U.S. patent application number 13/538745 was filed with the patent office on 2013-01-17 for luminescent phosphor compounds, articles including such compounds, and methods for their production and use.
This patent application is currently assigned to HONEYWELL INTERNATIONAL INC.. The applicant listed for this patent is James Kane, Carsten Lau, William Ross Rapoport. Invention is credited to James Kane, Carsten Lau, William Ross Rapoport.
Application Number | 20130015651 13/538745 |
Document ID | / |
Family ID | 47518513 |
Filed Date | 2013-01-17 |
United States Patent
Application |
20130015651 |
Kind Code |
A1 |
Lau; Carsten ; et
al. |
January 17, 2013 |
LUMINESCENT PHOSPHOR COMPOUNDS, ARTICLES INCLUDING SUCH COMPOUNDS,
AND METHODS FOR THEIR PRODUCTION AND USE
Abstract
Embodiments include luminescent phosphor compounds that include
one or more emitting ions and one or more disturbing ions, and
methods for their production. An emitting ion in the compound may
be characterized by a first decay time constant when the emitting
ion is undisturbed. However, a corresponding disturbing ion in the
compound, which is different from the emitting ion, causes the
emitting ion to have a pre-defined, target disturbed decay time
constant that is greater than zero and less than the first decay
time constant. An embodiment of an authentication system is
configured to measure the decay time constant of a phosphor
compound applied to an article, and to determine whether the decay
time constant corresponds to a phosphor compound that includes a
particular disturbing ion (e.g., in order to determine whether or
not the article is authentic).
Inventors: |
Lau; Carsten; (Garbsen,
DE) ; Kane; James; (Lawrenceville, NJ) ;
Rapoport; William Ross; (Bridgewater, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lau; Carsten
Kane; James
Rapoport; William Ross |
Garbsen
Lawrenceville
Bridgewater |
NJ
NJ |
DE
US
US |
|
|
Assignee: |
HONEYWELL INTERNATIONAL
INC.
Morristown
NJ
|
Family ID: |
47518513 |
Appl. No.: |
13/538745 |
Filed: |
June 29, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61508295 |
Jul 15, 2011 |
|
|
|
Current U.S.
Class: |
283/74 ;
252/301.4H; 252/301.4P; 252/301.4R; 428/389; 428/432; 428/469;
428/473; 428/537.5; 428/690; 442/59 |
Current CPC
Class: |
Y10T 428/2958 20150115;
C09K 11/08 20130101; C09K 11/77 20130101; B42D 25/36 20141001; B42D
25/29 20141001; B42D 25/382 20141001; Y10T 442/20 20150401; Y10T
428/31993 20150401; C09K 11/7774 20130101; B42D 25/00 20141001;
B42D 25/387 20141001; B42D 25/373 20141001; B41M 3/144
20130101 |
Class at
Publication: |
283/74 ;
252/301.4R; 252/301.4H; 252/301.4P; 428/690; 442/59; 428/432;
428/389; 428/469; 428/473; 428/537.5 |
International
Class: |
B42D 15/00 20060101
B42D015/00; C09K 11/78 20060101 C09K011/78; C09K 11/81 20060101
C09K011/81; C09K 11/85 20060101 C09K011/85; C09K 11/86 20060101
C09K011/86; B32B 29/00 20060101 B32B029/00; B32B 5/02 20060101
B32B005/02; B32B 17/06 20060101 B32B017/06; B32B 9/06 20060101
B32B009/06; B32B 27/06 20060101 B32B027/06; B32B 9/02 20060101
B32B009/02; C09K 11/77 20060101 C09K011/77; B32B 9/04 20060101
B32B009/04 |
Claims
1. A luminescent phosphor compound for security applications
comprising: one or more emitting ions and one or more disturbing
ions, wherein the one or more emitting ions have one or more first
decay time constants when the one or more emitting ions are
undisturbed, the one or more disturbing ions are different from the
one or more emitting ions, and the one or more disturbing ions are
included in the phosphor compound in a quantity that will cause at
least one of the one or more emitting ions to have a pre-defined,
target disturbed decay time constant that is greater than zero and
less than a corresponding one of the one or more first decay time
constants, and wherein the first decay time constant and the target
disturbed decay time constants can be distinguished by an
authentication device.
2. The luminescent phosphor compound of claim 1, wherein the one or
more emitting ions include one or more ions of one or more elements
selected from a group consisting of chromium, cerium, praseodymium,
neodymium, samarium, europium, gadolinium, terbium, dysprosium,
holmium, erbium, thulium, and ytterbium.
3. The luminescent phosphor compound of claim 1, wherein the one or
more disturbing ions include one or more ions of one or more
elements selected from a group consisting of chromium, manganese,
cerium, praseodymium, neodymium, samarium, europium, terbium,
dysprosium, holmium, erbium, thulium, ytterbium, iron, cobalt, and
nickel.
4. The luminescent phosphor compound of claim 1, wherein the one or
more disturbing ions include one or more ions of one or more
elements selected from a group consisting of praseodymium,
samarium, europium, terbium, and dysprosium.
5. The luminescent phosphor compound of claim 1, wherein one or
more disturbing ions cause the at least one of the one or more
emitting ions to have the target disturbed decay time constant by
absorbing energy discharged by the at least one of the one or more
emitting ions in transitioning from a storage level to a lower
energy level, and by discharging the energy non-radiatively.
6. The luminescent phosphor compound of claim 1, wherein at least
one of the one or more first decay time constants is in a range of
0.5 milliseconds to 10 milliseconds.
7. The luminescent phosphor compound of claim 1, wherein the target
disturbed decay time constant is in a range of 0.2 milliseconds to
8 milliseconds.
8. The luminescent phosphor compound of claim 1, wherein the target
disturbed decay time constant is within a range of 20 to 80 percent
of at least one of the one or more first decay time constants.
9. The luminescent phosphor compound of claim 1, wherein the
luminescent phosphor compound further comprises: one or more
additional emitting ions, which have one or more additional first
decay time constants when the one or more additional emitting ions
are undisturbed, wherein the one or more disturbing ions or one or
more additional disturbing ions cause at least one of the one or
more additional emitting ions to have one or more additional,
pre-defined target disturbed decay time constants that are greater
than zero and less than corresponding ones of the one or more
additional first decay time constants.
10. The luminescent phosphor compound of claim 1, wherein the
luminescent phosphor compound further comprises: one or more
additional disturbing ions, wherein the one or more disturbing ions
or the one or more additional disturbing ions cause at least one of
the one or more emitting ions or one or more additional emitting
ions, which have one or more additional first decay time constants
when the one or more additional emitting ions are undisturbed, to
have one or more additional, pre-defined target disturbed decay
time constants that are greater than zero and less than
corresponding ones of the one or more additional first decay time
constants.
11. The luminescent phosphor compound of claim 1, further
comprising a phosphor host crystal lattice material selected from a
group consisting of an oxide, a fluoride, an oxysulfide, a halide,
a borate, a silicate, a gallate, a phosphate, a vanadate, an
oxyhalide, an aluminate, a molybdate, a tungstate, a garnet, a
niobate, and a combination of the aforementioned host crystal
lattice materials.
12. A method for producing a luminescent phosphor compound
comprising the steps of: obtaining a baseline phosphor compound
that includes a phosphor host crystal lattice material, one or more
emitting ions, and a quantity of rare earth impurities, wherein the
baseline phosphor compound is characterized by one or more first
decay time constants; synthesizing a disturbed phosphor compound
that includes the phosphor host crystal lattice material, the one
or more emitting ions, the quantity of rare earth impurities, and a
quantity of one or more disturbing ions; measuring one or more
second decay time constants of the disturbed phosphor compound;
determining whether the one or more second decay time constants are
substantially equal to one or more target disturbed decay time
constants that are greater than zero and less than corresponding
ones of the one or more first decay time constants; and when at
least one of the one or more second decay time constants is not
substantially equal to the one or more target disturbed decay time
constants, repeating the synthesizing, measuring, and determining
steps for an additional candidate disturbed phosphor compound that
has an adjusted quantity of the one or more disturbing ions that is
different from the initial quantity.
13. The method of claim 12, wherein repeating the synthesizing step
comprises: increasing the quantity of the one or more disturbing
ions when the one or more second decay time constants are greater
than the one or more target disturbed decay time constants; and
decreasing the quantity of the one or more disturbing ions when the
one or more second decay time constants are less than the one or
more target disturbed decay time constants.
14. The method of claim 12, wherein the one or more emitting ions
include one or more ions elements selected from a group consisting
of chromium, cerium, praseodymium, neodymium, samarium, europium,
gadolinium, terbium, dysprosium, holmium, erbium, thulium, and
ytterbium.
15. The method of claim 12, wherein the one or more disturbing ions
include one or more ions of elements selected from a group
consisting of chromium, manganese, cerium, praseodymium, neodymium,
samarium, europium, terbium, dysprosium, holmium, erbium, thulium,
ytterbium, iron, cobalt, and nickel.
16. An article comprising: a substrate; and an authentication
feature on a surface of the substrate or integrated within the
substrate, wherein the authentication feature includes a
luminescent phosphor compound comprising one or more emitting ions
and one or more disturbing ions, wherein the one or more emitting
ions have one or more first decay time constants when the one or
more emitting ions are undisturbed, and the one or more disturbing
ions are different from the one or more emitting ions, and the one
or more disturbing ions are included in the phosphor compound in a
quantity that will cause at least one of the one or more emitting
ions to have a pre-defined, target disturbed decay time constant
that is greater than zero and less than a corresponding one of the
one or more first decay time constants.
17. The article of claim 16, wherein the article is selected from a
group consisting of an identification card, a driver's license, a
passport, identity papers, a banknote, a check, a document, a
paper, a stock certificate, a packaging component, a credit card, a
bank card, a label, a seal, a postage stamp, a liquid, a human, an
animal, and a biological sample.
18. The article of claim 16, wherein the substrate includes one or
more materials selected from a group consisting of paper, a
polymer, glass, a metal, a textile, and a fiber.
19. The article of claim 16, wherein the one or more emitting ions
include one or more ions elements selected from a group consisting
of chromium, cerium, praseodymium, neodymium, samarium, europium,
gadolinium, terbium, dysprosium, holmium, erbium, thulium, and
ytterbium.
20. The article of claim 16, wherein the one or more disturbing
ions include one or more ions of elements selected from a group
consisting of chromium, manganese, cerium, praseodymium, neodymium,
samarium, europium, terbium, dysprosium, holmium, erbium, thulium,
ytterbium, iron, cobalt, and nickel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/508,295, filed Jul. 15, 2011, currently
pending.
TECHNICAL FIELD
[0002] The present invention generally relates to radiation
emitting compounds, articles including such compounds, and methods
for their production and use and, more particularly relates to
luminescent phosphor compounds, articles including such compounds
as authentication features, and methods for their production and
use.
BACKGROUND
[0003] A luminescent phosphor compound is a compound that is
capable of emitting detectable quantities of radiation in the
infrared, visible, and/or ultraviolet spectrums upon excitation of
the compound by an external energy source. A typical luminescent
phosphor compound includes at least a host crystal lattice, an
emitting ion (e.g., of a rare earth metal), and in some cases, a
"sensitizing" ion (e.g., of a transition metal or of a different
rare earth metal that can absorb and transfer the energy to the
emitting rare earth metal ion). The production of radiation by a
phosphor compound is accomplished by absorption of incident
radiation by the emitting ion(s) or by either or both the host
crystal lattice and the sensitizing ion(s), energy transfer from
the host crystal lattice/sensitizing ion(s) to the emitting ion(s),
and radiation of the transferred energy by the emitting ion(s).
[0004] The selected components of a phosphor compound cause the
compound to have particular properties, including specific
wavelengths for its excitation energy ("exciting radiation"), and
specific spectral position(s) for peak(s) in energy emitted by the
emitting ions of the phosphor compound ("emitted radiation"). Not
every ion will have emission in all host crystal lattices. There
are many examples in which radiation that has the potential for
emission is quenched or the energy transfer from the absorbing ions
or the host crystal lattice to the emitting ions is so poor that
the radiation effects are barely observable. In other host crystal
lattices, the radiation effects can be very large and with quantum
efficiency near unity.
[0005] For a specific phosphor compound that does produce
observable emitted radiation, the spectral position(s) of the
peak(s) in its emitted radiation (i.e., its "spectral signature")
may be used to uniquely identify the phosphor compound from
different compounds. Primarily, the spectral signature is due to
the rare earth ion(s). However, spectral perturbations may be
present due to the influence of the host crystal lattice on the
various ions, typically through crystal field strength and
splitting. This holds true for the temporal behavior of the emitted
radiation, as well.
[0006] The unique spectral properties of some phosphor compounds
make them well suited for use in authenticating or identifying
articles of particular value or importance (e.g., banknotes,
passports, biological samples, and so on). Accordingly, luminescent
phosphor compounds with known spectral signatures have been
incorporated into various types of articles to enhance the ability
to detect forgeries or counterfeit copies of such articles, or to
track and identify the articles. For example, luminescent phosphor
compounds have been incorporated into various types of articles in
the form of additives, coatings, and printed or otherwise applied
authentication features.
[0007] An article that includes a luminescent phosphor compound may
be authenticated using specially designed authentication equipment.
More particularly, a manufacturer may incorporate a known phosphor
compound into its "authentic" articles. Such a phosphor compound
may be referred to as an "authenticating" phosphor compound (i.e.,
a phosphor compound having known spectral and possibly known
temporal properties, as well as particular excitation conditions,
which is used for identification and/or authentication purposes).
Authentication equipment configured to detect the authenticity of
such articles would have knowledge (e.g., stored information) of
the wavelengths of absorbable exciting radiation and the spectral
properties of emitted radiation associated with the authenticating
phosphor compound. When provided with a sample article for
authentication, the authentication equipment exposes the article to
exciting radiation having wavelengths that correspond with the
known wavelengths of absorption features of the luminescent
phosphor that lead directly or indirectly to the desired emitted
radiation. The authentication equipment senses and characterizes
the spectral parameters for any emitted radiation that may be
produced by the article. When the spectral signal of detected
emitted radiation is within the authenticating parameter range of
the detection apparatus that corresponds with the authenticating
phosphor compound (referred to as the "detection parameter space"),
the article may be considered authentic. Conversely, when the
authentication equipment fails to sense signals expected within the
detection parameter space, the article may be considered
unauthentic (e.g., a forged or counterfeited article).
[0008] The above-described techniques are highly-effective at
detecting and thwarting relatively unsophisticated forgery and
counterfeiting activities. However, individuals with the
appropriate resources and equipment may be able to reverse engineer
an authentication system and/or to employ spectrometry techniques
in order to determine the components of some phosphor compounds.
The phosphor compounds may then be reproduced and applied to
unauthentic articles, thus compromising the authentication benefits
that may otherwise be provided by a particular phosphor compound.
Accordingly, although a number of phosphor compounds have been
developed to facilitate article authentication in the
above-described manner, it is desirable to develop additional
compounds and techniques for authenticating articles, which may
render forgery and counterfeiting activities more difficult, and/or
which may prove beneficial for identifying and tracking articles of
particular interest. Furthermore, other desirable features and
characteristics of the present invention will become apparent from
the subsequent detailed description of the invention and the
appended claims, taken in conjunction with the accompanying
drawings and this background of the invention.
BRIEF SUMMARY
[0009] An embodiment of a luminescent phosphor compound includes an
emitting ion and a disturbing ion that is different from the
emitting ion and optionally a sensitizing ion. The emitting ion has
a first decay time constant when the emitting ion is undisturbed.
The disturbing ion causes the emitting ion to have a pre-defined,
disturbed decay time constant that is greater than zero and less
than the first decay time constant.
[0010] Another embodiment includes a luminescent phosphor compound
for security applications, which includes one or more emitting ions
and one or more disturbing ions. The one or more emitting ions have
one or more first decay time constants when the one or more
emitting ions are undisturbed. The one or more disturbing ions are
different from the one or more emitting ions, and the one or more
disturbing ions are included in the phosphor compound in a quantity
that will cause at least one of the one or more emitting ions to
have a pre-defined, target disturbed decay time constant that is
greater than zero and less than a corresponding one of the one or
more first decay time constants. The first decay time constant and
the target disturbed decay time constant can be distinguished by an
authentication device.
[0011] Another embodiment includes a method for producing a
luminescent phosphor compound that includes the step of obtaining a
baseline phosphor compound that includes a phosphor host crystal
lattice material, one or more emitting ions, and a quantity of rare
earth impurities, wherein the baseline phosphor compound is
characterized by one or more first decay time constants. The method
further includes synthesizing a disturbed phosphor compound that
includes the phosphor host crystal lattice material, the one or
more emitting ions, the quantity of rare earth impurities, and a
quantity of one or more disturbing ions. One or more second decay
time constants of the disturbed phosphor compound are measured. A
determination is made whether the one or more second decay time
constants are substantially equal to one or more target disturbed
decay time constants that are greater than zero and less than
corresponding ones of the one or more first decay time constants.
When at least one of the one or more second decay time constants is
not substantially equal to the one or more target disturbed decay
time constants, the synthesizing, measuring, and determining steps
are repeated for an additional candidate disturbed phosphor
compound that has an adjusted quantity of the one or more
disturbing ions that is different from the initial quantity.
[0012] An embodiment of an article includes a substrate and an
authentication feature on a surface of the substrate or integrated
within the substrate. The authentication feature includes a
luminescent phosphor compound comprising one or more emitting ions
and one or more disturbing ions and optionally one or more
sensitizing ions. The one or more emitting ions have one or more
first decay time constants when the one or more emitting ions are
undisturbed. The one or more disturbing ions are different from the
one or more emitting ions, and the one or more disturbing ions are
included in the phosphor compound in a quantity that will cause at
least one of the one or more emitting ions to have a pre-defined,
target disturbed decay time constant that is greater than zero and
less than the corresponding one of the one or more first decay time
constants.
[0013] An embodiment of a method for performing authentication of
an article includes the steps of exposing the article to exciting
radiation, discontinuing provision of the exciting radiation, and
detecting emitted radiation from the article at one or more
detection intervals. The method further includes the steps of
performing an analysis of information characterizing the emitted
radiation, and determining, based on the analysis, whether one or
more pre-defined, target disturbed decay times are within specified
ranges for a phosphor composition that includes one or more
emitting ions and one or more disturbing ions. When the one or more
decay times are within the specified ranges, the article is
identified as authentic. When the one or more decay times are not
within the specified ranges, the article is identified as
unauthentic.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Embodiments of the present invention will hereinafter be
described in conjunction with the following figures, wherein like
numerals denote like elements, and wherein:
[0015] FIG. 1 depicts potential components of a phosphor compound,
according to various example embodiments;
[0016] FIG. 2 is a graph illustrating decay time constant as a
function of disturbing ion concentration for an example phosphor
composition, in accordance with an example embodiment;
[0017] FIG. 3 is a flowchart of a method for producing a phosphor
compound, in accordance with an example embodiment;
[0018] FIG. 4 is a system for authenticating an article, in
accordance with an example embodiment;
[0019] FIG. 5 is a flowchart of a method for performing
authentication of an article that may include a phosphor compound,
in accordance with an example embodiment; and
[0020] FIG. 6 depicts a cross-sectional view of an article with
phosphor-containing, embedded and printed authentication features,
according to an example embodiment.
DETAILED DESCRIPTION
[0021] The following detailed description of various embodiments of
the invention is merely exemplary in nature and is not intended to
limit the inventive subject matter or the application and uses of
the inventive subject matter. Furthermore, there is no intention to
be bound by any theory presented in the preceding background or the
following detailed description.
[0022] Luminescent phosphor compounds, articles incorporating such
compounds, and methods of their manufacture and use are described
herein. The below-described phosphor compounds may be used for a
variety of applications including, but not limited to,
incorporating such phosphor compounds into articles to enhance
article authentication efforts. Embodiments of phosphor compounds,
described below, each include one or more "emitting ions," one or
more "disturbing ions," and optionally one or more sensitizing
ions. When one of these phosphor compounds is exposed to exciting
radiation, the exciting radiation may be absorbed directly by one
or more of the emitting ions, and/or optionally by one or more
sensitizing ions and/or by the host crystal lattice with a
subsequent transfer of the energy to one or more of the emitting
ions. In whichever manner the exciting radiation is absorbed, the
emitting ion(s) of the phosphor compound produces emitted radiation
having a unique spectral signature and a measurable decay time
constant. Without the disturbing ion(s), the emitted radiation
produced by the phosphor compound has a first decay time constant.
With the disturbing ion(s), however, the emitted radiation produced
by the phosphor compound has a second, non-zero decay time
constant, which is different from the first decay time constant
(e.g., shorter than the first decay time constant). The magnitude
of the reduction in the value of the decay time constant is a
function of the type(s) of disturbing ion(s), the nature(s) of the
disturbing ion(s), and the amount(s) of the disturbing ion(s)
substituted into the crystal lattice.
[0023] According to an embodiment, the quantity (or quantities) of
disturbing ion(s) substituted into an acquired lot of a host
crystal lattice is determined empirically based on an assessment of
the raw lot stock (also referred to as the "phosphor raw
materials," a "normal production phosphor," or a "baseline phosphor
compound" herein), which consists of the host crystal lattice, the
emitting ion(s), (optionally) the sensitizing ion(s), and a
quantity of rare earth impurities. The quantity (or quantities) of
disturbing ion(s) substituted into the crystal host lattice is
determined based on the assessment of the phosphor raw materials in
order to achieve a pre-defined, target decay time constant for a
phosphor compound being synthesized (referred to below as a "target
disturbed decay time constant").
[0024] As is known, the impurity levels can be very widely varying
in phosphor raw materials that may be used in the making of a
phosphor compound (e.g., raw materials obtained by a producer of
normal production phosphors). Available phosphor raw materials are
typically specified to be 99%, 99.9%, 99.95%, 99.99% or 99.999%
pure. This number gives the (weight) percentage of a desired rare
earth element (e.g., the desired emitting and sensitizing ions) in
a total of all the rare earth elements, all expressed as oxides,
which is typically abbreviated and referred to as "TREO" (Total
Rare Earth Oxides) in the certificates of analysis. In the case of
a 99.9% pure material, for example, the remainder is 0.1% or 1000
ppm (parts per million).
[0025] The remainder of the rare earth elements is made up of a
mixture of other rare earth element impurities (i.e., rare earth
elements other than the desired emitting and sensitizing ions).
More particularly, the remainder includes several, typically all,
of the rare earth ions. The relative concentrations of the rare
earth ions depend on the desired rare earth raw material. One may
expect that the closer the elements are in their properties, the
more difficult they are to separate from the desired rare earth
element. In general, rare earth elements that are close to each
other in the periodic table are more difficult to separate,
although that is not always the case. In addition, the impurity
pattern may change depending on the composition of the ore used to
generate the phosphor raw materials. That is, the rare earth
distribution pattern of the ore may influence the impurity pattern
in the rare earth raw material that goes into the synthesis of the
phosphor raw materials. Accordingly, it is very unlikely, over
time, to receive phosphor raw materials having the same starting
pattern and impurity amounts.
[0026] Referring again to the case of a 99.9% pure material, the
quantity of impurities is substantial when compared with the
quantities of emitting ions (and optionally sensitizing ions) that
are deliberately doped into a host lattice material. As will be
indicated in more detail below, such a quantity is even more
substantial when compared with quantities of one or more disturbing
ions that are substituted into the host crystal lattice, according
to an embodiment. However, the cost of phosphor raw materials
increases significantly as the purity level increases. For example,
the cost of ultra-pure material (e.g., 99.999% pure) is extremely
expensive, while the cost of reasonably pure material (e.g., 99.9%
pure) is substantially less expensive. Therefore, a phosphor
compound manufacturer may desire to use a least pure material with
which they may practically produce a phosphor compound having
desired characteristics. The amount and nature (i.e., type) of the
impurity rare earth ions, however, may then be different from raw
material lot to raw material lot, and also in many cases not fully
analyzed.
[0027] Not all impurity ions are of the same strength as disturbing
ion(s) that are substituted into a host crystal lattice, according
to an embodiment. In addition, not all impurity ions affect every
emitting ion, and they may not have the same influence in every
host crystal lattice. According to an embodiment, phosphor compound
synthesis methods are employed to ensure a substantially constant
quality of a synthesized phosphor compound. More particularly,
embodiments include methods for producing a phosphor compound
characterized by a decay time constant that is distinguishable from
a decay time constant of a phosphor made of the corresponding
phosphor raw materials, while being substantially equal to a
pre-defined, target decay time constant.
[0028] In addition, embodiments include synthesized phosphor
compounds that are characterized by a target decay time constant
despite the presence of a varying amount of impurity ions in
different lots of phosphor raw materials. In some cases, a phosphor
material lot may be of very low purity and/or may have such a large
percentage of naturally occurring rare earth ions (other than the
desired emitting ions) that the decay time constant of the phosphor
materials is actually below the target, disturbed decay time
constant. Because the decay time constant decreases as the quantity
of disturbing ions is increased (as will be discussed in
conjunction with FIG. 2), such phosphor raw materials would not be
convenient for use in synthesizing a disturbed phosphor compound
with the target decay time constant, unless additional processing
steps are performed to further purify the phosphor raw materials.
Selection of phosphor raw materials with a sufficiently high purity
and a reasonable cost is a cost/performance balance that can be
actively adjusted to create a phosphor compound with desired
properties (e.g., a desired, pre-defined, target decay time
constant) in an economical manner. According to an embodiment,
phosphor raw materials are selected, which have a decay time
constant that is higher that the target, disturbed decay time
constant, and disturbing ions are added to lower the decay time
constant of the synthesized phosphor compound to the target,
disturbed decay time constant.
[0029] The embodiments of phosphor compounds described below
increase the diversity of available materials that may be used for
authentication. The altered decay time constants that characterize
the phosphor compound embodiments discussed herein may be used, in
addition to spectral position, as a measurable quantity for the
purpose of authentication.
[0030] FIG. 1 depicts potential components of a phosphor compound
100, according to various example embodiments. According to various
embodiments, phosphor compound 100 includes a host crystal lattice
material 130, one or more emitting ions 110, and one or more
disturbing ions 120. Phosphor compound 110 also may include other
materials (e.g., one or more sensitizing ions), as well, although
such other materials are not specifically discussed herein.
[0031] As mentioned above, there are at least three mechanisms for
an emitting ion 110 to receive energy for subsequent radiation. For
example, in an embodiment, the emitting ion(s) 110 may be capable
of directly absorbing exciting radiation, and the emitting ion 110
may thereafter radiate at least some of the absorbed energy
(typically at a different wavelength from the exciting radiation).
In other embodiments, the host crystal lattice material 130 or an
ion thereof (e.g., a vanadate ion) may be capable of absorbing
exciting radiation directly, and transferring energy to the
emitting ion(s) 110. In yet another embodiment, the host crystal
lattice material 130 may contain one or more "lattice ions" that
may be substituted by one or more emitting ions 110 and disturbing
ions 120, and optionally one or more sensitizing ions that may
absorb exciting radiation and transfer the resulting energy to the
emitting ion(s) 110. Host crystal lattice absorption may be useful,
in some cases, although host crystal lattice absorption is not
particularly useful in a majority of cases. More typically, a
transition metal ion (e.g., chromium) or a rare earth metal ion
(e.g., erbium) is used as a sensitizing ion. These elements also
may act as emitting ions, or they also may transfer the energy to
other ions (e.g., emitting ion(s) 110), which then radiate the
transferred energy. Virtually all host crystal lattice materials
may act as absorbers in the ultraviolet range because the exciting
photon energy is very high in this range. However, this phenomenon
may not yield any emission at all from incorporated desired
ions.
[0032] The lattice ions that may be replaced are ions within the
host crystal lattice material 130 that may be substituted by one or
more sensitizing ions, if included, one or more emitting ions 110,
and one or more disturbing ions 120, up to and including 100%
substitution. 100% substitution is rare since most emitting ions
are concentration quenched well below a 100% substitution level.
However, there are a few notable exceptions in which particular
ions allow for greater substitutions since they can more easily be
separated in the host crystal lattice as described below. The
emitting and disturbing ions 110, 120 may be substituted at very
low substitution percentages (e.g., doped at less than 1%), medium
substitution percentages (e.g., from 1% to 20%), or high
substitution percentages (e.g., from 20% to 100%). For example, but
not by way of limitation, neodymium (Nd) may be substituted at
relatively low percentages up to 1.5%, holmium (Ho) and ytterbium
(Yb) may be substituted at medium percentages up to 20%, and erbium
(Er) may be substituted at relatively high percentages up to 60%,
although these and other ions may be substituted at different
percentages, as well. As used herein, the term "substituted" means
substituted at any percentage, including low, medium, and high
substitution percentages. The amount of each ion substituted into a
host lattice material is generally described in terms of atomic
percent, where the number of ions of the host lattice material that
may be replaced by sensitizing, emitting and/or disturbing ions is
equal to 100%. An ion of a host material that allows for
replacement with sensitizing, emitting and/or disturbing ions may
typically have similar size, similar loading, and similar
coordination preference as the ions it will be replaced with. As
various positions within a host crystal lattice may occur, the ions
on each of these positions will be accounted for 100 atomic
percent.
[0033] The host crystal lattice material 130 comprises a material
into which emitting ions 110 and disturbing ions 120 and optionally
sensitizing agents are incorporated (e.g., substituted). More
particularly, the host crystal lattice material 130 may be in the
form of a crystal lattice into which different chemical
constituents may substitute various positions within the lattice.
In various embodiments, the host crystal lattice material 130
includes a material selected from a group consisting of an oxide, a
fluoride, an oxysulfide, a halide, a borate, a silicate, a gallate,
a phosphate, a vanadate, an oxyhalide, an aluminate, a molybdate, a
tungstate, a garnet, and a niobate, although other host crystal
lattice materials may be used, as well. For example, but not by way
of limitation, the host crystal lattice 130 may include a yttrium
(Y) aluminum garnet (YAG, or Y.sub.3Al.sub.5O.sub.12), yttrium
oxysulfide (YOS, or Y.sub.2O.sub.2S), a gadolinium (Gd) gallium
garnet (GGG, Gd.sub.3Ga.sub.5O.sub.12), or other materials.
[0034] In various embodiments, the total concentration of emitting
ion(s) 110 substituted into the host crystal lattice material 130
is sufficient to cause the phosphor compound to produce a
detectable emission after being appropriately subjected to exciting
radiation. For example, the total concentration of emitting ion(s)
110 substituted in the host crystal lattice material may be in a
range from about 0.095 atomic percent to about 99.995 atomic
percent. However, the concentration of emitting ion(s) 110 that may
be substituted while still producing the functionality of the
phosphor compound (e.g., the functionality of producing an emission
upon exposure to exciting radiation) depends on the type of ion
that is being substituted. In other words, some ions may be
substituted at relatively high percentages while still maintaining
the functionality of the phosphor compound, but the functionality
may be defeated if other ions are substituted at the same,
relatively high percentages.
[0035] According to various embodiments, the emitting ion(s) 110
include one or more ions of elements selected from a group
consisting of chromium (Cr), cerium (Ce), praseodymium (Pr),
neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb),
dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and
ytterbium (Yb). For example, one or more of the emitting ion(s) 110
may have +3 valences, in an embodiment, although one or more of the
emitting ion(s) 110 may have different valences (e.g., +2 and/or
+4), in other embodiments.
[0036] In a phosphor compound according to any of a number of
embodiments, the disturbing ion(s) 120 within the phosphor compound
100 are different from the emitting ion(s) 110. The total
concentration of disturbing ion(s) 120 substituted into the host
crystal lattice material 130 may be in a range from about 0.0003
atomic percent to about 0.5 atomic percent, and is preferably
between about 0.001 and 0.2 atomic percent or more, in various
embodiments, although the disturbing ion(s) 120 may be included in
lower or higher atomic percentages, as well. The concentration of
disturbing ion(s) 120 substituted into the host crystal lattice
material 130 may be greater than any background impurity level for
the raw materials, while being at a sufficient concentration to
achieve a desired decay time constant. As will be explained in more
detail below, the concentration of disturbing ion(s) 120 is
directly proportional to the reduction in the decay time constant
for the phosphor compound. A benefit of adding the disturbing
ion(s) 120 in lower concentrations is that the disturbing ion(s)
120 may be very difficult to detect without access to sophisticated
equipment and techniques (e.g., Glow Discharge Mass Spectroscopy
(GDMS)). Accordingly, the elemental composition of a phosphor
compound, according to an embodiment, may be very difficult to
reverse engineer. For example, typical energy dispersive X-ray
microanalysis, electron backscatter diffraction, or micro X-ray
fluorescence systems may not be capable of quantifying elements
having low (e.g., 1% or less) concentrations in a phosphor
compound.
[0037] According to various embodiments, the disturbing ion(s) 120
include one or more ions of elements selected from a group
consisting of chromium (Cr), manganese (Mn), cerium (Ce),
praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu),
terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium
(Tm), ytterbium (Yb), iron (Fe), cobalt (Co), and nickel (Ni). For
example, one or more of the disturbing ion(s) 120 may have +3
valences, in an embodiment, although one or more of the disturbing
ion(s) 120 may have different valences (e.g., +2 and/or +4), in
other embodiments.
[0038] After exposure to exciting radiation, the emitting ion(s)
110 within the phosphor compound emit photons, and the intensity of
the emission over time may be observed. Upon removal of the
exciting radiation, the intensity of the emission decays over time,
and the rate of decay for each emitting ion 110 can be
characterized by a decay time constant. For example, for a simple
exponential decay in emission intensity, the decay time constant
can be represented by the constant .tau. in the equation:
I(t)=I.sub.0e.sup.-t/.tau., (Equation 1)
where t denotes time, I denotes the emission intensity at time t,
and I.sub.0 denotes the emission intensity at t=0 (e.g., t=0 may
correspond to the instant when the provision of exciting radiation
is discontinued). Although the emission intensity for some phosphor
compounds may decay according to the above, simple exponential
formula, the emission intensity for other phosphor compounds may be
affected by multiple exponential decays (e.g., when multiple
mechanisms affecting the decay are present). According to an
embodiment, each emitting ion 110 would be characterized by a first
decay time constant if the emitting ion were "undisturbed" within
the phosphor compound (e.g., as in a normal production phosphor).
The term "undisturbed," when applied to an emitting ion, refers to
the emitting ion being included in a phosphor compound that lacks a
corresponding disturbing ion that otherwise may have a significant
effect on the emissions of the emitting ion, where a "significant
effect" means an effect that is measurably greater than effects
that may otherwise be produced due to rare earth impurities (e.g.,
impurities present in small amounts, such as a few ppm) present in
the normal production phosphor. This decay time constant associated
with an undisturbed emitting ion is referred to herein as an
"undisturbed decay time constant," which characterizes a phosphor
compound (e.g., a normal production phosphor) that does not include
any disturbing ion(s) 120 beyond the level of rare earth impurities
that may be associated with the raw materials. As discussed
previously, the level of rare earth impurities in an "undisturbed"
phosphor compound depends on the purity level of the phosphor raw
materials. Although a relatively low level of impurities may
produce only minor changes to emitted radiation temporal properties
of the phosphor compound, higher levels of impurities may produce
more pronounced changes in the temporal properties of the phosphor
compound.
[0039] Embodiments include methods for producing disturbed phosphor
compounds characterized by emitted radiation temporal properties
(e.g., a target disturbed decay time constant) that are
significantly different from the emitted radiation temporal
properties of the corresponding normal production phosphor. In an
embodiment, addition of one or more disturbing ion(s) produces a
significant change in the emitted radiation temporal properties of
the corresponding normal production phosphor. As used herein, and
according to an embodiment, a "significant change" in an emitted
radiation temporal property may be defined as a reduction in a
decay time constant of a phosphor compound of 20% or more.
According to another embodiment, a "significant change" in an
emitted radiation temporal property may be defined as a reduction
in a decay time constant of a phosphor compound of only 10% or
more. As used herein, the term "undisturbed decay time constant"
means a decay time constant associated with an emission produced by
an emitting ion (e.g., one of emitting ions 110) that is present in
a phosphor compound that does not include a disturbing ion (e.g.,
one of disturbing ions 120) beyond the level of rare earth
impurities that may be associated with the phosphor raw materials
(or a normal production phosphor).
[0040] According to various embodiments, a phosphor compound (e.g.,
phosphor compound 100) does, however, include one or more
disturbing ions 120, and each disturbing ion 120 causes a
"significant change" to the undisturbed decay time constant for at
least one of the emitting ion(s) 110. According to an embodiment,
for a particular host crystal lattice and emitting ion 110, a
disturbing ion 120 is chosen that will produce a desired
significant change in the decay time constant for the phosphor
compound. Some disturbing ion(s) 120 may cause a significant change
to the decay time constant when included in a particular host
crystal lattice with a particular emitting ion 110, and other
disturbing ion(s) 120 may not cause a significant change to the
decay time constant (although those other disturbing ion(s) 120 may
cause significant changes when included in a different host crystal
lattice or with a different emitting ion 110). A decay time
constant that is altered by a disturbing ion 120 is referred to
herein as a "disturbed decay time constant." A "target disturbed
decay time constant" is a disturbed decay time constant that has a
pre-defined value. According to a particular embodiment, a quantity
of a disturbing ion 120 (or multiple disturbing ions) is
substituted into the host crystal lattice material 130 to cause an
emitting ion 110 (or multiple emitting ions) to have a disturbed
decay time constant (or more specifically, a target disturbed decay
time constant) that is greater than zero and less than the
undisturbed decay time constant for the emitting ion 110. In other
words, the disturbing ion(s) 120 have the effect of lowering the
decay time constant(s) of the emitting ion(s) 110, without
completely quenching the emissions. The quantity of disturbing
ion(s) 120 substituted into the host crystal lattice 130 in order
to achieve a target disturbed decay time constant for the phosphor
compound 100 depends on the level of impurities in the
corresponding phosphor raw materials, and this quantity is
determined empirically, as will be discussed in more detail below.
In various embodiments, the decrease in the decay time constant may
occur in nearly a linear fashion after a certain amount of
disturbing ion(s) 120 are added. The correlation also may follow a
non-linear equation, such as, but not limited to, a quadratic
function. A relationship may be predicted between the quantity of a
disturbing ion and the decay time constant. Accordingly, a phosphor
compound developer may pre-select a desired value for the target
disturbed decay time constant, and may produce a synthesized
phosphor compound that achieves that value by selecting from a
number of possible disturbing ions and predicting the quantities at
which they are included in the compound.
[0041] As will also be discussed in more detail below, an
authentication system (e.g., system 400, FIG. 4) is capable of
measuring decay time constants for phosphor compounds (e.g.,
phosphor compound 100). When a measured decay time constant for a
particular emitting ion 110 corresponds to a disturbed decay time
constant, the phosphor compound may be differentiated from a normal
production phosphor (i.e., the same compound that lacks the
disturbing ion(s) 120, which would have an undisturbed decay time
constant). More specifically, when the measured decay time constant
is substantially equal to a target disturbed decay time constant,
the phosphor compound may be considered to be an authenticating
phosphor compound. According to an embodiment, "substantially
equal" in this context means that the measured decay time constant
is within a relatively narrow range of decay time constants
corresponding to the target disturbed decay time constant. In order
to achieve a high level of security, it may be desirable for the
range of target disturbed decay time constants to be relatively
narrow (e.g., an upper limit of the range is within 5%, 10%, or
some other percentage of the lower limit of the range). In at least
some embodiments, the spectral signature of the phosphor compound
with disturbing ion(s) 120 may be substantially the same (in
wavelength) as the spectral signature of a corresponding normal
production phosphor, despite the differing decay time constants,
although this may not always be the case. Regardless, the quantity
of disturbing ion(s) 120 included in the phosphor compound 100
desirably is sufficient to enable a disturbed decay time constant
to be differentiated from a corresponding undisturbed decay time
constant. In addition, the difference between the disturbed and
undisturbed decay time constants should be sufficient to account
for production purity variations and potential measurement errors.
Accordingly, the various embodiments include phosphor compounds 100
with disturbed decay time constants (and more specifically target
disturbed decay time constants) that are detectably different from
the undisturbed decay time constants of corresponding normal
production phosphors, thus providing additional phosphor compounds
that may be used for authentication and other purposes.
[0042] The term "disturbed phosphor compound" means a phosphor
compound that includes one or more disturbing ions that have been
intentionally added to the phosphor compound, according to an
embodiment, whereas an "undisturbed phosphor compound" refers to
the same phosphor compound without the disturbing ions (beyond the
level of impurities that may be associated with the raw materials).
In some cases, an emitting ion (e.g., one of emitting ions 110,
FIG. 1) is excited via a direct absorption process, which includes
providing exciting radiation within the absorption band for the
emitting ion. Alternatively, the host crystal lattice or a
sensitizing ion may function as a path to excite the emitting ion,
as described previously. In the former case, the emission from the
emitting ion decays rapidly from the absorption resonance level to
a storage level. Generally, the absorption band is above the
storage level, although this is not always the case, and the decay
time from the absorption resonance level is very rapid compared to
the decay time from the storage level. From the storage level and
in the absence of an appropriate disturbing ion, spontaneous photon
emission may occur at a wavelength band determined by the storage
level and a lower energy level.
[0043] An appropriate disturbing ion for a particular emitting ion
may have a resonance with the storage level in transitioning from
the storage level to the lower energy level, which may allow
preferential energy transfer to the disturbing ion rather than via
the normal emission path (e.g., photon emission). For the
disturbing ion, the energy transferred from the emitting ion to the
disturbing ion (e.g., the energy "absorbed" by the disturbing ion)
may be discharged during a very rapid non-radiative decay to a
ground state. This leaves the disturbing ion back in the unexcited
state to repeat the process. In various embodiments, disturbing
ions may be selected, which tend to have very large numbers of
energy levels (e.g., Dy), although that is not a requirement. This
allows the disturbing ion to be at or near resonance for a
relatively large number of emitting ions (e.g., "good" radiative
ions), thus allowing the excited state energy for the emitting ions
to be rapidly siphoned off by the disturbing ion without as much of
a radiative output as would have occurred if the disturbing ion
were not present in the host crystal lattice material. As will be
explained in more detail below, the decay time constant(s) of the
emitted electromagnetic radiation from one or more of the emitting
ions 110 may be used to determine whether or not the phosphor
compound 100 corresponds to an authenticating phosphor
compound.
[0044] FIG. 2 is a graph 200 illustrating decay time constant (Tau)
as a function of disturbing ion concentration for an example
phosphor composition, in accordance with an example embodiment.
More particularly, graph 200 illustrates the effect on the decay
time constant, in milliseconds (ms), of 99.99% pure yttrium
aluminum garnet (YAG) with about 4% erbium (Er) substituted as the
emitting ion, and various quantities of dysprosium (Dy) substituted
as the disturbing ion.
[0045] Point 201 corresponds to a YAG:Er phosphor compound that
does not include any intentionally substituted dysprosium, although
the rare earth impurities in the YAG:Er raw materials almost
certainly contain some quantity of dysprosium, along with other
rare earth (and non-rare earth) impurities. As will be described in
more detail below, point 201 may quantify an experimental result
obtained (e.g., in block 304, FIG. 3) by measuring an undisturbed
decay time constant for a baseline phosphor compound. In contrast,
points 202-206 correspond to YAG:Er phosphor compounds that include
quantities of dysprosium (as the disturbing ion) at about 50 ppm,
100 ppm, 200 ppm, 400 ppm, and 800 ppm, respectively. As will also
be described in more detail below, the various quantities of
dysprosium may be considered to be "experimental quantities" of a
disturbing ion (e.g., as defined in block 306, FIG. 3), and points
202-206 may quantify experimental results obtained (e.g., in block
310, FIG. 3) by measuring the disturbed decay time constants for
the corresponding disturbed phosphor compounds.
[0046] Referring again to FIG. 2, between zero and 800 ppm
intentionally substituted dysprosium, the decay time constant falls
from about 5.00 ms to about 2.50 ms, which represents a reduction
of 50% in the decay time constant. As indicated, the decay time
constant reduction with increasing disturbing ion concentration is
nearly linear over the substitution range. A linear reduction may
not be observed, however, for many host crystal lattice, emitting
ion, and disturbing ion combinations. In addition to the reductions
in decay time constant, a significant signal reduction also may be
observed with increasing disturbing ion concentration. The signal
reduction also may be (or may not be) nearly linear over a
restricted substitution range.
[0047] As mentioned previously, embodiments include synthesizing a
disturbed phosphor compound with a pre-defined, target disturbed
decay time constant, where the decay time constant may be within a
relatively narrow range of decay time constants. For example, for
the YAG:Er phosphor compound of FIG. 2, it may be desired to
produce a disturbed YAG:Er phosphor compound by substituting a
quantity of dysprosium that results in a target disturbed decay
time constant of about 4.00 ms. More particularly, it may be
desired to produce a disturbed YAG:Er phosphor compound with a
disturbed decay time constant in a range 210 that encompasses the
target disturbed decay time constant of 4.00 ms. For example, the
target disturbed decay time constant may be any decay time constant
within a range of about 3.50 ms to about 4.50 ms, as indicated by
lower and upper range limits 212, 214. This range 210 corresponds
to the target disturbed decay time constant of 4.00 ms+/-12.5%
(e.g., a range of accuracy of +/-12.5%). As indicated in FIG. 2,
points 204 and 205 fall within range 210, and these points 204, 205
correspond to the addition of dysprosium at 200 ppm and 400 ppm,
respectively. Accordingly, for the given YAG:Er raw materials, in
order to produce a disturbed phosphor compound characterized by a
disturbed decay time constant within range 210, dysprosium could be
added in quantities of about 200 ppm, 400 ppm, or some quantity in
between.
[0048] Because the YAG:Er constituting the phosphor raw materials
already contained a certain quantity of rare earth impurities prior
to the intentional substitution of dysprosium as a disturbing ion,
the decay time constant corresponding to point 201 likely is
significantly lower than the decay time constant would be for an
ultra-pure (e.g., 99.999% pure) YAG:Er phosphor compound. However,
as discussed previously, the cost of ultra-pure material is
substantially higher than the cost of reasonably pure material, and
embodiments discussed below facilitate the production of disturbed
phosphor compounds having desired, pre-defined, disturbed decay
time constants using economically-priced phosphor raw materials. In
some cases, it may be desirable to use phosphor raw materials
having higher purity, however, because the phosphor yield using
higher purity materials may be higher than yields that may be
obtainable using lower purity materials. Accordingly, in selecting
the phosphor raw materials for use with the various embodiments,
cost/yield considerations may be taken into account.
[0049] FIG. 3 is a flowchart of a method for producing a phosphor
compound (e.g., phosphor compound 100, FIG. 1), in accordance with
an example embodiment. Generally, a phosphor compound in accordance
with an embodiment may be created using any of a number of
conventional processes that are known to those of skill in the art,
except that, according to an embodiment, a relatively small
proportion of one or more disturbing ions (e.g., disturbing ions
120, FIG. 1) are added to the compound using compatible source
molecule(s) that contain the disturbing ion(s), during creation of
the compound. The quantity (or quantities) of the disturbing ion(s)
may be determined based on an analysis of the phosphor raw
materials (i.e., the host crystal lattice, emitting ion(s),
(optional) sensitizing ion(s), and the included rare earth
impurities), and subsequent analysis of one or more candidate
phosphor compounds that include various quantities and/or types of
disturbing ion(s). Essentially, empirical techniques are employed
to produce a phosphor compound that is characterized by a target
disturbed decay time constant, where the target disturbed decay
time constant is achieved by substituting a quantity of disturbing
ion(s) into the host crystal lattice, and the quantity depends on
the purity of the raw lot stock, among other things. Although the
below description of the method describes analyzing only one
disturbed decay time constant (including comparisons with only one
target disturbed decay time constant), it is to be understood that
the method may be used to analyze multiple disturbed decay time
constants associated with multiple emitting ions, as well
(including comparisons with multiple target disturbed decay time
constants).
[0050] Prior to empirically determining a quantity (or quantities)
of disturbing ion(s) to include in the disturbed phosphor compound,
a chemical analysis may be performed on a baseline phosphor
compound (e.g., a phosphor compound generated using a particular
lot of phosphor raw materials) and/or its constituting raw
materials. As discussed above, the phosphor raw materials include
some quantity of impurities, which may consist of various
concentrations of different rare earth impurities. The chemical
analysis may include, for example, determining which of the
impurities affect the temporal behavior of the baseline phosphor
compound, and which do not. Rare element impurities that are very
close on the periodic table to the emitting ion(s) may have the
greatest effect. In addition, although some impurities may be
included at very low concentrations (e.g., trace amounts), they
still may have a pronounced effect on the temporal behavior of the
baseline phosphor compound. According to an embodiment, the
temporal behavior of the baseline phosphor compound and knowledge
acquired in the context of the chemical analysis may be used to
determine a suitable disturbing ion (or disturbing ion combination)
that produces the desired temporal behavior (e.g., a target
disturbed decay time constant).
[0051] The method may begin, in block 302, by obtaining (e.g., as
phosphor raw materials) or synthesizing a baseline phosphor
compound comprising a host lattice material, one or more emitting
ions, (optionally) one or more sensitizing ions, and some quantity
of rare earth impurities. As previously discussed, the quantity of
rare earth impurities defines the purity of the baseline phosphor
compound. Embodiments may be used with baseline phosphor compounds
having various quantities of rare earth impurities, including
significant quantities of rare earth impurities. For example,
embodiments may be used with baseline phosphor compounds having any
level of purity including baseline phosphor compounds characterized
as being 99%, 99.9%, 99.95%, 99.99% or 99.999% pure.
[0052] Synthesis of the baseline phosphor compound includes
preparing a combination of a phosphor host crystal lattice material
(e.g., host crystal lattice material 130, FIG. 1), one or more
emitting ions (e.g., one or more of emitting ions 110, FIG. 1), and
(optionally) one or more sensitizing ions to form a preliminary
phosphor compound. In some cases, this may be achieved using solid
state chemistry. For example, but not by way of limitation, when
the phosphor compound is an oxide phosphor, this may include
combining correct proportions of various oxides with oxides of the
emitting ion and the sensitizing ion. These oxides are mixed and
fired for a prescribed time. In other cases, solution chemistry
techniques may be used, in which the various materials are
dissolved, subsequently precipitated, and subsequently fired. As
discussed previously, when incorporated into the host lattice
material, each emitting ion selected for the compound has a first
decay time constant, which may be affected by the presence of the
impurities in the baseline phosphor compound.
[0053] Depending on the particular process used to create the
compound, other materials may be included in the combination of the
host crystal lattice material, emitting ion(s), and sensitizing
ion(s) in forming the baseline phosphor compound. For example, but
not by way of limitation, various fluxing agents and other
pre-cursors may be included within the baseline phosphor compound.
After combining the phosphor raw materials, the baseline phosphor
compound is post-processed. For example, but not by way of
limitation, post-processing may include performing any one or more
of the following processes to the baseline phosphor compound:
firing; annealing; suspension; precursor removal (e.g., to remove
fluxing agents); milling; sedimentation; and sonication.
[0054] In block 304, the decay time of the baseline phosphor
compound is measured at a pre-selected emission band/wavelength to
determine a baseline decay time constant (or an undisturbed decay
time constant). The baseline decay time constant may be used, for
example, to ensure that the disturbed decay time constant of a
disturbed phosphor compound is sufficiently different from the
decay time constant that characterizes the undisturbed phosphor
compound. Methods and apparatus for measuring decay times are
discussed in more detail in conjunction with FIGS. 4 and 5, later,
and such methods and apparatus are not discussed here for purposes
of brevity.
[0055] Once the baseline decay time constant is determined, an
iterative process of synthesizing and analyzing candidate phosphor
compounds is then performed, in order to determine a quantity (or
quantities) of disturbing ion(s) that should be substituted into
the host crystal lattice to achieve a target disturbed decay time
constant. In block 306, an initial experimental quantity for each
of one or more disturbing ions is defined. For example, the initial
experimental quantity for each disturbing ion initially may be a
relatively low quantity, and the iterative process may gradually
increase the quantity (e.g., in block 318) until the target
disturbed decay time constant is achieved. Conversely, the initial
experimental quantity for each disturbing ion initially may be a
relatively high quantity, and the iterative process may gradually
decrease the quantity (e.g., in block 314) until the target
disturbed decay time constant is achieved. The process flow
described below contemplates either method.
[0056] In block 308, a candidate disturbed phosphor compound is
synthesized comprising the phosphor raw materials in the baseline
phosphor compound (i.e., the host lattice material, the one or more
emitting ions, (optionally) one or more sensitizing ions, and the
rare earth impurities) and the initial experimental quantity of
each of the one or more disturbing ions. Synthesis of the disturbed
phosphor compound desirably is performed using substantially the
same processes as were used to synthesize the baseline phosphor
compound (e.g., step 302), although different processes also may be
used.
[0057] In block 310, the decay time of the candidate disturbed
phosphor compound is measured at the pre-selected emission
band/wavelength to determine a disturbed decay time constant for
the candidate disturbed phosphor compound. A determination is then
made whether the disturbed decay time constant is equal to the
target decay time constant, within an acceptable degree of accuracy
(e.g., within from 1% to 5% or some other degree of accuracy). For
example, a determination initially may be made, in block 312,
whether the disturbed decay time constant measured in block 310 is
less than the target decay time constant.
[0058] When the disturbed decay time constant is less than the
target decay time constant, an assumption may be made that the
experimental quantity of one or more of the disturbing ions in the
candidate disturbed phosphor compound is too high (e.g., the
disturbing ions are quenching too much of the emissions from the
emitting ion(s)). In such a case, the experimental quantity of at
least one of the one or more disturbing ions is decreased, in block
314. The method then iterates as shown, where a new candidate
disturbed phosphor compound is synthesized (in block 308) and
analyzed (in blocks 310, 312).
[0059] Referring again to block 312, when the disturbed decay time
constant is not less than the target decay time constant, a further
determination may be made, in block 316, whether the disturbed
decay time constant is greater than the target decay time. When the
disturbed decay time constant is greater than the target decay time
constant, an assumption may be made that the experimental quantity
of one or more of the disturbing ions in the candidate disturbed
phosphor compound is too low (e.g., the disturbing ions are not
quenching enough of the emissions from the emitting ion(s)). In
such a case, the experimental quantity of at least one of the one
or more disturbing ions is increased, in block 318. The method then
iterates as shown, where a new candidate disturbed phosphor
compound is synthesized (in block 308) and analyzed (in blocks 310,
312, and 316). It is to be understood that blocks 312 and 314 may
be performed in reverse order, in an alternate embodiment.
[0060] During the process of determining the quantity of disturbing
ion(s) to include in the disturbed phosphor compound, and once a
sufficient quantity of data has been collected, a relationship
(e.g., a correlation curve) may be established between the decay
time difference (i.e., the difference between a disturbed decay
time constant for a particular candidate disturbed phosphor
compound and the target decay time constant) and the amount of a
disturbing ion (or combination of disturbing ions) that should be
included in the phosphor compound to achieve the target, disturbed
decay time constant.
[0061] When a determination is made that the disturbed decay time
constant is equal to the target decay time constant within an
acceptable level of accuracy (i.e., both steps 312 and 316 yield a
negative result), an assumption may be made that a quantity of each
disturbing ion has been discovered, which yields a disturbed
phosphor compound that is characterized by the target disturbed
decay time constant. Accordingly, in block 320, the quantity of
each disturbing ion is considered to be established for the
particular lot of phosphor raw materials used in the process.
[0062] Once the quantity of each disturbing ion is determined
(e.g., using the method of FIG. 3), Bulk quantities of the
disturbed phosphor compound may then be synthesized using the
quantity of each disturbing ion determined using the method. The
resulting disturbed phosphor compound may then be incorporated into
any of a variety of articles so that the benefits of its various
characteristics may be realized. For example, but not by way of
limitation, the disturbed phosphor compound may be incorporated
into an article to provide a way of authenticating the article.
[0063] FIG. 4 is a system 400 for authenticating an article 450, in
accordance with an example embodiment. System 400 includes a
processing system 402, an exciting radiation generator 404, an
emitted radiation detector 406, data storage 408, and a user
interface 410, according to an embodiment. Processing system 402
may include one or more processors and associated circuitry, which
is configured to implement control and analysis processes (e.g., in
the form of executable software algorithms) associated with
authenticating an article (e.g., article 450). According to an
embodiment, processing system 402 is configured to provide control
signals to exciting radiation generator 404, which cause exciting
radiation generator 404 to direct exciting radiation 420 toward
article 450. In the control signals, processing system 402 may
specify the timing (e.g., start time, stop time, and/or duration)
of the provision of exciting radiation, and/or other parameters
associated with the particular exciting radiation to be generated
(e.g., intensities and/or other parameters). Typically, the
bandwidth of the exciting radiation is pre-determined based on the
excitation source that is included as part of the exciting
radiation generator 404 (e.g., the bandwidth of excitation produced
by a selected light emitting diode or laser diode). The various
timing and/or radiation generation parameters may be retrieved from
data storage 408, for example. Exciting radiation generator 404 may
include, for example but not by way of limitation, one or more
lasers, laser diodes, light-emitting diodes (LEDs), incandescent
filaments, lamps, or other excitation sources.
[0064] In addition to controlling exciting radiation generator 404,
processing system 402 is configured to provide control inputs to
emitted radiation detector 406, which cause emitted radiation
detector 406 to attempt to detect emitted radiation 422 produced by
article 450 in response to having absorbed (either directly or
indirectly) at least some of the exciting radiation 420. Emitted
radiation detector 406 may include, for example but not by way of
limitation, a spectral filter, one or more electro-optical sensors,
photomultiplier tubes, avalanche photodiodes, photodiodes,
charge-coupled devices, charge-injection devices, photographic
films, or other detection devices. In a particular embodiment, the
emitted radiation detector 406 includes a spectral filter
positioned between the article 450 and a photodetector. The
spectral filter passes light only within a spectral band of
interest, and rejects all other light. The photodetector has
sensitivity within the spectral band of interest, and accordingly
may detect light passing through the spectral filter that is within
that spectral band. The emitted radiation detector 406 may digitize
intensity values at one or more pre-selected intervals (e.g.,
starting at t=0, and then every 0.1 milliseconds thereafter, for
several intervals). Emitted radiation detector 406 provides
information to processing system 402 (e.g., the digitized intensity
values), which enables the temporal properties of any detected
radiation 422 to be characterized.
[0065] Processing system 402 is configured to analyze such
information, upon its receipt, in order to determine whether or not
the temporal properties of any detected radiation (e.g., the decay
time constant) correspond to the temporal properties of an
authenticating phosphor compound. In addition, in an embodiment,
processing system 402 may determine whether the magnitude of the
detected radiation is within a pre-determined range. For example,
information characterizing the temporal properties and the range of
emission magnitudes of one or more authenticating phosphor
compounds may be retrieved from data storage 408. According to
various embodiments, the system 400 may be used to detect the
temporal properties of emissions within a single, relatively narrow
frequency band (e.g., to detect emissions from a single emitting
ion), or the system 400 may be used to detect the temporal
properties of emissions within multiple frequency bands (e.g., to
detect emissions from multiple emitting ions). More specifically,
the system 400 may detect the decay time constants of emissions
within one or more frequency bands.
[0066] The system 400 may then determine whether the temporal
properties (and/or the emission magnitude) of detected radiation do
correspond to the temporal properties (and/or the emission
magnitude range) of an authenticating phosphor compound. For
example, the system 400 may determine whether the measured decay
time constant(s) equal target disturbed decay time constant(s)
associated with an authenticating phosphor compound. When the
temporal properties of the detected radiation do correspond to the
temporal properties of an authenticating phosphor compound,
processing system 402 may take some action associated with
identifying article 450 as an authentic article. For example,
processing system 402 may send a signal to user interface 410,
which causes user interface 410 to produce a user-perceptible
indication of authenticity (e.g., a displayed indicia, a light, a
sound, and so on), and/or processing system 402 may cause a routing
component of system 400 (not illustrated) to route article 450
toward a route or bin assigned for authentic articles.
Alternatively, when insufficient radiation is detected or the
temporal properties of detected radiation do not correspond to the
expected pre-determined authentication parameters of an
authenticating phosphor compound (e.g., the decay time constant
does not equal the target disturbed decay time constant),
processing system 402 may take some action associated with
identifying article 450 as an unauthentic article. For example,
processing system 402 may send a signal to user interface 410,
which causes user interface 410 to produce a user-perceptible
indication of non-authenticity (e.g., a displayed indicia, a light,
a sound, and so on), and/or processing system 402 may cause a
routing component of system 400 (not illustrated) to route article
450 toward a route or bin assigned for non-authentic articles.
[0067] User interface 410 may include any of a number of components
that may be manipulated by a user to provide inputs to system 400
(e.g., keyboards, buttons, touchscreens, and so on), or which may
be controlled by processing system 402 to produce user-perceptible
indicia (e.g., display screens, lights, speakers, and so on). The
above-described process may be initiated in response to user inputs
provided through the user's interaction with user interface 410,
for example. Alternatively, the above-described process may be
initiated automatically by the system 400, such as when the article
450 has been positioned in a location at which the excitation and
detection processes may be performed.
[0068] FIG. 5 is a flowchart of a method for performing
authentication of an article that may include a phosphor compound,
in accordance with an example embodiment. For example, embodiments
of the method depicted in FIG. 5 may be performed by an
authentication system (e.g., authentication system 400, FIG. 4).
The method may begin, in block 502, when an article to be
authenticated (e.g., article 450, FIG. 4) is received by the
authentication system. For example, the article may be manually
placed within an appropriate receptacle of the authentication
system, or the article may automatically be routed into the
receptacle (e.g., by a sorting or conveyor system).
[0069] In block 504, the article is exposed to exciting radiation.
For example, the article may be moved to an excitation position
(e.g., under an excitation window), and the processing system
(e.g., processing system 402, FIG. 4) may send a control signal to
an exciting radiation generator (e.g., exciting radiation generator
404, FIG. 4) that causes the exciting radiation generator to direct
exciting radiation toward the article. Alternatively, the exciting
radiation generator may continuously provide the exciting radiation
or the exciting radiation may be modulated.
[0070] In block 506, provision of the exciting radiation to the
article is discontinued. This may be accomplished either by turning
the exciting radiation off (e.g., in a system in which the article
may remain stationary and the exciting radiation is pulsed), or by
moving the article away from the area where the exciting radiation
is being directed and to a detection position (e.g., under a
detection window). The authentication system may then detect
emitted radiation (e.g., within one or more bands) from the article
(e.g., by emitted radiation detector 406, FIG. 4) at one or more
detection intervals, which are measured from the time that
direction of the exciting radiation toward the article was
discontinued. According to an embodiment, the system is configured
to detect emitted radiation in a range between about 700 nanometers
and about 2200 nanometers, although the system may be configured to
detect emitted radiation having lower or higher wavelengths, as
well.
[0071] Information characterizing the temporal behavior and, in
some cases, the intensity of detected, emitted radiation is then
analyzed. According to an embodiment, the decay time of emitted
radiation within one or more bands is determined, and a
determination is made, in block 510, whether the decay time(s) are
within specified ranges for the particular phosphor compound that
indicate that the decay time(s) are equal to target disturbed decay
time constant(s). For example, the specified ranges may indicate
levels of accuracy to which the measured decay time should
correlate with the corresponding target disturbed decay time
constants. In an embodiment, the decay time(s) may be determined
based on the detected intensities of the emitted radiation at
multiple times (e.g., t=0, t=0.1 millisecond, and so on). Although
the determinations of decay time within a single band may used as a
basis for authenticating an article, in an embodiment, the
determinations alternatively may be made by analyzing relative
intensities of emitted radiation in multiple bands (e.g., analysis
of the ratios of the intensities of emitted radiation in multiple
bands), in other embodiments. Analysis using the relative
intensities may be more desirable than an absolute intensity
evaluation, because various factors, which may not be readily
accountable for, may affect the accuracy of an absolute intensity
reading. For example, the intensity of emitted radiation may be
affected by soil and/or wear on the article or authentication
feature, variations in the printing of authentication features,
optical geometry, reflectivity of the substrate, light scattering
within the substrate, size and shape of the article, substrate
thickness versus penetration depth of the exciting radiation, and
the power level of the laser, to name a few factors.
[0072] When the temporal characteristics (e.g., the decay time
constant) of the emitted radiation are within the specified ranges
for the specific detection time (as determined in block 510), the
system may identify the article as being "authentic," and may take
a corresponding action, in block 512. For example, the system may
produce a user-perceptible indication of authenticity, and/or may
cause a routing component of the system to route the article toward
a route or bin assigned for authentic articles. Alternatively, when
the temporal characteristics of the emitted radiation are not
within specified ranges (as determined in block 510), the system
may identify the article as being "unauthentic," and may take a
corresponding action, in block 514. For example, the system may
produce a user-perceptible indication of non-authenticity, and/or
may cause a routing component of the system to route the article
toward a route or bin assigned for unauthentic articles.
[0073] FIG. 6 depicts a cross-sectional view of an article 600 that
includes a disturbed phosphor-containing material, according to an
example embodiment. For example, an embodiment of an article 600
may include embedded and/or surface-applied authentication features
610, 620, and/or the article 600 may include phosphor particles 630
that are evenly or unevenly dispersed within one or more components
of the article 600 (e.g., within substrate 602 and/or one or more
layers or other components of the article). The various relative
dimensions of the authentication features 610, 620 and particles
630 may not be to scale in FIG. 6. Although article 600 is
illustrated to include both embedded and surface-applied
authentication features 610, 620 and particles 630, another article
may include one or a combination of embedded authentication
features, surface-applied authentication features, and dispersed
phosphor particles. Finally, although only one each of embedded
authentication feature 610, 620 are shown in FIG. 6, an article may
include more than one of either type of authentication feature 610,
620.
[0074] Article 600 includes a substrate 602, which may be rigid or
flexible, and which may be formed from one or more layers or
components, in various embodiments. The variety of configurations
of substrate 602 are too numerous to mention, as the phosphor
compounds of the various embodiments may be used in conjunction
with a vast array of different types of articles. Therefore,
although a simple, unitary substrate 602 is illustrated in FIG. 6,
it is to be understood that substrate 602 may have any of a variety
of different configurations. In addition, although inanimate, solid
articles are discussed herein, it is to be understood that an
"article" also may include a human, an animal, a biological
specimen, a liquid sample, and virtually any other object or
material into or onto which a phosphor compound of an embodiment
may be included.
[0075] Embedded authentication feature 610 comprises one or more
rigid or flexible materials in which or onto which a disturbed
phosphor compound of an embodiment is included. For example, but
not by way of limitation, embedded authentication feature 610 may
be configured in the form of a discrete, rigid or flexible
substrate, a security thread, or another type of structure.
According to various embodiments, embedded authentication feature
610 may have a thickness 612 in a range of about one micron up to
the thickness 604 of the substrate 602, and embedded authentication
feature 610 may have a width and length that is less than or equal
to the width and length of the substrate 602.
[0076] Surface-applied authentication feature 620 may be, for
example but not by way of limitation, a printed authentication
feature or an authentication feature that includes one or more
rigid or flexible materials into which or onto which a phosphor
compound of an embodiment is included. For example, but not by way
of limitation, the surface-applied authentication feature 620 may
comprise an ink, pigment, coating, or paint that includes a
phosphor compound of an embodiment. Alternatively, the
surface-applied authentication feature 620 may comprise one or more
rigid or flexible materials into which or onto which a phosphor
compound of an embodiment is included, where the substrate is then
adhered or otherwise attached to a surface of the article substrate
602. According to various embodiments, surface-applied
authentication feature 620 may have a thickness 622 of about one
micron or more, and surface-applied authentication feature 620 may
have a width and length that is less than or equal to the width and
length of the substrate 602.
[0077] Phosphor particles 630 may be evenly or unevenly dispersed
within substrate 602, as shown in FIG. 6, or within one or more
other components of the article 600 (e.g., within one or more
layers or other components of the article), in other embodiments.
The phosphor particles 630 may be dispersed within substrate 602 or
another component, for example but not by way of limitation, by
mixing particles 630 into a base material (e.g., paper pulp,
plastic base resin, and so on) for the substrate 602 or other
component, and/or by impregnating the substrate 602 or other
component with a colloidal dispersion of the particles 630.
Impregnation may be performed, for example, by a printing,
dripping, or spraying process. Phosphor particles 630 may have
particle sizes in a range from 1 micron to 20 microns, in an
embodiment, although the phosphor particles 630 may be smaller or
larger than the above-given range, as well.
[0078] In various embodiments, article 600 may be any type of
article selected from a group that includes, but is not limited to,
an identification card, a driver's license, a passport, identity
papers, a banknote, a check, a document, a paper, a stock
certificate, a packaging component, a credit card, a bank card, a
label, a seal, a postage stamp, a liquid, a human, an animal, and a
biological sample. Substrate 602 may be any of various types of
substrates, and includes one or more materials selected from a
group that includes, but is not limited to, paper, a polymer,
glass, a metal, a textile, and a fiber.
[0079] While at least one exemplary embodiment has been presented
in the foregoing detailed description, it should be appreciated
that a vast number of variations exist. It should also be
appreciated that the exemplary embodiment or exemplary embodiments
are only examples, and are not intended to limit the scope,
applicability, or configuration of the inventive subject matter in
any way. Rather, the foregoing detailed description will provide
those skilled in the art with a convenient road map for
implementing an exemplary embodiment of the invention, it being
understood that various changes may be made in the function and
arrangement of elements described in an exemplary embodiment
without departing from the scope of the invention as set forth in
the appended claims and their legal equivalents.
* * * * *