Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
1997-02-20
2001-03-20
Davie, James W. (Department: 2881)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
C372S039000
Reexamination Certificate
active
06204514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ultraviolet electroluminescent element and a laser luminescent element capable of emitting in ultraviolet range.
2. Description of Related Art
Electroluminesce (hereinafter referred to as “EL”) which is generated by the application of a strong electric field to a fluorescence body has two types. One type is a current injection type EL, such as a light emitting diode. The other is a voltage excitation type EL. As voltage excitation type EL, a dispersion powder type EL panel in which material obtained by dispersing fine fluorescence powder into a synthetic resin or a glass powder is disposed between a transparent electrode and a back electrode, and a double insulation film EL panel in which a film-shaped fluorescent body emitting layer, made by vacuum evaporation or spattering method is completely covered by a dielectric insulating layer, is disposed between a transparent electrode and a back electrode are known. The emitting color of a voltage excitation type EL element varies with fluorescent material. A fluorescent material obtained by adding 0.3 to 0.5 weight percents of manganese to zinc sulfide (ZnS:Mn) provides yellow-orange color; SrS:Ce blue color, CaS:Ce or CaS:Er green color; and CaS:Eu red color. Fluorescent material ZnS:TmF
3
provides blue color; ZnS:TbF
3
green color; and ZnS:SmF
3
orange-red color.
In recent years, an injection type EL element with two layers of a hole transporting layer and an emitting layer has been highlighted.
FIG. 11
shows a cross-section of the two-layer EL element in which a hole transporting layer
93
and an emitting layer
94
are mounted on a transparent electrode (ITO)
92
, formed on a glass baseplate
91
, and an upper electrode
95
is formed thereon. Aromatic diamine derivative or polymethyl phenylsilane is used for the hole transporting layer
93
, and 8-hydroxy quinoline aluminum (Alq
3
), an emitting metal complex, is used for the emitting layer
94
. The upper electrode
95
is an electrode in which Mn and Ag are laminated. The hole transporting layer
93
transports holes and blocks electrons, which prevents the electrons from being transported to the electrode without rebonding with the holes.
When the EL element shown in
FIG. 11
is operated in continuous direct current mode under the condition of positive ITO and forward bias, a bright green emission color is generated.
FIG. 12
shows the emitting spectrum of the EL element and Alq
3
. In this figure, a solid line shows the spectrum of the EL element and a dotted line shows the spectrum of Alq
3
. The spectrum of the EL element coincides with that of Alq
3
, so that the EL is from Alq
3
[Polymer Preprints, Japan, 40(3), 1071(1991); Applied Physics Letter, 59(21), 2760].
In a paper “Polymer Preprints” [Polymer Preprints, Japan, 44(3), 325 (1995)] is stated that polysilane with oxygen bridge formation structure emits in an electrical field. According to the paper, polymethyl phenylsilane (PMPS) is painted on an ITO base plate and is bridged under heat, and then single-layer EL element with ITO/bridged PMPS/Al structure to which Al is evaporated emits in the electrical field with emission energy center of 1.8 eV. It is stated, in this paper, that normal polysilane without oxygen bridge formation structure does not emit.
SUMMARY OF THE INVENTION
In optical recording to record data to a recording medium through a ray, recording density can be improved as the recording wave length becomes shorter. Therefore, it is advantageous to use a small light source which emits in the ultraviolet range. Further, since many fluorescent pigments emit fluorescence while absorbing ultraviolet rays, if an ultraviolet plane light source is realized, it becomes possible to form a display panel by applying fluorescent pigments thereon. In an optical system using ultraviolet rays, if the emitting wave length purity of an ultraviolet ray source is high, it would become easy to design diffraction gratings and mirrors adopted to the system. Demand for such an ultraviolet ray source is strong.
An EL element with an emission spectrum in the visible range is already known as described above. However, no EL element emitting in the ultraviolet range is known. Besides, a conventional EL element is, as illustrated in
FIG. 12
, provided with a broad emission spectrum.
It is therefore an object of the present invention to provide an EL element capable of emitting ultraviolet rays with high wave length purity.
It is another object of the present invention to provide a solid laser luminescent element capable of emitting in a range that includes the ultraviolet range.
In the present invention, a thin film made from a polymer or an oligomer, which is formed by directly bonding elements selected from Si, Ge, Sn, and Pb (those elements may be the same as or different from each other) and used as an emission layer of an EL element or a laser luminescent element, accomplishes the above-mentioned objects. In order to cause the EL element or the laser luminescent element to emit efficiently, the polymer or oligomer needs to have six or more atoms in a main chain structure.
That is, the EL element or the laser luminescent element, according to the present invention, includes a thin film made from a polymer or an oligomer formed by directly bonding elements selected from Si, Ge, Sn, and Pb (those elements may be the same with each other or may be different from each other) and disposed between two electrodes. At least one of the electrodes is transparent. In the laser luminescent element, however, it is not always necessary for one of the electrodes to be transparent.
As a polymer or an oligomer in which elements selected from Si, Ge, Sn, and Pb are directly bonded (those elements may be the same as or different from each other), chemical formula 1 may be used as follows:
polymer or oligomer in which elements selected from Si, Ge, Sn, and Pb are the same as each other, and the elements are directly bonded, or chemical formula 2 may be used as follows:
polymer or oligomer in which elements selected from Si, Ge, Sn, and Pb are different from each other, and the elements are directly bonded.
Here, M represents Si, Ge, Sn, or Pb, and R
1
and R
2
represent substituents of the aforementioned elements. Both of them may be the same as or different from each other. Alkyl group, allyl group, phenoxy group, alkoxyl group, alkylamino group, alkylthio group, alcoholic hydroxy group or the like may be selected as R
1
and R
2
. However, they are not limited to the above-mentioned groups.
Here, M
1
and M
2
represent Si, Ge, Sn, or Pb, and R
3
, R
4
, R
5
, and R
6
represent substituents of the aforementioned elements. Both of them may be the same as or different from each other. Alkyl group, allyl group, phenoxy group, alkoxyl group, alkylamino group, alkylthio group, alcoholic hydroxy group or the like may be selected as R
1
and R
2
. However, they are not limited to the above-mentioned groups.
A polymer of any one of the four kinds of 14th group elements Si, Ge, Sn, and Pb basically has the same physical properties. So that it is possible to obtain an EL element and a laser luminescent element with an emission spectrum in the ultraviolet range from a polymer or an oligomer in which the above-mentioned elements are exchanged with each other. Since this kind of EL element has a narrow emission band, it is possible to produce EL elements and laser luminescent elements with different emission wave lengths by changing the kinds of 14th family elements or the sequence of elements.
It is known that the photoelectronic property of a polymer or an oligomer formed by directly bonding elements selected from Si, Ge, Sn, and Pb (those elements may be the same as or different from each other) strongly depends on the structure of the main chain. It is possible to control, more or less, the main chain structure through a substituent. Therefore, the selection of the substituent permits the property as an EL element or a laser lu
Ebihara Kenzo
Kira Mitsuo
Koshihara Shinya
Miyazawa Takashi
Davie James W.
Pillsbury Madison & Sutro LLP
The Institute of Physical and Chemical Research
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