CA2227461C - Doped amorphous and crystalline gallium oxides, alkaline earth gallates and doped zinc germanate phosphors as electroluminescent materials - Google Patents

Abstract

New oxide phosphors based on doped gallium oxides, alkaline earth gallates a nd germanates for electroluminescent display materials. Bright orange red electroluminescence has been obtained in amorphous and crystalline oxides Ga2O3:Eu for the first time. SrGa2O4 and SrGa4O9 doped with 1-8 mole % of Eu and Tb, CaGa2O4, Ca3Ga2O6 and CaGa4O7 doped with 1-4 mole % of Eu, Tb, Pr and Dy, BaGa2O4 doped with 1-2 mole % of Eu and Tb, have been prepared using RF magnetron sputtering onto ceramic dielectric substrates and annealed at 600 .degree.C - 950 .degree.C in air or Ar for 1-2 hours. Bright electroluminescent (EL) emission was obtained with wavelengths covering the visible sprectrum from 400 to 700 nm, and infrared emission above 700 nm wit h spectral peaks characteristic of rare earth transitions. The films of CaGa2O4 with 1 mole % Eu achieved 22 fL (75 cd/m2) at 60 Hz and had a maximum efficiency of 0.2 lm/w for red emission. An amorphous thin film of Ca3Ga2O6 with 2 mole % Eu achieved 34 fL in red EL at 60 Hz when annealed at 600 .degree.C. SrGa2O4 with 1 mole % Eu and 4 mole % Tb yielded "white" phosphor having red, green and blu e emission (13 fL at 60 Hz), and SrGa2O4 with 8 mole % Tb resulted in a blue and green phosphor measuring 30 fL at 60 Hz. Zn2Si0.5Ge0.5O4 containing Mn was sputtered using magnetron RF sputtering onto ceramic dielectric substrates and annealed at 700 .degree .C for 1 hour in air or argon. Bright green (540 nm) emission was obtained in electroluminescence: 110 fL (377 cd/m2) at 60 Hz with a maximum efficiency of 0.9 l/w. Moderately bright red emission (640 nm) was also obtained.

Description

DOPED AMORPHOUS AND CRYSTALLINE GALLIUM OXIDES, ALKALINE
EARTH GALLATES AND DOPED ZINC GERMANATE PHOSPHORS AS
ELECTROLUMINESCENT MATERIALS
FIELD OF THE INVENTION
The present invention relates to new phosphor materials exhibiting electroluminescence based on gallium oxide and methods for their production. More particularly, the invention relates to rare earth doped amorphous and crystalline alkaline earth gallate phosphors and rare earth doped amorphous and crystalline gallium oxide and methods for making these materials. The present invention also relates to new doped germanium oxide, ZnZSiXGe,-X04:Mn for use as electroluminescent display materials.
BACKGROUND OF THE INVENTION
Electroluminescence (EL) occurs by the emission of light from a phosphor in response to a sufficiently high electric field developed across the phosphor. Phosphor refers to those materials which emit light in response to the application of a field across the material. Thin film electroluminescent devices have a basic structure comprising a phosphor film or layer sandwiched between two electrodes. EL laminates are typically made by depositing the various layers onto a substrate such as quartz or glass, first a reflective metal layer onto the substrate onto which an insulating dielectric layer is deposited. The phosphor layer is then deposited onto the dielectric layer and then an optically transparent electrode, typically a transparent conducting oxide such as ITO is deposited onto the top surface of the phosphor layer. Application of an effective voltage between the two electrodes produces the electric field strength required to induce electroluminescence in the phosphor. The role of the dielectric layer is to reduce the voltage drop across the phosphor layer to avoid dielectric breakdown of the phosphor.
There is strong commercial interest to achieve the full spectral range in electroluminescent phosphors for visible display application and in particular for making colour flat panel displays. Sulphide phosphors are well known as efficient light emitters in electroluminescence as discussed in T.
Inoguchi, M. Takeda, Y. Kakihara, Y. Nakata, M. Yoshida, SID'74 Digest, p.
SUBSTITUTE SHEET (RULE 26) 84-85, 1974. These include ZnS:Mn and SrS:Ce. A significant drawback to these phosphors is that they are moisture sensitive and are prone to reacting with oxygen especially when electrically driven. Known electroluminescent materials being studied include materials such as SrS:RE, see W.A.Barrow, R.E. :.overt, C.N. King, Gigesi -i98~ Sliiinternational Symposium, Los Angeles, p. 249, SrGa2S4:RE and CaGa2S4:RE as disclosed in W.A. Barrow, R.C. Convert, E. Dickey, C.N. King, C. Laakso, S.S. Sun, R.T Tuenge, R.
Wentross, Digest 1993 SID International Symposium, Seattle, p. 761; W.
Halverson, T. Parodos, P. Colter, Display Phosphors Conference, San Diego, Nov.13-16, 1995, p.115; S.S. Sun, E. Dickey, R. Tuenge, R. Wentross, Display Phosphors Conference, San Diego, Nov.13-16, 1995, p.119; T. Yang, M. Chaichimansour, W. Park, B.K. Wagner, C.J. Summers, Display Phosphors Conference, San Diego, Nov.13-16, 1995, p.123; and T.S. Moss, D.C. Smith, J.A. Samuels, R.C. Dye, Display Phosphors Conference, San Diego, Nov.13-16, 1995, p.127. While these materials do achieve red, green and blue emission, the gallium based sulphides suffer from low brightness, difficulty of preparation and stability problems.
It has recently been demonstrated that in the gallate based family of materials, ZnGa204:Mn could achieve bright and stable electroluminescence, see T. Minami, S. Takata, Y. Kuroi, T. Maeno, Digest 1995 SID International Symposium, Orlando, p. 724; and T. Minami, Y. Kuroi, S. Takata, Display Phosphors Conference, San Diego, Nov.13-16, 1995, p.91. They obtained good green emission (200 cdlmz at 60 Hz at up to 0.9 Qmlw) but only obtained 0.5 cd/m2 blue, and 11.0 cd/m2 red at a drive frequency of 1000 Hz, which are not practical brightness values for a display by replacing Mn with Ce and Eu, respectively. They annealed these phosphor materials at 1020°C in argon.
More recently, Minami et al. have doped ZnGa204 with chromium to generate a better red phosphor, claiming 120 cd/m2 at 1000 Hz, as disclosed in T. Minami, Y. Kuroi, S. Takata, T. Miyata, presented at Asia Display'95, Oct. 16-18, Hamamatsu. However it is not feasible, to achieve full colour in ZnGa204 since rare earths are not compatible with this host lattice due to the size mismatch between Zn or Ga and the rare earth ions.
In the binary gallium oxide based system, (3-Gaz03 has the 8-alumina type structure with two different Ga sites, one in tetrahedral coord>,naticn and th~other in cctahedrai-coordtrration. High temperature heat treated (i-Ga203 is known to exhibit bright broad-band photoluminescence under 254 nm UV irradiation and cathodoluminescence between 340 and 650 nm as disclosed in W. C. Herbert, H. B. Minnier and J. J. Brown, Jr., J.
Electrochem. Soc. vol. 116, pp. 1019-1021 (1969). ~i-Ga203:Cr, the gallium analog of ruby, has been studied as a potential red to infrared tunable laser material because of the broad-band emission between 650 and 950 nm that is associated with the °T2 - °AZ transition of the Cr3+ ion in the octahedral site, see for example H. H. Tippins, Phys. Rev. vol. 137, pp. A865-A871 (1965), and D. Vivien, B. Viana, A. Revcolevschi, J. D. Barrie, B. Dunn, P. Nelson and 0. M. Stafsudd, J. Lum. vol. 39, pp. 29-33 (1987).
Even though there exists a significant difference in ionic radii of the rare earth ions and Ga3+, Ga203:Dy was reported to be a reasonably efficient photoluminescent phosphor with characteristic narrow Dye" fines in the blue (470-500 nm) and the yellow (570-600 nm) regions, see W. C.
Herbert, H. B. Minnier and J. J. Brown, J. Electrochem. Soc. vol. 115, pp.104 105 (1968). Other common rare earth dopants such as Eu3+ and Tb~, however, did not show efficient PL emission in (i-Ga203, see J. L. Sommerdijk and A. Bril, J. Electrochem. Soc. vol 122, pp. 952-954 (1975). Sommerdijk also disclosed the solubility of Dye in (3-Gaz03 to be only about 1 %. W. C.
Herbert, H. B. Minnier and J. J. Brown, J. Electrochem. Soc. vol. 115, pp.104-105 (1968) disclosed that maximum PL brightness occurred in the range of 5-10% (mole per cent) Dy concentration. The mechanism of the rare earth activation is still not clear.
Recently it has been demonstrated that Zn2Si04:Mn could achieve electroluminescence, see T. Miyata, T. Minami, Y. Honda and S.
Takata, SID '91 Digest, p. 286-289, 1991. Thin films were RF magnetron sputtered onto polished BaTi03 substrates using the method disclosed in T.
Minami, T. Miyata, S. Takata, I. Fukuda, SID'92 Digest, p. 162. A good brightness of 200 cd/m2 was achieved at fi0 Hz with an efficiency of 0.8 pmlW. A drawback to these films is that they had to be annealed at 1000°C
for s~ve~a~ aou~ s;-which severely limitsuheir applicability to practical substrates for displays.
As mentioned above, a major drawback to known electroluminescent materials is the need for post fabrication high temperature annealing (in the vicinity of 1000°C) of the films to produce electroluminescent behaviour. This need for high temperature treatment results in severe restrictions in the choice of substrates with only a limited number being available for use under these conditions. High temperature annealing also increases the cost of producing EL films rapidly on a large scale. Another limitation of many electroluminescent materials is that they are restricted to emitting at particular wavelengths or in a relatively narrow wavelength range, such as yellow ZnS:Mn or blue-green SrS:Ce which are not ideal for color displays that requires emission in the red, green and blue parts of the visible spectrum. Electroluminescent materials based on sulphides inherently suffer from chemical stability problems such as oxide formation (since oxides are generally thermodynamically more stable than sulphides) which changes the electronic properties of the material over time.
The classic EL phosphor, ZnS:Mn, is yellow and has a peak wavelength of 580nm. However, while it may be filtered red and green, most of the light is lost because only < 10% of the light is passed through the red and green filters. Similarly, a drawback of SrS:Ce, which is green-blue, is that only about 10% of the light is passed through a blue filter.
In the rare-earth doped oxides, narrow peaks that are red, green or blue result from dopants Eu+3 or Tb+3 so that little or no light is generated at wavelengths that are positioned in the visible spectrum away from the desired red, green and blue wavelengths.
It would therefore be very advantageous to provide a method of producing new electroluminescent materials which can be deposited at temperatures well below 1000°C thereby avoiding the requirement for high temperature annealing. It would also be advantageous to provide new electroluminescent materials which emit over a broader portion of the visible spectrum than known EL materials. More specifically it would be very advantageous to provide a white phosphor, and phosphors with red, green and blue emission.
Poort et al. CChem. Mat. (1995), 7(8), 1547-51 ) discloses photoluminescence properties of alkaline earth aluminates with and without gallium, namely Ba,_XSr,~Al2-yGay04:Eu+2 with x=0, 0.5, 1 and y=0, 1 and 2.
For both Ba and Sr compounds, in the absence of AI no photoluminescence was observed. When part of the gallium is replaced by aluminum, Eu'Z
photoluminescence was observed. EPA 490,621 discloses Zn2SiX Ge,_x04:Mn for use in cathode ray tubes or luminescent discharge lamps, i.e cathodoluminescence (CL) and photoluminescence (PL).
It would also be advantageous to provide a method of producing new EL materials that are chemically stable and do not react appreciably with water or oxygen and provide stable EL performance in which the brightness is maintained substantially constant during operation. Known color phosphors such as SrS:Ce and other sulphides are not stable in these respects.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide new electroluminescent materials based on oxides of gallium and germanium which exhibit electroluminescent behaviour over the visible portion of the electromagnetic spectrum useful in color electroluminescent flat panel displays. It is also an object of the present invention to provide a method of producing these new films which does not require post production high temperature annealing of the films in order to achieve electroluminescent behaviour.
A significant commercial advantage of the present invention is AMENDED SHfFT

that several new germanium and gallium oxide based electroluminescent materials and devices based thereon have been produced onto substrates at low temperatures and excellent electroluminescent behaviour has been obtained without the need for high temperature annealing as is common in other known systems. As deposited films of Ga203:Eu and films of Ca3Ga206:Eu and Zn2Ge04:Mn annealed at temperatures as low as 600°C
exhibit excellent electroluminescent properties. Therefore a very significant advantage of the present invention is that the new electroluminescent materials can be deposited onto a wide variety of substrates not normally useable as substrates for EL materials with those known oxide EL materials requiring high temperature annealing to produce electroluminescence.
Another commercially significant advantage of the present invention is that it provides new electroluminescent materials characterized as green, red and white phosphors which exhibit electroluminescence over the visible spectrum rather than emissions centred around a specific wavelength region, such as the yellow regions alone.
The inventors report for the first time electroluminescence of amorphous and crystalline Eu-doped gallium oxide, Ga203:Eu, and other related systems. In one aspect of the present invention, there is provided films of doped amorphous and crystalline gallium oxides, Ga203:Eu and Ga203:n,%Eu,n2%Cd exhibiting bright orange red electroluminescence where n,% is the mole percent amount of Eu present in Gaz03 and spans the range in which Eu is soluble in Ga203, and n2% is the mole percent amount of Cd present in Ga203 and spans the range in which Cd is soluble in Ga203.
The present invention also provides new gallate based oxides such as CaGa204, SrGa204 and BaGa204 which have been prepared in such a way as to exhibit superior electroluminescent properties including EL
efficiencies and brightnesses. The invention also provides other calcium and strontium gallates such as Ca3Ga206, CaGa40, and Sr3Ga409 which are also found to exhibit excellent EL. The structures of SrGa204 and BaGa204 are stuffed tridymite and that of CaGa204 is orthorhombic. The other two calcium RMENDEfl StiEEI

gallates, Ca3Ga206 and CaGa~O,Y crystallize in orthorhombic and monoclinic forms, respectively. Rare earth dopants are generally soluble in Sr, Ca and Ba compounds.
Specifically, CaGa2C~~:n%RE is provided wherein RE is a rare earth dopant selected from the group consisting of Eu, Tb, Pr and combinations thereof, r~% is the mole percent of RE present in CaGa204, and spans the range in which the rare earths are scalubie in CaGa20a.
Ca3Ga206:n%RE is provided wherein RE is a rare earth dopant selected from the group consisting of Eu and 'Tb and combinations thereof, n% is the mole percent of RE present in Ca3Ga2Q°, and spans the range in which the rare earth) are soluble in Ca3Ga~Ofi. CaGa~f~.,:n~'/oRE is provided wherein RE is a rare earth dopant selected from the group consisting of Eu, Dy , Tb and combinations thereof, n% is the mole percent oaf RE present in CaGa40,, and spans the range in which said rare earths are soluble in CaGa4Q, Sr3Ga409:n%Tb is another new electroluminescent phosphor wherein n% is the mole percent of Tb and spans the range in which Tb is soluble in Sr3Ga409.
The present invention provides a method for producing new electroluminescent zinc silicate-germinate films at lower annealing temperatures thereby permitting the use of more practical substrates. In this aspect of the invention there is provided a method of producing electroluminescent films at temperatures in the vicinity of 700°C. The process comprises replacing Si by Ge in Zn,SiCJ~:Mn filrrrs to produce films of Zn2SixGe,_x04:Mn exhibiting electroluminescence.
The present invention provides a n~eth~od of producing electroluminescence comprising providing an electroluminescent phosphor and applying a voltage across the electroluminescent phosphor. The electroluminescenl: phosphor may be any one c~f Ga~03:n%RE, wherein RE is a rare earth dopant selected from the group consisting of Eu, Dy and combinations thereof; Ga~03:n.,%Eu,n2c%C;d Sr~~aACJ~:n%RE wherein RE is a rare earth dopant selected from the group consisting of Eu, Tb and combinations thereof CaGa?O~:naI~RE wherein i~E is a rare earth dopant selected from the group consisting of Eu, Tb, Pr and combinations thereof;
BaGa204:n%RE, wherein RE is a rare earth dopant selected from the group consisting of Eu, Tb, and combinations thereof; Ca~Ga206:n%RE, wherein RE
is a rare earth dopant selected from the group consisting of Eu and Tb and combinations thereof; CaGa~,G;:n"J°RE wherein RE is a rare earth dopant selected from the group consisting of Eu, Dy, Tb and combinations thereof;
Sr3Ga409:n%Tb, wherein n% is the mole percent of Tb; Zn2SiX Ge,,_x04:n%Mn, wherein n% is the mole percent Mn in Zn~SiX Ge~_XG~ and x varies in the range from 0 < x < 1Ø
The present invention provides electroluminescent devices comprising a dielectric substrate having a conducting back electrode on a back surface thereof; an electroluminescent phosphor on a front surface of the dielectric substrate. A transparenfi electrode is deposited onto a top surface of the phosphor and means for applying a voltage between the transparent electrode and the conducting back electrode to develop an electric field across the phosphor.The phosphor may be Ga203:n%RE, wherein RE is a rare earth dopant selected trorrr the group consisting of Eu and Dy; Ga20~:n,%Eu,n2%Cd, wherein rr5% is the mole percent amount of Eu present in Ga203 and spans the range in which Eu is soluble in Ga2G3, and n2% is the mole percent amount of Cd present in Ga203 and spans the range in which Cd is soluble in Ga2G~ but not exceeding 14.3°!°, SrGa20~:n%RE
wherein RE is a rare earth dopant selected from the group consisting of Tb and combinations of Tb and Eu; CaGa~G~:n%RE wherein RE is a rare earth dopant selected from the group consisting of Eu, Tb, Pr and combinations thereof; BaGa204:n%RE, where RE is a rare earth dopant selected from the group consisting of Eu, Tb, and combinations thereof; Ca~GazO6:n%RE, where RE is a rare earth dopant selected frorr~ ~l:he group consisting of Eu and Tb and combinations thereof; CaGa~G-:n%RE: where RE is a rare earth dopant selected from the group consisting of Eu, Dy, Tb and combinations thereof; Sr3Ga40g:n%Tb, where n°!° is the mole percent of Tb;
Zn2SiX Ge,_x04;n%Mn, where n% is mole percent of Mn in Zn2Six Ge,_X04 and x varies in the range from 0 ~_ x <1.G.

BRIEF DESCRIPTION OF THE DRAWINGS
The new phosphor materials exhibiting electroluminescent behaviour forming the present invention will now be described, by way of example only, reference being had to the accompanying drawings, in which:
Figure 1 is a side view of an EL device structure using a commercial barium titanate substrate produced by AVX Corp.;
Figure 2 is a plot of brightness versus applied voltage of several thin films (8000A) of Ga203:2% Eu each annealed at the temperature indicated for one hour;
Figure 3 is a plot of the voltage dependancy of the electroluminescence efficiency for the thin film samples of Figure 2;
Figure 4 illustrates the x-ray diffraction patterns of Ga203:1 %Eu thin films deposited on Si and annealed at the different temperatures shown;
Figure 5 compares the electroluminescence spectra of Ga203:2% Eu thin films annealed at the indicated temperatures;
Figure 6 is a plot of the voltage dependence of both the efficiency and brightness of a device fabricated from Gaz03:2% Eu sputtered in a gas mixture of 5% Oz and 5% NZ in argon (Ar), followed by annealing in Ar at 950°C for 1 hour;
Figure 7 is a plot the EL spectra for two Ga203:1 %Dy films annealed at the indicated temperatures for 1 hour illustrating the presence of deep red emissions similar to the samples of Figure 5, attributed to to the emission of the ~-Ga203 host lattice;
Figure 8 shows the X-ray diffraction patterns of thin films sputtered from a CdGa204:0.5%Eu target and annealed at the indicated temperatures for one hour;
Figure 9 shows the electroluminescent brightness and efficiency for Ga203:0.5%Eu,Cd thin films annealed at 800°C for one hour;
Figure 10 compares the electroluminescent spectra (intensity versus wavelength) for Ga203:0.5%Eu,Cd and Ga203:2%Eu;
Figure 11 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL device formed by sputtering a thin film from Ca°.~Eu°.°,Ga204 onto an AVX substrate and annealed at 950°C for one hour in air;
Figure 12 shows the EL emission spectra for two phosphor films, both sputtered from Ca°.99Eu°.°,Ga204 with each annealed according to the indicated conditions;
Figure 13 is a plot of brightness and efficiency versus voltage at 60 Hz for EL phosphor films sputtered from Ca°.96Tb°.oaGaz~a on an AVX
substrate with each film annealed under the indicated conditions;
Figure 14 shows the EL emission spectra for the films of Figure 13;
Figure 15 shows the EL emission spectra for a phosphor film sputtered from Ca°.ssTb°.o2Pro.ozGaz~a onto an AVX substrate annealed as indicated;
Figure 16 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Ca°.98Tb°,°,Eu°_°,Ga204 onto an AVX substrate annealed under the indicated condition;
Figure 17 shows the EL emission spectrum for the thin film of Figure 16;
Figure 18 shows the EL emission spectrum for an EL phosphor film sputtered from Sr°.9sEu°.°~Ga204 under the indicated annealing condition;
Figure 19 is a.plot of brightness and efficiency versus voltage at 60 Hz for EL phosphor films sputtered from Sr°.92Tb°.°8Gaz04 and Sr°_~Tb°.~Ga204 on AVX substrates annealed under the indicated conditions;
Figure 20 shows the EL emission spectra for a phosphor film sputtered from Sr°.9sTb°.oaGa204 and annealed under the given conditions;
Figure 21 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Sr°.9sTbo.o4Eu°.o,Ga204 onto an AVX substrate annealed under the indicated condition;
Figure 22 shows the EL emission spectrum for the phosphor film of Figure 21;

Figure 23 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Bao.~Euo.o,Ga204 onto an AVX
substrate annealed under the indicated condition;
Figure 24 shows the EL emission spectrum for the phosphor filTTt of Fi~tir ~ ~3;
Figure 25 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Bao.98Tbo.o2Ga20a onto an AVX
substrate annealed under the indicated condition;
Figure 26 shows the EL emission spectrum for the thin film of Figure 25;
Figure 27 is a plot of brightness and efficiency versus voltage at 60 Hz for EL phosphor films sputtered from Ca2..94Euo_osGa206 onto AVX
substrates and annealed under the indicated conditions;
Figure 28 shows the EL emission spectra for the phosphor films of Figure 27;
Figure 29 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Cao.~Euo_o,Ga40, onto an AVX
substrate and annealed under the indicated condition;
Figure 30 shows the EL emission spectrum for the phosphor film of Figure 29;
Figure 31 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Cao.ssTbo.o,GaaO, onto an AVX
substrate and annealed under the indicated condition;
Figure 32 shows the EL emission spectrum for the phosphor film of Figure 31;
Figure 33 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Cao,sas~Yo.o,sGaaO, onto an AVX
substrate and annealed under the indicated condition;
Figure 34 shows the EL emission spectrum for the phosphor film of Figure 33;
Figure 35 is a plot of brightness and efficiency versus voltage at 60 Hz for an EL phosphor film sputtered from Sr2,88Tbo.,2GaaOs and annealed under the given condition;
Figure 36 shows the EL emission spectrum of the phosphor film of Figure 35;
Figure 37 compares tf,~e x-ray diffr action patterns for EL
phosphor films sputtered from Cao.~Euo.o,Ga204 onto AVX substrates and annealed at 700°C, 850°C and 950°C for 1 hour;
Figure 38 compares the x-ray diffraction patterns for thin films sputtered from Sro.~Euo.o,Ga204 onto BaTi03 and annealed at 700°C, 800°C
and 950 ° C for 1 hour;
Figure 39 compares the x-ray diffraction patterns for thin films sputtered from Ca2.94Euo.osGa206 onto AVX substrates and annealed at 700°C, 750°C, 800°C and 950°C for 1 hour;
Figure 40 compares the x-ray diffraction patterns for films sputtered from Ca°.99Euo.°,GaaO, onto AVX substrates and annealed at various temperatures for 1 hour, indicating the crystallization temperature for the compound is between 800°C and 850°C;
Figure 41 is a plot of brightness and efficiency versus applied voltage at 60 Hz for a green emitting EL phosphor film sputtered from Zn,.~Mno.o4Sio.5Geo.504 onto a Sherritt substrate and annealed under the given condition;
Figure 42 is a plot of brightness versus applied voltage at 60 Hz for a red emitting EL phosphor film sputtered from Zn,.~Mno.o4Sio.5Geo.$04 with no annealing;
Figure 43 compares the emission spectra of two EL films sputtered from Zn,.ssMn°.oaSi°.sGe°.sC4, one of the films being annealed and the other not annealed;
Figure 44 is a plot of brightness and EL efficiency versus applied voltage at 60 Hz for an EL phosphor film sputtered from Zn,.~Mno.o4Ge04 onto a Sherritt substrate and annealed under the indicated condition; and Figure 45 is a plot of operating voltage necessary to maintain a brightness of 12 fL in Ga203:2%Eu as a function of time, and the brightness as a function of operating time at 60 Hz and 400 Hz drive for an EL phosphor film sputtered from Sro.98Tbo.o2Ga204 onto an AVX substrate with fixed voltages us shown.
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term phosphor refers to substances which exhibit electroluminescence when a suitable or effective electric field is developed across them. The various elements used in the production of the new EL oxide based materials disclosed herein include gallium (Ga), germanium (Ge), silicon (Si), manganese (Mn), zinc (Zn), europium (Eu), terbium (Tb), cerium (Ce), dysprosium (Dy), cadmium (Cd), strontium (Sr), barium (Ba), calcium (Ca) and praseodymium (Pr).
A) NEW DOPED GALLIUM OXIDES EXHIBITING ELECTROLUMINESCENT
BEHAVIOUR
Film Preparation Target materials were intimate mixtures of Ga203 (Alfa Aesar, 99.999%) and appropriate amounts of rare earth (RE) oxide dopants. For the Ga203:(0.01 to 15% RE) where RE is Eu, Dy or mixtures thereof, powder mixtures of the GaZ03 with the appropriate dopant oxides) in the desired ratio were ground together in a mortar. Thin films were deposited on polished AVX BaTi03 substrates by RF magnetron sputtering using the mixed powder targets. All substrates are a BaTi03 based ferroelectric ceramic made by green sheet processing (AVX Corp).
Referring to Figure 1, a multi-layer thick film stack was manufactured to incorporate a BaTi03 underlayer 12, a screen-printed metal electrode 14 and finally a BaTi03 layer 16, 40 Nm thick on the surface of electrode 14. Impurities that are commonly incorporated in the BaTi03 in industry allow the substrates to have the desired dielectric constant (e~ _ 9000), temperature dependence and other properties. The phosphor layer 18 was deposited by sputtering which was effected with a 2" US gun at a substrate temperature between 200-250°C in an atmosphere of 10% OZ in argon and a pressure of 10 mTorr unless otherwise noted. The substrate holder was rotated in a planetary motion and tt°ie film thickness variation was less than 10%. Typical phosphor film thickness was 4000-8000 A. The sputter deposited thin films were either annealed in air at 600°C to 950°C for one hour or not annealed. A transparent indium tin oxide (ITO) top electrode layer 20 of 2000A was also deposited by sputtering. The EL brightness was measured with a H/linolta LS-100 luminance meter. EL efficiencies were measured by the Sawyer-Tower method. Emission spectra were taken with a computer-controlled SPEX 340E spectrometer.
Results 1. Gaz03:Eu (Comparative Example) Bright orange red electroluminescence (EL) characteristic of the Eu3+ emission was obtained. Brightness-Voltage (B-V) curves of devices made from thin films with nominal compositions Gaz03:2%Eu at a thickness of 8000 A are shown in Figure 2. The corresponding efficiencies for these films are shown in Figure 3. The results clearly indicate that the threshold voltage, V,h, increases with increasing annealing temperature. Except for the as-deposited thin films, the brightness and efficiency increase with decreasing annealing temperature as well. The optimum annealing temperature appears to be lower than "T00"C~.
X-ray diffraction patterns of Ga2O. :1 °/aEu thin films deposited on Si and annealed at various temperatures are shown in Figure 4. Even with 800°C annealing the thin film was still poorly crystallized. Below X00°C the thin film was essentially amorphous. It was not well crystallized until annealed at about 1000°C. These results suggest that there is no obvious correlation between the EL properties and the crystallinity of the thin films.
The EL spectra of Ga~0~:2%Eu thin films annealed at various temperatures are compared in Figure 5. Yhere is very little difference in the line shape as well as the line width, indicating again that the emission of Eu3+
is very much independent of the host lattice. Tna the inventors' knowledge this surprising behavior has never been reported before. ZnS:Tb is a well-known example of an efficient EL ~green;p phosphor with a size-mismatched dopant, but good crystallinity is known to be important in the generation of EL in ZnS-related phosphors.
The notable increase in the emission intensity above 700 nm at annealing temperatures higher than 700°C appears to be correlated to the crystallinity of the thin film of host material Ga2~~ ~. As will be shown later, this emission is due to the B-Ga20,~ host alone.
The B-V curves 'in Figure 2 show that devices with as-deposited and low temperature annealed thin phosphor films have large clamp voltages, or slow rise in brightness near the threshold. As shown in Figure 6, a device with Ga203:1 %Eu thin film sputtered in a gas mixture of 5% O~ and 5% N2 in argon, followed by annealing in argon at 950~C for 1 hour, appears to have a sharper turn-on. The use of a ZnGa.,(~,; buffer layer (1000 ~) between the BaTi03 substrate and the phosphor layer appears to increase the sharpness of the B-V curve as well, data not shown.
2. Gaz03:M (M =Cr, Ce, Dy) (Comparative Example) Even though Cr3" is an ideal dopant for the (3-Ga2O3 host in terms of charge and size, there is essentially no EL. emission observed due to Cry+.The EL spectrum of Ga203:1 %Cr is the same as that of Ga2G,:1 %Ce, which was sputtered in an atmosphere of 5% N~ and 5% ~Jz in argon and annealed at 950°C in argon. A deep red and near infrared emission in both cases has also been observed for C3a~~~3:Eu as well as in Ga203:1 %Dy, see Figure 7, and is thus clearly due to the emission of the (3-GazO~ host lattice. It is worth noting that a similar red ernissior~ in the room temperature photoluminescence spectrum of Ga~On,:Cr was attributed to the 4T;, - 4A2 transition of the Cry+. However, characteristic Cry' emission, especially the sharp R1 (690 nm) and R2 (597 nm) lines reported in the fluorescence spectrum of Ga203:Cr (see L.P. Sosman, T. Abritta, t7. Nakamura and M.M.F.D'Aguiar Neto, J. Mater. Sci. Lett., Vol. 14, pp. 19-20, (1995)) was absent in the EL spectrum. The lack of Ce3+ emission was very likely due to the existence of stable Ce4+ instead of the desired Ce3+. The Dy3+ emission appeared as two broad bands at 490 and 580 nm, in contrast with its photoluminescent emission spectrum of powder specimens where complicated fine structures have been observed even at room temperature.
The EL of Ga203:Dy is much weaker than Ga203:Eu. It is interesting to note that, even with a small concentration (0.5% mole per cent) of codoping with europium, a sharp threshold behaviour can be observed which was absent in all devices without europium. In fact, efficient EL has been obtained only in Eu-doped Ga203. These results suggest that europium is playing a very significant role in the charge injection of these EL
devices, probably through the ionization of Eu2+, which could exist partially in Ga203:Eu.
3. Ga203:Eu,Cd X-ray diffraction patterns of thin films sputtered from a CdGa204:Eu target and annealed at various temperatures are shown in Figure 8. The thin films were also amorphous when annealed below 700°C in air. No spinet CdGa204 phase was observed in the high temperature-annealed thin films. The only phase that could be detected was 8-Ga203.
Thus cadmium existed in the thin film only as a dopant, very likely due to the decomposition of CdO. The XRD patterns in Figure 8 strongly suggest that the Cd-doped Ga203:0.5%Eu,Cd thin films crystallize more easily than GaZ03:1 %Eu when compared with those in Figure 4.
Bright EL was also obtained with Ga203:0.5%Eu,Cd thin films.
The brightness and efficiency data for Ga203:0.5%Eu,Cd thin films annealed at 800°C for one hour in air are shown in Figure 9. There exists an obvious difference in the EL spectra of Ga203:0.5%Eu,Cd and Ga203:2%Eu as shown in Figure 10. The relative intensities of peaks at about 580, 655 and 700 nm were substantially weaker for Ga203:0.5%Eu,Cd. These results strongly suggest the existence of cadmium in the thin films although the amount of Cd WO 97/02721 PCTlCA96/00444 is not known.
The ionic radii of Cdz+ and Eu3+ are both too great for a simple substitution of the Ga3+ ion. The significant change in the emission spectra with Cd2+ codoping probably suggest a very complex association of the Eu3+
ion ~tith~ the host lattice that is sensit~Ve to the existence of other impurities like cadmium. Referring to Figure 9, it is worth noting that the luminescence levels of the best Ga203:0.5%Eu,Cd films are comparable with those of Ga203:2%Eu even though the Eu~" concentration is much lower in the former.
The effects of cadmium doping and the activator (Eu~) concentration on the EL properties are worthy of further investigations.
B) NEW DOPED ALKALINE EARTH GALLATE PHOSPHORS EXHIBITING
ELECTROLUMINESCENCE BEHAVIOUR
Film Preparation:
Commercial high purity SrC03 (99%), BaC03 (99.95%), Ga203 (99.999%) (from Alfa-Aesar), Ca0 (99.9%) (Aldrich), Tb40, (99.99%), Eu203 (99.9%), Pr60"(99.99%) and Dy203 (99.99%) (from Rhone-Poulenc) powders were mixed in appropriate ratios and fired at 1000°C to 1300°C
in air for 2-26 hours to form the desired phosphor powder. The compositions of the typical phosphor compounds and their firing conditions are listed in Table 1. The phosphor powders were then pressed and placed in a 2-inch RF magnetron gun (US gun).
An AVX ceramic substrate, as shown in Figure 1, was placed 4 cm above the gun. Sputtering was carried out at a gas pressure of 20 mtorr to grow thin films measuring 4000A to 9000A in thickness. Except otherwise indicated, the sputtering atmosphere usually consists of 5% OZ and 95% Ar. It is worth noting that 5-10%NZ gas has also been used when sputtering some Tb-doped phosphors, where nitrogen acts as an effective charge compensator and significantly improves the EL brightness of the resulting film. The thin films were annealed at between 600°C and 950°C
for 1 hour in air or Ar depending on the phosphors, and a layer of ITO (indium tin oxide) of ~2000A was grown by RF magnetron sputtering to form a transparent top electrode. The completed device structures are shown in Figure 1.
1 ) CaGa204: RE Phosphors:
The Eu doped materials were prepared with about 1 % Eu and were sputtered in a mixture of 5% OZ in Ar. The EL brightness and efficiency versus voltage curves at 60 Hz for Cao,yuo_°,Ga2C4 Nhosphor post-annealed at 950°C for one hour in air is shown in Figure 11 and the EL emission spectra for two films post annealed at 950°C and 700°C are shown in Figure 12.
Tb doped materials were prepared with between about 0.1 % to about 4% Tb. The EL performance at 60 Hz for Cao.~Tbo.oaGa204 sputtered in 5% 02, 10% Nz and 85% Ar atmosphere and post-annealed at 950°C for 1 hour in air or Ar, are shown in Figure 13 and the corresponding EL emission spectra are shown in Figure 14. It is worth noting that post-annealing in Ar significantly improves the EL brightness as well as the relative intensity of the blue peak situated at 490nm (5D3,'F,,o and $D4~'F6 transitions), which makes the overall emission look bluer.
The Tb and Pr doped materials were prepared with about 4%
(Tb + Pr) and were sputtered in a mixture comprising Ar:N2:02 in the ratio of 17:2:1 or Ar:02 in the ratio of 19:1. The EL emission spectrum for Cao,~Tbo_oZPro.o2Ga204 post-annealed at 850°C for 1 hour in air is shown in Figure 15.
The Tb and Eu doped materials were prepared with about 2%
(Tb + Eu) and were sputtered in a mixture comprising Ar:N2:0z in the ratio of 17:2:1. The EL performance and emission spectrum for Cao.~Tbo.o~Euo.o,Ga204 sputtered in 5% 02, 10% N2 and 85% Ar atmosphere and post-annealed at 950°C for 1 hour in Ar are shown in Figures 16 and respectively. It is to be noted that red, green and blue peaks appear in the spectrum so that this new material is considered a white phosphor.
2) SrGa204:RE Phosphors:
The Eu doped materials were prepared with about 1 % Eu and were sputtered in an Ar:02 mixture of 19:1. For Sro.99Euo.o,Ga204 annealed at 950°C for 1 hour in air the EL emission spectrum is shown in Figure 18.
The Tb doped materials were prepared with about 2% to 12%
Tb and were sputtered in pure argon (Ar). The brightness and efficiency data for Sro 92Tbo o8Ga2C)4 and fro 96Tbo.°4UazU4 are shown in Figure 19.
The EL
spectra for Sro ~6Tbo o4Ga~04 past-annealed in Ar are shown in Figure 20. It is worth noting that higher annealing temperature significantly enhances the emission peaks at 490nm ('G~-~'F, ~ and ''L)~--~'F~~ transitions), 438nm (SD3-~'Fa transition), 441nm (~D3--v'F4 transition) and 418nm (''D~ -'F5), which makes the overall emission colour look bluer as shown in Figure 20.
The Tb and Eu doped materials were prepared with about 5%
(Eu + Tb) and were sputtered in an Ar:Uz mixture of 19:1. The EL
performance and emission spectrum far ~r°gsTb~~4Euao.,Ga2G4 post-annealed at 950' for 1 hour in air are shown ire Figures 21 and 22 respectively. It is to be noted that this provides a white phosphor containing red, green and blue peaks.
3) BaGa204:RE Phosphors:
The films were produced by sputtering in an Ar:oz mixture of 19:1 and annealing 'in the range of '~00''C; to 950°C in air. The EL
performance at 60 Hz for Ban ~~Eu" ".;,G~a,;,0,~ (carnparative example) post-annealed at 850"C for 1 hour is shown in Figure 23. The corresponding EL
emission spectrum is shown in Figure 24.
The EL performance and emission spectrum for Bao g$Tbo °2Ga204 sputtered in 5% U~, 5% IVz and 90% Ar atmosphere and post-annealed at 950°C for 1 hour in Ar~ are shown in Figures 25 and 26 respectively.
4) Ca3GaZOs:RE Phosphors:
The Eu doped materials were prepared with about 2% Eu and were sputtered in an Ar:O° mixture of 19:1. The EL performances at 60 Hz for Caz~4Euo.osGa2~6 post-annealed at fi00"G, 750'C and 850'C for 1 hour in air are shown in Figure 27. The corresponding EL emission spectra are shown in Figure 28. It is worth noting that the EL pertormance is the best for the amorphous Caz.94Euo.~GaZO6 thin film, which is annealed at 600°C in air for one hour.
The Tb doped materials were prepared with about 2% Tb and were sputtered in an Ar:Oz mixture of 19:1. The EL of Ca2.94Tbo_osGa2O6 was wea'~c, with a ~axirrum brightness of 3 fL. at o~ H~. .
5) CaGa40~:RE Phosphors:
The Eu doped materials were prepared with about 1 % Eu and were sputtered in an Ar:02 mixture of 9:1. The EL performance at 60 Hi for the Cao.~Euo.o,GaaO, film sputtered in 10%02-90%Ar and post-annealed at 950°C for 1 hour in air is shown in Figure 29 and the EL emission spectrum is shown in Figure 30.
The Tb doped materials were prepared with about 1 % Tb. The EL performance and emission spectrum for the Cao.99Tbo.o,Ga40, film sputtered in 5%NZ-10%02-85%Ar and post-annealed at 950°C for 1 hour in air are shown in Figures 31 and 32, respectively.
The Dy doped materials were prepared with about 1.5% Dy and were sputtered in an Ar:02 mixture of 9:1. The EL performance and emission spectrum for the Cao.98s~Yo.o,sGa40, film sputtered in 10% 02- 90% Ar and post-annealed at 850°C for 1 hour in air are shown in Figures 33 and 34, respectively.
6) Sr3Ga409:Tb Phosphors:
The Tb doped materials were prepared with about 4% Tb and were sputtered in Ar. The EL performance for the Sr2.88Tbo_,ZGa409 film sputtered in pure Ar and post-annealed at 850°C for 1 hour in Ar is shown in Figure 35. Thus, Sr2.$8Tbo,,2Ga409 is quite efficient as an EL material. It is also quite notable that this material exhibits significant EL behavior as deposited without post fabrication annealing (19 fL at 60 Hz, data not shown).
The EL emission spectrum for the film is shown in Figure 36.
Phase confirmation by X-ray diffraction:
The x-ray diffraction patterns for Cao.99Euo.o,Ga204 thin films grown on AVX substrate and annealed at 700°C, 850°C and 950°C for 1 hour are shown in Figure 37. The patterns suggest that GaGa20a:Fu thin film is well-crystallized in orthorhombic form when annealed at above 850°G.
The x-ray diffraction patterns for the Sr~, a,~Euo ;;~Ga~~~~ thin films grown an BaTi03 and annealed at 700"C, 800''C and 950'C for 1 hour are shown in Figure 38, which confirms that the SrGa20~:F.u thin film is crystallized when annealed at 950°C but exhibits a strong preferred orientation. The x-ray diffraction patterns for Ca2 94Fuo.osaz~~ thin films annealed at various temperatures are shown in Figure 39, indicating the crystallization temperature for the compound is between 700"C and 750 'C Figure 40 shows the x-ray diffraction patterns for Cao 99Euo o,Ga40.r 'thin films annealed at various temperatures, indicating the crystallization temperature for the compound is between 800 ° C and 850 ° C.
C) Zn2SixGe,_M04:Mn PHOSPHORS EXHIBITING
ELECTROLUMINESCENCE BEHAVIOUR
Film Preparation:
Sylvania phosphor 2282 which is a powder of Zn2SiO4:Mn was mixed with 99.998% pure Ge02 powder, 99.9%> pure Zn0 powder and 99.9%
pure Mn0 powder in a ratio appropriate fior Zr~~ ~~Mno.U4S~0 SGeo.50a The mixed powder was ground together using a mortar and pestle and placed in a 2 inch RF magnetron gun (US gun). The films were deposited by sputtering from the powder mixture. A ceramic dielectric substrate (also referred to herein as the Sherritt substrate, described in P. Bailey, D. Carl~ner and X. Wu, SID'95 Digest, p. 484; and United States Patent No. 5,432,015) was placed 4 cm above the gun and sputtering was carried out ire a 5~-10 mtorr atmosphere of 5 - 20°l0 02 in argon for about 1 hour. The substrate temperature was about 240"'C and sputtering power was 10th watts. The samples were then either annealed in vacuum or in air at between ~650~C and 700"C for 1 hour or not annealed. For EL measurements, an indium tin oxide layer was subsequently sputter deposited onto the surface of the film.
Results:
The completed device is similar to that shown in Figure 1, except that the composition of the ceramic layers 12 and 16 (Figure 1 ) is not BaTiO3 in the case of Sherritt substrates. Eiectrolurr~inescence was observed and Figure 41 shows the characteristic brightness and efficiency data of a green-emitting Zn,,9~;Mno ~~Sio ~Ge~ ~;~:7~ ESL device, and Figure 42 shows the data of a red-emitting EL device. The red-emitting phosphor is amorphous by x-ray diffraction and is stable in air' up to 60C)''~. The emission spectra are shown in Figure 43. Manganese is known to substitute for zinc in the host lattice in manganese doped zinc silicates.
These results are commercially very useful as brightnesses of 50 cd/mz (or 15 fL) or more are useful for flat panel displays. These brightnesses compare favourably with brightnesses obtained in the best ZnS
green electroluminescent devices reported to date as disclosed in H. Ohnishi, SID'94 Digest, p. 129, 1994.
Devices were also made ar7 Sherritt substrates using Zn~Ge04:Mn (x=0)with the same procedures. The Mn doped materials were prepared with between about 1 ~J° k.o 6°r~~ Mn and were sputtered in a gas mixture comprising Ar with O~ in the range of between 5 to 20% onto substrates heated to between 200°~. to 600°~. 'The filrr~s were annealed in either vacuum or air.T'ypical brightness and efficiency data are shown in Figure 44 for a 2% Mn doping. The brightness and efficiency values are smaller than those of the mixed Si-Ge campour~ds. Annealing temperatures were also 700°C, but could be dropped to fi50"C far Zn2Ge04:Mn if a longer annealing time was used. For these germinates in which x=0, the EL
response exhibited a maximum in the vicinity of 2.5 mole percent manganese, indicating that a preferred range of %Mn is between about 0.5%
to about 4%.
It is to be understood that the nomenclature or notation used herein to identify the new phosphor materials is not to be interpreted as limiting in any way. For example, the percentage doping notation has been used in association with the doped gallium oxide compounds since it is not necessarily the case that the rare earth dopants substitute for gallium in the host lattice, white in other compounds the inventors believe substitution occurs and the stoichiametric formulas have been used.
It will also be understood by those skilled in the art that the allowable ranges of concentration of dopants ir~~ the different new phosphor materials disclosed herein will depend on the solubility limit of the dopant in the oxides. For example, a series of five targets comprising SrGa,~04:n%Tb were prepared in which n% was 2%. ~4%, 8%, 12°f° and 16%. Films were prepared by sputtering from these targets and annealed as disclosed above.
The sputtered films with dopant levels up to 12% were observed to be homogeneous, single phase films exY~ibiting EL, behaviour while film sputtered from the target with 16% Tb was inhomogeneous with clearly visible precipitates which exhibited poor EL behaviour. Hence in this case a solubility limit of about 15 % Tb in the SrGa ,CJ~ host lattice is estimated. The inventors reasonably contemplate that EL behavior is exhibited in all new phosphors disclosed herein in the range of dc~pant conc~entratiean corresponding to the solubility range of the dapant(s) in the host.
Those skilled in the art will understand that the EL
characteristics of the phosphors may vary within the solubility range of the dopant(s) in the host lattice. Electronic 'interactions between dopant ions may determine the prefered concentration of dopant ions for maximum brightness and efficiency. This phenomenon, known as concenfiration quenching, results in decreasing brightness and efficiency for doping concentrations beyond a certain point within the solubility limit such that there will be preferred dopant concentrations which give optimum EL properties.
In the case when the dopant in a host lattice comprises more than one element, the criteria for doping ranges involve the above considerations as well as the possibility of energy transfer between dopants of different chemical elements. Notwithstandir7g this, however, it will be understood by those skilled in the art that more than one chemically distinct dopant element may be simultaneously intraduceci into a host lattice and that EL may be obtained from each distinct dopant simultaneously so as to produce a spectrum of intensity versus wavelength which is a superposition of the spectra obtained from each dopant species when separately introduced into the host lattice.
It will be appreciated that sputtering has been disclosed herein as a suitable means for producing the phosphor films. During sputtering, the composition of the sputtered film will deviate from the composition of the source material forming the sputtering target. This raccurs due to a difference in sticking coefficients between the different elements being sputtered; a difference in the sputtering yields kaetween the elements of the target; and incorporation of chemicak elements (such as nitrogen) in the sputtering gas into the thin film that are not initially present in the sputtering target. It will be understood however' that these deviations are limited in magnitude such that the grown films do crystallize in those crystal structures, when annealed appropriately, expected from the target composition.
It will be appreciated by those skilled in the art that whRe the fabrication of the new electroluminescent phosphors disclosed herein has been described using sputtering as the film preparation method, other methods known to those in the art may be used. Other methods of fabrication include electron beam deposition, laser ablation°~" chemical vapour deposition, vacuum evaporation, molecular beam epitaxy, sok gel deposition and pkasma enhanced vacuum evaporation to mention a few.
Various thin film dielectrics used in electroluminescent applications include Si02, SiON, Ai20~, BaTi03, BaTa206, SrTi03 PbTi03, PbNbz06, Sm20~, Ta205 . TiO~,, Y,C~~;, Si,3Na, SiAION. These may be used as substrates in the present invention by depositing onto glass, silicon or quartz substrates, to mentian just a few.
Thick; films on ceramic substrates may also be used.. While many of the results disclosed herein were obtained using BaTi03 thick film dielectrics, other thick films an ceramic substrates may also be used. 'The ceramic substrate may be alumina (A120,) or the same ceramic as the thick film itself. Thick dielectric films of BaTi0.3, SrTiC7~, p'bZr03, PbTiO,~, to mention just a few, may also be used.
2~4 Variations of the EL laminate device configuration will be readily apparent to those skilled in the art. An alumina substrate may be used onto which the lower conductive electrode is deposited followed by the high dielectric constant material, the phosphor and then the outer transparent electrode. Alternatively, a conductive electrode ;c; ~ta;;t may be deposited onto the back of a thick, rigid dielectric substrate material onto the front of which the phosphor layer is deposited followed by the outer conductive electrode.

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Claims (54)

THEREFORE WHAT IS CLAIMED ID:

1. A method of producing electroluminescence, comprising;
providing an electroluminescent phosphor having a formula Ga2O3:n%RE, wherein RE is a rare earth dopant selected from the group consisting of Eu, Dy and combinations thereof, n% is the mole percent of RE present in Ga2O3 and spans the range in which said rare earth is soluble in Ga2O3, and applying a voltage across said electroluminescent phosphor.

2. An electroluminescent device, comprising;
a dielectric substrate, said dielectric substrate having a conducting back electrode on a back surface thereof;
an electroluminescent phosphor an a front surface of said dielectric substrate, said electroluminescent phosphor being Ga2O3:n%RE, wherein RE is a rare earth dopant selected from the group consisting of Eu and Dy, n% is the mole percent of RE present in Ga2O3 and spans the range in which said rare earth is soluble in Ga2O3;
a substantially transparent electrode deposited onto a top surface of said electroluminescent phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop an electric field across said electroluminescent phosphor.

3. The electroluminescent device according to claim 2 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from Ga2O3:n%Eu, wherein n% is in the range from 0.01 to 15%.

4. The electroluminescent device according to claim 3 wherein n% is 2%.

5. The electroluminescent device according to claim 2 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from Ga2O3:n%Dy.

6. The electroluminescent device according to claim 5 wherein n% is 1%.

7. An electroluminescent phosphor having the formula Ga2O3:n1%Eu,n2%C;d, wherein n1% is the mole percent amount of Eu present in Ga2O3 and spans the range in which Eu is soluble in Ga2O3, and n2% is the mole percent amount of Cd present in Ga2O3 and spans the range in which Cd is soluble in Ga2O3.

8. An electroluminescent device, comprising;
a dielectric substrate, said dielectric substrate having a conducting back electrode on a back surface thereof;
an electroluminescent phosphor an a front surface of said dielectric substrate, said electroluminescent phosphor being Ga2O3:n,%Eu,n2%Cd, wherein n1% is the mole percent amount of Eu present in Ga2O3 and spans the range in which Eu is soluble in Ga2O3, and n2% is the mole percent amount of Cd present in Ga2O3 and spans the range in which Cd is soluble in Ga2O3;
a substantially transparent electrode deposited onto a top surface of said phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop an electric field across said phosphor.

9. The electroluminescent device according to claim 8 wherein said electroluminescent phosphor is a Ga2O3:n1%Eu, n2%Cd layer formed by sputter deposition from a CdGa2O4:Eu source.

10. The electroluminescent device according to claim 9 wherein the combined mole percent of Eu and Cd is about 0.5%.

11. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula SrGa2O4:n%RE wherein RE is a rare earth dopant selected from the group consisting of Tb and combinations of Tb and Eu, n% is the mole percent of RE
present in SrGa2O4, and spans the range in which said rare earths are soluble in SrGa2O4; and applying a voltage across said electroluminescent phosphor.

12. An electroluminescent device, comprising;
a dielectric substrate, said dielectric substrate having a conducting back electrode on a back surface thereof;
an electroluminescent phosphor on a front surface of said dielectric substrate, said electroluminescent phosphor being SrGa2O4:n%RE wherein RE
is a rare earth dopant selected from the group consisting of Eu, Tb and combinations thereof, n% is the mole percent of RE present in SrGa2O4 and spans the range in which said rare earths are soluble in SrGa2O4;
a substantially transparent electrode deposited onto a top surface of said phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop an electric field across said phosphor.

13. The electroluminescent device according to claim 12 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Sr0.99Eu001Ga2O4.

14. The electroluminescent device according to claim 12 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Sr0.92Tb008Ga2O4.

15. The electroluminescent device according to claim 12 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Sr0.96Tb0.04Ga2O4.

16. The electroluminescent device according to claim 12 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Sri0.95Tb004Eu001Ga2O4.

17. An electroluminescent phosphor having the formula CaGa2O4:n%RE
wherein RE is a rare earth dopant selected from the group consisting of Eu, Tb, Pr and combinations thereof, n% is the mole percent of RE present in CaGa204, and spans the range in which said rare earths are soluble in CaGa2O4.

18. An electroluminescent device, comprising;
a dielectric substrate, said dielectric substrate having a conducting back electrode on a back surface thereof;
an electroluminescent phosphor on a front surface of said dielectric substrate, said electroluminescent phosphor being CaGa2O4:n%RE wherein RE
is a rare earth dopant selected from the group consisting of Eu, Tb, Pr and combinations thereof, n% is the mole percent of RE present in CaGa2O4, and spans the range in which said rare earths are soluble in CaGa2O4;
a substantially transparent electrode deposited onto a top surface of said phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop an electric field across said phosphor.

19. The electroluminescent device according to claim 18 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca0.99Eu0.01Ga2O4

20. The electroluminescent device according to claim 18 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca0.96Tb0.04Ga2O4

21. The electroluminescent device according to claim 18 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca0.96Tb0.02Pr0.02Ga2O4

22. The electroluminescent device according to claim 18 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca0.98Tb001Eu0.01Ga2O4.

23. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula BaGa2O4:n%RE wherein RE is a rare earth dopant selected from the group consisting of Tb and combinations of Tb and Eu n% is the mole percent of RE
present in BaGa2O4, and spans the range in which said rare earths are soluble in BaGa2O4; and applying a voltage across said electroluminescent phosphor.

24. An electroluminescent device, comprising:
a dielectric substrate, said dielectric substrate having a conducting back electrode on a back surface thereof;
an electroluminescent phosphor on a front surface of said dielectric substrate, said electroluminescent phosphor having a formula BaGa2O4:n%RE, wherein RE is a rare earth dopant selected from the group consisting of Eu, Tb, and combinations thereof, n% is the mote percent of RE present in BaGa2O4 and spans the range in which said rare earths are soluble in BaGa2O4;
a substantially transparent electrode deposited onto a top surface of said phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop are electric field across said phosphor.

25. The electroluminescent device according to claim 24 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ba0.98Tb0.02Ga2O4.

26. The electroluminescent device according to claim 24 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ba0.98Tb0.02Ga2O4.

27. An electroluminescent phosphor having the formula Ca3Ga2O6:n%RE
wherein RE is a rare earth dopant selected from the group consisting of Eu and Tb and combinations thereof. n% is the mole percent of RE present in Ca3Ga2O6, and spans the range in which said rare earths are soluble in Ca3Ga2O6.

28. An electroluminescent device, comprising;
a dielectric substrate, said dielectric substrate having a conducting back electrode on a back surface thereof;
an electroluminescent phosphor on a front surface of said dielectric substrate, said electroluminescent phosphor being Ca3Ga2O6:n%RE, wherein RE is a rare earth dopant selected from the group consisting of Eu and Tb and combinations thereof, n% is the mole percent of RE present in Ca3Ga2O6 and spans the range in which said rare earths are soluble in Ca3Ga2O6;
a substantially transparent electrode deposited onto a top surface of said phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop an electric field across said phosphor.

29. The electroluminescent device according to claim 28 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca2.94Eu0.06Ga2O6

30. The electroluminescent device according to claim 28 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca2.94Tb0.06Ga2O6.

31. An electroluminescent phosphor having the formula CaGa4O7:n%RE
wherein RE is a rare earth dopant selected from the group consisting of Eu, Dy , Tb and combinations thereof, n% is the mole percent of RE present in CaGa4O7, and spans the range in which said rare earths are soluble in CaGa4O7.

32. An electroluminescent device, comprising;
a dielectric substrate, said dielectric substrate having a conducting electrode on a back surface thereof;
an electroluminescent phosphor on a front surface of said dielectric substrate, said electroluminescent phosphor being CaGa4O7:n%RE wherein RE
is a rare earth dopant selected from the group consisting of Eu, Dy ; Tb and combinations thereof, n% is the mole percent of RE present in CaGa4O7, and spans the range in which said rare earths are soluble in CaGa4O7;
a substantially transparent electrode deposited onto a tap surface of said phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop an electric field across said phosphor.

33. The electroluminescent device according to claim 32 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca0.99Eu0.01Ga4O7.

34. The electroluminescent device according to claim 32 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca0.99Tb001Ga4O7.

35. The electroluminescent device according to claim 32 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Ca0.985Dy0015Ga4O7

36. An electroluminescent phosphor having the formula Sr3Ga4O9:n%Tb, wherein n% is the mole percent of Tb and spans the range in which Tb is soluble in Sr3Ga4O9.

37. An electroluminescent device, comprising;
a dielectric substrate, said dielectric substrate having a conducting electrode on a back surface thereof;
an electroluminescent phosphor an a front surface of said dielectric substrate, said electroluminescent phosphor being Sr3Ga4O9:n%Tb, wherein n%
is the mole percent of Tb and spans the range in which Tb is soluble in Sr3Ga4O9;
a substantially transparent electrode deposited onto a top surface of said phosphor; and means for applying a voltage between said transparent electrode and the conducting back electrode to develop an electric field across said phosphor.

38. The electroluminescent device according to claim 37 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Sr2.88Tb0.12Ga4O9.

39. The method according to claim 11 wherein %Tb is between 0.1% to 12%.

40. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula Zn2Si x Ge1-x O4:n%Mn, where n% is the mole percent of Mn and spans the range in which Mn is soluble in Zn2Si x Ge1-xO4:n% Mn and x varies in the range from 0 <=
x <1.0; and applying a voltage across said electroluminescent phosphor.

41. The method according to claim 40, wherein n% is in the range from 0.5%
to 5%.

42. An electroluminescent device, comprising:
a dielectric substrate having opposing surfaces, an electrode being located on one of said surfaces;
an electroluminescent phosphor layer located on the other surface of the dielectric substrate, said phosphor having the formula Zn2Si xGe1-xO4:n%Mn, where n% is the mole percent of Mn and spans the range in which Mn is soluble in Zn2Si x Ge1-xO4:n% Mn and x varies in the range from 0 <= x <1.0;
a substantially transparent electrode on a tap surface of said electroluminescent phosphor layer; and means for applying a voltage across said electroluminescent phosphor layer to develop an electric field through said phosphor layer.

43. The electroluminescent device according to claim 42, wherein n% is in the range from 0.5% to 5%.

44. The electroluminescent device according to claim 42 wherein said electroluminescent phosphor is a phosphor film formed by sputter deposition from a source material having a formula Zn1.96Mn004Si05Ge0.5O4.

45. The electroluminescent device according to claim 44 wherein said electroluminescent phosphor film is sputtered at a substrate temperature of about 240°C, said phosphor film characterized by being a red emitting phosphor.

46. The electroluminescent device according to claim 44 wherein said electroluminescent phosphor film is sputtered at a substrate temperature of about 240°C and annealed at about 700°C for about 1 hour in vacuum, said sputtered and annealed phosphor film characterized by being a green emitting phosphor.

47. The electroluminescent device according to claim 42 wherein said electroluminescent phosphar is a film formed by sputter deposition from a source material Zn2GeO4:n%Mn, n% being in the range from 0.5% to 5%, the sputtered film being annealed in air or vacuum.

48. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula Ga2O3:n1%Eu,n2%Cd, wherein n1% is the mole percent amount of Eu present in Ga2O3 and spans the range in which Eu is soluble in Ga2O3, and n2% is the mole percent amount of Cd present in Ga2O3 and spans the range in which Cd is soluble in Ga2O3; and applying a voltage across said electroluminescent phosphor.

49. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula CaGa2O4:n%RE wherein RE is a rare earth dopant selected from the group consisting of Eu, Tb, Pr and combinations thereof, n% is the mole percent of RE
present in CaGa2O4, and spans the range in which said rare earths are soluble in CaGa2O4; and applying a voltage across said electroluminescent phosphor.

50. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula Ca3Ga2O6:n%RE wherein RE is a rare earth dopant selected from the group consisting of Eu and Tb and combinations thereof, n% is the mole percent of RE present in Ca3Ga2O6, and spans the range in which said rare earths are soluble in Ca3Ga2O6; and applying a voltage across said electroluminescent phosphor.

51. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula CaGa4O7:n%RE wherein RE is a rare earth dopant selected from the group consisting of Eu, Dy, Tb and combinations thereof, n% is the mole percent of RE
present in CaGa4O7, and spans the range in which said rare earths are soluble in CaGa4O7; and applying a voltage across said electroluminescent phosphor.

52. A method of producing electroluminescence, comprising:
providing an electroluminescent phosphor having a formula Sr3Ga4O9:n% Tb, wherein n% is the mole percent of Tb and spans the range in which Tb is soluble in Sr3Ga4O9; and applying a voltage across said electroluminescent phosphor.

53. An electroluminescent phosphor having the formula SrGa2O4:n%RE, wherein n% RE is the mole percent of Tb alone or a combined amount of Tb and Eu and spans the range in which Tb or the combined amount of Tb and Eu are soluble in SrGa2O4.

54. An electroluminescent phosphor having the formula BaGa2O4:n%RE, wherein n% RE is the mole percent of Tb alone or a combined amount of Tb and Eu and spans the range in which Tb or the combined amount of Tb and Eu are soluble in BaGa2O4.