MOLECULAR LANTHANIDE COMPLEXES FOR PHOSPHOR APPLICATIONS
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to light emitting devices including a radiation source, and an
excitable phosphor. It more specifically relates to the application of a class of
chemical compounds for use as phosphors for the conversion of radiation into visible
light in light emitting devices.
Discussion of the Art
Lanthanide-based phosphors have applications in multi-component phosphor lighting
applications. Current lanthanide-based inorganic phosphors such as Y203:Eu and
LaP04:Ce,Tb, typically absorb 254 nm radiation effectively. For this reason, the
lanthanide-based inorganic phosphors are useful in mercury discharge applications,
such as fluorescent lighting. However, new high-efficiency light sources, such as
light emitting diodes (LEDs), require phosphors that readily absorb near ultraviolet
radiation in the 300-460 nm range where conventional lanthanide-based inorganic
phosphors typically do not strongly absorb.
LEDs and laser diodes (LD) have been produced from Group III-V alloys such as
gallium nitride (GaN). To form the LEDs, for example, layers of the alloys are
typically deposited epitaxially on a substrate, such as silicon carbide or sapphire, and
may be doped with a variety of n and p-type dopants to improve properties such as
light efficacy. With reference to the GaN-based LEDs, light is generally emitted in
the UV and/or blue range of the electromagnetic spectrum.
Recently, techniques have been developed for converting radiation emitted from
LEDs to useful light for illumination purposes. By using a phosphor excited by the
radiation generated by the LED, light of different wavelengths may be generated to
produce desired color points. For example, a combination of LED generated radiation
and phosphor converted light may produce visible light (e.g. white). There are few
known lanthanide-based phosphors which readily absorb in the UV wavelength
region and have efficient luminescence in the visible spectral region. This is
especially true for narrow-band red phosphors.
The known lanthanide phosphors which are applicable for lighting applications are
solid state compounds, such as Y2O3:Eu, which readily absorb radiation below
300nm, in the far UV range. Solid state compounds have specific ligands which can
not be easily varied on the molecular level. In contrast, the use of a molecular
compound permits the facile manipulation of the ligands on the molecular level,
which allows the compound to fulfill the design criteria for a given application.
A class of lanthanide-based molecular compounds which will act as phosphors
capable of readily absorbing electromagnetic radiation and converting that radiation
to visible light is therefore desirable.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the present invention, a light emitting device is
provided. The light emitting device includes a light emitting component and at least
one phosphor material. The phosphor material absorbs electromagnetic radiation
emitted by the light emitting component and converts that radiation to visible light of
the desired color.
The use of a lanthanide based molecular compound as a phosphor composition in
lighting applications is described. The phosphor composition contains a lanthanide,
Ln; P-diketonate ligands, A; and at least one additional ligand, B. The components of
the phosphor composition are combined in accordance with the formula LnAxBY,
where X and Y are integers ranging from about 1 to about 10.
A light emitting device containing a light source and a phosphor is provided. The
phosphor is a molecular compound of the formula LnAxBY, where Ln is a lanthanide,
A is P-diketonate ligands, B is an additional ligand, and X and Y are integers ranging
from about 1 to about 10.
A primary benefit of the invention resides in the ability to vary the components of the
phosphor composition on the molecular level to fulfill the design criteria for a given
application.
Another primary benefit of the invention resides in the efficient luminescence in the
visible spectral region.
Still further advantages and benefits of the present invention will become apparent to
those of ordinary skill in the art upon reading and understanding the following
detailed description of the various embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is an excitation spectrum of a molecular phosphor representative of the
present invention.
FIGURE 2 is an emission spectrum of a molecular phosphor representative of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention focuses on the use of a molecular lanthanide containing
compound as a phosphor in any configuration of a light emitting device containing a
light source, including, but not limited to, discharge lamps, fluorescent lamps, LEDs,
and LDs. While the use of the present phosphor is contemplated for a wide array of
lighting, the present invention is described with particular reference to and finds
particular application to LEDs. As used herein, the term "light" encompasses
radiation in the UV, IR, and visible regions of the electromagnetic spectrum.
Any configuration of a light source which includes a LED and a phosphor
composition is contemplated in the present invention. In an exemplary embodiment,
the phosphor is located adjacent to the LED. In another embodiment, the phosphor is
situated between encapsulant layers and is not in direct contact with the LED. In yet
another embodiment, the phosphor is dispersed throughout an encapsulating layer.
Notwithstanding these described configurations, the skilled artisan will recognize that
any LED configuration may be improved by the inclusion of the present inventive
phosphor.
The phosphor composition is a molecular compound comprising a lanthanide, Ln; 0-
diketonate ligands, A, and at least one additional ligand, B. The phosphor conforms
to the general formula LnAxBY, wherein X and Y are integers between about 1 and
10.
The choice of the lanthanide component of the molecular phosphor composition
determines the emission wavelength of the phosphor. For example, when the exciting
radiation is in the UV range and Ln = europium, the peak in the emission spectrum is
typically of longer wavelength (580-660 nm), and appears red. When the exciting
radiation is in the UV range and Ln = terbium, the peak in the emission spectrum is
typically of shorter wavelength, and appears green. When the exciting radiation is in
the UV range and Ln = thulium or cerium, the peak in the emission spectrum may be
of even shorter wavelength, and appear blue. It is therefore apparent that by choosing
the correct lanthanide component in the present inventive phosphor, UV radiation
from a LED can be converted to different visible colors.
The lanthanide component of the present invention is chosen from the group
consisting of lanthanum, yttrium, cerium, praseodymium, neodymium, samarium,
europium, gadolinium, terbium, dysoprosium, holmium, erbium, thulium, ytterbium,
lutetium, and mixtures thereof. The preferred lanthanide, or mixtures thereof, is
chosen to correspond to the emission wavelengths desired in the light emitting device.
The physical properties of the phosphor, such as the melting point, boiling point, and
the location and shape of the absorption spectrum can be manipulated by the choice of
the P-diketonate ligands, A, and the B ligands. The P-diketonate ligands are chosen
from the group including, but not limited to, ligands of the general formula
RCOCH2COR'. R and R' are independently chosen, and can be any functional group
which sufficiently stabilizes the ligand and complexes of the ligand with the
lanthanide and some combinations of B ligands. Exemplary functional groups for use
in the p-diketonate ligands are alkyl and substituted alkyl groups with between about
1 and about 20 carbons in the alkyl chain, preferably between about 1 and about 15
carbons in the alkyl chain, and most preferably between about 1 and about 10 carbons
in the alkyl chain. Exemplary alkyl groups include substituted and unsubstituted,
linear and branched methyl, ethyl, propyl, butyl, penta, hexa, hepta, octa, nona, deca,
and mixtures thereof. Preferred functional groups are selected from the group
consisting of, but not limited to, CH3, CH2F, CHF2, CF3, CH2CH3, CH(CH3)2,
C(CH3)3, C(C6H5)3, CH2NH2, CH(NH2)2, C(NH2)3, CH2[N(CH3)2], CH[N(CH3)2]2,
C[N(CH3)2]3, CH2{N[CH2(CH3)]2}, CH{N[CH2(CH3)]2}2, C{N[CH2(CH3)]2}3,
N[CH2(CH3)]2, N(CH3)2, Si(CH3)3, and mixtures thereof.
The physical properties of the present phosphor composition may also be varied by
the choice of the B ligand. The B ligand is preferably one or more ligand of the
general formula R"(ZCH2CH2)nZ'R"\ wherein R" and R'" are independently alkyl
or substituted alkyl groups and n is an integer between about 1 and about 10. Z and
Z' are independently chosen from the group including oxygen, sulfur, tertiary
phosphines, secondary phosphines, tertiary amines, secondary amines, and mixtures
thereof. The secondary phosphines, tertiary phosphines, secondary amines, and
tertiary amines are further functionalized from the group including hydrogen,
hydroxyl, alkyl, alkoxy, amine, ethers, esters, and mixtures thereof capable of
forming stable complexes with some combination of lanthanide and P-diketonate
ligands.
In addition, the B ligands may alternatively be one or more inorganic ligands capable
of forming stable complexes with some combination of lanthanide and P-diketonate
ligands. Inorganic ligands of this type include tetrahydrofuran, dioxane, pyridine,
2,2'-bipyridine, phenanthroline, and mixtures thereof.
In the general formula LnAxBY, X and Y are integers in the range of about 1 to about
12. X and Y are dependently chosen such that X+Y is not greater than the
coordination number of the chosen lanthanide. For example, if the lanthanide chosen
is europium, X+Y must be less than or equal to 12. It would be possible for X+Y to
be equal to a number less than the coordination number of the chosen lanthanide if,
for example, B is chosen to be a multidentate ligand, or if R or R' are chosen to be a
substituted alkyl groups which are capable of occupying more than one coordination
site on the lanthanide.
Preferred examples of this class of phosphors are
Ln(CF3COCH2COCF3)3[CH3(OCH2CH2)3OCH3],
Ln(CF3COCH2COCF3)3[CH3(OCH2CH2)2OCH3],
Ln(CF3COCH2COCF3)3(CH3OCH2CH2OCH3),
Ln(CF3COCH2COCH3)3[CH3(OCH2CH2)3OCH3],
Ln(CF3COCH2COCH3)3[CH3(OCH2CH2)2OCH3],
Ln(CF3COCH2COCH3)3(CH3OCH2CH2OCH3),
Ln(CF3COCH2COCF3)3(2,2 '-bipyridine)m, and
Ln(CF3COCH2COCH3)3(2,2'-bipyridine)m.
In these exemplary examples, Ln is any lanthanide, and m is an integer between about
1 and about 12. Many other examples of suitable phosphors which adhere to the
general formula LnAxBY are contemplated and will be obvious to the skilled artisan.
The above list is intended to be illustrative and should not be construed to be limiting
in any way.
The phosphor material of the present invention may additionally include more than
one phosphor, such as two or more different phosphors. Accordingly, the phosphors
may be mixed or blended to produce desired colors. It is generally known that
phosphor powders do not interact as a result of lamp making and they exhibit the
beneficial property that their spectra are cumulative in nature. Hence, the spectrum of
an LED that includes a blend of phosphors will be a linear combination of the spectra
of LEDs coated with the individual phosphors. For example, if a red phosphor of the
present invention, Eu(CF3COCH2COCF3)3[CH3(OCH2CH2)2OCH3] were mixed with
any blue phosphor, the light produced would appear purple to the eye.
In an exemplary embodiment, the physical characteristics of the red phosphor
Eu(CF3COCH2COCF3)3[CH3(OCH2CH2)2OCH3] are described by Figures 1 and 2.
Figure 1 is the excitation spectrum of the noted red phosphor and is a measurement of
the relative intensity of the red emission versus excitation wavelength, while the red
emission is measured at a constant wavelength. Figure 2 is the emission spectra of
the noted red phosphor and is a measurement of the relative intensity of emitted light
at various wavelengths while the excitation is held constant. In Figure 1, it can be
seen that when the emission intensity of the phosphor at 615 nm is measured, it is
most intense when excited by radiation in the range of about 300-450 nm, which is in
the near-UV range of the electromagnetic spectrum. Figure 2 shows that when the
excitation of the phosphor is held constant at 450 nm (the sample is excited only by
radiation at 450 nm), the emission wavelength of the phosphor is strongest in the
range of about 605-630 nm, which is perceived as red by the eye.
Light sources suited to use in the present invention include but are not limited to
GaN-based (InAlGaN) semiconductor devices. Suitable GaN semiconductor
materials for forming the light emitting components are generally represented by the
general formula In,GajAlKN, where I, J, and K are greater than or equal to zero, and
I+J+K=l. The nitride semiconductor materials may thus include materials such as
InGaN and GaN, and may be doped with various impurities, for example, for
improving the intensity or adjusting the color of the emitted light. LDs are similarly
formed from an arrangement of GaN layers. Techniques for forming LEDs are well
known in the art so that further discussion herein is deemed unnecessary to a full and
complete understanding of the present invention.
GaN-based light emitting devices are capable of emitting light with high luminance.
A suitable GaN-based LED device includes a substrate layer formed from a single
crystal of, for example, sapphire, silicon carbide, or zinc oxide. An epitaxial buffer
layer, of, for example, n+ GaN is located on the substrate, followed by a sequence of
epitaxial layers comprising cladding layers and active layers. Electrical contact is
made between two of the layers and corresponding voltage electrodes (through a
metal contact layer) to connect the LED to the circuit and source of power.
The wavelength of the light emitted by an LED is dependent on the configuration of
the semiconductor layers employed in forming the LED. As is known in the art, the
composition of the semiconductor layers and the dopants employed can be selected so
as to produce an LED with an emission spectrum which closely matches the
excitation spectrum of the phosphor material.
While the invention is described with particular reference to UV/blue light emitting
components, it should be appreciated that light emitting components which emit light
of a different region in the electromagnetic spectrum may also be used. For example,
a red-emitting LED or LD, such as an aluminum indium gallium phosphate
(AlInGaP) LED would also be applicable. Moreover, light emitting components such
as those found in discharge lamps and fluorescent lamps are also contemplated for use
with the present inventive phosphor compositions.
The invention has been described with reference to the preferred embodiment.
Obviously, modifications and alterations will occur to others upon reading and
understanding the preceding, detailed description. It is intended that the invention be
construed as including all such modifications and alterations insofar as they come
within the scope of the appended claims or the equivalents thereof.
WHAT IS CLAIMED IS:
1. A light emitting device comprising a light source and a phosphor
composition, wherein said phosphor composition comprises at least lanthanide, Ln; at
least P-diketonate ligand, A; and at least one additional ligand, B; combined in
accordance with the formula LnAxBY, where X and Y are integers.
2. The light emitting device of claim 1 wherein the lanthanide is selected
from the group consisting of lanthanum, cerium, praseodymium, neodynium,
samarium, europium, gadolinium, terbium, dysoprosium, holmium, erbium, thulium,
ytterbium, lutetium, and mixtures thereof.
3. The light emitting device of claim 1 wherein said p-diketonate ligands
are selected from the group consisting of the general formula RCOCH2COR'.
4. The light emitting device of claim 3 wherein the P-diketonate ligands
are different.
5. The light emitting device of claim 3 wherein the R and R' comprise
alkyl, or substituted alkyl substituents, with up to about 10 carbons in the alkyl chain.
6. The light emitting device of claim 5 wherein the R and R' are CF3.
7. The light emitting device of claim 1 wherein the B ligands are selected
from the group consisting of the general formula R"(Z'CH2CH2)nZ"R"', wherein R"
and R'" are independently alkyl or substituted alkyl groups, and mixtures thereof,
and wherein the ligands are able to form stable complexes with some combination of
Ln and A.
8. The light emitting device of claim 7 wherein the Z' and Z" are selected
from the group consisting of oxygen, sulfur, secondary phosphines, tertiary
phosphines, secondary amines, tertiary amines, and mixtures thereof.
9. The light emitting device of claim 7 wherein the Z' and Z" are
different.
10. The light emitting device of claim 8 wherein the secondary
phosphines, tertiary phosphines, secondary amines, and tertiary amines are further
functionalized with functional groups selected from the group consisting of hydrogen,
hydroxyl, alkyl, alkoxy, amine, ethers, esters, and mixtures thereof.
11. The light emitting device of claim 7 wherein said n is an integer
ranging from about 1 to about 10.
12. The light emitting device of claim 1 wherein the B ligands are selected from
the group consisting of inorganic ligands capable of forming stable complexes with
some combination of Ln and A, and mixtures thereof.
13. The light emitting device of claim 12 wherein the B ligands are selected from
the group consisting of tetrahydrofuran, dioxane, pyridine, 2,2'-bypyridine,
phenanthroline, their derivatives, and mixtures thereof.
14. The light emitting device of claim 1 wherein said X and Y are integers
ranging from about 1 to about 10.
15. The light emitting device of claim 1 wherein the phosphor composition
absorbs radiation in the UV range and emits light in the visible range of the
electromagnetic spectrum.
16. The light emitting device of claim 1 wherein the phosphor composition
is a molecular compound.
17. The light emitting device of claim 1 wherein an emission spectrum is
manipulated by varying the identity of the lanthanide.
18. The light emitting device of claim 1 further comprising additional
phosphors to achieve desired colors from the mix of phosphors.
19. The light emitting device of claim 1 wherein the location and shape of
the absorption spectrum is manipulated by varying the identity of said acetylacetonate
ligand, said B ligand, or both.
20. The light emitting device of claim 1 wherein said light source is a
discharge lamp such as a metal halide lamp, a fluorescent lamp, a LED, or a LD.
21. A light emitting device comprising a LED and a phosphor, the
phosphor comprised of the formula LnAxBY, wherein:
Ln is a lanthanide;
A is at least one P-diketonate ligand;
B is at least one additional ligand;
X is an integer ranging from about 1 to about 12; and
Y is an integer ranging from about 1 to about 12.
22. The light emitting device of claim 21 wherein the phosphor is a
molecular compound in which individual components can be varied to change the
absorption and emission characteristics of the phosphor.

A light source is provided which contains a light emitting component and at least one
phosphor material. The phosphor material absorbs radiation emitted by the light
emitting component and converts that radiation to visible light of a desired color. The
phosphor composition is a molecular compound of the formula LnAxBY, wherein Ln
is a lanthanide, A is -diketonate ligands, B is at least one additional ligand, and X
and Y are integers.