Coherent light generators – Particular active media – Insulating crystal
Reexamination Certificate
1999-11-22
2001-07-17
Healy, Brian (Department: 2874)
Coherent light generators
Particular active media
Insulating crystal
C372S012000, C372S013000, C372S040000, C372S043010
Reexamination Certificate
active
06263006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electroluminescent solid state devices, and more particularly, to an electroluminescent solid state device having a single crystalline metal oxide that is doped with one or more rare earth elements, and an oxygen and/or fluorine co-activator atom.
2. Description of the Related Art
Solid state electroluminescent devices generally include a body of a single crystalline material that emits electromagnetic radiation when an electrical bias is placed across the body. The body generally includes means for causing the excitation of electrons in order to generate the radiation. Such means can include a PN junction within the body, or a metal insulator n-type semiconductor (m-i-n) structure. The wavelength of the generated radiation is dependent on the composition of the material that comprises the body, including any dopants that are in the material.
Although early electroluminescent devices consisted of polycrystalline semiconductors, electroluminescent devices have been made from single crystalline semiconductor materials, particularly the group III-V compounds, and alloys thereof. It is known that doping a semiconductor with a rare earth element, such as erbium or terbium, provides a device that can generate radiation at a wavelength that is highly suitable for optical transmission purposes. However, it has been found that semiconductor devices that are doped with a rare earth element are not particularly efficient.
The concept of doping a transparent material with a rare earth element is known, for example, in U.S. Pat No. 5,262,365 to Oyobe et al. This patent provides a silica-based glass that is doped with a rare earth element, aluminum, and fluorine. Oyobe seeks to avoid the crystallization problem that occurs when silica glass is co-doped with a rare earth element and aluminum. A SiO
2
host glass is doped with the rare earth element erbium, or neodymium, aluminum, and fluorine. The glass composition of this patent is expressed by a glass matrix of a R
2
O
3
Al
2
O
3
SiO
3
system, wherein R represents a rare earth element, and fluorine doping is conducted by substituting the oxygen of the system with fluorine.
The use of a doped crystal to form a laser is known. For example, U.S. Pat. No. 5,299,218 to Ban et al describes a blue light laser having the three embodiments shown in FIGS. 1-2, FIG. 3, and FIG. 4. In FIGS. 1-2, an active layer is activated by electrons that are emitted by tips that are within a field emission tip array. This array is energized by an electrostatic field application apparatus. The electrons pass through a vacuum space, and then impact the active layer. This active layer may be a doped alkali halide crystal, i.e. NaI doped with Tl (NaI:Tl), LiI:Eu, or CsI:Tl, or the active layer may be an un-doped alkali halide crystal, i.e. NaI, or the active layer may be an anthracene crystal, a trans-stilbene crystal, or the like. In the FIG. 3 embodiment, the active layer is a fiber that acts as a light waveguide. The remainder of the FIG. 3 device is the same as FIGS. 2, 3. This active layer is formed by crystal growth of anthracene. In the FIG. 4 embodiment, the active layer is an alkali halide doped, or undoped crystal, or an organic crystal and the remainder of the structure is the same as the FIGS. 1, 2 embodiment.
Also of general interest relative to wavelength tuning is U.S. Pat No. 5,425,039 to Hsu et al wherein a tunable, single frequency, fiber optic laser is provided having an erbium:yttererbium phosphate glass fiber, or erbium:ytterbium phospho-silica glass fiber. A rare earth ion doped glass fiber is also mentioned. Wavelength tuning is achieved by temperature variation of laser gain cavity length, or by electromechanical variation of laser gain cavity length. Electromechanical tuning with a PZT transducer is also mentioned.
While prior devices have been generally useful for their limited intended purposes, it would be desirable to have an electroluminescent device that is doped with a rare earth element to achieve radiation at the desired wavelength, but which is formed of a material that provides greater efficiency to the device.
SUMMARY OF THE INVENTION
The present invention is directed to an electroluminescent solid state device that includes a single crystalline metal oxide body that is doped with one or more rare earth elements, and with oxygen and/or fluorine. Electron activation means are provided for injecting kinetic electrons into the body in order to generate radiation within the body.
This invention provides an electroluminescent device (
10
of
FIG. 2
) having a body of single crystalline metal oxide (
20
of
FIG. 2
) that is doped with one or more rare earth elements and with oxygen and/or fluorine, in combination with a means (
24
of
FIG. 2
) for injecting kinetic electrons into the body in order to generate radiation within the body.
In one embodiment of the invention, the two opposite ends of the elongated body of single crystalline metal oxide are parallel and are mirror polished to form a Fabry-Perot cavity, and thus provide for the body's coherent electromagnetic radiation output.
In another embodiment of the invention, an acoustic wave generator (
200
of
FIG. 4
) is provided on the body of single crystalline metal oxide in order to launch acoustic waves that travel back and forth down the length of the body. In this embodiment, the frequency of energization of the acoustic wave generator operates to control the wavelength of the body's coherent electromagnetic radiation output.
An object of this invention is to provide an excitation means (for example, a cold cathode excitation means), for impact exciting a single crystalline metal oxide body with electrons to thereby generate radiation within the body. The body is arranged to emit the generated radiation from a surface thereof. The body comprises a Fabry-Perot cavity, or the body is provided with a piezoelectric structure (see
FIG. 5
) that sends acoustic waves through the body in a manner to define the emission wavelength of the device.
In an embodiment of the invention, the body comprises single crystalline aluminum oxide that is doped with a rare earth element, such as erbium and/or terbium and with oxygen and/or fluorine.
The rare earth element is essential to the production of electromagnetic, or light emission from the metal oxide body, and the oxygen and/or fluorine atoms attach to the atoms of the rare earth element(s) and operate to put the rare earth element(s) into a 3+ state that is needed for emission to occur.
When the doped metal oxide body is impacted with kinetic electrons, energy is provided to one of the remaining electrons of the rare earth element(s), promoting the rare earth element(s) to a higher energy “excited” state, and emitting the difference energy between the “excited” state and a ground state as radiation.
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patent: 4081763 (1978-03-01), Vlasenko et al.
patent: 4093852 (1978-06-01), Olive et al.
patent: 4136435 (1979-01-01), Li
patent: 4371406 (1983-02-01), Li
patent: 5262365 (1993-11-01), Oyobe et al.
patent: 5299218 (1994-03-01), Ban et al.
patent: 5425039 (1995-06-01), Hsu et al.
patent: 5596671 (1997-01-01), Rockwell, III
patent: 6067308 (2000-05-01), Leksono et al.
Article entitled “Photoemission from GaN” By J. I. Pankove et al.,Applied Physics Letters, Jul. 1, 1974, No. 1, vol. 25, pp. 53 et seq.
Astralux, Inc.
Hancock E. C.
Healy Brian
Holland & Hart LLP
Sirr F. A.
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