Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2003-02-26
2004-12-21
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S506000, C313S113000
Reexamination Certificate
active
06833667
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an organic electroluminescence element used as a light source or a back light in various image forming apparatus or an light emitting element used in an optical communication equipment or the like, and or to an image forming apparatus and a terminal unit using thereof.
BACKGROUND OF THE INVENTION
An electroluminescence element is the so-called light emitting device utilizing electroluminescence of a solid fluorescent substance, and an inorganic electroluminescence element using an organic group material as a light emitter has come into a practical use until now, and has been aimed for development and application into some backlights in a liquid crystal display, a flat display or the like. However, a voltage required for allowing the inorganic electroluminescence element to emit light is high, that is, it is not less than 100 V, and it is difficult to emit blue light therefrom, thereby full color exhibition with three primary colors, that is, RGB, is difficult. Further, since the inorganic electroluminescence element includes a light emitter made of a material having a large refractive index, it can be greatly affected by total reflection at its interface or the like, and accordingly, the efficiency of extraction of light into the air with respect to actual light emission is extremely low, that is, 10 to 20%, and it is difficult to enhance the efficiency.
Meanwhile, studies as to luminescence elements made of organic materials have been attractively and variously executed for a long time. However, its luminous efficiency is extremely low, and accordingly, it has not yet been developed into studies direct for practical use.
However, W. Tang of Kodak Co. proposed, 1987, an organic electroluminescence element having a function separation type laminated structure in which an organic material is separated into two layers, that is, a hole transmit layer and a luminous layer, and it was found that the luminance which is not less than 1,000 cd/m
2
could be obtained therefrom (Refer to Applied Physics Letter, vol. 51, 1987, page 913 or the like, by C. W. Tang and S. A. Vanslayke). Thereafter, this organic electroluminescence element has been remarkably attractive, and studies for organic luminescence elements having a similar function separation type laminated structure are now prosperously made. In particular, an increase in efficiency and a prolongation of the use life thereof, which are indispensable for practical utilization thereof, have been sufficiently studied. Thus, these years, a display or the like using an organic electroluminescence element has been materialized.
Next, explanation will be made of a configuration of a typical conventional organic electroluminescence element with reference to
FIG. 25
which is a sectional view illustrating an essential portion of the conventional electroluminescence element and in which there are shown a substrate
1
, an anode
2
, a hole transport layer
3
, a luminous layer
4
, and a cathode
5
.
Referring to
FIG. 25
, the organic electroluminescence element is composed of the anode
2
which is formed on the substrate
1
made of glass or the like in a sputtering process, a resistive heating evaporation process or the like, and which is formed of a transparent conductive film made of ITO or the like, and the hole transport layer
3
which is formed on the anode
2
, similarly by the resistive heating evaporation process or the like, and which is made N,N-diphenyl-N, N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamin (which will be abbreviated as PTD) or the like, the luminous layer
4
which is formed on the hole transport layer
3
by a resistive heating evaporation process or the like, and which is made of 8-hydroxyquinoline aluminum (which will be hereinbelow abbreviated as Alq
3
) or the like, and the cathode
5
which is formed on the luminous layer
4
by a resistive heating evaporation process or the like, and which is formed of a metal film having a film thickness of 100 to 300 nm.
When a d.c. voltage or a d.c. current applied to the electroluminescence element having the above-mentioned configuration, using the anode
2
as a positive electrode and the cathode
5
as a negative electrode, holes are injected from the anode
2
into the luminous layer
4
through the intermediary of the hole transport layer
3
, and electrons are charged from the cathode
5
into the luminous layer
4
. In the luminous layer
4
, the holes and the electrons are recombined, and accordingly, excitons which are produced through the recombination are shifted from a normal state to an excited state so as to cause a luminous phenomenon.
Referring to
FIG. 26
which is a graph exhibiting a relationship between an energizing time and a relative luminance in an organic electroluminescence element, there are shown variation in luminance among three kinds of initial luminance.
Referring to
FIG. 27
which is a graph exhibiting a relationship between an energizing voltage and luminance in an organic electroluminescence element, as shown in
FIG. 26
, it is found, the higher the luminance, the shorter the energizing time or the service life. Further, as shown in
FIG. 27
, the energizing voltage has to be higher in order to enhance the luminance. Thus, in order to materialize an organic electroluminescence element capable of having a long service life and maintaining a high luminous function, it is important to lower the luminance and to enhance the luminous efficiency. However, in order to practically use the organic electroluminescence element, a sufficiently high degree of luminance is required, that is, it is ineffective to simply lower the luminance.
As mentioned above, the organic electroluminescence element has a correlation between its luminance and its service life. Thus, there has been demanded an organic electroluminescence which can fully satisfy both enhanced luminance and long service life.
In the above-mentioned organic electroluminescence element, light emitted from fluorescent substance in the luminous layer
4
is emitted omnidirectionally from the fluorescent substance as a center, and is then radiated into the atmospheric air by way of the hole transport layer
3
, the anode
2
and the substrate
1
. Alternatively, the light is once emitted in a direction reverse to a light extracting direction (a direction toward the substrate
1
), then it is reflected by the cathode
5
, and is then radiated into the atmospheric air by way of the luminous layer
4
, the hole transport layer
5
, the anode
2
and the substrate
1
.
However, during the course of passing through interfaces between mediums, light which is incident at an angle greater than an angle with which an emergent angle of refracted waves becomes 90 deg., that is, at a critical angle, cannot transmit through one of the interfaces if the refractive index of a medium on the incident side is grater than that of a medium on the emergent side, and accordingly, the light is totally reflected so that it cannot extracted into the atmospheric air.
It is noted here that the relationship between a refraction angle of light and refractive indices of different mediums at the interface between mediums is determined under the Snell's Law. In view of the Snell's Law, in the case of transmission of light from a medium having a refractive index n1 into a medium having a refractive index n2, a relationship n1*sin &thgr;1=n2*sin &thgr;2 is obtained between an incident angle &thgr;1 and an emergent angle &thgr;2. Accordingly, if n1>n2 is effected, the incident angle &thgr;1=sin
−1
(n2
1) with which &thgr;2=90 deg. can be obtained, has been well-known as a critical angle, and therefore, if the incident angle is greater than this value, the light is totally reflected at the interface between the mediums.
Thus, in an electroluminescence element in which light is isotropically radiated, light radiated at an angle grater than the critical angle repeats total reflection at the interface so that
Hamano Takafumi
Sasano Tomohiko
Sugiura Hisanori
Tanaka Yasuhiro
Wakita Naohide
Patel Vip
Stevens Davis Miller & Mosher LLP
LandOfFree
Organic electroluminescence element and image forming... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Organic electroluminescence element and image forming..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Organic electroluminescence element and image forming... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3284266