractive index n of the medium is greater than 1.5, the following approximate equation (3) may be used:
&eegr;=1/(2
n
2
) (3)
However, when the refractive index n of the medium is close to 1.00, the above equation (2) has to be used.
Since a thickness of the organic EL layer
13
and a thickness of the transparent electrode
12
are smaller than a wavelength of the light, a refractive index of the glass plate
11
mainly contributes to the external efficiency (&eegr;). The refractive index of the glass is generally in the range between about 1.5 and 1.6, so that the external efficiency (&eegr;) is about 0.2 (20%) according to the equation (3). The balance which is about 80% is lost as guided light by means of the total reflection between the glass plate
11
and the ambient air.
In the above, an example in which the inorganic or organic EL layer is used as a light emitting member has been explained, and the same explanation is applicable to a PL device in which a PL light emitting layer
15
is used as a light emitting member.
FIG. 12
shows a basic structure of the PL device in which a PL light emitting layer
15
is laminated on a glass plate
11
. With the PL device, when a ray such as an ultraviolet ray is irradiated onto the PL layer
15
, the PL layer
15
generates light, which ejects from the glass plate
11
. For the PL device, the external efficiency (&eegr;) is small as in the case of the above EL device, and much light is lost as the guided light.
DISCLOSURE OF THE INVENTION
As described above, the external efficiency upon drawing the light generated in the EL device or the PL device from the device into the ambient air (i.e. a coupling-out efficiency for surface emission) is small, and such a small external efficiency is a problem not only to the EL device or the PL device but also to a general problem throughout a light emitting device which ejects surface plane-form light generated in the device into the ambient air.
The present invention has been made considering the above problem, and an object of the present invention is to provide a light emitting device of which external efficiency to draw light outside is higher and of which surface luminance is higher, a substrate for such light emitting device and a process for the production of such light emitting device.
In the first aspect, the present invention provides a substrate for a light emitting device which substrate comprises an electrically conductive transparent film (electrically conductive and transparent film) which is in contact with at least one surface of a low refractive index member. The substrate leads to a higher external efficiency of light which passes through the low refractive index member into the air, so that using such substrate makes it possible to produce a light emitting device of which external efficiency is higher to draw the light into the outside of the device.
In the first aspect, the substrate for the light emitting device in the first embodiment is characterized in that it includes the electrically conductive transparent film which is in contact with the at least one surface of the low refractive index member of which refractive index is greater than 1 and not greater than 1.30. This substrate leads to a particularly higher external efficiency of light which passes through the low refractive index member into the air, so that using such substrate results in an effective light emitting device of which external efficiency is higher to draw the light into the outside of the device.
For example, the low refractive index member may be for example in the form of a layer, a sheet or a plate, and has the electrically conductive transparent film on one of two surfaces which define the low refractive index member. The low refractive index member may be considerably thicker in the above described form, and in such case, the low refractive index member may have substantially at least three surfaces, and for example it may be in the form of a rectangular parallelepiped, in which the low refractive index member may have two or more surfaces which have the electrically conductive transparent electrodes respectively. In the first embodiment of the first aspect, the refractive index of the low refractive index member is in the range preferably between 1.003 and 1.300 and more preferably between 1.01 and 1.2.
In the first aspect, the substrate for the light emitting device in the second embodiment is characterized in that the low refractive index member in the first embodiment of the first aspect is made of an aerogel. The aerogel may be any known aerogel as far as its refractive index is small as described above. In the substrate, when the aero
Kawano Kenji
Tsubaki Kenji
Tsutsui Tetsuo
Yokogawa Hiroshi
Yokoyama Masaru
Glick Edward J.
Matsushita Electric & Works Ltd.
Yun Jurie
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