GB2378438A - Luminescent phosphor - Google Patents

Luminescent phosphor Download PDF

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Publication number
GB2378438A
GB2378438A GB0218098A GB0218098A GB2378438A GB 2378438 A GB2378438 A GB 2378438A GB 0218098 A GB0218098 A GB 0218098A GB 0218098 A GB0218098 A GB 0218098A GB 2378438 A GB2378438 A GB 2378438A
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GB
United Kingdom
Prior art keywords
phosphor material
phosphor
material according
range
yttrium
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB0218098A
Other versions
GB0218098D0 (en
Inventor
James Kane
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BANK OF ENGLAND
Original Assignee
BANK OF ENGLAND
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BANK OF ENGLAND filed Critical BANK OF ENGLAND
Publication of GB0218098D0 publication Critical patent/GB0218098D0/en
Publication of GB2378438A publication Critical patent/GB2378438A/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—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
    • C09K11/7767—Chalcogenides
    • C09K11/7769—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
    • C09K11/7766—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
    • C09K11/7783—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

Abstract

A phosphor material, is of the form (X<SB>x</SB>R<SB>1-x</SB>)<SB>3</SB>Sc<SB>w</SB>(Ga<SB>y</SB>Cr<SB>1-y</SB>)<SB>5-w</SB>O<SB>12</SB>, where X is Yttrium or Gadolinium, R is any rare earth metal, w is any number in the range 0 to 2, x is any number greater than 0, y is any number in the range 0 to 0.9, and the material has a garnet structure. R can be Neodymium Nd. The phosphor may be used in printing inks for documents of value. Preferred phosphors are<BR> (Y<SB>0.99</SB>Nd<SB>0.01</SB>)<SB>3</SB> (Ga<SB>0.75</SB>Cr<SB>0.25</SB>)5 O<SB>12</SB>,<BR> (Y<SB>0.99</SB>Nd<SB>0.01</SB>)<SB>3</SB> Sc<SB>2</SB> (Ga<SB>0.75</SB>Cr<SB>0.25</SB>)<SB>3</SB> O<SB>12</SB> and<BR> (Gd<SB>0.99</SB>Nd<SB>0.01</SB>)<SB>3</SB> Sc<SB>2</SB>(Ga<SB>0.75</SB>Cr<SB>0.25</SB>)<SB>3</SB> O<SB>12</SB>

Description

<Desc/Clms Page number 1>
Title: Luminescent Phosphor Field of the Invention This invention relates to a luminescent phosphor and in particular a phosphor for use with printing inks, and also inks and documents of value including the phosphor.
Background to the Invention Luminescent phosphors are used in combination with printing inks when a valuable document, such as a bank-note, needs to be protected from fraudulent replication. Various phosphors are known for such use, in particular those based on a Garnet structure incorporating Yttrium and Aluminium. These Yttrium Aluminium Garnet compositions need to be used within ink at a high loading of about 20 per cent by weight to give an adequate luminescent response when the document is illuminated with an appropriate electromagnetic radiation. They are also extremely hard materials with a Mohs hardness in excess of 8.0 and as a result excessive wear occurs of printing elements used to mark documents with the phosphor containing ink. For the Mohs hardness scale, see pll of Philips Minerals, Rocks and Fossils, A. C. Bishop, A. R. Woolley and W. R. Hamilton, published August 1999.
The present invention aims to provide a luminescent phosphor to address certain problems associated with the prior art phosphors.
Summary of the Invention In accordance with a first aspect of the present invention, there is provided a phosphor material, wherein the material is of the form (XxR.j.,3Scw (GayCr,) 5-, where X is any element from the group Yttrium or Gadolinium, R is any rare earth metal, w is any number in the range 0 to 2, x is any number greater than 0, y is any number in the range 0-0. 9, and the material has a garnet structure. Within the crystal structure, the rare earth
<Desc/Clms Page number 2>
metal sits on the same sites as the Yttrium or Gadolinium, with the smaller Chromium, Scardium and Gallium sitting on two comparable but not identical sites in the ratio 3 to 2.
R is preferably chosen from the rare earth metals. Suitable elements include Neodymium Nd, Dysprosium Dy, Holium Ho and Thulium Tm.
Preferably I-x is much smaller than x, such that R acts as a dopant. Therefore preferably x is in the range 0.4 < x < 1. 0, and more preferably in the range 0.95 < x < 1. 0. Most
preferably, x is in the range 0. 99 x < 1. 0.
Preferably y is greater than l-y, and in a preferred range y is 0. 99-0. 50, and in a more preferred range y is 0.85-0. 60. For a particularly preferred material y is 0.75.
For particularly preferred materials, R is Neodymium with the Chromium-Neodymium coupling efficiency found in such materials being of particular advantage for producing a material of improved luminescence over existing Yttrium Aluminium Garnet compositions.
Generally w is selected to be either 0 or 2.
For materials where w is 0, and no Scandium is included in the material, a preferred material is of the form (XoNdooJGaoCroO.
Desirably X is Yttrium, with a particularly preferred material being of the form (Yo Nd 0 0)) 3 (G0. 75CrO 25) 5012 For materials where w is 2 and Scandium is included in the material, particularly preferred materials are of the form (GdNdooScGaCroO, ;, and (YoNdooSc 2 (Gao75Cro) 30, .
Preferably, the phosphor has a Mohs hardness of at most 7.0.
<Desc/Clms Page number 3>
Preferably, the phosphor particles have a diameter of up to 20 microns. More preferably the diameter is up to 5 microns (particularly for use in an ink). Most preferably, the phosphor particles have a diameter of up to 1 micron. Particle diameter may be reduced by grinding or milling.
In accordance with a further aspect of the invention, there is provided a document of value, the document having printed thereon or included therein or thereon phosphor material, the phosphor material being of the form (X, x) 3Scw (GayCr1) 5-won2 where X is any element from the group Yttrium or Gadolinium, R is any rare earth metal, w is any number in the range 0 to 2, x is any number greater than 0, y is any number less than 1, and the material has a garnet structure.
Preferably, the phosphor material is in accordance with the first aspect of the present invention, and is preferably in a powder form with a particle diameter of 20 microns or less. Thus a preferred particle diameter is between 20 microns to 0.01 microns.
Documents of value include security documents of intrinsic or perceived value such as banknotes, bonds, share certificates, passport, identity cards and documents, vouchers, credit and debit cards, electronic cash cards, vouchers, stamps and the like.
In accordance with a further aspect of the invention there is provided an ink comprising a phosphor material, a solvent and an additive, wherein the phosphor material is of the form (XR, x) 3Scw (GayCrjy) 0, where X is any element from the group Yttrium or Gadolinium, R is any rare earth metal, w is any number in the range 0 to 2, x is any number greater than 0, y is any number less than 1, and the material has a garnet or Perovskite structure.
Typically, an ink comprises: varnish 40-70% ; solvent 2-25%; extender 0-30%; pigment 0- 30% ; driers 0. 01-2% ; antioxidant 0-5% and phophor 1-30%. (All weights as a percentage of finished ink.)
<Desc/Clms Page number 4>
Preferably, the phosphor material is in accordance with the first aspect of the present invention.
The invention will now be described by way of example, and with reference to the accompanying drawing in which : Figure 1 shows a document of value printed with a phosphor material in accordance with the present invention.
Description Figure 1 shows a bank-note 10 having a strip of phosphor material 12 printed thereon, the phosphor material being luminous in response to electromagnetic radiation of a certain wavelength to luminesce. The phosphor material is a Yttrium Gallium Garnet composition activated with Chromium and co-activated with Neodymium having a formula (Yo99NdoQj) 3 (Gao75Cr (, ) 50. In this garnet structure, one per cent of the Yttrium is replaced with Neodymium and 25 per cent of the Gallium is replaced with Chromium.
This Yttrium Gallium Garnet composition produces a crystal structure with a lower crystal field than known phosphors such as Yttrium Aluminium Garnet. The crystal field is a measure of the rigidity or strength of a crystal lattice, and thus to a certain extent provides a measure of the hardness of the material, particularly where materials having the same crystal lattices are compared. Yttrium Aluminium Garnet is an extremely hard material with a Mohs hardness in excess of 8.0, and to produce an adequate luminescent response when printed onto a valuable document, the phosphor must be used in the ink at a high loading of around 20 per cent. The extreme hardness and high loading required for this prior art composition results in a large degree of wear of plates used to print the phosphor containing ink onto the documents, and as such means the punting plates need to be replaced regularly.
However the substantial concentration of Chromium in materials according to the present invention, particularly when y is in the range 0.85-0. 60, and with the coupling between the
<Desc/Clms Page number 5>
Neodymium and Chromium, produces a much lower crystal field than would be expected. This not only results in a lower Mohs hardness of 7.0 rather than 8. 0, but also provides an enhanced luminescent efficiency over the prior art materials.
In these phosphor materials, the peak of the broad Chromium absorption band moves to a longer wavelength as compared with Yttrium Aluminium Garnet (YAG). The emission band of the electromagnetic radiation source which is used to stimulate luminescence in the phosphor is more efficiently absorbed at this longer wavelength as this moved emission band more closely matches the absorption band of the phosphor. This produces an improved luminescent efficiency.
At the lower crystal field, the internal coupling efficiency of the Chromium and Neodymium is enhanced by as much as a factor of 2. The Yttrium Gallium Garnet (YGG) has a density of 5.0 and whilst having the same luminescent spectral response as YAG, is a factor of 3 more efficient. This enables an ink with 7 per cent by weight loading of YGG to give the equivalent luminescent response to an ink containing 20 per cent by weight loading of the YAG material. Thus the reduced ink-loading and lower Mohs hardness of the compositions in accordance with the present invention produce a phosphor which produces less wear of printing plates. Compositions with around 25 per cent of the Gallium replaced by Chromium are preferred, but the percentage of Chromium can be varied as long as there is sufficient coupling between the Neodymium and Chromium present in the material to produce reduced hardness and enhanced luminescent efficiency.
An ink carrying the phosphor is achieved by grinding the phosphor into a fine powder, typically with a phosphor particle diameter of less than 1 micron, and combining this phosphor pigment with constituents used to make an ink. Typical ink compositions, by weight % of finished ink, are varnish 40-70%, solvent 2-25%, extender 0-30%, pigment 0-30%, driers 0. 01-2%, antioxident 0-5% and finally phosphor pigment 1-30%.
Where the phosphor is used within and ink and thus comprises particles of diameter of the order of microns or less, a higher concentration of Chromium is necessary to absorb
<Desc/Clms Page number 6>
efficiently the excitation light in the limited thickness of the micron size particles loaded in the ink. Desirably for such application, 25% of the Gallium is replaced by Chromium, meaning I in 4 of the Gallium atoms in the Yttrium Gallium Garnet structure is replaced by a Chromium atom.
Other Garnet hosts incorporating Gallium similarly have the advantages of reduced Mohs hardness, and the lower the crystal field the lower the hardness, and the less wear of
printing plates and the like is expected. Thus Gadolinium Scandium Gallium Garnet, typically of composition (GdoNdooScGao-CroO, and Yttrium Scandium Gallium Garnet, typically of composition (YoNdo ScGaCroO, are also of use as having a lower crystal field than Yttrium Gallium Garnet.
Materials in accordance with the present invention are made by intimately mixing appropriate quantities of compounds containing the elements required. The resulting mixture is heated to a high temperature for several hours and then cooled. The cooled material is sieved and milled before being dried to produce the phosphor material.
To quantify the soft character of the materials of the present invention, a typical phosphor was tested for its abrasivity on a Schroder abrasion tester AT 11. A cylinder with 4 blades was suspended above a newly etched chrome test plate surface. In the presence of ink including the phosphor, the cylinder was rotated for 10, 000 revolutions (40,000 blade passes). A couloscope was used to measure abrasion of the test plate. The average and maximum wear (in microns) were measured. The phosphor according to the present invention resulted in half the abrasion of MF500, a product available from Giesecke & Devrient.

Claims (21)

  1. Claims l. A phosphor material, wherein the material is of the form (XxR,. 3Scw (GayCr1-y)5.
    W012, where X is any element from the group Yttrium or Gadolinium, R is any rare earth metal, w is any number in the range 0 to 2, x is any number greater than 0, y is any number in the range 0 to 0.9, and the material has a garnet structure.
  2. 2. A phosphor material according to claim I, wherein R is chosen from the rare earth metals.
  3. 3. A phosphor material according to claim I or claim 2, wherein 1-x is much smaller than x, such that R acts as a dopant.
  4. 4. A phosphor material according to claim 3, wherein x is in the range 0.95 < x <
    1.0.
  5. 5. A phosphor material according to claim 4, wherein x is in the range 0. 99 x <
    1.0.
  6. 6. A phosphor material according to any of the preceding claims, wherein y is greater than I-y.
  7. 7. A phosphor material according to claim 6, wherein y is in the range 0.99-0. 50.
  8. 8. A phosphor material according to claim 7, wherein y is in the range 0.85-0. 60.
  9. 9. A phosphor material according to claim 8, wherein y is 0.75.
    <Desc/Clms Page number 8>
  10. 10. A phosphor material according to any of the preceding claims, wherein R is Neodymium.
  11. 11. A phosphor material according to any of the preceding claims, wherein w is selected to be either 0 or 2.
  12. 12. A phosphor material according to claim 11, wherein w is 0 and R is Nd, and the
    material is of the form (XoNdooGaQyjCroO.
  13. 13. A phosphor material according to claim 11, w is 2 and R is Nd, and the material is of the form (Xo'9Ndo o\) 3SciGao 75CrO 25) 3012
  14. 14. A phosphor material according to any of the preceding claims, wherein X is Yttrium.
  15. 15. A phosphor material according to any of claims I to 13, wherein X is Gadolinium.
  16. 16. A phosphor material according to any one preceding claim in the form of phosphor particles having a size of at most 1 micron.
  17. 17. A document of value, the document having printed thereon or included therein or thereon a phosphor material, wherein the phosphor material is of the form (XxR,.
    ,) 3Scw(GayCr1y)5-wO12, where X is any element from the group Yttrium or Gadolinium, R is any rare earth metal, w is any number in the range 0 to 2, x is any number greater than 0, y is any number less than 1, and the material has a garnet structure.
  18. 18. A document of value according to claim 17 in which the phosphor material is in accordance with any one of claims 1 to 16.
    <Desc/Clms Page number 9>
  19. 19. An ink comprising a phosphor material, a solvent and an additive, wherein the phosphor material is of the form (XXR, JScw (GayCr,. y) 5-w02, where X is any element from the group Yttrium or Gadolinium, R is any rare earth metal, w is any number in the range 0 to 2, x is any number greater than 0, y is any number less than 1, and the material has a garnet structure.
  20. 20. An ink according to claim 19 in which the phosphor material is in accordance with any one of claims 1 to 16.
  21. 21. A phosphor material and document of value substantially as herein particularly described with reference to and as illustrated in the accompanying drawing.
GB0218098A 2001-08-04 2002-08-05 Luminescent phosphor Withdrawn GB2378438A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0119094A GB0119094D0 (en) 2001-08-04 2001-08-04 Improved luminescent phosphor

Publications (2)

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GB0218098D0 GB0218098D0 (en) 2002-09-11
GB2378438A true GB2378438A (en) 2003-02-12

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GB0119094A Ceased GB0119094D0 (en) 2001-08-04 2001-08-04 Improved luminescent phosphor
GB0218098A Withdrawn GB2378438A (en) 2001-08-04 2002-08-05 Luminescent phosphor

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GB0119094A Ceased GB0119094D0 (en) 2001-08-04 2001-08-04 Improved luminescent phosphor

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EP (1) EP1412452A1 (en)
GB (2) GB0119094D0 (en)
NO (1) NO20040515L (en)
WO (1) WO2003014258A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102017008868A1 (en) * 2017-09-21 2019-03-21 Giesecke+Devrient Currency Technology Gmbh Optical storage phosphor, method for checking an authenticity feature, apparatus for carrying out a method, authenticity feature and value document
DE102017008863A1 (en) 2017-09-21 2018-05-30 Daimler Ag Method for operating an autonomously driving vehicle with a traffic-adapted driving style

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4824598A (en) * 1987-10-20 1989-04-25 The United States Of America As Represented By The United States Department Of Energy Synthetic laser medium
EP0463369A1 (en) * 1990-06-29 1992-01-02 General Electric Company Transparent polycrystalline garnets
EP0467044A2 (en) * 1990-06-29 1992-01-22 General Electric Company Hole-trap-compensated scintillator material
EP0471926A2 (en) * 1990-06-29 1992-02-26 General Electric Company High speed, radiation tolerant, CT scintillator system employing garnet structure scintillators
US5391876A (en) * 1990-06-29 1995-02-21 General Electric Company Hole-trap-compensated scintillator material and computed tomography machine containing the same

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL9200939A (en) * 1991-05-31 1992-12-16 Hughes Aircraft Co Far-emitting area emitting luminescent material for cathode ray tubes.
WO1994017442A1 (en) * 1993-01-26 1994-08-04 Hughes-Jvc Technology Corporation Far-red emitting phosphor for cathode ray tubes

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4824598A (en) * 1987-10-20 1989-04-25 The United States Of America As Represented By The United States Department Of Energy Synthetic laser medium
EP0463369A1 (en) * 1990-06-29 1992-01-02 General Electric Company Transparent polycrystalline garnets
EP0467044A2 (en) * 1990-06-29 1992-01-22 General Electric Company Hole-trap-compensated scintillator material
EP0471926A2 (en) * 1990-06-29 1992-02-26 General Electric Company High speed, radiation tolerant, CT scintillator system employing garnet structure scintillators
US5391876A (en) * 1990-06-29 1995-02-21 General Electric Company Hole-trap-compensated scintillator material and computed tomography machine containing the same

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Publication number Publication date
WO2003014258A1 (en) 2003-02-20
EP1412452A1 (en) 2004-04-28
GB0119094D0 (en) 2001-09-26
NO20040515L (en) 2004-02-04
GB0218098D0 (en) 2002-09-11

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