WO2016061408A1 - Ceramique phosphorescente contenant des silicates metalliques pour une emission de lumiere jaune et blanche - Google Patents

Ceramique phosphorescente contenant des silicates metalliques pour une emission de lumiere jaune et blanche Download PDF

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WO2016061408A1
WO2016061408A1 PCT/US2015/055823 US2015055823W WO2016061408A1 WO 2016061408 A1 WO2016061408 A1 WO 2016061408A1 US 2015055823 W US2015055823 W US 2015055823W WO 2016061408 A1 WO2016061408 A1 WO 2016061408A1
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phosphor
atom
ceramics
ceramic
μιη
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PCT/US2015/055823
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Hiroaki Miyagawa
Bin Zhang
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Nitto Denko Corporation
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Definitions

  • the present invention relates to luminescent ceramic(s) and methods for making the same.
  • Phosphors and phosphor elements are used to produce light emissions. There is a continuing need for additional phosphors for a variety of applications.
  • Some embodiments include luminescent ceramics comprising: Sr 2 Si0 4 wherein the Sr 2 Si0 4 is doped or loaded with Eu or an ion thereof, in an amount that is about 0.01 atom% to about 5 atom% based upon the total number of atoms or ions of Eu or Sr; and wherein the luminescent ceramic comprises a sintered ceramic plate.
  • Some embodiments include a method of preparing the luminescent ceramics described herein, comprising sintering a composition comprising a calcined precursor powder at a temperature of about 700 °C to about 1000 °C for at least about 1 hour to adhere particles of the calcined precursor powder to one another to form a sintered ceramic plate, wherein the calcined precursor powder comprises Sr 2 Si0 4 loaded or doped with europium or an ion thereof.
  • the method for making a phosphor may comprise a calcined precursor powder mixture comprising at least 10% yellow- emitting silicate and less than 90% blue-emitting silicate; creating a precursor slurry with the calcined precursor powder; casting the precursor slurry on a substrate to form a cast tape; drying the cast tape at a temperature and time sufficient to remove the solvent and create a compact; debinding the compact at a temperature and time sufficient to remove the binder and maintain desired phosphor ceramic oxidation; and sintering the compact at a sufficient temperature and time sufficient to reduce the presence of secondary phases and retain the desired IQE characteristics.
  • providing the calcined powder mixture may comprise mixing the precursor materials in a solvent; drying the precursor materials while removing/evaporating the solvent; and calcining the dried precursor materials.
  • the solvent may be water or toluene.
  • the powder mixture may comprise a strontium carbonate, a silicon oxide, a dopant oxide precursor or combinations thereof.
  • the dopant oxide precursor may be EU2O3.
  • the powder mixture may further comprise a sintering aid.
  • the sintering aid may be NH 4 CI.
  • the powder mixture may further comprise a dispersant.
  • the dispersant may comprise FLOWLEN® G-700.
  • drying the powders to remove/evaporate solvent may be at about 80 °C for about 16 hours.
  • calcining the precursor powder may be at a temperature between 700 °C and 900 °C for about 30 minutes to about 4 hours.
  • the calcined powder may be calcined at about 750 °C for about 2 hours.
  • the calcined powder may be calcined at about 800 °C for about 2 hours.
  • providing the calcined powder mixture comprises mixing the precursor materials in a solvent; drying the precursor materials to remove/evaporate the solvent; and calcining the dried precursor materials.
  • a phosphor ceramic element may be manufactured according to the method(s) described herein.
  • the phosphor ceramic element may emit light having a wavelength of from about 420 nm to about 650 nm or from about 525 nm to about 600 nm.
  • phosphor ceramic element may comprise (a) a Sr-silicate phosphor composite, the composite comprising Sr 2 Si0 (SS) and Sr 3 MgSi 2 0 8 (SMS-312) phase phosphor composites; (b) a Sr-silicate phosphor composite, the composite comprising Sr 2 Si0 and Sr 2 MgSi 2 0 7 phase phosphor composites; and/or (c)a Sr-silicate phosphor composite, the composite comprising Sr 2 Si0 4 ; (d) or combinations thereof.
  • the phosphor is doped with europium (Eu 2+ ), in an amount of about 0.01 atom% to about 5 atom%.
  • the phosphor ceramic element may comprise Sr 2 Si0 4 or composite phases, wherein the phosphor ceramic element has a thickness of about 50 ⁇ to about 1000 ⁇ , and/or a surface having an area of at least about 1 cm 3 , wherein the surface is normal to the direction of the thickness, and/or wherein the phosphor ceramic element can comprise sintered particles having a diameter of less than about 50 ⁇ .
  • the phosphor ceramic element may comprise at least about 1 % to about 100% by volume of Sr 2 Si0 4 .
  • the phosphor ceramic element may comprise phases selected from Sr 3 MgSi 2 08, Sr 2 MgSi 2 0 7 , Sr 2 Si0 4 , or a combination thereof.
  • FIG. 1 is a schematic for an embodiment to make a silicate phosphor ceramic element using a tape casting methodology.
  • FIG. 2 depict plots showing light spectra of LED with and without a yellow-emitting SS phosphor ceramic plate described in Example 1 .
  • FIG. 3 is a plot showing X-Ray Diffraction (XRD) plots of embodiments of an SS-phosphor plate described in Example 1 .
  • FIG. 4 shows normalized photoluminescence emission spectra of Examples 3, 4, and 5 with different levels of Eu-doping.
  • FIG. 5 shows normalized photoluminescence excitation spectra of Examples 3, 4, and 5 with different levels of Eu-doping.
  • FIGS. 6A and 6B show SEM micrographs showing the surface morphology of Example 4.
  • FIG. 7 shows normalized photoluminescence emission spectra of various samples in Example 5 sintered at different temperatures.
  • FIG. 8 shows normalized photoluminescence excitation spectra of various samples in Example 5 sintered at different temperatures.
  • FIG.9 shows an SEM micrograph showing the morphology of SMS- 312 phosphor powders, processed in Example 6
  • FIG. 10 shows normalized photoluminescence emission spectra of Examples 4 and 6 with or without blue emitting SMS-312 phase.
  • FIG. 1 1 shows normalized photoluminescence excitation spectra of Examples 4 and 6 with or without blue emitting SMS-312 phase.
  • FIGS.12A and 12B show SEM micrographs showing the surface morphology of composite phosphor ceramics in Example 6.
  • the luminescent ceramic(s) may comprise a phosphor that can provide desired absorption and/or emissive characteristics. In some embodiments, the luminescent ceramic(s) may absorb light, or may have an absorptive peak, between about 300 nm and about 500 nm or between about 360 nm to about 430 nm.
  • the luminescent ceramic(s) may have emit light that is yellow and/or orange light or that emits, or has an emissive peak, that is between about 400 nm and about 650 nm; about 435 nm to about 550 nm; about 525 nm and about 660 nm; 530 nm and about 600 nm or any other combination of wavelengths within these ranges.
  • luminescent ceramic(s) emits yellow and/or orange light, which may be between, or have an emissive peak of, about 525 nm, 530 nm 560 nm, 580 nm, 590 nm, to about 580 nm, 590 nm, 600 nm, 620 nm, 660 nm and/or any combinations of the recited wavelengths.
  • the luminescent ceramic(s) may have emissive characteristics of yellow light, e.g., emission, or peak emission, between about 530 nm and about 600 nm.
  • the luminescent ceramic(s) may have emissive characteristics of orange light, e.g., emission, or peak emission, between about 570 nm or 590 nm to about 620 nm or 650 nm. In some embodiments, the luminescent ceramic(s) may have emissive characteristics of blue light, e.g., emission, or peak emission, between about 435 nm and about 500 nm. In some embodiments, the luminescent ceramic(s) may emit light that is yellow, orange, blue, or combinations thereof.
  • the luminescent ceramic(s) may also provide desired emissive characteristics without extensive thermal deterioration.
  • the luminescent ceramic(s) may comprise a silicate phosphor.
  • the silicate phosphor may comprise a strontium silicate phosphor.
  • the silicate phosphor may comprise Sr 2 Si0 4 .
  • the silicate phosphor may emit a yellow and/or orange light.
  • the silicate phosphor may emit a blue light.
  • the silicate phosphor may be a composite which emits yellow, orange, and blue light or combinations thereof.
  • the blue emitting silicate phosphor can be an secondary-phase strontium phosphor.
  • the luminescent ceramic(s) may comprise Sr-silicate phosphor or a Sr-silicate phosphor composite, the composite comprising Sr 2 Si0 and Sr 3 MgSi 2 0 8 -phase phosphor; Sr 2 Si0 and Sr 2 MgSi 2 0 7 -phase phosphor; Sr 2 Si0 4 ; or combinations thereof.
  • a luminescent ceramic(s) may comprise: Sr 2 Si0 4 , which is doped or loaded with Eu or an ion thereof.
  • the luminescent ceramic(s) may comprise Sr 2 Si0 4 which is doped or loaded with Eu.
  • a luminescent ceramic(s) may be a composite of Sr 2 Si0 4 doped or loaded with Eu, or an ion thereof, and Sr 3 MgSi 2 08 doped or loaded with Eu or an ion thereof.
  • the Sr-silicate may emit yellow light.
  • the yellow and/or orange emitting silicate phosphor can be a main phase Sr-silicate phosphor.
  • the Sr-silicate phosphor may emit blue light.
  • the Sr-phosphor may have a phase composition ratio of at least about 10% yellow/orange-emitting main-phase Sr phosphor and about 90% blue-emitting secondary Sr 3 MgSi 2 08 phase phosphor by volume.
  • the main-phase Sr silicate phosphor may comprise Sr, Si, and O.
  • the main-phase Sr silicate phosphor may exclude magnesium.
  • the phosphor phase composition may comprise at least 10%, at least 15%, at least 25%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 97% main-phase Sr silicate phosphor by volume.
  • the luminescent ceramic(s) may comprise substantially all main-phase Sr phosphor.
  • the remaining percentage of phosphor in the luminescent ceramic(s) may comprise secondary Sr 3 MgSi208 phase phosphor.
  • the Sr-phosphor may comprise about 40% to about 60% secondary- phase Sr phosphor.
  • the Sr-phosphor may comprise about 60% to about 40% Sr 3 MgSi 2 08 phase phosphor by volume.
  • the secondary-phase Sr-silicate phosphor may comprise Sr 2 MgSi 2 0 7 , Sr 2 Si0 , MgSiOs, Mg 2 Si0 4 , MgO, SrO, SrC03, Si0 2 , SrSi0 3 , or combinations thereof.
  • the yellow-emitting and/or main-phase Sr-silicate phosphor may comprise Sr 2 Si0 4 or doped Sr 2 Si0 4 phosphor.
  • the luminescent ceramic(s) may comprise Sr 3 MgSi 2 08 phase phosphor, doped Sr 3 MgSi 2 08 phase phosphor, or combinations thereof. In some embodiments, the luminescent ceramic(s) may comprise at least about 1 % to about 100% by volume of Sr 2 Si0 4 . In some embodiments, the luminescent ceramic(s) may comprise Sr 3 MgSi 2 0 8 , Sr 2 MgSi 2 0 7 , Sr 2 Si0 , or combinations thereof
  • the main Sr-silicate phosphor luminescent ceramic(s) may comprise multiple structural phases which may include, but are not limited to, monoclinic, rhombohedra, cubic, tetragonal, orthorhombic, perovskite structure (i.e., orthorhombic-dipyramidal), akermanite structure (i.e., tetragonal- scalenohedral), ringwoodite structure (i.e., isometric-hexoctahedral), fosterite structure (i.e., orthorhombic-dipyramidal), halite structure (i.e., cubic), and/or merwinite structure (i.e., monoclinic-prismatic).
  • monoclinic, rhombohedra cubic
  • tetragonal orthorhombic
  • perovskite structure i.e., orthorhombic-dipyramidal
  • akermanite structure i.e.
  • the Sr- silicate phosphor may comprise at least 10%, at least 15%, at least 25%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 97% Sr 2 Si0 , including doped or loaded Sr 2 Si0 , such as Sr 2 Si0 4 that is doped or loaded with Eu or an ion thereof.
  • the luminescent ceramic(s) may comprise a dopant to create a doped Sr-phosphor.
  • the dopant may comprise at least one naturally occurring element, e.g., non-noble gas elements.
  • the dopant may be selected from one of more elements including, but not limited to, lanthanide elements, e.g., Eu 2+ , which include elements with atomic numbers 57 through 71 . Details of suitably doped materials are presented in the U.S. Provisional Patent Application No. 61 /587,889, which is hereby incorporated by reference in its entirety.
  • the dopant may comprise of at least europium (Eu 2+ ).
  • doped or loaded europium to the total number of Sr and Eu atoms or ions has a relative atomic ratio of between about 0.01 at or about 0.1 atom% to about 5.0 atom%, such as about 0.01 atom%, about 0.05 atom%, about 0.1 atom%, about 0.5 atom%, about 1 atom%, about 1 .5 atom%, about 2.0 atom%, to about 3.5 atom%, about 4.0 atom%, about 5.0 atom% Eu 2+ , or any range combination of the above ratios.
  • Doped elements in some embodiments may also be elements that are incorporated into the crystal lattice of the Sr compound, for example, as substituted within defined positions within the crystal lattice or otherwise interstitially included within the crystal.
  • the Eu may be present in any suitable amount, such as about 0.01 atom% to about 5.0 atom%, about 0.05 atom% to about 2.0 atom%, about 0.1 atom% to about 1 .0 atom%, about 0.1 atom% to about 0.3 atom%, about 0.3 atom% to about 0.5 atom%, about 0.5 atom% to about 0.7 atom%, or about 0.7 atom% to about 1 .0 atom%, based upon the total number of atoms or ions of Eu or Sr.
  • the element may also comprise a sintering aid.
  • the sintering aid may include, but not limited to, ammonium salts (e.g., NH 4 CI); Si0 2; zirconium; magnesium; calcium; silicates and fluorides, such as, but not limited to tetraethoxysilane (TEOS), colloidal silica, and combinations thereof; oxides and fluorides such as, but not limited to, lithium oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, strontium oxide, boron oxide, calcium fluoride, and combinations thereof.
  • TEOS tetraethoxysilane
  • oxides and fluorides such as, but not limited to, lithium oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, strontium oxide, boron oxide, calcium fluoride, and combinations thereof.
  • the luminescent ceramic(s) may also comprise dispersants such as FLOWLEN®; fish oil; long chain polymers; steric acid; oxidized Menhaden Fish Oil (MFO); dicarboxylic acids such as, but not limited to succinic acid, ethanedioic acid, propanedioic acid, pentanedioic acid, hexanedioic acid, heptanedioic acid, octanedioic acid, nonanedioic acid, decanedioic acid, o- phthalic acid, p-phthalic acid; sorbitan monooleate; and combinations thereof.
  • dispersants such as FLOWLEN®
  • fish oil such as fish oil; long chain polymers; steric acid; oxidized Menhaden Fish Oil (MFO); dicarboxylic acids such as, but not limited to succinic acid, ethanedioic acid, propanedioic acid, pentane
  • the dispersant may be polymeric.
  • the polymeric dispersant may comprise an acidic group.
  • the acidic group may be a carboxylic acid group.
  • the polymeric dispersant may be selected from FLOWEN® G-700, G-900, and/or G-1500 (Kyoeisha Chemical Co. Ltd., Osaka, Japan).
  • organic binders may be present in the luminescent ceramic(s).
  • the organic binders may include, but are not limited to, vinyl polymers such as polyvinyl butyral (PVB), polyvinyl alcohol (PVA), polyvinyl chloride (PVC), polyvinyl acetate (PVAc), polyacrylonitrile, copolymers thereof; polyethyleneimine; poly methyl methacrylate (PMMA); vinyl chloride-acetate; and combinations thereof.
  • PVB polyvinyl butyral
  • PVB polyvinyl alcohol
  • PVC polyvinyl acetate
  • PVB polyacrylonitrile
  • plasticizers may be present in the luminescent ceramic(s), and may include Type 1 and Type 2 plasticizers.
  • Type 1 plasticizers may generally decrease the glass transition temperature (T g ) and can make the luminescent ceramic(s) more flexible.
  • Type 2 plasticizers may enable more flexible and more deformable layers and may reduce the amount of spaces resulting from lamination.
  • Type 1 plasticizers may include, but are not limited to, butyl benzyl phthalate, dicarboxylic/tricarboxylic ester-based plasticizers such as, but not limited to, phthalate-based plasticizers such as, but not limited to, castor oil (which typically comprises more than 90 mol% fatty acids with long aliphatic chains), phthalates, n- butyl phthalate, dibutyl phthalate, dioctyl phthalate, butyl benzyl phthalate, mixed esters phthalate, dimethyl phthalate, bis(2-ethylhexyl) phthalate, diisononyl phthalate, bis(n-butyl)phthalate, butyl benzyl phthalate, diisodecyl phthalate, di-n- octyl phthalate, diisooctyl phthalate, diethyl phthalate, diisobutyl phthalate, di
  • Type 2 plasticizers may include, but not limited to, dibutyl maleate, diisobutyl maleate, and combinations thereof; glycols, polyalkylene glycols, polyethylene glycol, polypropylene glycol, triethylene glycol, dipropylglycol benzoate, and combinations thereof.
  • plasticizers may include, but are not limited to, benzoates, epoxidized vegetable oils, sulfonamides, N-ethyl toluene sulfonamide, N-(2-hydroxypropyl)benzene sulfonamide, N-(n-butyl)benzene sulfonamide, organophosphates, tricresyl phosphate, tributyl phosphate, glycols/polyethers, triethylene glycol dihexanoate, tetraethylene glycol diheptanoate, and combinations thereof; alkyl citrates, triethyl citrate, acetyl triethyl citrate, tributyl citrate, acetyl tributyl citrate, trioctyl citrate, acetyl trioctyl citrate, trihexyl citrate, acetyl trihexyl citrate, acetyl trihexyl
  • solvents may also be present in the luminescent ceramic(s).
  • solvents may include, but are not limited to, water, a lower alkanol, ethanol, methanol, isopropyl alcohol, xylenes, cyclohexanone, acetone, toluene, methyl ethyl ketone, and combinations thereof. Some embodiments may use a mixture of xylenes and ethanol for solvents.
  • the luminescent ceramic(s) comprising Sr 2 Si0 4 or composite phases may have a thickness of about 10 ⁇ to about 1000 ⁇ , about 5 ⁇ to about 500 ⁇ , about 40 ⁇ to about 500 ⁇ , or about 50 ⁇ to about 150 ⁇ (such as about 60 ⁇ or about 100 ⁇ ). These thicknesses may be produced by sintering ceramic compacts having a thickness of about of about 10 ⁇ to about 1000 ⁇ , about 5 ⁇ to about 500 ⁇ , about 40 ⁇ to about 500 ⁇ , or about 50 ⁇ to about 150 ⁇ ( such as about 60 ⁇ or about 100 ⁇ ).
  • a device may comprise a number of ceramic plates.
  • the devices described in the examples below comprise 3 or 5 ceramic plates, which were sintered together.
  • the thicknesses above refer to a single plate.
  • the Sr 2 Si0 4 or composite phase comprising element may have a surface having an area of at least about 0.1 cm 2 or about 1 cm 2 wherein the surface is normal to the direction of the thickness.
  • the phosphor ceramic element may comprise sintered particles having a diameter of less than about 50 ⁇ .
  • the Sr-phosphor ceramic element is a product of the methods described herein.
  • the method may comprise providing a calcined precursor powder mixture comprising at least 10% yellow-emitting silicate and less than 90% blue-emitting silicate; creating a precursor slurry with the calcined precursor powder; casting the precursor slurry on a substrate to form a cast tape; drying the cast tape at a temperature and time sufficient to remove the solvent, to maintain desired polymer characteristics, and not to thermally adversely affect the polymer binder, (e.g., at about 20 °C to about 80 °C) to obtain green sheet and/or create a compact; debinding the green sheet and/or compact at a temperature and time sufficient to remove the binder and maintain desired phosphor ceramic oxidation state (e.g., at about 850 °C for about 2 hours in air); and sintering the compact at a sufficient temperature and time sufficient to produce a yellow-emitting silicate plate (e.g., at about 800 ).
  • the silicate phosphor ceramic may comprise a blue-emitting silicate ceramics, e.g., Sr 3 MgSi208. In some embodiments, the silicate phosphor ceramics may comprise a yellow-emitting silicate ceramics, e.g., Sr 2 Si0 4 .
  • a calcined powder mixture such as a powder comprising Sr 2 Si0 4 for sintering, may comprise mixing the precursor materials in a solvent; drying the precursor materials to remove/evaporate the solvent; and calcining the dried precursor materials at elevated temperatures.
  • the solvent may selected from water, alcohol (including isopropanol), ketones, xylene, toluene, or combinations thereof.
  • the casting solvent can be a solvent such as water, alcohol, toluene, etc.
  • the powder mixture may comprise a strontium carbonate.
  • the powder mixture comprises silicon oxide.
  • the powder mixture may further comprise a dopant oxide precursor.
  • the dopant oxide precursor may be EU2O3.
  • the powder mixture may further comprise a sintering aid.
  • the sintering aid may be an ammonium salt.
  • the ammonium salt may be NH 4 CI.
  • the powder mixture may further comprise a dispersant.
  • the dispersant comprises FLOWLEN® G-700.
  • drying the powders to remove solvent may occur at about 80 °C for about 16 hours.
  • the aqueous slurry may comprise NH 4 CI.
  • the solvent may removed from the slurry by drying at about 20 °C to about 80 °C for about 5 minutes (1 .5 m traveling at about 0.2 m per minute) depending upon the solvents present.
  • the method may comprise providing a calcined precursor powder, such as a powder comprising Sr 2 Si0 and a dopant or loaded element for sintering to form a luminescent ceramic plate.
  • providing a calcined precursor powder may comprise providing a first and a second calcined precursor powder.
  • the first precursor powder may be yellow-emitting phosphor powder.
  • the first precursor powder may be Sr 2 Si0 4 .
  • the second precursor powder may be a blue-emitting silicate phosphor, e.g., a second Sr-silicate phosphor phase powder.
  • the second phosphor phase powder may be Sr 3 MgSi0 8 .
  • the method may provide adding the appropriate amounts of the respective precursor powder to affect the desired phosphor composite ratios.
  • Calcination also referred to as calcining is a thermal treatment process in air or oxygen applied to powders and powder mixtures to increase the powder size, bring about a thermal decomposition and/or phase transition, or remove a volatile fraction.
  • the calcining may be performed at temperatures below the melting point of the product materials.
  • the calcining includes decomposing carbonate precursor minerals.
  • the method may comprise calcining a carbonate precursor into a carbon dioxide, a metal oxide, phase material, or combinations thereof.
  • the method may comprise calcining a strontium carbonate into carbon dioxide and a strontium oxide and/or other phase materials.
  • the precursor powder may be calcined at a temperature between about 400 °C to about 1 100 °C or about 600 °C to about 1000 °C, for about 1 hour to about 72 hours.
  • calcining the precursor powder may be at a temperature between 700 °C and 900 °C for about 30 minutes to about 4 hours.
  • calcining the powder may be at about 800 °C for about 2 hours.
  • calcining the powder may be at about 750 °C for about 2 hours.
  • the first and second phosphor powders may be calcined separately, e.g., Sr 2 Si0 may be calcined separately from Sr 3 MgSi0 8 .
  • the first and second phosphor powders may be calcined concurrently, e.g., Sr 2 Si0 4 may be calcined concurrently with Sr 3 MgSi0 8 .
  • a method for making a Sr-phosphor ceramic may comprise providing a Sr-phosphor green form, and then sintering the resulting form at a temperature between about 800 °C and about 1 100 °C or about 700 °C and about 1000 °C for about 30 minutes to about 60 hours so that the resulting phosphor composition comprises at least 10 vol% secondary-phase Sr-phosphor and no more than 90 vol% Sr 3 MgSi 2 08 phase phosphor.
  • the resulting form may be either a green form or a Bisque-fired form and is dependent on whether or not the form is debinded before sintering.
  • the method may also comprise tape-casting a slurry comprising a calcined phosphor precursor prior to sintering.
  • the cast tape may be laminated before sintering at between 10 MPa to about 1000 MPa and between about 20 °C to about 100 °C.
  • the green form may be debinded at about 400 °C to about 1000 °C to obtain the blank samples before sintering.
  • a method for providing a Sr-silicate phosphor ceramic green form may comprise creating a precursor slurry with the calcined precursor powder.
  • the method may comprise mixing the precursor materials in a solvent and heating to remove/evaporate the solvent.
  • providing the calcined powder may include calcining the dried precursor, solvent-removed materials.
  • the calcining may be performed at a sufficient temperature and time to convert at least a portion of the carbonate precursors into metal oxide precursor and carbon dioxide. In some embodiments at least about 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the carbonate precursors may converted into metal oxide precursors.
  • the precursor slurry may comprise phosphor precursors. In some embodiments, the slurry may comprise at least two phosphor precursors. In some embodiments, the slurry may comprise a solvent. In some embodiments, the precursor slurry may optionally include additional compounds including, but not limited to, dopants, dispersants, plasticizers, binders, sintering aids, and/or solvents. In some embodiments, the precursors may comprise any or all of strontium oxides, magnesium oxides, carbonates and or salts.
  • the precursors may be selected from at least Sr 2 MgSi 2 0 7 , Sr 2 Si0 4 , MgSiOs, Mg 2 Si0 4 , MgO, SrO, Si0 2 , SrC0 3 , SrCa0 3 , SrSi0 3 , or combinations thereof.
  • the phosphor precursors may include silicates.
  • the silicate may comprise Si0 2 .
  • the sintering aid may comprise H 3 BO 3 , NH 4 CI, or combinations thereof.
  • the precursor materials mixed in a solvent may be dried to remove the solvent.
  • the precursor-solvent mixture may be dried at a temperature between about 30 °C, 40 °C, 60 °C, 70 °C to about 90 °C, 100 °C, 1 10 °C, 150 °C, and/or any above temperature bound by these ranges.
  • the precursor-solvent mixture may be dried at about 80 °C overnight, e.g., for about 16 hours.
  • the dried precursor powder may be ground into a powder.
  • the method for providing a calcined precursor powder mixture may comprises calcining a phosphor precursor powder.
  • calcining the precursor powder is performed or occurs at a temperature between about 500 °C to about 1 100 °C from about 30 minutes to about 10 hours such that the initially sized particles are enlarged.
  • the maximum temperature of the calcining operation may be less than the melting temperature of the particles.
  • calcining the green form may occur at a temperature between about 400 °C, about 600 °C, about 700 °C; to about 900 °C, about 950 °C, about 1000 °C, about 1 100 °C, or any other temperature bound by these ranges.
  • calcining the precursor powder may occur for a duration of about 0.5 hours, 1 hour, 1 .5 hours, to about 3 hours, 6 hours, 7 hours, 8 hours, 10 hours, 20 hours, 40 hours, 80 hours, or any duration within a range bounded by any of these values.
  • the calcining may be performed in any combination of the aforementioned temperature and duration ranges.
  • the calcining may occur at about 750 °C for about 2 hours.
  • the resulting material may be gently ground after heating to dislodge fused together particles to form a calcined powder.
  • the method for making a phosphor ceramic element may comprise creating a precursor slurry with the calcined precursor powder, such as precursor slurry comprising a powder comprising Sr 2 Si0 and a dopant or another element mixed with the Sr 2 Si0 4 .
  • the method may comprise mixing the calcined phosphor powder, particles or nano- particles with a dispersant, sintering aid, solvent, or combinations thereof.
  • the method may further comprise ball milling the mixture using a milling ball of a material which is different from the non-oxide element of the powder, e.g., does not contain strontium, magnesium, silica and/or europium, to produce a milled first slurry.
  • the milled first slurry may be mixed with a Type 1 and/or Type 2 plasticizer and organic binder to produce a second slurry and milling the second slurry to produce a milled second slurry.
  • the method may comprise making a slurry for fabricating silicate phosphor sheets by tape casting.
  • particles of calcined powders may be mixed with dispersants, activators, sintering aids, solvents, or combinations thereof, and subsequently mixed by ball milling for about 0.5 hours to about 100 hours, about 6 hours to about 48 hours, about 12 hours to about 24 hours, about 16 hours, or any other duration bound by these ranges.
  • This ball-milled slurry may be mixed with a polymeric binder such as, but not limited to, polyvinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVK), and plasticizers such as, but not limited to, castor oil, benzyl n-butyl phthalate (BBP), and polypropylene glycol (PPG).
  • PVK polyvinyl butyral-co-vinyl alcohol-co-vinyl acetate
  • plasticizers such as, but not limited to, castor oil, benzyl n-butyl phthalate (BBP), and polypropylene glycol (PPG
  • the average molecular weight (MW) of PPG may be in the range of about 100 Da to about 50,000 Da; about 1 ,000 Da to about 20,000 Da, or about 5,000 Da.
  • binders and plasticizers may be either directly added and mixed with slurry or may be dissolved in advance in solvent then added to slurry.
  • additional polymer binder e.g., a polymeric binder solution in water and/or alcohol
  • additional polymer binder e.g., a polymeric binder solution in water and/or alcohol
  • the milling balls are, in one embodiment, comprised of material different from components of the mixture, e.g., if the mixture comprises strontium, magnesium, and/or silicon, then the ball material may then comprise Zr0 2 .
  • the slurry may be passed through a filter to separate the ball and slurry; and/or the aggregate ceramic particles.
  • the viscosity of the slurry is adjusted in the range of about 10 centipoise (cP) to about 8,000 cP, about 100 cP to about 5,000 cP, about 500 cP to about 3,000 cP, or any other viscosity bound by these ranges.
  • the method may include tape casting the milled second slurry to produce a cast tape formed of an emissive material having the desired absorption and/or emissive characteristics.
  • a slurry with appropriate viscosity may be cast on a releasing substrate, e.g., a silicone coated MYLAR®(polyethelene terephthalate, PET) substrate, with a comma/doctor blade with an adjustable gap.
  • the thickness of cast tape may be adjusted by changing the comma blade gap, slurry viscosity, and/or casting rate.
  • the cast tape may be dried at a temperature sufficient to remove the casting solvent.
  • the cast tape may be dried at a temperature sufficient to maintain a desired oxidation state of the resultant ceramics. In some embodiments, the Eu 2+ oxidation state may be substantially maintained. In some embodiments, the cast tape may be dried at about 20 °C) to about 100 °C, about 40 °C to about 90 °C, about 50 °C to about 80 °C, or any other temperature in a range bounded by any of these values. In some embodiments, the drying may be performed in at least two different heat zones. In some embodiments, the material may be dried in two different heat zones of an automated roll-to-roll tape caster with a length of at least 1 .5 cm each at about 0.2 m/min substrate travel.
  • green sheets with various thicknesses may be obtained after evaporation of solvent from the cast tape.
  • the gap of the comma blade may be changed in the range of about 30 ⁇ to about 1200 ⁇ , about 50 ⁇ to about 800 ⁇ , about ⁇ 80 to about 600 ⁇ , or any other distance bound by these ranges.
  • the casting rate may be in the range of about 0.05 m/min to about 1 .50 m/min, about 0.10 m/min to about 1 .00 m/min, about 0.15 m/min to about 0.50 m/min, or any other casting rate bound by these ranges.
  • the thickness of green sheets may be adjusted in the range of about 10 ⁇ to about 1000 ⁇ , about 20 ⁇ to about 400 ⁇ , about 40 ⁇ to about 200 ⁇ , about 50 ⁇ to about 120 ⁇ , or about 60 ⁇ to about 100 ⁇ .
  • a person of ordinary skill in the art will be able to choose an appropriate set of parameters to obtain a particular green sheet thickness without going beyond the scope of the disclosed embodiments.
  • the method of providing a luminescent ceramic(s) may comprise tape casting the green form after calcining (or grinding, if calcining is not performed), as shown in the schematic of FIG. 1 .
  • Tape casting may comprise creating slurry from a green form and then casting the slurry on a releasing substrate to form a tape.
  • the slurry may comprise water.
  • the slurry may then be cast on a releasing substrate (e.g., a silicone coated polyethylene terephthalate substrate) to form a tape.
  • the slurry may be cast onto a moving carrier using a comma blade and dried to form a tape.
  • the thickness of the cast tape may be adjusted by changing the gap between the comma blade and the substrate.
  • the gap between the comma blade and the moving carrier may be in the range of about 20 ⁇ to about 1200 ⁇ , about 50 ⁇ to about 800 ⁇ about 80 ⁇ -nicrons to about 600 ⁇ , or any other distance bound by these ranges.
  • the speed of the moving carrier may have a rate in the range of about 0.05 m/min to about 1 .50 m/min, about 0.10 m/min to about 1 .00 m/min, about 0.15 m/min to about 0.50 m/min, or any other rate bound by these ranges.
  • the tape may be expected to have a thickness between about 20 ⁇ to about 400 ⁇ .
  • the tapes may be optionally cut into desired shapes after tape casting.
  • two or more tapes may be optionally laminated to form an assembly.
  • the lamination step may include stacking two or more tapes (e.g., about 2 tapes to about 100 tapes) and subjecting the stacked tapes to heat and uniaxial pressure (e.g., pressure perpendicular to the tape surface).
  • the stacked tapes may be heated above the glass transition temperature of the binder and/or material included in the tape and compressed uniaxially using metal dies.
  • the stacked tapes may be heated between about 25 °C to about 95 °C, or about 80 °C.
  • the stacked cast tape may be vacuum-bagged at room temperature.
  • the stacked cast tape may be isostatically or uniaxially compressed.
  • the compression pressure may be in the range of about 1 MPa to about 500 MPa, about 1 MPa to about 100 MPa, about 30 MPa to about 60 MPa, about 42 MPa, or any other pressure bound by these ranges.
  • the heat and pressure may be applied for about 1 minute to about 180 minutes, about 5 minutes to about 3 hours, about 5 to about 30 minutes, about 20 minutes, or any other duration bound by these ranges.
  • the thickness of the assembly may be adjusted (e.g., by adding additional layers) to vary the thickness of the emissive element.
  • Lamination may optionally include forming various shapes (e.g., holes or pillars) or patterns into the assembly by, for example, using shaped dies.
  • the sintering may be performed between alumina (AI2O3) plates.
  • the alumina plates may have between 20% and 60% porosity, e.g., about 40% porosity.
  • the method may comprise sandwiching plural green samples.
  • sandwiched green samples are between alumina plates with about 40% porosity to reduce the warping, cambering, and bending of green samples during debinding and sintering.
  • a plurality of green samples may be stacked between porous AI2O3 cover plates alternatively.
  • the green forms undergo debinding at temperatures sufficient to remove substantially all of the casting solvent and organic components, such as binders, plasticizers, and dispersants, and to maintain the desired oxidation state of the resultant phosphor ceramics.
  • the cast sheet may be debinded at a temperatures from about 300 °C to about 1 100 °C, about 500 °C to about 900 °C, about 600 °C to about 900°C, about 850 °C, or any other temperature bound by these ranges.
  • the debinding temperature may be reached after ramping from room temperature to the desired level at a rate of about 0.01 °C/min to about 10 °C/min, about 0.05 °C/min to about 5 °C/min, about 0.5 °C/min to about 1 .0 °C/min, or any other rate bound by these ranges for about 30 minutes to about 36 hours in an oven depending upon the thickness of the laminated green sheets. While not wanting to be limited by theory, it is believed that the debinding step burns off substantially all of the binding additives in the cast tape prior to sintering. In some embodiments, the mixture is debinded at about 850 °C for about 2 hours.
  • the method may comprise sintering in a reducing atmosphere.
  • reducing atmosphere refers to an atmosphere that has a greater tendency to reduce a composition than air.
  • reducing atmospheres may include, but are not limited to, atmospheres comprising reducing and/or inert gases such as nitrogen, argon, hydrogen gas, ammonia, hydrazine, carbon monoxide, or combinations thereof. Any reducing gas may also be diluted with nitrogen gas or an inert gas to provide a reducing atmosphere.
  • the reducing atmosphere may comprise nitrogen gas or hydrogen gas.
  • the atmosphere may be a mixture of hydrogen, nitrogen, and argon gases.
  • the amount hydrogen gas may range between about 0.5% and about 10%, wherein the amount of nitrogen or argon gas may correspondingly range from between about 99.5% and about 90%.
  • a reducing atmosphere may comprise a mixture of from about 0.5% (v/v) to about 10% (v/v) hydrogen gas and about 90% (v/v) to about 99% (v/v) nitrogen gas or from about 1 % (v/v) to about 5% (v/v) hydrogen gas and about 95% (v/v) to about 99% (v/v) nitrogen gas, or about 3%(v/v) hydrogen gas and about 97% (v/v) nitrogen gas.
  • the method may comprise sintering the compacts at a temperature sufficient to achieve the desired ceramic phase while maintaining the desired end characteristics, e.g., high IQE (greater than 90%).
  • the secondary-phase may be reduced by maintaining the sintering temperature within a preferred temperature range.
  • the sintering can be performed at a temperature from about 700 °C to about 1 100 °C, about 750 °C to about 1050 °C, about 800 °C to about 1000 °C, about 800 °C to about 900 °C, or about 900 °C to about 1000 °C, for about 1 hour to about 100 hours, about 2 hours to about 36 hours, or any other temperature or duration within these ranges such that the ceramics comprise the substantially single-phase Sr- silicate phosphor as described above.
  • the method may comprise sintering at a temperature between about 750 °C, about 800 °C, or about 850 °C; to about 900 °C, about 1000 °C, or about 1050 °C or any other temperature in a range bounded by any of these values.
  • the sintering duration ranges from about 1 hour, about 2 hours, about 3 hours, or about 6 hours to about 7 hours, about 8 hours, about 10 hours, or any or any other duration bound within these ranges.
  • the sintering duration can be about 750 °C to about 1000 °C for about 8 hours. During sintering, many different silicate phases can be formed.
  • a precursor powder such as a precursor powder comprising Sr 2 Si0 4 loaded or doped with europium or an ion thereof, may be sintered at a temperature of about 700 °C to about 1000 °C, about 700 °C to about 800 °C, about 800 °C to about 900°C, about 800 °C to about 950 °C, or about 900 °C to about 1000 °C, for at least about 1 hour, about 4 hours, or about 6 hours; and/or up to about 12 hours, about 24 hours, or about 100 hours.
  • Sr 2 Si0 4 can be sintered at low temperature ( ⁇ 700 °C) but the resulting phosphor ceramics do not have good optical properties (high IQE and good light absorption) as a good phosphor material. At higher sintering temperatures, denser materials can be obtained but with the loss of IQE. To get the Sr-silicate phosphor plates with high quantum efficiency, the materials may be sintered at 850 °C (e.g. for about 8 hours) resulting in a ceramic plate characterized with a high density and high light transmission. The result is a Sr-phosphor ceramic element.
  • the luminescent ceramics described herein may have an internal quantum efficiency of at least about 60%, about 70%, about 80%, about 90%, about 95%, or about 99%.
  • the debinding and the sintering may be performed in separate steps. In some embodiments, the debinding and sintering may be performed concurrently.
  • Embodiment 1 A method for making a silicate phosphor ceramics comprising:
  • a calcined precursor powder mixture comprising at least 10% yellow-emitting silicate and less than 90% blue-emitting silicate; creating a precursor slurry with the calcined precursor powder;
  • Embodiment 2 The method of embodiment 1 , wherein providing the calcined powder mixture comprises mixing the precursor materials in a solvent; drying the precursor materials in a solvent to remove the solvent; and calcining the dried precursor materials.
  • Embodiment 3 The method of embodiment 1 or 2, wherein the solvent is selected from water and toluene.
  • Embodiment 4 The method of embodiment 1 , 2, or 3, wherein the powder mixture comprises a Sr carbonate.
  • Embodiment s. The method of embodiment 1 , 2, 3, or 4 wherein the powder mixture comprises a silicon oxide.
  • Embodiment 6 The method of embodiment 1 , 2, 3, 4, or 5, wherein the powder mixture comprises a dopant oxide precursor.
  • Embodiment 7 The method of embodiment 6, wherein the dopant oxide precursor is Eu 2 0 3 .
  • Embodiment 8 The method of embodiment 1 , 2, 3, 4, 5, 6, or 7, wherein the powder mixture further comprises a sintering aid.
  • Embodiment 9 The method of embodiment 1 , 2, 3, 4, 5, 6, 7, or 8, wherein the sintering aid is NH 4 CI.
  • Embodiment 10 The method of embodiment 1 , 2, 3, 4, 5, 6, 7, or 8, wherein the powder mixture further comprises a dispersant.
  • Embodiment 11 The method of embodiment 10, wherein the dispersant comprises FLOWLEN® G-700.
  • Embodiment 12 The method of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1 1 , further comprising laminating plural green sheets.
  • Embodiment 13 The method of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1 1 , wherein the drying the powders to remove solvent is at about 80 °C for about 16 hours.
  • Embodiment 14 The method of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, or 13, wherein calcining the precursor powder is at a temperature between 700 °C and 900 °C for about 30 minutes to about 4 hours.
  • Embodiment 15 The method of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, or 14, wherein the calcined powder is calcined at about 800 °C for about 2 hours.
  • Embodiment 16 A phosphor ceramic element manufactured according to the method of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, or 15.
  • Embodiment 17 The phosphor ceramic element of embodiment 16, wherein the phosphor ceramic element emits light having a wavelength of 420 nm to 650 nm.
  • Embodiment 18 The phosphor ceramic element of embodiment 16 or 17, wherein the phosphor ceramic element emits light having a wavelength of 525 to 600 nm.
  • Embodiment 19 The phosphor ceramic element of embodiment 16 or 17, comprising:
  • a Sr-silicate phosphor composite the composite comprising Sr 2 Si0 and Sr 3 MgSi 2 08 phase phosphor composites
  • Embodiment 20 The phosphor ceramic element of embodiment 16, 17, 18, or 19, wherein the phosphor is doped with Europium (Eu 2+ ), in an amount that is about 0.01 wt% to about 5 wt%.
  • Eu 2+ Europium
  • Embodiment 21 A phosphor ceramic element comprising Sr 2 Si0 4 or composite phases, wherein the phosphor ceramic element has a thickness of about 50 ⁇ to about 1000 ⁇ , and a surface having an area of at least about 1 cm 3 , wherein the surface is normal to the direction of the thickness, and wherein the phosphor ceramic element comprises sintered particles having a diameter of less than about 50 ⁇ .
  • Embodiment 22 The phosphor ceramic element of embodiment 20, comprising 1 -100% by volume of Sr 2 Si0 4 .
  • Embodiment 23 The phosphor ceramic element of embodiment 20, wherein the phases are Sr 3 MgSi 2 0 8 , Sr 2 MgSi 2 0 7 , Sr 2 Si0 4 , or a combination thereof.
  • Embodiment 24 Luminescent ceramics comprising:
  • the Sr 2 Si0 4 is doped or loaded with Eu or an ion thereof, in an amount that is about 0.01 atom% to about 5 atom% based upon the total number of atoms or ions of Eu and Sr;
  • the luminescent ceramic comprises a sintered ceramic plate.
  • Embodiment 25 The luminescent ceramics of embodiment 24, wherein the luminescent ceramics comprise Sr 2 Si0 4 .
  • Embodiment 26 The luminescent ceramics of embodiment 24 or 25, wherein Eu or an ion thereof is present in an amount that is about 0.05 atom% to about 2 atom% based upon the total number of atoms or ions of Eu and Sr.
  • Embodiment 27 The luminescent ceramics of embodiment 24, 25, or 26, wherein Eu or an ion thereof is present in an amount that is about 0.1 atom% to about 1 atom% based upon the total number of atoms or ions of Eu and Sr.
  • Embodiment 28 The luminescent ceramics of embodiment 24, 25, 26, or 27 formed by sintering a ceramic precursor compact having a thickness of 10 ⁇ to 1000 ⁇ .
  • Embodiment 29 The luminescent ceramics of embodiment 24, 25, 26, 27, or 28, wherein the sintered ceramic plate has a thickness of 5 ⁇ to 500 ⁇ .
  • Embodiment 30 The luminescent ceramics of embodiment 24, 25, 26, 27, 28, or 29, wherein the sintered ceramic plate has an internal quantum efficiency of luminescence that is at least about 90%.
  • Embodiment 31 The luminescent ceramics of embodiment 24, 25, 26, 27, 28, 29, or 30, wherein the sintered ceramic plate is a composite of Sr 2 Si0 4 doped or loaded with Eu, or an ion thereof, and Sr3MgSi 2 08 doped or loaded with Eu or an ion thereof, wherein Eu is present in an amount that is 0.01 atom% to about 5 atom% based upon the total number of atoms or ions of Eu and Sr.
  • Embodiment 32 A method of preparing the luminescent ceramics of embodiment 24, 25, 26, 27, 28, 29, 30, or 31 , comprising sintering a composition comprising a calcined precursor powder at a temperature of about 700 °C to about 1000 °C for at least about 1 hour to adhere particles of the calcined precursor powder to one another form to form a sintered ceramic plate, wherein the calcined precursor powder comprises Sr 2 Si0 loaded or doped with europium or an ion thereof.
  • Embodiment 33 The method of embodiment 32, wherein the composition comprising a calcined precursor powder is sintered at a temperature of about 800 °C to about 950 °C for at least about 1 hour to adhere particles of the calcined precursor powder to one another to form a sintered ceramic plate.
  • Embodiment 34 The method of embodiment 32 or 33, wherein sintering is carried out under a reducing atmosphere.
  • Embodiment 35 The method of embodiment 34, wherein the reducing atmosphere comprises 1 % (v/v) to about 10% (v/v) hydrogen gas dispersed in an inert gas.
  • Embodiment 36 The method of embodiment 35, wherein the inert gas is
  • Embodiment 37 The luminescent ceramics of embodiment 24, 25, 26, 27, 28, 29, 30, or 31 or the method of embodiment 32, 33, 34, 35, or 36, wherein the Eu is Eu 2+ .
  • the solid content of this binder solution was 30 wt%.
  • the slurry was then cast on 75 ⁇ thick silicone-coated polyethylene terephthalate MYLAR® substrate film (Hansung Systems Inc., Seoul, South Korea) using an automated roll- to-roll tape caster with a comma blade at a cast rate of 200 mm/min.
  • the green sheet thickness of Sr-silicate phosphor ceramics with 1 .0 atom% Eu-doping was about 60 ⁇ thick.
  • the cast tape was dried at room temperature on the automated roll-to-roll tape caster with the total length of 3.0 m to finally obtain a Sr-silicate ceramic green sheet whose ceramic content is 62.5 vol%.
  • the dried green sheet was cut to be about 100 mm x 100 mm using a razor blade.
  • a sample consisted of five layers of 60 ⁇ thick 1 .0 atom% Eu-doped Sr-silicate layers. Laminates were assembled on an anodized aluminum plate, and the assembly was vacuum-bagged before isostatic pressing. The assembly was laminated using a cold isostatic press (CIP) at 42 MPa and 85 °C for 10 min using an ILS-66 isostatic lamination press (Keko Equipment, Zuzemberk, Slovenia). As a result, an approximately 280 ⁇ thick green laminate was obtained.
  • CIP cold isostatic press
  • the green laminates were then laser-cut to the size of a 20 mm x 20 mm cubic shape using a VLS 2.30 laser engraving and cutting system (Universal Laser Systems, Scottsdale, AZ) with a 25 W C0 2 laser for the following Bisque-firing.
  • VLS 2.30 laser engraving and cutting system Universal Laser Systems, Scottsdale, AZ
  • the polymeric binder was removed from the laminated compacts.
  • the laminated compacts were placed between AI2O3 porous cover plates with 40% nominal porosity to avoid warping, cambering, and bending of the laminated compacts during the debinding process.
  • a plurality of green laminate compacts was stacked between porous Al 2 0 3 cover plates (ESL ElectroScience, King of Prussia, PA), alternately.
  • the laminated compacts were heated to about 850 °C for about 2 h in air using a ST-1700C-445 box furnace (SentroTech Corporation, Brea, OH) for debinding and Bisque-firing.
  • the heating and cooling rates were ⁇ 0.7 °C/min and ⁇ 4.0 °C/min, respectively.
  • the debinded/Bisque-fired blank samples were fully sintered at about 850 °C to about 1 1 10°C for 8 h in 97% N 2 /3% H 2 gas atmosphere, which is slightly higher than the atmospheric pressure, using a GSL-1600X-80 alumina tube furnace (MTI Corporation, Richmond, CA).
  • Total light transmittance (Tt%) of the obtained ceramic plates was First, air without any sample was irradiated with continuous spectrum light from a halogen lamp source (150 W MC2563, Otsuka Electronics, Inc., Osaka, Japan) to obtain reference transmission data. The phosphor ceramic plate was placed and irradiated. The transmitted spectrum was acquired by multi channel photo detector (MCPD 7000, Otsuka Electronics, Inc. Osaka, Japan) for each sample. Tt% at 800 nm wavelength of light was used as a quantitative measure of transparency of the obtained ceramics. Tt% of Example 1 were summarized in Table 1 .
  • the luminescence efficiency of silicate phosphor ceramics can be evaluated as Internal Quantum Efficiency (IQE) by measuring the emission from the phosphor ceramics under irradiation of standard excitation light with predetermined intensity using high sensitivity multi channel photo detector (MCPD 7000, Otsuka Electronics, Inc, Osaka, Japan).
  • MCPD 7000 high sensitivity multi channel photo detector
  • the IQE of phosphor ceramics is the ratio of the number of photons generated from the phosphor to the number of photons of excitation light which are actually absorbed by the phosphor. Due to low transparency of the processed phosphor ceramics, the IQE of the silicate phosphor ceramics was measured by the set up which is in general useful for characterizing phosphor powders.
  • This IQE value can provide a very useful indication of the efficiency of the wavelength-converting phosphor ceramics.
  • Each ceramics whose size is approximately 15 mm x 15 mm was applied for the IQE measurement using an Otsuka Electronics MCPD 7000 multi channel photo detector system together with required optical components such as optical fibers, small integrating spheres, light sources, monochromator, and sample holder.
  • the silicate phosphor ceramics was irradiated with a Xe lamp (150 W, L2274) at 405 nm wavelength after passing through a monochromator.
  • An emission spectrum was acquired by using an integrating sphere, and the number (Q em ) of photons of emitted light was calculated.
  • the irradiation spectrum of 405 nm wavelength after passing through a monochromator was collected with 50% reflectance standard target (SPECTRALON®, Labsphere Inc., North Sutton NH), and then the number (Q ex ) of photons of irradiated light in 405 nm was calculated.
  • continuous spectrum light from a halogen lamp source 150 W, MC2563 was used for irradiation and applied on the 50% reflectance standard target to acquire the reflectance spectrum as a reference for the reflectance spectrum measurement.
  • FIG. 2 is a plot showing examples of light spectra of a 410 nm wavelength near-UV LED (LUXEON® LHUV-0400, Philips-Lumileds, San Jose, CA) applied with 100 mA current with and without yellow-emitting Sr-silicate phosphor ceramics.
  • LLUXEON® LHUV-0400 Philips-Lumileds, San Jose, CA
  • X-ray diffraction (XRD) technique was performed to characterize the crystal structures of the processed phosphor ceramic plates after the sintering process.
  • XRD X-ray diffraction
  • the diffractogram step was 0.02° 2 ⁇ , a count time at each angle of 1 .2 sec, and a 2 ⁇ range from 10-70°.
  • the divergence and scatter slits set up for the Rigaku MINIFLEXTM II for all measurements were 1 .25°, and the receiving slit was 0.3 mm.
  • the XRD diffraction in FIG. 3 confirmed that the phase of the ceramics is Sr 2 Si0 4 regardless of monoclinic or orthorhombic crystal after the end of the sintering process.
  • monoclinic 3-Sr 2 Si0 4 appears to be the dominant phase with minimal existence of orthorhombic a-Sr 2 Si0 4 .
  • orthorhombic a-Sr 2 Si0 4 appears more stable at sintering temperatures above 850 °C. and the amount of orthorhombic a-Sr 2 Si0 4 phase increased with increasing sintering temperature, whereas decreasing the amount of monoclinic ⁇ - Sr 2 Si0 4 phase.
  • Monoclinic 3-Sr 2 Si0 4 phase eventually disappeared while obtaining pure orthorhombic a-Sr 2 Si0 4 phase, after sintering at above 1 100 °C
  • Example 2 In order to prepare 0.25 atom% Eu-doped Sr 2 Si0 phosphor plates, samples in Example 2 were prepared as the same in Example 1 , except that 66.28 g SrCOs, 13.52 g Si0 2 , 198 mg Eu 2 0 3 , 400 mg of NH 4 CI (0.5 wt pph of total amount of Sr-silicate phosphor precursor powders), 1 .60 g (2.0 wt. pph of total amount of Sr- silicate precursor powders) FLOWLEN® G-700 dispersant (Kyoeisha Chemical Co.
  • aqueous acrylic polymer solution whose solid content is 35 wt%, as a main component of polymeric binder for final green sheet, 79 mg 2,4,7,9- tetramethyl-5-decyne-4,7-diol ethoxylate as a defoamer for aqueous slurry, 2.37 g PL005 plasticizer (Polymer Innovations, Vista, CA) as a plasticizer, and 18.00 g MILLI-Q® water were added to a 4 oz (0.12 L) polypropylene (PP) thick wall jar, whose inner diameter was 80 mm (Parkway Plastics Inc., Piscataway, NJ), for aqueous slurry preparation.
  • PP polypropylene
  • the resultant aqueous slurry was filtered through a syringe-aided metal screen filter with pore size of 0.05 mm in order to remove aggregated ceramic particles. All slurry was then cast on 75 ⁇ thick silicone-coated polyethylene terephthalate MYLAR® substrate film (Hansung Systems Inc., Seoul, South Korea) using an automated roll-to-roll tape caster with a comma blade at a cast rate of 200 mm/min.
  • the green sheet thickness of Sr-silicate phosphor ceramics with 0.25 atom% Eu-doping was about 100 ⁇ thick.
  • the cast tape was dried at about 50 °C to about 80 °C at two different heat zones of the automated roll-to-roll tape caster with a length of 1 .5 m each to finally obtain a Sr-silicate ceramic green sheet whose ceramic content is 52.5 vol%, assuming that the density of the Sr-silicate phosphor is 4.00g/cc whereas that of the acrylic polymer is 1 .05g/cc.
  • Tt% and IQE of Example 2 were summarized in Table 1 .
  • Example 3 In order to prepare 1 .0 atom% Eu-doped Sr-silicate phosphor plate, samples in Example 3 was prepared as the same in Example 2, except that 29.08 g calcined Sr-silicate precursor powder with 1 .0 atom% Eu-doping prepared as described in Example 1 , 873 mg (3.0 wt.
  • Tt% and IQE of Example 3 were summarized in Table 1 .
  • the high IQE (>90%) was obtained when the samples were sintered at ⁇ 850°C.
  • Photoluminescence emission (PL) and excitation (PLE) properties of a sample showing >90% IQE in Example 3 were studied with a Horiba FLUOROMAXTM 3 fluorescence spectrophotometer with a photomultiplier tube operating at 400 V, and a 150 W Xe lamp used as the excitation lamp.
  • PL spectrum of Example 3 sintered at 850 °C in the mixed gas of 97 vol% N 2 /3 vol% H 2 was collected with 405 nm excitation as shown in FIG. 4, whereas PLE spectrum was collected with 450 nm emission as shown in FIG. 5.
  • the strong PL spectrum at the peak position of 540 nm directly means that the ionic state of Eu dopant in Sr/Ba- silicate phosphor ceramics showing >90% IQE was Eu 2+ .
  • Example 4 In order to prepare 0.25 atom% Eu-doped Sr-silicate phosphor plate, samples in Example 4 was prepared as the same in Example 3, except that 32.74g calcined Sr-silicate precursor powder with 0.25atom% Eu-doping prepared as described in Example 2, 982mg (3.0 wt. pph of the Sr-silicate precursor powder) G- 700 dispersant (Kyoeisha Chemical Co.
  • aqueous acrylic polymer solution whose solid content is 35 wt%, as a main component of polymeric binder for final green sheet
  • 844mg PL005 plasticizer Polymer Innovations, Vista, CA
  • 84 mg 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate as a defoamer for aqueous slurry
  • 14.86 g 2-Propanol (IPA) were added to a 4 oz (0.12 L) polypropylene (PP) thick wall jar, whose inner diameter is 80 mm (Parkway Plastics Inc., Piscataway, NJ), for slurry preparation whose solvent is the mixture of water and IPA.
  • Tt% and IQE of Example 4 were summarized in Table 1 .
  • the high IQE (>90%) was obtained when the samples were sintered at ⁇ 850 °C.
  • Photoluminescence emission (PL) and excitation (PLE) properties of a sample showing >90% IQE in Example 4 were studied with a Horiba FLUOROMAXTM 3 fluorescence spectrophotometer with a photomultiplier tube operating at 400 V, and a 150 W Xe lamp used as the excitation lamp.
  • PL spectrum of Example 4 sintered at 850 °C in the mixed gas of 97 vol% N 2 /3 vol% H 2 was collected with 405 nm excitation as shown in FIG. 4, whereas PLE spectrum was collected with 450 nm emission as shown in FIG. 5.
  • the peak position was slightly shifted to lower wavelength to be 530 nm with decreasing Eu-doping, compared with Example 3 in FIG. 4.
  • the strong PL spectrum at the peak position of 530 nm directly means that the ionic state of Eu dopant in Sr/Ba-silicate phosphor ceramics showing >90% IQE was Eu 2+ . No clear difference of PLE spectra while decreasing Eu-doping was observed, comparing Examples 3 and 5 in FIG. 5.
  • FIGS. 6A and 6B show the SEM micrograph of the surface of the phosphor ceramics with 50 atom% Ba-doping and 0.25 atom% Eu- doping.
  • FIG. 6B shows an enlarged portion of the surface in FIG. 6A. This image was collected with an acceleration voltage of 10 kV. It was seen that the phosphor ceramics did not appear fully densified as a large number of pores were observed on the surface of the phosphor ceramics as shown in FIG. 6B.
  • a binder solution of polymeric binder and plasticizers was firstly prepared by dissolving 25.20 g polyvin
  • Tt% and IQE of Example 5 were summarized in Table 1 .
  • the high IQE (>90%) was obtained when the samples were sintered at ⁇ 900°C.
  • Photoluminescence emission (PL) and excitation (PLE) properties of various samples in Example 5 were studied.
  • PL spectrum of Example 5 sintered at 850 °C in the mixed gas of 97 vol% N 2 /3 vol% H 2 was collected with 405 nm excitation as shown in FIG. 4, whereas PLE spectrum was collected with 450 nm emission as shown in FIG. 5.
  • the peak position of PL spectrum of Example 5 remained the same as that of Example 4.
  • the strong PL spectrum at the peak position of 530 nm directly means that the ionic state of Eu dopant in Sr/Ba-silicate phosphor ceramics showing >90% IQE was Eu 2+ .
  • composite phosphor ceramic sample in Example 6 was prepared as the same in Example 5 except the following.
  • Sr3MgSi 2 08 (SMS-312) blue phosphor powders with 0.25 atom% Eu-doping was prepared with 43.92 g SrCOs, 4.01 g MgO, 1 1 .95 g Si0 2 , 131 mg Eu 2 0 3 , 420 mg (0.7 wt.
  • pph of total amount of SMS-312 precursor powders NH 4 CI as a sintering aid, 1 .20 g FLOWLENTM G-700 dispersant (Kyoeisha Chemical Co. Ltd., Osaka, Japan), and 175 g methanol were added to a 16 oz (0.46 L) polypropylene (PP) thick wall jar, whose inner diameter is 80 mm (Parkway Plastics Inc., Piscataway, NJ), for precursor powder mixing in order to prepare 0.25 atom% Eu-doped SMS-312 phosphor powders.
  • PP polypropylene
  • SMS-312 precursor powder materials The wet mixture of these SMS-312 precursor powder materials was ball-milled with 650 g Zr0 2 milling media of about 10 mm to about 15 mm diameter for 16 h. The mixture was then dried at 80 °C in air for more than 16 h, and the dried mixture was gently ground with agate pestle and mortal. The mixed powder was processed at 900 °C for 2 h in air, followed by 1350 °C for 8 h in 97 vol% N 2 /3 vol% H 2 reducing atmosphere to obtain the SMS-312 phosphor powder. The heating rate of this process was about 5.0 °C/min. (-800 °C), 4.0 °C/min. (800- 1200 °C), and ⁇ 1 .9 °C/min.
  • IQE of the obtained powder was measured and summarized for reference in Table 1 .
  • the IQE value of the processed SMS-312 blue phosphor powder was measured to be 90%.
  • small amount of the SMS-312 powders were dropped on Gecko Tape (Nitto Denko, Osaka, Japan) consisting of bundles of carbon nanotubes, allowing us to observe samples using SEM without either gold or platinum coating.
  • FIG. 9 shows the SEM micrograph of the processed SMS-312 powders. It was seem that the particle size is far larger than a few micrometers in Fig. 9.
  • the slurry of the composite phosphor ceramics was then cast on 75 ⁇ thick silicone-coated polyethylene terephthalate MYLAR® substrate film (Hansung Systems Inc., Seoul, South Korea) using an automated roll-to-roll tape caster with a comma blade at a cast rate of 200 mm/min.
  • the blade gap of the film applicator was adjusted depending on the desired green sheet thickness.
  • the green sheet thickness the composite phosphor ceramics with was e.g. 80 ⁇ thick.
  • the cast tape was dried at room temperature on the automated roll-to-roll tape caster with a total length of 3.0 m, to finally obtain the ceramic green sheet for the composite phosphor ceramics.
  • the ceramic content of the dried green sheet is.
  • Tt% and IQE of Example 6 were summarized in Table 1 .
  • the high IQE (>90%) of the composite phosphor ceramics was obtained when the samples were sintered at ⁇ 850°C.
  • Example 6 [00106] PL and PLE properties of a sample showing >90% IQE in Example 6 were studied with a Horiba FLUOROMAXTM 3 fluorescence spectrophotometer. PL spectrum of Example 6 sintered at 850 °C in the mixed gas of 97 vol% N 2 /3 vol% H 2 was collected with 405 nm excitation as shown in FIG. 10, whereas PLE spectrum was collected with either 450 nm (blue) or 540 nm (yellow) emission as shown in FIG. 1 1 . Data of Example 4 are shown as the neat yellow- emitting phosphor for comparison in both FIGS. 10 and 1 1 . In FIG.
  • the PL spectra were normalized with the peak value of the yellow emission near 540 nm. Interestingly, the strong PL spectrum at 450 nm was observed in FIG. 10. Therefore, the PL spectrum of the yellow/blue composite phosphor ceramics resembles the spectrum of white LED consisting of blue LED and yellow-emitting phosphor (e.g., Ce-doped yttrium aluminum garnet). This also suggests that ionic condition of the doped Eu element in the blue SMS-312 phosphor is mainly Eu 2+ , although the sintering temperature of this composite phosphor ceramics is much lower than that of neat SMS-312 phosphor ceramics reported in a separate previous patent application. There is no clear difference between PLE spectra between Examples 4 and 6 when the light emission is 540 nm.
  • FIGS. 12A and 12B show the SEM micrograph of the surface of the composite phosphor ceramics of Example 7. This image was collected with an acceleration voltage of 10 kV. It was seen that the surface of the composite phosphor ceramics was completely covered with nanoscale powder-like structure as seen in a high magnification image of FIG. 12B. It should be noted that the large grain SMS-312 phosphor crystals were observed everywhere on the ceramic surface as indicated with white arrows in a low magnification image of FIG. 12A.

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Abstract

L'invention concerne un élément luminophore en céramique Sr-silicate, ayant des caractéristiques d'émission entre environ 420 nm et environ 650 nm, l'élément comportant Sr2SiO4 et Sr3MgSi2O8, ou Sr2SiO4 et Sr2MgSi2O7 et comportant en outre entre environ 0,01 % et environ 5,0 % en pourcentage atomique d'Europium (Eu2+). L'invention concerne également des procédés de fabrication de l'élément luminophore selon la présente invention.
PCT/US2015/055823 2014-10-15 2015-10-15 Ceramique phosphorescente contenant des silicates metalliques pour une emission de lumiere jaune et blanche WO2016061408A1 (fr)

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