U.S. patent application number 12/668145 was filed with the patent office on 2010-09-23 for solar cells.
Invention is credited to Gert De Cremer, Dirk De Vos, Johan Hofkens, Lesley Pandey, Maarten Roeffaers, Bert Sels, Tom Vosch.
Application Number | 20100236611 12/668145 |
Document ID | / |
Family ID | 39929721 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100236611 |
Kind Code |
A1 |
De Cremer; Gert ; et
al. |
September 23, 2010 |
SOLAR CELLS
Abstract
The present invention concerns a photovoltaic device comprising
a wavelength conversion layer with an assembly of oligo atomic
metal clusters confined in molecular sieve.
Inventors: |
De Cremer; Gert; (Langdorp,
BE) ; De Vos; Dirk; (Holsbeek, BE) ; Hofkens;
Johan; (Brecht, BE) ; Roeffaers; Maarten;
(Hasselt, BE) ; Sels; Bert; (Balen, BE) ;
Vosch; Tom; (Kessel-Lo, BE) ; Pandey; Lesley;
(Vilvoorde, BE) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE, FOURTH FLOOR
ALEXANDRIA
VA
22314-1176
US
|
Family ID: |
39929721 |
Appl. No.: |
12/668145 |
Filed: |
July 7, 2008 |
PCT Filed: |
July 7, 2008 |
PCT NO: |
PCT/BE08/00051 |
371 Date: |
June 1, 2010 |
Current U.S.
Class: |
136/252 |
Current CPC
Class: |
C09K 11/02 20130101;
Y02E 10/52 20130101; C09K 11/58 20130101; H01J 61/44 20130101; G06K
19/06046 20130101 |
Class at
Publication: |
136/252 |
International
Class: |
H01L 31/00 20060101
H01L031/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 2007 |
GB |
0713250.9 |
Dec 14, 2007 |
GB |
0724442.9 |
Feb 7, 2008 |
GB |
0802265.9 |
Feb 11, 2008 |
GB |
0802400.2 |
Feb 21, 2008 |
GB |
0803185.8 |
Claims
1-18. (canceled)
19. A photovoltaic device comprising an electrode or an electrode
layer (2), an electrolyte or electrolyte layer (3) and a counter
electrode or counter electrolyte layer (4) wherein the photovoltaic
device further comprises a wave length conversion layer with
assembly of oligo atomic metal clusters confined in molecular
sieves (1) to convert solar radiation that excites oligo atomic
metal clusters confined in molecular sieves into a emission of
radiation with a higher wave length
20. The photovoltaic device according to claim 19, wherein the
conversion layer (1) is between the electrode or electrode layer
(2) and the counter electrode or electrode layer (4).
21. The photovoltaic device according to claim 19, further
comprising a transparent surface (5) on the electrode or electrode
layer.
22. The photovoltaic device according to claim 19, wherein the
conversion layer (1) is positioned on the element that is formed by
an outer electrode or electrode layer (2) which with the counter
electrode or electrode layer (4) sandwiches an electrolyte or
electrolyte layer (3).
23. The photovoltaic device according to claim 21, wherein the
conversion layer (1) is positioned between the transparent surface
element (5) and the outer electrode or electrode layer (2).
24. The photovoltaic device according to claim 19, wherein the
conversion layer comprises assembly of small Au and/or Ag clusters
confined in molecular sieves.
25. The photovoltaic device according to claim 24, wherein the
assembly of small Au and/or Ag clusters confined in molecular
sieves are embedded in a matrix.
26. The photovoltaic device according to claim 25, wherein the
matrix further comprises a particle binder.
27. The photovoltaic device according to claim 19, wherein the
small clusters are clusters of 1-100 atoms.
28. The photovoltaic device according to claim 19, wherein the
small clusters are oligo atomic clusters.
29. The photovoltaic device according to claim 19, wherein the
molecular sieves are a microporous material.
30. The photovoltaic device according to claim 19, wherein the
molecular sieves are selected from among microporous materials
selected from the group consisting of zeolites, porous oxides,
silicoaluminophosphates and aluminosilicates.
31. The photovoltaic device according to claim 19, wherein the
molecular sieves are zeolites selected from the small pore zeolites
among zeolite A-like materials such as zeolite 3A, Zeolite 13X,
Zeolite 4A and Zeolite 5A, and ZKF, and combinations thereof.
32. The photovoltaic device according to claim 19, wherein the
molecular sieves are large pore zeolites from the group consisting
of Mordenite, ZSM-5, MCM-22, Ferrierite, Faujasites X and Y.
33. The photovoltaic device according to claim 19, wherein the
molecular sieves are selected from among molecular sieves MCM-41,
MCM-48, HSM SBA-15, and combinations thereof.
34. The photovoltaic device according to claim 19, wherein the
pores of the molecular sieves containing the small clusters of Au
and/or Ag are coated by a coating matrix or are closed by stopper
molecules.
35. The photovoltaic device according to claim 19, wherein the
molecular sieves containing the small clusters of metals are tuned
to convert solar radiating with a wave length below 560 nm into a
radiation with a wave length above 560 nm.
36. The photovoltaic device according to claim 19, wherein the
molecular sieves containing the small clusters of metals are tuned
by solar radiation excitation to emit radiation at a wave length
between 400 and 750 nm.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a wavelength
converter for increasing solar panel yields and to a solar cell
comprising such converter. More particularly the present invention
concerns the conversion of UV radiation to visible emission by
confined metal atomic clusters, preferably silicium, silver, copper
and gold, and more particularly to the use of molecular sieves
comprising oligo atomic silver clusters as an additional material
in solar panels for increasing the efficiency of converting solar
light to electricity.
BACKGROUND OF THE INVENTION
[0002] We are already familiar with the use of solar panels
composed of a plurality of solar cells, which make use of the
photovoltaic effect to convert energy from the sun into electric
energy. Solar radiation is composed of photons, which are particles
that have a variable energy depending on the wavelength of the
emissions in the solar spectrum (see FIG. 13 for the solar
spectrum). When the photons fall onto the surface of the
semiconductor material forming a photovoltaic cell they may either
be reflected, absorbed or pass through the cell.
[0003] Photovoltaic devices are capable of converting solar
radiation into usable electrical energy. These devices can be
fabricated by sandwiching certain semiconductor materials between
two electrical contacts. As disclosed in U.S. Pat. No. 4,064,521,
which is incorporated herein by reference to the extent necessary
to effect a thorough understanding of the background of the present
invention, one semiconductor material that can be used is a body of
amorphous silicon deposited by glow discharge in silane.
Photovoltaic devices utilizing amorphous silicon typically contain
one or more pn or inverted pn junctions.
[0004] There are certain materials that, upon absorbing this type
of radiation, generate positive and negative charge couples, i.e.
electrons (e-) and holes (h+) which, on being produced, move
randomly through the volume of the solid and, if there is no
external or internal determining factor, the opposing sign charges
recombine and neutralize each other mutually. On the other hand, if
a permanent electric field is created in the interior of the
material, the positive and negative charges will be separated by
this field, which produces a difference of potential between the
two areas of material.
[0005] For instance, commonly used are the semiconductors which are
build on materials of which the atoms contain four valence
electrons, commonly such solid-state semiconductor that are build
on intrinsic elements of the group consisting of silicon (Si),
germanium (Ge), and carbon, of which silicon is preferred primarily
because it is more tolerant of heat, can be doped by adding
trivalent impurity atoms (for instance the atoms of the group
consisting of Aluminum (Al), Gallium (Ga), Boron (B) and Indium
(In)) to turn the intrinsic semiconductors into the so called
p-type material or with the pentavalent impurity atoms (for
instance the impurities of the group consisting of Phosphorus (P),
Arsenic (As), Antimony (Sb) and Bismuth (Bi)) to turn the intrinsic
semiconductors into the so called n-type material. Such n-type
materials contain more electrons (negative charges) than required
by the covalent bonds which can be forced into conduction with
relatively little energy for instance when such a valence electron
absorbs enough energy, it jumps from the valence band to the
conduction band resulting that a gap is left in the covalent bond,
referred to as a hole. The p-type material with trivalent
impurities contains more positive charges or valence-band holes.
When joined together the p-type material and n-type material form a
depleted zone or the so called pn junction and the free electrons
in the n-type material of the n-type material containing an excess
of electrons is allowed to diffuse (wander) across the junction to
the p-type material having an excess of holes and when free
electrons cross the pn junction, they get trapped in one of the
valence-band holes in the p-type material, with the following
results of a net positive charge in the n-type material and a net
negative charge in the p-type material and the buildup of (-)
charges on the p side of the pn junction repelling electrons from
coming over from the n side (referred to as the so called barrier
potential). On one side of the depleted zone is positively charged
n-type material, and on the other is negatively charged -p-type
material. If there were any electrons free in this zone, they would
be attracted to the positively charged n-type material. Generally
this event is triggered by sun's photon, a photon of light hitting
one of the atoms in this depleted zone with enough energy, knocking
an electron loose from the atom here and whereby the this `freed`
electron moving into the conduction band and being attracted and
moves toward the positively charged n-type silicon. Whenever an
electron leaves the depleted zone, a hole is created and to fill
this hole, an electron will move over from the p-side. The
photovoltaic cell being build on this materials hereby functions as
a pn junction diode, allowing electons (electrical current) to flow
from n, through an external circuit, and back into p, then from p
to n in the pn junction; and not vice versa, or reverse flow and
the diode conducts electrical current when the n-type material is
more negative than the p-type material.
[0006] If these two areas are interconnected by means of an
external circuit, at the same time as the solar radiation falls
onto the material an electric current will be produced that will
run round the external circuit.
[0007] Important parts of a solar cell are the intermediate layers
made up of semiconductor materials, as it is at the heart of
materials of this type where the electron current proper is
created. These semiconductors are specially treated to form two
layers in contact with each other, which are doped differently
(type p and type n) to form a positive electric field on one side
and a negative one on the other. In addition, solar cells are
formed by an upper layer or mesh composed of an
electrically-conductive material, which has the function of
collecting the electrons from the semiconductor and transferring
them to the outer circuit and a lower layer or mesh of
electrically-conductive material, which has the function of
completing the electric circuit. At the top of the cell too it is
also usual to have an encapsulating transparent material to seal
the cell and protect it from unfavorable environmental conditions
and it may also be provided with a reflection-inhibiting layer in
order to increase the proportion of radiation absorbed. The cells
are usually connected to one another, encapsulated and mounted on a
structure in the form of a carrier or frame, thereby shaping the
solar panel.
[0008] A second generation of photovoltaic materials exist which
are based on the use of thin epitaxial deposits of semiconductors
on lattice-matched wafers. There are two classes of epitaxial
photovoltaics--space and terrestrial. Space cells typically have
higher air mass zero AM0 efficiencies (28-30%) in production, but
have a higher cost per watt. Their "thin-film" cousins have been
developed using lower-cost processes, but have lower AM0
efficiencies (7-9%) in production. The advent of thin-film
technology contributed to a prediction of greatly reduced costs for
thin film solar cells that has yet to be achieved. Examples of
technologies/semiconductor materials include amorphous silicon,
polycrystalline silicon, micro-crystalline silicon, cadmium
telluride, copper indium selenide/sulfide. An advantage of
thin-film technology theoretically results in reduced mass so it
allows fitting panels on light or flexible materials, even
textiles. The advent of thin GaAs-based films for space
applications (so-called "thin cells") with potential AM0
efficiencies of up to 37% are currently in the development stage
for high specific power applications. Second generation solar cells
now comprise a small segment of the terrestrial photovoltaic
market, and most of the space market.
[0009] A third-generation photovoltaics are very different from the
previous semiconductor devices as they do not rely on a traditional
p-n junction to separate photogenerated charge carriers. For space
applications quantum well devices (quantum dots, quantum ropes,
etc.) and devices incorporating carbon nanotubes are being
studied--with a potential for up to 45% AM0 production efficiency.
For terrestrial applications, these new devices include
photoelectrochemical cells, polymer solar cells, nanocrystal solar
cells, dye-sensitized solar cells and are still in the research
phase.
[0010] A `fourth-generation` of solar cells may consist of
composite photovoltaic technology, in which polymers with nano
particles can be mixed together to make a single multispectrum
layer. Then the thin multispectrum layers can be stacked to make
multispectrum solar cells more efficient and cheaper based on
polymer solar cell and multijunction technology. The layer that
converts different types of light is first, then another layer for
the light that passes and last is an infra-red spectrum layer for
the cell--thus converting some of the heat for an overall solar
cell composite. Companies working on fourth-generation
photovoltaics and providing various alternatives in this field
include Xsunx, Konarka Technologies, Inc., Nanosolar, Dyesol and
Nanosys.
[0011] A problem in the art is that the efficiency for absorbing UV
radiation in commonly used solar cells is low, compared to visible
light which is more efficiently converted in electricity. Moreover
the efficiency of these and the new generation photovoltaics can
yet be increased if more of the sun's spectrum of radiation can be
turned into electricity. For instance the photoresponse of
thin-film amorphous silicon p-i-n devices to radiation below 400 nm
non existing or light radiation whose wavelength lies between
400-560 nanometers is less efficient than expected from
measurements of the optical absorption of the overlying layers. The
short wavelength, i.e., "blue," response of the device may be low
for several reasons: the electric field at the p/i interface may be
weak, slowing carrier transport and permitting more carriers to
recombine; the electron or hole lifetime may be reduced at the
front of the device due to contamination; and interface
recombination at the p/i interface may remove carriers and prevent
their collection.
[0012] Present invention solves this problem by integrating
molecular sieves comprising oligo atomic silver clusters to
converts UV radiating in visible light in solar cell. For instance
a layer with molecular sieves comprising oligo atomic silver
clusters which converts UV radiating in visible light can be on the
transparent layer of the solar cell, increasing the efficiency of
electricity production.
[0013] In recent years, expertise has been gained in the synthesis
of zeolites with desired properties by the choice of the structure
directing agent (SDA), control of the synthesis conditions, and
post-synthesis treatments. (Ref: van Bekkum, H., Flanigen, E. M.,
Jacobs, P. A., Jansen, J. C. (editors) Introduction to Zeolite
Science and Practice, 2nd edition. Studies in Surface Science and
Catalysis, 2001, 137; Corma, A., Chem. Rev., 1997, 97, 2373-2419;
Davis, M. E., Nature, 2002, 417, 813-821; Davis, M. E., et al.,
Chem. Mater., 1992, 4, 756-768; de Moor P-P. E. A. et al., Chem.
Eur. J., 1999, 5(7J, 2083-2088; Galo, J. de A. A., et al., Chew.
Rev., 2002, 102, 4093-4138.) At the same time, the family of
ordered mesoporous materials has been greatly expanded by the use
of different surfactants and synthesis conditions. (Ref: Corma, A.,
Chem. Rev., 1997, 97, 2373-2419; Davis, M. E., Nature, 2002, 417,
813-821; Galo, J. de A. A., et al., Chem. Rev., 2002, 102,
4093-4138; Ying, J. Y., et al., Angew. Chem. Int. Ed., 1999, 3S,
56-77.) The use of the appropriate template enables the control of
the pore size, distribution and connectivity during the zeolite
synthesis. For example, use of surfactants such as
cetyltrimethylammonium bromide or dodecyltrimethylammonium bromide
generally results in formation of mesoporous materials. In a
preferred embodiment, the molecular sieves are one or more selected
from the group consisting of mordenite, ZSM-5, A-zeolite,
L-zeolite, faujasite, ferrierite, chabazite type of zeolites, and
mixtures of the foregoing zeolites.
[0014] The materials of present invention, for instance zeolites
containing oligo silver atom clusters, are cheap and non toxic.
Zeolites are currently used in large quantities in washing powder
and silver despite its antimicrobial properties, has no known toxic
effect on human tissue. Colloidal silver is for instance widely
been marketed as a dietary supplement for protective activity
against oxidative stress and reactive oxygen species formation.
[0015] In contrast to bulk metals which are devoid of a band gap,
and hence are good electric conductors, small Au or Ag clusters
display interesting emissive properties from discrete energy
levels. This phenomenon has been demonstrated e.g., for silver
smaller than 100 atoms in rare gas matrices, in aqueous solutions
and on silver oxide films. Quantum chemical calculations confirm
the molecular character and discrete energy states of these small
silver clusters. (Ref: 1. Johnston, R. L. (2002) Atomic and
Molecular Clusters (Taylor & Francis, London and New York);
Rabin, I., Schulze, W., Ertl, G., Felix, C., Sieber, C., Harbich,
W., & Buttet, J. (2000) Chemical Physics Letters 320, 59-64.;
Peyser, L. A., Vinson, A. E., Bartko, A. P., & Dickson, R. M.
(2001) Science 291, 103-106; Lee, T.-H., Gonzalez, J. I., &
Dickson, R. M. (2002) Proc. Natl. Acad. Sci. USA 99, 10272-10275;
Lee, T. H., Gonzalez, J. I., Zheng, J., & Dickson, R. M. (2005)
Accounts of Chemical Research 38, 534-541; Bonacic-Koutecky, V.,
Mitric, R., Burgel, C., Noack, H., Hartmann, M., & Pittner, J.
(2005) European Physical Journal D 34, 113-118; Lee, T.-H., Hladik,
C. R., & Dickson, R. M. (2003) Nano Letters 3, 1561-1564;
Rabin, I., Schulze, W., & Ertl, G. (1999) Chemical Physics
Letters 312, 394-398; Felix, C., Sieber, C., Harbich, W., Buttet,
J., Rabin, I., Schulze, W., & Ertl, G. (1999) Chemical Physics
Letters 313, 105-109; Rabin, I., Schulze, W., & Ertl, G. (1998)
Crystal Research and Technology 33, 1075-1084; Rabin, 1, Schulze,
W., & Ertl, G. (1998) Journal of Chemical Physics 108,
5137-5142; Konig, L., Rabin, I., Schulze, W., & Ertl, G. (1996)
Science 274, 1353-1355; Zheng, J. & Dickson, R. M. (2002)
Journal of the American Chemical Society 124, 13982-13983;
Bonacic'-Koutecky, V., Veyret, V., & Mitric', R. (2001) Journal
of Chemical Physics 115, 10450-10460; Bonacic-Koutecky, V.,
Pittner, J., Boiron, M., & Fantucci, P. (1999) Journal of
Chemical Physics 110, 3876; Bonacic'-Koutecky, V., Cespiva, L.,
Fantucci, P., & Koutecky, J. (1993) Journal of Chemical Physics
98, 7981-7994; Yoon, J., Kim, K. S., & Baeck, K. K. (2000)
Journal of Chemical Physics 112, 9335-9342; Fedrigo, S., Harbich,
W., & Buttet, J. (1993) Journal of Chemical Physics 99,
5712-5717.)
[0016] The major problem in the study and creation of small Au or
Ag clusters is aggregation to large nanoparticles and eventually to
bulk metal, with loss of emission. Here, it is demonstrated that
the use of porous structures with limited pore, cavity and tunnel
sizes, overcomes the aggregation problem enabling emissive
entities, which are stable in time.
[0017] Silver cluster in molecular sieves exhibit remarkable
stability. (Ref: Bogdanchikova, N. E., Petranovskii, V. P.,
Machorro, R., Sugi, Y., Soto, V. M., & Fuentes, S. (1999)
Applied Surface Science 150, 58-64.) Bogdanchikova et al. found
that the stability of the silver clusters depends on the acid
strength, which may be related to the composition, e.g., the
SiO.sub.2/Al.sub.2O.sub.3 molar ratio, of the molecular sieves.
Silver clusters in mordenites having weak acidic sites are stable
for at least 50 months, a sufficiently long period with respect to
the application in mind for use in a visible light source.
Disappearance of the clusters was linked to oxidation. Reduction of
the clusters or an oxygen-free or -poor device obviously could
increase the stability even more. In one embodiment in the present
invention, Au or Ag clusters are protected from oxidation due to
encapsulation in the molecular sieves. Additionally, if required,
an external coating of the material crystals or capping of the pore
entrances can be used to further protect the occluded metal
clusters.
[0018] The current state of the art has never suggested or
demonstrated the room temperature conversion of invisible light,
e.g., with energy in the UV region, to a lower energy, e.g.,
visible light, by oligo atomic metal clusters embedded in molecular
sieves.
[0019] Some technologies of the art concern the photophysical
properties of zeolites loaded with silver. For instance, Chen et
al. loaded Y zeolites with AgI, instead of silver clusters, and
pumped or charged with 254 nm light, however, without observation
or description of visible emission. (Chen, W., Joly, A. G., &
Roark, J. (2002) Physical Review B 65, 245404 Artn 245404, U.S.
Pat. No. 7,067,072 and U.S. Pat. No. 7,126,136). Calzaferri et al.
demonstrated absorption of 254 nm light by silver metal containing
zeolites without any notification of emission (Calzaferri, G.,
Leiggener, C., Glaus, S., Schurch, D., & Kuge, K. (2003)
Chemical Society Reviews 32, 29-37.). Kanan et al., showed some
emission intensity for silver(I)-exchanged zeolite Y, however only
when excited at temperatures below 200 K. (Kanan, M. C., Kanan, S.
M., & Patterson, H. H. (2003) Research on Chemical
Intermediates 29, 691-704).
[0020] In summary, the examples do not meet the requirement for
applications in wave length converting systems to improve the
efficiency of a photovoltaic medium for instance a photovoltaic
medium
[0021] Present invention concerns the field of improved
photovoltaic cells, and related, comprising e.g., white light and
colored luminescent materials with emission of visible white or
colored light. Such devices thus comprise luminescent materials for
photoluminescence based lighting generated through the action of
confined metal oligo atomic clusters, more particularly oligo
atomic silver clusters loaded in molecular sieves (e.g., zeolites
like the A3, A4 and A5 zeolite).
[0022] It was particularly found that such emissive materials have
properties that are capable of converting light in the UV radiation
range such as, but not limited to 254 nm, to visible light. An
additional advantage is the tunability of the devices over the
whole UV excitation range. Furthermore, the emissive materials of
present invention do not show large absorptions in the visible
range, which would lower the overall emission efficiency of the
system.
[0023] The present invention relates generally to white and colored
light emission using confined oligo atomic metal clusters, and more
particularly to the use of molecular sieves comprising of these
oligo atomic metal clusters as luminescent materials for
photoluminescence based converting of UV radiation into visible
light or for functioning as wave length converter of UV radiation
into visible light.
SUMMARY OF THE INVENTION
[0024] The present invention increases the efficiency of
electricity production from solar cells by converting the UV
portion of the solar spectrum to visible light.
[0025] In accordance with the purpose of the invention, as embodied
and broadly described herein, the invention concerns a photocell
comprising molecular sieves with oligo atomic metal clusters or
with confined metal atomic clusters, preferably of the group
consisting of silicium, silver, copper and gold, which molecular
sieves convert solar radiation comprising wavelengths below 560 nm,
preferably below 500 nm, preferably below 450 nm, yet more
preferably below 400 nm, and most preferably below 300 nm, into
radiation into the higher wavelength spectrum of visible light for
instance above 560 nm.
[0026] In accordance with the purpose of the invention, the
invention comprises an assembly of small clusters of the noble
metals of the group consisting of gold, silver, platinum,
palladium, silicium and rhodium, preferably Au and/or Ag clusters
confined in molecular sieves, preferably zeolites, for converting
invisible radiation emitted by a radiation source at room
temperature or at an higher temperature to visible light and
further a transparent envelope said illumination system. Such
illumination system can further comprising a transmission means or
transmission element for transmitting the visible light in a
desired direction. In one aspect of the invention, the conversion
system of present invention comprises a radiation source (the sun),
which has medium wave UV (UVC) ray radiation, Far UV (FUV) or
vacuum UV (VUV) ray radiation and Extreme UV (EUV) or deep UV (XUV)
ray radiation.
[0027] In one aspect of the invention, the conversion system of
present invention comprises an assembly containing oligo atomic
metal clusters, e.g., of Au, Ag and/or alloys thereof, confined in
molecular sieves, which are embedded in a matrix. Such matrix may
further comprise a particle binder. The assembly can be a powder
assembly of small Au and/or Ag clusters confined in molecular
sieves.
[0028] The conversion system can be used for the generation of
white light and or specific colored light and at a predetermined
color temperature.
[0029] The clusters in the conversion system of present invention
are oligo atomic clusters for instance of 1-100 atoms. The
molecular sieves in this invention are selected from the group
consisting of zeolites, porous oxides, silicoaluminophosphates,
gallophosphates, zincophophates, titanosilicates and
aluminosilicates, or mixtures thereof. In a particular embodiment
of present invention the molecular sieves of present invention are
selected from among large pore zeolites from the group consisting
of ZSM-5, MCM-22, ferrierite, faujastites X and Y. The molecular
sieves in another embodiment of present invention are materials
selected from the group consisting of zeolite 3A, Zeolite 13X,
Zeolite 4A, Zeolite 5A and ZKF.
[0030] In a particular embodiment of present invention the pores of
the molecular sieves containing the small clusters of, e.g., Au
and/or Ag are coated with a matrix, or are closed by stopper
molecules.
[0031] Furthermore the present invention also involves methods for
converting at room temperature and above, invisible radiation to
visible light comprising conversion of exciting radiation at a
wavelength below 400 nm from said radiation sources by direct
contact with or via radiation transmission means, element or medium
to an assembly of small Au and/or Ag clusters confined in molecular
sieves.
[0032] To transfer the non-visible radiation into visible light,
the light system of present invention does not require the presence
of charge compensating anions, such as oxalate, hydroxide, azide,
carbonate, bicarbonate, sulfate, sulfite, chlorate, perchlorate,
acetate and formate to be in charge association with the noble
metals, such as the small metal clusters.
[0033] Further scope of applicability of the present invention
becomes apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art from
this detailed description. It is to be understood that both the
foregoing general description and the following detailed
description are exemplary and explanatory only and are not
restrictive of the invention, as claimed.
DETAILED DESCRIPTION
Detailed Description of Embodiments of the Invention
[0034] "Room temperature" as used in this application means a
temperature between 12-30.degree. C. (Celsius), preferably between
16 and 28.degree. C., more preferably 17 and 25.degree. C. and most
preferably it is taken to be roughly 20 to 23 degrees.
[0035] By the term luminescence or emissive, the following types
are included: chemoluminescence, crystalloluminescence,
electroluminescence, photoluminescence, phosphorescence,
fluorescence, thermoluminescence.
[0036] Oligo atomic metal clusters include clusters ranging from 1
to 100 atoms of the following metals (sub nanometer size), Si, Cu,
Ag, Au, Ni, Pd, Pt, Rh, Co and Ir or alloys thereof such as Ag/Cu,
Au/Ni etc. The clusters can be neutral, positive or negatively
charged. The oligo atomic metal clusters can be small oligo atomic
silver- (and/or gold) molecules containing 1 to 100 atoms.
[0037] The articles "a" and "an" are used herein to refer to one or
more than one (i.e., at least one) of the grammatical object of the
article. By way of example, "an element" means one element or more
than one element.
[0038] The terms "comprise" and "comprising" are used in the
inclusive, open sense, meaning that additional elements may be
included.
[0039] The term "including" is used to mean "including but not
limited to". "Including" and "including but not limited to" are
used interchangeably.
[0040] The term "in particular" is used to mean "in particular but
not limited to". And the term "particularly" is used to mean
"particularly but not limited to"
[0041] The term "zeolite" also refers to a group, or any member of
a group, of structured aluminosilicate minerals comprising cations
such as sodium and calcium or, less commonly, barium, beryllium,
lithium, potassium, magnesium and strontium; characterized by the
ratio (Al+Si):O=approximately 1:2, an open tetrahedral framework
structure capable of ion exchange, and loosely held water
molecules, that allow reversible dehydration. The term "zeolite"
also includes "zeolite-related materials" or "zeotypes" which are
prepared by replacing Si.sup.4+ or Al.sup.3+ with other elements as
in the case of aluminophosphates (e.g., MeAPO, SAPO, ElAPO, MeAPSO,
and ElAPSO), gallophosphates, zincophophates, titanosilicates, etc.
The zeolite can be a crystalline porous material with a frame work
as described in Pure Appl. Chem., Vol. 73, No. 2, pp. 381-394,
.COPYRGT.2001 IUPAC or provided in the Zeolite Framework Types
database of the IZA structure commission where under the following
structure types, as defined by the International Zeolite
Association such as ABW type, ACO type, AEI type, AEL type, AEN
type, AET type, AFG AFI type, AFN type, AFO type, AFR type, AFS
type, AFT type, AFX type, AFY type, AHT type, ANA type, APC type,
APD type, AST type, ASV type, ATN type, ATO type, ATS type, ATT
type, ATV type, AWO type, AWW type, BCT type, *BEA type, BEC type,
BIK type, BOG type, BPH type, BRE type, CAN type, CAS type, CDO
type, CFI type, CGF type, CGS type, CHA type, -CHI type, -CLO type,
CON type, CZP type, DAC type, DDR type, DFO type, DFT type, DOH
type, DON type, EAB type, EDI type, EMT type, EON type, EPI type,
ERI type, ESV type, ETR type, EUO type, EZT type, FAR type, FAU
type, FER type, FRA type, GIS type, GIU type, GME type, GON type,
GOO type, HEU type, IFR type, IHW type, IMF type, ISV type, ITE
type, ITH type, ITW type, IWR type, IWV type, IWW type, JBW type,
KFI type, LAU type, LEV type, LIO type, -LIT type, LOS type, LOV
type, LTA type, LTL type, LTN type, MAR type, MAZ type, MEI type,
MEL type, MEP type, MER type, MFI type, MFS type, MON type, MOR
type, MOZ type, MSE type, MSO type, MTF type, MTN type, MTT type,
MTW type, MWW type, NAB type, NAT type, NES type, NON type, NPO
type, NSI type, OBW type, OFF type, OSI type, OSO type, OWE type,
-PAR type, PAU type, PHI type, PON type, RHO type, --RON type, RRO
type, RSN type, RTE type, RTH type, RUT type, RWR type, RWY type,
SAO type, SAS type, SAT type, SAV type, SBE type, SBN type, SBS
type, SBT type, SFE type, SFF type, SFG type, SFH type, SFN type,
SFO type, SGT type, SIV type, SOD type, SOS type, SSF type, SSY
type, STF type, STI type, *STO type, STT type, SZR type, TER type,
THO type, TOL type, TON type, TSC type, TUN type, UEI type, UFI
type, UOZ type, USI type, UTL type, VET type, VFI type, VNI type,
VSV type, WEI type, --WEN type, YUG type and ZON type. The term
"zeolite" also includes "zeolite-related materials" or "zeotypes"
which are prepared by replacing Si4+ or Al3+ with other elements as
in the case of aluminophosphates (e.g., MeAPO, ALPO, SAPO, ElAPO,
MeAPSO, and ElAPSO), gallophosphates, zincophophates,
titanosilicates, etc. or other zeolites described in this
application.
[0042] The term "molecular sieves" as used herein refers to a solid
with pores of the size of molecules or oligo atomic clusters. It
includes, but is not limited to microporous and mesoporous
materials. In the nomenclature of the molecular sieves the pore
size of <20 Amstrong (A) is considered microporous and 20-500
.ANG. is considered mesoporous.
[0043] The term "microporous carrier" as used herein refers to a
solid with pores the size of molecules. It includes but is not
limited to microporous materials, ALPOs and (synthetic) zeolites,
pillared or non-pillared clays, carbon molecular sieves,
microporous titanosilicates such as ETS-10, microporous oxides.
Microporous carriers can have multimodal pore size distribution,
also referred to as ordered ultramicropores (typically less than
0.7 nm) and supermicropores (typically in the range of about 0.7-2
nm). A particular type of microporous carriers envisaged within the
present invention, are the molecular sieve zeolites. Zeolites are
the aluminosilicate members of the family of microporous carriers
which may be an ordered crystalline structure or amorphous.
[0044] The pore size of molecular sieves can further be influenced
by the nature of the templating molecules in the synthesis. The
addition of swelling agents to the synthesis mixture can further
affect the pore size of the resulting molecular sieve. Zeolites
with different pore size have been well characterized and described
by Martin David Foster in "Computational Studies of the Topologies
and Properties of Zeolites", The Royal Institution of Great
Britain, Department of Chemistry, University College London, a
thesis submitted for the degree of Doctor of Philosophy, London,
January 2003.
[0045] A comprehensive list of the abbreviations utilized by
organic chemists of ordinary skill in the art appears in the first
issue of each volume of the Journal of Organic Chemistry; this list
is typically presented in a table entitled Standard List of
Abbreviations.
[0046] For purposes of this invention, the chemical elements are
identified in accordance with the Periodic Table of the Elements,
CAS version, Handbook of Chemistry and Physics, 67th Ed., 1986-87,
inside cover. Contemplated equivalents of the zeolitic structures,
subunits and other compositions described above include such
materials which otherwise correspond thereto, and which have the
same general properties thereof, wherein one or more simple
variations of substituents are made which do not adversely affect
the efficacy of such molecule to achieve its intended purpose. In
general, the compounds of the present invention may be prepared by
the methods illustrated in the general reaction schemes as, for
[example, described below, or by modifications thereof, using
readily available starting materials, reagents and conventional
synthesis procedures. In these reactions, it is also possible to
make use of variants which are in themselves known, but are not
mentioned here. [0047] a. "the molecular sieve matrix is selected
from among microporous materials, selected from among zeolites,
porous oxides, silicoaluminophosphates and aluminosilicates" [0048]
b. "zeolite selected from among the family of small pore sized
zeolites such as zeolite A and ZKF, and combinations thereof"
[0049] c. "large pore zeolites such as ZSM-5, MCM-22, ferrierite,
faujastites X and Y and microporous molecular sieves" [0050] d.
"The matrix can also be a molecular sieve selected from among
molecular sieves MCM-41, MCM-48, HSM, SBA-15, and combinations
thereof" [0051] e. "Methods are available in the art for
preparation of microporous zeolites." [0052] f. "As used herein,
microporous zeolites preferably have a pore size of about 3
angstroms to about 14 angstroms"
[0053] The term microporous materials also include amorphous
microporous solids. Alternative amorphous microporous solids can be
used for present invent. For instance amorphous microporous mixed
oxides having, in dried form, a narrow pore size distribution (half
width <.+-.10% of the pore diameter) of micropores with
diameters in the range of <3 nm and the preparation of said
amorphous microporous mixed oxides have been well described in U.S.
Pat. No. 6,121,187 and others have been well documented in
WO0144308, U.S. Pat. No. 6,753,287, U.S. Pat. No. 6,855,304, U.S.
Pat. No. 6,977,237, WO2005097679, U.S. Pat. No. 7,055,756 and U.S.
Pat. No. 7,132,093 "Several documents are cited throughout the text
of this specification. Each of the documents herein (including any
manufacturer's specifications, instructions etc.) are hereby
incorporated by reference; however, there is no admission that any
document cited is indeed prior art of the present invention.
[0054] The oligo atomic metal clusters confined in molecular sieves
or microporous structures can be incorporated in membranes or films
for instance by embedding in transparent matrix materials such as
silicone, epoxy, adhesives, polymethylmethacrylate, polycarbonate.
Moreover the molecular sieves or the ordered comprising oligo
atomic silver clusters of present invention can be incorporated in
paints or fluids of film formers for coating on surface surfaces.
Media (paints, gelling liquids, elastomers) are available and
methods of manufacturing to achieve such membranes or films, for
instance a filled elastomeric polymer, which comprise the
oligo-atomic metal clusters confined in molecular sieves or in
ordered porous oxides (microporous or mesoporous or mixed
mesoporous/microporous) or porous materials with nanometer
dimension (0.3-10 nm) windows, channels and cavity architectures.
Typical but not exclusive examples of such elastomeric polymers are
polydimethylsiloxane (silicone rubber), polyisobutene (butyl
rubber), polybutadiene, polychloroprene, polyisoprene,
styrene-butadiene rubber, acrylonitrile-butadiene rubber (NBR),
ethene-propene-diene-rubber (EPDM) and
acrylonitrile-butadiene-styrene (ABS). Such films or membranes of
the molecular sieves comprising oligo atomic silver clusters;
ordered mesoporous and/or microporous oxides comprising oligo
atomic silver clusters or porous materials with nanometer dimension
(e.g. 0.3-10 nm) windows, channels and cavity architectures
comprising oligo atomic silver clusters can be coated on a
substrate. Following the ASTM (American Society for Testing and
Materials) standards, `elastomers` are defined as "macromolecular
materials that return to approximately the initial dimensions and
shape after substantial deformation by a weak stress and release of
the stress". Elastomers are sometimes also referred to as `rubbery
materials`. A `rubber` is defined as "a material that is capable of
recovering from large deformations quickly and forcibly, and can
be, or already is, modified to a state in which it is essentially
insoluble (but can swell) in boiling solvent, such as benzene,
toluene, methyl ethyl ketone, and ethanol/toluene azeotrope".
[0055] In the preparation of membranes with the oligo atomic metal
clusters confined in the microporous structures, the microporous
structures are first dispersed in an appropriate solvent. An
appropriate solvent is a solvent of low ionic strength, for
instance an ionic strength of a value in the range of 1 mmol/L to
0.05 mol/L, and should be able to dissolve the elastomer as well,
or at least, should be partially miscible with the solvent in which
the membrane forming polymer is dissolved. To improve the
dispersion, ultrasonic wave treatment, high speed mixing,
modification reactions, can be applied.
[0056] The content of porous structures with oligo atomic metal
clusters confined therein and polymer, in the dispersion, may range
from 1 wt % to 80 wt %, preferably 20 wt % to 60 wt %. The
dispersion is stirred for a certain time to allow (polymer/filler)
interactions to establish, to improve dispersion and possibly to
let a chemical reaction take place. When appropriate, the
dispersion can be heated or sonicated.
[0057] The metal clusters in microporous materials are in molecular
sieves or microporous structures, may be incorporated in paints or
printing inks (e.g. printable matrix printing ink or printable
paints, varnishes (e.g. overprinting varnishes) and paints for
depositing, spraying, printing or painting a layer or a coating on
a substrate. Printing inks or paints of the art which are suitable
for comprising the emitting materials of present invention are for
instance hard resins, colophony-modified phenol resins, maleate
resins, hydrogenated mineral oil cuts, synthetic aromatic oils,
alkyd resins in particular hydrocarbon resins and/or a colophony
resin ester and dialkyl ether such as di-n-dodecyl ether,
di-n-undecyl ether, allyl-n-octyl ether, n-hexyl-n-undecyl ether as
a vehicle. Particular suitable solvents are the resin(s)
water-insoluble fatty acid esters of polyvalent alcohols or
ethinols. Suitable printing inks in the art are described in U.S.
Pat. No. 4,028,291, U.S. Pat. No. 4,169,821, U.S. Pat. No.
4,196,033, U.S. Pat. No. 4,253,397, U.S. Pat. No. 4,262,936, U.S.
Pat. No. 4,357,164, U.S. Pat. No. 5,075,699, U.S. Pat. No.
5,286,287, U.S. Pat. No. 5,431,721, U.S. Pat. No. 5,886,066, U.S.
Pat. No. 5,891,943, U.S. Pat. No. 6,613,813 and U.S. Pat. No.
5,965,633. Such emitting material of present invention may be
painted, printed or coated on the substrate.
[0058] Solvent casting or coating is used as the membrane
preparation process.
[0059] A particular method of coating is solution-depositing of the
molecular sieves comprising oligo atomic silver clusters comprises
spray-coating, dip-casting, drop-casting, evaporating,
blade-casting, or spin-coating the molecular sieves comprising
oligo atomic silver clusters; ordered mesoporous and/or microporous
oxides comprising oligo atomic silver clusters or porous materials
with nanometer dimension (e.g. 0.3-10 nm) windows, channels and
cavity architectures with an assembly of oligo atomic metal
clusters confined in such structures (hereinafter the porous
structures with oligo atomic metal clusters confined therein) onto
a substrate
[0060] The (polymer/porous structures with oligo atomic metal
clusters confined therein) dispersion can be cast on a non-porous
support from which it is released afterwards to form a
self-supporting film. One way tot realise this is by soaking it
previously with a solvent, which has a low affinity for the
dispersion. Also, the support can be treated with adhesion
promoters. After casting or coating, the solvent is evaporated and,
if necessary, a heat treatment can be applied to finish the
cross-linking reactions. The heat treatment can possibly occur
under vacuum conditions to remove the remaining solvent. The
resulting supported membranes be a filled elastomer with the
thickness of this selective layer in a range from 0.01 .mu.m to 500
.mu.m, preferably from 0.1 to 250 .mu.m and yet more preferably
from 10 to 150 .mu.m.
[0061] The most important elastomers are polyisoprene (natural or
synthetic rubber (IR)), polychloroprene (chloroprene rubber (CR)),
butyl rubber (BR), styrene-butadiene rubber (SBR),
acrylonitrile-butadiene rubber (NBR), ethene-propene-diene-rubber
(EPDM), acrylonitrile-butadiene-styrene (ABS), chlorosulfonated
polyethylene (CSM), I polyacrylate (polyacrylic rubber),
polyurethane elastomers, polydimethylsiloxane (PDMS, sometimes more
generally referred to as silicone rubber), fluorosilicones and
polysulfides. Polystyrene is a thermoplastic polymer that
particularly resistant to irradiation.
[0062] The films with the porous structures of present invention
may need particular characteristics according to its environment of
use. A variety of alternatives polymers that provide design freedom
which preparation protocols are available in the art to design
complex shapes, to consolidate parts into fewer components,
simplify production, to produce transparent and precolored
components, to reduce part weight, to reduce noise when the porous
structures with oligo atomic metal clusters is moving, to have a
reliable performance at elevated temperature, to have chemical
resistance in harsh climates, to have the desired stiffness,
strength and toughness, to have hydrolytic stability over time, to
have electrical properties to have a desired physical
appearance
[0063] Polymers that are suitable for incorporation of the porous
structures of present invention are for instance Spire.TM. family
of ultra polymers such as 1) KetaSpire.RTM. polyetheretherketone
(PEEK) which is easy-to-mold ultra polymer offering outstanding
chemical resistance and mechanical performance up to 300.degree. C.
(570.degree. F.) or AvaSpire.RTM. modified PEEK, a PEEK-based
formulations or 2) PrimoSpire.RTM. self-reinforced polyphenylene
(SRP) known to be designable in a very stiff, strong unreinforced
polymer with a remarkable combination of surface hardness, chemical
resistance and inherent flame-retardant properties or 3)
EpiSpire.TM., an high-temperature sulfone (HTS) known to be a
transparent amorphous polymer with excellent creep resistance at
temperatures up to 265.degree. C. (510.degree. F.) or 4)
Torlon.RTM. polyamide-imide (PAI) with higher strength and
stiffness that most thermoplastic up to 275.degree. C. (525.degree.
F.) combined with superior resistance to chemicals, creep and wear.
Other polymers that are suitable for incorporation of the porous
structures with oligo atomic metal clusters confined therein of
present invention are the family of amorphous sulfone polymers such
as 1) Udel.RTM. PSU known to be designable into tough, transparent
plastic with exceptional chemical resistance, good hydrolytic
stability and an HDT of 345.degree. F. (174.degree. C.) or the 2)
Mindel.RTM. modified polysulfone with superior electrical
propertiesor 3) the Radel.RTM. R (PPSU) known to deliver a
super-tough transparent plastic with an HDT of 405.degree. F.
(207.degree. C.), excellent chemical resistance and the unique
ability to be steam sterilized without significant loss of
properties or 4) the Radel.RTM. A (PES) know to deliver a
transparent plastic with a high HDT of 400.degree. F. (204.degree.
C.) and good chemical resistance or the Acudel.RTM. modified PPSU.
Other polymers that are suitable for incorporation of the porous
structures with oligo atomic metal clusters confined therein of
present invention are for instance the semi-crystalline aromatic
polyamides such as for instance the Amodel.RTM. polyphthalamide
(PPA) known to deliver a high-temperature nylon with exceptional
mechanical properties, an HDT of 535.degree. F. (280.degree. C.),
excellent chemical resistance and low moisture uptake or the
Ixef.RTM. polyarylamide (PA MXD6) known to deliver aesthetic,
structural specialty nylon that combines outstanding stiffness with
exceptional surface appearance, plus low and slow water uptake, and
great flow properties. Other polymers that are suitable for
incorporation of the porous structures with oligo atomic metal
clusters confined therein of present invention are for instance
semi-crystalline polymers such as the Primef.RTM. polyphenylene
sulfide (PPS) which delivers a high-flow, structural plastic with
good temperature and chemical resistance as well as inherent flame
retardant properties or the Xydar.RTM. liquid crystal polymer (LCP)
known to deliver high-flow, high-temperature plastic with an HDT of
570.degree. F. (300.degree. C.), and extremely high chemical
resistance. These are available with design and processing guides
form Solvay Advanced Polymers.
[0064] A particular example of manufacturing emitting film based on
the porous structures oligo atomic metal clusters confined therein
of present invention and a polymer is for instance the use of
polydimethylsiloxane (PDMS), RTV-615 A and B (density 1.02 g/ml)
and the adhesion promoter (SS 4155) which are obtainable from
General Electric Corp. (USA). Component A is a prepolymer with
vinyl groups. Component B has hydride groups and acts as
cross-linker and EPDM (Keltan 578 from DSM) and porous structures
with oligo atomic metal clusters confined therein of present
invention which are well dried before use.
[0065] Such can be produced by preparing dispersing a powder of the
porous structures with oligo atomic metal clusters confined therein
of present invention (for instance a zeolite comprising oligo
atomic silver clusters) in hexane. adding the cross-linker (RTV 615
B) to the dispersion of porous structures with oligo atomic metal
clusters confined therein of present invention and stirring this
mixture at 40.degree. C. for two hours to allow sufficient time to
establish strong interactions between both phases. Adding the
prepolymer (RTV 615 A) and stirring the mixture for another hour at
60.degree. C. to induce prepolymerisation. Pouring the (PDMS/ZSM-5
CBV 3002) in a petridish and allowing the solvent to evaporate for
several hours and the resulting film was cured at 100.degree. C.
The content of the solid components (i.e. PDMS and filler) in the
casting solution was 18.5 wt %. The RTV 615 A/B ratio for optimal
polymer curing was 7 in order compensate for the loss of hydride
groups due to their reaction with the surface silanol groups on the
zeolite (normally it is in a 10/1 ratio, as proposed by the
manufacturer to be the ratio for optimal curing).
[0066] For flexible substrates thermoplastics (e.g., Polyethylene
naphthalate (PEN), Polyethersulfone (PES), Polycarbonate (PC),
Polyethylene terephthalate (PET), Polypropylene (PP), oriented
polypropylene (OPP), etc.), and glass (e.g., borosilicate)
substrates may be used for these applications. Low liquidus
temperature material, which typically has a low liquidus
temperature (or in specific embodiments a low glass transition
temperature can be used form a barrier layer on a flexible
substrate and can be can be deposited onto the flexible substrate
by, for example, sputtering, co-evaporation, laser ablation, flash
evaporation, spraying, pouring, frit-deposition, vapor-deposition,
dip-coating, painting or rolling, spin-coating, or any combination
thereof. The porous structures with oligo atomic metal clusters
confined therein can be incorporated into the low liquidus
temperature materials. Such low liquidus temperature material
includes, but is not limited to, tin fluorophosphate glass,
chalcogenide glass, tellurite glass and borate glass.
[0067] The molecular sieves comprising oligo atomic silver clusters
as luminescent materials find a variety of other beside
applications such as secondary light sources in fluorescence lamps
thanks to their high emission intensity, exceptional photostability
and large stokes shift. The space-resolved activation of the
emission intensity can also be used in data storage
application.
[0068] An example of such emissive particles are those prepared by
exchanging 8.+-.1 (w/w) of silver ions (from AgNO3) in a zeolite 3A
(K-form; see Example 10). The subsequent heat treatment causes a
partial (auto)reduction of the silver species. FIGS. 10 a (1) and b
(1) show a typical scanning image of a roughly 3 by 3 .mu.m
silver-containing zeolite under a confocal microscope using a
picosecond (ps) pulsed 375 nm (doubled Ti:Sapphire; see Example 10)
excitation source of 10 and 20 W/cm2 for 10a respectively 10b. In
the crystal shown in FIG. 10a, three individual diffraction limited
spots are activated by 20 minute irradiation with the same ps 375
nm source at low power (10 W/cm2) (panels 1 till 4). This
illustrates the write and read possibilities of the material in
data storage applications. The crystal in FIG. 10b is totally
activated by high power (16.7 kW/cm2) 375 nm excitation. After 5
minutes a 10-fold increase of the emission intensity as indicated
in FIG. 10b (2) is realized. Another 20 minutes of high-intensity
irradiation caused the emission to reach a steady state at a
20-fold intensity increase, as seen in FIG. 10b (3). FIG. 10c shows
a true color image (in this application in grey scale) of the same
crystal under UV-excitation at 16.7 kW/cm2 observed through the
eyepiece of the microscope. In contrast to quantum dots [S. K.
Ghosh, S. Kundu, M. Mandal, S. Nath, T. Pal, Journal of
Nanoparticle Research 2003, 5, 577], being another type of bright
and photostable emitters, the luminescence of this material doesn't
show any blinking since the emission originates from multiple
silver particle emitters confined within one crystal (see Example
10).
[0069] The dynamics of the activation process were monitored by
recording emission spectra at 1 s intervals (or 10 s for the lowest
excitation intensity). Plotting the emission intensity maxima of
these spectra as a function of time upon different UV powers,
reveals a sigmoidal behavior with characteristic lag times of up to
a few hundreds of seconds at low excitation powers before the
actual activation takes place (FIG. 11). There is an UV-induced
electron transfer from the lattice oxygen to the silver species,
yielding reduced silver that may form highly emissive clusters.
After activation the emission intensity mostly reaches a
steady-state which is maintained over at least several hours
without or with minor photobleaching. The maximum slope in the
sigmoidal activation curves shows a non-linear relationship with
the applied excitation power (FIG. 11, inset). Fitting the data to
a power function yields an exponent of 2.24, which indicates that
multiple photons are involved in the formation of the activated
cluster, either by a two-photon absorption process or by the
occurrence of two independent simultaneous photochemical reactions,
causing the reaction kinetics to be of a higher order with respect
to the excitation intensity. There an equilibrium between
Ag0-cluster creation and destruction of the weak Ag--Ag bonds upon
UV-illumination. If the steady-state intensity is reached for a
certain excitation power, an additional activation can still take
place at higher excitation power until a new steady-state level is
reached. This means that the equilibrium between formation and
destruction can be shifted by variations in excitation power.
[0070] Spectral analysis revealed that the dominant species after
activation have a strong greenish emission with a distinct maximum
in intensity at 541.8.+-.3.8 nm (FIG. 12) upon 375 nm excitation.
Comparison with the heterogeneous emission spectra of the loaded
crystals before activation, having emission maxima ranging from 493
till 541 nm, indicates that only a limited amount of cluster types
are very specifically formed upon photoactivation and dominate the
emission spectrum.
[0071] The extremely high luminescence intensity originating from
one single activated crystal allows recording wavelength dependent
decays by single-photon counting using a PMT detector with an
instrumental response function of 90 ps (Table 1). After activation
the luminescence decay shows three distinct components of
approximately 100 ps, 1 ns and 4 ns. The obtained decays were
analyzed globally and fitted by a tri-exponential decay using a
time-resolved fluorescence analysis software program (TRFA) [H. K.
Beyer, P. A. Jacobs, J. B. Uytterhoeven, Journal of the Chemical
Society-Faraday Transactions I 1979, 75, 109] keeping the
characteristic decay times, .tau., identical for all emission
wavelengths. At higher emission wavelengths, the contribution of
the fast decay component, and to a less extent also the medium
decay component, decreases in favor of the slowest decay (see also
Supporting Information). The fact that the three contributions can
be spectrally separated indicates the existence of multiple
emitting species, being either different silver nanoclusters or
identical nanoclusters having different interactions with the
zeolite lattice or coordination spheres.
TABLE-US-00001 TABLE 1 Contributions and decay times of the
different fluorescence decay components measured for two single
crystals at different emission wavelengths, obtained by global
analysis with linked .tau.-values for all emission wavelengths of
one crystal. Graphical representation of the data can be found in
the Supporting Information. Crystal 1.sup.[a] Crystal 2.sup.[b]
.alpha.0.12 ns .alpha.0.92 ns .alpha.3.41 ns .alpha.0.20 ns
.alpha.1.26 ns .alpha.4.03 ns .lamda..sub.em. (nm) (%) (%) (%) (%)
(%) (%) 460 16.1 39.0 45.0 28.0 56.3 15.7 480 11.7 36.1 52.2 23.2
56.6 20.1 500 7.6 30.2 62.3 16.3 52.7 30.9 520 4.5 24.4 71.1 8.7
41.5 49.7 540 2.7 20.7 76.6 5.2 32.3 62.5 560 1.6 18.6 79.7 3.6
25.0 71.4 580 1.5 16.9 81.7 2.7 19.8 77.4 600 1.4 15.9 82.8 2.5
15.8 81.7 620 1.2 17.3 81.5 2.6 13.7 83.7 640 1.3 20.9 77.7 2.7
11.88 5.5 .sup.[a].chi..sup.2 of the global fit = 1.039; excitation
power: 1.83 kW/cm.sup.2 .sup.[b].chi..sup.2 of the global fit =
1.174; excitation power: 16.7 kW/cm.sup.2.
[0072] An in-depth microscopic characterization of the emissive
properties of Ag-loaded zeolites is presented. The controllable
space-resolved photoactivation of the emission with a
diffraction-limited resolution has interesting applications data
storage devices. Due to the large stokes-shift, broad emission
range and high photostability upon UV-illumination, this highly
emissive material can serve as wave length conversion material in
solar cells.
EXAMPLES
Example 1
Preparation
[0073] Various methods for the production of metal ion exchanged
molecular sieves are available in the art. A method similar as
described by Jacobs et al. (Jacobs, P. A. & Uytterhoeven, J.
B., 1979, Journal of the Chemical Society-Faraday Transactions 175,
56-64) was used for incorporating silver ions in molecular sieves
and creating silver clusters. However lots of parameters like
loading percentage of the zeolites, exchange time, length of
temperature treatment, initial, gradient and final temperature of
the temperature treatment, presence of gasses during the
temperature treatment (e.g. in vacuum, in presence of oxygen, in
presence of oxygen and nitrogen, in presence of hydrogen, in
presence of CO and/or CO.sub.2 gas) and the presence of moisture in
the air influences the finally formed types of clusters, oxidation
state of the clusters and distribution and polydispersity of the
types of clusters formed.
Example 2
Emission
[0074] It was demonstrated that metal ion cluster especially silver
in confined molecular sieves have a distinct and tunable emission
throughout the VIS and NIR part of the electromagnetic spectrum
while they are all excitable in the UV region. Thanks to the host
matrix the confined metal clusters are prevented from aggregation
with each other to form bigger non emissive nanoparticles. Also
they can be shielded from the outside environment (e.g. oxygen) if
required by adding a silicon coating around the molecular
sieves.
Example 3
Conversion Medium for Solar Cells
[0075] The molecular sieve materials comprising the oligo metal
clusters confined therein or microporous materials comprising the
oligo metal clusters confined therein and mixtures thereof can be
used to convert UV radiation into visible light. This layer then
emits visible (white) light which is then absorbed by the solar
cell and converted into an electric current. By mixing different
metal cluster containing molecular sieves containing different
clusters, different spectral properties can be generated. By
changing the ratios of the mixed materials a whole range of light
colors can be generated, including white light. If one however
wants light of a particular color, one can select a specific metal
cluster emission. The synthesis of the oligo metal clusters with
the desired emissive properties can be tuned by changing the
synthesis parameters. By adjusting the material by either mixing
several different color emitting crystals together or creating
multiple colored emitting species in one crystal one can create a
white light emission.
Example 4
UV Radiation Source
[0076] The solar radiation spectrum will be used, see FIG. 13.
Example 5
Support Material for the Molecular Sieves Containing Oligo Atomic
Metal Clusters
[0077] Some support material might have to be added to structurally
hold the molecular sieves containing the small Au or Ag clusters
(FIG. 3) to receive the sun radiation and to make sure that the
emission exits the surrounding covering shell in a homogenous way.
This supporting material can be anything as long as it is resistant
to UV and visible radiation, does not absorb too much of the sun
radiation and is heat resistant.
Example 6
Emissive Visible Light Source
[0078] The molecular sieve materials comprising the oligo metal
clusters confined therein or microporous materials comprising the
oligo metal clusters confined therein and mixtures thereof are used
as wavelength converters in the production of lamps similar to
currently used fluorescent lamps. By mixing different metal cluster
containing molecular sieves containing different clusters,
different spectral properties can be generated. By changing the
ratios of the mixed materials a whole range of light colors can be
generated, including white light. If one however wants light of a
particular color, one can select a specific metal cluster emission.
FIG. 1 illustrates this example, showing a 3A zeolite exchanged
with silver (10% weight) that was thermally treated (24 hours at
450.degree. C.) resulting in a partial reduction and formation of
small silver clusters in the host matrix. Under UV excitation a
green/yellow color can be observed. Other reduction methods, for
example by adding H.sub.2 gas to a silver ion exchanged solution of
zeolites resulted in dominantly blue emission. By adding more
silver, emission in the red part of the visible spectrum was
created (see also FIG. 1). The synthesis of the oligo metal
clusters with the desired emissive properties can be tuned by
changing the synthesis parameters. Under the microscope using UV
excitation one can see clearly distinct crystals of uniform but
different color (FIG. 2). In this sample crystals of different
colors were present; however synthesis also allows the production
of only one type of emissive species to be present. The orange
emitting sample show in FIG. 1 for example diplayed yellow and red
crystals on the microscope under UV excitation. FIG. 3 shows a
schematic drawing of the wave length converting molecular sieves or
mesoporous materials with the oligo metal clusters confined therein
(EM) which are embedded in a support material (SM). A the UV and
low wave length light (e.g.; <400 nm) solar radiation excites
the layer of the material. By adjusting the material by either
mixing several different color emitting crystals together or
creating multiple colored emitting species in one crystal one can
create a white light emission. For colored visible emissive lamps
one can use just one type of crystal that just emits one color.
Example 7
Support material for the molecular sieves containing oligo atomic
metal clusters
[0079] Some support material might have to be added to structurally
hold the molecular sieves containing the small metal clusters e.g.
small Au or Ag clusters exposed to the sun radation and to make
sure that the emission radiates the photovoltaic elements. This
supporting material can be anything as long as it is resistant to
UV and visible radiation, does not absorb too much UV radiation
from the primary UV source and is heat resistant.
Example 8
Tunable Color of Excitation and Emission of the Visible Emission
Source
[0080] The molecular sieves containing the oligo atomic clusters
can be excited by UV, blue or violet light resulting in emission of
light with a larger wave length as described in example 3. However
by changing or tuning the excitation wavelength or by using
multiple excitation wavelengths coming from one or multiple sources
and by tuning the different ratios of excitation power between the
different wavelengths, it is possible to tune the color of the
visible emission. In this way one could have one emissive device
which output color can be tuned by the end user. This effect can be
achieved by using different oligo atomic clusters in the molecular
sieves that have a different emissive responds on different UV,
blue light or violet light wavelengths. This is also illustrated in
FIG. 3. An example of this was synthesized where irradiation of the
materials with 360 nm light resulted in blue emission while
exciting at 254 nm resulted in yellow emission. If one would excite
with the two wavelengths, 254 nm and 360 nm at same time and by
changing the ratios of excitation power, one could create a whole
range of emission colors between blue and yellow and all the
possible sum colors.
Example 9
High and Stable Luminescence Materials
Synthesis of Ag-Exchanged Zeolite A-Materials
[0081] Zeolite 3A (Union Carbide; 500 mg) was suspended in 100 mL
MQ-water containing 13.+-.1 weight percent of silver nitrate
(8.+-.1% Ag). After stirring in the dark for 2 hours the ion
exchange (.+-.17% of the zeolite's cation exchange capacity) was
stopped. The material was poured on a Buchner filter and
extensively washed with MQ-water. This washing stepped proved a
quantitative silver exchange since no precipitation with chlorides
was observed in the washing water. The recovered white powder on
top of the filter was heated at 450.degree. C. Celsius for 1 day.
After this heat treatment a white to sometimes slightly yellowish
powder was obtained. The powder was stored in the dark under dry
atmosphere.
Bulk Characterization of the Ag-Loaded Zeolites
[0082] Emission spectra were recorded at different excitation
wavelengths ranging from 260 nm till 660 nm at 20 nm intervals on a
Horiba Jobin Yvon FluoroLog fluorimeter. The powder was sandwiched
between two quartz plates and mounted in the fluorimeter. Emission
was detected in "front face mode". At least three distinct emissive
species can be identified from these spectra, as seen in FIG.
4.
Single Crystal Measurements
Description of the Setup
[0083] As an excitation light source, the frequency doubled output
(375 nm, 8.18 MHz, 0.8 ps FWHM) of a mode-locked Ti:Sapphire laser
(Tsunami, Spectra Physics) was used to excite the single crystal.
The excitation light, circularly polarized by use of a Berek
polarization compensator (New Focus), was directed by using a
dichroic beam splitter into the oil-immersion objective (Olympus,
1.3 N.A., 100.times.) of an inverted microscope (Olympus IX70)
equipped with a scanning stage (Physics Instruments). The
excitation power was adjusted with a neutral density wheel at the
entrance port of the microscope. The fluorescence was collected by
the same objective, filtered (400 nm longpass, Chroma Technology),
split with a non-polarizing beam splitter (50:50) and focused for
one path into a polychromator (Spectra Pro150 Acton Research
Corporation) coupled to a back illuminated liquid nitrogen cooled
CCD camera (LN/CCD-1340.times.400, Princeton Instruments) in order
to record fluorescence spectra with a resolution down to 1 nm. The
other path was focused onto an avalanche photo-diodes (SPCMAQ-15,
EG & G Electro Optics) and used to get scanning images. These
scanning images were obtained using an excitation power of 15
W/cm.sup.2 and for each pixel the intensity was integrated over 2
ms.
[0084] For the decay measurements at specific wavelengths, all the
fluorescence was collected and focused into a 100 micron multimode
optical fiber. The output of the fiber was mounted at the entrance
of a double monochromator (Sciencetech 9030, 6 nm bandwith) and the
fluorescence was detected with a microchannel plate photomultiplier
(MCP-PMT, R3809U, Hamamatsu) equipped with a time correlated single
photon counting card (Becker & Hickl, SPC 830). The
fluorescence decay analysis was performed with a home-made
time-resolved fluorescence analysis (TRFA) software which takes
pulse deconvolution into account, based on the Marquardt algorithm
that uses a reweighted iterative reconvolution method of the
instrumental response function of the setup with tri-exponential
model function (M).sup.1:
IRF j M j = i [ a ij exp ( - j T / k .tau. i ) ] + U ( 1 )
##EQU00001##
with j ranging from 1 till k with k the number of channels over
which the photons of a decay are spread and i the number of
exponential terms. Here T is the time window of the experiment, a
and t are amplitude and decay time and U is a constant accounting
for non-correlated background. The experimental instrument response
function was determined in the order of 90 ps by using the
scattering of the laser on the cover glass.
[0085] The fluorescence decays were analyzed first individually in
terms of decays times .tau..sub.t and their associated
pre-exponential factors a.sub.i. The final curve-fitting was done
by global analysis using a tri-exponential decay function with
linked .tau.-values for all the decays of one crystal recorded at
different emission wavelengths over the emission spectrum and the
fitting parameters were determined by minimizing (non linear least
squares) the global, reduced chi-square .chi..sup.2.sub.g. The
contribution of the decay times recovered after the global analysis
was estimated using the relative amplitudes:
.alpha. i = .alpha. i .tau. i i a i .tau. i ( 1 ) ##EQU00002##
[0086] The goodness of the fits was judged for each fluorescence
decay trace separately as well as for the global fluorescence decay
by the values of the reduced .chi..sup.2, and the visual inspection
of the residuals and autocorrelation function.
[0087] All decay curves presented here had a .chi..sup.2 value
below 1.46 (most of them even below 1.1). As an example, three
decay curves of crystal 1 for three different emission wavelength
from the tri-exponential global fit are shown in FIG. 5. The
residuals show a perfect random behaviour indicative for the high
quality of the global fit.
[0088] The trends in contribution of the different decay components
as a function of lifetime for the two crystals presented in the
article are graphically highlighted in FIG. 6.
Measuring Single Crystal Emission Spectra and Constructing
Activation Curves
[0089] Emission spectra where measured as a function of time (one
spectrum every second) for a single crystal. The obtained spectra
were smoothed using a binomial filter. The wavelength of maximum
emission at the end of the activation process was determined and
the intensity at this wavelength was plotted during the entire
activation process to construct the activation graphs in FIG. 1 of
the article.
[0090] FIG. 7 shows that after the emission reaches its plateau
intensity upon a certain UV illumination power, this irradiated
spot can be further activated by increasing the excitation power.
This observation suggests that these plateaus are representing
steady-state conditions, typical for each excitation power in which
cluster formation and destruction are in equilibrium.
Single Crystal Emission Time Transient and Autocorrelation
Graph
[0091] FIG. 8 shows the emission intensity time transient (binned
at 500 .mu.s; recorded using the APD connected to the Becker &
Hickl SPC830 counting card) before (upper part) and after (lower
part) photoactivation by UV irradiation, together with the
autocorrelation graph performed directly on the photon arrival
times. From these graphs it is concluded that the single crystal's
emission doesn't show blinking or intensity fluctuations in a time
range from less than 1 .mu.s till 0.1 s. The assumption that the
individual crystals contain a big amount of emitters is therefore
reasonable.
SEM Pictures of the Ag-Loaded Zeolites.
[0092] SEM-pictures of the used zeolites (after loading with silver
and calcinations) are recorded using a Philips XL30-FEG (FIG. 8).
The average crystal size is about 3 .mu.m. For about 20% of the
observed crystals larger aggregates (presumably silver
nanoparticles) can be resolved at the crystal's outer surface.
These relatively big particles are supposed to be non-emissive.
Moreover, for the fluorescence microscope experiments we always
focused as much as possible in the center of a crystal. As the
pinhole in the emission path efficiently rejects out-of-focus
light, we can be sure that the observed emission and
photoactivation originates from intra-zeolite silver particles.
DRAWING DESCRIPTION
Brief Description of the Drawings
[0093] The present invention will become more fully understood from
the detailed description given herein below and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0094] The present invention will become more fully understood from
the detailed description given herein below and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0095] FIG. 1: provides photograph with an example of different
colors of emission of zeolite 3A filled with silver when excited
with 254 nm UV light.
[0096] FIG. 2: Image of the detected emission of individual zeolite
crystals (taken from the sample in FIG. 1 on the right) excited
with UV light under the microscope. Clearly individual brightly
colored crystals are present.
[0097] FIG. 3: Scheme of an emissive layer of microporous oligo
metal clusters containing material for wave length conversion in
solar cells.
[0098] FIG. 4: Emission spectra of Ag-exchanged zeolite A powder at
different excitation wavelengths.
[0099] FIG. 5: Three fluorescence decay curves and their global
fitting results for crystal 1.
[0100] FIG. 6: Relative contributions of the decay components as a
function of emission wavelengths for crystal
[0101] FIG. 7: Activation curves of the same spot in a Ag,K-zeolite
upon successive illumination at 0.32 and 1.0 kW/cm2.
[0102] FIG. 8: Intensity time transient binned at 0.5 ms (left)
with the corresponding autocorrelation (G(.tau.)) graph (right) for
a single Ag loaded zeolite 3A before (upper part) and after (lower
part) photoactivation by UV irradiation.
[0103] FIG. 9: SEM pictures of Ag-loaded zeolite 3A crystals.
[0104] FIG. 10: a) False color emission image of a single
silver-exchanged zeolite A crystal before photoactivation (1) and
after consecutive activation of three individual spots (2, 3 and 4)
in one crystal by irradiation with a ps 375 nm laser at 10
W/cm.sup.2 during 20 minutes for each spot through a confocal
microscope. b) Total activation of a single crystal. (1) shows the
crystal before activation. After 5 min of irradiation by a 16.7
kW/cm.sup.2 pulsed 375 nm beam the intensity increased by a factor
10 (2). Another 20 minutes of activation at the same power yielded
a total intensity increase of a factor 20. Note the increased
scaling range from (1) till (3). The images in a) and b) were taken
by a confocal microscope under irradiation by a 375 nm pulsed
excitation source of respectively 10 and 20 W/cm.sup.2, with 2 ms
integration time per pixel. c) True color image taken with a
digital camera (Canon PowerShot A710 IS with a 400 nm longpass
filter in front of the lens to filter out the excitation light)
through the eye piece of the microscope showing the green emission
from the same zeolite after complete activation at 16.7 kW/cm.sup.2
excitation power.
[0105] FIG. 11. Log-log plot of the time evolution of the emission
intensity (I) (activation curves) of 11 different single Ag-loaded
zeolite crystals excited with four different intensities for the
activation. The inset shows a plot of the maximum activation rate
(dI/dt of the linear part of the activation curves) achieved for
each crystal as a function of excitation power. These data points
were fitted by a power function and show a non-linear behavior.
[0106] FIG. 12. a) Emission spectrum before and after
photoactivation for one single crystal. The dotted line shows the
spectrum before activation in real scale with respect to the
spectrum after activation (full line), while the dashed line
represents the spectrum before activation normalized (.times.13) to
the maximum intensity after activation. b) Emission maximum before
and after photoactivation for 12 single crystals. This maximum
shifts from a broad range before activation to a rather small band
around 540 nm after photoactivation. All spectra were taken upon
excitation by a 375 nm ps laser at excitation powers ranging from
33 W/cm2 till 9.5 kW/cm2.
[0107] FIG. 13: displays the solar radiation spectrum
[0108] FIG. 14: is a schematic diagram showing a cross-sectional
structure of solar cell that comprises the wavelength converter
material (conversion layer). The conversion layer which comprises
the molecular sieves with the confined metal atomic clusters is
present on top of a solar cell with its elements identified by a
number code. 1 is the conversion layer (the layer comprising the
molecular sieves with the confined metal atomic clusters). The
Conversion layer [1) an additionally be covered by a transparent
substrate layer (not shown). 2 is an electrode which is transparent
or integrated in a transparent layer and 4 concerns the counter
electrode. The general type of solar cell material [3] concerns the
electrolyte layer with or without other extra elements.
[0109] FIG. 15: is a schematic diagram showing a cross-sectional
structure of solar cell that comprises the wavelength converter
material (conversion layer) of present invention. The solar cell
comprises the molecular sieves with the confined metal atomic
clusters (in the conversion layer). In this particular embodiment
of present invention the solar cell has between an electrode (2)
formed on a surface of a transparent substrate (5) and a counter
electrode (4), a layer of molecular sieves with confined metal
atomic clusters (conversion layer) and an electrolyte layer
(3).
* * * * *