Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – In combination with or also constituting light responsive...
Reexamination Certificate
2002-02-25
2003-01-28
Wilson, Allan R. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
In combination with or also constituting light responsive...
C257S079000, C257S080000
Reexamination Certificate
active
06512249
ABSTRACT:
Japanese Patent Application No. 2001-49776, filed on Feb. 26, 2001, and Japanese Patent Application No. 2002-48116, filed on Feb. 25, 2002, are hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
The present invention is related to a light emitting device using electroluminescence (EL), and related to a display device and an electronic instrument with employment of this light emitting device.
In EL light emitting elements using the electroluminescence (EL), since light emissions are carried out in an isotropic manner and thus, directivities of the EL light emitting elements are inappropriate, there are the following difficulties. That is, considering a specific direction of the EL light emitting element, intensity of light is lowered and emitted light cannot be utilized in high efficiencies.
BRIEF SUMMARY OF THE INVENTION
The present invention may provide a light emitting device capable of utilizing light in a higher efficiency, while increasing intensity of light along a specific direction.
The present invention may provide a display device using the above-described light emitting device, and an electronic instrument with employment of the light emitting device
A light emitting device according to one aspect of the present invention, comprises:
a substrate; and
a light emitting element section formed over the substrate,
wherein the light emitting element section includes:
a first light emitting layer in which light is generated due to electroluminescence;
one pair of electrode layers used to apply an electric field to the first light emitting layer;
a second light emitting layer which absorbs light generated in the first light emitting layer and generates light having a longer wavelength than a wavelength of the absorbed light; and
one pair of dielectric multilayer films which are formed under and above the second light emitting layer, respectively,
wherein a wavelength range of light that is reflected by the pair of dielectric multilayer films includes a wavelength range of light generated in the second light emitting layer.
In accordance with this light emitting device, after the light generated in the first light emitting layer due to the electroluminescence is absorbed by the second light emitting layer, light having longer wavelength than that of the absorbed light is generated in the second light emitting layer. The light generated in the second light emitting layer emits through the dielectric multilayer films to the substrate. As a result, it is possible to obtain a light emitting device that can emit light efficiently due to light excitation.
Also, since the wavelength range of the light that is reflected by the dielectric multilayer films includes the wavelength range of the light generated in the second light emitting layer, the light generated in the second light emitting layer is shut up between the dielectric multilayer films, so that the light propagation in the direction intersecting with the surface of the substrate can be restricted. As a result, the light having a very narrow light emission spectral width in the direction intersecting with the surface of the substrate can be obtained efficiently. Further, the light generated in the second light emitting layer may be emitted in a direction intersecting with the substrate, so that a surface light emission may be achieved.
This light emitting device of the present invention may have the following features (1) to (10):
(1) A wavelength range of the light generated in the first light emitting layer and a wavelength range of the light absorbed by the second light emitting layer may at least partially overlap with each other. In this feature, the light generated in the first light emitting layer can be absorbed by the second light emitting layer efficiently.
(2) A wavelength at a highest emission intensity in a wavelength range of the light generated in the second light emitting layer may be longer than a wavelength at a highest emission intensity in a wavelength range of the light generated in the first light emitting layer.
(3) The pair of dielectric multilayer films may include a first dielectric multilayer film and a second dielectric multilayer film,
the first dielectric multilayer film maybe formed closer to the first light emitting layer than the second dielectric multilayer film and
a reflectance of the first dielectric multilayer film may be larger than a reflectance of the second dielectric multilayer film.
In this feature, the light generated in the second light emitting layer may be emitted from the second light emitting layer toward the substrate.
(4) The first light emitting layer may include an organic light emitting material which emits light by the electroluminescence,
(5) The second light emitting layer may include a host material and a dopant material,
the host material may absorb the light generated in the first light emitting layer so that an excited state occurs, and the dopant material may be excited due to a transfer of the excited state of the host material to the dopant material, and the excited dopant material may emit light having a longer wavelength than a wavelength of the light absorbed by the host material.
(6) The second light emitting layer may include an organic light emitting material, and
the organic light emitting material may absorb the light generated in the first light emitting layer so that the organic light emitting material is excited, and the excited organic light emitting material may emit light having a longer wavelength than a wavelength of the absorbed light,
(7) A propagation direction of the light emitted from the first light emitting layer may be substantially equal to a propagation direction of the light emitted from the second light emitting layer
(8) This light emitting device may further comprise an optical member which collects the light emitted from the first light emitting layer.
In this feature, since the optical member is formed, after the light emitted from the first light emitting layer is collected, the collected light may be entered into the second light emitting layer. As a result, the utilization efficiency of light may be improved.
In this case, the optical member may be formed between the first light emitting layer and the second light emitting layer.
In this case, the optical member may be a lens layer of refractive index distribution type.
(9) The second light emitting layer may include photonic crystal that restricts light propagated in a surface direction of the substrate.
In accordance with this feature, since the photonic crystal is formed in the second light emitting layer, the light propagates in the surface direction of the substrate can be controlled in the second light emitting layer. Furthermore, the light generated in the first light emitting layer can be utilized in a higher efficiency.
In this case, the surface direction of the substrate implies a direction parallel to a surface of the substrate on which the first and second light emitting layers, and the dielectric multilayer films are stacked.
In this case, a pitch of the photonic crystal may be defined based on a wavelength of the light generated in the second light emitting layer.
(10) The light emitting device may include a plurality of the light emitting element sections, and
the second light emitting layers of the emitting element sections may generate light having different wavelengthes.
In this case, the second light emitting layers may be formed in the same level.
In this case, the light emitting element sections may be separated from one another by a bank.
This light emitting device may be applied to a display device. This display device may be applied to various sorts of electronic instruments. This light emitting device may further be applied to various sorts of electronic instruments. A concrete example of the display device and a concrete example of these electronic instruments will be discussed later.
Next, part of materials which may be employed in the respective sections of the light emitting device of the present invention will now be
Kaneko Takeo
Koyama Tomoko
Oliff & Berridg,e PLC
Seiko Epson Corporation
Wilson Allan R.
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