WO2006072919A2 - Illumination system comprising barium magnesium aluminate phosphor - Google Patents

Illumination system comprising barium magnesium aluminate phosphor Download PDF

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Publication number
WO2006072919A2
WO2006072919A2 PCT/IB2006/050051 IB2006050051W WO2006072919A2 WO 2006072919 A2 WO2006072919 A2 WO 2006072919A2 IB 2006050051 W IB2006050051 W IB 2006050051W WO 2006072919 A2 WO2006072919 A2 WO 2006072919A2
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phosphor
emission
illumination system
green
blue
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PCT/IB2006/050051
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French (fr)
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WO2006072919A3 (en
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Thomas JÜSTEL
Walter Mayr
Wouter Johannes Marcel Schrama
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Philips Intellectual Property & Standards Gmbh
Koninklijke Philips Electronics N. V.
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Publication of WO2006072919A2 publication Critical patent/WO2006072919A2/en
Publication of WO2006072919A3 publication Critical patent/WO2006072919A3/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
    • C09K11/59—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing silicon
    • C09K11/592—Chalcogenides
    • 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
    • C09K11/64—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing aluminium
    • C09K11/641—Chalcogenides
    • C09K11/643—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
    • C09K11/7734—Aluminates
    • 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
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/7777—Phosphates
    • 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
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/778—Borates
    • 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
    • C09K11/7784—Chalcogenides
    • C09K11/7787—Oxides
    • 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
    • C09K11/7795—Phosphates
    • 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
    • C09K11/7797—Borates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/38—Devices for influencing the colour or wavelength of the light
    • H01J61/42—Devices for influencing the colour or wavelength of the light by transforming the wavelength of the light by luminescence
    • H01J61/44—Devices characterised by the luminescent material
    • 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

  • Illumination system comprising barium magnesium aluminate phosphor
  • the present invention generally relates to an illumination system comprising a radiation source and a fluorescent material comprising a barium magnesium aluminate phosphor.
  • the invention also relates to a barium magnesium aluminate phosphor for use in such illumination system. More particularly, the invention relates to an illumination system and a fluorescent material comprising a barium magnesium aluminate phosphor for the generation of specific, colored light, including white light, by luminescent down conversion and additive color mixing based on a ultraviolet radiation emitting radiation source.
  • a fluorescent lamp as an illumination system is especially contemplated.
  • Fluorescent lamps typically have a transparent discharge vessel enclosing a sealed discharge space containing an inert gas and mercury vapor as well as means for igniting and maintaining a discharge, such as electrodes.
  • the mercury When subjected to a current provided by electrodes, the mercury ionizes to produce radiation having primary wavelengths of 185 nm and 254 nm. This ultraviolet radiation, in turn, excites phosphors on the inside surface of the discharge vessel to produce visible light which is emitted from the discharge vessel.
  • Today's phosphors blends are typically chosen to emit light in each of the three primary colors red, green and blue. Fluorescent lamps comprising three phosphors for emission of red, green and blue light are referred to as three -band lamp or trichromatic fluorescent lamps.
  • An improved blue phosphor is known from EP529956, characterized by having a composition represented by the following general formula: (Mi- y - z Eu y Mn z )O-aAl 2 ⁇ 3 wherein M stands for at least one element selected from the group consisting of Mg, Ca, Sr, and Ba and a, y, and z stand for numerical values satisfying the expressions, 1.5 ⁇ a ⁇ 1.
  • M stands for at least one element selected from the group consisting of Mg, Ca, Sr, and Ba
  • a, y, and z stand for numerical values satisfying the expressions, 1.5 ⁇ a ⁇ 1.
  • the present invention provides an illumination system comprising a radiation source and luminescent material comprising a barium magnesium aluminate phosphor of general formula (Ba 1 _ x Sr x ) 1 _ a Mg3_bAl 1 4 ⁇ 2 5:Eu a Mnb, wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0.
  • a radiation source and luminescent material comprising a barium magnesium aluminate phosphor of general formula (Ba 1 _ x Sr x ) 1 _ a Mg3_bAl 1 4 ⁇ 2 5:Eu a Mnb, wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0.
  • the illumination system comprising barium magnesium aluminate phosphor of general formula (Ba 1 _ x Sr x ) 1 _ a Mg3_bAl 1 4 ⁇ 2 5:Eu a Mnb, wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0, exhibits an excellent emission intensity under excitation by a source of radiation in the UV range of the electromagnetic spectrum. It is an advantage of the phosphors used, that they have a broad excitation spectrum, which makes them not only useful for mercury low pressure discharge lamps (fluorescent lamps) but also for mercury high pressure discharge lamps and xenon excimer discharge lamps.
  • the radiation source provides radiation in the UV range of the electromagnetic spectrum during operation.
  • Such radiation sources comprise the rare gas/mercury discharge plasma of low-pressure mercury discharge lamps, high-pressure mercury discharge lamps, xenon excimer discharge lamps and gas discharge displays, such as plasma discharge panels.
  • the illumination system according to the invention is equipped with a luminescent material comprising at least one second red phosphor, wherein the second phosphor is selected from the group of (Y 1 ⁇ aGd x )BO 3 IEUa, (Y 1 _ x _ a Gd x )(V 1 _ y P y )O 4 :Eu a wherein 0 ⁇ x ⁇ l, 0 ⁇ y ⁇ l, 0 ⁇ a ⁇ 0.3 and x + a ⁇ l.
  • the illumination system according to the invention is equipped with a luminescent material comprising also at least one third green phosphor, wherein the third phosphor is selected from the group of Ce 005 Tb 035 MgAl 11 O 19 , LaPO 4 :Ce,Tb and GdMgB 5 O 10 :Ce,Tb.
  • An illumination system can provide a composite white output light that is well balanced with respect to color.
  • the composite white output light has a greater amount of emission in the blue color range than the conventional lamp. This characteristic makes the device ideal for applications in which a true color rendition is required.
  • Such applications of the invention include inter alia backlighting of liquid crystal displays, general illumination, traffic lighting and street lighting.
  • the blue to green phosphors according to the present invention have a band emission in blue to green region, peaking around 450 nm and 520 nm, when excited by 147 or 173 nm radiation from xenon gas mixture discharge or by the254 nm radiation from mercury discharge.
  • the dopants present in the phosphor do not undergo any change in their valence state when heated to high temperatures of about 600 degree C, one of the essential conditions required during the process of lamp manufacturing (baking). Furthermore the phosphor does not degrade on continuous irradiation by light of wavelength 254 nm. In addition, it is easily synthesizable and stable.
  • This blue phosphor is useful for an improvement of CRI in high efficiency tricolor (trichromatic) fluorescent lamps based on rare-earth phosphors, where a blend of three different inorganic compounds each emitting in different regions viz., blue (450 nm), green (540 nm) and red (610 nm) mixes upon to give out white light, when excited by mercury discharge at low pressure corresponding to radiation of wavelength 254 nm.
  • This luminescent material can be applied as green phosphor in very high quality fluorescent lamps.
  • This green phosphor is also useful in plasma display panels (PDP) as the green component.
  • PDP plasma display panels
  • the phosphor needs to get excited with short wavelength UV radiation that is compatible with the xenon discharge plasma excitation.
  • the phosphors used in television tubes a short decay time is necessary to avoid afterglow or persistence.
  • the lifetime of an electron in the excited state of europium(II)-ion, when doped in any inorganic crystal lattice is very short.
  • the phosphors co-activated with europium(II) are preferred to avoid afterglow.
  • the present invention focuses on a fluorescent material comprising a barium magnesium aluminate phosphor activated by europium(II) and/or manganese(II) in any configuration of an illumination system comprising a source of primary radiation, including, but not limited to discharge lamps, fluorescent lamps, phosphor converted LEDs and plasma displays.
  • a source of primary radiation including, but not limited to discharge lamps, fluorescent lamps, phosphor converted LEDs and plasma displays.
  • the term "radiation” encompasses radiation in the UV, IR and visible regions of the electromagnetic spectrum.
  • the fluorescent material according to the invention comprises as a phosphor a barium magnesium aluminate activated by europium and/or manganese.
  • the phosphor conforms to the general formula (Ba 1 _ x Sr x ) 1 _ a Mg3_bAl 1 4 ⁇ 2 5:Eu a Mnb, wherein 0 ⁇ x ⁇ l. O ⁇ a ⁇ 0.2, O ⁇ b ⁇ 0.2, a + b > O.
  • the phosphor of general formula (Ba ⁇ x S ⁇ i. a Mgs. b Al ⁇ O ⁇ iEU a Mn b , wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0 comprises a host lattice with the main components of barium, magnesium, aluminum and oxygen and europium and/or manganese as activators.
  • This class of phosphor material is based an activated luminescence of a barium magnesium aluminate host lattice.
  • the host lattice is supposed to have a structure consisting of puckered layers containing the divalent earth alkaline cations, barium and eventually strontium, and oxygen, and blocks of spinel units MgAl 2 O 4 .
  • the phosphors according to the invention comprise a higher portion of spinel units in comparison to the conventional BaMgAl 10 O 17 .
  • the activator ions europium and/or manganese are incorporated.
  • barium magnesium aluminate phosphors activated by europium(II) and/or manganese(II) are responsive to a broad energetic portions of the electromagnetic spectrum.
  • the excitation band is found to be a broad band (120-400 nm). Hence, it is clear that these phosphors can be excited efficiently with radiation of wavelength 254 as well as 172 nm.
  • the fluorescent material has ideal characteristics for converting the UV radiation of a mercury arc discharge or a xenon excimer discharge into visible white or colored light.
  • FIG. 2 shows the CIE color triangle with the color points of green BaMg 3 Al 14 O 2S iMn in comparison to conventional BaMgAl 1 OO 17 IMn and Zn 2 Si0 4 :Mn.
  • the blue narrow-band emission originates from a d ⁇ f optical transition on europium(II).
  • the emission of manganese(II) in BaMgAl 10 O 17 : Eu, Mn in the green range of the electromagnetic spectrum is an example for a broad d ⁇ d emission band.
  • the green emission is generated by a d ⁇ d optical transition on the Mn -ion with high spin d electronic configuration (all electrons have their spin oriented in the same 4 6 direction).
  • the optical transition leading to emission is T 1 ⁇ A 1 .
  • 3 2 4 1 configurations in ground- and excited state are t ) e ) and t ) e ) , respectively.
  • the emission generated reflects how the optical properties of the ion depend on its chemical environment. Activation with europium(II), which occupies the earth alkaline sites of the host lattice, yields a highly efficient phosphor with emission maximum near 450 nm. The full width at half maximum is about 50 nm so that the emission is useful in supplying narrow-band blue emission in a trichromatic phosphor blend.
  • the incorporation of manganese at the magnesium sites results in efficient energy transfer from europium to manganese either the emission of manganese providing for a very saturated green peak at around 520 nm
  • the method for producing a phosphor of the present invention is not particularly restricted, and it can be produced by any method, which will provide the barium magnesium aluminate phosphor according to the invention.
  • a preferred process for producing a phosphor according to the invention is referred to as the solid-state method. In this process, the phosphor precursor materials are mixed in the solid state and are heated so that the precursors react and form a powder of the phosphor material.
  • the method includes a step of dry blending a mixture of starting components such as barium carbonate and/or strontium carbonate, magnesium oxide alumina, europium(III) oxide and/or manganese carbonate.
  • a flux such as magnesium fluoride may be added.
  • the blended mixture is fired at about 1250° to 1280° C in a reducing atmosphere to reduce Eu(III) to Eu(II).
  • the resulting phosphor is broken up or crushed into smaller particles.
  • Phosphor powders can also be made by liquid precipitation.
  • a solution which includes soluble phosphor precursors, is chemically treated to precipitate phosphor particles or phosphor particle precursors. These particles are typically calcined at an elevated temperature to produce the phosphor compound.
  • phosphor particle precursors or phosphor particles are dispersed in slurry, which is then spray dried to evaporate the liquid.
  • the particles are thereafter sintered in the solid state at an elevated temperature to crystallize he powder and form a phosphor.
  • the spray-dried powder is then converted to an oxide phosphor by sintering at an elevated temperature to crystallize the powder and to form the phosphor.
  • the fired powder is then lightly crushed and milled to recover phosphor particles of desired particle size.
  • Specific embodiment 1 1. BaMg 3 Al 14 O 25 : 10%Eu
  • the starting materials 7.103 g (36.00 mmol) BaCO 3 , 3.385 g (mmol)
  • MgO, 2.318 g (37.2 mmol) MgF 2 , 28.56 g (280.00 mmol) Al 2 O 3 , and 0.704 g (2.00 mmol) Eu 2 O 3 are thoroughly blended in an agate mortar.
  • the obtained blend is annealed for 2 h at 1265 0 C in a nitrogen/hydrogen atmosphere. Afterwards the obtained sintering material is crushed and the powder is milled on a roller bench for several hours, which yields a fine powder with an average particle size of 3 - 5 ⁇ m.
  • the quantum efficiency under 254 nm excitation is 92.1%, whereby the absorption is 77 %.
  • the starting materials 7.894 g (40.00 mmol) BaCO 3 , 3.192 g (79.20 mmol) MgO, 2.318 g (37.20 mmol) MgF 2 , 28.560 g (280.00 mmol) Al 2 O 3 , and 0.552 g (4.80 mmol) MnCO 3 are thoroughly blended in an agate mortar.
  • the obtained blend is annealed for 2 h at 1265 0 C in a nitrogen/hydrogen atmosphere. Afterwards the obtained sintering material is crushed and the powder is milled on a roller bench for several hours, which yields a fine powder with an average particle size of 3 - 5 ⁇ m.
  • the decay curve can be fitted by a monoexponential decay function with a decay constant T 1 Ze of 5 ms.
  • the invention is also concerned with an illumination system comprising a radiation source and luminescent material comprising a phosphor of general formula (Ba 1 _ x Sr x ) 1 . a Mg 3 . b Al 14 0 25 :Eu a Mn b , wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0.
  • Radiation sources include such as those found in discharge lamps and fluorescent lamps, such as mercury low and high-pressure discharge lamps, xenon discharge lamps, and discharge lamps based on molecular radiators.
  • any configuration of an illumination system which includes a source of UV-radiation and luminescent material comprising a phosphor of general formula (Ba 1- x Sr x ) 1 _ a Mg3-bAl 14 0 2 5:Eu a Mnb, wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0 is contemplated in the present invention, preferably with addition of other well-known phosphors, which can be combined to achieve a specific color or white light when irradiated by a radiation source emitting primary UV light as specified above.
  • the radiation source is a low- pressure mercury arc discharge.
  • FIG. 1 shows a schematic view of a fluorescent lamp with luminescent layer comprising a phosphor.
  • a fluorescent lamp 10 comprises, in one embodiment, a cylindrical discharge vessel 11 of light transparent material, such as glass and the like, having a coating 12 of a phosphor composition deposited upon its interior surface.
  • An end cap 14 enclosed and forms a gas-tight seal 15 at each opposite end of cylinder 11.
  • a filament 16 is positioned adjacent to each end cap within the bore of tube 11 and includes a pair of leads 17a, 17b passing through and supported by the associated end cap 14.
  • a quantity of mercury vapor 18 is initially deposited, at manufacture, within the cylindrical volume bounded by phosphor layer 12 and end caps 14.
  • a source 22 of alternating-current electrical energy, a switch 23 and ballast means 24 are in electrical series connection between a first lead 17a of each opposite filament 16.
  • Starting means 25 is coupled between the remaining leads 17b of each of the pair of filaments 16. It should be understood that other known fluorescent lamp embodiments may be equally well utilized and may allow certain of the circuit components (such as starting means 25) to be dispensed with.
  • starting means 25 causes a flow of current through each of filaments 16 responsive to the closure of switch 23.
  • Starting means 25 thereafter causes a sudden cessation of current flow to cause ballast means 24 to generate a relatively high voltage between filaments 16 to cause a flow of current to be initiated to establish a conventional mercury arc discharge.
  • the phosphor is excited by the energy-rich mercury resonance lines 26a, 26b at 254 and 185 nm and re-emits a significant portion of the impinging energy as quanta 27, 28 of visible light having spectral characteristics determined by the composition of the specific blend of the fluorescent materials utilized for the phosphor coating in the individual tube.
  • the luminescent layer of an preferred embodiment of the lamp according to the invention typically comprises a trichromatic phosphor blend of a blue phosphor of general formula (Ba 1 _ x Sr x ) 1 _ a Mg3_bAl 1 4 ⁇ 2 5:Eu a Mnb, wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0 having an emission peak in the 440 to 470 nm wavelength range, a green phosphor selected from the group of Ceo ⁇ sTbo LaPO 4 ICe 5 Tb and GdMgBsO 1O iCe 5 Tb having an emission peak in the 505 to 530 nm wavelength range and a red phosphor selected from the group of (Y 1 -X-SGd x )BO 3 IEUa, (Y 1 - x - a Gd x )(V 1 - y P
  • a phosphor of general formula (Ba 1 - X Sr x J 1 - a Mg 3- bAl 14 0 2 5:Eu a Mnb, wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0 is used as the blue component ( ⁇ 450 nm) in such trichromatic lamp.
  • Y 2 O 3 IEu is used as the red component
  • Ceo ⁇ sTbo 35 MgAl 11 O ⁇ is used as the green component.
  • said tri-phosphor blend utilizes approximately 5% by weight of the europium- activated barium magnesium aluminate phosphor as the blue color emission component, approximately 27.5 weight percent of the aforementioned terbium- activated Ceo ⁇ sTbo phosphor as the green color emission phosphor component, and approximately 67.5 weight percent of the conventional europium-activated yttrium oxide phosphor component to produce the desired performance.
  • a cool white (4100 0 K) color point lamp can be achieved with said preferred tri- phosphor blend as a top layer in representative proportions of 13 weight percent blue color emission phosphor, 36.5 weight percent green color emission component, and 50.5 weight percent red color emission phosphor component.
  • the weight proportions in the preferred tri-phosphor blend is further adjusted to contain 8 weight percent blue color emission phosphor, 27.5 weight percent green color emission phosphor component, and 64.5 weight percent red color emission phosphor component.
  • a full-color plasma flat-panel display consists of an intermittent atmosphere pressure xenon discharge as a radiation source, which excites red, green and blue phosphors to form color images.
  • phosphors convert the vacuum ultraviolet (VUV) emission of the xenon discharge plasma with an emission at 147 nm and 173 nm respectively into visible light.
  • VUV vacuum ultraviolet
  • Divalent europium activated (Ba 1 _ x Sr x ) 1 _ a Mg3_bAl 1 4 ⁇ 2 5 :Eu with its narrow blue emission can be successfully applied in plasma display panels since the phosphor is efficiently excited to blue emission by VUV radiation.
  • Divalent manganese activated (Ba 1 _ x Sr x ) 1 _ a Mg 3 _ b Al 14 ⁇ 25 :Mn with its broad band green emission can be successfully applied in plasma display panels since the phosphor is efficiently excited to very saturated green emission by VUV radiation.
  • the short decay time with a decay constant ⁇ y e of about l ⁇ s makes the phosphor according to the invention desirable for plasma display panel applications as that reduces tailing in moving images.
  • FIG. 1 shows a schematic side view of a fluorescent lamp comprising a luminescent material comprising a phosphor of general formula b Al 14 0 2 5:EuaMnb, wherein 0 ⁇ x ⁇ l, 0 ⁇ a ⁇ 0.2, 0 ⁇ b ⁇ 0.2, a + b > 0.
  • Fig. 2 shows the CIE color triangle with the color points of green BaMg 3 Al 14 O 2S iMn in comparison to BaMgAl 1 QO 17 IMn and Zn 2 Si0 4 :Mn.
  • Fig. 4 shows the emission spectrum Of BaMg 3 Al 14 O 2S :10%Eu,4%Mn

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Abstract

An illumination system comprising a radiation source and luminescent material comprising a phosphor of general formula (Ba1-xSrx)1-aMg3-bA114O25:EuaMnb, wherein 0 < x < 1, 0 < a < 0.2, 0 < b < 0.2, a + b > 0 can provide composite white output light that has a greater amount of emission in the blue color range than the conventional lamp. This characteristic makes the device ideal for applications in which a true color rendition is required. The invention is also concerned with a blue to green phosphor of general formula (Ba1-xSrx)1-aMg3-bAl14O25:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0.

Description

TITLE OF THE INVENTION
Illumination system comprising barium magnesium aluminate phosphor
BACKGROUND OF THE INVENTION
The present invention generally relates to an illumination system comprising a radiation source and a fluorescent material comprising a barium magnesium aluminate phosphor. The invention also relates to a barium magnesium aluminate phosphor for use in such illumination system. More particularly, the invention relates to an illumination system and a fluorescent material comprising a barium magnesium aluminate phosphor for the generation of specific, colored light, including white light, by luminescent down conversion and additive color mixing based on a ultraviolet radiation emitting radiation source. A fluorescent lamp as an illumination system is especially contemplated. Fluorescent lamps typically have a transparent discharge vessel enclosing a sealed discharge space containing an inert gas and mercury vapor as well as means for igniting and maintaining a discharge, such as electrodes. When subjected to a current provided by electrodes, the mercury ionizes to produce radiation having primary wavelengths of 185 nm and 254 nm. This ultraviolet radiation, in turn, excites phosphors on the inside surface of the discharge vessel to produce visible light which is emitted from the discharge vessel. Today's phosphors blends are typically chosen to emit light in each of the three primary colors red, green and blue. Fluorescent lamps comprising three phosphors for emission of red, green and blue light are referred to as three -band lamp or trichromatic fluorescent lamps. The three phosphors for emission of red, green and blue light that are currently used in trichromatic fluorescent lamps, do not all exhibit the same life stability. Especially the barium magnesium aluminate phosphors that are prevalently used as the blue light component degrade faster in comparison to the green and red phosphors. Due to the degradation process, the color point, i.e. the color coordinates, of the blue phosphor shifts towards green. This shift compromises also the performance of the lamp in general.
In view of these problems, some efforts have been directed to improvement of the existing blue barium magnesium aluminate phosphors and the development of new phosphors. An improved blue phosphor is known from EP529956, characterized by having a composition represented by the following general formula: (Mi-y-zEuyMn z)O-aAl2θ3 wherein M stands for at least one element selected from the group consisting of Mg, Ca, Sr, and Ba and a, y, and z stand for numerical values satisfying the expressions, 1.5 < a < 1. Yet in view of the prior art, there is still a demand for an illumination system with a further improved barium magnesium aluminate phosphor.
Thus the present invention provides an illumination system comprising a radiation source and luminescent material comprising a barium magnesium aluminate phosphor of general formula (Ba1_xSrx)1_aMg3_bAl14θ25:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b ≤ 0.2, a + b > 0.
The illumination system comprising barium magnesium aluminate phosphor of general formula (Ba1_xSrx)1_aMg3_bAl14θ25:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0, exhibits an excellent emission intensity under excitation by a source of radiation in the UV range of the electromagnetic spectrum. It is an advantage of the phosphors used, that they have a broad excitation spectrum, which makes them not only useful for mercury low pressure discharge lamps (fluorescent lamps) but also for mercury high pressure discharge lamps and xenon excimer discharge lamps.
Preferably the radiation source provides radiation in the UV range of the electromagnetic spectrum during operation.
Such radiation sources comprise the rare gas/mercury discharge plasma of low-pressure mercury discharge lamps, high-pressure mercury discharge lamps, xenon excimer discharge lamps and gas discharge displays, such as plasma discharge panels. Typically the illumination system according to the invention is equipped with a luminescent material comprising at least one second red phosphor, wherein the second phosphor is selected from the group of
Figure imgf000003_0001
(Y1^aGdx)BO3IEUa, (Y1_x_aGdx)(V1_yPy)O4:Eua wherein 0 ≤ x ≤ l, 0 ≤ y ≤ l, 0 < a ≤ 0.3 and x + a < l.
Typically the illumination system according to the invention is equipped with a luminescent material comprising also at least one third green phosphor, wherein the third phosphor is selected from the group of Ce005Tb035MgAl11O19, LaPO4:Ce,Tb and GdMgB5O10:Ce,Tb.
An illumination system according to the present invention can provide a composite white output light that is well balanced with respect to color. In particular, the composite white output light has a greater amount of emission in the blue color range than the conventional lamp. This characteristic makes the device ideal for applications in which a true color rendition is required.
The color of human skin, foliage, green vegetables and blue colors become more vivid and saturated and are perceived as more pleasant than under illumination with conventional fluorescent lamps. Such applications of the invention include inter alia backlighting of liquid crystal displays, general illumination, traffic lighting and street lighting.
According to another aspect of the invention a barium magnesium aluminate phosphor of general formula (Ba1_xSrx)1_aMg3_bAl14O25:EuaMnb, wherein 0 < x < 1, 0 < a < 0.2, 0 < b < 0.2, a + b > 0 is provided.
The blue to green phosphors according to the present invention have a band emission in blue to green region, peaking around 450 nm and 520 nm, when excited by 147 or 173 nm radiation from xenon gas mixture discharge or by the254 nm radiation from mercury discharge.
They also exhibit better stability or life when excited with VUV (147 and 173 nm) radiations from Xe discharge in a plasma display than the currently available commercial phosphors used in plasma display panels. The dopants present in the phosphor do not undergo any change in their valence state when heated to high temperatures of about 600 degree C, one of the essential conditions required during the process of lamp manufacturing (baking). Furthermore the phosphor does not degrade on continuous irradiation by light of wavelength 254 nm. In addition, it is easily synthesizable and stable.
In one preferred embodiment of the invention a blue phosphor of general formula (Ba1-xSrx)1_aMg3_bAl14025:EuaMnb, wherein x= 0, b= 0, a = 0.1 is provided. This blue phosphor is useful for an improvement of CRI in high efficiency tricolor (trichromatic) fluorescent lamps based on rare-earth phosphors, where a blend of three different inorganic compounds each emitting in different regions viz., blue (450 nm), green (540 nm) and red (610 nm) mixes upon to give out white light, when excited by mercury discharge at low pressure corresponding to radiation of wavelength 254 nm.
In another embodiment of the invention a green phosphor according to general formula (Ba1_xSrx)1_aMg3_bAl14θ25:EuaMnb, wherein x = 0, a = 0, b = 0.04 is provided. This luminescent material can be applied as green phosphor in very high quality fluorescent lamps.
This green phosphor is also useful in plasma display panels (PDP) as the green component. Here, the phosphor needs to get excited with short wavelength UV radiation that is compatible with the xenon discharge plasma excitation.
For the phosphors used in television tubes, a short decay time is necessary to avoid afterglow or persistence. The lifetime of an electron in the excited state of europium(II)-ion, when doped in any inorganic crystal lattice is very short. Hence, the phosphors co-activated with europium(II) are preferred to avoid afterglow.
DETAILED DESCRIPTION OF THE INVENTION The present invention focuses on a fluorescent material comprising a barium magnesium aluminate phosphor activated by europium(II) and/or manganese(II) in any configuration of an illumination system comprising a source of primary radiation, including, but not limited to discharge lamps, fluorescent lamps, phosphor converted LEDs and plasma displays. As used herein, the term "radiation" encompasses radiation in the UV, IR and visible regions of the electromagnetic spectrum.
While the use of the present fluorescent material is contemplated for a wide array of illumination, the present invention is described with particular reference to and finds particular application to illumination systems comprising low-pressure mercury discharge as source of primary radiation. The fluorescent material according to the invention comprises as a phosphor a barium magnesium aluminate activated by europium and/or manganese. The phosphor conforms to the general formula (Ba1_xSrx)1_aMg3_bAl14θ25:EuaMnb, wherein 0 ≤ x ≤ l. O ≤ a ≤ 0.2, O < b < 0.2, a + b > O.
The phosphor of general formula (Ba^xS^i.aMgs.bAl^O^iEUaMnb, wherein 0 < x ≤ l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0 comprises a host lattice with the main components of barium, magnesium, aluminum and oxygen and europium and/or manganese as activators. This class of phosphor material is based an activated luminescence of a barium magnesium aluminate host lattice.
The host lattice is supposed to have a structure consisting of puckered layers containing the divalent earth alkaline cations, barium and eventually strontium, and oxygen, and blocks of spinel units MgAl2O4. The phosphors according to the invention comprise a higher portion of spinel units in comparison to the conventional BaMgAl10O17.
Within the three-dimensional network the activator ions europium and/or manganese are incorporated.
These barium magnesium aluminate phosphors activated by europium(II) and/or manganese(II) are responsive to a broad energetic portions of the electromagnetic spectrum.
The excitation band is found to be a broad band (120-400 nm). Hence, it is clear that these phosphors can be excited efficiently with radiation of wavelength 254 as well as 172 nm. Thus the fluorescent material has ideal characteristics for converting the UV radiation of a mercury arc discharge or a xenon excimer discharge into visible white or colored light.
When excited with radiation of wavelength 254 nm, these materials are found to emit a narrow band with a peak in the range 450 nm for high Eu(II)- concentrations and in the range 520 nm for high Mn(II)-concentrations as shown in FIG. 2 of the drawings accompanying this application. Fig. 2 shows the CIE color triangle with the color points of green BaMg3Al14O2SiMn in comparison to conventional BaMgAl1OO17IMn and Zn2Si04:Mn. The blue narrow-band emission originates from a d → f optical transition on europium(II).
The emission of manganese(II) in BaMgAl10O17: Eu, Mn in the green range of the electromagnetic spectrum is an example for a broad d → d emission band.
2+ The green emission is generated by a d → d optical transition on the Mn -ion with high spin d electronic configuration (all electrons have their spin oriented in the same 4 6 direction). The optical transition leading to emission is T1 → A1 . The electronic
3 2 4 1 configurations in ground- and excited state are t ) e ) and t ) e ) , respectively. The emission generated reflects how the optical properties of the ion depend on its chemical environment. Activation with europium(II), which occupies the earth alkaline sites of the host lattice, yields a highly efficient phosphor with emission maximum near 450 nm. The full width at half maximum is about 50 nm so that the emission is useful in supplying narrow-band blue emission in a trichromatic phosphor blend.
Replacing some of the europium(II) in a europium(II)-activated phosphor according to the invention by manganese(II) as a co-activator has the effect, that the manganese(II) produces secondary emission that is concentrated in the green region of the visible spectrum, instead of a typical narrow-band secondary emission from europium-activated barium magnesium aluminate phosphor that is generally centered in the blue region of the visible spectrum. The amount of manganese as a co- activator can vary, depending on the amount of green color that may be required in the white output light for a particular application.
If the host is activated with manganese(II), the incorporation of manganese at the magnesium sites results in efficient energy transfer from europium to manganese either the emission of manganese providing for a very saturated green peak at around 520 nm
This means that, when emission of more greenish than blue light is required, e.g. for photolithography, it can be achieved by increasing the degree of substitution with manganese(II).
But co-activating with europium(II) enhances the absorption strength of the phosphors at 254 nm and also at 172 nm.
As long as a < b still a green emitting phosphor is obtained. But when the proportion of europium(II) is lower than the proportion of manganese, luminance decreases because the number of excited emission centers of photoluminescence due to europium(II) decreases. The method for producing a phosphor of the present invention is not particularly restricted, and it can be produced by any method, which will provide the barium magnesium aluminate phosphor according to the invention. A preferred process for producing a phosphor according to the invention is referred to as the solid-state method. In this process, the phosphor precursor materials are mixed in the solid state and are heated so that the precursors react and form a powder of the phosphor material. The method includes a step of dry blending a mixture of starting components such as barium carbonate and/or strontium carbonate, magnesium oxide alumina, europium(III) oxide and/or manganese carbonate. A flux such as magnesium fluoride may be added.
Then the blended mixture is fired at about 1250° to 1280° C in a reducing atmosphere to reduce Eu(III) to Eu(II). The resulting phosphor is broken up or crushed into smaller particles.
Phosphor powders can also be made by liquid precipitation. In this method, a solution, which includes soluble phosphor precursors, is chemically treated to precipitate phosphor particles or phosphor particle precursors. These particles are typically calcined at an elevated temperature to produce the phosphor compound.
In yet another method, phosphor particle precursors or phosphor particles are dispersed in slurry, which is then spray dried to evaporate the liquid. The particles are thereafter sintered in the solid state at an elevated temperature to crystallize he powder and form a phosphor. The spray-dried powder is then converted to an oxide phosphor by sintering at an elevated temperature to crystallize the powder and to form the phosphor. The fired powder is then lightly crushed and milled to recover phosphor particles of desired particle size. Specific embodiment 1 1. BaMg3Al14O25: 10%Eu The starting materials 7.103 g (36.00 mmol) BaCO3, 3.385 g (mmol)
MgO, 2.318 g (37.2 mmol) MgF2, 28.56 g (280.00 mmol) Al2O3, and 0.704 g (2.00 mmol) Eu2O3 are thoroughly blended in an agate mortar. The obtained blend is annealed for 2 h at 12650C in a nitrogen/hydrogen atmosphere. Afterwards the obtained sintering material is crushed and the powder is milled on a roller bench for several hours, which yields a fine powder with an average particle size of 3 - 5 μm. The quantum efficiency under 254 nm excitation is 92.1%, whereby the absorption is 77 %. The lumen equivalent of the obtained emission spectrum is 63 ImAV and the colour point in the CIE 1931 colour diagram is at x = 0.151 and y = 0.057. Fig. 3 shows emission spectrum Of BaMg3Al14O2S :10%Eu (λ eχc=254 nm).
Specific embodiment 2 BaMg3Al14O25: 10%Eu4%Mn The starting materials 7.103 g (36.00 mmol) BaCO3, 3.192 g (79.20 mmol) MgO, 2.318 g (37.20 mmol) MgF2, 0.552 g (4.80 mmol) MnCO3, 28.560 g (280 mmol) Al2O3, and 0.704 g (2.00 mmol) Eu2O3 are thoroughly blended in an agate mortar. The obtained blend is annealed for 2 h at 12650C in a nitrogen/hydrogen atmosphere. Afterwards the obtained sintering material is crushed and the powder is milled on a roller bench for several hours, which yields a fine powder with an average particle size of 3 - 5 μm. The quantum efficiency under 254 nm excitation is 80%, whereby the absorption is 70 %. The lumen equivalent of the obtained emission spectrum is 206 ImAV and the colour point in the CIE 1931 colour diagram is at x = 0.149 and y = 0.222. Fig. 4 shows emission spectrum of BaMg3Al14O25 :10%Eu,4%Mn (λ
Figure imgf000009_0001
Specific embodiment 3 BaMg3A114O25:4%Mn
The starting materials 7.894 g (40.00 mmol) BaCO3, 3.192 g (79.20 mmol) MgO, 2.318 g (37.20 mmol) MgF2, 28.560 g (280.00 mmol) Al2O3, and 0.552 g (4.80 mmol) MnCO3 are thoroughly blended in an agate mortar. The obtained blend is annealed for 2 h at 12650C in a nitrogen/hydrogen atmosphere. Afterwards the obtained sintering material is crushed and the powder is milled on a roller bench for several hours, which yields a fine powder with an average particle size of 3 - 5 μm. The lumen equivalent of the obtained emission spectrum is 515 ImAV and the colour point in the CIE 1931 colour diagram is at x = 0.185 and y = 0.738. The decay curve can be fitted by a monoexponential decay function with a decay constant T1Ze of 5 ms. Fig. 5 shows emission spectrum Of BaMg3Al14O25 :4%Mn (λ eχc=160 nm).
The invention is also concerned with an illumination system comprising a radiation source and luminescent material comprising a phosphor of general formula (Ba1_xSrx)1.aMg3.bAl14025:EuaMnb, wherein 0 < x ≤ l, 0 < a < 0.2, 0 < b < 0.2, a + b > 0. Radiation sources include such as those found in discharge lamps and fluorescent lamps, such as mercury low and high-pressure discharge lamps, xenon discharge lamps, and discharge lamps based on molecular radiators.
Any configuration of an illumination system which includes a source of UV-radiation and luminescent material comprising a phosphor of general formula (Ba1- xSrx)1_aMg3-bAl14025:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0 is contemplated in the present invention, preferably with addition of other well-known phosphors, which can be combined to achieve a specific color or white light when irradiated by a radiation source emitting primary UV light as specified above. In a preferred embodiment of the invention the radiation source is a low- pressure mercury arc discharge.
A detailed construction of one embodiment of such illumination system will now be described.
FIG. 1 shows a schematic view of a fluorescent lamp with luminescent layer comprising a phosphor. A fluorescent lamp 10 comprises, in one embodiment, a cylindrical discharge vessel 11 of light transparent material, such as glass and the like, having a coating 12 of a phosphor composition deposited upon its interior surface. An end cap 14 enclosed and forms a gas-tight seal 15 at each opposite end of cylinder 11. A filament 16 is positioned adjacent to each end cap within the bore of tube 11 and includes a pair of leads 17a, 17b passing through and supported by the associated end cap 14. A quantity of mercury vapor 18 is initially deposited, at manufacture, within the cylindrical volume bounded by phosphor layer 12 and end caps 14.
A source 22 of alternating-current electrical energy, a switch 23 and ballast means 24 are in electrical series connection between a first lead 17a of each opposite filament 16. Starting means 25 is coupled between the remaining leads 17b of each of the pair of filaments 16. It should be understood that other known fluorescent lamp embodiments may be equally well utilized and may allow certain of the circuit components (such as starting means 25) to be dispensed with.
As is well known, in operation starting means 25 causes a flow of current through each of filaments 16 responsive to the closure of switch 23. Starting means 25 thereafter causes a sudden cessation of current flow to cause ballast means 24 to generate a relatively high voltage between filaments 16 to cause a flow of current to be initiated to establish a conventional mercury arc discharge.
The phosphor is excited by the energy-rich mercury resonance lines 26a, 26b at 254 and 185 nm and re-emits a significant portion of the impinging energy as quanta 27, 28 of visible light having spectral characteristics determined by the composition of the specific blend of the fluorescent materials utilized for the phosphor coating in the individual tube.
The luminescent layer of an preferred embodiment of the lamp according to the invention typically comprises a trichromatic phosphor blend of a blue phosphor of general formula (Ba1_xSrx)1_aMg3_bAl14θ25:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0 having an emission peak in the 440 to 470 nm wavelength range, a green phosphor selected from the group of Ceo βsTbo
Figure imgf000011_0001
LaPO4ICe5Tb and GdMgBsO1OiCe5Tb having an emission peak in the 505 to 530 nm wavelength range and a red phosphor selected from the group of
Figure imgf000011_0002
(Y1-X-SGdx)BO3IEUa, (Y1-x-aGdx)(V1-yPy)O4:Eua wherein 0 ≤ x ≤ l, 0 ≤ y ≤ l, 0 < a ≤ 0.3 and x + a < l, having an emission peak in the 600 to 670 nm wavelength range.
According to one embodiment a phosphor of general formula (Ba1-XSrxJ1- aMg3-bAl14025:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0 is used as the blue component (λ =450 nm) in such trichromatic lamp. Y2O3IEu is used as the red component, Ceo όsTbo 35MgAl11O^ is used as the green component.
According to another embodiment phosphor of general formula (Ba1- xSrx)1-aMg3-bAl14025:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0 may be used as the green component (λ =520 nm) in a trichromatic lamp.
In a fluorescent lamp providing white color illumination at a warm white (30000K) lamp color point said tri-phosphor blend utilizes approximately 5% by weight of the europium- activated barium magnesium aluminate phosphor as the blue color emission component, approximately 27.5 weight percent of the aforementioned terbium- activated Ceo όsTbo
Figure imgf000011_0003
phosphor as the green color emission phosphor component, and approximately 67.5 weight percent of the conventional europium-activated yttrium oxide phosphor component to produce the desired performance.
A cool white (41000K) color point lamp can be achieved with said preferred tri- phosphor blend as a top layer in representative proportions of 13 weight percent blue color emission phosphor, 36.5 weight percent green color emission component, and 50.5 weight percent red color emission phosphor component. For a white (35000K) color point lamp the weight proportions in the preferred tri-phosphor blend is further adjusted to contain 8 weight percent blue color emission phosphor, 27.5 weight percent green color emission phosphor component, and 64.5 weight percent red color emission phosphor component.
There are also a number of display applications where a blue to green phosphor with better stability longer life stability and short decay time would significantly improve the display's performance. The blue to green component is very important, as it improves the color temperature of the display.
A full-color plasma flat-panel display consists of an intermittent atmosphere pressure xenon discharge as a radiation source, which excites red, green and blue phosphors to form color images. In a plasma display panel phosphors convert the vacuum ultraviolet (VUV) emission of the xenon discharge plasma with an emission at 147 nm and 173 nm respectively into visible light.
Divalent europium activated (Ba1_xSrx)1_aMg3_bAl14θ25 :Eu with its narrow blue emission can be successfully applied in plasma display panels since the phosphor is efficiently excited to blue emission by VUV radiation. Divalent manganese activated (Ba1_xSrx)1_aMg3_bAl14θ25:Mn with its broad band green emission can be successfully applied in plasma display panels since the phosphor is efficiently excited to very saturated green emission by VUV radiation. The short decay time with a decay constant τye of about lμs makes the phosphor according to the invention desirable for plasma display panel applications as that reduces tailing in moving images.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic side view of a fluorescent lamp comprising a luminescent material comprising a phosphor of general formula
Figure imgf000012_0001
bAl14025:EuaMnb, wherein 0 < x < l, 0 ≤ a < 0.2, 0 < b < 0.2, a + b > 0.
Fig. 2 shows the CIE color triangle with the color points of green BaMg3Al14O2SiMn in comparison to BaMgAl1QO17IMn and Zn2Si04:Mn. Fig. 3 shows the emission spectrum Of BaMg3Al14O2S :10%Eu (λ eχc=254 nm).
Fig. 4 shows the emission spectrum Of BaMg3Al14O2S :10%Eu,4%Mn (λ
Figure imgf000013_0001
Fig. 5 shows the emission spectrum of BaMg3Al14O25 :4%Mn (λ eχc=160 nm).

Claims

CLAIMS:
1. Illumination system comprising a radiation source and luminescent material comprising a phosphor of general formula (Ba1_xSrx)1_aMg3_bAl14θ25:EuaMnb, wherein 0<x<l,0≤a< 0.2, 0 < b < 0.2, a + b > 0.
2. Illumination source according to claim 1, wherein the radiation source provides radiation in the UV range of the electromagnetic spectrum during operation.
3. Illumination system according to claim 1, wherein the luminescent material comprises at least one second red phosphor and at least one third green phosphor.
4. Illumination system according to claim 3, wherein the second red phosphor is selected from the group of
Figure imgf000014_0001
(Y1_x_aGdx)Bθ3:Eua, (Y1-x- aGdx)(V1_yPy)O4:Eua wherein 0≤x≤l,0≤y≤l,0<a≤0.3andx + a<l.
5. Illumination system according to claim 3, wherein the third green phosphor is selected from the group of Ceo βsTbo
Figure imgf000014_0002
LaPO4:Ce,Tb and GdMgB5O10:Ce,Tb.
6. Phosphor of general formula (Ba1_xSrx)1_aMg3_bAl14θ25:EuaMnb, wherein
0≤x<l,0≤a≤ 0.2, 0 < b < 0.2, a + b > 0.
7. Phosphor according to claim 6, wherein x= 0, b= 0, a = 0.1.
8. Phosphor according to claim 6, wherein x = 0, a = 0, b = 0.04.
9. Use of phosphor according to claim 6 for display applications.
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