Coherent light generators – Particular active media
Reexamination Certificate
2000-11-16
2002-09-24
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Reexamination Certificate
active
06456636
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 the Related Art
Electroluminesce (hereinafter referred to as “EL”) which is generated by application of strong electric field to a fluorescence body has two types, one is a current injection type EL such as a light emitting diode and another is a voltage excitation type EL. As the voltage excitation type EL, there are known a dispersion powder type EL panel in which material that is 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 and is disposed between a transparent electrode and a back electrode. The emitting color of a voltage excitation type EL element varies with a 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. Besides, fluorescent material ZnS:TmF
3
provides blue color; ZnS:TbF
3
green color; and ZnS:SmF
3
orange-red color.
Further, in recent years, an injection type EL element with two hole transporting layers and an emitting layer has been highlighted.
FIG. 11
shows a cross section of the two-layer EL element, in which on a transparent electrode (ITO)
92
, that is formed on a glass base plate
91
, are mounted a hole transporting layer
93
and an emitting layer
94
, and an upper electrode
95
is further formed thereon. Aromatic diamine derivative or polymethyl phenylsilane is used for the hole transporting layer
93
, and 8-hydroxy quinoline aluminum (Alq
3
), that is 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
functions to transport holes and to block 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 media through a light ray, recording density can be improved as recording wave length becomes shorter, therefore, it is advantageous to utilize a small light source which emits in the ultraviolet range. Further, since many fluorescent pigments emit fluorescence while absorbing ultraviolet light, if an ultraviolet plane light source is realized, it becomes possible to constitute a display panel by applying fluorescent pigment thereon. In an optical system utilizing ultraviolet light, if the emitting wavelength purity of an ultraviolet light source should be too high, it would be easy to design diffraction gratings and mirrors which are adopted to the system. As described above, latent demand for an ultraviolet light source which is easily handled is strong.
An EL element with 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 typically illustrated in
FIG. 12
, produces a broad emission spectrum.
It is therefore an object of the present invention to provide an EL element capable of emitting ultraviolet light with high wavelength purity.
It is another object of the present invention to provide a solid laser luminescent element capable of emitting in a range including the ultraviolet range.
In the present invention, a thin film made from a polymer or oligomer which is formed by directly bonding elements which are selected from Si, Ge, Sn, and Pb (those elements may be the same as each other or may be different from each other) as an emission layer of an EL element or a laser luminescent element is utilized to accomplish the above-mentioned objects. In order to cause the EL element or the laser luminescent element to efficiently emit, 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 is characterized in that a thin film made from a polymer or oligomer which is formed by directly bonding elements selected from Si, Ge, Sn, and Pb (those elements may be the same as each other or may be different from each other) is disposed between two electrodes, and at least one of the electrodes is transparent. In case of the laser luminescent element, however, it is not always necessary that one of the electrodes be transparent.
As the polymer or oligomer in which elements selected from Si, Ge, Sn, and Pb are directly bonded (those elements may be the same as each other or may be different from each other), there may be used as described below chemical formula 1, 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 as described below chemical formula 2, 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, and both of them may be the same as each other 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, and may be the same as each other 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
2
, R
3
, R
4
and R
6
, however, they are not limited to the above-mentioned groups.
Polymers consisting of four kinds of 14th group elements Si, Ge, Sn, and Pb have basically the same physical properties, so that it is possible to obtain an EL element and a laser luminescent element with emission spectrum in the ultraviolet range from polymer or oligomer in which the above-mentioned elements are exchanged with each other. Since this kind of EL element has considerably narrow emission band, it is possible to produce EL elements and laser luminescent elements with different emission wave lengths by changing the kinds of 4th group elements or a sequence of element arrangements.
It is known that the photoelectronic property of a polymer or oligomer which is formed by directly bonding elements selected from Si, Ge, Sn, and Pb (those elements may be the slame as each other or may be
Ebihara Kenzo
Kira Mitsuo
Koshihara Shinya
Miyazawa Takashi
Suzuki Toshihiro
Davie James W.
Rosenthal & Osha L.L.P.
The Institute of Physical & Chemical Research
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