WO2001070902A1 - Method for preparing efficient low voltage phosphors and products produced thereby - Google Patents
Method for preparing efficient low voltage phosphors and products produced thereby Download PDFInfo
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- WO2001070902A1 WO2001070902A1 PCT/US2001/003574 US0103574W WO0170902A1 WO 2001070902 A1 WO2001070902 A1 WO 2001070902A1 US 0103574 W US0103574 W US 0103574W WO 0170902 A1 WO0170902 A1 WO 0170902A1
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- phosphor
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- 238000000034 method Methods 0.000 title claims description 34
- 239000002243 precursor Substances 0.000 claims abstract description 81
- 150000004703 alkoxides Chemical class 0.000 claims abstract description 44
- 239000007787 solid Substances 0.000 claims abstract description 37
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical group O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 28
- 239000000203 mixture Substances 0.000 claims abstract description 27
- 239000002019 doping agent Substances 0.000 claims abstract description 22
- 238000006482 condensation reaction Methods 0.000 claims abstract description 19
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- 238000006460 hydrolysis reaction Methods 0.000 claims abstract description 19
- 229910052751 metal Inorganic materials 0.000 claims abstract description 17
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- 229910021485 fumed silica Inorganic materials 0.000 claims abstract description 6
- 239000002245 particle Substances 0.000 claims description 47
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 34
- 239000000758 substrate Substances 0.000 claims description 13
- 238000005136 cathodoluminescence Methods 0.000 claims description 12
- 238000001035 drying Methods 0.000 claims description 12
- 239000003795 chemical substances by application Substances 0.000 claims description 11
- 239000003153 chemical reaction reagent Substances 0.000 claims description 10
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- 239000011541 reaction mixture Substances 0.000 claims description 6
- WGTYBPLFGIVFAS-UHFFFAOYSA-M tetramethylammonium hydroxide Chemical compound [OH-].C[N+](C)(C)C WGTYBPLFGIVFAS-UHFFFAOYSA-M 0.000 claims description 6
- 230000001965 increasing effect Effects 0.000 claims description 5
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- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 claims description 3
- 229910044991 metal oxide Inorganic materials 0.000 claims description 3
- 150000004706 metal oxides Chemical class 0.000 claims description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 2
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 2
- 229910017053 inorganic salt Inorganic materials 0.000 claims description 2
- 229910001463 metal phosphate Inorganic materials 0.000 claims description 2
- 229910052976 metal sulfide Inorganic materials 0.000 claims description 2
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical compound S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 claims description 2
- 238000005401 electroluminescence Methods 0.000 claims 3
- 239000003381 stabilizer Substances 0.000 claims 1
- 238000006243 chemical reaction Methods 0.000 abstract description 5
- 239000007795 chemical reaction product Substances 0.000 abstract 1
- 229910052605 nesosilicate Inorganic materials 0.000 abstract 1
- 230000006911 nucleation Effects 0.000 abstract 1
- 238000010899 nucleation Methods 0.000 abstract 1
- 150000004762 orthosilicates Chemical class 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 42
- 239000011701 zinc Substances 0.000 description 22
- 239000011572 manganese Substances 0.000 description 21
- -1 phosphor compound Chemical class 0.000 description 12
- 238000009833 condensation Methods 0.000 description 10
- 230000005494 condensation Effects 0.000 description 10
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 9
- 229910052725 zinc Inorganic materials 0.000 description 9
- 239000002105 nanoparticle Substances 0.000 description 8
- 239000000843 powder Substances 0.000 description 7
- 230000002028 premature Effects 0.000 description 7
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 6
- 239000002904 solvent Substances 0.000 description 6
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 5
- 239000012190 activator Substances 0.000 description 5
- 230000004927 fusion Effects 0.000 description 5
- 229910052748 manganese Inorganic materials 0.000 description 5
- 238000002360 preparation method Methods 0.000 description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000001354 calcination Methods 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- 238000010894 electron beam technology Methods 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- 241000894007 species Species 0.000 description 4
- XNWFRZJHXBZDAG-UHFFFAOYSA-N 2-METHOXYETHANOL Chemical compound COCCO XNWFRZJHXBZDAG-UHFFFAOYSA-N 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 3
- 150000001242 acetic acid derivatives Chemical class 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
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- 239000010453 quartz Substances 0.000 description 3
- 229910002012 Aerosil® Inorganic materials 0.000 description 2
- 229910002015 Aerosil® 150 Inorganic materials 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- LNYNHRRKSYMFHF-UHFFFAOYSA-K europium(3+);triacetate Chemical compound [Eu+3].CC([O-])=O.CC([O-])=O.CC([O-])=O LNYNHRRKSYMFHF-UHFFFAOYSA-K 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000001976 improved effect Effects 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- UQIRCVPINUNHQY-UHFFFAOYSA-N manganese(2+);methanolate Chemical compound [Mn+2].[O-]C.[O-]C UQIRCVPINUNHQY-UHFFFAOYSA-N 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 238000005215 recombination Methods 0.000 description 2
- 230000006798 recombination Effects 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 238000013519 translation Methods 0.000 description 2
- 238000002525 ultrasonication Methods 0.000 description 2
- 239000011787 zinc oxide Substances 0.000 description 2
- YNPXMOHUBANPJB-UHFFFAOYSA-N zinc;butan-1-olate Chemical compound [Zn+2].CCCC[O-].CCCC[O-] YNPXMOHUBANPJB-UHFFFAOYSA-N 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 241000282326 Felis catus Species 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 239000004964 aerogel Substances 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000003491 array Methods 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- RWZKAROCZDFJEI-UHFFFAOYSA-N ethanol;zinc Chemical compound [Zn].CCO.CCO RWZKAROCZDFJEI-UHFFFAOYSA-N 0.000 description 1
- 230000005281 excited state Effects 0.000 description 1
- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium oxide Inorganic materials O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
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- 230000000977 initiatory effect Effects 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000004020 luminiscence type Methods 0.000 description 1
- MIVBAHRSNUNMPP-UHFFFAOYSA-N manganese(2+);dinitrate Chemical compound [Mn+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MIVBAHRSNUNMPP-UHFFFAOYSA-N 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 239000002159 nanocrystal Substances 0.000 description 1
- 239000011858 nanopowder Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- PVADDRMAFCOOPC-UHFFFAOYSA-N oxogermanium Chemical compound [Ge]=O PVADDRMAFCOOPC-UHFFFAOYSA-N 0.000 description 1
- 230000002688 persistence Effects 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 238000003980 solgel method Methods 0.000 description 1
- 238000003746 solid phase reaction Methods 0.000 description 1
- 238000010671 solid-state reaction Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 239000011550 stock solution Substances 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- JXNCWJJAQLTWKR-UHFFFAOYSA-N zinc;methanolate Chemical compound [Zn+2].[O-]C.[O-]C JXNCWJJAQLTWKR-UHFFFAOYSA-N 0.000 description 1
- TYSXNZUFDKPFED-UHFFFAOYSA-N zinc;propan-1-olate Chemical compound [Zn+2].CCC[O-].CCC[O-] TYSXNZUFDKPFED-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/0838—Aluminates; Silicates
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
Definitions
- the present invention generally relates to methods for prepa ⁇ ng cathodolummescent phosphors using a sol-gel condensation technique, as well as to products made from these methods.
- the present invention relates to methods for prepa ⁇ ng cathodolummescent phosphors (e.g., orthosi cate-based phosphors) exhibiting supe ⁇ or b ⁇ ghtness and efficiency, making them especially suitable for low voltage operation m va ⁇ ous applications such as flat panel displays, field emitter displays (FEDs), electroluminescent displays (ELDs), TVs, and the like.
- FEDs field emitter displays
- ELDs electroluminescent displays
- Phosphors in general comp ⁇ se a wide band gap semiconductor mat ⁇ x with homogeneously dispersed activator ions withm.
- accepted mechanisms of light output in cathodoluminescence phosphors include electron-induced creation of excitons, which can result in photon emission through recombination of the holes and electrons.
- lattice defects, impurities, charge traps, etc. can impede the efficient recombination of these charge earners, thus causing the nonradiative decay of the excited states It is believed that the phosphor crystal structure should be as close to perfect as possible to achieve efficient emission of light
- cathodolummescent phosphors are made for high ⁇ oltage (i.e., approximately 5-20 kV) applications.
- b ⁇ ght and efficient phosphors that are especially suited for low voltage operation (at or below about 1-6 kV, preferably 2-3 kV) do not exist in the prior art.
- Low bias voltages reduce the se ⁇ ous problems of elect ⁇ cal insulation breakdown and arcing.
- cathodolummescent phosphors such as those based on orthosi cates with grain sizes of a few micrometers, are prepared by mixing micron-sized or larger precursor particles and fi ⁇ ng at high temperatures to induce solid reactions.
- particles of Mn-doped zinc oxide (ZnO) are mixed with S ⁇ 0 2 particles and fired at high temperatures to produce the phosphor compound Zn : S ⁇ 0 :Mn via solid reaction
- ZnO Mn-doped zinc oxide
- Example I which is incorporated herein by reference for all purposes, discloses phosphor nanoscale powder prepared by forming a solution or slurry comp ⁇ sing phosphor precursors and then fi ⁇ ng the solid residue of the solution or slurry
- a mixture of Zn and Mn(JJ) or Cu(H) precursors e.g., zinc and manganese(U) acetates
- ethanol e.g., ethanol
- Mn e.g., zinc and manganese(U) acetates
- the mixed alkoxide/acetate is then cooled and hydrolyzed ith tetramethylammonium hydroxide to form a sol comp ⁇ sing of a suspension of mixed nanoparticles of metal oxides.
- AEROSIL fumed silica (7 nm in diameter
- a Zn-Mn alkoxide solution is first prepared from Zn and Mn alkoxide precursors without hydrolysis or forming particles
- an inhibitor such as mt ⁇ c acid is typically added to prevent premature
- the second precursor particles e.g., fumed silica
- the second precursor particles are then added to the solution of the Zn-Mn alkoxide mixture, followed by induced precipitation of the first precursor by sol-gel condensation reaction, the precipitated first precursor being in intimate contact with and around the second precursor particles.
- phosphors e.g., orthosilicate phosphors
- x-ra ⁇ imaging displays in lieu of photographic plates), and the like.
- phosphors e.g., orthosilicate phosphors
- phosphors e.g., orthosilicate phosphors
- the present invention provides a method for prepa ⁇ ng phosphors comp ⁇ sing the steps of
- Figure 1 compares the b ⁇ ghtness (cd/m 2 ) of the Zn 2 S ⁇ 0 :Mn phosphor of inventive
- Example 1 against a commercial Zn 2 S ⁇ O 4 -Mn phosphor (RCA PI) at va ⁇ ous beam voltages.
- Figure 2 compares the luminous efficiency (lm/W) of the Zn 2 S ⁇ 0 4 :Mn phosphor of inventive Example 1 against a commercial Zn 2 S ⁇ 0 4 :Mn phosphor (RCA PI) at va ⁇ ous beam voltages.
- solid particle precursors e.g.,
- S ⁇ 0 2 nanocrystals are initially mixed with a solution of an alkoxide precursor (e g., zinc alkoxide) and a dopant precursor (e g , manganese alkoxide), at suitable concentrations and proportions, before solid oxide (e g., ZnO and MnO) particles form.
- an alkoxide precursor e g., zinc alkoxide
- a dopant precursor e g , manganese alkoxide
- solid oxide e g., ZnO and MnO
- a sol-gel hydrolysis-condensation reaction is then induced in the presence of the solid particle precursor so as to permit the formation of a coating of a doped alkoxide gel polymer around each solid particle precursor.
- the coating may, but not necessa ⁇ ly, have non-umform thickness around the solid particle In the drying and fi ⁇ ng process, an oxide shell, in complete contact with the solid particle precursor, is formed.
- the contact area is much larger than m the case when the synthesis involves mixing of solid precursor particles.
- a lower temperature a much shorter solid reaction time as well as supe ⁇ or homogeneity can be expected
- a solution containing at least an alkoxide precursor and a dopant precursor is first provided.
- the solution also comp ⁇ ses a hydrolysis agent and/or a reagent capable of inhibiting premature condensation reaction in the solution p ⁇ or to the addition of the solid particle precursor.
- the alkoxide precursor can be any alkoxide that can form a phosphor and is suitably a metal alkoxide.
- metal alkoxide precursors include, but are not limited to zinc alkoxides.
- zinc alkox ⁇ de(s) When selected, they may be selected from zinc methoxide, zinc ethoxide, zinc propoxide, zinc butoxide, and others.
- the dopant precursor is selected from an acetate, an alkoxide, an organometal c compound, or an inorganic salt of the metal (dopant ion), and mixtures thereof.
- the dopant is selected from an acetate, an alkoxide, an organometal c compound, or an inorganic salt of the metal (dopant ion), and mixtures thereof.
- metal alkoxides such as manganese methoxide, as well as acetates such as europium acetate; successful results would also be expected for other dopant precursor species such as manganese nitrate.
- the solvent is any liquid that can provide a solution of the above-desc ⁇ bed alkoxide precursor, dopant precursor, and other optional reagents without mterfe ⁇ ng with the subsequent sol-gel reactions.
- the solvent is an organic solvent such as 2-methoxyethanol or ethanol.
- the hydrolysis agent can be selected from va ⁇ ous compounds such as water, tetramethylammonium hydroxide or mixtures thereof.
- a reagent capable of preventing premature hydrolysis and/or condensation reactions in the initial solution is desirably present. If present, it may selected from va ⁇ ous compounds such as mt ⁇ c acid, hydrochlo ⁇ c acid, and mixtures thereof.
- the order of adding the components of the solution is also not limited. Typically, the alkoxide precursor and the dopant precursor are dissolved in the solvent and refluxed for an approp ⁇ ate time. Then, additional solvent, hydrolysis agent and/or a reagent capable of preventing hydrolysis may be added continuously or incrementally.
- the resulting solution is usually transparent and remains stable for an extended pe ⁇ od of time (e.g., 30 days)
- the amount of the va ⁇ ous components in the solution is not particularly limited and can be determined on a case-by-case basis by one skilled in the art.
- the amounts of the alkoxide precursor and the dopant precursor are such that the molar ratio of the dopant precursor to the alkoxide precursor is from about 1/100 to about 5/100.
- the amount of solvent can range from about 1.000 to about 100,000 ml per mole of alkoxide precursor.
- the amount of the hydrolysis agent may range from about 0 to about 10 moles per mole of alkoxide precursor and depends on the number of alkoxide groups per precursor molecule, while the amount of the reagent capable of preventing premature hydrolysis and or condensation (i.e., p ⁇ or to step (b) in the method abo ⁇ e) in the solution may range from about 0 to about 1 mole per mole of alkoxide precursor.
- p ⁇ or to step (b) in the method abo ⁇ e) in the solution may range from about 0 to about 1 mole per mole of alkoxide precursor.
- There is an optimal dopant to host metal ratio usually determined empi ⁇ cally as a tradeoff between having enough dopants for light output and not having enough dopant that they quench themselv es through non-radiative channels. Too much hydrolysis agent may induce premature or immediate sol-gel condensation reaction, while too much condensation inhibitor may prevent the condensation reaction altogether.
- the solid particle precursor is then added.
- the solid particle precursor is nanoparticulate. although particles in the micron range may be used.
- nanoparticulate and “nanoparticles.” it is meant that the particles have a greatest dimension of about 100 nm or less, and should be as small in size as possible, preferably less than 10 nm.
- these nanoparticles may be silica, metal oxide, metal sulfide, metal oxysulfide, metal hahde. metal carbonate, metal phosphate, metal sulfate. semiconductor-oxide (e.g., germanium oxide), pure metal or mixtures thereof.
- silica such as fumed silica, V 2 0 5 , Y 2 S 3 , GdOS 2 , ZnO. GdS l7 La 2 0 radical A1 2 0,, CdS, and the like may be used.
- AEROSIL ® fumed silica from Degussa Corporation can be used.
- the amount of solid particle precursor usually is close to the stoichiomet ⁇ c amount determined b ⁇ the phosphor compound, although the proportions for optimal light output are to be adjusted (or fine-tuned) empi ⁇ cally. Obviously, if the proportions are too far off, the desired phosphor compound and crystal structure cannot be formed properly.
- the mixing of the solid particle precursor and the solution is preferably performed under conditions preventing any condensation reactions. Preferably, the mixture is subjected to treatment such as ultrasonication to ensure good dispersion of the solid particle precursor. If a hydrolysis agent is not included in the solution of the alkoxide precursor and the dopant precursor, it may be added at any point du ⁇ ng or after the mixing of the solid particle precursor and the solution.
- the solution of the first precursor alkoxide and the dopant alkoxide can be made first without the addition of H 2 0 (or another alternative hydrolysis reagent).
- the solid particle precursor is then mixed with the solution, followed by the addition of H 2 0 (or another hydrolysis reagent) with or without any additional stabilization (1 e , inhibiting) reagents
- a sol-gel condensation reaction is initiated This is usually accomplished by subjecting the mixture to a temperature from about 50° C to several hundred degrees 0 C for several minutes to several hours At this point, a polyme ⁇ c alkoxide gel is formed around each particle of the solid particle precursor
- additional or optional components and/or ingredients may be added at an approp ⁇ ate point in the process of the present invention
- an alcohol such as ethanol
- the optional alcohol may be present in an amount of from about 1,000 to about 10 000 ml/mole of alkoxide precursor If too much optional alcohol is used, not enough mate ⁇ al may be transferred or processed per layer
- the mixture containing the polyme ⁇ c alkoxide gel is then subject to drying and fi ⁇ ng to form the phosphors of the present invention
- the mixture containing the gel is first spread uniformly over a substrate (e g , a metal plate, quartz plate, or the unpolished side of a silicon wafer) to form a film
- a substrate e g , a metal plate, quartz plate, or the unpolished side of a silicon wafer
- Conventional techniques such as dipping, spm-coating, and other methods may be used to apply the gel on the substrate
- the film is d ⁇ ed at about 100° to about 300° C for a few minutes, either continuously under the same conditions or stepwise under different conditions More than one layer may be deposited on the substrate
- the film is then fired at about 800° to about 1,400° C, depending on the phosphor compound, for about 0 25 to about 1 hour to obtain the final phosphor product
- the temperature will depend on the nature of the solid precursors and is determined by their fusion and solid state reactions
- the present invention is not rest ⁇ cted to the formation of thick films as desc ⁇ bed in the embodiments earlier
- the mixture of the solid particle precursor (e g , silica nanopowder) and the doped-alkoxide solution first mixed at room temperature p ⁇ or to sol-gel condensation reactions, can simply be heated to some elevated temperature such as 150° C in a crucible to evaporate the solvent and complete the sol-gel condensation reaction, followed by similar procedures of heating and calcination in oxygen
- the resulting solid can be ground and be used directly as a phosphor powder.
- Blue, green, and red phosphors are contemplated herein.
- Blue phosphors include, but are not limited to, Y 2 S ⁇ O,-.Ce, which can be made from ytt ⁇ um alkoxide, ce ⁇ um alkoxide, and S ⁇ 0 2 .
- Green phosphors include, but are not limited to, ZnS ⁇ 0 4 :Mn, which can be made from zinc alkoxide, manganese alkoxide, and S ⁇ 0 2 .
- Red phosphors include, but are not limited to Y 2 0 2 S:Eu, which can be made from ytt ⁇ um alkoxide, europium acetate, and Y S ⁇ Of course, other species are also contemplated. For a
- YV0 4 :Eu phosphor a Y-Eu alkoxide solution is first made and stabilized against premature condensation. Then V 2 0, nanoparticles are mixed with the Y-Eu alkoxide solution. Sol-gel condensation is then induced, followed by the drying and calcination at suitable temperatures. As desc ⁇ bed previously, the solid particle precursor can be larger than 0.1 micron size (exceeding the nanometer size regime) Advantage can still be gained by the intimate contact between the particle and the shell of other oxides surrounding it before calcination.
- aerogel precursors which comp ⁇ se high porosity structures made of interconnected nanoparticles can be used.
- the high porosity up to 99%, provides the extremely high surface/volume ratio required for high surface contact between the solid precursor and the su ⁇ ounding oxide shell.
- Example 1 (B) w The same procedure used in Example 1 (B) w as used except that the Si/Zn molar ratio was 0.5.
- the thickness of the commercial phosphor film was intentionally made to be much thicker than the thick film in Example 1 above.
- the film should be sufficiently thick so that none of the inducing electrons travel through the film without colliding with the phosphors, although it is also known that there would be no difference beyond a certain thickness.
- the two substrates were adhered side by side using a conductive glue on a chrome-coated glass plate mounted on a translation stage in the vacuum system.
- the cathodoluminescence was measured on the thick film, followed by a translation to the commercial film, and subsequent CL measurement without changing any electron beam parameters.
- the electron beam voltage was adjusted to additional values and the same comparative CL measurements were taken. No charging problem in either film was observed even at the lowest beam voltage used.
- CL measurements for the phosphors of Examples 2 and 3 were not undertaken, these phosphors visibly exhibited a distinct luminescence similar to that of Example 1.
- the present invention represents a new and improved method for manufacturing orthosilicate-based phosphors having high cathodoluminescence, i.e., brightness and luminous efficiency, at low electron beam voltages.
- the thick film made in Example L far from being optimized has already outperformed the commercial phosphor at all voltages up to the highest (3120V) studied.
- the phosphors of the present invention are the much higher luminous efficiencies at the low voltages and the continued linear rise in brightness with increasing voltage.
- the brightness and the luminous efficiency of the commercial RCA PI phosphor begins to level off.
- the luminous efficiency is 3.45 lm/watt for the thick film of the present invention, whereas it is only 0.73 lm/watt for the RCA PI powder film.
- the co ⁇ esponding efficiencies are 4.54 lm watt and 2.94 lm watt for the inventive thick film and the RCA PI powder film, respectively.
- the brightness and luminous efficiency tend to level off at higher voltages.
- the present invention the brightness continues to increase linearly and the efficiency levels off much more slowly at the higher voltages.
Abstract
Doped phosphors (e.g., metal orthosilicates) are made by adding a solid particulate precursor to a solution of an alkoxide precursor and a dopant precursor before hydrolysis is allowed to occur. The mixture is then allowed to hydrolyze, resulting in a sol-gel condensation reaction. The solid particulate precursor can be fumed silica, and acts as a nucleation site for the sol-gel reaction product. After the sol-gel reaction, the mixture is dried and fired to form phosphors. The phosphors are especially suitable for applications in which there is low voltage operation.
Description
METHOD FOR PREPARING EFFICIENT LOW VOLTAGE PHOSPHORS AND
PRODUCTS PRODUCED THEREBY
Background of the Invention
1. Field of the Invention
The present invention generally relates to methods for prepaπng cathodolummescent phosphors using a sol-gel condensation technique, as well as to products made from these methods. In particular, the present invention relates to methods for prepaπng cathodolummescent phosphors (e.g., orthosi cate-based phosphors) exhibiting supeπor bπghtness and efficiency, making them especially suitable for low voltage operation m vaπous applications such as flat panel displays, field emitter displays (FEDs), electroluminescent displays (ELDs), TVs, and the like.
2. Description of the Background Art
Phosphors in general compπse a wide band gap semiconductor matπx with homogeneously dispersed activator ions withm. Currently accepted mechanisms of light output in cathodoluminescence phosphors, though not well understood, include electron-induced creation of excitons, which can result in photon emission through recombination of the holes and electrons. However, lattice defects, impurities, charge traps, etc. can impede the efficient recombination of these charge earners, thus causing the nonradiative decay of the excited states It is believed that the phosphor crystal structure should be as close to perfect as possible to achieve efficient emission of light
Current commercially-available cathodolummescent phosphors are made for high \oltage (i.e., approximately 5-20 kV) applications. On information and belief, bπght and efficient phosphors that are especially suited for low voltage operation (at or below about 1-6 kV, preferably 2-3 kV) do not exist in the prior art. Thus, it would be very desirable to provide cathodolummescent phosphors having supeπor bnghtness and efficiency at low voltages (e.g.. below about 2000 volts) for field emitter displays mainly due to the requirement of the very close proximity of the phosphor screen to the electron source (i.e., the field emitter arrays). Low bias
voltages reduce the seπous problems of electπcal insulation breakdown and arcing.
Many conventional cathodolummescent phosphors, such as those based on orthosi cates with grain sizes of a few micrometers, are prepared by mixing micron-sized or larger precursor particles and fiπng at high temperatures to induce solid reactions. For example, to make green Mn-doped zinc-orthosi cate phosphors, particles of Mn-doped zinc oxide (ZnO) are mixed with Sι02 particles and fired at high temperatures to produce the phosphor compound Zn:Sι0 :Mn via solid reaction The objective of this conventional method would be to cause homogeneous fusion of the precursor components, uniform incorporation of the activator (or dopant) species, and good crystal structure formation. However, due to the slowness of solid fusion/reactions, especially between large particles, good homogeneity is not easily achieved. Lattice defects and even non-stoichiometπcal components can result, leading to poor semiconductor electronic band structures, including gap states that can easily cause nonradiative decay. Furthermore, portions that have an activator (e.g., Mn) deficiency can be formed, contπbutmg to a "dead layer" that gives no light output. Other portions can potentially have excess amounts of the activator species which can quench each other, resulting in decreased light output. U.S. Patent No. 5,985.176 to Rao discloses Mn2+-actιvated zinc orthosi cate phosphors having the empmcal formula:
Zn(2-x)Mn Sι04 wherein 0.005 < x < 0.15. The phosphors descπbed in this patent are said to exhibit the properties of "improved bπghtness and decreased persistence" (column 3, lines 3-12) and are made by using the sol-gel process (column 3, lines 13-24 and column 5, line 7 to column 6, line
11). According to the patent, a high degree of homogeneity is achievable because the starting mateπals are mixed at the molecular level in a solution (column 3, lines 27-29) Unlike the present invention, however, this patent discloses the use of tetraethoxysilane (TEOS) instead of a solid precursor Commonly-owned, copending U.S. Application No. 09/398,947, filed on August 2. 1998. which is incorporated herein by reference for all purposes, discloses phosphor nanoscale powder prepared by forming a solution or slurry compπsing phosphor precursors and then fiπng the solid residue of the solution or slurry In Example I of the '947 application, a mixture of Zn and Mn(JJ) or Cu(H) precursors (e.g., zinc and manganese(U) acetates) is refluxed in ethanol to obtain a mixed solution of alkoxides/acetates of 1 wt.% Zn, with the amount of Mn being in the range of 1-4% with respect to the weight of Zn. The mixed alkoxide/acetate is then cooled and hydrolyzed ith tetramethylammonium hydroxide to form a sol compπsing of a suspension of
mixed nanoparticles of metal oxides. After that. AEROSIL" fumed silica (7 nm in diameter,
Degussa Corporation) is introduced into the sol to form a suspension of the particle precursors. Following ultrasonication, cooling, and drying, the resulting mixed gel is then pre-fired, cooled, ground, and fired. In contrast, in a typical embodiment of the present invention, a Zn-Mn alkoxide solution is first prepared from Zn and Mn alkoxide precursors without hydrolysis or forming particles In fact, an inhibitor such as mtπc acid is typically added to prevent premature
(i.e.. before introduction of the second precursor particles) precipitation of particles. The second precursor particles (e.g., fumed silica) are then added to the solution of the Zn-Mn alkoxide mixture, followed by induced precipitation of the first precursor by sol-gel condensation reaction, the precipitated first precursor being in intimate contact with and around the second precursor particles.
Summary of the Invention
It is an object of the present invention to provide a method for prepaπng phosphors (e.g., orthosilicate phosphors) having supeπor bπghtness and efficiency.
It is also an object of the present invention to provide a method for prepaπng phosphors (e.g., orthosilicate phosphors) particularly adapted for use in low voltage operation (e.g., less than 5 kV) in applications such as flat panel displays, field emitter displays (FEDs), plasma displays, phosphor components for electroluminescent displays (ELDs), screens for TVs, field emission and plasma displays that do not have conventional screens (i.e., luminescent components built into or on the substrate). x-ra\ imaging displays (in lieu of photographic plates), and the like.
It is another object of the present invention to provide a method for prepaπng phosphors (e.g., orthosilicate phosphors) having a relatively uniform crystal structure and stoichiometry so as to achieve efficient emission of light.
It is yet another object of the present invention to provide a method for prepaπng phosphors (e.g., orthosilicate phosphors) exhibiting continued higher bπghtness and/or luminous efficiency with increasing voltage.
It is a further object of the present invention to provide a method for prepaπng phosphors (e.g-, orthosilicate phosphors), wherein the method provides more favorable conditions (e.g., shorter fiπng duration) for the homogenous fusion of the precursors than that used in the manufacture of commercial orthosi cate-based phosphors
These and other objects of the present invention are achieved by adding solid particle precursors to an activator ion-doped alkoxide solution, inducing a sol-gel condensation, drying the mixture, and then calcinating (or fiπng) the resulting mixture. Thus, in one aspect, the present invention provides a method for prepaπng phosphors compπsing the steps of
(a) providing a solution compπsing an alkoxide precursor and a dopant precursor; (b) mixing said solution with a solid particle precursor,
(c) inducing a sol-gel condensation reaction to form a sol-gel condensation reaction mixture;
(d) drying the sol-gel condensation reaction mixture; and
(e) fiπng the dπed reaction mixture at a temperature sufficient to form phosphors. In other aspects, phosphor products made in accordance with the present invention are also contemplated
Brief Description of the Drawings
Figure 1 compares the bπghtness (cd/m2) of the Zn2Sι0 :Mn phosphor of inventive
Example 1 against a commercial Zn2SιO4-Mn phosphor (RCA PI) at vaπous beam voltages.
Figure 2 compares the luminous efficiency (lm/W) of the Zn2Sι04:Mn phosphor of inventive Example 1 against a commercial Zn2Sι04:Mn phosphor (RCA PI) at vaπous beam voltages.
Description of the Preferred Embodiments
It has been discovered that, in compaπson to conventional or commercial phosphor production technology, the present invention achieves a different and a more favorable condition for the homogeneous fusion of the precursors. In this invention, solid particle precursors (e.g.,
Sι02 nanocrystals) are initially mixed with a solution of an alkoxide precursor (e g., zinc alkoxide) and a dopant precursor (e g , manganese alkoxide), at suitable concentrations and proportions, before solid oxide (e g., ZnO and MnO) particles form. A sol-gel hydrolysis-condensation reaction is then induced in the presence of the solid particle precursor so as to permit the formation of a coating of a doped alkoxide gel polymer around each solid particle precursor. It should be noted that the coating may, but not necessaπly, have non-umform thickness around the solid particle In the drying and fiπng process, an oxide shell, in complete
contact with the solid particle precursor, is formed. Thus, the contact area is much larger than m the case when the synthesis involves mixing of solid precursor particles. In particular, a lower temperature, a much shorter solid reaction time as well as supeπor homogeneity can be expected In the present invention, a solution containing at least an alkoxide precursor and a dopant precursor is first provided. Typically, but not necessaπly, the solution also compπses a hydrolysis agent and/or a reagent capable of inhibiting premature condensation reaction in the solution pπor to the addition of the solid particle precursor.
The alkoxide precursor can be any alkoxide that can form a phosphor and is suitably a metal alkoxide. Such metal alkoxide precursors include, but are not limited to zinc alkoxides. When zinc alkoxιde(s) are selected, they may be selected from zinc methoxide, zinc ethoxide, zinc propoxide, zinc butoxide, and others.
There is also no limitation with respect to the dopant precursor, so long as a phosphor can be produced Typically, the dopant is selected from an acetate, an alkoxide, an organometal c compound, or an inorganic salt of the metal (dopant ion), and mixtures thereof. Good results have been obtained using metal alkoxides such as manganese methoxide, as well as acetates such as europium acetate; successful results would also be expected for other dopant precursor species such as manganese nitrate.
The solvent is any liquid that can provide a solution of the above-descπbed alkoxide precursor, dopant precursor, and other optional reagents without mterfeπng with the subsequent sol-gel reactions. Usually, the solvent is an organic solvent such as 2-methoxyethanol or ethanol. If present in the initial solution, the hydrolysis agent can be selected from vaπous compounds such as water, tetramethylammonium hydroxide or mixtures thereof.
Additionally, a reagent capable of preventing premature hydrolysis and/or condensation reactions in the initial solution is desirably present. If present, it may selected from vaπous compounds such as mtπc acid, hydrochloπc acid, and mixtures thereof. The order of adding the components of the solution is also not limited. Typically, the alkoxide precursor and the dopant precursor are dissolved in the solvent and refluxed for an appropπate time. Then, additional solvent, hydrolysis agent and/or a reagent capable of preventing hydrolysis may be added continuously or incrementally. The resulting solution is usually transparent and remains stable for an extended peπod of time (e.g., 30 days) The amount of the vaπous components in the solution is not particularly limited and can be determined on a case-by-case basis by one skilled in the art. Typically, the amounts of the alkoxide precursor and the dopant precursor are such that the molar ratio of the dopant precursor
to the alkoxide precursor is from about 1/100 to about 5/100. The amount of solvent can range from about 1.000 to about 100,000 ml per mole of alkoxide precursor. Further, the amount of the hydrolysis agent may range from about 0 to about 10 moles per mole of alkoxide precursor and depends on the number of alkoxide groups per precursor molecule, while the amount of the reagent capable of preventing premature hydrolysis and or condensation (i.e., pπor to step (b) in the method abo\e) in the solution may range from about 0 to about 1 mole per mole of alkoxide precursor. There is an optimal dopant to host metal ratio, usually determined empiπcally as a tradeoff between having enough dopants for light output and not having enough dopant that they quench themselv es through non-radiative channels. Too much hydrolysis agent may induce premature or immediate sol-gel condensation reaction, while too much condensation inhibitor may prevent the condensation reaction altogether.
After the solution containing at least the alkoxide precursor and the dopant precursor is provided, a solid particle precursor is then added. Typically, the solid particle precursor is nanoparticulate. although particles in the micron range may be used. By the term "nanoparticulate" and "nanoparticles." it is meant that the particles have a greatest dimension of about 100 nm or less, and should be as small in size as possible, preferably less than 10 nm.
Typically, these nanoparticles may be silica, metal oxide, metal sulfide, metal oxysulfide, metal hahde. metal carbonate, metal phosphate, metal sulfate. semiconductor-oxide (e.g., germanium oxide), pure metal or mixtures thereof. Specifically, silica such as fumed silica, V205, Y2S3, GdOS2, ZnO. GdSl7 La20„ A120,, CdS, and the like may be used. With respect to silica, AEROSIL® fumed silica from Degussa Corporation can be used. The amount of solid particle precursor usually is close to the stoichiometπc amount determined b\ the phosphor compound, although the proportions for optimal light output are to be adjusted (or fine-tuned) empiπcally. Obviously, if the proportions are too far off, the desired phosphor compound and crystal structure cannot be formed properly. It should be noted that the mixing of the solid particle precursor and the solution is preferably performed under conditions preventing any condensation reactions. Preferably, the mixture is subjected to treatment such as ultrasonication to ensure good dispersion of the solid particle precursor. If a hydrolysis agent is not included in the solution of the alkoxide precursor and the dopant precursor, it may be added at any point duπng or after the mixing of the solid particle precursor and the solution. For example, the solution of the first precursor alkoxide and the dopant alkoxide can be made first without the addition of H20 (or another alternative hydrolysis reagent). The solid particle precursor is then mixed with the solution, followed by the
addition of H20 (or another hydrolysis reagent) with or without any additional stabilization (1 e , inhibiting) reagents
After the mixing of the solid particle precursor and the solution is complete, a sol-gel condensation reaction is initiated This is usually accomplished by subjecting the mixture to a temperature from about 50° C to several hundred degrees0 C for several minutes to several hours At this point, a polymeπc alkoxide gel is formed around each particle of the solid particle precursor
It should be understood here that additional or optional components and/or ingredients may be added at an appropπate point in the process of the present invention For example, it may be desirable to incorporate an alcohol, such as ethanol in the mixture (after the sol-gel condensation has taken place) of the present inv ention to promote drying and spreadability of the mixture on a substrate If used, the optional alcohol may be present in an amount of from about 1,000 to about 10 000 ml/mole of alkoxide precursor If too much optional alcohol is used, not enough mateπal may be transferred or processed per layer
The mixture containing the polymeπc alkoxide gel is then subject to drying and fiπng to form the phosphors of the present invention In one embodiment, the mixture containing the gel is first spread uniformly over a substrate (e g , a metal plate, quartz plate, or the unpolished side of a silicon wafer) to form a film Conventional techniques such as dipping, spm-coating, and other methods may be used to apply the gel on the substrate After the layer is applied, the film is dπed at about 100° to about 300° C for a few minutes, either continuously under the same conditions or stepwise under different conditions More than one layer may be deposited on the substrate
The film is then fired at about 800° to about 1,400° C, depending on the phosphor compound, for about 0 25 to about 1 hour to obtain the final phosphor product The temperature will depend on the nature of the solid precursors and is determined by their fusion and solid state reactions
As would be apparent to one skilled in the art, the present invention is not restπcted to the formation of thick films as descπbed in the embodiments earlier Instead of drying the precursor mixture on a substrate the mixture of the solid particle precursor (e g , silica nanopowder) and the doped-alkoxide solution, first mixed at room temperature pπor to sol-gel condensation reactions, can simply be heated to some elevated temperature such as 150° C in a crucible to evaporate the solvent and complete the sol-gel condensation reaction, followed by similar procedures of heating and calcination in oxygen The resulting solid can be ground and be used
directly as a phosphor powder.
The same approach used in this invention can be applied to the preparation of any phosphor for which one of the precursors, excluding the dopant precursor, is in solid particle (typically nanoparticle) form and the other precursors exist in or can be converted to alkoxides in solution form. The important factor is to mix the precursors before any precipitation or condensation has occuπed in the alkoxide solution. Blue, green, and red phosphors are contemplated herein. Blue phosphors include, but are not limited to, Y2SιO,-.Ce, which can be made from yttπum alkoxide, ceπum alkoxide, and Sι02 . Green phosphors include, but are not limited to, ZnSι04:Mn, which can be made from zinc alkoxide, manganese alkoxide, and Sι02 . Red phosphors include, but are not limited to Y202S:Eu, which can be made from yttπum alkoxide, europium acetate, and Y S^ Of course, other species are also contemplated. For a
YV04:Eu phosphor, a Y-Eu alkoxide solution is first made and stabilized against premature condensation. Then V20, nanoparticles are mixed with the Y-Eu alkoxide solution. Sol-gel condensation is then induced, followed by the drying and calcination at suitable temperatures. As descπbed previously, the solid particle precursor can be larger than 0.1 micron size (exceeding the nanometer size regime) Advantage can still be gained by the intimate contact between the particle and the shell of other oxides surrounding it before calcination.
Additionally, instead of using distinct particle precursors, aerogel precursors which compπse high porosity structures made of interconnected nanoparticles can be used. The high porosity, up to 99%, provides the extremely high surface/volume ratio required for high surface contact between the solid precursor and the suπounding oxide shell.
EXAMPLES
The following examples illustrate certain embodiments of the present invention. However, they are not to be construed to limit the scope of the present invention in any way.
Example 1
(A) Preparation of Mixed Zn-Mn Alkoxide Solution. A mixture of 1.0136 g of zinc butoxide and 0.0101 g of manganese methoxide at a molar ratio of Mn/Zn=0.018 was dissolved m 10.0 ml of 2-methoxyethanol and refluxed for 1 hour at 80° C, under nitrogen flow, to give a clear, light brown 0.48M (Zn) solution (stock). A mixture
of 19 0 ml of 2-methoxyethanol, 0.15 ml of water and 0.02 ml of nitπc acid (the latter being a reagent for inhibiting premature hydrolysis and condensation) was added to 5.0 ml of the stock solution to give a final 0.1M (Zn) solution. The solution remained transparent with no precipitation The solution remained clear and stable for many weeks.
(B) Introduction of the Silica Nanoparticles:
0 010 g of AEROSLL® 150 (Sι02, 7 nm diameter, Degussa Corporation) was introduced into 3 70 ml of the above 0.1M alkoxide solution (in a proportion with a molar ratio of Sι/Zn=0.45) at room temperature and ultrasonicated for dispersion of the AEROSIL® 150 particles At this point no condensation reaction had taken place, as evidenced by the settling of the AEROSIL® 150 particles over a relatively short time and the solution above them remained clear.
(C) Initiation of Sol-Gel Condensation Reactions-
The mixture in (B) was heated to and maintained at 80° C while being agitated. In about 90 minutes the solution became homogeneous and translucent.
(D) Preparation of Mixed Thick Film:
(1) A fixed small quantity of the mixture in (C) was spread as uniformly as possible over the back unpolished side of a 1 x 1 cm piece of silicon wafer at room temperature and then dπed at 100° C for 5 minutes, followed by further drying at 200° C for 5 minutes in room atmosphere.
(2) A second layer of the mateπal was added on top of the layer in (1) using the same dispensing and drying procedure. It should be noted at this point that as many layers as desired could be added. In this example, a 40 layer thick film was built up using the same procedure (3) The thick film in (2) was heated in a quartz tube oven under flowing oxygen for
30 minutes at 350° C. The temperature was then increased to 1050° C over 1 5 hours and maintained at this temperature for 15 minutes. The oven was then turned off to allow a slow cooling down to room temperature.
Example 2
(A) Preparation of the Mixed Zn-Mn alkoxide Solution:
The same solution as in Example 1 (A) was used
(B) Introduction of the Silica Nanoparticles:
The same procedure used in Example 1 (B) w as used except that the Si/Zn molar ratio was 0.5.
(C) No Initial Heating:
The mixture in (B) was kept at room temperature. The solution, except for the silica powder, remained clear.
(D) Preparation of Thick Mixed Film-
(1 ) The mixture in (C) was shaken to ensure uniform dispersion of the silica powder before dispensing in the same manner as in Example 1 (D) ( 1 ), except drying w as performed at about 100° C
(2) A thick film consisting of 6 layers w as made by repeating (1) six times. (3) The thick film in (2) was heated in a quartz tube oven under flowing oxygen at
875° C for 30 minutes. It was then cooled slowly to room temperature.
Example 3
An eight-layer thick film on a Pt film-coated silicon substrate (polished side) w as made using otherwise the same procedures and conditions as in Example 2.
Cathodoluminescence Measurements
Cathodoluminescence (CL) properties of the thick films made in Examples 1 through 3 were observed, and the CL for the thick film made in Example 1 was measured at an electron beam voltage of 320-3120 volts using a Minolta CS- 1000 spectroradiometer and processed with ND filter compensation and wavelength calibration The chromaticity parameter (CIE 1931) were measured to be x=0.2065. y = 0.7122. The bπghtness and the luminous efficiency are plotted in Figures 1 and 2. respectively In comparative studies, to account for possible differences due to substrates and other factors, a powder film of the commercial Zn2Sι04.Mn (RCA PI phosphor from Sarnoff Corporation) was placed on the same type of silicon substrate. The thickness of the commercial phosphor film was
intentionally made to be much thicker than the thick film in Example 1 above. In this regard, it is known that the film should be sufficiently thick so that none of the inducing electrons travel through the film without colliding with the phosphors, although it is also known that there would be no difference beyond a certain thickness. The two substrates were adhered side by side using a conductive glue on a chrome-coated glass plate mounted on a translation stage in the vacuum system. The cathodoluminescence was measured on the thick film, followed by a translation to the commercial film, and subsequent CL measurement without changing any electron beam parameters. Then the electron beam voltage was adjusted to additional values and the same comparative CL measurements were taken. No charging problem in either film was observed even at the lowest beam voltage used. Although CL measurements for the phosphors of Examples 2 and 3 were not undertaken, these phosphors visibly exhibited a distinct luminescence similar to that of Example 1.
As shown in Figures 1 and 2. the present invention represents a new and improved method for manufacturing orthosilicate-based phosphors having high cathodoluminescence, i.e., brightness and luminous efficiency, at low electron beam voltages. For example, the thick film made in Example L far from being optimized, has already outperformed the commercial phosphor at all voltages up to the highest (3120V) studied. Especially significant for the phosphors of the present invention are the much higher luminous efficiencies at the low voltages and the continued linear rise in brightness with increasing voltage. By contrast, the brightness and the luminous efficiency of the commercial RCA PI phosphor begins to level off. Specifically, at 320 volts, the luminous efficiency is 3.45 lm/watt for the thick film of the present invention, whereas it is only 0.73 lm/watt for the RCA PI powder film. At 520 volts, the coπesponding efficiencies are 4.54 lm watt and 2.94 lm watt for the inventive thick film and the RCA PI powder film, respectively. For most commercial phosphors, the brightness and luminous efficiency tend to level off at higher voltages. On the other hand, in the present invention, the brightness continues to increase linearly and the efficiency levels off much more slowly at the higher voltages.
Claims
1. A method for prepaπng phosphors compπsing the steps of:
(a) providing a solution compπsing an alkoxide precursor and a dopant precursor; 0 (b) mixing said solution w ith a solid particle precursor;
(c) inducing a sol-gel condensation reaction to form a sol-gel condensation reaction mixture;
(d) drying the sol-gel condensation reaction mixture; and
(e) fiπng the dπed reaction mixture at a temperature sufficient to form phosphors.
2. The method according to claim 1. w herein said solution further compπses a hydrolysis agent.
3. The method according to claim 1. wherein a hydrolysis agent is added after said step (b).
4. The method according to claim 3, wherein said hydrolysis agent is added immediately before step (c).
5. The method according to claim 1. wherein said solution further compπses a reagent capable of inhibiting condensation reactions before step (b) (stabilizing agent) in said solution.
6. The method according to claim 1. wherein said solid particle precursor have an average particle size of from about 2 to about 10,000 nm.
7. The method according to claim 2. wherein said hydrolysis agent is selected from the group consisting of water.
8. The method according to claim 3. wherein said hydrolysis agent is selected from the group consisting of water, tetramethylammonium hydroxide, and mixtures thereof.
9. The method according to claim 1. wherein said dopant precursor is an alkoxide. an acetate, an organometal c compound, an inorganic salt, or mixtures thereof.
10. The method according to claim 1, wherein said solid particle precursor is silica, metal oxide, metal sulfide, metal oxysulfide, metal ha de, metal carbonate, metal phosphate, metal sulfate. semiconductor-oxide, pure metal or mixtures thereof.
11. The method according to claim 10, wherein said solid particle precursor is fumed silica
12. A phosphor product obtained from the process according to claim 1.
13. The phosphor product according to claim 12. wherein said product is included in a TV screen, a field emission display, a plasma display, a phosphor screen, a phosphor component for an electroluminescence display, a field emission or plasma display that does not have a conventional screen (i.e., luminescent components built into or on a substrate), an x-ray imaging display, or a detector for x-ray or charged particles.
14. A phosphor product according to claim 12, wherein the cathodoluminescence of said phosphor product increases substantially in a linear fashion with increasing voltage.
15. The phosphor product according to claim 14, wherein said product is included in a TV screen, a field emission display, a plasma display, a phosphor screen, a phosphor component for an electroluminescence display, a field emission or plasma display that does not have a conventional screen (i.e., luminescent components built into or on a substrate), an x-ray imaging display, or a detector for x-ray or charged particles.
16. A phosphor product according to claim 14, wherein the cathodoluminescence of said product increases substantially in a linear fashion at increasing voltages between 2.0 kV and 3.5 kV
17. The phosphor product according to claim 16, wherein said product is included in a TV screen, a field emission display, a plasma display, a phosphor screen, a phosphor component for an electroluminescence display, a field emission or plasma display that does not have a conv entional screen (i.e., luminescent components built into or on a substrate), an x-ray imaging display, or a detector for x-ray or charged particles.
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US2252500A (en) * | 1939-12-07 | 1941-08-12 | Gen Electric | Method of preparing fluorescent materials |
US5985176A (en) * | 1997-12-04 | 1999-11-16 | Matsushita Electric Industrial Co., Ltd. | Method of preparing high brightness, shorter persistence zinc orthosilicate phosphor |
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US3927224A (en) * | 1971-12-15 | 1975-12-16 | Owens Illinois Inc | Luminescent and/or photoconductive materials |
US4517037A (en) * | 1981-11-02 | 1985-05-14 | Aluminum Company Of America | Refractory composition comprising nitride filler and colloidal sol binder |
US4931312A (en) * | 1986-02-10 | 1990-06-05 | North American Philips Corporation | Sol-gel process for producing liminescent thin film, and film so produced and devices utilizing same |
US4965091A (en) * | 1987-10-01 | 1990-10-23 | At&T Bell Laboratories | Sol gel method for forming thin luminescent films |
US5387480A (en) * | 1993-03-08 | 1995-02-07 | Dow Corning Corporation | High dielectric constant coatings |
JP2770299B2 (en) * | 1993-10-26 | 1998-06-25 | 富士ゼロックス株式会社 | Thin-film EL element, method of manufacturing the same, and sputtering target used therefor |
US5824622A (en) * | 1994-01-12 | 1998-10-20 | E. I. Du Pont De Nemours And Company | Porous microcomposite of perfluorinated ion-exchange polymer and metal oxide, a network of silica, or a network of metal oxide and silica derived via a sol-gel process |
US5611961A (en) * | 1994-09-14 | 1997-03-18 | Osram Sylvania Inc. | Method of preparing manganese activated zinc orthosilicate phosphor |
US5622750A (en) * | 1994-10-31 | 1997-04-22 | Lucent Technologies Inc. | Aerosol process for the manufacture of planar waveguides |
US5695809A (en) * | 1995-11-14 | 1997-12-09 | Micron Display Technology, Inc. | Sol-gel phosphors |
US5667724A (en) * | 1996-05-13 | 1997-09-16 | Motorola | Phosphor and method of making same |
US5985173A (en) | 1997-11-18 | 1999-11-16 | Gray; Henry F. | Phosphors having a semiconductor host surrounded by a shell |
-
2000
- 2000-03-17 US US09/531,159 patent/US6402985B1/en not_active Expired - Fee Related
-
2001
- 2001-02-05 WO PCT/US2001/003574 patent/WO2001070902A1/en active Application Filing
-
2002
- 2002-03-06 US US10/090,630 patent/USH2131H1/en not_active Abandoned
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US2252500A (en) * | 1939-12-07 | 1941-08-12 | Gen Electric | Method of preparing fluorescent materials |
US5985176A (en) * | 1997-12-04 | 1999-11-16 | Matsushita Electric Industrial Co., Ltd. | Method of preparing high brightness, shorter persistence zinc orthosilicate phosphor |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
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FR2829770A1 (en) * | 2001-09-17 | 2003-03-21 | Centre Nat Rech Scient | Preparing precursor component of luminophoric powder or crystals in form of aerogel comprises adding organic solvent, mixing under agitation, and eliminating solvent by drying in autoclave |
WO2003025087A1 (en) * | 2001-09-17 | 2003-03-27 | Centre National De La Recherche Scientifique (Cnrs) | Method for making phosphor powder precursor materials |
Also Published As
Publication number | Publication date |
---|---|
USH2131H1 (en) | 2005-11-01 |
US6402985B1 (en) | 2002-06-11 |
US20020081373A1 (en) | 2002-06-27 |
WO2001070902B1 (en) | 2002-02-14 |
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