U.S. patent application number 11/509174 was filed with the patent office on 2006-12-14 for photo-luminescence layer in the optical spectral region and in adjacent spectral regions.
Invention is credited to Hartmut Frob, Matthias Kurpiers, Karl Leo.
Application Number | 20060280869 11/509174 |
Document ID | / |
Family ID | 5647415 |
Filed Date | 2006-12-14 |
United States Patent
Application |
20060280869 |
Kind Code |
A1 |
Frob; Hartmut ; et
al. |
December 14, 2006 |
Photo-luminescence layer in the optical spectral region and in
adjacent spectral regions
Abstract
This invention relates to a photoluminescent layer in the
optical and adjoining spectral regions based on a solid solution of
organic dyes. The photoluminescent layer includes organic dye
molecules with a low dye concentration and a matrix material of
metal oxides, with the matrix material having a slightly
sub-stoichiometric oxygen content. A method and a device for
producing the photoluminescent layer are described.
Inventors: |
Frob; Hartmut;
(Reinhardtsgrimma, DE) ; Kurpiers; Matthias;
(Dresden, DE) ; Leo; Karl; (Dresden, DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Family ID: |
5647415 |
Appl. No.: |
11/509174 |
Filed: |
August 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10204585 |
Nov 26, 2002 |
7101626 |
|
|
PCT/DE00/00498 |
Feb 23, 2000 |
|
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11509174 |
Aug 24, 2006 |
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Current U.S.
Class: |
427/255.23 ;
118/715; 427/157 |
Current CPC
Class: |
C09K 11/06 20130101;
C23C 14/06 20130101 |
Class at
Publication: |
427/255.23 ;
427/157; 118/715 |
International
Class: |
C23C 14/00 20060101
C23C014/00 |
Claims
1. Method for producing a photoluminescent layer on a substrate
that emits light in the optical and adjoining spectral regions, in
which organic dye and silicon oxide are deposited on a substrate
under high vacuum, with the desired volume concentration of the dye
in the matrix material being produced by setting the rate of vapor
deposition of the components, characterized by the fact that the
suboxide is vaporized for the deposition of silicon oxide, or a
metal oxide is deposited instead of silicon oxide, with the
particular suboxide of the metal oxide being vaporized.
2. Method pursuant to claim 1, characterized by the fact that SiO
or Ti.sub.2O.sub.3 is vaporized as the silicon or metal
suboxide.
3. Method pursuant to claim 1, characterized by the fact that the
rate of vapor deposition of the dye is set by temperature control
of the vaporizer source.
4. Method pursuant to claim 3, characterized by the fact that the
desired layer thickness is set by the rate of vapor deposition and
the open time of the diaphragm located between vaporizer source and
substrate.
5. Device for implementing the method pursuant to claim 1, in which
a dye vaporizer and a metal oxide vaporizer whose vapor jets are
aimed at a substrate are provided in a vacuum chamber, with the dye
vaporizer being cup-shaped and consisting, viewed from the inside
toward the outside, of a quartz cuvette, a graphite block, a
heater, a shield, and a jacket, with a thermocouple being provided
in the bottom center of the cup between the quartz cuvette and the
graphite block, and with a cover constricted to a cut-out hole
being provided in the cup-shaped opening of the dye vaporizer,
characterized by the fact that the cover constricted to a cut-out
hole is connected to the quartz cuvette and displaced toward the
dye, so that the cut-out hole in the cover has a temperature like
that of the heated quartz cuvette.
6. Device pursuant to claim 5, characterized by the fact that the
jacket is a water-cooled copper jacket.
7. Method pursuant to claim 2, characterized by the fact that the
rate of vapor deposition of the dye is set by temperature control
of the vaporizer source.
8. Device for implementing the method pursuant to claim 2, in which
a dye vaporizer and a metal oxide vaporizer whose vapor jets are
aimed at a substrate are provided in a vacuum chamber, with the dye
vaporizer being cup-shaped and consisting, viewed from the inside
toward the outside, of a quartz cuvette, a graphite block, a
heater, a shield, and a jacket, with a thermocouple being provided
in the bottom center of the cup between the quartz cuvette and the
graphite block, and with a cover constricted to a cut-out hole
being provided in the cup-shaped opening of the dye vaporizer,
characterized by the fact that the cover constricted to a cut-out
hole is connected to the quartz cuvette and displaced toward the
dye, so that the cut-out hole in the cover has a temperature like
that of the heated quartz cuvette.
9. Device for implementing the method pursuant to claim 3, in which
a dye vaporizer and a metal oxide vaporizer whose vapor jets are
aimed at a substrate are provided in a vacuum chamber, with the dye
vaporizer being cup-shaped and consisting, viewed from the inside
toward the outside, of a quartz cuvette, a graphite block, a
heater, a shield, and a jacket, with a thermocouple being provided
in the bottom center of the cup between the quartz cuvette and the
graphite block, and with a cover constricted to a cut-out hole
being provided in the cup-shaped opening of the dye vaporizer,
characterized by the fact that the cover constricted to a cut-out
hole is connected to the quartz cuvette and displaced toward the
dye, so that the cut-out hole in the cover has a temperature like
that of the heated quartz cuvette.
10. Device for implementing the method pursuant to claim 4, in
which a dye vaporizer and a metal oxide vaporizer whose vapor jets
are aimed at a substrate are provided in a vacuum chamber, with the
dye vaporizer being cup-shaped and consisting, viewed from the
inside toward the outside, of a quartz cuvette, a graphite block, a
heater, a shield, and a jacket, with a thermocouple being provided
in the bottom center of the cup between the quartz cuvette and the
graphite block, and with a cover constricted to a cut-out hole
being provided in the cup-shaped opening of the dye vaporizer,
characterized by the fact that the cover constricted to a cut-out
hole is connected to the quartz cuvette and displaced toward the
dye, so that the cut-out hole in the cover has a temperature like
that of the heated quartz cuvette.
11. Device pursuant to claim 8, characterized by the fact that the
jacket is a water-cooled copper jacket.
12. Device pursuant to claim 9, characterized by the fact that the
jacket is a water-cooled copper jacket.
13. Device pursuant to claim 10, characterized by the fact that the
jacket is a water-cooled copper jacket.
14. A method comprising: vaporizing an organic dye and a suboxide
of silicon or metal to form a photoluminescent layer having the
organic dye embedded in a matrix material derived from the
suboxide; and adjusting the vapor deposition rate of the organic
dye so that the concentration of the organic dye is less than 0.65
volume percent with respect to the matrix material, wherein the
matrix material has a sub-stoichiometric oxygen content.
15. The method of claim 14, further comprising, during the
vaporization, allowing the matrix material to react with residual
oxygen to cause the sub-stoichiometric oxygen content of the matrix
material to be at least 97.5% of the stoichiometric oxygen content
of the matrix material.
16. The method of claim 14, wherein the suboxide is a silicon
suboxide or a titanium suboxide.
17. The method of claim 14, wherein the matrix material is
SiO.sub.x or TiO.sub.x.
18. The method of claim 17, wherein x is at least 1.95 and less
than 2.
19. The method of claim 14, wherein an average spacing between
molecules of the organic dye within the matrix material is at least
about 50 nanometers.
20. The method of claim 14, wherein molecules of the organic dye
occupy a single plane within the matrix material.
21. The method of claim 14, wherein the concentration of the
organic dye is at least 0.1 volume percent with respect to the
matrix material.
22. The method of claim 14, wherein the photoluminescent layer is
formed on a substrate.
23. The method of claim 14, wherein the photoluminescent layer
emits light in an optical or adjoining spectral region.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Pursuant to 35 U.S.C. .sctn. 120, this application is a
divisional application of U.S. application Ser. No. 10/204,585,
filed on Aug. 22, 2002, which is the U.S. National Phase
application of WIPO Application No. PCT/DE00/00498, filed on Feb.
23, 2000. The contents of the prior applications are incorporated
herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates to a photoluminescent composition
(e.g., a layer) as well as related articles, methods, and
devices.
BACKGROUND
[0003] A more or less effective luminescence conversion has already
been used for some time in various fields, for example in radiation
detector technology. In general, functional units that are used for
luminescence conversion are based on absorption/emission processes.
Utilized is the fact that there is a shift of luminescence to
longer wavelengths compared to absorption in most cases, for
energetic reasons. This phenomenon can be used, for example, for
spectral matching of detector sensitivity to a radiation
source.
[0004] Furthermore, the property of luminescence radiation no
longer to be bound to the direction of the incident radiation is of
interest, since concentration of radiation in a medium can be
realized by total reflection at the interfaces.
[0005] A recent example is the production of "white" light by way
of partial conversion of the radiation from a blue luminescent
diode. The LUCOLED (P. Schlotter, R. Schmidt, J. Schneider, Appl.
Phys. A 64, 417 (1997)) utilizes this principle. A portion of the
high-energy blue luminescent radiation is absorbed by a suitable
layer in the beam direction and is emitted again shifted toward
lower energies, so that a white color impression is produced by
additive mixing. DE 196 25 622 A1 describes such a light-radiating
semiconductor component with a semiconductor body emitting
radiation and with a luminescence conversion element. The
semiconductor body has a sequence of semiconductor layers that
emits electromagnetic radiation with a wavelength .lamda. of
.ltoreq.520 nm, and the semiconductor conversion element converts
radiation of a first spectral subregion of the radiation emitted by
the semiconductor body from radiation originating from a first
wavelength region into radiation of a second wavelength region, so
that the semiconductor component emits radiation from a second
spectral subregion of the first wavelength region and radiation of
the second wavelength region. Thus, for example, radiation emitted
by the semiconductor body is absorbed with spectral selectivity by
the luminescence conversion element and is emitted in the
longer-wavelength region (in the second wavelength region). In this
method, organic dye molecules are imbedded in an organic
matrix.
[0006] DE 196 38 667 A1 also discloses a semiconductor component
with a semiconductor body emitting radiation and a luminescence
conversion element that emits mixed-color light, with the
luminescence conversion element having a luminous inorganic
substance, in particular a phosphor.
[0007] Besides spectral suitability with regard to the
corresponding application, such a layer has two principal
requirements: The photoluminescence quantum yield must be high,
usually clearly greater than 50%, and its stability must permit
long service lives, usually more than 10,000 hours.
[0008] The basic concept for realizing such a layer with organic
dyes consists of separating and immobilizing molecules in a matrix
so that they behave like monomers with optical properties similar
to a liquid solution, particularly with high quantum yield.
Polymers and sol-gel layers are known as matrices.
[0009] Mixed layers that were produced from the organic dye
3,4,9,10-perylenetetracarboxylic acid dianhydride (PTCDA) and
SiO.sub.2 by co-vaporization onto quartz substrates under high
vacuum are described in H. Frob, K. Kurpiers, K. Leo, CLEO '98, San
Francisco/CA, May 1998, 210; 1998 OSA Technical Digest Series Vol.
6, published by Optical Society of America ("The Frob
publication"). The concentration range studied was 0.65-100 vol. %.
It was observed that the absorption and emission spectra for
decreasing concentrations gradually approach those in a liquid
solution, and for the lowest concentration a photoluminescence
quantum yield of about 50% is achieved at room temperature (FIG. 6,
corresponding to FIG. 2 of the Frob publication).
[0010] A device used for this purpose is described by M. A. Herman,
H. Sitter, Molecular Beam Epitaxy, Ch. 2 (Sources of Atomic and
Molecular Beams), Springer 1989, pp. 29-59. A dye vaporizer and a
metal oxide vaporizer are provided in a vacuum chamber, whose vapor
beam is aimed at a substrate, with the dye vaporizer being
cup-shaped and consisting, viewed from the inside toward the
outside, of a quartz cuvette, a graphite block, a heater, a shield,
and a jacket, with a thermocouple being placed between the quartz
cuvette and the graphite block in the bottom center of the cup.
[0011] FIG. 7 shows the normalized absorption and emission of 30-nm
thick layers for a pure and a diluted dye layer. It is important
that the spectra of the diluted layers can be fitted to those of
monomers with their typical vibrational progression. It is found
that the line width remains constant for all low concentrations;
its enlargement compared to that observed in liquid solution is not
surprising, considering the inhomogeneous conditions of the
surroundings of the molecule.
[0012] The authors hold a weakening Forster transfer because of the
increasing mean molecular separation responsible for the increase
of quantum yields toward lower concentrations, and they expect a
maximum at about 0.1 vol. %, but of course without experimental
confirmation of this. No predictions are made about the lifetime,
with regard to which all organic conversion layers so far have
foundered.
SUMMARY OF THE INVENTION
[0013] The invention relates to a photoluminescent composition
(e.g., a layer) as well as related articles, methods, and
devices.
[0014] It is important for the solution of the problem that organic
dye molecules are imbedded in an inorganic, amorphous or
nanocrystalline matrix. The use of a silicon or metal suboxide in
the vaporization is especially crucial for the optical stability of
the photoluminescent layer. During the deposition of the silicon or
metal suboxide in mixed vaporization of the components under high
vacuum on the substrate, the suboxide reacts with residual gaseous
oxygen of the high vacuum, with a slightly sub-stoichiometric
oxygen content being reached by the matrix material under suitable
vapor deposition conditions (characterized by the ratio of oxygen
partial pressure to rate of vapor deposition). It is characteristic
of the sub-stoichiometric oxygen content that with a matrix
material of SiO.sub.x or TiO.sub.x x is between 1.95 and 2. A
precise adjustment of the dye vapor deposition rate is necessary.
For a low dye concentration, a definite adjustment to a low dye
deposition rate (down to <10.sup.-5 nm/s) is critically
important. In certain embodiments, a temperature-regulated dye
vaporizer is used for this purpose.
[0015] The vaporizer pursuant to the invention differs from the dye
vaporizers known from the state of the art in the fact that the
cover in the cup-shaped opening of the dye vaporizer constricted to
a cut-out hole is connected to the quartz cuvette and is displaced
toward the dye, so that the cut-out hole in the cover has a
temperature like that of the heated quartz cuvette.
[0016] In some embodiments, the configuration of the
photoluminescent layer makes it possible by extremely low dye
surface densities, for example, to provide luminescence standards
with almost ideal point sources of light for appropriately equipped
microscopes (for example optical near-field microscopes, confocal
luminescence microscopes) for the determination of resolving power
and optical transmission functions or tests for the determination
of the optical properties of individual molecules.
[0017] The benefits produced by the invention in particular, lie in
the fact that a material is available that satisfies practical
requirements with regard to optical stability with an average
number of excitation/de-excitation cycles per molecule greater than
10.sup.11, that can be applied to very diverse substrates by dry
technology (mixed vaporization of the components under high
vacuum), and that at the same time has the highest known
concentration of dyes in solutions without having photoluminescence
quantum yields limited by aggregation or by Forster transfer.
[0018] Embodiments advantageously provide high optical stability
for a photoluminescent layer based on a solid solution of organic
dyes, as measured by the numerical midpoint of the
excitation/deexcitation cycles per molecule before a fixed value of
the decline of photoluminescence of the overall system.
DESCRIPTION OF DRAWINGS
[0019] The invention is explained in detail below with reference to
examples of embodiment. The drawings show:
[0020] FIG. 1 an illustration of the photoluminescence quantum
yield of 30-nm thick layers with various dye concentrations
[0021] FIG. 2 an illustration of the change of photoluminescence
with high-intensity irradiation
[0022] FIG. 3 an illustration of the luminescence of SiO.sub.x
layers with equal amounts of the dye MPP with different dye
concentration
[0023] FIG. 4 a dye vaporizer pursuant to the invention in cross
section
[0024] FIG. 5 an Arrhenius plot for calibrating the dye
vaporizer
[0025] FIG. 6 an illustration of the photoluminescence quantum
yield of PTCDA-SiO.sub.2 mixed layers at room temperature
[0026] FIG. 7 normalized absorption and emission of 30-nm thick
layers for pure and diluted PTCDA layers
DETAILED DESCRIPTION
[0027] A photoluminescent layer is described. The layer is
photoluminescent in the optical and adjoining spectral regions. The
layer is typically a solid solution of organic dye molecules within
a silicon oxide or metal oxide. The layer can be applied (e.g.,
vapor deposited) on a substrate.
[0028] Applications of the layer include using the layer to provide
white light, using the layer to input or output light to or from a
waveguide, using the layer as a radiation detector, or using the
layer as a point source for testing near-field microscopes or the
like. In general, the layer is applied on a substrate for
particular applications.
Example 1
[0029] In Example 1, 3,4,9,10-perylenetetracarboxylic acid
dianhydride (PTCDA) was incorporated in an SiO.sub.x matrix, where
1.95<x<2. The layer is produced by thermal vaporization at
operating pressures of about 10.sup.-4 Pa produced by a
turbomolecular pump, with SiO having been vapor-deposited at a
deposition rate of 10.sup.-2 nm/s for the production of the matrix,
which reacts on the substrate with residual gaseous oxygen to give
SiO.sub.x. The quartz resonators used in this multiple-source vapor
deposition for the independent control of deposition rate and layer
thickness are shielded from the other sources. To be able to
measure even very small deposition rates, the measuring head for
PTCDA is at a small distance from the vaporizer; this is possible
with no problems because of the comparatively low vaporization
temperature (typically 300-400.degree. C.). For extremely small
rates of vapor deposition, a temperature-regulated dye vaporizer
was developed that permits stable rates down to <10.sup.-5 nm/s
for a period of at least one hour.
[0030] Radiationless energy transmission to nonradiating traps is
the limiting factor for luminescence quantum yield. To reach a
quantum yield similar to that in liquid solution, volume
concentrations of about 0.1% are necessary in the present system
(FIG. 1). Compared to the data given in H. Frob, M. Kurpiers, K.
Leo, CLEO '98, San Francisco/CA, May 1998, 210, 1998 OSA Technical
Digest Series Vol. 6, published by Optical Society of America, both
a lower concentration was achieved and the quantum yields were
determined and corrected with greater accuracy.
[0031] Results of studies of the optical stability of the layer are
shown in FIG. 2. To achieve adequately high excitation densities, a
confocal microscope was used (excitation wavelength 532 nm); the
luminescence was detected. After an initially severe
non-exponential decline, a state is reached that can be described
by a lifetime with about 10.sup.11 excitation cycles per molecule,
a value that is about 2 orders of magnitude above the best known in
such systems.
[0032] One possible application is found as a photoluminescent
layer in a system similar to the LUCOLED (P. Schlotter, R. Schmidt,
J. Schneider, Appl. Phys. A 64, 417 (1997)). Applied to luminous
densities occurring in luminescent diodes, service lives of the
order of magnitude of 10.sup.5 hours would be expected, based on
the data in FIG. 2.
Example 2
[0033] Production is analogous to that in Example 1, using
N,N-dimethylperylene-3,4,9,10-bisdicarboximide (MPP), and the same
effects are observed relative to the context of the invention:
Increase of the photoluminescence quantum yield with decreasing
concentration (FIG. 3) and optical stability in the aforementioned
sense of about 10.sup.11 excitation cycles per molecule. The fact
that the quantum yield becomes maximum at comparatively higher
concentrations is due to the smaller absorption strength of MPP
compared to that of PTCDA.
Example 3
[0034] Production is analogous to that in Example 1, with the
difference that (a) the vapor deposition rate of PTCDA is extremely
low, typically <10.sup.-5 nm/s, and (b) the PTCDA vapor jet to
the substrate is released by suitable diaphragms for only a very
short time. Assuming that the procedure is performed extremely
cleanly and exactly, dye molecules in this way can be placed
enclosed by matrix material, with an average lateral molecular
spacing of more than 100 nm being achievable. An optical near-field
microscope at this time can achieve a resolving power of better
than 50 nm; with a cover layer of 5 nm SiO.sub.x over the dye layer
there is thus a test that permits determining the point
transmission function by a direct path, or with which optical
properties of individual molecules can be determined.
[0035] FIG. 4 shows a dye vaporizer that is placed in a vacuum
chamber with a metal oxide vaporizer to carry out the procedure.
The vapor jet of each vaporizer is aimed at a substrate. Diaphragms
can be placed between vaporizers and substrate to interrupt the
vapor deposition. The dye vaporizer shown in FIG. 4, viewed from
the inside to the outside, consists of a quartz cuvette 1, a
graphite block 2, a heater 3, a shield 4, and a water-cooled copper
jacket 5. There is a thermocouple 7 in the bottom center of the cup
between the quartz cuvette 1 and the graphite block 2. There is a
cover constricted to a cut-out hole in the cup-shaped opening of
the dye vaporizer which is connected to the quartz cuvette 1 and is
displaced toward the dye 6, so that the cut-out hole in the cover
has a temperature like that of the heated quartz cuvette 1.
[0036] This dye vaporizer provides the capability of definitely
setting an extremely low dye vapor deposition rate of <10.sup.-5
nm/s, since such rates are not accessible to direct measurement.
Such low rates of deposition are achieved by using the
temperature-regulated dye vaporizer with high temperature
distribution homogeneity in the quartz cuvette 1, with a small
heated cut-out hole in the cover of the quartz cuvette 1, and
extrapolation based on calibration with an Arrhenius plot (FIG.
5).
* * * * *