Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-03-20
2004-04-27
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S504000, C428S917000
Reexamination Certificate
active
06727646
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting device using an organic light-emitting layer capable of emitting light by electrically pumping or the like and having a two-dimensional photonic band gap structure.
2. Related Art
Semiconductor light-emitting devices utilizing photonic crystals are being studied in recent years (for example, Japanese Patent Application Laid-open No. 9-232669). These types of semiconductor light-emitting devices are expected to produce a resonator which can firmly confine light within crystals and to provide coherent light at an extremely high efficiency.
However, when a semiconductor is used, a boundary area of unit medium layers (each one unit in the periodical structure) becomes irregular and is affected by impurities because in semiconductors the unit medium layers are formed by crystals. It is thus difficult to obtain a uniform periodical structure and to produce a high performance light-emitting device having superior characteristics as photonic crystals. In addition, when a semiconductor is used, there is a limitation to the combination of materials with different refractive indices.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a light-emitting device which can produce light with a narrow spectrum width with remarkably high efficiency and can be manufactured from an organic light-emitting material utilizing a two-dimensional photonic band gap.
The light-emitting device as the first aspect of the present invention comprises:
an optical section having a two-dimensional periodical refractive index distribution and capable of forming a photonic band gap;
a defect section formed on part of the optical section and designed so that the energy level caused by the defect is within a prescribed emission spectrum; and
an organic light-emitting layer.
The light-emitting device has an organic light-emitting layer capable of emitting light by electrically pumping or optical pumping. For example, when the electrically pumping is used, electrons and holes are injected into the organic light-emitting layer respectively from a pair of electrode layers (cathode and anode). Light is emitted when the molecules return to the ground state from the excited state by recombination of the electrons and holes in the organic light-emitting layer. At this time, light with a wavelength in the photonic band gap of the above optical section cannot be transmitted through the optical section. Only the light with a wavelength equivalent to the energy level caused by the defects can be transmitted through the optical section. Therefore, light with a very narrow emission spectrum width with inhibited spontaneous emission in two dimensions can be obtained at high efficiency by specifying the width of energy level caused by the defect.
Any materials can be used for the optical section in the present invention insofar as the materials have a two-dimensional periodical refractive index distribution and are capable of forming a photonic band gap. The optical section may have a structure such as a grating-shaped structure, a multi-layer structure, a column or other columnar-shaped structure, or combinations of these structures.
The defect section of the organic light-emitting layer and the optical section may have the following configurations.
(1) The organic light-emitting layer formed in the defect section also functions as the defect section.
(2) The organic light-emitting layer also functions as part of the defect section and as one type of medium layer of the optical section.
More particularly, the light-emitting device may have the following structure.
(A) The light-emitting device as the second aspect of the invention comprises:
a first optical section having a periodical refractive index distribution in a first direction and being capable of forming a photonic band gap;
a second optical section having, a periodical refractive index distribution in a second direction which is perpendicular to a first direction, the second optical section being capable of forming a photonic band gap; and
a defect section formed in at least one of the first and second optical sections and designed so that the energy level caused by the defect is within a prescribed emission spectrum; and
an organic light-emitting layer.
Light with a very narrow emission spectrum width with inhibited spontaneous emission in two-dimensions can be obtained at high efficiency by the combination of the first optical section which inhibits propagation of light in a first direction (X direction) and the second optical section which inhibits propagation of light in a second direction (Y direction).
(B) The light-emitting device as the third aspect of the invention comprises:
an optical section having a periodical refractive index distribution in first and second directions and capable of forming a two-dimensional photonic band gap;
a defect section formed on the optical section and designed so that the energy level caused by the defect is within a prescribed emission spectrum; and
an organic light-emitting layer,
wherein the optical section includes columnar-shaped first medium layers arranged in a square lattice shape and second medium layers formed between the first medium layers.
light with a very narrow emission spectrum width with inhibited spontaneous emission in two dimensions and two-directions can be obtained at high efficiency by the columnar-shaped first medium layers arranged in a square lattice shape and second medium layers formed between the first medium layers.
(C) The light-emitting device as the fourth aspect of the invention comprises:
an optical section having a periodical refractive index distribution in first, second and third directions and capable of forming a two-dimensional photonic band gap;
a defect section formed on part of the optical section which is designed so that the energy level caused by the defect is within a prescribed emission spectrum; and
an organic light-emitting layer.
light with a very narrow emission spectrum width with inhibited spontaneous emission in two dimensions and three-directions can be obtained at high efficiency by the optical section having a periodical refractive index distribution in first, second and third directions and capable of forming a two-dimensional photonic band gap, such as an optical section including columnar-shaped first medium layers arranged in a triangular lattice or a honey-comb lattice and second medium layers formed between the first medium layers.
(D) The light-emitting device as the fifth aspect of the invention comprises:
an optical section having a concentric and periodical refractive index distribution and capable of forming a two-dimensional photonic band gap;
a defect section formed on the optical section and designed so that the energy level caused by the defect is within a prescribed emission spectrum; and
an organic light-emitting layer,
wherein the optical section includes columnar-shaped first medium layers arranged regularly and second medium layers formed between the first medium layers.
This structure of the optical section inhibits spontaneous emission in the directions of two dimensions.
In the above described light-emitting device the organic light-emitting layer has materials which can emit light by electrically pumping and the light-emitting device may comprise a pair of electrode layers for applying an electric field to the organic light-emitting layer.
Preferably, the light-emitting device in these aspects of the invention further comprises at least one of a hole transport layer or an electron transport layer.
The use of an organic light-emitting layer has the following advantages over the case in which the photonic band gap is formed by a semiconductor. Specifically, the light-emitting device comprising the organic light-emitting layer is less affected by the irregular state and impurities of the boundary area of the light-emitting layer than the case of using semiconductors, whereby excellent characteristics from the photonic band ga
Kaneko Takeo
Koyama Tomoko
Patel Ashok
Seiko Epson Corporation
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