U.S. patent application number 14/305769 was filed with the patent office on 2014-11-06 for particulate compositions having plural responses to excitation radiation.
This patent application is currently assigned to CABOT SECURITY MATERIALS, INC.. The applicant listed for this patent is Cabot Security Materials, Inc.. Invention is credited to Steven R. Cordero, Scott T. Haubrich, Jainisha Shah.
Application Number | 20140326899 14/305769 |
Document ID | / |
Family ID | 43031510 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140326899 |
Kind Code |
A1 |
Haubrich; Scott T. ; et
al. |
November 6, 2014 |
Particulate Compositions Having Plural Responses to Excitation
Radiation
Abstract
A particulate composition comprises a plurality of particles
wherein at least one of the particles comprises at least two
different crystalline and/or glass phases, each phase comprising a
host lattice and a dopant sensitive to electromagnetic radiation.
The different phases simultaneously produce different responses on
exposure to photons of the same energy, whereby the output from the
particulate composition when exposed to said photons is the sum of
the responses from the different phases.
Inventors: |
Haubrich; Scott T.;
(Albuquerque, NM) ; Shah; Jainisha; (Rio Rancho,
NM) ; Cordero; Steven R.; (Albuquerque, NM) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cabot Security Materials, Inc. |
Albuquerque |
NM |
US |
|
|
Assignee: |
CABOT SECURITY MATERIALS,
INC.
Albuquerque
NM
|
Family ID: |
43031510 |
Appl. No.: |
14/305769 |
Filed: |
June 16, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13496663 |
Mar 16, 2012 |
8791439 |
|
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PCT/US2010/051092 |
Oct 1, 2010 |
|
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14305769 |
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61247693 |
Oct 1, 2009 |
|
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Current U.S.
Class: |
250/459.1 |
Current CPC
Class: |
G01N 2021/6495 20130101;
H04N 5/33 20130101; C09K 11/7792 20130101; G01N 2021/6497 20130101;
G07D 7/1205 20170501; G07D 7/12 20130101; F41J 2/02 20130101; G01N
21/64 20130101; Y10T 428/2982 20150115; G01J 3/108 20130101 |
Class at
Publication: |
250/459.1 |
International
Class: |
G01N 21/64 20060101
G01N021/64 |
Claims
1-13. (canceled)
14. A method for authenticating and differentiating between a
series of articles, the method comprising: applying to each article
a security feature comprising a particulate composition comprising
at least one particle having at least two different crystalline
and/or glass phases, the different phases simultaneously producing
different responses on exposure to photons of the same energy,
whereby the output from the particulate composition when exposed to
said photons is the sum of the responses from the different phases;
varying the ratio of the amounts of the different phases in the
particulate compositions applied to the different articles whereby
each article produces a different output on exposure to said
photons of a given energy; exposing each article to on exposure to
photons of said given energy; measuring the output from each
article; and authenticating the articles.
15. The method of claim 14, wherein each phase is sensitive to
electromagnetic radiation in the UV, visible or IR regions of the
electromagnetic spectrum.
16. The method of claim 14, wherein the different phases produce
different emission spectra on exposure to photons of the same
energy.
17. The method of claim 16, wherein the different phases produce
emission spectra with peaks at different wavelengths on exposure to
said photons of the same energy.
18. (The method of claim 16, wherein each phase produces an
emission spectrum with multiple peaks on exposure to photons of the
same energy and the ratio of the relative intensities of the peaks
differs between the phases.
19. The method of claim 16, wherein the different phases emit
radiation having different decay rates on exposure to said photons
of the same energy.
20. (The method of claim 14, wherein each phase of said at least
one particle has a different selective absorbance to photons at the
same wavelength.
21. The method of claim 14, wherein each phase of said at least one
particle has a different extinction coefficient to photons at
different wavelengths.
22. The method of claim 14, wherein the composition has an average
particle size of less than about 10 .mu.m.
23. The method of claim 14, wherein the composition has an average
particle size of from about 0.1 .mu.m to about 3 .mu.m.
24. The method of claim 22, wherein at least about 90 weight
percent of the particles are not larger than twice said average
particle size.
25. The method of claim 14, wherein the composition is composed of
substantially spherical particles.
26. The method of claim 14, wherein the article is selected from
the group consisting of a credit card, a driver's license, a
passport, a check, currency, a bond, a ticket, a tax stamps, a
banknote, a cigarette pack tear tape, a security thread, and an
identification card.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of and claims priority to
U.S. application Ser. No. 13/496,663, filed on Mar. 16, 2012, which
claims priority to international application PCT/US2010/051092,
filed on Oct. 1, 2010, which claims priority to U.S. Provisional
Patent Application No. 61/247,693, filed on Oct. 1, 2009. All three
applications are hereby incorporated by reference in their
entirety.
FIELD
[0002] This invention relates to particulate compositions having
plural responses to excitation radiation and their use in security
applications.
BACKGROUND
[0003] Phosphors are compositions that are capable of emitting
useful quantities of radiation in the visible, infrared and/or
ultraviolet spectrums upon excitation of the phosphor compound by
an external energy source. Due to this property, phosphor compounds
have long been utilized in cathode ray tube (CRT) screens for
televisions and similar devices, as taggants for authenticating
documents and products, and as luminescent coatings in fluorescent
lamps, x-ray scintillators, light emitting diodes, and fluorescent
paints. Typically, inorganic phosphor compounds include a host
lattice containing a small amount of an emitter or dopant ion.
[0004] Conventional phosphor compositions have a defined response
(e.g., emission) to a given excitation by electromagnetic
radiation. Phosphor compositions may, for example, convert one
wavelength to a second wavelength whether ultraviolet to visible,
ultraviolet to infrared, visible to visible, visible to infrared,
infrared to infrared, or infrared to visible. Phosphor compositions
may also emit near the wavelength they absorb.
[0005] When used in security applications, phosphor compositions
are applied to articles to be authenticated and some basic property
of the phosphor, generally the wavelength of the emitted radiation,
is monitored by a detector to provide an indication or "tag" of
whether an article being tested in genuine. In some applications,
it is necessary to differentiate between a series of tagged
articles and, although this can be achieved by applying different
phosphor compositions which emit radiation of different
wavelengths, this has the disadvantage of requiring a monitoring
system with multiple detectors capable of separating and reading
the different wavelengths.
[0006] For certain applications, including differentiation between
a series of tagged articles, it would be advantageous to have
phosphor compositions that can controllably emit different
responses, e.g., emissions, to a single or multiple energy sources.
For example, U.S. Published Patent Application No. 2009/0007815
discloses a particulate composition having a first response to a
first electromagnetic radiation and, after intermediate exposure to
a second electromagnetic radiation, a second response to the first
electromagnetic radiation, different from the first response.
[0007] According to the present invention, a multiphase
photosensitive particle is provided, in which the same particle
contains multiple different phases, each producing a different
response when excited by radiation of the same energy or different
energies so that the overall output of the particle is equal to the
sum of the responses between the phases. By varying the relative
amounts of the different phases it is possible to produce a series
of particles with different outputs useful in security applications
requiring authentication and differentiation between articles.
SUMMARY
[0008] In one aspect, the invention resides in a particulate
composition comprising at least one particle having at least two
different crystalline and/or glass phases, each phase comprising a
host lattice and a dopant sensitive to electromagnetic radiation
and the different phases simultaneously producing different
responses on exposure to photons of the same energy or different
energies, whereby the output from the particulate composition when
exposed to said photons is the sum of the responses from the
different phases.
[0009] Conveniently, each phase is sensitive to electromagnetic
radiation in the UV, visible or IR regions of the electromagnetic
spectrum.
[0010] Conveniently, the different phases produce different
emission spectra on exposure to photons of the same energy.
[0011] In one embodiment, the different phases produce emission
spectra with peaks at different wavelengths on exposure to photons
of the same energy.
[0012] In another embodiment, each phase produces an emission
spectrum with multiple peaks on exposure to photons of the same
energy and the ratio of the relative intensities of the peaks
differs between the phases.
[0013] In yet another embodiment, the different phases emit
radiation having different decay rates on exposure to photons of
the same energy.
[0014] In a further embodiment, the phases have different selective
adsorbance to photons of the same energy.
[0015] Alternatively, the phases have different extinction
coefficients for photons of different energy.
[0016] In a further aspect, the invention resides in a method for
authenticating and differentiating between a series of articles,
the method comprising:
[0017] (a) applying to each article a particulate composition
comprising a plurality of particles wherein at least one of the
particles comprises at least two different crystalline and/or glass
phases, each phase comprising a host lattice and a dopant sensitive
to electromagnetic radiation and the different phases
simultaneously producing different responses on exposure to photons
of the same energy or different energies, whereby the output from
the particulate composition when exposed to said photons is the sum
of the responses from said different phases;
[0018] (b) varying the ratio of the amounts of the different phases
in the particulate compositions applied to the different articles
whereby each article produces a different output on exposure to
said photons of the same or different energies;
[0019] (c) exposing each article to photons of the same or
different energies; and
[0020] (d) measuring the output from each article.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1(a) and (b) are X-ray diffraction (XRD) patterns of
the composite materials C-1 and C-2 respectively of Example 1.
[0022] FIGS. 2(a) to (d) are SEM images of pure
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 (FIG. 2a), pure
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 (FIG. 2b), composite C-1
(FIG. 2c) and composite C-2 (FIG. 2d).
[0023] FIGS. 3(a) to (c) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 components (FIG. 3a), the
mixture M1 and composite C-1 (FIG. 3b), and the mixture M-2 and
composite C-2 (FIG. 3c) after excitation with 365 nm UV light.
[0024] FIGS. 3(d) to (f) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 components (FIG. 3d), the
mixture M1 and composite C-1 (FIG. 3e), and the mixture M-2 and
composite C-2 (FIG. 3f) after excitation with 254 nm UV light.
[0025] FIGS. 4(a) to (c) are XRD patterns of the composites C-3,
C-4 and C-5 respectively of Example 2.
[0026] FIGS. 5(a) to (f) are SEM images of pure
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 (FIG. 5a), pure
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 (FIG. 5b), pure
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 (FIG. 5c), composite C-3 (FIG. 5d),
composite C-4 (FIG. 5e) and composite C-5 (FIG. 5f).
[0027] FIGS. 6(a) to (c) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 components (FIG. 6a), the
composites C-3, C-4 and C-5 (FIG. 6b), and the mixtures with
identical compositions M-3, M-4 and M-5 (FIG. 6c) after excitation
with 365 nm UV light.
[0028] FIGS. 6(d) to (f) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 components (FIG. 6d), the
composites C-3, C-4 and C-5 (FIG. 6e), and the mixtures with
identical compositions M-3, M-4 and M-5 (FIG. 6f) after excitation
with 254 nm UV light.
[0029] FIG. 7 is an XRD pattern of composite C-6 of Example 3.
[0030] FIGS. 8 (a) to (c) are SEM images of pure
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3, pure
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 and composite C-6
respectively.
[0031] FIGS. 9(a) and (b) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 components (FIG. 9a)
and the composite C-6 and the mixture M-6 (FIG. 9b) after
excitation with 365 nm UV light.
[0032] FIGS. 9(c) and (d) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 components (FIG. 9c)
and the composite C-6 and the mixture M-6 (FIG. 9d) after
excitation with 254 nm UV light.
[0033] FIGS. 10(a) and (b) are XRD patterns of the composites C-7
and C-8 respectively of Example 4.
[0034] FIGS. 11(a) to (d) are SEM images of pure
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12, pure
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9, composite C-7 and
composite C-8 respectively.
[0035] FIGS. 12(a) to (c) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 components (FIG. 12a),
the mixture M7 and the composite C-7 (FIG. 12b), and the mixture M8
and the composite C8 (FIG. 12c) after excitation with 365 nm UV
light.
[0036] FIGS. 12(d) to (f) compare the PL emission spectra of the
individual pure (Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 components (FIG. 12d),
the mixture M7 and the composite C-7 (FIG. 12e), and the mixture M8
and the composite C8 (FIG. 12f) after excitation with 254 nm UV
light.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0037] Described herein is a particulate composition comprising a
plurality of particles wherein at least one, and preferably
substantially all, of the particles comprises at least two
different crystalline and/or glass phases and wherein each phase
comprises a host lattice and a dopant sensitive to electromagnetic
radiation. Moreover, the different phases are selected so that they
simultaneously produce different responses on exposure to photons
of the same energy or different energies. In this way the output
from the particulate composition when exposed to such photons is
the sum of the responses from the different phases.
[0038] Since the output of the composition in response to
excitation is equal to the sum of the responses from the different
phases, by varying the relative amounts of the phases, it is
possible to produce a series of particulate compositions each with
a different characteristic output. This facility is particularly
useful in security applications when it is necessary not only to
authenticate a single article, but also to differentiate between
different authentic articles, for example, banknotes of different
denominations. Thus, by applying a different particulate
composition, each with a unique ratio between the amounts of the
different phases, to each article to be authenticated, it is
possible to measure the output from the different compositions in
response to excitation radiation to uniquely identify each
article.
[0039] Depending on the selection of the particular host
lattice/dopant combination, particulate compositions as described
herein can be produced so as to be sensitive to electromagnetic
radiation over a wide range of the electromagnetic spectrum. For
many practical applications, preference may be given to
compositions sensitive to radiation in the UV, visible or IR
regions of the spectrum, but in other applications it may be useful
to produce compositions sensitive to radiation in one or more of
the radio, microwave, X-ray and gamma ray regions of the
spectrum.
[0040] In one embodiment, the present particulate composition
comprises at least one particle having at least two different
crystalline and/or glass phases which behave as photoluminescent
phosphors with different emission characteristics in response to
exposure to photons of a given energy. For example, the different
phases can be arranged to produce emission spectra with peaks at
different wavelengths on exposure to said photons of the same
energy. Alternatively, each phase can be arranged to produce an
emission spectrum with multiple peaks on exposure to photons of the
same energy but with the ratio of the relative intensities of the
peaks differing between the phases. As a further alternative, the
different phases can be arranged to emit radiation having different
decay rates on exposure to said photons of the same energy.
[0041] In principal, where the different phases in the particulate
composition behave as photoluminescent phosphors, any known
phosphor host lattice may be used in each phase if it is possible
to incorporate at least one type of luminescent dopant atom into
said host lattice to result in a luminescent composition. Examples
of host lattices which may be useful include compounds comprising a
cation containing at least one element selected from Groups 2, 3
12, and 13 of the Periodic Table and the lanthanide elements, and
an anion containing at least one element selected from Groups 13,
14, 15, 16 and 17 of the Periodic Table. Typically, the or each
cation element is selected from yttrium, lanthanum, gadolinium,
lutetium, zinc, magnesium, calcium, strontium, and barium and the
or each anion element is selected from boron, aluminum, gallium,
silicon, germanium, nitrogen, phosphorous, arsenic, oxygen, sulfur,
selenium, fluorine, chlorine, bromine, iodine. Particular lattice
materials suitable for use in the present phosphor compositions
include yttrium oxide, yttrium phosphate, yttrium sulfides, yttrium
oxysulfides, yttrium aluminates, such as Y.sub.3Al.sub.5O.sub.12
(YAG), YAlO.sub.3 (YAP) and Y.sub.4Al.sub.2O.sub.9 (YAM), and
yttrium silicon nitrides and oxynitrides, such as YSi.sub.3N.sub.5
and Y.sub.2Si.sub.11N.sub.20O, erbium aluminates, such as
Er.sub.3Al.sub.5O.sub.12 and ErAlO.sub.3 (YAP), barium magnesium
aluminates, gadolinium oxide and gadolinium gallates, such as
Gd.sub.3Ga.sub.5O.sub.12, lanthanum oxide, lanthanum phosphate,
neodymium phosphate, zirconia, ceria, zinc silicates, and strontium
silicates. Mixed lattice compositions can also be employed.
[0042] The dopants employed herein are typically ions of lanthanide
elements, including cerium, praseodymium, neodymium, samarium,
europium, terbium, dysprosium, holmium, erbium, thulium, ytterbium
and mixtures thereof. Other elements that can be used as the dopant
ion in the present particulate composition include magnesium,
chromium, manganese, cobalt, iorn, renium, osmium, molybdenum,
titanium, copper, silver, nickel, tin, lead, zinc and mixtures
thereof. Generally, the dopant is present as an oxygen-containing
compound, such as a metal oxide, a silicate, borate, phosphate,
oxysulfide or aluminate.
[0043] The amount of dopant present in the luminescent composition
is not narrowly defined and generally can range from about 0.1 to
about 99 mole %, such as from about 1 to about 80 mole %, for
example from about 5 to about 70 mole %, conveniently from about 5
to about 25 mole % of the total luminescent composition.
[0044] In producing particulate phosphor compositions with
different emissions from the same particle, use is made of the fact
that the host structure and site symmetry of a phosphor material
strongly influence its spectral properties. Thus, for example,
europium doped yttrium oxide and europium doped yttrium phosphate
have different site symmetries, host structures and host lattices
and so, when excited, generally have different emission spectra and
decay rates. The lifetime for the decay of the oxide emission is
1.15 ms, whereas that for the phosphate emission is 3.0 ms. It is
therefore possible to tune the observable decay rate to any value
in the range 1.15 to 3.0 ms, by making particles with varying
amounts of the mixed phases.
[0045] In addition, as shown in Table 1, different rare earth
phosphates have different crystal structures, for example the
xenotime phase and the monazite phase, with different rare earth
(RE) to rare earth distances. The longer these distances, there is
less orbital overlap and cross talk between the dopants, which in
turn leads to less concentration quenching of the dopants and hence
longer decay times.
TABLE-US-00001 TABLE 1 Phosphate Space group Symmetry RE-RE
distance (.ANG.) YPO.sub.4 141/amd Tetragonal 3.7-5.2 EuPO.sub.4
P121/n1(14) Monoclinic 4.0-5.9 LaPO.sub.4 P121/n1(14) Monoclinic
4.1-5.9 YbPO.sub.4 141/amd Tetragonal 3.7-5.9 Nd.sub.3PO.sub.7
C1M1(8) Monoclinic 3.7-5.9
[0046] In another embodiment, the present particulate composition
comprises at least one particle having at least two different
crystalline and/or glass phases which have different selective
absorbance to photons of the same energy due to the phases having
different extinction coefficients at the wavelength of the photons.
As a result the amount of incident radiation absorbed by the
particulate composition will depend on the relative amounts of the
different phases in the composition.
[0047] Alternatively, the present particulate composition comprises
at least one particle having at least two different crystalline
and/or glass phases which have different extinction coefficients to
photons of different wavelength. Thus, when exposed to a mixed
radiation source, the distribution of wavelengths in the output
from the particulate composition will depend on the relative
amounts of the different phases in the composition.
[0048] Typically, the present particulate composition is in the
form of particles having a small average size. Although the
preferred average size will vary according to the application of
the composition, in most cases the average particle size is less
than about 10 .mu.m, preferably less than about 5 .mu.m, more
preferably less than about 3 .mu.m, such as from about 0.1 .mu.m to
about 3 .mu.m, typically about 2 .mu.m. As used herein, the average
particle size is the weight average particle size.
[0049] Generally, it is preferred that the particulate composition
also has a narrow particle size distribution, such that the
majority of particles are substantially the same size. Preferably,
at least about 90 weight percent of the particles and more
preferably at least about 95 weight percent of the particles are
not larger than twice the average particle size. Thus, when the
average particle size is about 2 .mu.m, it is preferred that at
least about 90 weight percent of the particles are not larger than
4 .mu.m and it is more preferred that at least about 95 weight
percent of the particles are not larger than 4 .mu.m. Further, it
is preferred that at least about 90 weight percent of the
particles, and more preferably at least about 95 weight percent of
the particles, are not larger than about 1.5 times the average
particle size. Thus, when the average particle size is about 2
.mu.m, it is preferred that at least about 90 weight percent of the
particles are not larger than about 3 .mu.m and it is more
preferred that at least about 95 weight percent of the particles
are not larger than about 3 .mu.m.
[0050] The particles are also preferably substantially spherical in
shape. That is, the particles are not jagged or irregular in shape.
Spherical particles are particularly advantageous because they are
able to disperse and coat an article more uniformly with a reduced
average thickness. Although the particles are substantially
spherical, the particles may become faceted as the crystallite size
increases and approaches the average particle size.
[0051] The individual components of the particles advantageously
have a high degree of purity, that is, a low level of impurities.
Impurities are those materials that are not intended in the final
product. Thus, the dopant ion is not considered as an impurity. The
level of impurities in the present phosphor powders is preferably
not greater than about 1 atomic percent, more preferably not
greater than about 0.1 atomic percent, and even more preferably not
greater than about 0.01 atomic percent.
[0052] In one embodiment, the phosphor particles are provided with
a surface coating that substantially encapsulates the outer surface
of the particles. Such coatings can assist in reducing degradation
of the phosphor material due to moisture or other influences and
can also create a diffusion barrier such that activator ions cannot
transfer from one particle to another, thereby altering the
luminescence characteristics. Coatings can also control the surface
energy levels of the particles. It is to be appreciated that any
coating on the particles of the present composition is not
considered as one of the two different crystalline and/or glass
phases present in one or each particle of the composition.
[0053] The coating can be a metal, metal oxide or other inorganic
compound such as a metal sulfide, or can be an organic compound.
For example, a metal oxide coating can advantageously be used, such
as a metal oxide selected from the group consisting of SiO.sub.2,
MgO, Al.sub.2O.sub.3, ZnO, SnO.sub.2 or In.sub.2O.sub.3.
Particularly preferred are coatings are SiO.sub.2 and
Al.sub.2O.sub.3. Semiconductive oxide coatings such as SnO.sub.2 or
In.sub.2O.sub.3 can also be advantageous in some applications due
to the ability of the coating to absorb secondary electrons that
are emitted by the phosphor. Metal coatings, such as copper, can be
useful for phosphor particles used in direct current
electroluminescent applications In addition, phosphate coatings,
such as zirconium phosphate or aluminum phosphate, can also be
advantageous for use in some applications.
[0054] The coating should encapsulate the entire particle, but
should be sufficiently thin that the coating does not interfere
with light transmission. Preferably, the coating has an average
thickness of at least about 2 nanometers, more preferably at least
about 5 nanometers, but not greater than about 200 nanometers, more
preferably not greater than about 100 nanometers, and even more
preferably not greater than about 50 nanometers. In one embodiment,
the coating has a thickness of from about 2 to about 50 nanometers,
such as from about 2 to about 10 nanometers. Further, the particles
can include more than one coating substantially encapsulating the
particles to achieve the desired properties.
[0055] The coating, either particulate or non-particulate, can also
include a pigment or other material that alters the light
characteristics of the phosphor. Red pigments can include compounds
such as the iron oxides (Fe.sub.2O.sub.3), cadmium sulfide
compounds (CdS) or mercury sulfide compounds (HgS). Green or blue
pigments include cobalt oxide (CoO), cobalt aluminate
(CoAl.sub.2O.sub.4) or zinc oxide (ZnO). Pigment coatings are
capable of absorbing selected wavelengths of light leaving the
phosphor, thereby acting as a filter to improve the color contrast
and purity.
[0056] In addition, the phosphor particles can be coated with an
organic compound, such as PMMA (polymethylmethacrylate),
polystyrene or similar organic compounds, including surfactants
that aid in the dispersion and/or suspension of the particles in a
flowable medium. The organic coating is preferably not greater than
about 100 nanometers thick and is substantially dense and
continuous about particle. The organic coatings can advantageously
prevent corrosion of the phosphor particles, especially in
electroluminescent lamps, and also can improve the dispersion
characteristics of the particles in a paste or other flowable
medium.
[0057] The coating can also be comprised of one or more monolayer
coatings, such as from about 1 to 3 monolayer coatings. A monolayer
coating is formed by the reaction of an organic or an inorganic
molecule with the surface of the phosphor particles to form a
coating layer that is essentially one molecular layer thick. In
particular, the formation of a monolayer coating by reaction of the
surface of the phosphor powder with a functionalized organosilane
such as halo- or amino-silanes, for example hexamethyldisilazane or
trimethylsilylchloride, can be used to modify and control the
hydrophobicity and hydrophilicity of the phosphor powders. Metal
oxides (e.g. ZnO or SiO.sub.2) or metal sulfides (e.g. Cu.sub.2S)
can also be formed as monolayer coatings. Monolayer coatings can
allow for greater control over the dispersion characteristics of
the phosphor powder in a wide variety of paste compositions and
other flowable mediums.
[0058] The monolayer coatings may also be applied to phosphor
powders that have already been coated with an organic or inorganic
coating, thus providing better control over the corrosion
characteristics (through the use of a thicker coating) as well as
dispersibility (through the use of a monolayer coating) of the
phosphor powder.
[0059] Although the present particulate composition can be produced
by any known method which allows the production of a single
particle with at least two different crystalline and/or glass
phases, preferred methods include spray pyrolysis and pyrolysis
using a flame reactor, as discussed in more detail below. Thus
these methods not only facilitate preparation of multiphase
particles but also generate spherical particles of the desired size
and size distribution.
[0060] In spray pyrolysis, a precursor medium is produced which
comprises a precursor to at least one the components of the
phosphor composition dissolved or suspended in a liquid carrier,
while the remaining components, if any, of the composition are
dispersed as particles in the liquid carrier. The liquid carrier is
then atomized to produce an aerosol comprising droplets dispersed
and suspended in a carrier gas. The aerosol is then heated at a
temperature of at least 200.degree. C., generally from about
300.degree. C. to about 1500.degree. C., in order to: (1) remove at
least a portion of the liquid carrier in the droplets; and (2)
convert the or each precursor to the corresponding component of the
particulate composition.
[0061] By the term "precursor" is meant any compound capable of
being chemically converted under the conditions employed in the
spray pyrolysis process to at least one component of the final
particulate composition. Suitable precursors therefore include
inorganic salts of the elements contained in the particulate
composition, such as nitrates, sulfates and chlorides.
[0062] Generally, where the precursor medium contains solid
particles of at least one component of the final particulate
composition, the solid particles are arranged to have a particle
size of between about 0.1 micron and about 100 micron, such as
between about 1 micron and about 10 micron.
[0063] The precursor medium can be converted into aerosol form
using any suitable device that disperses liquid into droplets, such
as for example, a spray nozzle. Examples of suitable spray nozzles
include ultrasonic spray nozzles, multi-fluid spray nozzles and
pressurized spray nozzles. Ultrasonic spray nozzles generate
droplets of liquid by using piezoelectric materials that vibrate at
ultrasonic frequencies to break up a liquid into small droplets.
Pressurized nozzles use pressure and a separator or screen in order
to break up the liquid into droplets. In some cases, pressurized
nozzles may involve use of some vapor that is generated from the
liquid itself in order to pressurize and break up the liquid into
droplets. One advantage of using ultrasonic and pressurized nozzles
is that an additional fluid is not required to generate liquid
droplets. This may be useful in situations where the precursor
dissolved in the liquid vehicle is sensitive and/or incompatible
with other common fluids used in multi-fluid spray nozzles.
[0064] In addition to the use of a spray nozzle for dispersing the
liquid medium, any other suitable device or apparatus for
generating disperse droplets of liquid may be used. One example of
a device that is useful in generating droplets of liquid is an
ultrasonic generator. An ultrasonic generator uses transducers to
vibrate liquids at very high frequencies which break up the liquid
into droplets. One example of an ultrasonic generator that is
useful in the present process is disclosed in U.S. Pat. No.
6,338,809, incorporated herein by reference in its entirety.
Another example of a device that is useful in generating droplets
of liquid is a high energy atomizer such as those used in carbon
black production.
[0065] Generally, whatever method is employed to atomize the
precursor medium, the aerosol produced is arranged to have an
average droplet size between about 1 and about 100 microns, such as
between about 3 and about 50 microns, for example between about 5
and about 30 micron. In certain cases, it may be desirable to
introduce one or more precursors and/or components of the final
particulate composition to the spray conversion reactor as dry
powders.
[0066] Further details of the spray pyrolysis process can be found
in U.S. Pat. No. 6,180,029, and in U.S. Patent Application
Publication No. 20070096057, the entire contents of which are
hereby incorporated herein as if set forth herein in full. See also
U.S. Patent Application Publication Nos. 20060166057, 20060165898,
20060165910; and 20060162497, the entireties of which are
incorporated herein by reference.
[0067] In the flame reactor process, a nongaseous precursor of at
least one component of the desired particulate composition is
introduced into a flame reactor heated by at least one flame. The
nongaseous precursor is introduced into the flame reactor in a very
hot zone, also referred to herein as a primary zone, that is
sufficiently hot to cause the component of the nongaseous precursor
to be transferred into the gas phase of a flowing stream in the
flame reactor, followed by a particle nucleation from the gas
phase. In some embodiments, the temperature in at least some
portion of this primary zone, and sometimes only in the hottest
part of the flame, is high enough so that substantially all of
materials flowing through that portion of the primary zone are in
the gas phase. The component of the nongaseous precursor may enter
the gas phase by any mechanism. For example, the nongaseous
precursor may simply vaporize, or the nongaseous precursor may
decompose and the component enter the gas phase as part of a
decomposition product. Eventually, however, the component then
leaves the gas phase as particle nucleation and growth occurs.
Removal of the component from the gas phase may involve simple
condensation as the temperature cools or may include additional
reactions involving the component that results in a non-vapor
reaction product. In addition to this primary zone where the
component of the nongaseous precursor is transferred into the gas
phase, the flame reactor may also include one or more subsequent
zones for growth or modification of the nanoparticulates. In most
instances, the primary zone will be the hottest portion within the
flame reactor.
[0068] One suitable flame reactor is disclosed in U.S. Patent
Application Publication No. 2006/0162497, published on Jul. 27,
2006, the entire contents of which are incorporated herein by
reference. Using a flame reactor, conversion temperatures in excess
of 1000.degree. C., such as from about 1200.degree. C. to about
3000.degree. C. can be attained.
[0069] Multiphase particles of the type employed in the present
particulate composition can be produced by the spray processes
described above either in a single stage process or in multiple
stages. For example, where a single stage process is employed, the
feed to the pyrolysis step may contain precursors to two or more
host lattice materials and to one or more dopant materials thereby
allowing the formation of particles each containing different
phosphorescent phases. Alternatively, a multistage process can be
used in which a particle having a single phosphorescent phase is
produced in a first pyrolysis stage and this particle is then used
as part of the feed to a second pyrolysis stage.
[0070] The particulate compositions described herein can be
employed to produce security features on articles such as credit
cards, driver's licenses, passports, checks, currency, bonds,
tickets, tax stamps, banknotes, cigarette pack tear tapes, thin
films (e.g., for shrink wrap applications), security thread, ID
cards and the like. As used herein, the term "security feature"
means a feature that is placed on an article (e.g., a label, a
document such as a passport, check, bond, banknote, currency, or
ticket), directly or indirectly, for the purpose of authenticating
the article. The particulate compositions can also be incorporated
directly into packaging to authenticate packaged products.
[0071] This is conveniently achieved by combining the particulate
composition with a liquid to form a flowable medium, such as an
ink, paste or slurry, and then applying a coating comprising the
composition onto a substrate. In addition to the particulate
composition, such a flowable medium may comprise one or more of the
following: a liquid vehicle, an anti-agglomeration agent, one or
more additives (e.g., surfactants, polymers, biocides, thickeners,
etc.), other particulates (metallic and/or non-metallic), and other
components. The medium may be deposited onto a substrate by
virtually any printing process, such as ink-jet printing, screen
printing, intaglio printing, roll printing, lithographic printing
and gravure printing.
[0072] The invention will now be more particularly described with
reference to the following non-limiting Examples and the
accompanying drawings.
[0073] All the individual and composite materials described in the
Examples were made by spray pyrolysis using soluble metal
precursors and phosphoric acid. The first step in spray pyrolysis
was the formation of an aqueous solution comprising all the
required elements in the form of soluble inorganic salts (metal
nitrates) and (when needed) phosphoric acid in the desired ratios.
Next, the liquid carrier was atomized with an ultrasonic generator
using membrane transducers to produce an aerosol comprising
droplets dispersed and suspended in compressed air as a carrier
gas. The aerosol was then heated to a temperature high enough to
ensure i) the removal of at least a portion of the liquid carrier
in the droplets, ii) convert (decompose) the precursors to the
corresponding components of the particulate composition. When
necessary a final post treatment step at higher temperatures was
added in order to complete the precursor conversion.
[0074] Powder X-ray diffraction (XRD) analyses were carried out on
a Bruker D-8 Advance instrument using Ni-filtered Cu-K.alpha.
radiation at 40 kV/40 mA. XRD patterns were recorded between 10 and
95 degrees 2.theta. at 0.02 deg/step and 1.25 sec/step collecting
time. Initial phase identification was performed using the EVA
software package (Bruker-AXS, 2007) and the ICDD-PDF 4 database.
Quantitative Rietveld analyses based on least squares fitting of
the weighted f-factors of all observed and calculated XRD peaks
were performed using the TOPAZ software. This method yielded data
about the exact particulates phase composition and components'
crystallites size.
[0075] Scanning electron microscope (SEM) studies were carried out
using a Hitachi S-5200 field emission SEM, generally operated at an
accelerating voltage of 2.0 and 10.0 kV, coupled with a PGT EDS
system and PGT Spirit software for elemental mapping and EDS.
[0076] Particles size distributions were measured using a Honeywell
X100 series Microtrac Particle Size Analyzer and Automated Small
Volume Recirculator (ASVR), capable of analyzing particle mixtures
in the size range of 0.12 to 704 microns. The powders were prepared
in a water suspension with Darvan C and sonicated externally using
a Branson 450 Sonic Horn.
[0077] Photoluminescence spectra of the powders were recorded using
a bench top spectrofluorometer (QuantaMaster.TM., Photon Technology
International). The excitation and emission bandwidths were held
constant yielding a measurement relative standard deviation of 5%
for all samples. The spectrofluorometer is outfitted to measure
phosphorescence lifetime as well. In this configuration the sample
is irradiated with a flash lamp and the resulting intensity
temporal profile is measured with a time gated photo detector. In
either measurement, optical filters are used to remove undesirable
stray light. Photoluminescence spectra were recorded using
excitation with 365 and 254 nm UV, and the lifetimes with 365 nm
UV, respectively.
Example 1
[0078] Single phase particulate materials having the compositions
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 were produced by spray
pyrolysis and were used to produce two different physical mixtures
having the compositions (i) 35.5 wt %
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3+64.5 wt %
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 and (ii) 26 wt %
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3+74 wt %
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7.
[0079] In addition, spray pyrolysis was employed to produce two
two-phase composite particulate materials having the same
compositions as the physical mixtures, namely
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.-
7=35.5:64.5 wt % and 26:74 wt %, respectively. The compositions of
the physical mixtures and composite materials are summarized in
Table 2.
TABLE-US-00002 TABLE 2 Sample ID code Composite
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub-
.3PO.sub.7 = 35.5:64.5 wt % C-1 Composite
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub-
.3PO.sub.7 = 26.5:73.5 wt % C-2 Mixture
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.3-
PO.sub.7 = 35.5:64.5 wt % M-1 Mixture
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.3-
PO.sub.7 = 26.5:73.5 wt % M-2
[0080] Powder X-ray diffraction (XRD) analysis of the composite
materials confirmed the presence of two crystalline phases in both
composite materials--(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 (see FIG. 1).
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 was identified as a new phase
isostructural to Dy.sub.3PO.sub.7 and consequent Rietveld structure
refinement yielded the following parameters: S.G. Cm, a=12.6407
.ANG., b=12.6309 .ANG., c=11.9895 .ANG., .beta.=108.75.degree.,
R.sub.Bragg=4.3%, R.sub.wp=6.7%.
[0081] Quantitative Rietveld analysis of the XRD patterns confirmed
the target compositions of the composites, for example
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3=35.6 wt % and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7=64.4 wt % for C-1
(theoretical values: 35.5 wt % and 64.5 wt %, respectively) [see
FIG. 2]. The Eu distribution in the two phases was confirmed in the
two components and the composite material by least squares fitting
of the weighted f-factors of all observed and calculated XRD
peaks--the lower the R.sub.w value the better the fit. For example
the free variation of the Y:Eu ratio in
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 yielded occupancy factors of
Y=0.93 and Eu=0.08 which practically match the theoretical
ones.
[0082] In a similar way, the best fit (R.sub.w=7.34%) composite C-1
was achieved assuming statistical distribution of Eu in both
components, followed by R.sub.w=7.55% for the cases assuming Eu
presence in only one of the components and the worst fit yielding
R.sub.w=7.55% resulted from the assumption that there is no Eu in
any of the two components.
[0083] Scanning electron microscopy (SEM-EDX) analyses confirmed
that both single phase components,
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7, were mixed within the
composite particles forming individual micro crystallites less than
50 nm--much smaller than those of the pure components (200-400 nm)
made by the same process (see FIG. 2).
[0084] Particles size distribution (PSD) studies confirmed that the
composite materials have a narrow PSD within the range 1-5 microns
and average particles diameter d-50 of about 2 microns, as shown in
Table 3 below.
TABLE-US-00003 TABLE 3 PSD (micrometers) of the composites C-1 and
C-2 Percentiles C-1 C-2 10% 1.06 0.96 50% 1.87 1.58 95% 4.62
3.81
[0085] The photoluminescence (PL) emission spectra of the
composites C-1 and C-2 after excitation with 365 and 254 nm UV
light are compared to those of the mixtures with the same
composition (M-1 and M-2) and the pure
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 components in FIG. 3.
[0086] The steady state PL spectra of the individual components
show strong peaks with maxima at 614 nm for
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and 620 nm for
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7, respectively. The spectra of
the composites C-1 and C-2 show broad peaks with maxima at 620 nm
and shoulders at 614 nm. Overall, the spectra can be described as
being closer to that of the (Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7
component with weaker effects arising from the
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 component. This shows that the
PL spectra of the composite materials are dominated by the emission
of heavier mass fraction of (Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7
which is consistent with the compositions of C-1 and C-2,
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7=64.4 and 73.5 wt %,
respectively. In contrast, the PL spectra of the mixtures M-1 and
M-2 show peaks with maxima at 614 nm and shoulders at 620 nm, i.e.
these are dominated by the emission of
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3. This effect is more
pronounced in the case of C-1
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3=35.6%) and decreases with the
decrease of the mass fraction of
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3
(C-2:(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3=26.5%).
[0087] The integral intensity of all samples is a function of the
crystallites size and hence depends on the relative area of the
grain boundaries and the amounts of crystal lattice defects. The
measurements of the dynamic property lifetime (.tau.) of the same
species show more complex relations. It is proportional to the mass
fraction and to the crystallites size of the individual
components.
Example 2
[0088] Single phase materials have the compositions
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7,
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 and three three-phase composite
particulate materials containing
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 and
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 in different ratios were produced
by spray pyrolysis. In addition, three physical mixtures with
compositions identical to those of the composite materials were
produced by mixing the pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 and
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 in the desired ratios. The
compositions of the physical mixtures and composite materials are
summarized in Table 4.
TABLE-US-00004 TABLE 4 Sample ID code Composite
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).su-
b.3PO.sub.7: C-3 (Y.sub.0.92Eu.sub.0.08)PO.sub.4 = 34:37:29 wt %
Composite
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).su-
b.3PO.sub.7: C-4 (Y.sub.0.92Eu.sub.0.08)PO.sub.4 = 40:49:11 wt %
Composite
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).su-
b.3PO.sub.7: C-5 (Y.sub.0.92Eu.sub.0.08)PO.sub.4 = 16:78:5 wt %
Mixture
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.-
3PO.sub.7: M-3 (Y.sub.0.92Eu.sub.0.08)PO.sub.4 = 34:37:29 wt %
Mixture
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.-
3PO.sub.7: M-4 (Y.sub.0.92Eu.sub.0.08)PO.sub.4 = 40:49:11 wt %
Mixture
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.-
3PO.sub.7: M-5 (Y.sub.0.92Eu.sub.0.08)PO.sub.4 = 16:78:5 wt %
[0089] XRD analysis of the composite materials confirmed the
presence of three crystalline
phases--(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 and
(Y.sub.0.92Eu.sub.0.08)PO.sub.4, see FIG. 4. The exact ratios of
the crystalline components cited in Table 4 were determined by
Rietveld analysis of the corresponding XRD patterns.
[0090] Scanning electron microscopy (SEM-EDX) analyses confirmed
that the single phase
components--(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 and
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 formed individual micro
crystallites within the composite particles of less than 50
nm--much smaller than those of the pure components made by the same
process, see FIG. 5.
[0091] Particles size distribution (PSD) studies confirmed that the
three composite materials have a narrow PSD within the range 1-3
microns and average particles diameter d-50 of about 1.3 microns,
as shown in Table 5.
TABLE-US-00005 TABLE 5 PSD (micrometers) of the composites C-3, C-4
and C-5 Percentiles C-3 C-4 C-5 10% 0.86 0.89 0.92 50% 1.30 1.31
1.35 95% 2.96 2.84 2.99
[0092] The photoluminescence (PL) emission spectra after excitation
with 365 and 254 nm UV light of the pure
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3,
(Y.sub.0.92Eu.sub.0.08)PO.sub.4 and
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 components are compared to
those of the composites C-3, C-4 and C-5 and the mixtures with
identical compositions M-3, M-4 and M-5 in FIG. 6.
[0093] The steady state PL spectra of the individual components
show strong peaks with maxima at 614 nm for
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3, 595 and 625 nm for
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7 and 620 nm for
(Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7, respectively. It is worthy
of note that while the relative PL emission intensities of the pure
components after excitation at 365 nm are comparable, the intensity
of pure (Y.sub.0.92Eu.sub.0.08)PO.sub.4 after excitation at 254 nm
is close to zero, see FIGS. 6(a) and (b).
[0094] The spectra of the composites C-3, C-4 and C-5 show broad
peaks with maxima centered at 620 nm and can be described as being
closer to that of the (Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7
component with weaker effects arising from the other two
components. This shows that the composites' PL spectra are
dominated by the emission of the component with the heavier mass
fraction which is consistent with the corresponding compositions in
Table 5. In contrast, the PL spectra of the mixtures M-3 and M-4
show peaks with maxima at 614 nm and shoulders at 620 nm, i.e.
these are dominated by the emission of
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 which mass fraction is
comparable to that of (Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7. In the
case of M-5 the spectrum is again dominated by the heaviest
fraction (Y.sub.0.92Eu.sub.0.08).sub.3PO.sub.7.
[0095] The integral intensity of all samples is a function of the
crystallites size and, hence, depends on the relative area of the
grain boundaries and the amounts of crystal lattice defects. The
measurement of the dynamic property lifetime (.tau.) of the same
species shows more complex relations. It is proportional to the
mass fraction and to the crystallites size of the individual
components.
Example 3
[0096] Single phase particulate material of composition
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 and a two-phase
composite particulate material of composition 22.8 wt %
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3/77.2 wt %
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 were produced by spray
pyrolysis. In addition, a physical mixture with composition
identical to that of the composite material have been made by
mixing pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 in the same ratio, as
shown in Table 6.
TABLE-US-00006 TABLE 6 Sample ID code Composite
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).su-
b.4Al.sub.2O.sub.9 = C-6 22.8:77.2 wt % Mixture
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.-
4Al.sub.2O.sub.9 = M-6 22.8:77.2 wt %
[0097] Powder XRD analysis of the composite material C-6 confirmed
the presence of two crystalline phases in the composite
material--(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9, see FIG. 7.
Quantitative Rietveld analysis of the XRD pattern yielded the exact
ratio of the components,
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3:(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.-
2O.sub.9=22.8:77.2 wt %.
[0098] Scanning electron microscopy (SEM-EDX) analyses confirmed
that both single phase components,
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9, were mixed within the
composite particles forming individual micro crystallites
comparable to those of the pure components (100-300 nm) made by the
same process, see FIG. 8.
[0099] Particles size distribution (PSD) studies confirmed that the
composite materials have a narrow PSD within the range 0.7-3.7
microns and average particles diameter d-50 of about 1.4 microns,
as shown in Table 7.
TABLE-US-00007 TABLE 7 PSD of composite C-6 Percentiles Microns 10%
0.69 50% 1.35 95% 3.72
[0100] The photoluminescence (PL) emission spectra of composite C-6
after excitation with 365 and 254 nm UV light are compared to those
of pure (Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 samples in FIG. 9.
[0101] The steady state PL spectra of the individual components
show strong peaks with maxima at 614 nm for
(Y.sub.0.92Eu.sub.0.08).sub.2O.sub.3 and 610 nm for
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9, respectively. The
spectra of the composite C-6 and the mixture M-6 show very similar
peaks with maxima at 614 nm and shoulders at 610 nm. Overall, the
spectra can be described as a linear combination of those of the
individual components. It is worth noticing that the satellite
peaks at 590-600 and 630 nm have higher intensity when excited with
254 nm than 365 nm UV light, which is consistent with the stronger
emission of (Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 when
excited with 254 nm UV light.
[0102] The integral intensities of the composite C-6 and the
corresponding mixture M-6 are a function of the crystallites size
and, hence, depend on the relative area of the grain boundaries and
the amounts of crystal lattice defects. The measurements of the
dynamic property lifetime (.tau.) of the same species show more
complex relations. It is proportional to the mass fraction and to
the crystallites size of the individual components.
Example 4
[0103] Single phase particulate materials of composition
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 and two two-phase
composite particulate materials of compositions
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12/(Y.sub.0.92Eu.sub.0.08).sub-
.4Al.sub.2O.sub.9 in different ratios as shown in Table 6 were
produced by spray pyrolysis. In addition, two physical mixtures
with compositions identical to those of the composite materials
were produced by mixing pure
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 in the desired ratios,
again as shown in Table 8.
TABLE-US-00008 TABLE 8 Sample ID code Composite
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12:(Y.sub.0.92Eu.sub-
.0.08).sub.4Al.sub.2O.sub.9 = C-7 91.4:8.6 wt % Composite
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12:(Y.sub.0.92Eu.sub-
.0.08).sub.4Al.sub.2O.sub.9 = C-8 21.8:78.2 wt % Mixture
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12:(Y.sub.0.92Eu.sub.0-
.08).sub.4Al.sub.2O.sub.9 = M-7 91.4:8.6 wt % Mixture
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12:(Y.sub.0.92Eu.sub.0-
.08).sub.4Al.sub.2O.sub.9 = M-8 21.8:78.2 wt %
[0104] Powder XRD analysis of the composite materials confirmed the
presence of two crystalline phases in both composite
materials--(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9, see FIG. 10.
Quantitative Rietveld analysis of the XRD patterns yielded the
exact compositions of the composites as given in Table 8.
[0105] Scanning electron microscopy (SEM-EDX) analyses confirmed
that both single phase components,
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9, were mixed within the
composite particles forming individual micro crystallites that are
comparable to those of the pure components (100-300 nm) made by the
same process, see FIG. 11.
[0106] Particles size distribution (PSD) studies confirmed that the
composite materials have a narrow PSD within the range 1-5 microns
and average particles diameter d-50 of about 2 microns, see Table
9.
TABLE-US-00009 TABLE 9 PSD (micrometers) of the composites C-7 and
C-8 Percentiles C-7 C-8 10% 0.96 0.75 50% 1.86 1.42 95% 4.61
5.13
[0107] The photoluminescence (PL) emission spectra of the
composites C-7 and C-8 after excitation with 365 and 254 nm UV
light are compared to those of pure
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 samples in FIG.
12.
[0108] The steady state PL spectra of the individual components
when excited with 365 nm UV show strong peaks with maxima at 595,
600, 615 and 635 nm for
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and only a weak peak
at 610 nm for (Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9,
respectively. In contrast, when excited with 254 nm UV, the
intensity of the emission spectra of
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 is virtually zero
while that of (Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 shows
strong peaks with maxima at 585-605, 615, 630 and 660 nm. The
spectra of the composites C-7 and C-8 and the mixtures M-7 and M-8
show strong peaks with maxima that coincide with the maxima for
(Y.sub.0.92Eu.sub.0.08).sub.3Al.sub.5O.sub.12 and
(Y.sub.0.92Eu.sub.0.08).sub.4Al.sub.2O.sub.9 when excited with 365
and 254 nm, respectively. This shows that PL spectra of the
composites are dominated by the emission of the component with the
heavier mass fraction which is consistent with the corresponding
compositions given in Table 8.
[0109] The integral intensities of all samples are a function of
the crystallites size and, hence, depend on the relative area of
the grain boundaries and the amounts of individual crystal lattices
defects. The measurements of the dynamic property lifetime (.tau.)
of the same species show more complex relations. It is proportional
to the mass fraction and to the crystallites size of the individual
components.
[0110] While the present invention has been described and
illustrated by reference to particular embodiments, those of
ordinary skill in the art will appreciate that the invention lends
itself to variations not necessarily illustrated herein. For this
reason, then, reference should be made solely to the appended
claims for purposes of determining the true scope of the present
invention.
* * * * *