U.S. patent application number 13/449147 was filed with the patent office on 2012-09-06 for porous light-emitting compositions.
This patent application is currently assigned to LOS ALAMOS NATIONAL SECURITY, LLC. Invention is credited to Eve Bauer, Anthony K. Burrell, Quanxi Jia, Thomas M. McCleskey, Alexander H. Mueller.
Application Number | 20120225315 13/449147 |
Document ID | / |
Family ID | 40938141 |
Filed Date | 2012-09-06 |
United States Patent
Application |
20120225315 |
Kind Code |
A1 |
Burrell; Anthony K. ; et
al. |
September 6, 2012 |
Porous Light-Emitting Compositions
Abstract
Light-emitting devices are prepared by coating a porous
substrate using a polymer-assisted deposition process. Solutions of
metal precursor and soluble polymers having binding properties for
metal precursor were coated onto porous substrates. The coated
substrates were heated at high temperatures under a suitable
atmosphere. The result was a substrate with a conformal coating
that did not substantially block the pores of the substrate.
Inventors: |
Burrell; Anthony K.; (Los
Alamos, NM) ; McCleskey; Thomas M.; (Los Alamos,
NM) ; Jia; Quanxi; (Los Alamos, NM) ; Bauer;
Eve; (Los Alamos, NM) ; Mueller; Alexander H.;
(Los Alamos, NM) |
Assignee: |
LOS ALAMOS NATIONAL SECURITY,
LLC
Los Alamos
NM
|
Family ID: |
40938141 |
Appl. No.: |
13/449147 |
Filed: |
April 17, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12322419 |
Jan 30, 2009 |
8158247 |
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13449147 |
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61063153 |
Jan 30, 2008 |
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61063154 |
Jan 30, 2008 |
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Current U.S.
Class: |
428/613 ;
428/212; 428/312.6; 428/312.8; 428/319.1 |
Current CPC
Class: |
C09K 11/671 20130101;
Y10T 428/24496 20150115; Y10T 428/249978 20150401; Y10T 428/24999
20150401; Y10T 428/249969 20150401; Y10T 428/268 20150115; Y10T
428/24942 20150115; Y10T 428/24997 20150401; Y10T 428/12479
20150115; C09K 11/54 20130101; H01L 31/02322 20130101; Y10T
428/24149 20150115; Y10T 428/249953 20150401; Y10T 428/249967
20150401; H01L 31/055 20130101 |
Class at
Publication: |
428/613 ;
428/319.1; 428/312.6; 428/312.8; 428/212 |
International
Class: |
B32B 9/04 20060101
B32B009/04; C09K 11/08 20060101 C09K011/08; B32B 5/18 20060101
B32B005/18 |
Goverment Interests
STATEMENT REGARDING FEDERAL RIGHTS
[0002] This invention was made with government support under
Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1-8. (canceled)
9. A porous light-emitting composition, comprising: a
nanostructured support, a conformal coating of a high refractive
index material on said nanostructured support, and a phosphor
coating on the conformal coating.
10. The porous light-emitting composition of claim 9, wherein said
nanostructured support comprises a mesoporous silicon or silica
support.
11. The porous light-emitting composition of claim 10, wherein said
mesoporous silicon or silica support has pore sizes in a range from
1 to 20 nm.
12. The porous light-emitting composition of claim 9, wherein said
nanostructured support comprises an inverse opal or a photonic
crystal.
13. The porous light-emitting composition of claim 9, wherein said
nanostructured support comprises a nanostructured, high surface
area metal oxide or metal nitride support.
14. The porous light-emitting composition of claim 9, wherein said
phosphor coating comprises a transition metal oxide or a
lanthanide-doped metal oxide.
15. The porous light-emitting composition of claim 9, said high
refractive index material of said conformal coating comprises a
metal oxide.
16. The porous light-emitting composition of claim 9, wherein said
high refractive index material of said conformal coating comprises
a transition metal oxide or a lanthanide oxide.
17. The porous light-emitting composition of claim 9, wherein said
high refractive index material of said conformal coating comprises
a zirconium oxide, a bismuth oxide, or a tantalum oxide.
18. The porous light-emitting composition of claim 9, wherein the
nanostructured support is filled with an index matching
material.
19. The porous light-emitting composition e of claim 9, further
comprising a layer upon said porous substrate that is adapted for
controlling and guiding light emission from the structure.
20. The porous light-emitting composition of claim 9, further
comprising at least two separate metal containing films on surfaces
of said porous substrate.
21. The light-emitting device of claim 9, wherein the device has an
output of white light.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/063,154 entitled "Composite Phosphors Based
on Coating Porous Substrates," filed Jan. 30, 2008, and U.S.
Provisional Application Ser. No. 61/063,153 entitled
"Polymer-Assisted Deposition of Conformal Films on Porous
Materials," both hereby incorporated by reference.
FIELD OF THE INVENTION
[0003] The present new light-emitting devices that result from
conformal films on porous materials, in particular luminescent
metal oxide films, and more particularly these luminescent metal
oxide films deposited on porous alumina and silica structures
resulting in composite phosphors or scintillators.
BACKGROUND OF THE INVENTION
[0004] Phosphors find applications in many Light Emitting Devices
("LED"). Thin films of phosphors are used in many imaging and LED
applications from radiation detection to solid state lighting. The
key properties of phosphors include quantum yield, stability and
lifetime. In particular for LEDs the efficiency of conversion of
high energy blue excitation light to the white light is a key
factor for the overall LED efficiency. Phosphors are an integral
part of any LED, and unfortunately contribute significantly to
efficiency losses. The loss mechanisms include fundamental losses
innate to the phosphor conversion material (nonradiative decay
paths that lead to reduced quantum yields) and reduced extraction
efficiency. The reductions in extraction efficiency include radial
emission from the phosphor and wave guiding at interfaces.
Phosphors are often applied in an epoxy layer over the high energy
emitting GaN light source. If smooth layers are applied, effective
wave guiding can occur that channels light to the sides of the
device. Efforts have been made to reduce this effect through
surface roughening but extraction efficiencies remain at or near
60% in the best cases. Typically phosphors are only available as
powders or as thin film coatings.
[0005] One of the major obstacles in the development of high
efficiency systems is loss due to wave guiding when thin film
phosphors are used. Thin films help to minimize losses from self
absorption, but the planar interface between the phosphor layer and
other layers in the device lead to interfaces with different
refractive indexes. At these interfaces all light from the phosphor
that hits the interface at an angle greater than the critical angle
as defined by Snell's Law is effectively reflected at the surface
and wave guided to the edges of the film. One way to avoid this
problem is to place the phosphor as a thin film on a three
dimensional structure with vertical structures that allow the light
to propagate in the desired direction. As the surface area of the
3-dimensional structure increases, more phosphor can be excited
resulting in higher light yield. Porous structures offer great
potential, but they are very difficult to coat. Two potential
substrates include porous anodiscs that consist of a honeycomb
structure with straight channels having pore diameters from 20 to
200 nm, and a second structure is posed on porous inverse opal
structures having well defined connected cavities that can be
readily controlled to the hundreds of nanometers, up to 500 nm.
Both of these structures have high surface areas but the nanometer
scale porosity with openings or cavities less than 900 nm make them
very difficult to coat by traditional line-of-site techniques. More
complex structures include mesoporous silica, such as Mobile
Crystalline Materials ("MCMs") which possess to some degree of
ordered arrays of non intersecting hexagonal channels with the pore
diameter of these materials within mesoporous range between 1 to 20
nm. Porous structures of this invention, therefore include pores in
a range of from 1 to 500 nm.
[0006] Over the past 10 years, photonic crystal ("PC") structures
have emerged as perhaps the ultimate platform for microdevices that
can manipulate light in all three dimensions. These artificial
microstructures consist of a periodic repetition of dielectric
elements, which creates forbidden and allowed energy bands for
photons. PCs represent a major new frontier in optoelectronics due
to their ability to coherently manipulate light.
[0007] This manipulation is essential for enabling new concepts
such as producing negative indices of refraction, tailoring the
photonic density of states, controlling spontaneous emission rates,
and modifying and controlling black-body radiation. It has been
predicted [Shanhui Fan, et al., Phys. Rev. Lett. 78, 3294 (1997)]
that a weakly penetrating etched photonic lattice on the surface of
an LED can suppress all lateral modes, causing the light to be
emitted primarily in the vertical direction.
[0008] Photonic crystal ("PC") structures have emerged as perhaps
the ultimate platform for micro-devices that can manipulate light
in all three dimensions. PCs represent a major new frontier for a
diverse set of properties including their ability to coherently
manipulate light. It has been predicted that a weakly penetrating
etched photonic lattice on the surface of an LED can suppress all
lateral modes, causing the light to be emitted primarily in the
vertical direction. PCs have been restricted to a subset of
materials that can be formed in the sol-gel processing. It is not
possible to make PCs from just any material, which limits their
potential properties. Coating is one way to add functionality, but
traditional techniques Pulsed laser deposition ("PLD") and Chemical
Vapor Deposition ("CVD") cannot coat the complex porous structures.
Sol-gel can penetrate the pores but does not result in conformal
coatings since metal oxide oligomers form in the bulk solution. The
primary technique used for effective coating of 3-D materials such
as inverse opal structures is Atomic Layer Deposition ("ALD"). ALD
is limited in that thicker coatings require many steps and only
single component coatings can be readily applied. Polymer-Assisted
Deposition ("PAD") can deposit conformal coatings of complex metal
oxides on nano-structured 3-D supports. This ability to form
conformal coatings has led to the formation of completely new
compositions of coated mesoporous silicon (silica) that emit light.
Light emission from mesoporous silicon has been reported previously
but never from conformally-coated materials.
[0009] A scintillator is a material that is transparent in the
scintillation or emission wavelength range and that responds to
incident radiation by emitting a light pulse. From such materials,
generally single crystals, it is possible to manufacture detectors
in which the light emitted by the crystal that the detector
comprises is coupled to a light-detection means and produces an
electrical signal proportional to the number of light pulses
received and to their intensity. Such detectors are used especially
in industry for thickness or weight measurements and in the fields
of nuclear medicine, physics, chemistry and oil exploration. A
family of known scintillator crystals widely used is of the
thallium-doped sodium iodide Tl:NaI type. This scintillating
material, discovered in 1948 by Robert Hofstadter and which forms
the basis of modern scintillators, still remains the predominant
material in this field in spite of almost 50 years of research on
other materials. However, these crystals have a scintillation decay
which is not very fast. A material that is also used is CsI that,
depending on the applications, may be used pure or doped either
with thallium ("Tl") or with sodium ("Na"). One family of
scintillator crystals that has undergone considerable development
is of the bismuth germanate ("BGO") type. The crystals of the BGO
family have high decay time constants, which limit the use of these
crystals to low count rates. A more recent family of scintillator
crystals was developed in the 1990s and is of the cerium-activated
lutetium oxyorthosilicate Ce:LSO type. However these crystals are
very heterogeneous and have very high melting points (about 2200
degrees Celsius). The development of new scintillating materials
for improved performance is the subject of many studies. One of the
parameters that it is desired to improve is the energy resolution.
This is because in the majority of nuclear detector applications,
good energy resolution is desired. The energy resolution of a
nuclear radiation detector actually determines its ability to
separate radiation energies which are very close. It is usually
determined for a given detector at a given energy, such as the
width at mid-height of the peak in question on an energy spectrum
obtained from this detector, in relation to the energy at the
centroid of the peak. The smaller the value of the energy
resolution, the better the quality of the detector.
[0010] Nevertheless, lower values of resolution are of great
benefit. For example, in the case of a detector used to analyze
various radioactive isotopes, improved energy resolution enables
improved discrimination of these isotopes. While thin film
scintillators have limited utility in applications where energy
resolution is needed in radiation detection, they have major
applications in imaging systems such as X-ray imaging device.
[0011] X-ray imaging devices in which the scintillator for
converting an X-ray into visible light, or the like, and the
imaging devices for receiving the visible light, or the like, are
used in combination and more particularly a resolution-variable
X-ray imaging device whose resolution can be changed as occasion
demands and an X-ray CT apparatus. As the X-ray imaging device for
capturing an image by visualizing an X-ray, there are some devices
that can sense directly an X-ray and others that can visualize an
X-ray by using the scintillator and then capture an image by using
the imaging device such as CCD, or the like. In this case high
quantum yield and very short lifetimes are desirable.
[0012] Conventional neutron detectors typically include devices
that operate as ionization chambers or proportional counters. Each
of the available methods demonstrates different strengths, but all
share the common goals of high neutron efficiency, minimum
gamma-ray sensitivity or gamma/neutron discrimination. Other
systems, including scintillators doped with .sup.6Li, or .sup.10B,
have been examined with mixed results. One of the prime
difficulties in these systems is the gamma-ray rejection
characteristics of the system. In addition, many of the detector
materials are air and water sensitive or the scintillators employ
heavy elements that limit gamma-ray rejection or have slow response
times thanks to the long relaxation times. Scintillators have the
added complication that often single crystals are required to avoid
light loss, making it difficult to add large amounts of boron or
lithium to increase the neutron cross-section absorption. While
there are obvious advantages to the use of solid-state neutron
detectors, to date these are outweighed by their disadvantages.
Coating scintillators onto three dimensional structures which can
then be filled with neutron stooping material may provide a new
class of neutron detector.
[0013] Yttrium orthovanadate ("YVO.sub.4") is an excellent
polarizer and laser host material in its single-crystal form.
Europium doping of YVO.sub.4 results in a red phosphor used in
cathode ray tubes and color television in its powdered form.
Europium-doped YVO.sub.4 thin films have been prepared through a
variety of deposition techniques such as sol-gel process, CVD, PLD
and microwave-assisted chemical solution deposition. YVO.sub.4
films prepared with these methods suffer from lack of
crystallographic orientation control and the incorporation of
vanadium-poor or rich nonstoichiometric phases.
[0014] Preparation of thin film scintillators is a difficult
process. Generally, scintillators have a complex chemical
composition and many methods to prepare high quality thin films are
based upon high vacuum techniques.
[0015] Chemical solution deposition techniques have been generally
viewed as less capital intensive (see, Lange, "Chemical Solution
Routes to Single-Crystal Thin Films", Science, vol. 273, pp.
903-909, 1996 and Schwartz, "Chemical Solution Deposition of
Perovskite Thin Films", Chemistry of Materials, vol. 9, pp.
2325-2340, 1997). Also, chemical solution techniques are not
generally limited to flat surfaces.
SUMMARY OF THE INVENTION
[0016] To achieve the foregoing and other objects, and in
accordance with the purposes of the present invention, as embodied
and broadly described herein, the present invention provides a
porous light-emitting composition having a porous structure having
pores, an interior surface, and an exterior surface, and a film of
a phosphor that coats said interior and exterior surfaces of said
porous structure without substantially blocking the pores of said
porous structure.
[0017] The invention also includes a porous light-emitting
composition having a nanostructured support, a conformal coating of
a high refractive index material on said nanostructured support,
and a phosphor coating on the conformal coating.
[0018] The invention includes new porous light-emitting
compositions that are phosphors on three dimensional substrates,
and new phosphors based upon coated porous structures. The coated
porous structure maintains porosity which may be filled with a
liquid, gel, or solid. Filling the cavities with materials of
refractive index that match the substrates refractive index can
lead to enhanced light output for thick devices such as
scintillator based radiation detectors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a plot of an x-ray diffraction ("XRD") of
Eu-doped YVO.sub.4 on display glass and c-cut sapphire.
[0020] FIG. 2 shows a plot of an emission spectrum (excitation at
280 nm) of Eu YVO.sub.4 on display glass (2 coats; dashed line) and
Anodisc.RTM. filter (1 coat; solid line).
[0021] FIG. 3 shows a selection excitation and emission spectra of
Tb doped alumina on an Anodisc.RTM. filter at varying Tb
concentrations.
[0022] FIG. 4 shows a plot of an emission spectrum (excitation at
300 nm) of Anodisc.RTM. filter with one coat of Eu:YVO.sub.4 dry
(solid) and wetted (dashed).
[0023] FIG. 5 shows emission spectra of Eu:YVO.sub.4 coated silica
inverse opal filled with CCl.sub.4 in the cavities.
DETAILED DESCRIPTION
[0024] The present invention provides new porous light emitting
compositions that include conformal films on porous substrates. The
structure of the conformal film can be amorphous, composite,
polycrystalline, nanocrystalline, or microcrystalline depending
upon the chemistry of the solution, the substrate used for the film
deposition and growth, and the post-thermal treatment
conditions.
[0025] An aspect of the present invention involves the use of
Polymer-Assisted Deposition ("PAD"), which employs a coating
solution made by adding a metal precursor to a suitable polymer.
The polymer actively binds the metal, encapsulating it to prevent
chemical reactions that may lead to undesired phases of metal
oxide. PAD is a low-cost chemical solution method and effectively
eliminates problems such as uneven distribution of the metal oxide
on the substrate, unwanted reactivity of the metal resulting in the
formation of undesired phases, and the difficulty of obtaining the
desired metal/metal ratios when coating a substrate with more than
one metal oxide. The PAD technique is a bottom-up growth technique
that enables coating complex 3-D structures.
[0026] It has been found that the metal-containing conformal films
made in accordance with the present invention can be uniform
throughout the porous structure and without clogging or filling the
pores of the porous structure. This is in contrast to various prior
techniques that often result in non-uniform coating, or incomplete
complete coating of the porous structure or clogging or significant
reduction of the surface area of the final nanocomposite. The
application of this technique on nanostructured supports provides
new light emitting materials.
[0027] Metal-containing films (the metal oxide, metal, the nitride
and the like) of the present invention are conformal films, i.e.,
they are homogeneous films throughout the internal pores of the
porous supports that do not greatly reduce the surface area by
clogging pore openings.
[0028] Phosphors are often complex mixtures such as europium-doped
yttrium vanadate or lanthanide-doped silicates that may include
metals from more than one category. The conformal metal-containing
films prepared by the present process can include a metal oxide
with a single metal, can be a metal oxide with two metals or three
metals or may be a metal oxide including four or more metals. Among
the conformal metal oxides films that can be prepared by the
present process are phosphor films including europium-doped yttrium
vanadate, terbium-doped alumina, and the like.
[0029] Metal-containing films that can be prepared by the present
process can include a metal-containing film with a single metal,
can be a metal containing film with two metals or three metals or
may be a metal containing film including four or more metals. Among
the metal oxide phosphors that can be prepared by the present
process are included europium doped yttrium vanadate, terbium-doped
alumina and the like.
[0030] In one aspect of the present invention, composites can be
prepared including with various additional additives to provide
tailoring of the material properties. Among the additives can be
nanoparticles, especially nanoparticles of various metals such as
transition metals, lanthanide metals or main group metals,
nanoparticles of various metal oxides including one or more metal
such as a transition metal, a lanthanide metal or a main group
metal, nanoparticles of various metal nitrides including one or
more metal such as a transition metal, a lanthanide metal or a main
group metal, nanoparticles of various metal carbides including one
or more metal such as a transition metal, a lanthanide metal or a
main group metal, nanoparticles of various metal chalcogenides
including one or more metal such as a transition metal, a
lanthanide metal or a main group metal, nanoparticles of various
metal pnictogenides including one or more metal such as a
transition metal, a lanthanide metal or a main group metal,
nanoparticles of various metal borides including one or more metal
such as a transition metal, a lanthanide metal or a main group
metal, or nanoparticles of various metal silicides including one or
more metal such as a transition metal, a lanthanide metal or a main
group metal. Examples of such nanoparticles can include titanium
dioxide, strontium oxide, erbium oxide and the like, such
nanoparticles suitable for modifying the electronic properties of
metal containing films of a different material.
[0031] Also, various quantum dot materials, e.g., cadmium selenide
dots having a coating of zinc sulfide, such quantum dot materials
being well known to those skilled in the art, may be added to the
various metal containing films in accordance with the present
invention.
[0032] In one embodiment of the present invention, the porous
substrate can be an inverse opal structure based on an oxide
framework. The oxide framework can consist of silica, borate,
zirconium oxide, titanium oxide, and the like. The size of the
cavities of the support framework can be varied from hundreds of
microns down to tens of nanometers.
[0033] In one embodiment of the present invention, the porous
substrate can be a porous alumina membrane. The size of the pores
can be varied from microns down to nanometers.
[0034] In one embodiment of the present invention, the porous
substrate can be a mesoporous silica structure. The size of the
pores can be varied from microns down to 1 nanometer.
[0035] In one embodiment of the present invention, the porous
substrate can be a mesoporous silica structure coated with simple
metal oxides, not generally consider phosphors, that result in a
new material that emits light. The size of the pores can be varied
from microns down to 1 nanometer.
[0036] In one embodiment of the present invention, the resulting
porous structure with the metal-containing coating from the PAD
deposition may be subsequently filled with a liquid, gel or solid.
The conformal coating does not fill the pore volume so that the
pores may be filled with a subsequent step to add functionality
including high Z materials for gamma-ray absorption,
boron-containing materials for neutron absorption, materials with a
refractive index to match the substrate in order to increase the
light output of the phosphor and the like.
[0037] In one embodiment of the present invention, the nanoporous
substrate can be coated first with a high refractive index material
then a second layer of a phosphor can be added.
[0038] In one embodiment of the present invention, the nanoporous
substrate can be coated first with a high refractive index material
then multiple layers of phosphors can be added.
[0039] The post-thermal treatment conditions such as post-annealing
temperature and ambient change in a wide range depending on the
objectives of the materials deposited. For example, to grow oxide
films of europium doped yttrium vanadate on porous alumina
membranes or silica inverse opals, the temperature can be ramped up
to 120.degree. C. at 10.degree./min and held for 1 hour and then
ramped the temperature to 450.degree. C. at 10.degree./min and held
for 1 hour to burn off the polymer. Finally the temperature can be
ramped to 700.degree. C. at 10.degree./min and held for 1 hour to
cause a crystalline structure and enhance the luminescence of the
phosphor.
[0040] Aqueous solutions containing polyethylenimine ("PEI") bound
to single metal ethylenediaminetetraaceticacid ("EDTA") complexes
were prepared, characterized by ICP and mixed to give the final
solutions for coating. Thin films on display glass and quartz were
prepared by spin coating and coatings on Anodisc.RTM. membrane
filters were prepared by a dip coating method that allowed the
solution to penetrate the pores of the alumina. The coated
substrates were then thermally treated up to a temperature of
700.degree. C. to induce crystallization of the Eu:YVO.sub.4. The
resulting film composition, determined by Rutherford backscattering
spectrometry ("RBS"), of Y.sub.0.94V.sub.1.00Eu.sub.0.08S.sub.0.06
confirms the europium doping level and indicates the presence of
residual sulfate from the vanadyl sulfate precursor used in
preparing the vanadium solution. XRD of the films (FIG. 1) shows
only the expected peaks for YVO.sub.4. The fluorescence results
(FIG. 2) show strong red emission (for films with only 2 coats)
from the .sup.5D.sub.0.fwdarw..sup.7F.sub.2 transition of europium
at 618 nm indicating the europium is in a low symmetry environment
as expected. There is no indication of phase separation in the
films.
[0041] Ellipsometry results indicated film thickness of
152.3.+-.2.5 nm for the 4 coats of Eu:YVO.sub.4 on glass and
87.2.+-.0.2 nm for the 2 coats of Eu:YVO.sub.4 on c-cut sapphire
with a roughness of 6.2.+-.0.1 nm. Each single coat yields a film
thickness of approximately 40 nm. AFM measurements gave MSR
roughness values of 1.3 nm for the bare glass substrate, 6.0 nm for
the Eu:YVO.sub.4 film on glass and 4.1 nm for the Eu:YVO.sub.4 film
on c-cut sapphire. These MSR roughness values are as low as those
obtained by PLD. This is astonishing considering the initial
thermal process involves simply placing a spin coated substrate
onto a hot surface at 550.degree. C. for 30 seconds. During this
time, water from the film is evaporated and the polymer is removed
resulting in a remarkably clear, smooth film with no cracks.
[0042] Unlike many other deposition techniques, PAD is not a
line-of-sight process. It is a solution technique that can coat all
aspects of a surface. We chose to demonstrate the ability to coat
deep narrow channels using the commercially available Anodisc.RTM.
membrane filters made from Anapore.RTM. porous membranes. The
membranes are initially 60 .mu.m thick with a closely packed
honeycomb of 200 nm diameter channels through the membrane. The
pores in the membrane are not periodically arranged into a photonic
lattice, but they have the same general dimensions used in photonic
crystals. The solution readily wets into the pores by capillary
action. The resulting materials have phosphor throughout the
channels, and maintain porosity. Scanning Electron Microscopy
("SEM") confirms the open pore structure. The porosity is further
demonstrated by the fact that water is able to wet into and through
the coated Anodisc.RTM. membrane filters resulting in high
transparency. Other solution techniques such as sol-gel clog and
fill pores as opposed to depositing conformal coatings.
Anodisc.RTM. membrane filters with a single coating show the strong
europium emission (FIG. 2). These coated porous discs are highly
luminescent and appear much brighter than the thin films on display
glass. Part of this increased luminescence comes from reduced wave
guiding on the porous material. Wave guiding at the surface
interface in the thin films leads to strong luminescence at the
edges but prevents light from exiting the surface when it hits the
surface at an angles>the critical angle as defined by Snell's
Law. Other effects such as increased absorption as the excitation
light interacts with the walls of the channels and increased
surface area may also factor in the remarkable emission.
[0043] Excitation and emission spectra were recorded for
Eu:YVO.sub.4 thin films coated on display glass. The sharp emission
of europium is readily observed with 2 coats of Eu:YVO.sub.4 on
c-cut sapphire and one cat on a porous Anodisc.RTM. membrane
filters (FIG. 2). The excitation spectra of all of the coated
materials have a peak at <300 nm that corresponds to the
absorption of vanadate. The Anodisc.RTM. membrane filters were
given a single coating of Eu:YVO.sub.4. The discs emit both dry and
wet. Strong emission is observed from a completely wetted disc
suggesting that surface quenching of the europium is not
significant and refractive index matching helps limit scattering.
FIG. 4 shows excitation emission spectra from coating another
phosphor Tb doped alumina onto the Anodisc.RTM. membrane
filters.
[0044] Coating onto inverse opals with 360 nm diameter cavities is
also possible with high refractive index metal oxides (for example,
coating of the silica-based inverse opals with zirconium oxide).
Surface area measurements and SEMS confirm that the coating is
conformal with open pores that maintain the high surface area.
[0045] Coating onto titanium-based inverse opals with 360 nm
diameter cavities is also possible with high refractive index metal
oxides (for example coating of the titanium-based inverse opals
with zirconium oxide). Surface area measurements and SEMS confirm
that the coating is conformal with open pores that maintain the
high surface area.
[0046] Coating onto silica-based inverse opals with 360 nm diameter
cavities was successful. FIG. 4 shows the fluorescence spectrum of
Eu:YVO.sub.4 coated onto the inverse opal structure. Surface area
measurements and SEMs confirm that the coating is conformal with
open pores that maintain the high surface area. These cavities can
then be filled with CCl.sub.4 which reduces the light scattering at
the interfaces and maintains the strong emission seen in FIG.
5.
[0047] Coating onto mesoporous silica (MCM-41) was also successful.
Surface area measurements and SEMs confirm that the coating is
conformal and the mesoporous silica still contains open pores that
maintain the high surface area.
[0048] The present invention is more particularly described in the
following EXAMPLES, which are intended as illustrative only, since
numerous modifications and variations will be apparent to those
skilled in the art.
[0049] Example A describes the preparation of solutions used in the
deposition and formation of the metal-containing conformal films.
Examples B through F describe the deposition of such conformal
metal-containing films on porous supports. Polyethylenimine ("PEI")
was obtained from BASF as a water-free, branched, polymer with an
average MW of 50,000. Water was deionized via reverse osmosis
(having a resistivity>16 MOhms) ("M.OMEGA.").
Example A
Solutions
[0050] A yttrium solution was prepared by mixing 1.3 g yttrium
nitrate hexahydrate (99.9%, ALFA AESAR) with 1.0 g HEDTA (ALDRICH,
99.995% pure) and 1.0 g BASF polyethyleneimine polymer. The
resulting solution was filtered through a 0.45 micron filter,
diluted to 200 mL with nano pure water, and purified by Amicon
filtration with a 3,000 MW cut-off filter. The final concentrated
solution was 133 mM yttrium, determined by ICP/AES.
[0051] A europium solution was prepared by mixing 1.0 g of europium
nitrate hexahydrate (99.9%, ACROS) with 1.0 g HEDTA (ALDRICH,
99.995% pure) and 1.0 g BASF polyethyleneimine polymer. The
resulting solution was filtered through a 0.45 micron filter,
diluted to 200 mL, and purified by Amicon filtration with a 3,000
MW cut-off filter. The final concentrated solution was 136 mM
europium.
[0052] A vanadium solution was prepared by mixing 1.0 g vanadyl
sulfate (ACROS) with 1.0 g HEDTA (ALDRICH, 99.995% pure) and 1.0 g
BASF polyethyleneimine polymer. The resulting solution was filtered
through a 0.45 micron filter, diluted to 200 mL, and purified by
Amicon filtration with a 3,000 MW cut-off filter. The final
concentrated solution was 230 mM vanadium, determined by
ICP/AES.
[0053] A terbium solution was prepared by mixing 1 g terbium
chloride TbCl.sub.3 hexahydrate (99.9%, ACROS) with 1.0 g HEDTA
(ALDRICH, 99.995% pure) and 1.0 g BASF polyethyleneimine polymer.
The resulting solution was filtered through a 0.45 micron filter,
diluted to 200 mL with nano pure water, and purified by Amicon
filtration with a 3,000 MW cut-off filter. The final concentrated
solution was 143 mM terbium, determined by ICP/AES.
[0054] An aluminum solution was prepared by mixing 2.0 g of
aluminum nitrate nanohydrate (99.997%, ALDRICH) with 2.0 g HEDTA
(ALDRICH, 99.995% pure) and 8.7 g of a 30% aqueous solution of
polyethyleneimine polymer (POLY SCIENCES INC.). The resulting
solution was filtered through a 0.45 micron filter, diluted to 200
mL, and purified by Amicon filtration with a 3,000 MW cut-off
filter. The final concentrated solution was 180 mM aluminum.
[0055] A hafnium coating solution was prepared by mixing 2.0 g of
HfOCl.sub.2 (ALDRICH, 99.99% pure), 2.0 g HEDTA, 2 grams BASF
polyethyleneimine polymer, and concentrated ammonium hydroxide
(NH.sub.4OH (FISHER) in deionized (18 MOhms) H.sub.2O was added
until the solution was clear. The resulting solution was filtered
through a 0.45 micron filter, diluted to 200 mL with nano pure
water, and purified by Amicon filtration with a 3,000 MW cut-off
filter. The final concentrated solution was 163 mM Hf, determined
by ICP/AES. This solution was rotovapped to further concentrate it,
resulting in a final concentration of 250 mM Hf.
[0056] A titanium coating solution was prepared by mixing small
aliquots of the titanium solution (a mixture of 2.5 g of 30%
peroxide into 30 mL water and then slowly adding 2.5 g titanium
tetrachloride) to a solution containing 1 g PEI, 1 g EDTA, and 30
mL water, while maintaining pH at 7.5, until precipitation
occurred. The final Ti concentration was 408 mM.
[0057] A zirconium solution was prepared by mixing 2.04 g of
zirconyl nitrate, (ZrO(NO.sub.3).sub.2, ALDRICH, 35 wt % Zr), 2.0 g
HEDTA (ALDRICH, 99.995% pure), 2 grams BASF polyethyleneimine
polymer, and concentrated ammonium hydroxide (NH.sub.4OH (FISHER)
in deionized (18 MOhms) H.sub.2O was added until the solution was
clear. The resulting solution was filtered through a 0.45 micron
filter, diluted to 200 mL with nano pure water, and purified by
Amicon filtration with a 3,000 MW cut-off filter. The final
concentrated solution was 225 mM Zr, determined by ICP/AES.
[0058] A solution including zinc chloride, dipotassium
ethylenediaminetetraaceticacid ("K.sub.2EDTA") and PEI was prepared
as follows. An aqueous solution of 2.0 grams of dipotassium
ethylenediaminetetraaceticacid in 30 mL of water was prepared. To
this solution was added 0.75 grams of zinc chloride and the
solution was stirred. After stirring, 2 grams of polyethylenimine
were added and the pH was adjusted to 9 with addition of 10% HCl.
The solution was placed in an Amicon ultrafiltration unit
containing a PM 10 ultrafiltration membrane designed to pass
materials having a molecular weight<10,000 g/mol. The solution
was diluted to 200 mL, and then concentrated by ultrafiltration to
20 mL in volume. Inductively coupled plasma-atomic emission
spectroscopy showed that the final solution had 24.2 mg/mL of
Zn.
Example B
[0059] P1--Photonic Crystals with one coat of YV/5% Eu were
prepared as follows. SiO.sub.2 crystals were coated with YV/5% Eu
using the PAD method of coating. Coating solutions were made by
mixing calculated volumes of each solution to obtain a 1:1 mol
ratio of Y to V. A calculated volume of Eu solution was added to
the Y/V solution to obtain a 5% mol ratio of Eu. 283 mg of the
solution was then dropped onto 32 mg of P1 photonic crystals in a
20-mL scintillation vial. The vial was rotated to ensure total
coverage of the crystals by the coating solution. The coated
crystals were then rotovapped under negative pressure in order to
cause the solution to penetrate the cavities within the photonic
crystals and remove excess water. When the crystals appeared dry,
the crystals were transferred to a ceramic crucible. The crystals
were then annealed in air with the following heating program: The
temperature was ramped to 120.degree. C. at 10.degree./min and held
for 1 hour. The temperature was ramped to 450.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
700.degree. C. at 10.degree./min and held for 1 hour.
Example C
[0060] P1--Photonic Crystals with two coats of YV/5% Eu were
prepared as follows. SiO.sub.2 crystals were coated with YV/5% Eu
using the PAD method of coating. Coating solutions were made by
mixing calculated volumes of each solution to obtain a 1:1 mol
ratio of Y to V. A calculated volume of Eu solution was added to
the Y/V solution to obtain a 5% mol ratio of Eu. 194 mg of the
solution was then dropped onto 32 mg of P1 photonic crystals in a
20-mL scintillation vial. The vial was rotated to ensure total
coverage of the crystals by the coating solution. The coated
crystals were then rotovapped under negative pressure in order to
cause the solution to penetrate the cavities within the photonic
crystals and remove excess water. When the crystals appeared dry,
the crystals were transferred to a ceramic crucible. The crystals
were then annealed in air with the following heating program: The
temperature was ramped to 120.degree. C. at 10.degree./min and held
for 1 hour. The temperature was ramped to 450.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
700.degree. C., 10.degree./min and held for 1 hour. The crystals
were removed from the crucible and placed in a scintillation vial.
Another 245 mg of YV/5% Eu solution were dropped onto the crystals
with 1 coat of YV/5% Eu. The vial was rotated to ensure total
coverage of the crystals by the coating solution. The coated
crystals were then rotovapped under negative pressure in order to
cause the solution to penetrate the cavities within the photonic
crystals and remove excess water. When the crystals appeared dry,
the crystals were transferred to a ceramic crucible. The crystals
were then annealed in air with the following heating program: The
temperature was ramped to 120.degree. C., 10.degree./min and held
for 1 hour. The temperature was ramped to 450.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
700.degree. C. at 10.degree./min and held for 1 hour.
Example D
[0061] P3--Photonic Crystals with one coat of YV/5% Eu were
prepared as follows. SiO.sub.2 crystals were coated with YV/5% Eu
using the PAD method of coating. Coating solutions were made by
mixing calculated volumes of each solution to obtain a 1:1 mol
ratio of Y to V. A calculated volume of Eu solution was added to
the Y/V solution to obtain a 5% mol ratio of Eu. 228 mg of the
solution was then dropped onto 32 mg of P3 photonic crystals in a
20-mL scintillation vial. The vial was rotated to ensure total
coverage of the crystals by the coating solution. The coated
crystals were then rotovapped under negative pressure in order to
cause the solution to penetrate the cavities within the photonic
crystals and remove excess water. When the crystals appeared dry,
the crystals were transferred to a ceramic crucible. The crystals
were then annealed in air with the following heating program: The
temperature was ramped to 120.degree. C. at 10.degree./min and held
for 1 hour. The temperature was ramped to 450.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
700.degree. C. at 10.degree./min and held for 1 hour.
Example E
[0062] Alumina anodiscs coated with 1 coat YV/5% Eu were prepared
as follows. Anodisc porous alumina membranes were coated with a
YV/5% Eu solution using the PAD method of coating. The membranes
coated were 60 .mu.m thick with a closely packed honeycomb of 200
nm diameter channels through the membrane. Membranes were wetted
with the a coating solution made up of a 1:1 ratio of Y:V and 5%
Eu. Coating solutions were made by mixing calculated volumes of
each solution to obtain a 1:1 mol ratio of Y to V. A calculated
volume of Eu solution was added to the Y/V solution to obtain a 5%
mol ratio of Eu. A 60 .mu.L, volume of solution was placed on a
glass slide, and the Anodisc.RTM. membrane filters were wetted with
the solution by sliding them through the solution on the slide. The
Anodisc.RTM. membrane filters were then placed on upside down
ceramic crucibles and fired in a furnace in air with the following
program: The temperature was ramped to 120.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
450.degree. C. at 10.degree./min and held for 1 hour. The
temperature was ramped to 700.degree. C. at 10.degree./min and held
for 1 hour.
Example F
[0063] Alumina anodiscs coated with 1 coat Tb doped Aluminum were
prepared as follows. Anodisc porous alumina membranes were coated
with an aluminum solution doped with 1%, 3%, 5%, 7%, and 10% Tb
using the PAD method of coating. The membranes coated were 60 .mu.m
thick with a closely packed honeycomb of 200 nm diameter channels
through the membrane. Coating solutions were made by mixing
calculated volumes of each solution to obtain a 1%, 3%, 5%, 7%, and
10% mol ratio of Tb. A 60 .mu.L, volume of solution was placed on a
glass slide, and the Anodisc.RTM. membrane filters were wetted with
the solution by sliding them through the solution on the slide. The
Anodisc.RTM. membrane filters were then placed on upside down
ceramic crucibles and fired in a furnace in air with the following
program: The temperature was ramped to 120.degree. C.,
10.degree./min and held for 1 hour. The temperature was ramped to
450.degree. C. at 10.degree./min and held for 1 hour. The
temperature was ramped to 700.degree. C. at 10.degree./min and held
for 1 hour.
Example G
[0064] P3--Photonic Crystals with one coat of YV/5% Eu were
prepared as follows. TiO.sub.2 crystals were coated with YV/5% Eu
using the PAD method of coating. Coating solutions were made by
mixing calculated volumes of each solution to obtain a 1:1 mol
ratio of Y to V. A calculated volume of Eu solution was added to
the Y/V solution to obtain a 5% mol ratio of Eu. 228 mg of the
solution was then dropped onto 32 mg of photonic crystals in a
20-mL scintillation vial. The vial was rotated to ensure total
coverage of the crystals by the coating solution. The coated
crystals were then rotovapped under negative pressure in order to
cause the solution to penetrate the cavities within the photonic
crystals and remove excess water. When the crystals appeared dry,
the crystals were transferred to a ceramic crucible. The crystals
were then annealed in air with the following heating program: The
temperature was ramped to 120.degree. C. at 10.degree./min and held
for 1 hour. The temperature was ramped to 450.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
700.degree. C. at 10.degree./min and held for 1 hour.
Example H
[0065] Titania photonic crystals with one coat of YV/5% Eu were
prepared as follows. TiO.sub.2 crystals were coated with YV/5% Eu
using the PAD method of coating. Coating solutions were made by
mixing calculated volumes of each solution to obtain a 1:1 mol
ratio of Y to V. A calculated volume of Eu solution was added to
the Y/V solution to obtain a 5% mol ratio of Eu. 228 mg of the
solution was then dropped onto 32 mg of P3 photonic crystals in a
20-mL scintillation vial. The vial was rotated to ensure total
coverage of the crystals by the coating solution. The coated
crystals were then rotovapped under negative pressure in order to
cause the solution to penetrate the cavities within the photonic
crystals and remove excess water. When the crystals appeared dry,
the crystals were transferred to a ceramic crucible. The crystals
were then annealed in air with the following heating program: The
temperature was ramped to 120.degree. C. at 10.degree./min and held
for 1 hour. The temperature was ramped to 450.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
700.degree. C. at 10.degree./min and held for 1 hour.
Example I
[0066] The zirconium-coated inverse opals were prepared by diluting
192 mg of the zirconium solution with 107 mg of deionized (18
M.OMEGA.) H.sub.2O. The solution was then dropped onto 32 mg of
titanium oxide photonic crystals in a 20-mL scintillation vial. The
vial was rotated to ensure total coverage of the crystals by the
coating solution. The coated crystals were then rotovapped under
negative pressure in order to cause the solution to penetrate the
cavities within the photonic crystals and remove excess water. When
the crystals appeared dry, the crystals were transferred to a
ceramic crucible. The crystals were then annealed in air with the
following heating program: The temperature was ramped to
120.degree. C. at 10.degree./min and held for 1 hour. The
temperature was ramped to 450.degree. C. at 10.degree./min and held
for 1 hour. The temperature was ramped to 500.degree. C. at
10.degree./min and held for 1 hour.
Example J
[0067] The hafnium-coated inverse opals were prepared by taking 200
mg of the hafnium solution and diluting with 100 mg of deionized
(18 M.OMEGA.) H.sub.2O. The solution was then dropped onto 32 mg of
the titanium dioxide photonic crystals in a 20-mL scintillation
vial. The vial was rotated to ensure total coverage of the crystals
by the coating solution. The coated crystals were then rotovapped
under negative pressure in order to cause the solution to penetrate
the cavities within the photonic crystals and remove excess water.
When the crystals appeared dry, the crystals were transferred to a
ceramic crucible. The crystals were then annealed in air with the
following heating program: The temperature was ramped to
120.degree. C., 10.degree./min and held for 1 hour. The temperature
was ramped to 450.degree. C., 10.degree./min and held for 1 hour.
The temperature was ramped to 500.degree. C., 10.degree./min and
held for 1 hour.
Example K
[0068] The titanium-coated inverse opals were prepared by taking
200 mg of the titanium solution and diluting with 100 mg of
deionized (18 M.OMEGA.) H.sub.2O. The solution was then dropped
onto 32 mg of the titanium oxide photonic crystals in a 20-mL
scintillation vial. The vial was rotated to ensure total coverage
of the crystals by the coating solution. The coated crystals were
then rotovapped under negative pressure in order to cause the
solution to penetrate the cavities within the photonic crystals and
remove excess water. When the crystals appeared dry, the crystals
were transferred to a ceramic crucible. The crystals were then
annealed in air with the following heating program: The temperature
was ramped to 120.degree. C. at 10.degree./min and held for 1 hour.
The temperature was ramped to 450.degree. C., 10.degree./min and
held for 1 hour. The temperature was ramped to 500.degree. C.,
10.degree./min and held for 1 hour.
Example L
[0069] A first layer of hafnium was coated onto an inverse opal by
taking 200 mg of the hafnium solution and diluting with 100 mg of
deionized (18 M.OMEGA.) H.sub.2O. The solution was then dropped
onto 32 mg of the titanium dioxide photonic crystals in a 20-mL
scintillation vial. The vial was rotated to ensure total coverage
of the crystals by the coating solution. The coated crystals were
then rotovapped under negative pressure in order to cause the
solution to penetrate the cavities within the photonic crystals and
remove excess water. When the crystals appeared dry, the crystals
were transferred to a ceramic crucible. The crystals were then
annealed in air with the following heating program: The temperature
was ramped to 120.degree. C., 10.degree./min and held for 1 hour.
The temperature was ramped to 450.degree. C., 10.degree./min and
held for 1 hour. The temperature was ramped to 500.degree. C.,
10.degree./min and held for 1 hour. Then this material was coated
with YV/5% Eu using the PAD method of coating. Coating solutions
were made by mixing calculated volumes of each solution to obtain a
1:1 mol ratio of Y to V. A calculated volume of Eu solution was
added to the Y/V solution to obtain a 5% mol ratio of Eu. 228 mg of
the solution was then dropped onto 32 mg of photonic crystals in a
20-mL scintillation vial. The vial was rotated to ensure total
coverage of the crystals by the coating solution. The coated
crystals were then rotovapped under negative pressure in order to
cause the solution to penetrate the cavities within the photonic
crystals and remove excess water. When the crystals appeared dry,
the crystals were transferred to a ceramic crucible. The crystals
were then annealed in air with the following heating program: The
temperature was ramped to 120.degree. C. at 10.degree./min and held
for 1 hour. The temperature was ramped to 450.degree. C. at
10.degree./min and held for 1 hour. The temperature was ramped to
700.degree. C. at 10.degree./min and held for 1 hour.
[0070] The foregoing description of the invention has been
presented for purposes of illustration and description and is not
intended to be exhaustive or to limit the invention to the precise
form disclosed, and obviously many modifications and variations are
possible in light of the above teaching. The embodiments were
chosen and described in order to best explain the principles of the
invention and its practical application to thereby enable others
skilled in the art to best utilize the invention in various
embodiments and with various modifications as are suited to the
particular use contemplated. It is intended that the scope of the
invention be defined by the claims appended hereto.
* * * * *