WO2013070676A2 - Phosphors of rare earth and transition metal doped ca1+xsr1-xgayin2-yszse3-zf2;methods of manufacturing and applications - Google Patents

Phosphors of rare earth and transition metal doped ca1+xsr1-xgayin2-yszse3-zf2;methods of manufacturing and applications Download PDF

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WO2013070676A2
WO2013070676A2 PCT/US2012/063825 US2012063825W WO2013070676A2 WO 2013070676 A2 WO2013070676 A2 WO 2013070676A2 US 2012063825 W US2012063825 W US 2012063825W WO 2013070676 A2 WO2013070676 A2 WO 2013070676A2
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phosphor composition
formula
composition according
phosphor
rare earth
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PCT/US2012/063825
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French (fr)
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WO2013070676A3 (en
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Partha S. Dutta
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Auterra, Inc.
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Priority to KR1020147015609A priority Critical patent/KR20140100954A/en
Priority to EP12847310.5A priority patent/EP2788451A4/en
Priority to CN201280054731.3A priority patent/CN104334683A/en
Priority to CA2854027A priority patent/CA2854027A1/en
Publication of WO2013070676A2 publication Critical patent/WO2013070676A2/en
Publication of WO2013070676A3 publication Critical patent/WO2013070676A3/en

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    • 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
    • C09K11/88—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing selenium, tellurium or unspecified chalcogen elements
    • C09K11/881—Chalcogenides
    • C09K11/886—Chalcogenides with rare earth metals
    • 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
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/7729—Chalcogenides
    • C09K11/7731—Chalcogenides with alkaline earth metals
    • 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
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/7732—Halogenides
    • C09K11/7733—Halogenides with alkali or alkaline earth metals
    • 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
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7783—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals one of which being europium
    • C09K11/779—Halogenides
    • C09K11/7791—Halogenides with alkali or alkaline earth metals
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
    • H05B33/14—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the electroluminescent material, or by the simultaneous addition of the electroluminescent material in or onto the light source

Definitions

  • the present invention is directed to rare earth and/or transition metal doped Cai +x Sri_ x Ga y In 2 - y S z Se 3 - z F 2 (0 ⁇ x ⁇ l, 0 ⁇ y ⁇ 2, 0 ⁇ z ⁇ 3) compounds that may be used for photon energy down conversion applications and the synthesis thereof.
  • Solid state lighting (SSL) technologies based on light emitting diodes (LEDs) are promising for a number of applications including general illumination, displays, medical systems, communication systems, etc.
  • Significant growth in the SSL industry will be based on the availability of high efficiency, high power white LEDs.
  • Currently available commercial white LEDs especially for warm white are not quite satisfactory for most general illumination applications.
  • Their overall light output, luminous efficacy, color properties, and life must improve and the cost must be reduced before white LEDs can experience widespread usage in general lighting applications.
  • Two popular methods for creating white light sources are (a) using phosphor based wavelength conversion structures and (b) using mixed color LEDs (red, blue and green referred to as RGB). Both these methods have their own advantages.
  • RGB based white LEDs offers the capability to tune colors in real time and better color properties in display applications.
  • RGB white light LED systems require sophisticated active feedback control to keep the light at a stable color because the red, green and blue LEDs are created from different semiconductor materials.
  • the overall efficiency of RGB lighting system is low mainly due to low quantum efficiency of gallium indium nitride (Gai_ x In x N) direct emission green LEDs with peak emission wavelength near 555 nm (the peak of the human eye sensitivity). This is referred to as the "green gap" in the industry.
  • the external quantum efficiency (EQE) of green LEDs needs to improve significantly.
  • PC-LED Phosphor-converted white light-emitting diodes
  • Hybrid approaches for white light sources are also potential for general illumination purposes.
  • LEDs of individual wavelengths red, blue, green, yellow, amber, etc.
  • the individual wavelength LEDs may be either direct emission LEDs or PC-LEDs.
  • PC-LEDs for green emission wavelengths in the green-gap
  • low efficiency direct emission green LEDs are better suited than the low efficiency direct emission green LEDs.
  • LED based backlighting are anticipated to provide superior color gamut compared to the existing cold cathode fluorescent lamp (CCFL).
  • Numerous benefits for LED backlighting lighting for LCD displays include: no mercury, much longer source life, greater than 30,000 hours, compared to CCFL, less prone to breaking.
  • LED based displays are less energy efficient and higher in cost compared to CCFL based displays.
  • LED based light sources with different emission wavelengths.
  • Applications in biotechnology, indoor agriculture, photo-chemical reactions, adaptive illumination, photo-therapy, data communication, etc. are just a few examples.
  • PC-LEDs are attractive proposition since development of high efficiency phosphors of various emission wavelengths can be done simultaneously (short time period) with relatively low investments.
  • UV blue or ultraviolet
  • PC-LEDs with large number of emission wavelengths may be developed.
  • PC-LEDs also offer tremendous opportunities due to their simplicity and lower cost of fabrication, tunable and wide spectral characteristics, low power consumption and ease of operation, etc. Due to these reasons, intense research is being conducted world-wide in the area of down conversion phosphors that may be excited by blue LEDs.
  • High efficiency phosphors compounds have been studied extensively and sufficiently developed for UV excitation such as used in existing CFL (compact fluorescent lamp), CRT (cathode ray tube), CCFL (cold cathode fluorescent lamp), etc.
  • CFL compact fluorescent lamp
  • CRT cathode ray tube
  • CCFL cold cathode fluorescent lamp
  • these phosphors have poor absorption and wavelength conversion efficiencies for excitation sources in the blue region of the visible spectrum (400-480 nm).
  • Current research in new phosphor compounds is targeted towards the development of materials that possess high absorption coefficient for blue wavelengths and high quantum efficiencies for converting blue to longer wavelength photons. Rigorous search for high efficiency phosphor materials and unique composition of matter continues at the present time. Some of the high efficiency phosphor compounds found to-date are discussed below.
  • Phosphor-converted white LEDs are commonly achieved by using a yellow phosphor with a blue LED or by using red, green, blue (RGB) phosphors with a UV LED.
  • RGB red, green, blue
  • One of the most popular yellow phosphors presently used in commercial white LEDs is Y 3 Al 5 0i 2 :Ce 3+ (YAG:Ce). Since the successful development of Gai_ x In x N blue LEDs, researchers have investigated four broad categories of high efficiency phosphors for white LED applications with various degrees of success.
  • Yttrium aluminum garnet family (Y x Gdi_ x ) 3 (Al y Gai_ y ) 5 0i 2 : Ce 3+ , Pr 3+ with 0 ⁇ x ⁇ 1.
  • Silicate garnet family ML 2 QR 4 O 12 : Ce 3+ , Eu 3+ .
  • M is elements from the group IIA (Mg, Ca, Sr, Ba).
  • L is rare earth elements from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
  • Q is elements from the group IVA (Si, Ge, Sn, Pb).
  • R is elements from the group IIIA (B, Al, Ga, In, Tl).
  • Vanadate garnet family Ca 2 aMg 2 V 3 0i 2 : Eu 3+ .
  • Alkaline earth metal silicates family (Bai_ x _ y Sr x Ca y )Si0 4 :Eu 2+ series such as Ca 3 MgSi 2 0 8 : Eu 2+ , Sr 3 MgSi 2 0 8 : Eu 2+ , Ba 3 MgSi 2 0 8 : Eu 2+ , and their mixtures; Ba 2 MgZnSi 2 0 4 :Eu 2+ , Sr 3 Si0 5 :Eu 2+ , Li 2 SrSi0 4 :Eu 2+ , and A 2 Si0 4 : Eu 2+ , D where A is elements from group II (Sr, Ba,Ca,Zn,Cd,Mg) and D is elements such as F,Cl,Br,I,N,S,P.
  • A is elements from group II (Sr, Ba,Ca,Zn,Cd,Mg) and D is elements such as F,Cl,Br,I,N,
  • M is elements from group IIA (Mg, Ca, Sr, Ba) such as Cai_ x Sr x S:Eu 2+ , Cai_ x Sr x Se:Eu 2+ , Cai_ x Sr x S y Sei_ y :Eu 2+ with 0 ⁇ x ⁇ 1 and 0 , y ⁇ 1.
  • Metal nitrides family M x Si y N z :Eu 2+ , Ce 3+
  • M Mg, Ca, Sr, Ba, Ln, Y, Yb, Al such as Sr 2 Si 5 N 8 :Eu 2+ , Ba 2 Si 5 N 8 :Eu 2+ , (Sr 1 . x . y Ba x Ca y ) 2 Si 5 N 8 :Eu 2+ , CaAlSiN 3 :Eu 2+ , Ca x Al y Si z N 3 :Ce 3+ , CaSiN 2 :Ce 3+ .
  • Figure 1 shows a typical PC-LED structure excited by a blue or UV LED.
  • Figure 2a shows the PL spectrum of the phosphor (solid curve) in Example 1 and (dashed curve) in Example 2.
  • Figure 2b shows the PL spectrum of the phosphor in Example 3.
  • Figure 2c shows the PL spectrum of the phosphor in Example 4.
  • Figure 2d shows the PL spectrum of the phosphor in Example 5.
  • Figure 3 shows the powder XRD of the phosphor in Example 1.
  • the present invention provides a composition of matter Cai +x Sri_ x Ga y In 2 - y S z Se 3 _ Z F 2 : D wherein 0 ⁇ x ⁇ l, 0 ⁇ y ⁇ 2 and 0 ⁇ z ⁇ 3 and further wherein D is one or more rare earth and/or transition metal impurities selected from the group consisting of Eu, Ce, Pr, Tb, Ru, Er, Mn and/or mixtures thereof.
  • the composition of matter of the present invention may be incorporated as an active element or as a passive element for applications including, but not limited to, electrical, mechanical, magnetic, optical, thermal, chemical, electronic, optoelectronic, photonic, power generation, bio-chemical, and cosmetic applications.
  • Suitable uses for the composition of matter of the present invention include, but are not limited to, use as a solid substrate, a thin film, a colloidal solution, a light emission device, a light detection device, a power generation device, a wavelength conversion device, an optical filter, a light carrier (waveguide or fiber), a printing ink, a paint, a light modulator device, an optical switch, a reflective surface, a catalyt, a photo-therapy device, a photo-bio-reactor, a chemical reactor, a bio-chemical reactor, a laser gain medium, a photo-transistor, and/or a fluorescent tag.
  • the present invention further provides a synthesis method for a composition of matter Cai +x Sri_ x Ga y In 2 - y S z Se 3 - z F 2 : D wherein 0 ⁇ x ⁇ l, 0 ⁇ y ⁇ 2 and 0 ⁇ z ⁇ 3 and further wherein D is one or more rare earth and/or transition metal impurities selected from the group consisting of Eu, Ce, Pr, Tb, Ru, Er, Mn and/or mixtures thereof comprising the steps of: (a) liquid phase reaction, (b) grinding and homogenization of alloyed ingredients, and (c) solid phase reaction.
  • the present invention provides rare earth and/or transition metal doped Ca 1+x Sr 1 _ x Ga y In 2 - y S z Se 3 -zF2 (0 ⁇ x ⁇ l, 0 ⁇ y ⁇ 2, 0 ⁇ z ⁇ 3, particularly 0 ⁇ x ⁇ l, 0 ⁇ y ⁇ 2, 0 ⁇ z ⁇ 3) compounds, or alloys, that may be used for photon energy down conversion applications.
  • the rare earth and/or transition metal impurities used as dopants/activators include, but are not limited to, Eu, Ce, Pr, Tb, Ru, Er, Mn and/or mixtures thereof. These alloys absorb photons of higher energy and emit photons of lower energy.
  • the alloy can absorb UV or blue or green wavelength photons and emit green or yellow or red wavelength photons.
  • the absorption characteristics of the phosphor can be tuned by the chemical composition of the alloy.
  • the emission characteristics of the phosphor can be tuned by the chemical composition of the alloy and the activator species.
  • the quantum efficiency of the alloy is decided by the crystalline phase and the defects in the material. Defects include bulk point defects, bulk extended defects and surface defects such as dangling bonds.
  • the dopants/activators are present in minute quantities for emission of low energy photons by absorbing higher energy photons. Generally, the dopant is present in an amount in the range of from about 0 .001 mol% to about 10 mol%.
  • the alloy composition represented by x, y and z, the dopant species and the dopant concentrations are selected to tune the position and width of the emission peak.
  • alloy compositions in accordance with the present invention include, but are not limited to, Ca 2 Ga 2 S 3 F2, CaSrGa 2 SSe 2 F 2 , CaSrGaInSe 3 F 2 , CaSrGa 2 S 3 F 2 , Ca 2 Ga 2 SSe 2 F 2 , and/or mixtures thereof.
  • Eu 2+ doped CaSrGa 2 SSe 2 F 2 with peak emission wavelength in the range of from about 540 nm to about 600 nm and Eu 2+ doped Ca Ga SSe 2 F with peak emission wavelength in the range of from about 540 to about 600 nm are preferred.
  • the subscripts in each example represent the mole fractions of the elements present in the compound.
  • group II, III, VI and VII elements other than Ca, Sr, Ga, In, S, Se, and F, such as Mg, Ba, Zn, Cd, Al, O, Te, CI, and/or mixtures thereof, either result in poor quantum efficiency or high moisture sensitivity of the phosphor powder.
  • Crucial performance characteristics of phosphors include: (a) degradation of output lumens under actual operating conditions (continuous illumination), (b) quantum efficiency at higher operating temperatures (typically encountered during LED operations), (c) shift in peak emission wavelength at operating temperature, (d) optical absorption coefficient for the higher energy photons used for excitation, (e) optical transparency of phosphor for the emission wavelength, (f) easy to handle during device fabrication and integration into passive and active structures, and (g) cost of manufactured product suitable for applications. Satisfying these stringent performance criteria requires careful optimization of the alloy composition and the synthesis process. In the present invention, we have used a multi-step synthesis process to systematically alter the compositions and study the effect of alloy composition on the quantum conversion efficiencies.
  • a method of synthesis of the composition of the present invention is also disclosed using Ca, Sr, Ga, In, S, and Se elements wherein at least one of the elements is in a fluoride compound, such as calcium fluoride (CaF), and one or more dopant impurities selected from the group consisting of rare earth metals, transition metals and/or mixtures thereof is disclosed.
  • a fluoride compound such as calcium fluoride (CaF)
  • dopant impurities selected from the group consisting of rare earth metals, transition metals and/or mixtures thereof is disclosed.
  • Synthesis methods for use in the present invention include, but are not limited to, synthesis in a single pot from a high temperature melt (liquid phase); synthesis in a single pot by solid state reaction process; and synthesis in a single pot by exposing a liquid of selected elements to the vapor of other reactant elements.
  • Other crystalline synthesis methods as would be known by those skilled in the art may be used.
  • the procedure for synthesis and characterization of the disclosed phosphor class comprises the following sequential steps:
  • Reactants in elemental or compound form are mixed together at room temperature into a homogeneous powder form.
  • the reactants mixed in this step depend on the process used for high temperature reaction in subsequent steps. For example, if a vapor phase reaction is used, only a sub-set of the reactants are mixed together at room temperature. The remaining reactants are mixed at high temperature from vapor phase.
  • Suitable reactants include, but are not limited to, elemental reactants (Ca, Ga, Sr, S, Se), compounds Sr(OH) 2 , SrC0 3 , SrCl 2 , SrO, SrF 2 , CaO, CaF 2 , Ga 2 0 3 , GaCl 3 , GaS, GaSe, CaS, SrS, SrSe, EuCi 3 , Er 2 (3 ⁇ 4, EuF 2 , CeCi 3 , and/or mixtures thereof.
  • elemental reactants Ca, Ga, Sr, S, Se
  • the homogeneous powder is reacted inside a high temperature furnace under vacuum or inert gas ambient.
  • the ambient plays an important role on the surface chemical composition of the reacted alloy which in turn impacts the performance characteristics of the phosphor.
  • the homogeneous powder is then annealed at high temperature under vacuum or inert gas ambient.
  • the purpose of this step is multi-fold: (a) to selectively evaporate and eliminate un-reacted species from the powder, (b) to selectively tune the surface alloy composition by decomposing a sub-set of the compounds present, (c) to homogenize the spatial chemical composition across each crystallite in the powder, (d) to grow the size of high quality crystallites from previously present nuclei, (e) to alter the crystallographic phase of the alloy, (f) to modify the morphology of the crystallites present in the powder, (g) to relieve the stress in the crystallites created during the grinding process, (h) to eliminate point and extended defects present in the crystallites, (i) to perform surface passivation of dangling bonds, and (j) to effectively activate the dopant species.
  • the annealed powder is then grinded finely and chemically washed to clean the surface and expose the high quality/pristine surface of the crystallites. Selection of chemicals is made to avoid degradation of the crystal structure or significant alteration of the chemical composition of the alloy.
  • the phosphor particle/crystal extraction may use selective chemical etching solutions.
  • the chemical etching solution has a pH in the range of from about 8 to about 12 and comprises water and a base, including but not limited to, KOH, NaOH, NH 4 OH, and/or mixtures thereof.
  • the chemically treated powder is transferred to a storage medium such as an organic solution to avoid exposure to moisture and air.
  • the powder is dried under inert gas or vacuum or directly transferred to an epoxy mixture for fabricating the wavelength conversion device.
  • Dried powders are also used for a variety of chemical, micro-structural and crystallographic characterizations using energy dispersive x-ray analysis (EDX), secondary electron microscopy (SEM), transmission electron microscopy (TEM), powder x-ray diffraction (XRD), surface x-ray photoelectron spectroscopy (XPS), and particle size analysis using photon correlation spectroscopy (PCS).
  • EDX energy dispersive x-ray analysis
  • SEM secondary electron microscopy
  • TEM transmission electron microscopy
  • XRD powder x-ray diffraction
  • XPS surface x-ray photoelectron spectroscopy
  • PCS photon correlation spectroscopy
  • thin solid films are formed by mixing the phosphor powder with an epoxy (typically used for forming the optical dome on LED devices for light extraction) and coated on a glass plate.
  • the epoxy-phosphor mixture is baked around 80 °C under nitrogen or argon gas flow to form a solid film.
  • the solid film is characterized for its optical properties. Characterization techniques include photoluminescence spectroscopy (PL) and absorption spectroscopy (ABS).
  • Figure 1 shows a typical PC-LED structure excited by a blue or UV LED.
  • a blue LED (excitation wavelength: 451 nm) is used.
  • compositions resulting in bluish green to red emission may be obtained by a variation of Cai +x Sri_ x Ga y In 2 - y S z Se 3 - z F 2 (0 ⁇ x ⁇ l, 0 ⁇ y ⁇ 2, 0 ⁇ z ⁇ 3) doped with impurities such as Eu, Ce, Tb, Yb, Mn, and/or mixtures thereof.
  • Example 1 Eu 2+ doped CaSrGa 2 SSe 2 F 2 is synthesized by reacting pre- synthesized SrSe, GaSe, GaS, CaF 2 , and EuCl 3 .
  • One mole fraction of each compound (SrSe, GaSe, GaS, CaF 2 ) is used.
  • the EuCL is 4 weight % of the total weight of other compounds. The mixture is reacted at a temperature of 1000 °C under argon ambient for a period of 2 hours. A yellow green luminescent ingot is obtained.
  • the ingot is crushed into a fine powder and re- annealed at a temperature of 850 °C under hydrogen ambient for a period of 30 minutes to obtain a yellow green luminescent free flowing powder.
  • the powder is chemically washed in a KOH- water solution (pH in the range of 9-10) and dried with nitrogen gas.
  • the PL spectrum of the phosphor is shown in Figure 2a (solid curve).
  • the powder XRD of the phosphor is shown in Figure 3.
  • the wall plug efficiency of the PC-LED fabricated using the dried powder and excited by blue LED (451 nm) is measured to be about 1 17-121 lumens/watt.
  • Example 2 To demonstrate the peak emission tunability of the alloy composition of the present invention as a function of elemental ratios, Eu 2+ doped Ca2Ga2SSe2F2 is synthesized by reacting pre-synthesized CaS, GaSe, CaF 2 , and EUCI3. One mole fraction of each compound CaS and CaF 2 is taken. Two mole fractions of GaSe are used. The EuCL, is 4 weight % of the total weight of other compounds. The mixture is reacted at a temperature of 1000 °C under argon ambient for a period of 2 hours. A yellow orange luminescent ingot is obtained.
  • the ingot is crushed into a fine powder and re-annealed at a temperature of 850 °C under hydrogen ambient for a period of 30 minutes to obtain a yellow orange luminescent free flowing powder.
  • the powder is chemically washed in a KOH-water solution (pH in the range of 9-10) and dried with nitrogen gas.
  • the PL spectrum of the phosphor is shown in Figure 2a (dashed curve).
  • Example 3 Eu 2+ doped CaSrGa 2 S 3 F 2 is synthesized by reacting pre- synthesized SrS:Eu 2+ , GaS and CaF 2 . One mole fraction of SrS:Eu 2+ and CaF 2 and eight moles (excess) of GaS are used. The Eu 2+ is 2 weight % of the total weight of SrS in the synthesized compound. The mixture is reacted at a temperature of 900 °C under argon ambient for a period of 48 hours, followed by reacting at 1050 °C for 12 hours.
  • the reaction mixture is cooled slowly at a rate of 2 °C per hour to a temperature of 950 °C, followed by a rapid cooling cycle to room temperature at a rate of 50 °C per hour.
  • Crystallites of green luminescence are obtained embedded in excess of GaS.
  • the crystallites are extracted by washing the reacted mixture in KOH-water mixture (pH: 10-1 1) for a period of 12 hours.
  • the extracted crystallites are crushed into a fine powder and re-annealed at a temperature of 900 °C under argon ambient for a period of 12 hours to obtain a green luminescent free flowing powder.
  • the PL spectrum of the phosphor exhibits a broad peak around 530 nm when excited by a blue LED (451 nm) as shown in Figure 2b.
  • Example 4 Eu 2+ doped Cai .5 Sr 0 .5 Ga 2 S 3 F 2 is synthesized by reacting pre- synthesized SrS:Eu 2+ , CaS:Eu 2+ , GaS and CaF 2 .
  • One mole fraction of CaS:Eu 2+ and CaF 2 one- half mole fraction of SrS:Eu 2+ and eight moles (excess) of GaS are used.
  • the Eu 2+ is 2 weight % of the total weight of SrS and CaS in the synthesized compound.
  • the mixture is reacted at a temperature of 850 °C under argon ambient for a period of 48 hours, followed by reacting at 950 °C for 24 hours.
  • the reaction mixture is cooled slowly at a rate of 2 °C per hour to a temperature of 900 °C, followed by a rapid cooling cycle to room temperature at a rate of 50 °C per hour.
  • Crystallites of greenish yellow luminescence are obtained embedded in excess of GaS.
  • the crystallites are extracted by washing the reacted mixture in mild KOH-water mixture (pH: 8-9) for a period of 36 hours.
  • the extracted crystallites are crushed into a fine powder and re- annealed at a temperature of 850 °C under argon ambient for a period of 24 hours to obtain a greenish yellow luminescent free flowing powder.
  • the PL spectrum of the phosphor exhibits a broad peak around 545 nm when excited by a blue LED (451 nm) as shown in Figure 2c.
  • Example 5 Eu 2+ doped Ca 2 Ga 2 S 3 F 2 is synthesized by reacting pre-synthesized CaS:Eu 2+ , GaS and CaF .
  • One mole fraction of CaS:Eu 2+ and CaF and two moles of GaS are used.
  • the Eu 2+ is 2 weight % of the total weight of CaS.
  • the mixture is reacted at a temperature of 1000 °C under argon ambient for a period of 24 hours. Large particulates of yellow luminescence are obtained.
  • the particulates are crushed into a fine powder and re-annealed at a temperature of 850 °C under argon ambient for a period of 12 hours to obtain a yellow luminescent free flowing powder.
  • the PL spectrum of the phosphor exhibits a broad peak around 555 nm when excited by a blue LED (451 nm) as shown in Figure 2d.
  • Example 6 Cai .5 Sro.5Ga 2 S 3 F 2 doped with Eu 2+ , Ce 3+ , and Mn 2+ is synthesized by reacting pre-synthesized SrGa 2 S 3 : Ce , SrGa 2 S 3 : Eu , CaGa 2 S 3 : Ce , CaGa 2 S 3 : Eu , CaGa 2 S 3 : Mn 2+ , and CaF 2 . Appropriate mole fractions of the individual alloys are used to obtain the final alloy composition of Cai .5 Sro.5Ga 2 S 3 F 2 .
  • the Eu 2+ , Ce 3+ and Mn 3+ are used in the range of 0.2 and 2 weight % of the total weight of the individual pre-synthesized alloys in which the dopants are incorporated.
  • the pre-synthesized precursors and CaF 2 are mixed in powder form and reacted at a temperature around 1000 °C under argon ambient for a period of 70 hours. Thereafter the reaction mixture is rapidly cooled to room temperature at a rate of 300 °C per hour. A coarse powder with a light yellow color was obtained.
  • the powder is grinded to a fine texture and re- annealed at a temperature of 850 °C under argon ambient for a period of 24 hours to obtain a fine light yellow color luminescent powder.
  • the PL spectrum of the phosphor When excited by a near ultraviolet (UV) LED with emission around 375 nm or a blue LED with emission around 400 nm, the PL spectrum of the phosphor exhibits a broad emission covering the range of 400 nm to 700 nm. The resulting mixture of emission colors results in white light.
  • UV near ultraviolet
  • Example 7 Phosphor synthesized using the method described in Example 6 with varying concentrations of Ce 3+ , Eu 2+ and Mn 2+ (in the individual pre-synthesized precursors) are used to fabricate white LEDs with different correlated color temperatures (CCT).
  • CCT correlated color temperatures
  • excitation sources such as near UV LEDs in the 375-390 nm range, blue and cyan LEDs in the 400-500 nm range.
  • the synthesized phosphor is mixed with silicone and coated onto the excitation LED source. The LEDs are illuminated using appropriate voltage and drive current as specified for the excitation source.
  • the correlated color temperature (CCT) covering various hues of the white light in the range of 2500 K-10,000K are obtained by varying the ratio of Eu 2+ : Ce 3+ : Mn 2+ concentration.
  • the present invention is not restricted to different hues of white light in the range specified above.
  • a wide range of color mixtures within the International Commission on Illumination (CIE) chromaticity coordinates can be obtained.
  • the alloy composition can also be varied keeping the concentration of the rare earth dopants the same for tunability of the emission spectrum and thereby the color mixture.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
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  • Luminescent Compositions (AREA)

Abstract

Energy down conversion phosphors represented by the chemical formula Ca1+xSr1-xGayIn2-ySzSe3-zF2 where (0≤x≤ l, 0≤y≤2, 0≤z≤3) doped with rare earth and/or transition metal elements is disclosed. Dopant impurities may be one or more species such as Eu, Ce, Mn, Ru, and/or mixtures thereof present as activators. The molar fractions x, y and z, the dopant species and the dopant concentration may be varied to tune the peak emission wavelength and/or the width of the emission peak.

Description

Phosphors of rare earth and transition metal doped Cai+xSri-xGayIn2-ySzSe3-zF2; methods of manufacturing and applications
Background
[0001] The present invention is directed to rare earth and/or transition metal doped Cai+xSri_xGayIn2-ySzSe3-zF2 (0≤ x≤ l, 0≤y≤ 2, 0≤ z≤3) compounds that may be used for photon energy down conversion applications and the synthesis thereof.
[0002] Solid state lighting (SSL) technologies based on light emitting diodes (LEDs) are promising for a number of applications including general illumination, displays, medical systems, communication systems, etc. Significant growth in the SSL industry will be based on the availability of high efficiency, high power white LEDs. Currently available commercial white LEDs especially for warm white are not quite satisfactory for most general illumination applications. Their overall light output, luminous efficacy, color properties, and life must improve and the cost must be reduced before white LEDs can experience widespread usage in general lighting applications. Two popular methods for creating white light sources are (a) using phosphor based wavelength conversion structures and (b) using mixed color LEDs (red, blue and green referred to as RGB). Both these methods have their own advantages. The RGB based white LEDs offers the capability to tune colors in real time and better color properties in display applications. On the other hand, RGB white light LED systems require sophisticated active feedback control to keep the light at a stable color because the red, green and blue LEDs are created from different semiconductor materials. Currently the overall efficiency of RGB lighting system is low mainly due to low quantum efficiency of gallium indium nitride (Gai_xInxN) direct emission green LEDs with peak emission wavelength near 555 nm (the peak of the human eye sensitivity). This is referred to as the "green gap" in the industry. To achieve high luminous efficacy for mixed color LEDs, the external quantum efficiency (EQE) of green LEDs needs to improve significantly. However, there are fundamental material challenges due to which high EQE for epitaxially grown Gai_xInxN based direct emission green LEDs has not been achieved to-date. Phosphor-converted white light-emitting diodes (PC-LED) are rapidly progressing to meet the solid-state lighting goals of 200 lumens per watt (lm/W) by 2020 set by the United States Department of Energy (U.S. DOE). Presently available commercial white LEDs are delivering about 100 lumens per watt. However to reach 200 lm/W, significant improvements are needed at several stages, including internal quantum efficiency, extraction efficiency from the chip, and phosphor system efficiency, which includes phosphor conversion efficiency and extraction efficiency at the LED package level. Hybrid approaches for white light sources are also potential for general illumination purposes. In this approach, LEDs of individual wavelengths (red, blue, green, yellow, amber, etc.) with highest efficiencies are integrated into a system to provide color mixing. The individual wavelength LEDs may be either direct emission LEDs or PC-LEDs. In this regard, higher efficiency PC-LEDs for green emission wavelengths (in the green-gap) are better suited than the low efficiency direct emission green LEDs.
[0003] For display applications such as the Liquid Crystal Displays (LCD), LED based backlighting are anticipated to provide superior color gamut compared to the existing cold cathode fluorescent lamp (CCFL). Numerous benefits for LED backlighting lighting for LCD displays include: no mercury, much longer source life, greater than 30,000 hours, compared to CCFL, less prone to breaking. However, presently LED based displays are less energy efficient and higher in cost compared to CCFL based displays. Apart from the traditional general illumination and display technologies, there is a vast commercial market for LED based light sources with different emission wavelengths. Applications in biotechnology, indoor agriculture, photo-chemical reactions, adaptive illumination, photo-therapy, data communication, etc. are just a few examples.
[0004] For solid state light sources to be feasible for large scale deployment, there are few criteria that needs to be satisfied: higher wall plug efficiencies, low cost, availability of light sources with a variety of spectral content, ease of manufacturing and integration within systems, etc. Availability of light sources with any desirable peak emission wavelengths across the visible light spectrum will be necessary for a multitude of future applications. While direct emission LEDs based on semiconductor p-n junction diodes are available for discrete wavelengths, developing the technologies for high efficiency devices for a large number of emission wavelengths is not feasible. For direct emission LED development for any new emission wavelength, long term (5-10 years) and huge investments are necessary. In addition, integration and active control of large number of direct emission LEDs in a high efficacy light source is problematic and would be cost prohibitive as well as consume higher power during operation. PC-LEDs are attractive proposition since development of high efficiency phosphors of various emission wavelengths can be done simultaneously (short time period) with relatively low investments. Using the blue or ultraviolet (UV) direct emission Gai_xInxN and Ali_xGaxN LEDs as excitation source for phosphors, PC-LEDs with large number of emission wavelengths may be developed. PC-LEDs also offer tremendous opportunities due to their simplicity and lower cost of fabrication, tunable and wide spectral characteristics, low power consumption and ease of operation, etc. Due to these reasons, intense research is being conducted world-wide in the area of down conversion phosphors that may be excited by blue LEDs.
[0005] High efficiency phosphors compounds have been studied extensively and sufficiently developed for UV excitation such as used in existing CFL (compact fluorescent lamp), CRT (cathode ray tube), CCFL (cold cathode fluorescent lamp), etc. However these phosphors have poor absorption and wavelength conversion efficiencies for excitation sources in the blue region of the visible spectrum (400-480 nm). Current research in new phosphor compounds is targeted towards the development of materials that possess high absorption coefficient for blue wavelengths and high quantum efficiencies for converting blue to longer wavelength photons. Rigorous search for high efficiency phosphor materials and unique composition of matter continues at the present time. Some of the high efficiency phosphor compounds found to-date are discussed below.
[0006] Phosphor-converted white LEDs are commonly achieved by using a yellow phosphor with a blue LED or by using red, green, blue (RGB) phosphors with a UV LED. One of the most popular yellow phosphors presently used in commercial white LEDs is Y3Al50i2:Ce3+ (YAG:Ce). Since the successful development of Gai_xInxN blue LEDs, researchers have investigated four broad categories of high efficiency phosphors for white LED applications with various degrees of success. These high phosphors falls in the following categories: (i) metal oxides, (ii) metal sulfides, selenides and thiogallates, (iii) metal nitrides and (iv) metal oxo-nitrides. Some of these high efficiency blue wavelength excitable phosphors with emission peak tunable across the visible spectrum are already being used in white LED fabrication. The chemical compositions of these phosphors are listed below:
[0007] Yttrium aluminum garnet family: (YxGdi_x)3(AlyGai_y)50i2: Ce3+, Pr3+ with 0 < x < 1.
[0008] Silicate garnet family: ML2QR4O12: Ce3+, Eu3+. Here M is elements from the group IIA (Mg, Ca, Sr, Ba). L is rare earth elements from the group consisting of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Q is elements from the group IVA (Si, Ge, Sn, Pb). R is elements from the group IIIA (B, Al, Ga, In, Tl).
[0009] Vanadate garnet family: Ca2 aMg2V30i2: Eu3+.
[0010] Mixed oxides family: (Y2-x-yEuxBiy)03: Eu3+, a2Gd2B207: Ce3+, Tb3+, YCa3M3B40i5: Eu3+ where M is elements from group IIIA (Al, Ga, In), LaCeSr2A105:Ce3+, Ba2Al204 :Eu2+ .
[0011] Alkaline earth metal silicates family: (Bai_x_ySrxCay)Si04:Eu2+ series such as Ca3MgSi208: Eu2+, Sr3MgSi208: Eu2+, Ba3MgSi208: Eu2+, and their mixtures; Ba2MgZnSi204:Eu2+, Sr3Si05:Eu2+, Li2SrSi04:Eu2+, and A2Si04: Eu2+, D where A is elements from group II (Sr, Ba,Ca,Zn,Cd,Mg) and D is elements such as F,Cl,Br,I,N,S,P.
[0012] Alkaline earth metal sulfides and selenides, MS: Eu2+ and MSe: Eu2+. Here M is elements from group IIA (Mg, Ca, Sr, Ba) such as Cai_xSrxS:Eu2+, Cai_xSrxSe:Eu2+, Cai_ xSrxSySei_y:Eu2+ with 0< x< 1 and 0 , y < 1. [0013] Alkaline earth metal thiogallates: metal sulfide thiogallates such as (SrMgCaBa)(GaAlIn)2S4 :Eu2+ and metal sulfo-selenide thiogallates such as MA2(SxSey)4:B; MA4(SxSey)7:B; M2A4(SxSey)7:B; (Ml)m(M2)nAp(SxSey)q; where M = Be,Mg,Ca,Sr,Ba,Zn; Ml = Be,Mg,Ca,Sr,Ba,Zn; M2 = Be,Mg,Ca,Sr,Ba,Zn; A = Al,Ga,In,Y,La,Gd; B = Eu,Ce,Cu,Ag,Al,Tb,Cl,Br,F,I,Mg,Pr,K,Na,Mn. The range of compositions covered for high efficiency sulfo-selenide thiogallate phosphors are as follows: m = 0 to l; n = 0 to l ; m + n = l (close to 1); p = close to 2 or close to 4; q = close to 4 or close to 7; when p = close to 2, q = close to 4; when p = close to 4, q = close to 7; x = 0 to 1 ; y = 0 to l ; x + y = 0.75 to 1.25; x + y = 0.5 to 1.5; B = 0.0001 to 10 mole %.
[0014] Metal nitrides family: MxSiyNz:Eu2+, Ce3+ where M = Mg, Ca, Sr, Ba, Ln, Y, Yb, Al such as Sr2Si5N8:Eu2+, Ba2Si5N8:Eu2+, (Sr1.x.yBaxCay)2Si5N8:Eu2+, CaAlSiN3:Eu2+, CaxAlySizN3:Ce3+, CaSiN2:Ce3+.
[0015] Metal oxo-nitrides family: MSi202N2:Eu2+ where M = Ba, Sr, Ca, etc., (SrCa)p/2Alp+qSi12.p.qOqN16.q:Eu2+, (CaxMy)(Si,Al)12(0,N)16:Eu2+ where M = Eu,Tb,Yb,Er group element, LixMyLnzSii2_(m+n)Al(m+n)OnNi6-n:Eu2+ where M = Ca, Mg, Y and Ln = Eu, Dy, Er, Tb, Yb, Ce, SrSiAl203N2:Eu2+.
[0016] According to the US Department of Energy (DOE) roadmap for phosphor development targets for 2015, quantum yield of 90% across the entire visible spectrum, color uniformity, color stability, thermal sensitivity and reduced optical scattering require the search for new phosphor materials and/or fine tuning the compositions of known phosphors. Therefore, it is the object of the present invention to synthesize selective crystalline phases of various alloy systems that have higher quantum conversion efficiencies and performance characteristics suitable for device fabrication and operation. It is a further object of the present invention to provide new alloy compositions that have been demonstrated to yield high wall plug efficiency and high efficacy light sources.
Brief Description of the Drawings
[0017] The disclosure itself will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein:
[0018] Figure 1 shows a typical PC-LED structure excited by a blue or UV LED.
[0019] Figure 2a shows the PL spectrum of the phosphor (solid curve) in Example 1 and (dashed curve) in Example 2.
[0020] Figure 2b shows the PL spectrum of the phosphor in Example 3.
[0021 ] Figure 2c shows the PL spectrum of the phosphor in Example 4. [0022] Figure 2d shows the PL spectrum of the phosphor in Example 5.
[0023] Figure 3 shows the powder XRD of the phosphor in Example 1.
Summary of the Invention
[0024] The present invention provides a composition of matter Cai+xSri_xGayIn2-ySzSe3_ ZF2: D wherein 0≤x < l, 0≤y≤2 and 0≤ z <3 and further wherein D is one or more rare earth and/or transition metal impurities selected from the group consisting of Eu, Ce, Pr, Tb, Ru, Er, Mn and/or mixtures thereof. The composition of matter of the present invention may be incorporated as an active element or as a passive element for applications including, but not limited to, electrical, mechanical, magnetic, optical, thermal, chemical, electronic, optoelectronic, photonic, power generation, bio-chemical, and cosmetic applications. Suitable uses for the composition of matter of the present invention include, but are not limited to, use as a solid substrate, a thin film, a colloidal solution, a light emission device, a light detection device, a power generation device, a wavelength conversion device, an optical filter, a light carrier (waveguide or fiber), a printing ink, a paint, a light modulator device, an optical switch, a reflective surface, a catalyt, a photo-therapy device, a photo-bio-reactor, a chemical reactor, a bio-chemical reactor, a laser gain medium, a photo-transistor, and/or a fluorescent tag.
[0025] The present invention further provides a synthesis method for a composition of matter Cai+xSri_xGayIn2-ySzSe3-zF2: D wherein 0≤ x≤ l, 0≤y≤ 2 and 0≤ z < 3 and further wherein D is one or more rare earth and/or transition metal impurities selected from the group consisting of Eu, Ce, Pr, Tb, Ru, Er, Mn and/or mixtures thereof comprising the steps of: (a) liquid phase reaction, (b) grinding and homogenization of alloyed ingredients, and (c) solid phase reaction.
[0026] Other features, aspects, and advantages of the present invention will become better understood with reference to the following description.
Detailed Description of this Invention
[0027] The present invention provides rare earth and/or transition metal doped Ca1+xSr1_xGayIn2-ySzSe3-zF2 (0 < x≤ l, 0≤y < 2, 0 < z < 3, particularly 0 < x < l, 0 < y < 2, 0 < z <3) compounds, or alloys, that may be used for photon energy down conversion applications. The rare earth and/or transition metal impurities used as dopants/activators include, but are not limited to, Eu, Ce, Pr, Tb, Ru, Er, Mn and/or mixtures thereof. These alloys absorb photons of higher energy and emit photons of lower energy. For example, the alloy can absorb UV or blue or green wavelength photons and emit green or yellow or red wavelength photons. The absorption characteristics of the phosphor can be tuned by the chemical composition of the alloy. The emission characteristics of the phosphor can be tuned by the chemical composition of the alloy and the activator species. The quantum efficiency of the alloy is decided by the crystalline phase and the defects in the material. Defects include bulk point defects, bulk extended defects and surface defects such as dangling bonds.
[0028] The dopants/activators are present in minute quantities for emission of low energy photons by absorbing higher energy photons. Generally, the dopant is present in an amount in the range of from about 0 .001 mol% to about 10 mol%. The alloy composition represented by x, y and z, the dopant species and the dopant concentrations are selected to tune the position and width of the emission peak.
[0029] Examples of alloy compositions in accordance with the present invention include, but are not limited to, Ca2Ga2S3F2, CaSrGa2SSe2F2, CaSrGaInSe3F2, CaSrGa2S3F2, Ca2Ga2SSe2F2, and/or mixtures thereof. In particular, Eu2+ doped CaSrGa2SSe2F2 with peak emission wavelength in the range of from about 540 nm to about 600 nm and Eu2+ doped Ca Ga SSe2F with peak emission wavelength in the range of from about 540 to about 600 nm are preferred. The subscripts in each example represent the mole fractions of the elements present in the compound.
[0030] The use of group II, III, VI and VII elements other than Ca, Sr, Ga, In, S, Se, and F, such as Mg, Ba, Zn, Cd, Al, O, Te, CI, and/or mixtures thereof, either result in poor quantum efficiency or high moisture sensitivity of the phosphor powder. Crucial performance characteristics of phosphors include: (a) degradation of output lumens under actual operating conditions (continuous illumination), (b) quantum efficiency at higher operating temperatures (typically encountered during LED operations), (c) shift in peak emission wavelength at operating temperature, (d) optical absorption coefficient for the higher energy photons used for excitation, (e) optical transparency of phosphor for the emission wavelength, (f) easy to handle during device fabrication and integration into passive and active structures, and (g) cost of manufactured product suitable for applications. Satisfying these stringent performance criteria requires careful optimization of the alloy composition and the synthesis process. In the present invention, we have used a multi-step synthesis process to systematically alter the compositions and study the effect of alloy composition on the quantum conversion efficiencies. It has been observed that even though the peak emission of a specific alloy system activated with a specific dopant remains the same, light emission properties such as quantum conversion efficiency, wall plug efficiency of the device, the emission peak width, the output lumens with time for continuously operated devices is dependent on the crystalline phase and/or elemental ratios in the alloy. [0031] A method of synthesis of the composition of the present invention is also disclosed using Ca, Sr, Ga, In, S, and Se elements wherein at least one of the elements is in a fluoride compound, such as calcium fluoride (CaF), and one or more dopant impurities selected from the group consisting of rare earth metals, transition metals and/or mixtures thereof is disclosed. Synthesis methods for use in the present invention include, but are not limited to, synthesis in a single pot from a high temperature melt (liquid phase); synthesis in a single pot by solid state reaction process; and synthesis in a single pot by exposing a liquid of selected elements to the vapor of other reactant elements. Other crystalline synthesis methods as would be known by those skilled in the art may be used.
[0032] Generally, the procedure for synthesis and characterization of the disclosed phosphor class comprises the following sequential steps:
[0033] Reactants in elemental or compound form are mixed together at room temperature into a homogeneous powder form. The reactants mixed in this step depend on the process used for high temperature reaction in subsequent steps. For example, if a vapor phase reaction is used, only a sub-set of the reactants are mixed together at room temperature. The remaining reactants are mixed at high temperature from vapor phase.
[0034] Suitable reactants include, but are not limited to, elemental reactants (Ca, Ga, Sr, S, Se), compounds Sr(OH)2, SrC03, SrCl2, SrO, SrF2, CaO, CaF2, Ga203, GaCl3, GaS, GaSe, CaS, SrS, SrSe, EuCi3, Er2(¾, EuF2, CeCi3, and/or mixtures thereof.
[0035] The homogeneous powder is reacted inside a high temperature furnace under vacuum or inert gas ambient. The ambient plays an important role on the surface chemical composition of the reacted alloy which in turn impacts the performance characteristics of the phosphor.
[0036] Reacted alloy is grounded into a fine powder and homogenized thoroughly at room temperature.
[0037] The homogeneous powder is then annealed at high temperature under vacuum or inert gas ambient. The purpose of this step is multi-fold: (a) to selectively evaporate and eliminate un-reacted species from the powder, (b) to selectively tune the surface alloy composition by decomposing a sub-set of the compounds present, (c) to homogenize the spatial chemical composition across each crystallite in the powder, (d) to grow the size of high quality crystallites from previously present nuclei, (e) to alter the crystallographic phase of the alloy, (f) to modify the morphology of the crystallites present in the powder, (g) to relieve the stress in the crystallites created during the grinding process, (h) to eliminate point and extended defects present in the crystallites, (i) to perform surface passivation of dangling bonds, and (j) to effectively activate the dopant species. [0038] The annealed powder is then grinded finely and chemically washed to clean the surface and expose the high quality/pristine surface of the crystallites. Selection of chemicals is made to avoid degradation of the crystal structure or significant alteration of the chemical composition of the alloy. The phosphor particle/crystal extraction may use selective chemical etching solutions. Generally, the chemical etching solution has a pH in the range of from about 8 to about 12 and comprises water and a base, including but not limited to, KOH, NaOH, NH4OH, and/or mixtures thereof.
[0039] The chemically treated powder is transferred to a storage medium such as an organic solution to avoid exposure to moisture and air.
[0040] The powder is dried under inert gas or vacuum or directly transferred to an epoxy mixture for fabricating the wavelength conversion device. Dried powders are also used for a variety of chemical, micro-structural and crystallographic characterizations using energy dispersive x-ray analysis (EDX), secondary electron microscopy (SEM), transmission electron microscopy (TEM), powder x-ray diffraction (XRD), surface x-ray photoelectron spectroscopy (XPS), and particle size analysis using photon correlation spectroscopy (PCS).
[0041] For the optical characterization and device fabrication, thin solid films are formed by mixing the phosphor powder with an epoxy (typically used for forming the optical dome on LED devices for light extraction) and coated on a glass plate. The epoxy-phosphor mixture is baked around 80 °C under nitrogen or argon gas flow to form a solid film.
[0042] The solid film is characterized for its optical properties. Characterization techniques include photoluminescence spectroscopy (PL) and absorption spectroscopy (ABS).
[0043] The following non-limiting examples illustrate certain aspects of the present invention.
[0044] For PC-LED characterization, wall plug efficiency is measured. Figure 1 shows a typical PC-LED structure excited by a blue or UV LED. A blue LED (excitation wavelength: 451 nm) is used.
[0045] The examples below exemplify the role of alloy composition on the emission wavelength and final device performance. The present invention is not restricted to either wavelength range or device performance quoted herein. Compositions resulting in bluish green to red emission may be obtained by a variation of Cai+xSri_xGayIn2-ySzSe3-zF2 (0≤x≤l, 0≤y≤ 2, 0≤ z <3) doped with impurities such as Eu, Ce, Tb, Yb, Mn, and/or mixtures thereof.
[0046] Example 1: Eu2+ doped CaSrGa2SSe2F2 is synthesized by reacting pre- synthesized SrSe, GaSe, GaS, CaF2, and EuCl3. One mole fraction of each compound (SrSe, GaSe, GaS, CaF2) is used. The EuCL; is 4 weight % of the total weight of other compounds. The mixture is reacted at a temperature of 1000 °C under argon ambient for a period of 2 hours. A yellow green luminescent ingot is obtained. The ingot is crushed into a fine powder and re- annealed at a temperature of 850 °C under hydrogen ambient for a period of 30 minutes to obtain a yellow green luminescent free flowing powder. The powder is chemically washed in a KOH- water solution (pH in the range of 9-10) and dried with nitrogen gas. The PL spectrum of the phosphor is shown in Figure 2a (solid curve). The powder XRD of the phosphor is shown in Figure 3. The wall plug efficiency of the PC-LED fabricated using the dried powder and excited by blue LED (451 nm) is measured to be about 1 17-121 lumens/watt.
[0047] Example 2: To demonstrate the peak emission tunability of the alloy composition of the present invention as a function of elemental ratios, Eu2+ doped Ca2Ga2SSe2F2 is synthesized by reacting pre-synthesized CaS, GaSe, CaF2, and EUCI3. One mole fraction of each compound CaS and CaF2 is taken. Two mole fractions of GaSe are used. The EuCL, is 4 weight % of the total weight of other compounds. The mixture is reacted at a temperature of 1000 °C under argon ambient for a period of 2 hours. A yellow orange luminescent ingot is obtained. The ingot is crushed into a fine powder and re-annealed at a temperature of 850 °C under hydrogen ambient for a period of 30 minutes to obtain a yellow orange luminescent free flowing powder. The powder is chemically washed in a KOH-water solution (pH in the range of 9-10) and dried with nitrogen gas. The PL spectrum of the phosphor is shown in Figure 2a (dashed curve).
[0048] Example 3: Eu2+ doped CaSrGa2S3F2 is synthesized by reacting pre- synthesized SrS:Eu2+, GaS and CaF2. One mole fraction of SrS:Eu2+ and CaF2 and eight moles (excess) of GaS are used. The Eu2+ is 2 weight % of the total weight of SrS in the synthesized compound. The mixture is reacted at a temperature of 900 °C under argon ambient for a period of 48 hours, followed by reacting at 1050 °C for 12 hours. The reaction mixture is cooled slowly at a rate of 2 °C per hour to a temperature of 950 °C, followed by a rapid cooling cycle to room temperature at a rate of 50 °C per hour. Crystallites of green luminescence are obtained embedded in excess of GaS. The crystallites are extracted by washing the reacted mixture in KOH-water mixture (pH: 10-1 1) for a period of 12 hours. The extracted crystallites are crushed into a fine powder and re-annealed at a temperature of 900 °C under argon ambient for a period of 12 hours to obtain a green luminescent free flowing powder. The PL spectrum of the phosphor exhibits a broad peak around 530 nm when excited by a blue LED (451 nm) as shown in Figure 2b.
[0049] Example 4: Eu2+ doped Cai.5Sr0.5 Ga2S3F2 is synthesized by reacting pre- synthesized SrS:Eu2+, CaS:Eu2+, GaS and CaF2. One mole fraction of CaS:Eu2+ and CaF2, one- half mole fraction of SrS:Eu2+ and eight moles (excess) of GaS are used. The Eu2+ is 2 weight % of the total weight of SrS and CaS in the synthesized compound. The mixture is reacted at a temperature of 850 °C under argon ambient for a period of 48 hours, followed by reacting at 950 °C for 24 hours. The reaction mixture is cooled slowly at a rate of 2 °C per hour to a temperature of 900 °C, followed by a rapid cooling cycle to room temperature at a rate of 50 °C per hour. Crystallites of greenish yellow luminescence are obtained embedded in excess of GaS. The crystallites are extracted by washing the reacted mixture in mild KOH-water mixture (pH: 8-9) for a period of 36 hours. The extracted crystallites are crushed into a fine powder and re- annealed at a temperature of 850 °C under argon ambient for a period of 24 hours to obtain a greenish yellow luminescent free flowing powder. The PL spectrum of the phosphor exhibits a broad peak around 545 nm when excited by a blue LED (451 nm) as shown in Figure 2c.
[0050] Example 5: Eu2+ doped Ca2Ga2S3F2 is synthesized by reacting pre-synthesized CaS:Eu2+, GaS and CaF . One mole fraction of CaS:Eu2+ and CaF and two moles of GaS are used. The Eu2+ is 2 weight % of the total weight of CaS. The mixture is reacted at a temperature of 1000 °C under argon ambient for a period of 24 hours. Large particulates of yellow luminescence are obtained. The particulates are crushed into a fine powder and re-annealed at a temperature of 850 °C under argon ambient for a period of 12 hours to obtain a yellow luminescent free flowing powder. The PL spectrum of the phosphor exhibits a broad peak around 555 nm when excited by a blue LED (451 nm) as shown in Figure 2d.
[0051] Example 6: Cai.5Sro.5Ga2S3F2 doped with Eu2+, Ce3+, and Mn2+ is synthesized by reacting pre-synthesized SrGa2S3: Ce , SrGa2S3: Eu , CaGa2S3: Ce , CaGa2S3: Eu , CaGa2S3: Mn2+, and CaF2. Appropriate mole fractions of the individual alloys are used to obtain the final alloy composition of Cai.5Sro.5Ga2S3F2. The Eu2+, Ce3+ and Mn3+ are used in the range of 0.2 and 2 weight % of the total weight of the individual pre-synthesized alloys in which the dopants are incorporated. The pre-synthesized precursors and CaF2 are mixed in powder form and reacted at a temperature around 1000 °C under argon ambient for a period of 70 hours. Thereafter the reaction mixture is rapidly cooled to room temperature at a rate of 300 °C per hour. A coarse powder with a light yellow color was obtained. The powder is grinded to a fine texture and re- annealed at a temperature of 850 °C under argon ambient for a period of 24 hours to obtain a fine light yellow color luminescent powder. When excited by a near ultraviolet (UV) LED with emission around 375 nm or a blue LED with emission around 400 nm, the PL spectrum of the phosphor exhibits a broad emission covering the range of 400 nm to 700 nm. The resulting mixture of emission colors results in white light.
[0052] Example 7: Phosphor synthesized using the method described in Example 6 with varying concentrations of Ce3+, Eu2+ and Mn2+ (in the individual pre-synthesized precursors) are used to fabricate white LEDs with different correlated color temperatures (CCT). A variety of excitation sources are used such as near UV LEDs in the 375-390 nm range, blue and cyan LEDs in the 400-500 nm range. The synthesized phosphor is mixed with silicone and coated onto the excitation LED source. The LEDs are illuminated using appropriate voltage and drive current as specified for the excitation source. The correlated color temperature (CCT) covering various hues of the white light in the range of 2500 K-10,000K are obtained by varying the ratio of Eu2+ : Ce3+ : Mn2+ concentration. The present invention is not restricted to different hues of white light in the range specified above. A wide range of color mixtures within the International Commission on Illumination (CIE) chromaticity coordinates can be obtained. The alloy composition can also be varied keeping the concentration of the rare earth dopants the same for tunability of the emission spectrum and thereby the color mixture.
[0053] The foregoing description of the embodiments of this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the above described invention.

Claims

Claims:
1. A phosphor composition having the formula Cai+xSri_xGayIn2-ySzSe3-zF2 :D,
wherein 0≤x≤ 1, 0≤ y≤ 2 and 0≤z <3 and wherein D is a dopant comprising one or more rare earth and transition metal elements.
2. A phosphor composition having the formula Cai+xSri_xGayIn2-ySzSe3-zF2 :D,
wherein 0 <x < l, 0 < y < 2 and 0 <z <3 and wherein D is a dopant comprising one or more rare earth and transition metal elements.
3. A phosphor composition according to claim 1 wherein the one or more rare earth and transition metal elements are selected from the group consisting of Eu, Ce, Pr, Tb, Ru, Er, Mn and/or mixtures thereof.
4. A phosphor composition according to claim 1 having the formula Ca2Ga2S3F2 :D.
5. A phosphor composition according to claim 1 having the formula CaSrGa2SSe2F2 :D.
6. A phosphor composition according to claim 1 having the formula CaSrGaInSe3F2 :D.
7. A phosphor composition according to claim 1 having the formula CaSrGa2S3F2 :D.
8. A phosphor composition according to claim 1 having the formula Ca2Ga2SSe2F2 :D.
9. A phosphor composition according to claim 1 having the formula CaSrGa2SSe2F2 :Eu2+ with a peak emission wavelength of about 550 nm.
10. A phosphor composition according to claim 1 having the formula CaSrGa2S3F2 :Eu2+ with a peak emission wavelength of about 530 nm.
11. A phosphor composition according to claim 1 having the formula Ca1.sSro.sGa2S3F2 :Eu2+ with a peak emission wavelength of about 545 nm.
12. A phosphor composition according to claim 1 having the formula Ca2Ga2S3F2 :Eu2+ with a peak emission wavelength of about 555 nm.
13. A phosphor composition according to claim 1 having the formula Ca2Ga2SSe2F2 :Eu+2 with peak emission wavelength of about 600 nm.
14. A phosphor composition according to claim 1 having the formula Ca1.sSro.sGa2S3F2 :Eu2+, Ce3+, Mn2+ with emission wavelength covering the range from about 400 to about 700 nm.
15. A phosphor composition according to claim 1 having the formula Ca1.sSro.sGa2S2SeF2 :Eu2+, Ce3+, Mn2+ with emission wavelength covering the range from about 400 to 700 nm.
16. A phosphor composition according to claim 1 having the formula Cai .5Sro.5Gai.5Ino.5S2SeF2 :Eu2+, Ce3+, Mn2+ with emission wavelength covering the range from 400 to 700 nm.
17. A method of synthesis of a phosphor composition having the formula Cai+xSri_xGayIn2_ ySzSe3_zF2 :D, wherein 0≤ x≤ 1, 0≤ y≤ 2 and 0≤ z < 3 and wherein D is a dopant comprising one or more rare earth and transition metal elements, the method comprising using a single pot high temperature melt to incorporate at least some of the D dopants into the crystal lattice of the phosphor composition.
18. The method of claim 14 further comprising grinding and homogenization of the phosphor composition and dopants D.
19. A method of synthesis of a phosphor composition having the formula Cai+xSri_xGayIn2_ ySzSe3_zF2 :D, wherein 0≤ x≤ 1, 0≤ y≤ 2 and 0≤ z <3 and wherein D is a dopant comprising one or more rare earth and transition metal elements, the method comprising using a single pot solid state reaction to incorporate at least some of the D dopants into the crystal lattice of the phosphor composition.
20. The method of claim 16 further comprising grinding and homogenization of the phosphor composition and dopants D.
21. A method of phosphor particle/crystal extraction for a phosphor composition having the formula Ca1+xSri_xGayIn2_ySzSe3-zF2 :D, wherein 0 < x < 1, 0≤ y≤ 2 and 0 < z < 3 and wherein D is a dopant comprising one or more rare earth and transition metal elements using a chemical etching solution.
22. The method of claim 18, wherein the chemical etching solution comprises water, KOH, NaOH, NH4OH and/or mixtures thereof and further wherein the chemical etching solution has a pH in the range of from about 8 to about 12.
23. An active element or a passive element comprising the phosphor composition of claim 1 for electrical, mechanical, magnetic, optical, thermal, chemical, electronic, optoelectronic, photonic, power generation, bio-chemical, and cosmetic applications.
PCT/US2012/063825 2011-11-10 2012-11-07 Phosphors of rare earth and transition metal doped ca1+xsr1-xgayin2-yszse3-zf2;methods of manufacturing and applications WO2013070676A2 (en)

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