U.S. patent application number 15/996117 was filed with the patent office on 2018-11-29 for encapsulated quantum dots in porous particles.
The applicant listed for this patent is Lumileds LLC. Invention is credited to Patrick John Baesjou, Marcel Rene Bohmer, Johannes Franciscus Maria Cillessen, Antonius Wilhelmus Maria De Laat, Wilhelmus Cornelis Keur, Roelof Koole, Jan Cornelis Kriege, Paulus Hubertus Gerardus Offermans, Godefridus Johannes Verhoeckx, Emile Johannes Karel Verstegen.
Application Number | 20180340674 15/996117 |
Document ID | / |
Family ID | 51579376 |
Filed Date | 2018-11-29 |
United States Patent
Application |
20180340674 |
Kind Code |
A1 |
Koole; Roelof ; et
al. |
November 29, 2018 |
ENCAPSULATED QUANTUM DOTS IN POROUS PARTICLES
Abstract
The invention provides a process for the production of a
(particulate) luminescent material comprising particles, especially
substantially spherical particles, having a porous inorganic
material core with pores, especially macro pores, which are at
least partly filled with a polymeric material with luminescent
quantum dots embedded therein, wherein the process comprises (i)
impregnating the particles of a particulate porous inorganic
material with pores with a first liquid ("ink") comprising the
luminescent quantum dots and a curable or polymerizable precursor
of the polymeric material, to provide pores that are at least
partly filled with said luminescent quantum dots and curable or
polymerizable precursor; and (ii) curing or polymerizing the
curable or polymerizable precursor within pores of the porous
material, as well as a product obtainable thereby.
Inventors: |
Koole; Roelof; (Eindhoven,
NL) ; Bohmer; Marcel Rene; (Eindhoven, NL) ;
Kriege; Jan Cornelis; (Eindhoven, NL) ; Verhoeckx;
Godefridus Johannes; (Eindhoven, NL) ; Offermans;
Paulus Hubertus Gerardus; (Eindhoven, NL) ; Baesjou;
Patrick John; (Eindhoven, NL) ; Keur; Wilhelmus
Cornelis; (Eindhoven, NL) ; Cillessen; Johannes
Franciscus Maria; (Eindhoven, NL) ; Verstegen; Emile
Johannes Karel; (Eindhoven, NL) ; De Laat; Antonius
Wilhelmus Maria; (Eindhoven, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lumileds LLC |
San Jose |
CA |
US |
|
|
Family ID: |
51579376 |
Appl. No.: |
15/996117 |
Filed: |
June 1, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14763886 |
Jul 28, 2015 |
10030851 |
|
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PCT/IB2014/059970 |
Mar 19, 2014 |
|
|
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15996117 |
|
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61803563 |
Mar 20, 2013 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 11/025 20130101;
C09K 11/02 20130101; F21Y 2115/10 20160801; F21V 7/30 20180201;
C23C 16/403 20130101; F21K 9/64 20160801; C09K 11/08 20130101; B05D
1/18 20130101; F21V 9/32 20180201; C23C 16/45525 20130101 |
International
Class: |
F21V 9/30 20180101
F21V009/30; C23C 16/455 20060101 C23C016/455; C23C 16/40 20060101
C23C016/40; C09K 11/08 20060101 C09K011/08; F21K 9/64 20160101
F21K009/64; C09K 11/02 20060101 C09K011/02; B05D 1/18 20060101
B05D001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2014 |
EP |
14153775.3 |
Mar 13, 2014 |
EP |
14159373.1 |
Claims
1. A luminescent material comprising particles having a porous
inorganic material core wherein the pores are at least partly
filled with polymeric material with luminescent quantum dots
embedded therein.
2. A luminescent material according to claim 1, wherein the
particles comprise an encapsulation encapsulating at least a part
of the core.
3. A luminescent material according to claim 2, wherein the
encapsulation comprises a coating that at least partly coats the
particles with an inorganic coating selected from the group
consisting of a silicon containing oxide, an aluminum containing
oxide, a zirconium containing oxide, a glass, a titanium containing
oxide, a hafnium containing oxide and an yttrium containing
oxide.
4. A luminescent material according to claim 2, wherein the
encapsulation comprises a multi-layer coating that coats the
particles, wherein the multi-layer coating comprises an organic
polymer coating and an inorganic coating, or at least two coatings
selected from the group of a silicon containing oxide, an aluminum
containing oxide, a zirconium containing oxide, a glass, a titanium
containing oxide, a hafnium containing oxide and an yttrium
containing oxide.
5. The luminescent material according to claim 1, wherein the
particles have particle sizes in the range of 1-500 .mu.m, wherein
the porous inorganic material comprises one or more of a porous
silica, a porous alumina, a porous glass, a porous zirconia, and a
porous titania, wherein the pores have mean pore sizes in the range
of 0.1-10 .mu.m, wherein the polymeric material comprises one or
more of an acrylate, silicone, or epoxy type polymer, wherein the
encapsulation comprises an inorganic coating.
6. A wavelength converter comprising a light transmissive solid
matrix with the luminescent material according to claim 1.
7. The wavelength converter according to claim 6, further
comprising a second luminescent material.
8. A lighting device comprising: a light source configured to
generate light source light, the luminescent material according to
claim 1 wherein the luminescent material is configured to convert
at least part of the light source light into visible luminescent
quantum dot light.
9. The lighting device according to claim 8, wherein the
luminescent quantum dots are selected from the group consisting of
core-shell quantum dots, with the core selected from the group
consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe,
CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe,
CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe,
HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe,
HgZnSeS, HgZnSeTe, HgZnSTe, GaN, GaP, GaAs, AlN, AlP, AlAs, InN,
InP, InGaP, InAs, GaNP, GaNAs, GaPAs, AlNP, AlNAs, AlPAs, InNP,
InNAs, InPAs, GaAlNP, GaAlNAs, GaAlPAs, GaInNP, GaInNAs, GaInPAs,
InAlNP, InAlNAs, and InAlPAs nanoparticles.
10. The lighting device according to claim 8, comprising a
wavelength converter comprising a light transmissive solid matrix,
the wavelength converter, arranged at a zero or non-zero distance
from the light source, wherein the lighting device further
comprises a second luminescent material, wherein the second
luminescent material under excitation with light has another
wavelength distribution of the luminescence than the luminescent
quantum dots.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 14/763,886, filed Jul. 28, 2015, and entitled "ENCAPSULATED
QUANTUM DOTS IN POROUS PARTICLES", which is 371 Application of
International Application No. PCT/IB2014/059970, filed Mar. 19,
2014, which claims priority to U.S. Provisional Application No.
61/803,563, filed Mar. 20, 2013, European Application No.
14153775.3, filed Feb. 4, 2014, and European Application No.
14159373.1, filed Mar. 13, 2014. U.S. application Ser. No.
14/763,886, International Application No. PCT/IB2014/059970, U.S.
Provisional Application No. 61/803,563, European Application No.
14153775.3, European Application No. 14159373.1 and are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a (particulate) luminescent
material, as well as to a production process for such (particulate)
luminescent material. The invention further relates to a wavelength
converter and lighting device comprising such (particulate)
luminescent material.
BACKGROUND OF THE INVENTION
[0003] Quantum dot (QD) based lighting is known in the art.
WO2012021643, for instance, describes systems and methods that
relate to quantum dot structures for lighting applications. In
particular, quantum dots and quantum dot containing inks
(comprising mixtures of different wavelength quantum dots) are
synthesized for desired optical properties and integrated with an
LED source to create a trichromatic white light source. The LED
source may be integrated with the quantum dots in a variety of
ways, including through the use of a small capillary filled with
quantum dot containing ink or a quantum dot containing film placed
appropriately within the optical system. These systems may result
in improved displays characterized by higher color gamuts, lower
power consumption, and reduced cost. For instance, WO2012021643
describes a method of generating trichromatic white light
comprising contacting light from a light source capable of emitting
blue light with an optical material comprising a host material and
first quantum dots capable of emitting green light and second
quantum dots capable of emitting red light, wherein the weight
percent ratio of the first quantum dots to the second quantum dots
in the optical material is in a range from about 9:1 to about 2:1,
and generating trichromatic white light from a combination of the
light from the light source, the light from the first quantum dots
and the light from the second quantum dots.
SUMMARY OF THE INVENTION
[0004] Nanoparticles such as quantum dots (QDs) can possess
properties which make them advanced luminescent materials to be
used in solid state lighting. Here below, nanoparticles, such as
quantum dots, that have the ability to give (visible) luminescence
are also indicated as "light converter nanoparticles" or
"luminescent nanoparticles". They can e.g. be used in converting
blue light to other colors, for obtaining high quality white light
with high efficacy. Nanoparticles such as QDs have the advantage of
a narrow emission band and color tunablility by varying the size of
the particles.
[0005] Quantum Dots (QDs) are seen as a promising phosphor for LED
applications. The narrow emission band (about 25-50 nm) and high
quantum efficiency (QE) (>90% at 100.degree. C.) makes them
superior phosphors especially in the red, where alternative
inorganic and organic phosphors show a much broader emission band.
An overall improvement up to 20% in efficacy is expected in case
QDs can be used as red phosphor in LEDs for general lighting
applications. For backlight application the gain in efficacy can be
even more, because the narrow band emission of both green and red
QDs can be matched with the band pass filter of the LCD. All in
all, QDs are envisaged to be an important green and/or red phosphor
for LED applications in the near future.
[0006] A major problem of QDs towards application is their
sensitivity towards oxygen and water. Due to photo-oxidation,
and/or instability of the QD-ligand interface by photochemical
reactions with water and/or oxygen, QDs need to be hermetically
sealed from oxygen and water in order to remain their high QE upon
light exposure and elevated temperature. One option is to
seal/encapsulate the QDs on a module level, e.g. by sealing
glass-sandwiches with an epoxy or other (semi-hermetic) seal.
However, it is preferred to have a particulate material which is
hermetically sealed on a micro-level.
[0007] Micro milling QDs in a first host towards micro particles
and subsequent encapsulation of these particles or mixing the micro
beads in another host is an option but may also have disadvantages.
For example, the non-spherical shape and large size distribution
which is obtained upon micro milling will hamper proper mixing of
micro particles into a second host, and hinder hermetic
encapsulation by a secondary coating. Another disadvantage of micro
beads in general is the mismatch in thermal expansion coefficient
between QD-host material (typically an acrylate, silicone, or other
polymer) and the encapsulation material (preferably an inorganic
material such as alumina or silica). A too large mismatch between
thermal expansions may cause e.g. cracks. It was found that when
using organic micro beads, which are known from the prior art, such
micro beads, even when these are substantially spherical, can
hardly be coated with an inorganic coating, which is a preferred
coating, without substantial mismatch in thermal expansion. This
may lead to life time reduction. An irregular shape such as
obtained by micro milling increases the chance of crack-formation
even further in case of a large CTE mismatch.
[0008] Hence, it is an aspect of the invention to provide a
luminescent material, especially a particulate luminescent
material, and/or a wavelength converter and/or a lighting device,
which preferably further at least partly obviate one or more of
above-described drawbacks. It is further an aspect of the invention
to provide a process for the production of such luminescent
material, especially such particulate luminescent material.
[0009] Here, amongst others a macro porous silica or alumina
particle that is filled with for instance a curable QD-polymer
resin mixture is proposed. After filling (the pores of the macro
porous silica or alumina (or other porous material), the
QD/polymer/macro porous silica composite particles can for instance
be encapsulated with silica, alumina, or other sealant (or a
(multi-layer) combination of two or more of these). The problem of
differences in thermal expansion coefficient may largely be solved.
Alternative or additional advantages may be that there is no need
to first create micro beads of the QD/host material, with its
concomitant difficulties and disadvantages. Instead, one may make
use of prefabricated available porous particles. Further, the
adherence of an inorganic coating to the inorganic micro particle
may substantially be better as compared to the combination of an
organic micro bead with inorganic sealant. The thermal expansion
coefficient (CTE) mismatch between the inorganic coating and an
organic particle may be large whereas in the present invention the
thermal mismatch may be small (or even substantially zero). In
addition, the final composite particle may be substantially
non-scattering due to refractive index matching of polymer and
silica, and the final matrix, such as a (silicone) resin, in which
the composite particles may be dispersed. Further, knowing that
seals are not always perfect, it is advantageous that there may be
a certain tolerance for pinholes in the seal, because--in
principle--only the pores of the silica particles need to be
sealed. The resulting sealed composite particles can hence be
processed in air, and mixed with for example optical grade
silicones for final application to the LED.
[0010] Alternatively, the filled and cured macro porous particles
are used as such (i.e. without secondary encapsulation) by mixing
them directly in a silicone or other suitable host material for LED
applications. Stability and miscibility of QDs is found to be
highly dependent on the exact formulation of the first host.
However, this first dedicated host may not be the preferred host
material for LED applications, for example because of processing
conditions, costs, or stability. Therefore, the macro porous silica
particles (PSP's) filled with the preferred QD-host material (e.g.
an acrylate), can be mixed with the preferred LED host material
(e.g. a silicone). Mixing of silica particles in e.g. silicones is
well known and used in the field already.
[0011] Finally, the filled and cured macro porous particles can be
used as such (i.e. without secondary encapsulate) by mixing them
directly in a hermetic second host material, e.g. a semi-hermetic
epoxy, or hermetic (low melting) glass, etc. In contrast, as
indicated above mixing of QDs directly into such host materials was
found to be difficult in view of flocculation, non-miscibility, and
poor stability.
[0012] Therefore, in a first aspect the invention provides a
process for the production of a (particulate) luminescent material
comprising particles, especially substantially spherical particles,
having a porous inorganic material core with pores, especially
macro pores, which are at least partly filled with a polymeric
material with luminescent nanoparticles, especially quantum dots,
embedded therein, wherein the process comprises (i) impregnating
the particles of a particulate porous inorganic material with pores
with a first liquid ("ink") comprising the luminescent
nanoparticles, especially quantum dots, and a curable or
polymerizable precursor of the polymeric material, to provide pores
that are at least partly filled with said luminescent
nanoparticles, especially quantum dots, and curable or
polymerizable precursor; and (ii) curing or polymerizing the
curable or polymerizable precursor within pores of the porous
material. In a specific embodiment, the process further comprises
(iii) applying an encapsulation (such as coating, or embedding in a
matrix, or both) to the thus obtained particles (with pores that
are at least partly filled with a polymeric material with
luminescent nanoparticles, especially quantum dots, embedded
therein). In this way the particles may be at least partly be
coated, or especially even be entirely be coated (i.e. especially a
conformal coating).
[0013] In a further aspect, the invention also provides a
(particulate) luminescent material or a solid matrix comprising
such (particulate) luminescent material, obtainable by the process
of the invention. Hence, the invention also provides a
(particulate) luminescent material comprising particles having a
porous inorganic material core with pores which are at least partly
filled with polymeric material with luminescent nanoparticles,
especially quantum dots, embedded therein. Further, the invention
also provides a wavelength converter comprising a light
transmissive solid matrix with the (particulate) luminescent
material (as defined herein, and/or obtainable according to the
process defined herein) embedded therein.
[0014] The invention is further described with reference to quantum
dots as specific embodiment of (luminescent) nanoparticles.
[0015] In yet a further aspect, the invention also provides a
lighting device comprising (i) a light source configured to
generate light source light, (ii) the (particulate) luminescent
material as defined herein or obtainable by the process as defined
herein, wherein the (particulate) luminescent material is
configured to convert at least part of the light source light into
visible luminescent quantum dot light. As indicated above, the
(particulate) luminescent material may be embedded in a light
transmissive solid matrix.
[0016] With the above described invention, advantageously a well
processable QD-based luminescent material may be provided, for
instance as particulate luminescent material. With the invention,
the QD may be well shielded from the environment, thereby
contributing to the lifetime of the QDs.
[0017] Further, in embodiments the (macro porous) particles are at
least partly, especially substantially entirely, enclosed by the
encapsulation. The encapsulation may be a (multi) layer (coating),
but may also comprise a (solid matrix), see also below. Such
encapsulation may even further improve lifetime. Especially, an
encapsulation comprising an inorganic material, even more
especially such inorganic material having a coefficient of thermal
expansion (CTE) having a value which is identical to the CTE of the
inorganic material of the core, or only differing with a factor
within a range of 1/5-5, especially 1/3-3, such as 2/3-3/2 of the
CTE value of the inorganic material of the core, may be
advantageous in view of life time. The smaller the difference
between the CTE of the inorganic core material and the (inorganic)
coating material, the smaller the mismatch, and the longer the
lifetime of the (particulate) luminescent material may be. Also, a
more spherical shape of the particle will reduce the chance on
fractures. Residual voids in the macro porous particle (small
volumes not filled with the polymeric material containing the QDs)
may assist in preventing cracks in the encapsulating coating as
they provide a volume into which the polymeric material can expand
without exerting force on the matrix material or on the
encapsulation.
[0018] The inorganic host or core material is not necessarily
encapsulated with an inorganic material, such as in the form of a
coating or matrix, but the inorganic host may also be encapsulated
with an organic material (organic coating or matrix). Hence, in
general the first layer of material--if available--encapsulating
the porous inorganic material core has a CTE differing with the CTE
of the porous inorganic material core with a factor within a range
of 1/5-5, especially 1/3-3, such as 2/3-3/2. For instance, the core
may be of alumina and the encapsulation may be alumina, or an epoxy
or acrylate with a low CTE. Hence, in some embodiments the process
further comprises applying an encapsulation to the particles
obtained after curing or polymerizing. Likewise, the invention thus
also provides a particulate luminescent material wherein the
particles comprise an encapsulation encapsulating at least part of
the particle (i.e. the core is at least partially encapsulated).
Especially, the encapsulation comprises an inorganic coating, even
more especially the encapsulation comprises a coating which
comprises at least a layer in direct physical contact with the
core, wherein this layer essentially consists of an inorganic
material, and even more especially consists of the same inorganic
material as the core. Hence, the (particulate) inorganic host
especially comprises a porous silica, a porous alumina, a porous
glass, a porous zirconia (ZrO2), or a porous titania, and the
coating (at least) comprises silica coating, an alumina coating, a
glass coating (same type of glass), a zirconia coating, or a
titania coating, respectively.
[0019] In case the particles are not coated, the particles in fact
are the porous cores per se. Hence, the term "core" or "porous
core" especially refers herein to the porous particle, not (yet)
coated or encapsulated, or not (yet) coated and encapsulated. A
coating may especially enclose at least 50%, even more at least
80%, yet even more especially at least 95%, such as 100% of the
entire outer surface area (A) of the particle. Hence, the particles
may be entirely enclosed by a shell. The term shell does not
necessarily refer to spherical shells; the shell may also be
non-spherical (see also below).
[0020] Here, the encapsulation may relate to a coating, such as a
single layer coating or a multi-layer coating. Such coating
encloses at least part of the particle, especially the entire
particle (i.e. a shell enclosing the core). In this way, the
quantum dots are substantially shielded from the environment in a
first line of protection by the polymeric host material, and by a
second line of protection by the encapsulation that may form a
shell around the entire core. The cores may be spherical, but are
not necessarily spherical. Hence, the shell may also not
necessarily be spherical. For instance, the macro porous particle
filled with the QD in host material may be egg-like shaped, and the
shell may thus have the shape of an eggshell.
[0021] Especially, the coating comprises an inorganic material. In
embodiments, the coating consists of inorganic material. In
specific embodiments, the process comprises providing the
encapsulation by (at least partly) coating the particles with an
inorganic coating, typically a metaloxide coating, such as selected
from the group consisting of a silicon containing oxide, an
aluminum containing oxide, a zirconium containing oxide, a glass, a
titanium containing oxide, a hafnium containing oxide and an
yttrium containing oxide.
[0022] Here, the term "silicon containing oxide" may relate to the
class of silicon containing oxides, such as silicates, like
SiO44-group containing oxides, SiO32-group containing oxides,
Si4O104-containing oxides, etc., but especially also SiO2 (silica).
Examples are e.g. Mg2SiO4, Mg3(OH)2Si4O10, and thus SiO2. The term
"aluminum containing oxide" may relate to the class of aluminum
containing oxides, such as aluminates, like MgAl2O4, BaMgAl10O17,
Y3Al5O12, and especially Al2O3. The term "titanium containing
oxide" may relate to the class of titanium containing oxides, such
as titanates, like Ba2TiO4, CaTiO3, but also Li2TiO3, and
especially TiO2. In other embodiments, the inorganic coating is
selected from the group consisting of indium metal oxide coatings,
such as selected from the group consisting of an indium tin oxide
(ITO) coating, and an indium zinc oxide coating may be applied. In
yet other embodiments, the coating comprises an inorganic coating
selected from the group consisting of a zirconia coating (ZrO2) and
a tin oxide (SnO2) (SNO) coating. Especially, the coating (as
embodiment of an encapsulation) is selected from one or more of the
group of silica, alumina, ITO, and SNO. Combinations of such
materials, or multi-layer coatings comprising layers with different
compositions, such as described above, may also be applied.
Examples of glasses are e.g. borate glasses, phosphate glasses,
borosilicate glasses, etc.
[0023] Alternatively or additionally, also an organic coating may
be applied, such as a Parylene coating ((chemical vapor deposited)
poly(p-xylylene) polymer coating) or a poly vinyl alcohol (PVA)
coating, etc.
[0024] The coating may comprise a single layer coating, or a
multi-layer coating. The multi-layer coating may comprise a
plurality of different layers, stacked to each other. In
embodiments, one or more of such layers are inorganic materials
layers. Alternatively or additionally, in embodiments, one or more
of such layers are organic materials layers. In a specific
embodiment, a first layer comprises an organic (material) layer,
which may be relatively easily applied to the particles, and a
second layer, more remote from the core, comprises an inorganic
(material) layer. Especially, inorganic material layers are
applied, as these may give the best hermetic encapsulation and as
these may give the best CTE match. The coating(s) may amongst
others be applied in a gas phase process, for instance using a
fluidic bed reactor. In a specific embodiment, the process
comprises providing the encapsulation by (at least partly)
(multi-layer) coating the particles in a gas phase process,
especially in a fluid bed reactor, by atomic layer deposition
(ALD). As known in the art, atomic layer deposition is a thin film
deposition technique that is especially based on the sequential use
of a gas phase chemical process. The majority of ALD reactions use
two chemicals, typically called precursors. These precursors react
with a surface one at a time in a sequential, self-limiting, manner
Especially by exposing the precursors to the growth surface
repeatedly, a thin film is deposited. Several ALD methods are known
in the art, such as plasma enhanced ALD or thermally assisted ALD.
An example of a suitable process is described in WO2010100235A1,
which is herein incorporated by reference. However, also other
coating methods than ALD may be applied. Powder ALD is known in the
art.
[0025] Wet-chemical growth of a metal oxide coating such as a
silica coating may be achieved by for example sol-gel chemistry or
alternative precipitation methods. The inorganic surface of the
metaloxide particle is a suitable starting point for further growth
of a metaloxide shell by sol-gel chemistry. For instance, a silica
coating around a porous silica particle can be achieved by addition
of a silica precursor such as TEOS (Tetraethyl orthosilicate) in a
water medium (can be done in both acidic and basic environment),
also referred to as the Stober process. Preferably, the chemical
growth of the inorganic encapsulation layer is performed in a
non-aqueous medium. In other instances it may be desired to first
provide an organic coating layer to the particle (first coating),
and then applying the wet chemical grown metal oxide coating(s) to
prevent QDs to be exposed to water.
[0026] However, other coating process for coating particles may
also be applied, such as e.g. described in WO2010/100235. Chemical
vapor deposition and/or atomic layer deposition may amongst others
be applied to provide the (multi-layer) coating.
[0027] Hence, in specific embodiments, the invention also provides
applying an encapsulation to the particles obtained after curing or
polymerizing, wherein the process comprises providing the
encapsulation by multi-layer coating the particles, especially in a
gas phase process, especially using a fluidic bed reactor, wherein
the thus obtained multi-layer coating comprises a first coating
layer in contact with the core, wherein the first coating layer
comprises in a specific embodiment an organic polymer coating, and
wherein the multi-coating comprises a second coating layer,
relative to the first coating layer more remote from the core, and
wherein the second coating layer comprises an inorganic coating.
Hence, the invention also provides a particulate luminescent
material comprising particles having a porous inorganic material
core with pores which are at least partly filled with polymeric
material with luminescent quantum dots embedded therein, wherein
the cores are encapsulated with a coating, especially a multi-layer
coating.
[0028] In an alternative embodiment, the thus obtained multi-layer
coating comprises a first coating layer in contact with the core,
wherein the first coating layer comprises in a specific embodiment
an inorganic coating, and wherein the multi-coating comprises a
second coating layer, relative to the first coating layer more
remote from the core, and wherein the second coating layer
comprises an organic polymer coating. An advantage thereof may be
that the application of an inorganic coating to the particle (core)
may be relatively easy due the chemistry match. This may especially
be the case when the inorganic material core has the same lattice
constant and/or substantially consists of the same elements as the
coating. Hence, when an inorganic coating is applied, the inorganic
material core may be used as basis to grow the inorganic coating
material on. As indicated above, especially the first coating layer
is in contact with the core over at least 50% of the surface area
of the core, even more especially at least at least 95%, such as
100% of the entire outer surface area (A) of the particle (or
core).
[0029] Therefore, in an embodiment the thus obtained multi-layer
coating comprises an organic polymer coating and an inorganic
coating. The multi-layer coating may thus comprise one or more
inorganic coatings (i.e. coating layers) and one or more organic
coatings (i.e. coating layers), which may optionally alternate and
form a stack of alternating inorganic and organic layers.
[0030] The (multi-layer) coating may especially have a thickness in
the range of 10 nm-10 .mu.m, such as especially 50 nm-2 .mu.m. In
general, the coating thickness is smaller than the particle
diameter.
[0031] With the coating process, particles are obtained comprising
a core and a shell. The shell may have a thickness of at least 10
nm, like at least 50 nm (see above). The shell may especially
comprise an inorganic layer. The core comprises the luminescent
nano particles. However the shell does substantially not comprise
such particles. Hence, porous inorganic particles may be provided,
with luminescent nanoparticles in the pores, and with the porous
particle enclose by a shell which does (substantially) not comprise
such luminescent nanoparticles. Especially, the thickness of the
shell is at least 10 nm. Such particles may however be embedded in
a matrix, see also below.
[0032] Alternatively, or also additionally, the invention also
provides the (particulate) luminescent material embedded in a
matrix (a further embodiment of an encapsulation). Such matrix is
especially a body or layer, such as a self-supporting layer,
wherein within the matrix a plurality of the particles (with
inorganic (porous) cores and luminescent nano particles within the
pores) is available. For instance, these particles may be dispersed
therein. Such matrix may be a waveguide or have wave guiding
properties (see also below). Hence, in a further aspect the
invention also provides a process wherein the process (further)
comprises providing the encapsulation by embedding the particles in
a light transmissive (solid) matrix. Also, the invention thus
provides a wavelength converter comprising a light transmissive
(solid) matrix with the particulate luminescent material. The
matrix may comprises one or more materials selected from the group
consisting of a transmissive organic material support, such as
selected from the group consisting of PE (polyethylene), PP
(polypropylene), PEN (polyethylene napthalate), PC (polycarbonate),
polymethylacrylate (PMA), polymethylmethacrylate (PMMA) (Plexiglas
or Perspex), cellulose acetate butyrate (CAB), silicone (such as
especially polymethylphenylsilicone), polyvinylchloride (PVC),
polyvinyl alcohol (PVA), polyethyleneterephthalate (PET), (PETG)
(glycol modified polyethylene terephthalate), PDMS
(polydimethylsiloxane), and COC (cyclo olefin copolymer). However,
in another embodiment the matrix (material) may comprise an
inorganic material. Preferred inorganic materials are selected from
the group consisting of (low melting) glasses, (fused) quartz, and
transmissive ceramic materials. Also hybrid materials, comprising
both inorganic and organic parts may be applied. Especially
preferred are silicones, PMMA, epoxies, PET, transparent PC, or
glass as material for the matrix (material). Note that the above
mentioned one or more materials selected from the group consisting
of a transmissive organic material support may also be applied as
polymeric material with luminescent quantum dots in the pores.
Hence, a precursor for such material may also be applied as curable
or polymerizeble precursor (for the polymeric material wherein the
quantum dots may be embedded in the pores of the inorganic
cores).
[0033] When the matrix comprises a polymeric matrix, the polymeric
matrix may especially substantially be identical to the polymeric
material in the pores wherein the quantum dots are embedded.
[0034] However, in another embodiment, the polymeric matrix may be
produced, in the presence of the particulate luminescent material,
with a curable or polymerizable precursor that may be substantially
different to the curable or polymerizable precursor that is used to
cure or polymerize within the pores of the porous material (see
further also below). Hence, a larger freedom of choice of materials
for the polymeric matrix is possible with the present
invention.
[0035] Especially, the (particulate) luminescent material is
enclosed by an encapsulate or encapsulation. As used herein,
"encapsulation" may amongst others refer to protection against a
particular element or compound, for example, oxygen (O2) (such as
in the form of air) and/or water. In an embodiment, encapsulation
can be complete (also referred to herein as full encapsulation).
Especially, in an embodiment the particulate luminescent material
is at least partially encapsulated by a material that is
substantially impervious to oxygen. In an embodiment, the
particulate luminescent material is at least partially encapsulated
by a material that is substantially impervious to moisture (e.g.
water). In an embodiment, the particulate luminescent material is
at least partially encapsulated by a material that is substantially
impervious to air. In an embodiment, the particulate luminescent
material is at least partially encapsulated by a material that is
substantially impervious to oxygen and moisture. In another
embodiment, the particulate luminescent material is entirely
encapsulated by a material that is substantially impervious to one
or more of oxygen and moisture. As indicated above, especially an
encapsulate at least comprising an inorganic coating may be
beneficial for such protection.
[0036] As will be clear to a person skilled in the art, a
combination of two or more encapsulations may be possible, such as
a particulate luminescent material with particles encapsulated with
a coating (such as a multi-layer coating), which are embedded in a
matrix. Hence, the process may also comprise one or more of (i)
providing the encapsulation (to the particulate luminescent
material) by embedding the particles in a light transmissive solid
matrix, and (ii) providing the encapsulation by (at least partly)
coating the particles and subsequently embedding the particles in a
light transmissive solid matrix.
[0037] At least part of the encapsulation is transmissive for
light, especially in the visible, and will thereby allow excitation
light to reach the wavelength converter nano particles and allow
emission light therefrom (at least in the visible) escape from the
encapsulated wavelength converter. Especially, the encapsulation,
such as the matrix material, is transmissive for light having a
wavelength selected from the range of 380-750 nm. For instance, the
matrix material may be transmissive for blue, and/or green, and/or
red light. Especially, the encapsulation, such as the matrix
material is transmissive for at least the entire range of 420-680
nm. Especially, the encapsulation, such as the matrix material may
have a light transmission in the range of 50-100%, especially in
the range of 70-100%, for light generated by the light source of
the lighting unit (see also below) and having a wavelength selected
from the visible wavelength range. In this way, the encapsulation,
such as the matrix material is transmissive for visible light from
the lighting unit. The transmission or light permeability can be
determined by providing light at a specific wavelength with a first
intensity to the material and relating the intensity of the light
at that wavelength measured after transmission through the
material, to the first intensity of the light provided at that
specific wavelength to the material (see also E-208 and E-406 of
the CRC Handbook of Chemistry and Physics, 69th edition,
1088-1989).
[0038] The wavelength converter may be transparent or translucent,
but may especially be transparent. When the wavelength converter is
transmissive, light of the light source may not entirely be
absorbed by the wavelength converter. Especially when using blue
light, this may be of interest, as the blue light may be used to
excite the light luminescent materials and may be used to provide a
blue component (in white light).
[0039] Hence, the invention also provides a wavelength converter
comprising a light transmissive solid matrix with the (particulate)
luminescent material as defined herein, or obtainable according to
the process as defined herein, embedded therein.
[0040] The term "particulate" luminescent material relates to a
luminescent material comprising particles. The particles in this
invention will comprise an inorganic host, which will in generally
not be designed to be luminescent, though this is not excluded. The
host comprises pores, which are, at least partly, filled with
polymeric material. The polymeric material contains nano particles,
especially QDs, embedded therein. Hence, the pores comprise QDs,
which may not only be at the surface of the pores, but which may
mainly be distributed over the polymer within the pore. The
particulate luminescent material is herein also indicated as
"composite particles".
[0041] As indicated above, the inorganic host particles after
impregnation with the quantum dots and after curing and/or
polymerization may be used as such. In such instance, the particles
have no coating. However, also in these embodiments the term "core"
is applied, though the particle may entirely consist of such core.
Optionally the particles are encapsulated. This may be a coating,
i.e. in principle each particle may include a coating around the
core: core-coating particles. However, the particles may also be
embedded in a matrix, such as a film or body: such matrix
encapsulates a plurality of the (optionally coated) cores. In each
of these embodiments and variants, the pores of the cores enclose
quantum dots.
[0042] The (particulate) inorganic host especially comprises a
porous silica, a porous alumina, a porous glass, a porous zirconia
(ZrO2), and a porous titania. In yet another embodiment, the
(particulate) inorganic host especially comprises silicon carbide
(SiC), hydrotalcite, steatite (soapstone), cordierite (a magnesium
iron aluminum cyclosilicate), and niobia (diniobium pentoxide).
Hence, in yet another embodiment, the (particulate) inorganic host
comprises a porous glass. Examples of glasses are e.g. borate
glasses, phosphate glasses, borosilicate glasses, etc. Examples of
porous glasses are e.g. Vycor.RTM. glasses, such as e.g. porous
glass 7930, though other porous glasses may also be applied.
[0043] Note that in an embodiment the particles of a particulate
porous inorganic material, i.e. the inorganic host may include a
combination of different type of particles. This may include one or
more of different type of particle sizes, like bi-modal or
poly-modal particle size distributions and chemically different
types of particles, like a combination of porous silica and porous
alumina.
[0044] The pore sizes are especially in the range of 0.05-50 .mu.m,
such as in the range of 0.1-10 .mu.m. The pore sizes can especially
be defined as the dimensions of the pore perpendicular to a pore
axis. For instance, the pore size may be the width or height or
diameter. Pore sizes may especially be determined mercury intrusion
porosimetry (especially for larger pores) and gas
absorption/desorption (for smaller pores), as known to the person
skilled in the art. Pores can have various shapes such as channels,
inkpots and slits. Pores may be interconnected. The mean pore sizes
are especially in the range of 0.05-50 .mu.m, such as in the range
of 0.1-10 .mu.m.
[0045] Further, the particle sizes may in general be in the range
of 0.5-800 .mu.m, such as 1-500 .mu.m, especially in the range of
2-20 .mu.m, like 2-10 .mu.m. Here, the particle size especially
refers to the number averaged particle size, such as for instance
may be derived with SEM analysis and optically estimating the
particle sizes, or with a Malvern particle size analyzer or other
laser based particle size analysis. Particle size may also be
derived from microscope measurements, such as with SEM. Especially,
the mean particle sizes may in general be in the range of 0.5-800
.mu.m, such as 1-500 .mu.m, especially in the range of 2-20 .mu.m,
like 2-10 .mu.m. Hence, the particles are herein also indicated as
micro particles.
[0046] As will be clear to a person skilled in the art, the pore
sizes will (in general) be smaller than the particle sizes. In
general, also the mean pore sizes are smaller than the mean
particle sizes. With the present invention, it is possible for the
first time to provide a quantum dot based micro particulate
material with good lighting properties. Hence, the present
luminescent material may be used in conventional processes like
processing in a luminescent layer on a LED die or dispersing in a
matrix of a LED dome or including in a coating material for a
luminescent coating (like in a fluorescent lamp).
[0047] Especially, the porous inorganic particles are rounded
particles, especially well rounded particles, such as substantially
spherical particles. This may be advantageous in view of processing
of the particles, such as when coating a paste comprising the
particle on a transmissive window of a lighting device such as a T8
tube (commonly known to a person skilled in the art of lighting).
Further, the rounded shape of the porous inorganic particles may
also facilitate formation of a complete and uniform coating therein
(if applicable) and reduce the chance on crack-formation at the
particle/coating interface Especially, the number averaged
circularity is larger than 0.92, especially larger than 0.95, such
as at least 0.98. Here, the circularity is defined as 4.pi.A/P2,
wherein A is the surface area of the particle (assuming the pores
to be closed), and P its perimeter. Circularity is a ratio of the
perimeter of a circle with the same area as the particle. Hence,
very well processable luminescent particles may be created based on
well-defined porous particles, like porous silica particles.
[0048] In a specific embodiment, the porous inorganic material
comprises one or more of the above described materials, such as one
or more of a porous silica, a porous alumina, a porous glass, a
porous zirconia, and a porous titania, the pores have mean pore
sizes (dp) in the range of 0.1-10 .mu.m, and the precursor
comprises a curable acrylate. Especially acrylates, but also
silicones, may work well to embed the QDs in.
[0049] The porous inorganic material or the cores, before filling
and before applying an optional coating, may include an outer layer
comprising filling openings. The particles may e.g. comprise an
outer layer that comprises the same material as the core material,
but is more densified and/or the outer layer may comprise a
coating. Such coating may block part of the pores. In embodiments
wherein such coating blocks part of the pores, the coating will
also comprise filling holes. The total area of the filing holes in
the outer layer or coating may include 5-95% of the total outer
surface area (A) of the core, such as 20-80% of the area. Such
porous inorganic particles with an outer layer are commercially
available as Trisoperl particles from Vitrabio-Biosearch/VitraBio
GmbH.
[0050] Therefore, especially the invention also provides a
luminescent material as defined herein, wherein the particles
comprise an encapsulation encapsulating at least part of the core,
wherein the porous inorganic material comprises one or more of a
porous silica, a porous alumina, a porous glass, a porous zirconia,
and a porous titania, wherein the pores have mean pore sizes (dp)
in the range of 0.1-10 .mu.m, and wherein the polymeric material
especially comprises one or more of an acrylate, silicone, or epoxy
type polymer (or a silicone type polymer), and wherein the
encapsulation especially comprises an inorganic coating. As
indicated above, an inorganic coating in combination with the
inorganic core may have advantages with respect to CTE match,
though suitable organic coatings in view of CTE may also be found.
Further, such inorganic coating may relatively be easily applied on
the core. In addition, as indicated above, the inorganic coating
may be relatively impervious for water and/or gas. Optionally, also
an organic coating in combination with the inorganic core may be
applied, especially when the CTE difference is smaller than a
factor in the range of 1/5-5 (i.e. CTE of inorganic core material
divided by the CTE of the coating material is in the range of
1/5-5).
[0051] These pores are at least partly filled with the first liquid
(curable ink). Especially, the pores may substantially be filled
with the first liquid. Impregnation may be applied in conformance
with the incipient wetness technique. Alternatively (or
additionally), after impregnation the impregnated particles and
remaining first liquid are separated from each other. However, in
the case of incipient wetness, the remaining first liquid may be
substantially zero, as in incipient wetness technique, the volume
of the first liquid will be chosen to be substantially equal to the
pore volume. Hence, in embodiments impregnation is applied in
conformance with the incipient wetness technique or after
impregnation the impregnated particles and remaining first liquid
are separated from each other.
[0052] In a further embodiment, before impregnation the particles
are subjected to a sub atmospheric pressure. This may facilitate
penetration of the precursor (liquid) with QDs into the pores. By
the sub atmospheric pressure, gas is removed to make the filling
more complete. Alternatively or additionally, the pores of the
porous inorganic material are hydrophobized. For instance, the
pores may be coated with a silane. A method for hydrophobizing the
inner pore surfaces is e.g. through the application of hydrophobic
silane monolayers. These monolayers consist of a reactive inorganic
head group that binds covalently to the (siliceous) surface and an
organic tail that self-organizes to form a dense network of
hydrocarbon chains. Because these coatings are only one monolayer
thick, their dimensions are no more than a few nm in thickness,
such as e.g. less than 10 nm. Alternatively or additionally, a
Teflon coating may be applied. Alternatively or additionally, the
impregnation may be (further) facilitated by subjecting the
particles while and/or after having contacted with the precursor
(liquid) with QDs to an elevated pressure, such as 1.2 bar or
higher.
[0053] As indicated above, the polymeric material that hosts the
QDs may be obtained by curing or polymerizing the curable or
polymerizable precursors within the pores of the porous material.
Hence, having introduced the curable precursor, curing may be
started. Alternatively (or additionally), having introduced
polymerizable precursor, polymerization may be started.
[0054] The liquid may thus comprise the luminescent quantum dots
and a curable or polymerizeble precursor. The liquid is thus (in
general) not a solvent, but may in embodiments essentially consist
of the luminescent quantum dots and a curable or polymerizeble
precursor and optionally other materials, wherein the optionally
other materials are especially selected from the group consisting
of a particulate material and an inorganic material, such as a
particulate inorganic material, like a scattering material or an
inorganic particulate luminescent material. The optional other
material may in embodiments also comprise a dye (see further also
below). In some fields, polymerization is also considered curing.
Here, curing especially refers to cross-linking.
[0055] For instance, the polymerizable precursor may comprise
polymerizable monomers. In such instance, the polymeric material
hosting the QDs within the pores is based on radical polymerizable
monomers. The phrase "wherein the polymeric (host) material is
based on radical polymerizable monomers", may especially indicate
that the polymer host material is obtainable by reaction monomers
that are able to form polymers by radical polymerization. A
non-limiting number of examples of such polymers are mentioned
below, and the person skilled in the art may derive therefrom which
monomers (i.e. monomer precursors) may be used (see further also
below). Such monomer thus especially includes one or more
radical-polamerizable groups (which may be used for polymeriation
with a photo initiator upon irradiation). Such monomers may in an
embodiment include different type of monomers. Especially, the
radical polymerizable monomers are selected from the group
consisting of a vinyl monomer, an acrylate monomer, and a
combination of a thiol and a diene.
[0056] As can for instance be derived from WO 03/093328, examples
of monomers polymerizable by a free radical polymerization process
include, but are not limited to, alpha-olefins; dienes such as
butadiene and chloroprene; styrene, alpha-methyl styrene, and the
like; heteroatom substituted alpha-olefins, for example, vinyl
acetate, vinyl alkyl ethers for example, ethyl vinyl ether,
vinyltrimethylsilane, vinyl chloride, tetrafluoroethylene,
chlorotrifluoroethylene, N-(3-dimethylaminopropyl methacrylamide,
dimethylaminopropyl methacrylamide, acrylamide, methacrylamide, and
similar derivatives; acrylic acids and derivatives for example,
acrylic acid, methacrylic acid, crotonic acid, acrylonitrile,
acrylic esters substituted with methoxy, ethoxy, propoxy, butoxy,
and similar derivatives for example, methyl acrylate, propyl
acrylate, butyl acrylate, methyl methacrylate, methyl crotonate,
glycidyl methacrylate, alkyl crotonates, and related esters; cyclic
and polycyclic olefin compounds for example, cyclopentene,
cyclohexene, cycloheptene, cyclooctene, and cyclic derivatives up
to C20; polycyclic derivates for example, norbornene, and similar
derivatives up to C20; cyclic vinyl ethers for example, 2,
3-dihydrofuran, 3,4-dihydropyran, and similar derivatives; allylic
alcohol derivatives for example, vinylethylene carbonate,
disubstituted olefins such as maleic and fumaric compounds for
example, maleic anhydride, diethylfumarate, and the like; and
mixtures thereof.
[0057] As can be derived from e.g. WO 2011/031871, additional
examples of monomers include, but are not limited to, allyl
methacrylate, benzyl methyl acrylate, 1,3-butanediol
dimethacrylate, 1,4-butanediol dimethacrylate, butyl acrylate,
n-butyl methacrylate, ethyl methacrylate, 2-ethyl hexyl acrylate,
1,6-hexanediol dimethacrylate, Bisphenol A ethoxylate diacrylate,
4-hydroxybutyl acrylate, hydroxyethyl acrylate, 2-hydroxyethyl
methacrylate, 2-hydroxypropyl acrylate, isobutyl methacrylate,
lauryl methacrylate, methacrylic acid, methyl acrylate,
2,2,3,3,4,4,5,5-octafluoropentyl acrylate, pentaerythritol
triacrylate, 2,2,2-trifluoroethyl 2-methyl acrylate,
trimethylolpropane triacrylate, acrylamide
n,n,-methylene-bisacryl-amide phenyl acrylate, and divinyl
benzene.
[0058] Many of these types of monomers are acrylate systems. Hence,
the term "acrylate" may refer to any of those above mentioned
systems such as acrylate, meth(yl)acrylate, butyl acrylate, lauryl
methacrylate, etc. etc. Likewise, vinyl monomer may refer to any
monomer comprising a vinyl group.
[0059] The phrase "wherein the polymeric (host) material is based
on radical polymerizable monomers" does not exclude the presence of
e.g. cross-linkers in the monomeric starting material. For the
synthesis of the wavelength converter, see below.
[0060] In principle, the polymer obtained may be any polymer, such
as a linear polymer, a (hyper)branched polymer, a cross-linked
polymer, a star polymer, a dendrimer, a random copolymer, an
alternating copolymer, a graft copolymer, a block copolymer, and a
terpolymer. The polymeric (host) material may in an embodiment be
or comprise a resin.
[0061] Especially those radical polymerizable monomers are applied,
which lead to a light transmissive polymer. In the embodiment of
the invention, the (light transmissive polymer) is a polymer which
shows high light transmission. Preferably a mean absorption of less
than 5%/mm more preferentially less than 2%/mm, especially less
than 1%/mm (per mm polymer thickness) in the wavelength region
400-700 nm. Hence, in an embodiment the first polymer is a polymer
having an absorption of less than 5%/mm, more preferentially less
than 2%/mm and most preferentially less than 1%/mm in the
wavelength range of 400-700 nm. Note that the transmission and
absorption of the polymer is related to the polymer per se, i.e.
the polymeric (host) material, and not to the transmission of the
wavelength converter (i.e. including the wavelength converter
nanoparticles). Especially, the maximum absorption (of the polymer)
is less than 20%/mm, even more especially less than 10%/mm, over
the entire wavelength region 400-700 nm. Transmission (T) and
absorption (A) relate as A=1-To/Ti, wherein Ti is the intensity of
the visible light impinging on the item (such as the polymer or the
converter) and To being is the intensity of the light escaping at
the other side of the item. The transmission or light permeability
can be determined by providing light at a specific wavelength with
a first intensity to the material and relating the intensity of the
light at that wavelength measured after transmission through the
material, to the first intensity of the light provided at that
specific wavelength to the material (see also E-208 and E-406 of
the CRC Handbook of Chemistry and Physics, 69th edition,
1088-1989).
[0062] As can e.g. be derived from WO 2011/031871, examples of
polymers, for example and without limitation, are polyethylene,
polypropylene, polystyrene, polyethylene oxide, polysiloxane,
polyphenylene, polythiophene, poly (phenylene-vinylene),
polysilane, polyethylene terephthalate and poly
(phenylene-ethynylene), polymethylmethacrylate,
polylaurylmethacrylate, polycarbonate, epoxy, and other epoxies.
Similar as what has been said with respect to monomers, some of
these types of polymers are acrylate systems. Hence, the term
"polyacrylate" may refer to any of those above mentioned systems
such as polyacrylate, polymeth(yl)acrylate, polybutyl acrylate,
polylauryl methacrylate, etc. etc. Likewise, vinylpolymer may refer
to any polymer based on monomers comprising a vinyl group, such as
polyethylene, polyprolylene, etc. etc.
[0063] In view of light transmission and/or chemical stability
and/or production process considerations, especially the polymeric
(host) material is selected from the group consisting of a poly
vinyl polymer (such as a poly ethylene, a poly propylene, etc.), a
poly acrylate polymer (such as a poly acrylate, a poly
methacrylate, a poly laurylmethacrylate, etc.) and a thiol-ene
polymer (such as polythiophene).
[0064] The term "radical initiator based material" refers to the
remains of the radical initiator that can be found or evaluation
from the composition of the polymeric (host) material. This radical
initiator based material may include unreacted radical initiator,
but also radical initiator that has been reacted. In case radical
initiator has been consumed, it refers to groups in the polymeric
(host) material that originate from the radical initiator. The term
"radical initiator" may in an embodiment refer to a plurality of
different radical initiators.
[0065] The free radical polymerization process is well known and
involves a reaction initiated by the formation of a free radical
from a free radical generator, for example a peroxide or azo
initiator. A reaction is initiated by addition of the free radical
to an unsaturated monomer molecule that subsequently adds, in a
step-wise manner, to additional unsaturated monomers to form a
growing chain or polymer.
[0066] As can e.g. be derived from WO 03/093328, examples of free
radical initiators include, but are not limited to, the following:
organic peroxides like: t-alkyl peroxyesters, tert-butyl
peroxybenzoate, tert-butyl peroxyacetate, ter-butyl peroxypivalate,
tert-butyl peroxymaleate, monoperoxycarbonates, OO-tert-butyl
O-isopropyl monoperoxycarbonate, diperoxyketals, ethyl 3,
3-di-(tert-amylperoxy)-butyrate, n-butyl-4,4-di
(tertbutylperoxy)-valerate, 1,1-di (tert-butylperoxy)-cyclohexane,
1,1-di (tert-amylperoxy)-cyclohexane, dialkyl peroxides, 2,5-di
(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 2,5-di
(tert-butylperoxy)-2,5-dimethylhexane, di-tert-amyl peroxide,
di-tert-butyl peroxide, dicumyl peroxide, t-alkyl hydroperoxides,
tert-butyl hydroperoxide, ter-amyl hydroperoxide, alpha-cumyl
hydroperoxide, ketone peroxides, methyl ethyl ketone peroxide,
cyclohexanone peroxide, 2,4-pentanedione peroxide, isobutyryl
peroxide, isopropyl peroxydicarbonate, di-n-butyl
peroxydicarbonate, di-sec-butyl peroxydicarbonate, tert-butyl
perneodecanoate, dioctanoyl peroxide, didecanoyl peroxide,
diproprionyl peroxide, didecanoyl peroxide, dipropionyl peroxide,
dilauroyl peroxide, tert-butyl perisobutyrate, tert-butyl
peracetate, tert-butyl per-,5, 5-trimethyl hexanoate; azo compounds
like: 2,2'-azobis [4-methoxy-2, 4-dimethyl] pentanenitrile,
2,3'-azobis [2,4-dimethyl] pentanenitrile, 2,2'-azobis
[isobutyronitrile]; carbon-carbon initiators like:
2,3-dimethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane,
1,1,2,2-tetraphenyl-1,2-bis (trimethylsiloxy) ethane; inorganic
peroxides like: hydrogen peroxide, potassium peroxydisulfate;
photoinitiators like: benzophenone 4-phenylbenzophenone, xanthone
thioxanthone, 2-chlorothioxanthone, 4,4'-bis (N, N'-dimethylamino
benzophenone), benzyl, 9,10-phenanthraquinone, 9,10-anthraquinone,
alpha,alpha-dimethyl-alpha-hydroxyacetophenone,
(1-hydroxycyclohexyl)-phenylmethanone, benzoin ethers, like methyl,
ethyl, isobutyl, benzoin ethers,
alpha,alpha-dimethoxy-alpha-phenylacetophenone,
1-phenyl-1,2-propanedione, 2-(O-benzoyl)oxime,
diphenyl(2,4,6-trimethylbenzoyl)phosphineoxide,
alpha-dimethylamino-alpha-ethyl-alpha-benzyl-3,5-dimethyl-4-morpholinoace-
tophenone, etc.
[0067] As can for instance be derived from WO 2011/031871, there
are in general two classes of photoinitiators. In the first class,
the chemical undergoes unimolecular bond cleavage to yield free
radicals. Examples of such photoinitiators include benzoin ethers,
benzyl ketals, a-dialkoxy-acetophenones, a-amino-alkylphenones, and
acylphosphine oxides. The second class of photoinitiators is
characterized by a bimolecular reaction where the photo initiator
reacts with a co-initiator to form free radicals. Examples of such
are benzophenones/amines, thioxanthones/amines, and titanocenes
(visible light). A non-exhaustive listing of specific examples of
photoinitiators that may be useful with a photo-polymerizable
monomer for particle preparation include the following from CIBA:
IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173
(2-hydroxy-2-methyl-1-phenyl-1-propanone), IRGACURE 2959
(2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone),
DAROCUR MBF (Methylbenzoylformate), IRGACURE 754 (oxy-phenyl-acetic
acid 2-[2 oxo-2 phenyl-acetoxy-ethoxy]-ethyl ester and
oxy-phenyl-acetic 2-[2-hydroxy-ethoxy]-ethyl ester), IRGACURE 651
Alpha, (alpha-dimethoxy-alpha-phenylacetophenone), IRGACURE 369
(2-Benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone),
IRGACURE 907
(2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone),
DAROCUR TPO (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide),
IRGACURE 819 (phosphine oxide, phenyl bis (BAPO) (2,4,6-trimethyl
benzoyl)), IRGACURE 784 (bis(eta
5-2,4-cyclopentadien-1-yl)Bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titan-
ium), IRGACURE 250
(iodonium(4-methylphenyl)[4-(2-methylpropyl)phenyl]-hexafluorophosphate(1-
-).)
[0068] An example of a thermal initiator is benzoyl peroxide and
azo-isobutyro-nitril (AIBN) (see further also below). In addition
to or alternative to such azo initiator, a peroxide initiator can
also be used. Further, in addition to or alternative to such
initiator, also photo initiators such as
.alpha.,.alpha.-dimethoxy-.alpha.-phenylacetophenone can be
used.
[0069] The polymerization may be started by heating and or
irradiating the radical polymerizable polymers, especially may be
started by (at least) irradiating the radical polymerizable
monomers. Especially, polymerization may be initiated photo
chemically upon irradiation with high energetic rays such as UV,
X-rays, gamma rays, electrons. If in the substantial absence of
radical (photo)initiator the polymerization may be started by (e.g.
UV) irradiation of the mixture (including the radical polymerizable
monomers). In some cases it may be desirable to heat up the mixture
above the glass transition of the system in order to reach complete
polymerization. When polymerization starts, the temperature may
again be lowered below the glass transition temperature; after
termination, the thus obtained wavelength converter may in some
embodiments be cooled down below the glass transition temperature.
However, also other methods may be applied, as will be clear to the
person skilled in the art. Especially, during polymerization the
temperature will not be higher than the boiling point of the
monomer(s) used.
[0070] Preferably, before polymerization starts (substantially),
the partial pressure of oxygen over the mixture may substantially
be reduced. For instance, the mixture may be provided in a
low-oxygen atmosphere, or after providing the mixture but before
polymerization, the oxygen partial pressure is lowered. In an
embodiment, the polymerization takes place in a low-oxygen
environment, like a glove box. Especially, an inert gas may be
applied, like one or more of Ar, CO2 or N2. Optionally,
polymerization may take place under reduced pressure.
Alternatively, the oxygen amount in the gas over the mixture, at
least during polymerization, is less than 1 ppm, such as less than
0.2 ppm. Hence, the method may especially comprise polymerizing the
radical polymerizeble monomers while maintaining the mixture in an
inert gas atmosphere.
[0071] An alternative polymer may be a silicone, such as especially
polymethyl phenyl silicone, PDMS, polysilsesquioxane, or other type
of siloxane compounds. Hence, the precursor may also comprise a
polymerizeble silicone precursor. For instance, hydrosylisation
with a Pt catalyst may be applied. In an embodiment, through the
hydrosilation reaction between an ethylenically unsaturated epoxide
and an SiH-containing silicone a curable epoxysilicone product can
be made. This may be catalyzed by catalyzed by a quaternary
ammonium, phosphonium or arsonium hexahaloplatinate.
[0072] In a specific embodiment, the precursor comprises a
precursor for a siloxane (silicone). Especially, the silicone may
be an optical grade commercial (polymerizeble or curable) silicone,
as available from e.g. Dow, Shinetsu, or Wacker.
[0073] Further, addition polymerization may be an option, e.g. to
epoxided or poly urethanes, etc. Other mechanisms for
polymerization are UV, thermal, with or without a catalyst,
etc.
[0074] For instance, the curable precursor may comprise curable
polymers. In such instance, the polymeric material hosting the QDs
within the pores is based on curable polymers.
[0075] For example, a liquid polymer (within the pores) can be
turned into a solid or gel by cross-linking the polymer chains
together. Examples of liquid polymers that can be cross-linked are
for instance described in EP 0246875, wherein mercaptan-terminated
liquid polymer with a cross-linking component is cross-linked. In
another embodiment, silicones can be cured.
[0076] As indicated above, the luminescent material in general
comprises particles with within the pores thereof the polymeric
material hosting the luminescent quantum dots. The term "quantum
dots" or "luminescent quantum dots" may also refer to a combination
of different type of quantum dots, i.e. quantum dots that have
different spectral properties. The QDs are herein also indicated as
"wavelength converter nanoparticles".
[0077] The quantum dots or luminescent nanoparticles, which are
herein indicated as wavelength converter nanoparticles, may for
instance comprise group II-VI compound semiconductor quantum dots
selected from the group consisting of (core-shell quantum dots,
with the core selected from the group consisting of) CdS, CdSe,
CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe,
ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe,
CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe,
CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe and HgZnSTe.
In another embodiment, the luminescent nanoparticles may for
instance be group III-V compound semiconductor quantum dots
selected from the group consisting of (core-shell quantum dots,
with the core selected from the group consisting of) GaN, GaP,
GaAs, AlN, AlP, AlAs, InN, InP, InGaP, InAs, GaNP, GaNAs, GaPAs,
AlNP, AlNAs, AlPAs, InNP, InNAs, InPAs, GaAlNP, GaAlNAs, GaAlPAs,
GaInNP, GaInNAs, GaInPAs, InAlNP, InAlNAs, and InAlPAs. In yet a
further embodiment, the luminescent nanoparticles may for instance
be I-III-VI2 chalcopyrite-type semiconductor quantum dots selected
from the group consisting of (core-shell quantum dots, with the
core selected from the group consisting of) CuInS2, CuInSe2,
CuGaS2, CuGaSe2, AgInS2, AgInSe2, AgGaS2, and AgGaSe2. In yet a
further embodiment, the luminescent nanoparticles may for instance
be (core-shell quantum dots, with the core selected from the group
consisting of) I-V-VI2 semiconductor quantum dots, such as selected
from the group consisting of (core-shell quantum dots, with the
core selected from the group consisting of) LiAsSe2, NaAsSe2 and
KAsSe2. In yet a further embodiment, the luminescent nanoparticles
may for instance be core-shell quantum dots, with the core selected
from the group consisting of) group (IV-VI compound semiconductor
nano crystals such as SbTe. In a specific embodiment, the
luminescent nanoparticles are selected from the group consisting of
(core-shell quantum dots, with the core selected from the group
consisting of) InP, CuInS2, CuInSe2, CdTe, CdSe, CdSeTe, AgInS2 and
AgInSe2. In yet a further embodiment, the luminescent nanoparticles
may for instance be one of the group (of core-shell quantum dots,
with the core selected from the group consisting of) II-VI, III-V,
I-III-V and IV-VI compound semiconductor nano crystals selected
from the materials described above with inside dopants such as
ZnSe:Mn, ZnS:Mn. The dopant elements could be selected from Mn, Ag,
Zn, Eu, S, P, Cu, Ce, Tb, Au, Pb, Tb, Sb, Sn and Tl. Herein, the
luminescent nanoparticles based luminescent material may also
comprise different types of QDs, such as CdSe and ZnSe:Mn.
[0078] It appears to be especially advantageous to use II-VI
quantum dots. Hence, in an embodiment the semiconductor based
luminescent quantum dots comprise II-VI quantum dots, especially
selected from the group consisting of (core-shell quantum dots,
with the core selected from the group consisting of) CdS, CdSe,
CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe,
ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe,
CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe,
CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe and HgZnSTe,
even more especially selected from the group consisting of CdS,
CdSe, CdSe/CdS and CdSe/CdS/ZnS.
[0079] The luminescent nanoparticles (without coating) may have
dimensions in the range of about 2-50 nm, such as 2-20 nm,
especially 2-10 nm, even more especially 2-5 nm; especially at
least 90% of the nanoparticles have dimension in the indicated
ranges, respectively, (i.e. e.g. at least 90% of the nanoparticles
have dimensions in the range of 2-50 nm, or especially at least 90%
of the nanoparticles have dimensions in the range of 2-5 nm). The
term "dimensions" especially relate to one or more of length,
width, and diameter, dependent upon the shape of the
nanoparticle.
[0080] In an embodiment, the wavelength converter nanoparticles
have an average particle size in a range from about 1 to about 1000
nanometers (nm), and preferably in a range from about 1 to about
100 nm. In an embodiment, nanoparticles have an average particle
size in a range from about 1 to about 20 nm. In an embodiment,
nanoparticles have an average particle size in a range from about 1
to about 10 nm.
[0081] Typical dots are made of binary alloys such as cadmium
selenide, cadmium sulfide, indium arsenide, and indium phosphide.
However, dots may also be made from ternary alloys such as cadmium
selenide sulfide. These quantum dots can contain as few as 100 to
100,000 atoms within the quantum dot volume, with a diameter of 10
to 50 atoms. This corresponds to about 2 to 10 nanometers. For
instance, spherical particles such as CdSe, InP, or CuInSe2, with a
diameter of about 3 nm may be provided. The luminescent
nanoparticles (without coating) may have the shape of spherical,
cube, rods, wires, disk, multi-pods, etc., with the size in one
dimension of less than 10 nm. For instance, nanorods of CdSe with
the length of 20 nm and a diameter of 4 nm may be provided. Hence,
in an embodiment the semiconductor based luminescent quantum dots
comprise core-shell quantum dots. In yet another embodiment, the
semiconductor based luminescent quantum dots comprise dots-in-rods
nanoparticles. A combination of different types of particles may
also be applied. Here, the term "different types" may relate to
different geometries as well as to different types of semiconductor
luminescent material. Hence, a combination of two or more of (the
above indicated) quantum dots or luminescent nano-particles may
also be applied.
[0082] One example, such as derived from WO 2011/031871, of a
method of manufacturing a semiconductor nanocrystal is a colloidal
growth process. Colloidal growth occurs by injection an M donor and
an X donor into a hot coordinating solvent. One example of a
preferred method for preparing mono disperse semiconductor
nanocrystals comprises pyrolysis of organometallic reagents, such
as dimethyl cadmium, injected into a hot, coordinating solvent.
This permits discrete nucleation and results in the controlled
growth of macroscopic quantities of semiconductor nanocrystals. The
injection produces a nucleus that can be grown in a controlled
manner to form a semiconductor nanocrystal. The reaction mixture
can be gently heated to grow and anneal the semiconductor
nanocrystal. Both the average size and the size distribution of the
semiconductor nanocrystals in a sample are dependent on the growth
temperature. The growth temperature necessary to maintain steady
growth increases with increasing average crystal size. The
semiconductor nanocrystal is a member of a population of
semiconductor nanocrystals. As a result of the discrete nucleation
and controlled growth, the population of semiconductor nanocrystals
that can be obtained has a narrow size distribution of diameters.
The small size distribution of diameters can also be referred to as
a size. Preferably, a mono disperse population of particles
includes a population of particles wherein at least about 60% of
the particles in the population fall within a specified particle
size range.
[0083] In an embodiment, nanoparticles can comprise semiconductor
nanocrystals including a core comprising a first semiconductor
material and a shell comprising a second semiconductor material,
wherein the shell is disposed over at least a portion of a surface
of the core. A semiconductor nanocrystal including a core and shell
is also referred to as a "core/shell" semiconductor nanocrystal.
Any of the materials indicated above may especially be used as
core. Therefore, the phrase "core-shell quantum dots, with the core
selected from the group consisting of" is applied in some of the
above lists of quantum dot materials.
[0084] For example, the semiconductor nanocrystal can include a
core having the formula MX, where M can be cadmium, zinc,
magnesium, mercury, aluminum, gallium, indium, thallium, or
mixtures thereof, and X can be oxygen, sulfur, selenium, tellurium,
nitrogen, phosphorus, arsenic, antimony, or mixtures thereof.
Examples of materials suitable for use as semiconductor nanocrystal
cores include, but are not limited to, ZnO, ZnS, ZnSe, ZnTe, CdO,
CdS, CdSe, CdTe, MgS, MgSe, GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS,
HgSe, HgTe, InAs, InN, InP, InGaP, InSb, AlAs, AIN, AlP, AlSb, TIN,
TIP, TlAs, TlSb, PbO, PbS, PbSe, PbTe, Ge, Si, an alloy including
any of the foregoing, and/or a mixture including any of the
foregoing, including ternary and quaternary mixtures or alloys.
[0085] The shell can be a semiconductor material having a
composition that is the same as or different from the composition
of the core. The shell comprises an overcoat of a semiconductor
material on a surface of the core semiconductor nanocrystal can
include a Group IV element, a Group II-VI compound, a Group II-V
compound, a Group III-VI compound, a Group III-V compound, a Group
IV-VI compound, a Group compound, a Group II-IV-VI compound, a
Group II-IV-V compound, alloys including any of the foregoing,
and/or mixtures including any of the foregoing, including ternary
and quaternary mixtures or alloys. Examples include, but are not
limited to, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, MgS, MgSe,
GaAs, GaN, GaP, GaSe, GaSb, HgO, HgS, HgSe, HgTe, InAs, InN, InP,
InGaP, InSb, AlAs, AIN, AlP, AlSb, TIN, TIP, TlAs, TlSb, PbO, PbS,
PbSe, PbTe, Ge, Si, an alloy including any of the foregoing, and/or
a mixture including any of the foregoing. For example, ZnS, ZnSe or
CdS overcoatings can be grown on CdSe or CdTe semiconductor
nanocrystals. An overcoating process is described, for example, in
U.S. Pat. No. 6,322,901. By adjusting the temperature of the
reaction mixture during overcoating and monitoring the absorption
spectrum of the core, over coated materials having high emission
quantum efficiencies and narrow size distributions can be obtained.
The overcoating may comprise one or more layers. The overcoating
comprises at least one semiconductor material which is the same as
or different from the composition of the core. Preferably, the
overcoating has a thickness from about one to about ten monolayers.
An overcoating can also have a thickness greater than ten
monolayers. In an embodiment, more than one overcoating can be
included on a core.
[0086] In an embodiment, the surrounding "shell" material can have
a band gap greater than the band gap of the core material. In
certain other embodiments, the surrounding shell material can have
a band gap less than the band gap of the core material.
[0087] In an embodiment, the shell can be chosen so as to have an
atomic spacing close to that of the "core" substrate. In certain
other embodiments, the shell and core materials can have the same
crystal structure.
[0088] Examples of semiconductor nanocrystal (core)shell materials
include, without limitation: red (e.g., (CdSe)ZnS (core)shell),
green (e.g., (CdZnSe)CdZnS (core)shell, etc.), and blue (e.g.,
(CdS)CdZnS (core)shell (see further also above for examples of
specific wavelength converter nanoparticles, based on
semiconductors. Note that the shell as (inorganic) coating as
described herein, may be a coating on the semiconductor
nanocrystal. Should this QD be a core-shell nanoparticle, then the
(inorganic coating) is a coating on the shell, i.e. a shall at
least partially, even more especially entirely, enclosing the
luminescent nanoparticle.
[0089] Especially, the wavelength converter comprises 0.01-25 wt. %
wavelength converter nanoparticles (especially QDs) relative to the
total weight of the wavelength converter, such as 0.1-5 wt. %, The
concentration of the QDs in the first host material is preferably
between 0.5% and 25% wt. The concentration of porous particles
(comprising the QDs in the first curable host) in the second host
matrix determines the overall concentration of QDs in the
wavelength converter. In an embodiment, semiconductor nanocrystals
preferably have ligands attached thereto, such as e.g. described in
WO 2011/031871. In an embodiment, the ligands can be derived from
the coordinating solvent used during the growth process. In an
embodiment, the surface can be modified by repeated exposure to an
excess of a competing coordinating group to form an overlayer.
[0090] For example, a dispersion of the capped semiconductor
nanocrystal can be treated with a coordinating organic compound,
such as pyridine, to produce crystallites which disperse readily in
pyridine, methanol, and aromatics but no longer disperse in
aliphatic solvents. Such a surface exchange process can be carried
out with any compound capable of coordinating to or bonding with
the outer surface of the semiconductor nanocrystal, including, for
example, carboxylic acids, phosphines, thiols, amines and
phosphates. The semiconductor nanocrystal can be exposed to short
chain polymers which exhibit an affinity for the surface and which
terminate in a moiety having an affinity for a liquid medium in
which the semiconductor nanocrystal is suspended or dispersed. Such
affinity improves the stability of the suspension and discourages
flocculation of the semiconductor nanocrystal.
[0091] More specifically, the coordinating ligand can have the
formula:
(Y-)k-n-(X)-(-L)n
wherein k is 2, 3 4, or 5, and n is 1, 2, 3, 4 or 5 such that k-n
is not less than zero; X is O, OS, O--Se, O--N, O--P, O--As, S,
S=0, S02, Se, Se=0, N, N=0, P, P=0, C=0 As, or As=0; each of Y and
L, independently, is H, OH, aryl, heteroaryl, or a straight or
branched C2-18 hydrocarbon chain optionally containing at least one
double bond, at least one triple bond, or at least one double bond
and one triple bond. The hydrocarbon chain can be optionally
substituted with one or more C1-4 alkyl, C2-4 alkenyl, C2-4
alkynyl, C1-4 alkoxy, hydroxyl, halo, amino, nitro, cyano, C3-5
cycloalkyl, 3-5 membered heterocycloalkyl, aryl, heteroaryl, C1-4
alkylcarbonyloxy, C1-4 alkyloxycarbonyl, C1-4 alkylcarbonyl, or
formyl. The hydrocarbon chain can also be optionally interrupted by
-0-, --S--, --N(Ra)--, --N(Ra)--C(0)-0-, -0-C(0)-N(Ra)-,
--N(Ra)--C(0)-N(Rb)-, --O--C(0)-0-, --P(Ra)--, or --P(0)(Ra)-. Each
of Ra and Rb, independently, is hydrogen, alkyl, alkenyl, alkynyl,
alkoxy, hydroxylalkyl, hydroxyl, or haloalkyl. An aryl group is a
substituted or unsubstituted cyclic aromatic group. Examples
include phenyl, benzyl, naphthyl, tolyl, anthracyl, nitrophenyl, or
halophenyl. A heteroaryl group is an aryl group with one or more
heteroatoms in the ring, for instance furyl, pyridyl, pyrrolyl,
phenanthryl.
[0092] Further ligands may especially be one or more of oleic acid,
and tri-octyl phosphine, and tri-octyl phosphine oxide. Hence,
ligands may especially be selected from the group of acids, amines,
phosphines, phosphine oxides and thiols.
[0093] A suitable coordinating ligand can be purchased commercially
or prepared by ordinary synthetic organic techniques, for example,
as described in J. March, Advanced Organic Chemistry. Other ligands
are described in U.S. patent application Ser. No. 10/641,292 for
"Stabilized Semiconductor Nanocrystals", filed 15 Aug. 2003, which
issued on 9 Jan. 2007 as U.S. Pat. No. 7,160,613, which is hereby
incorporated by reference in its entirety. Other examples of
ligands include benzylphosphonic acid, benzylphosphonic acid
including at least one substituent group on the ring of the benzyl
group, a conjugate base of such acids, and mixtures including one
or more of the foregoing. In an embodiment, a ligand comprises
4-hydroxybenzylphosphonic acid, a conjugate base of the acid, or a
mixture of the foregoing. In an embodiment, a ligand comprises
3,5-di-teri-butyl-4-hydroxy benzyl-phosphonic acid, a conjugate
base of the acid, or a mixture of the foregoing. Additional
examples of ligands that may be useful with the present invention
are described in International Application No. PCT/US2008/010651,
filed 12 Sep. 2008, of Breen, et al., for "Functionalized
Nanoparticles And Method" and International Application No.
PCT/US2009/004345, filed 28 Jul. 2009 of Breen et al., for
"Nanoparticle Including Multi-Functional Ligand and Method", each
of the foregoing being hereby incorporated herein by reference.
[0094] As indicated above, the present process may also be applied
for non-quantum dot luminescent nano particles.
[0095] After having introduced the first liquid into the pores of
the particulate porous inorganic material, optionally the material
may be washed. In case of an incipient wetness technique for
filling the pores, this may not be necessary, but when there is a
surplus of first liquid, it may be desirable to wash the particles.
This may in an embodiment be done after separating the particulate
material from the first liquid. Especially, the washing liquid is a
non-solvent for the polymerizeble precursor. A non-solvent may be
defined as a liquid wherein a material, here the polymerizeble
precursor does not dissolve or only solves up to an amount of 0.01
g/l. Hence, the invention also provides a process wherein before
curing or polymerizing but after impregnation the particles are
washed with a solvent, especially with a solvent which is a
non-solvent for the curable or polymerizable precursor. In a
specific embodiment, there is no washing at all before curing or
polymerizing.
[0096] Hence, in general, the process may include filling the pores
with the first liquid, separating the particles with (at least
partly filled pores) from the first liquid, optionally washing the
particles, and curing/polymerizing the curable or polymerizable
precursor (which is (at least) available in the pores. Separation
may be done with techniques known in the art, such as filtration,
(gravity) sedimentation and decanting, etc. An interesting option
is to use a filter. On such filter, such as a Buchner funnel, the
micro particles are collected. The micro particles may be washed,
if desired, to remove excess and/or remaining first liquid at the
surface of the particles. Hence, especially the invention also
provides a process wherein before curing or polymerizing but after
impregnation the particles, the impregnated particles and possible
remaining first liquid are separated. Thereafter, the material in
the pores of the porous cores may be subjected to the
curing/polymerization. Herein, the term "possible remaining first
liquid" is applied, as in the case of an incipient wetness
technique, or a deliberate filling amount of first liquid smaller
than the pore volume, may lead to a situation wherein there is no
remaining liquid to be removed.
[0097] If desired, however, this washing may deliberately be used
to remove the precursor. In such instances it appears that the
nanoparticles remain in the pores, without polymerizeble precursor,
or with substantially no polymerizeble precursor. In such
embodiment, curing may lead to a very low amount or no polymeric
material. In such embodiment, it may be desirable to embed the
particles in a matrix (see also above for matrices). Therefore, in
a further aspect the invention provides a process for the
production of a (particulate) luminescent material comprising
particles, especially substantially spherical particles, having a
porous inorganic material core with pores, especially macro pores,
which are at least partly filled with a polymeric material with
luminescent nanoparticles, especially quantum dots, embedded
therein, wherein the process comprises (i) impregnating the
particles of a particulate porous inorganic material with pores
with a first liquid ("ink") comprising the luminescent
nanoparticles, especially quantum dots, and (optionally) a curable
or polymerizeble precursor of the polymeric material, to provide
pores that are at least partly filled with said luminescent
nanoparticles, especially quantum dots, and (optional) curable or
polymerizeble precursor, washing the thus obtained particles with a
solvent for the curable or polymerizeble, or with a solvent for the
first liquid; optionally (ii) curing or polymerizing the curable or
polymerizeble precursor within pores of the porous material. In a
specific embodiment, the process further comprises (iii) applying
an encapsulation (such as coating, or embedding in a matrix, or
both) to the thus obtained particles (with pores that are at least
partly filled with luminescent nanoparticles, especially quantum
dots). Hence, in these embodiment, the first liquid may not
necessarily include a polymerizeble (or curable) material. Thus,
with a suitable solvent, i.e. a solvent for the first liquid may be
washed away (rinsed out) while the particles appear to stay
embedded in the pores. A solvent for the first liquid may of course
also be a combination of solvents. Further, the solvent for the
first liquid may especially be a solvent or combination of solvents
that is able to solve the one or more liquid components of the
first liquid.
[0098] In general, the first liquid is a liquid wherein the
nanoparticles can be well dispersed.
[0099] In yet a further embodiment, after filling the pores with
the first liquid (with quantum dots) and curing and/or polymerizing
the curable or polymerizeble material (with QDs) in the pores, the
particles are subjected to a second filling. This second filling
can be done with the same first liquid. However, this second
filling can also be done with the same first liquid without QDs.
Though in general the pores are well filled, such second filling
may be used to completely fill the pores in case a first filling of
the pores might not have been (deliberately) complete. Of course,
such multi-stage process may also be applied to fill with different
types of QD's. In this way a layered QD structure may be obtained
within the pores. It may for instance be advantageous to fill the
pores partly first with a first type of QDs' and thereafter with a
second type of QD's (according to the process as described herein),
wherein especially the first type of QD's emit at a longer
wavelength than the second type of QD's.
[0100] As indicated above, the invention also provides a wavelength
converter per se, i.e. a wavelength converter comprising a light
transmissive solid matrix with the (particulate) luminescent
material (as defined herein, and/or obtainable according to the
process defined herein) embedded therein (see also above).
[0101] Especially, such wavelength converter may further comprise a
second luminescent material. Especially, the second luminescent
material under excitation with light has (will have) another
wavelength distribution of the luminescence than the luminescent
quantum dots. For instance, even QD's with substantially the same
chemical composition (of the core), but having other dimensions may
already result in different emissions. This second luminescent
material may thus have a different emission than the quantum dots
or mixture of quantum dots (under the same excitation wavelength).
Optionally, however, the second luminescent material may also be
excited by luminescence light of the QDs.
[0102] By using a mixture of different types of QDs and/or a second
luminescent material, the luminescence of the wavelength converter,
and thus, where applicable, also the lighting device light of the
lighting device may be tuned.
[0103] Also other species (in addition to the monomers and the
wavelength converter nanoparticles) may be present in the starting
mixture (of the curable or polymerizable precursor and QDs and/or
the precursor of a polymeric host material (matrix) and may be
incorporated in the polymeric (host) material. For instance,
reflective particles like TiO2 particles may also be incorporated.
Also inorganic luminescent material, not having nanoparticle
character, like micron sized particulate inorganic luminescent
materials may be present, as well as the above indicated
cross-linker. Information about the monomers and the wavelength
converter nanoparticles, as well as about the optional radical
initiator, are indicated above. As can also be derived from the
above, the mixture (i.e. especially the first liquid comprising the
luminescent quantum dots and a curable or polymerizable precursor
of the polymeric material) may comprise 0.01-25 wt. % wavelength
converter nanoparticles relative to the total weight of the
mixture.
[0104] As indicated above, the invention also provides a lighting
device comprising (i) a light source configured to generate light
source light, (ii) the (particulate) luminescent material as
defined herein or obtainable by the process as defined herein,
wherein the (particulate) luminescent material is configured to
convert at least part of the light source light into visible
luminescent quantum dot light.
[0105] In a specific embodiment, the lighting device comprises the
wavelength converter as defined herein, arranged at a non-zero
distance from the light source. However, also other arrangements
may be chosen to arrange the (particulate) luminescent material at
a non-zero distance from the light source (such as at a non-zero
distance from an LED die). It may be advantageous, in view of
efficiency and/or stability, to arrange the QDs, or especially the
wavelength converter, at a non-zero distance, such as 0.5-50 mm,
like 1-50 mm, from the light source. Hence, in an embodiment, the
wavelength converter may be configured at a non-zero distance of
the light source.
[0106] Alternatively or additionally, the luminescent material or
the wavelength converter is directly applied to a light emitting
surface of the light source, such as directly on an LED die (see
also above).
[0107] Further, the method may comprise enclosing the thus obtained
wavelength converter by an encapsulation, especially an oxygen
non-permeable encapsulation. Especially, this encapsulation is
applied while the wavelength converter is still under the reduced
oxygen and water atmosphere. Hence, the wavelength converter may
(also) be encapsulated. The wavelength converter may be a film, a
layer, such as a self supporting layer, or a body.
[0108] The wavelength converter can be configured as light exit
window of the lighting device. Hence, in such embodiment, light
from the light source and converter light (see further below) may
emanate from the lighting device via and from the wavelength
converter (during use of the device). The wavelength converter may
also be configured in reflective mode. For instance, a light mixing
chamber may comprise one or more wall(s) comprising the wavelength
converter (reflective mode) and/or an exit window comprising the
wavelength converter (transmissive mode).
[0109] The wavelength converter (or more precisely the wavelength
converter nanoparticles) is (are) radiationally coupled to the
light source (or, as indicated above, a plurality of light
sources). The term "radiationally coupled" especially means that
the light source and the wavelength converter are associated with
each other so that at least part of the radiation emitted by the
light source is received by the wavelength converter (and at least
partly converted into luminescence). The term "luminescence" refers
to the emission which emits the wavelength converter nanoparticles
emit upon excitation by the light source light of the light source.
This luminescence is herein also indicated as converter light
(which at least comprises visible light, see also below).
[0110] The wavelength converter will in general also be configured
downstream of the light source. The terms "upstream" and
"downstream" relate to an arrangement of items or features relative
to the propagation of the light from a light generating means (here
the especially the light source), wherein relative to a first
position within a beam of light from the light generating means, a
second position in the beam of light closer to the light generating
means is "upstream", and a third position within the beam of light
further away from the light generating means is "downstream".
[0111] The device is especially configured to generate device
light, which at least partly comprises the converter light, but
which may optionally also comprise (remaining) light source light.
For instance, the wavelength converter may be configured to only
partly convert the light source light. In such instance, the device
light may comprise converter light and light source light. However,
in another embodiment the wavelength converter may also be
configured to convert all the light source light.
[0112] Hence, in a specific embodiment, the lighting device is
configured to provide lighting device light comprising both light
source light and converter light, for instance the former being
blue light, and the latter comprising yellow light, or yellow and
red light, or green and red light, or green, yellow and red light,
etc. In yet another specific embodiment, the lighting device is
configured to provide only lighting device light comprising only
converter light. This may for instance happen (especially in
transmissive mode) when light source light irradiating the
wavelength converter only leaves the downstream side of the
wavelength converter as converted light (i.e. all light source
light penetrating into the wavelength converter is absorbed by the
wavelength converter).
[0113] The term "wavelength converter" may also relate to a
plurality of wavelength converters. These can be arranged
downstream of one another, but may also be arranged adjacent to
each other (optionally also even in physical contact as directly
neighboring wavelength converters). The plurality of wavelength
converters may comprise in an embodiment two or more subsets which
have different optical properties. For instance, one or more
subsets may be configured to generate wavelength converter light
with a first spectral light distribution, like green light, and one
or more subsets may be configured to generate wavelength converter
light with a second spectral light distribution, like red light.
More than two or more subsets may be applied. When applying
different subsets having different optical properties, e.g. white
light may be provided and/or the color of the device light (i.e.
the converter light and optional remaining light source light
(remaining downstream of the wavelength converter). Especially when
a plurality of light sources is applied, of which two or more
subsets may be individually controlled, which are radiationally
coupled with the two or more wavelength converter subsets with
different optical properties, the color of the device light may be
tunable. Other options to make white light are also possible (see
also below).
[0114] The lighting device may be part of or may be applied in e.g.
office lighting systems, household application systems, shop
lighting systems, home lighting systems, accent lighting systems,
spot lighting systems, theater lighting systems, fiber-optics
application systems, projection systems, self-lit display systems,
pixelated display systems, segmented display systems, warning sign
systems, medical lighting application systems, indicator sign
systems, decorative lighting systems, portable systems, automotive
applications, green house lighting systems, horticulture lighting,
or LCD backlighting.
[0115] As indicated above, the lighting unit may be used as
backlighting unit in an LCD display device. Hence, the invention
provides also a LCD display device comprising the lighting unit as
defined herein, configured as backlighting unit. The invention also
provides in a further aspect a liquid crystal display device
comprising a back lighting unit, wherein the back lighting unit
comprises one or more lighting devices as defined herein.
[0116] Preferably, the light source is a light source that during
operation emits (light source light) at least light at a wavelength
selected from the range of 200-490 nm, especially a light source
that during operation emits at least light at wavelength selected
from the range of 400-490 nm, even more especially in the range of
440-490 nm. This light may partially be used by the wavelength
converter nanoparticles (see further also below). Hence, in a
specific embodiment, the light source is configured to generate
blue light.
[0117] In a specific embodiment, the light source comprises a solid
state LED light source (such as a LED or laser diode).
[0118] The term "light source" may also relate to a plurality of
light sources, such as 2-20 (solid state) LED light sources. Hence,
the term LED may also refer to a plurality of LEDs.
[0119] The term white light herein, is known to the person skilled
in the art. It especially relates to light having a correlated
color temperature (CCT) between about 2000 and 20000 K, especially
2700-20000 K, for general lighting especially in the range of about
2700 K and 6500 K, and for backlighting purposes especially in the
range of about 7000 K and 20000 K, and especially within about 15
SDCM (standard deviation of color matching) from the BBL (black
body locus), especially within about 10 SDCM from the BBL, even
more especially within about 5 SDCM from the BBL.
[0120] In an embodiment, the light source may also provide light
source light having a correlated color temperature (CCT) between
about 5000 and 20000 K, e.g. direct phosphor converted LEDs (blue
light emitting diode with thin layer of phosphor for e.g. obtaining
of 10000 K). Hence, in a specific embodiment the light source is
configured to provide light source light with a correlated color
temperature in the range of 5000-20000 K, even more especially in
the range of 6000-20000 K, such as 8000-20000 K. An advantage of
the relative high color temperature may be that there may be a
relative high blue component in the light source light.
[0121] The terms "violet light" or "violet emission" especially
relates to light having a wavelength in the range of about 380-440
nm. The terms "blue light" or "blue emission" especially relates to
light having a wavelength in the range of about 440-490 nm
(including some violet and cyan hues). The terms "green light" or
"green emission" especially relate to light having a wavelength in
the range of about 490-560 nm. The terms "yellow light" or "yellow
emission" especially relate to light having a wavelength in the
range of about 540-570 nm. The terms "orange light" or "orange
emission" especially relate to light having a wavelength in the
range of about 570-600. The terms "red light" or "red emission"
especially relate to light having a wavelength in the range of
about 600-750 nm. The term "pink light" or "pink emission" refers
to light having a blue and a red component. The terms "visible",
"visible light" or "visible emission" refer to light having a
wavelength in the range of about 380-750 nm.
[0122] The term "substantially" herein, such as in "substantially
all light" or in "substantially consists", will be understood by
the person skilled in the art. The term "substantially" may also
include embodiments with "entirely", "completely", "all", etc.
Hence, in embodiments the adjective substantially may also be
removed. Where applicable, the term "substantially" may also relate
to 90% or higher, such as 95% or higher, especially 99% or higher,
even more especially 99.5% or higher, including 100%. The term
"comprise" includes also embodiments wherein the term "comprises"
means "consists of". The term "and/or" especially relates to one or
more of the items mentioned before and after "and/or". For
instance, a phrase "item 1 and/or item 2" and similar phrases may
relate to one or more of item 1 and item 2. The term "comprising"
may in an embodiment refer to "consisting of" but may in another
embodiment also refer to "containing at least the defined species
and optionally one or more other species".
[0123] Furthermore, the terms first, second, third and the like in
the description and in the claims, are used for distinguishing
between similar elements and not necessarily for describing a
sequential or chronological order. It is to be understood that the
terms so used are interchangeable under appropriate circumstances
and that the embodiments of the invention described herein are
capable of operation in other sequences than described or
illustrated herein.
[0124] The devices herein are amongst others described during
operation. As will be clear to the person skilled in the art, the
invention is not limited to methods of operation or devices in
operation.
[0125] It should be noted that the above-mentioned embodiments
illustrate rather than limit the invention, and that those skilled
in the art will be able to design many alternative embodiments
without departing from the scope of the appended claims. In the
claims, any reference signs placed between parentheses shall not be
construed as limiting the claim. Use of the verb "to comprise" and
its conjugations does not exclude the presence of elements or steps
other than those stated in a claim. The article "a" or "an"
preceding an element does not exclude the presence of a plurality
of such elements. The invention may be implemented by means of
hardware comprising several distinct elements, and by means of a
suitably programmed computer. In the device claim enumerating
several means, several of these means may be embodied by one and
the same item of hardware. The mere fact that certain measures are
recited in mutually different dependent claims does not indicate
that a combination of these measures cannot be used to
advantage.
[0126] The invention further applies to a device comprising one or
more of the characterizing features described in the description
and/or shown in the attached drawings. The invention further
pertains to a method or process comprising one or more of the
characterizing features described in the description and/or shown
in the attached drawings.
[0127] The various aspects discussed in this patent can be combined
in order to provide additional advantages. Furthermore, some of the
features can form the basis for one or more divisional
applications.
[0128] Most of the embodiments described above include the filling
of the pores with a first liquid ("ink") including a curable or
polymerizeble precursor (and luminescent nanoparticles, especially
luminescent quantum dots). Alternatively, the pores maybe filled
with the luminescent nanoparticles in a liquid that is not
subsequently cured or polymerized. For instance, the first liquid
may evaporate thereby leaving the luminescent nanoparticles in the
pores of the porous inorganic material core. Thereafter, the cores
may be coated, especially via an atomic layer deposition process.
Hence, in a further aspect, the invention also provides a process
for the production of a luminescent material comprising particles
having a porous inorganic material core with pores which are at
least partly filled with luminescent quantum dots, wherein the
process comprises: impregnating the particles of the particulate
porous inorganic material with pores with a first liquid comprising
the luminescent nanoparticles, such as luminescent quantum dots, to
provide pores that are at least partly filled with said luminescent
nanoparticles, such as luminescent quantum dots and liquid material
(especially a solvent for the luminescent quantum dots); and
optionally removing the liquid. Thereafter, optionally the porous
inorganic material with pores at least partly filled with the
luminescent nanoparticles, such as luminescent quantum dots may be
coated with a coating, especially via an ALD process, to provide a
coating on the (individual) particles. This coating or shell may
have a thickness of at least 10 nm. The above described embodiments
in relation to the particles, the luminescent nanoparticles, the
coating and the encapsulation, etc., also apply to this aspect (i e
luminescent nanoparticles in pores not being embedded in a polymer)
of the invention. Especially, the coating (on the at least partly
filled porous inorganic material with pores) as described herein
encloses the particles entirely (core-shell particles (with the
cores being the inorganic cores)). The invention also provides such
luminescent material per se as well as a wavelength converter
and/or a lighting device comprising such luminescent material (or
wavelength converter comprising such luminescent material). Hence,
in a further aspect the invention also provides a luminescent
material comprising particles having a porous inorganic material
core with pores which are at least partly filled with luminescent
quantum dots (120), and wherein especially the particles are coated
with an inorganic coating (of at least 10 nm thickness). Hence, the
luminescent nano particles are especially enclosed in the pores and
are protected by the coating closing said pores. Thus, especially,
the particles have one or more (even more especially all) of the
following features (i) having particle sizes (ps) in the range of
1-500 .mu.m, (ii) wherein the particles comprise an encapsulation
encapsulating at least part of the core, (iii) wherein the porous
inorganic material comprises one or more of a porous silica, a
porous alumina, a porous glass, a porous zirconia, and a porous
titania, (iv) wherein the pores have mean pore sizes (dp) in the
range of 0.1-10 .mu.m, and (v) wherein the encapsulation (220)
comprises an inorganic coating. Such particles may further be
embedded in a polymeric matrix, to provide e.g. the wavelength
converter. A suitable solvent to introduce the luminescent
nanoparticles, such as luminescent quantum dots, into the pores
especially comprise one or more of an alkane (such as hexane,
heptane), toluene, chloroform, an alcohol (such as one or more of
ethanol and butanol), and water. Ligands attached to the
nanoparticles may facilitate solvation of the nano particles in the
solvent (see also above).
BRIEF DESCRIPTION OF THE DRAWINGS
[0129] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying schematic
drawings in which corresponding reference symbols indicate
corresponding parts, and in which:
[0130] FIGS. 1A, 1B, 1C, 1D, and 1E schematically depict some
aspects of an embodiment of the process and of the luminescent
material;
[0131] FIGS. 2A, 2B, 2C, 2D, and 2E schematically depict some
aspects of an embodiment of the lighting device;
[0132] FIGS. 3A, 3B, 3C, and 3D shows the in-situ impregnation of
Trisoperl PSP's with Ebecryl 150. The black interior (non-filled
parts) slowly disappear over time;
[0133] FIG. 4 shows a fluorescent microscope image showing that
these particles show bright QD emission;
[0134] FIG. 5A shows a HR-SEM image of a cross-section of an ALD-a
particle. FIGS. 5B, 5C, and 5D, respectively, show the elemental
analysis by EDX of the regions indicated in the HR-SEM FIG. 5A
(image spectra 4, 5, 7, respectively).
[0135] FIG. 6A shows the normalized photoluminescence intensity (PL
I) as function of time (t, in seconds) for a non-impregnated sample
and impregnated sample, in N2 and in air atmosphere. All
measurements are performed at 10 W/cm2 blue flux and 100.degree.
C.; FIG. 6B shows the normalized photoluminescence intensity (PL I)
as function of time for impregnated samples with and without ALD
coating, in N2 and in air atmosphere. All measurements are
performed at 10 W/cm2 blue flux and 100.degree. C. FIG. 6C shows
the normalized photoluminescence intensity (PL I) as function of
time (t, in seconds) for impregnated samples with and without ALD
coating, in N2 and in air atmosphere. All measurements are
performed at 10 W/cm2 blue flux and 100.degree. C.; and also FIG.
6D shows the normalized photoluminescence intensity (PL I) as
function of time (t, in seconds) for impregnated samples with and
without ALD coating, in N2 and in air atmosphere. All measurements
are performed at 10 W/cm2 blue flux and 100.degree. C. Whereas in
FIGS. 6B and 6C the curves for "Impregnated ALD-a/c, air" are a
continuation in time of the same samples indicated in the same
graphs, respectively, as "Impregnated ALD-a/c, N2", FIG. 6D shows
the curve (curve 4) "Impregnated ALD-c, air" which is obtained
after the impregnated ALD particles are directly subjected to
photoluminescence measurements under air conditions (thus without
an earlier measurement of the PL as function of time under N2). The
curves in FIGS. 6A, 6B, 6C, and 6D are indicated below in table
1.
TABLE-US-00001 [0136] TABLE 1 overview of curves in FIGS. 6A, 6B,
6C, and 6D FIG. Curve 1 Curve 2 Curve 3 Curve 4 FIG. 6A no impreg-
no impreg- impregnated, impregnated, nation, N2 nation, air no ALD,
N2 no ALD, air FIG. 6B impregnated, impregnated, impregnated,
impregnated, no ALD, N2 no ALD, air ALD-a, N2 ALD-a, air FIG. 6C
impregnated, impregnated, impregnated, impregnated, no ALD, N2 no
ALD, air ALD-c, N2 ALD-c, air FIG. 6D impregnated, impregnated,
impregnated, impregnated, no ALD, N2 no ALD, air ALD-c, N2 ALD-c,
air
[0137] FIG. 7A SEM image of a cross-section of an ALD-b particle.
The spectra (S1- S3) show the elemental analysis by EDX of the
regions indicated in the SEM image (FIGS. 7B, 7C, and 7D,
respectively); FIGS. 8A and 8B show SEM images of the fill opening
of a non-ALD coaled PSP batch 1 (8a) and ALD-b coated PSP (8b);
FIG.8C shows a SEM of particles in more detail. The fill openings
are clearly visible.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0138] FIG. 1A schematically depicts first particles 20 having a
porous inorganic material core 21 and pores 22 which can be
combined with a liquid comprising curable or polymerizable
precursor 111. The liquid is indicated with reference 711. The
liquid further comprises quantum dots 120 and optionally a second
luminescent material 150. This second luminescent material 150 is
indicated as discrete items, such as particles, but may however
also comprise molecules, like inorganic molecules or organic
molecules, that are molecularly dispersed in the liquid 711. In an
embodiment, the liquid 711 comprises as liquid components
essentially curable or polymerizable precursor 111 and optionally
cross-linkers or initiators for polymerization. The particles 20
and the liquid 711 are mixed (stage I), whereby particles with
filled pores are obtained (stage II). After filling, excess of
liquid 711 may be removed.
[0139] Then, the curable or polymerizable precursor is brought to
curing or polymerization. This may for instance be done by
providing UV light and/or thermal energy, etc. to the curable or
polymerizable precursors. After reaction, stage III is obtained
with particles 20 with at least partly filled pores, which are
filled with polymeric material 110 with luminescent quantum dots
embedded therein. This particulate material is luminescent, and
will give light upon excitation by UV and/or blue light, due to the
presence of the QDs. This particulate material is herein also
indicated as luminescent material 2. In this stage, the particles
20 are identical to the porous cores 21.
[0140] Optionally, the process may be continued by encapsulating
the thus obtained particulate luminescent material 2, with one or
more of a coating and a host matrix. Embodiments of products
thereof are schematically depicted in FIGS. 1B and 1C,
respectively. The result of a coating process is shown in stage IV,
wherein the particles 20 are enclosed by encapsulation 220, and
here in the form of a coating 320. Coating may for instance be
performed in a fluid bed reactor with coating precursors that form
a coating on the particles 20, optionally after further processing
steps.
[0141] FIG. 1B schematically depicts an embodiment wherein a
multilayer coating 320 is applied to such luminescent material
particle 20, here with a first layer 321, directly adjacent to the
core, and further remote a second layer 322, directly adjacent to
the first layer 321. For instance, the former layer may be a thin
inorganic layer, and the second layer may be a thick(er) inorganic
layer (or vice versa). Optionally, a plurality of alternating first
and second layers may be applied, which may be all organic, all
inorganic, or a combination thereof. For example, the multilayer
coating comprises alternating first and second layers of an
inorganic material, for instance alternating first and second
layers of an aluminum containing oxide and a titanium containing
oxide, or alternating first and second layers of an aluminum
containing oxide and a zirconium containing oxide. The total
thickness of the multilayer coating may be in the range of 20-100
nm, more preferably in the range of 30-80 nm. The thickness of the
first and second layers may be in the range of 0.2-10 nm, more
preferably in the range of 1-5 nm.
[0142] FIG. 1C schematically depicts the particulate luminescent
material 2 embedded in a matrix 420. Such system may also be
indicated as wavelength converter 100. By way of example, this
wavelength converter 100 comprises also the second luminescent
material 150. FIG. 1D schematically depicts an embodiment wherein
the particles obtained in stage III are embedded in the matrix 420.
The polymeric material (110; see FIG. 1A) can be seen as primary
encapsulation, the coating 320 can be seen as secondary
encapsulation, and the matrix 420 can be seen as tertiary
encapsulation.
[0143] FIG. 1E schematically depicts an example of a luminescent
material particle 20 with a coating 320 (by way of example a single
layer 321, though a multi-layer may also be possible. Here, the
quantum dots 120 have been introduced into the pores without a
polymerizeble or curable precursor. For instance, the liquid with
the quantum dots 120 have been introduced, may have been evaporated
before the coating 320 has been applied.
[0144] FIGS. 1A(IV), 1B, 1C, and 1E all show schematically
embodiments wherein the (first) coating layer is in contact with
the core over 100% of the entire outer surface area (A) of the
particle (or core). Note that these luminescent material particles
20 comprise inorganic cores 21 with (optionally) a coating or shell
320 surrounding the cores. In the pores of these pores, luminescent
nano particles or quantum dots 120 are available. These
nanoparticles may also be core-shell type particles (not
specifically depicted). Hence core-shell type quantum dots may be
available in the pores of cores that on their turn are coated with
a coating or encapsulation (or shell).
[0145] Pore size is indicated with reference dp, which in general
indicates a mean dimension of pore width or pore diameter. The
particle size is indicated with ps, which in general indicates a
mean dimension of particle width, particle length or particle
diameter.
[0146] FIG. 2A schematically depicts a lighting device 1. The
lighting device 1 comprises a light source 10 configured to
generate light 11, such as blue or UV light, or both. Here, by way
of example two light sources 10 are depicted, though of course more
than two, or only one, may be present. Further, the lighting device
1 comprises the luminescent material 2. The (particulate)
luminescent material 2 is configured to convert at least part of
the light source light 11 into visible luminescent quantum dot
light 121, e.g. one or more of green, yellow, orange and red light.
Here, a light converter 100 is depicted, such as e.g. depicted in
FIG. 1C. By way of example, the lighting device 1 further comprises
the second luminescent material 150, which provides upon excitation
second luminescent material light or luminescence 151. This
luminescence 151 will in general have another spectral light
distribution than the visible luminescent quantum dot light 121.
All light generated by the lighting device is indicated with
lighting device light 5, which in this schematic embodiment
comprises visible luminescent quantum dot light 121 and the
optional second luminescent material light 151. Note that the
luminescent quantum dots, or here the light converter 100, is
arranged at a non-zero distance d from the light source(s) 10.
[0147] As indicated above, the inorganic host particles after
impregnation with the quantum dots and after curing and/or
polymerization may be used as such (i.e. after stage III in FIG.
1A). In such instance, the particles have no coating. However, also
in these embodiments the term "core" is applied, though the
particle may entirely consist of such core. Optionally the
particles are encapsulated (stage IV in FIG. 1A; FIGS. 1B-1D). This
may be a coating (stage IV in FIG. 1A; FIG. 1B) i.e. in principle
each particle may include a coating around the core: core-coating
particles. However, the particles may also be embedded in a matrix,
such as a film or body: (FIGS. 1C & 1D) such matrix
encapsulates a plurality of the coated cores (FIG. 1C) or a
plurality of non-coated cores (FIG. 1D); of course, combinations of
coted cores and non-coated cores may also be possible. In each of
these embodiments and variants, the pores of the cores enclose
quantum dots.
[0148] Here, and also in the schematically FIGS. 2B and 2C, a
module 170 is shown, with a wall 171, a cavity 172, and a
transmissive window 173. The wall 171 and the transmissive window
173 here enclose cavity 172. In FIGS. 2A-2C, the transmissive
window 173 is used as an envelope, or as part of an envelope. Here,
the transmissive window envelopes at least part of the cavity 172.
Note that the transmissive window is not necessarily flat. The
transmissive window, comprising in embodiments the matrix, may also
be curved, like in the embodiment of a TLED or in a retrofit
incandescent lamp (bulb).
[0149] In FIG. 2B, by way of example, the second luminescent
material 150 is arranged as part of one or more of the light
sources 10. For instance, the light source 10 may comprise a LED
with the second luminescent material 150 on the dye or dispersed in
a (silicone) dome.
[0150] In FIG. 2C, by way of example the second luminescent
material 150 is applied as (upstream) coating to the transmissive
window 173, which again in this embodiment comprises the light
converter 100.
[0151] FIG. 2D schematically depicts an embodiment wherein the
luminescent material 2, or in fact the light converter, is directly
applied on the light exit face of a light source 10, here e.g. the
LED die 17 of a LED.
[0152] Hence, the second luminescent material can e.g. be present
in the first polymeric material (110) or the light transmissive
solid matrix (420).
[0153] FIG. 2E schematically depicts a light source 10 with a layer
of luminescent material 2. For instance, this layer may be arranged
on (the surface of) a LED die 111.
[0154] Other configurations are also possible, like for instance a
plurality of LEDs, or other light sources, in contact with (an
extended) light converter 100. As indicated above, another term for
light converter is wavelength converter. For instance, the light
converter may be a dome like light converter, with one or more
light sources, especially LEDs, adjacent thereto.
[0155] Hence, in an embodiment QDs are dispersed in an ink of
monomers/oligomers that can be cured upon irradiation or heating or
polymerized. Ideally, the QDs are well-dispersed, and the QD-host
combination is known to show highly stable behavior under blue flux
and elevated temperature (such as between 50 and 150.degree. C., or
especially between 75.degree. C. and 125.degree. C.). Macro porous
silica with a size of 0.5-500 .mu.m and pores of 0.1-10 .mu.m are
mixed with the QD-ink, and the ink is allowed to fill the micro
pores of the silica particles. Filling of the pores may be
facilitated by evacuating the porous particles before adding the
QD-ink. The filled composite particles are isolated from the
mixture, and the ink within the particles is cured or polymerized.
The cured or polymerized composite particles are optionally
subsequently coated with an inorganic seal material.
[0156] By way of example, some QD-ink combinations are
mentioned:
[0157] QDs dispersed in acrylates (monomers or oligomers)
[0158] QDs dispersed in silicones (mainly oligomers)
[0159] QDs dispersed in epoxies (monomers or oligomers)
[0160] QDs dispersed in any other curable polymer resin (monomers
or oligomers)
[0161] Prior to filling it is preferred to completely dry the
porous particles to reduce the water content to a minimum.
Typically a sintering step is used to dry the porous silica or
other porous material.
[0162] After curing or polymerization of the QD-ink within the
(silica) particles the composite particles are isolated. The
isolated composite particles are then optionally sealed with
preferably an inorganic coating using:
[0163] Deposition technique from gas-phase, using a fluidic bed
reactor (PVD, ALD, etc.)
[0164] Growing an inorganic shell from precursor materials in a
chemical (wet chemical or chemical vapor deposition) synthesis
[0165] Alternatively an organic seal material such as an epoxy or
perylene or parylene is deposited on the outside of the composite
particle.
[0166] Alternatively, the isolated porous particles can be inserted
directly (without sealing) into a hermetic host material, such as
an epoxy (e.g. DELO Katiobond 686) or low-melting point glass.
[0167] The end result is a sealed composite QD/polymer/inorganic
material particle which can be processed further in air, similar to
how YAG:Ce phosphors are currently treated. The particles can for
example be mixed with an optical grade silicone and then deposited
on the LED or substrate.
[0168] Below examples especially describe routes wherein porous
silica particles (Trisoperl) are first impregnated with QD-acrylic
matrix, then filtered to remove excess acrylic, and then cured.
After the curing step, the particles may optionally be washed with
toluene or other solvent. As expected, it is found that the porous
silica particles are filled with acrylic after all these steps.
[0169] First, it was shown that impregnation of porous silica
particles with acrylic can be followed in-situ by a microscope:
porous silica particles that are non-filled and embedded in a
liquid appear black due to scattering. Filled porous silica
particles appear transparent. Filling of porous silica particles
can therefore nicely be recorded. As examples, Ebecryl 150 and
Sylgard 184, a PDMS silicone, were used. porous silica particle
within the liquids are black due to scattering, but the porous
silica particle with liquid inside the droplet are transparent
(hence filled). It is hereby shown that a high viscous silicone
such as Sylgard 184 or an acrylate easily fill up the pores of the
porous silica particles. In high viscous Ebecryl, it was observed
that filling takes roughly 100-500 seconds, in low viscous IBMA
(Isobornyl methacrylate) it was observed that filling is a matter
of seconds. Eventually, all particles appear transparent.
[0170] FIGS. 3A, 3B, 3C, and 3D show the impregnation of Trisoperl
PSPs in ebecryl 150 at different time intervals. It is seen that
the particles at short time interval still have a partly black
interior, which is slowly disappearing over time. In high viscous
Ebecryl, it was observed that filling takes roughly 100-500
seconds, in IBMA it was observed that filling is a matter of
seconds. Eventually, all particles appear transparent.
[0171] When the in-situ impregnated particles are exposed to
UV-light (which can be done under a microscope ("in-situ") as
well), "cracking" within the interior of the particles is observed.
This is attributed to shrinkage of the acrylic upon cure (can be up
to 10%), and subsequent delamination of the acrylic from the
interior walls, creating new scattering pores. For silicones the
shrinkage seems to be much smaller (few percent) and the cracking
is not observed.
[0172] An embodiment of the impregnation process was performed,
consisting of the following step:
1--Mix QDs (0.1-1 wt. %) in ebecryl 150 or a 80/20 mixture of
IBMA/HDDA 2--Add 0.5% wt irgacure (optional) 3--Add 1 gram of
triosperl porous silica particles to 5 grams of the QD-acrylic
mixture 4--Gently stir/shake for 10 minutes 5--Apply the
QD-acrylic-porous silica particle mixture on a filter, which is
placed on a Buchner funnel 6--Apply vacuum to the funnel for 1-10
minutes 7--Flush the porous silica particles on the filter with
ethanol, heptanes, toluene, or another solvent (optional) 8--Remove
the powder from the filter 9--Spread the powder over a glass plate
or vial and cure with UV under N2 flow 10--Disperse the cured
powder in toluene and apply an ultrasound treatment 11--Remove the
toluene, resulting in the impregnated powder.
[0173] Amongst others, 0.1% wt QDs and 0.5% wt. PI (photo
initiator), which are impregnated and cured according to step 1-9
(but without step 7).
[0174] In a further example, Trisoperl particles were impregnated
according to step 1-11, without step 7. In this case, a 0.1% wt
dispersion of Crystalplex QDs in heptanes was made in IBMA/HDDA (5
g) to which 1 gram of porous silica particles were added, and 0.5%
wt photoinitiator (irgacure). After filtration the powder was cured
for 10 minutes in an N2 flow with UV light. This results in a
sticky powder, which was converted into a loose powder of
individual porous silica particles by dispersing it in toluene and
giving it a 1 minute US treatment. The toluene was removed and the
particles were applied on a glass disc for in-situ investigations
under the microscope. When these porous silica particles were
brought into contact with Ebecryl, the particles did not show
re-filling, but were transparent instantaneously. In addition, some
particles exhibit a brown color and cracks, which indicates that
the acrylate within the particles is cured, and does not re-fill
again. This is explained by the fact that porous silica particles
that are well impregnated and cured will have clogged pores that
does not allow for a (quick) secondary fill with ebecryl. However,
it is sometimes observed that these can be re-filled with toluene,
which is not surprising in view of its low viscosity.
[0175] The fluorescent microscope images (FIGS. 3A, 3B, 3C, and 3D)
show that these particles show bright QD emission. Here, Trisoperl
porous silica particles impregnated with 0.1% wt QDs in IBMA/HDDA.
The porous silica particles were cured and given an ultra sonic
treatment in toluene, after which they were spread out on a glass
plate, to which a droplet of Ebecryl was added.
[0176] Different silica particles were tested on their suitability
of the present process for making the luminescent material. A
non-exhaustive list is given in table 2 below:
TABLE-US-00002 TABLE 2 listing of some silica particles that were
used in the experiments Particle size (.mu.m) Pore size (nm) Type 1
30-70 100-450 Type 2 About 30 About 160 Type 3 About 30 150-200
[0177] Especially type 3 are very spherical particles (circularity
over 0.95), which facilitates the application of a coating on the
particles (if desired).
[0178] Stability measurements on the quantum dot filled particulate
porous luminescent material were performed under N2 flow. It
appeared that the stability of the QDs in the porous silica
particles is very similar to the same commercial QD-based
nanoparticles directly dispersed in IBMA/HDDA without porous
particles. However, the present luminescent material is easy to
handle, can be used in state of the art coating processes or matrix
dispersing processes, and does not need oxygen and/or water free
environments. It also appears that the quantum efficiency of the
QD's in the pores is about the same or even the same as those of
the original quantum dots.
[0179] Mercury porosimetry was used to determine the degree to
which the pores of the silica particles were filled after the
impregnation step. First, it was determined that the Trisoperl
particles without any treatment have a specific pore volume of 1.09
cm3/g powder. Second, it was determined the specific pore volume of
Ebecryl and IBMA/HDDA filled Trisoperl particles without a solvent
washing step (step 7) is 0.06 cm3/g (Ebecryl) and 0.00 cm3/g (not
detectable) (IBMA/HDDA), respectively. This confirms that the
Trisoperl particles are almost complete filled with cured acrylic
ink.
[0180] Using the impregnation method described above (using Buchnel
funnel), subsequently an ALD coating around the impregnated
particles was applied. In some experiments, the coating comprises
50 nm of alumina. With ALD coating, the stability of QDs in air is
improved (relative to impregnated particles without acoating). With
ALD coating, it is shown that the QD stability in air is similar to
the stability in Nitrogen, which shows that the ALD coating is
successfully applied, and keeps water/air outside the impregnated
particles. The experiments are described in further detail
below.
Example 1 Preparation of Impregnated Particles
[0181] Trisoperl particles were impregnated according as follows: 1
gram of 5% wt dispersion of Crystalplex QDs in heptanes was added
to IBMA/HDDA (5 g). This results in a 1% wt dispersion QDs in
IBMA/HDDA, to which 1 gram of PSPs were added, and 0.5% wt
photoinitiator (irgacure 184). The powder-acrylate mixture was put
on a Buchner funnel, and filtrated for a few minutes in the
glovebox. After filtration the powder was cured for 4 minutes with
UV light in the glovebox. This results in a sticky powder, which
was converted into a loose powder of individual PSPs by dispersing
it in toluene and giving it a 15 minute US treatment in a close
vial, hence no contact with ambient air. Next, the toluene was
removed in the glovebox, by decanting, followed by evacuation of a
few hours to remove all toluene. FTIR measurements show that the
acrylic has a 95% conversion rate, which means a nearly complete
curing of the acrylate. A subset of these particles was mixed into
ebecryl 150 for QE and stability measurements. The QE of these QDs
was measured to be 51% and 52% for two different impregnation
experiments. The QE of the QDs in HDDA/IBMA without impregnation
was measured at 69%. This means there is a loss in QE upon
impregnation, curing, and bringing into a second matrix. The reason
for this drop is unclear, but likely due to the additional
processing steps. The QE data are summarized in Table 3.
Example 2 Plasma Enhanced ALD on Impregnated PSP
[0182] 50 mg of the impregnated PSP (batch 1) was spread out over a
silicon wafer (outside the glovebox), and inserted into the Emerald
chamber (for plasma enhanced ALD) of an ASM dual chamber ALD
system. A 50 nm alumina layer was applied using the plasma-enhanced
ALD process at 100 C, using TMA (trimethylaluminium) and O2 as
reactive gasses. After deposition, the powder was harvested and
mixed into Ebecryl 150 (with 1% wt irgacure 184) to make cured
films of the ALD-coated PSP's in a secondary matrix. As described
above in example 1, reference samples of the same impregnated PSP's
without ALD were also made, in addition to films of plain QDs in
IBMA/HDDA (no impregnation). In all cases, the samples consisted of
a 100 .mu.m acrylic layer, in between two glass plates. The QE of
the ALD-coated PSP's using plasma enhanced ALD (called sample ALD-a
from here on) had a QE of 50%, which is the same as before ALD
coating (batch 1, 52%). The ALD coating thus has (almost) no impact
on the QE of the QDs.
TABLE-US-00003 TABLE 3 overview of QE data on various films: PL QE
Description ALD (%) QDs in IBMA/HDDA (no impregnation) No ALD 69
QDs in IBMA/HDDA impregnated PSP - No ALD 52 batch 1 QDs in
IBMA/HDDA impregnated PSP - No ALD 51 batch 2 ALD -a coated PSP
batch 1 Plasma @ 100.degree. C. 50 ALD -b coated PSP batch 1
Thermal @ 150.degree. C. 31 ALD -c coated PSP batch 2 Thermal @
100.degree. C. 33
[0183] The QE's are relatively low. This is due to the fact that
commercial QD material was used with a relative low initial QE.
Much higher QE's are possible when QDs of a better quality are
applied, but those are not readily commercially available on a
large scale.
[0184] A small part of the ALD coated particles from ALD-a was used
to make cross-sections and investigate in SEM. FIG. 5A shows a SEM
image of PSP's with ALD-a coating. In the prepared Schliffs
(cross-sections) some of the particles were not fully embedded in
the epoxy carrier. As a result the images provide a 3D view on the
particle, where 3 different regions can be identified. In addition,
these particles offered the possibility to analyze the coating of
the particles using selected area EDX. The first region is the
interior of the PSP (e.g. at location of spectrum 7), where the
porous structure can be clearly identified. The EDX recorded at
location "spectrum 7" is also shown, in which only silicon can be
observed, no aluminium. The second region is the outside of the
PSP, where a more dense silica shell is present (called "egg-shell"
from here on). It is known from these particular PSPs that they
have a dense silica shell around the particle, except for some
"fill-openings" (see also SEM images in appendix). An EDX spectrum
recorded at this region (spectrum 5) indeed shows only silicon. The
third region that can be identified is an additional thin layer on
top of the "egg shell", which is the aluminium oxide layer applied
by ALD. The EDX spectrum recorded at this location (spectrum 4)
clearly shows that indeed aluminium is present, confirming that the
ALD coating has resulted in deposition of alumina on the shell of
the particles. In the SEM image it can be seen that this second
layer is very conformal. The fact that at the top part (at location
of spectrum 5) the silica egg shell is exposed is attributed to the
grinding applied to make the cross-sections (preparation of
schliffs).
[0185] From the SEM image and EDX it appears that the alumina
coating is quite conformal and also covers the fill openings.
However, the SEM may not be very quantitative in determining the
exact coverage by alumina, and also may not provide statistical
information to which extent all particles are coated equally well.
XPS (X-ray photo spectroscopy) is a technique which probes the
outer few nm of substrates on elemental composition. An analysis of
XPS on the plasma-enhanced ALD coated particles (ALD-a) are
summarized in Table 4, where a comparison is made with an uncoated
PSP (no ALD batch 1). The uncoated particles show only silica, and
some Cd, Zn, and Se from the QDs. The organic material likely
originates from contamination from the substrate, or acrylic
exposed to the outside. In contrast, the ALD-coated particles
display primarily aluminium oxide as inorganic coating, and most
importantly no silicon could be detected. Since the detection limit
of silicon in this measurement is .about.0.1%, it is concluded that
at least 99% of the surface has been coated with aluminium
oxide.
TABLE-US-00004 TABLE 4 summary of XPS measurements on sample ALD-a,
and a blanc (no ALD coating). Numbers give the atomic weight %, and
sum up to ~100%: Al 2p C 1s Cd 3d O 1s Se 3p3 Si 2p Zn 2p3 Peak
74.2 284.8 103.5 Present as Al2O3 org SiO2 Blanc -- 46 0.5 39 0.3
14 0.81 ALD-a 22 32 -- 47 -- -- 0.03
[0186] Since the ALD coating is applied to improve the stability of
QDs in air, the photoluminescence stability was measured before and
after impregnation, and with and without ALD coating. All
measurements were performed under the same conditions of 10 W/cm2
blue flux (using a 450 nm blue laser), and 100.degree. C.
temperature. The fast drop seen in these measurements after
.about.5000 seconds is due to the raise in temperature from
25.degree. C. to 100.degree. C.; the thermal quench causes a quick
drop in PL intensity.
[0187] FIG. 6A shows the stability curves of the reference sample
of QDs in IBMA/HDDA without impregnation (QE of 69%), and with
impregnation (batch 1, QE of 52%). The samples were first measured
in a flow of nitrogen, with the 100 .mu.m QD film still sandwiched
between two glass plates to avoid any diffusion of water/air into
the sample. The curves show fairly similar behavior, with a
degradation rate after .about.250.000 seconds of 1.3E-6 and 1.5E-6
s-1 respectively. Such degradation under these conditions is very
typical for this combination of commercial QDs and IBMA/HDDA
acrylic. The results show that the impregnation process as such has
no effect on the QD PL stability. There is a difference visible
between the two curves initially; the curve 3 shows more
photobrightening than the curve 1. Photobrightening is a phenomenon
observed frequently for QDs, is not well understood, and also
beyond the scope of this invention. Hence, we will not go into
details of this photobrightening effect further.
[0188] When both samples are measured in air (where the top glass
plate was removed to allow water/air to quickly reach the laser
spot) the samples show a dramatic increase in degradation rate. The
impregnated sample appears to behave slightly better than the
sample without impregnation, which may be attributed to the longer
diffusion length of water/air into the silica particles.
[0189] FIG. 6B shows the same stability curves of the impregnated
sample without ALD in N2 and in air, and in addition the stability
curve of the impregnated samples with Plasma Enhanced ALD coating
(sample ALD-a). First, in N2 atmosphere it is observed that the
stability of the impregnated sample is not affected by the ALD
coating; after 250.000 seconds it shows a very similar degradation
rate of 1.4E-6 s-1. Fluorescence microscopy shows that the total
impregnated sphere luminesces: there is no `dead skin` caused by
the deposition process. Most importantly, a clear difference in
stability between the ALD coated and non-coated sample is observed
when measured in air. The ALD-coated sample shows a degradation
rate in air that is very similar to that in N2 (again 1.4E-6). The
fact that the degradation rate in N2 and air are so similar,
provides evidence for the fact that the ALD coating is very
effective in keeping water/air outside the silica particle.
Example 3 Thermal ALD @ 150 C on Impregnated PSP
[0190] 30 mg of the impregnated PSP (batch 1) was spread out over a
silicon wafer (outside the glovebox), and inserted into the Pulsar
chamber (for thermal ALD) of an ASM dual chamber ALD system. A 50
nm alumina layer was applied using the thermal ALD process at 150
C, using TMA (trimethylaluminium) and O3 as reactive gasses. After
deposition, the powder was harvested and mixed into Ebecryl 150
(with 1% wt irgacure 184) to make cured films of the ALD-coated
PSP's in a secondary matrix. The QE of the ALD-coated PSP's using
thermal ALD at 150.degree. C. (called sample ALD-b from here on)
had a QE of 31%, which is a drop of 20% compared to before ALD
coating (batch 1, QE of 52%).
[0191] A small part of the thermal ALD coated particles from ALD-b
was used to make cross-sections and investigate in SEM. FIG. 7A
shows a SEM image of PSP's with ALD-b coating. In the prepared
Schliffs (cross-sections) some of the particles were not fully
embedded in the epoxy carrier. As a result the images provide a 3D
view on the particle, where 3 different regions can be identified.
In addition, these particles offered the possibility to analyze the
coating of the particles using selected area EDX. The first region
is the interior of the PSP (at location of spectrum 3(S3) (FIG.
7D)), where the porous structure can be clearly identified. The EDX
recorded at location "spectrum 3" is also shown, in which only
silicon can be observed, no aluminium. The second region is the
outside of the PSP, where a more dense silica shell is present
(called "egg-shell"). It is known from these particular PSPs that
they have a dense silica shell around the particle, except for some
"fill-openings" (see also SEM images in appendix). An EDX spectrum
recorded at this region (spectrum 2; S2 (FIG. 7C)) indeed shows
only silicon. The third region that can be identified is an
additional thin layer on top of the "egg shell", which is the
aluminium oxide layer applied by ALD. The EDX spectrum recorded at
this location (spectrum 1; S1 (FIG. 7B)) clearly shows that indeed
aluminium is present, confirming that the ALD coating has resulted
in deposition of alumina on the shell of the particles. In the SEM
image it can be seen that this alumina layer is very conformal. The
fact that at the top part (at location of spectrum 2 (S2)) the
silica egg shell is exposed is attributed to the grinding applied
to make the cross-sections (preparation of schliffs).
[0192] As mentioned above, the PSP are covered by a dense "egg
shell" of silica, and have a few so-called fill openings per
particles, which allows impregnation of the particles by the
QD-acrylic ink. To ensure a complete seal of the PSP, also the
fill-opening needs to be coated with alumina. FIGS. 8A-8B show SEM
images of such fill openings of PSPs that are not coated with ALD
(FIG. 8A, PSP batch 1) and of PSPs that are coated with thermal ALD
(FIG. 8B, ALD-b). The non-coated PSP clearly shows that the
egg-shell (bright ring) is discontinuous at this opening (in SEM, a
bright appearance reflects a high density of inorganic material).
The ALD-coated sample shows that the fill-opening has been coated
by alumina, and that the alumina actually protrudes into the pores.
It is known that ALD coatings can be very conformal because the
molecular precursors can diffuse/penetrate into small pores (such
as the 200 nm pores here). For that reason, the overall alumina
deposition in this porous area of the fill opening is likely to be
higher than on top of the egg shell (which is rather smooth), which
can be qualitatively recognized by the relatively "thick" brighter
appearance of the outer part of the fill opening compared to the
coating around the egg shell. It is anticipated that the filling of
these pores by ALD coating is beneficial to obtain a well sealed
PSP.
Example 4 Thermal ALD @ 100 C on Impregnated PSP
[0193] 100 mg of the impregnated PSP (batch 2) was spread out over
a silicon wafer (outside the glovebox), and inserted into the
Pulsar chamber (for thermal ALD) of an ASM dual chamber ALD system.
A 50 nm alumina layer was applied using the thermal ALD process at
150.degree. C., using TMA (trimethylaluminium) and O3 as reactive
gasses. After deposition, the powder was harvested and mixed into
Ebecryl 150 (with 0.5% wt irgacure 184) to make cured films of the
ALD-coated PSP's in a secondary matrix. The QE of the ALD-coated
PSP's using thermal ALD (called sample ALD-c from here on) had a QE
of 33%, which is a drop of 20% compared to before ALD coating
(batch 2, 51%). This, and previous example show that thermal ALD
causes a substantial drop in QE, which cannot be attributed to
solely temperature, since ALD-a (plasma enhanced) was also
performed at 100.degree. C. The ozone used for thermal ALD could be
the cause for the drop in QE, but this was not investigated
further.
[0194] From the edx in example 3 it is not conclusive that the
aluminium oxide coating is 100% conformal, neither does it give
statistical information over all particles. An analysis of XPS on
thermal-enhanced ALD coated particles at 100.degree. C. (a duplo
experiment of ALD-c) shows that no silica can be observed anymore
after alumina deposition. It is concluded that both plasma enhanced
and thermal ALD are able to conformally coat the surface of these
porous silica particles with at least 99% coverage.
[0195] Since the ALD coating is applied to improve the stability of
QDs in air, the photoluminescence stability was measured before and
after impregnation, and with and without ALD coating. All
measurements were performed under the same conditions of 10 W/cm2
blue flux (using a 450 nm blue laser), and 100 C temperature.
[0196] The stability of impregnated versus non-impregnated samples
was discussed in example 2, and showed that impregnation has no
influence on the QD PL stability in N2. However, in air, a dramatic
degradation was observed for both cases. FIG. 6C summarizes the
results of impregnated PSP without ALD coating (batch 1, also shown
in example 2), and with thermal ALD coating (ALD-c). The curve 3 in
FIG. 6C shows that the PL stability of QDs is not affected by the
ALD coating, since it is very similar as compared to without ALD
coating (curve 1). In addition, it is clear that the sample with
ALD coating shows a very similar decay rate in N2 as compared to
air after 250.000 seconds (1.3E-6 and 1.9E-6 s-1 respectively),
whereas the non-ALD samples shows much worse stability in air
compared to nitrogen. Again, it is concluded that also a thermal
ALD coating is very effective in keeping water/air outside the
porous silica particles.
[0197] FIGS. 6B and 6C show the curves (curve 3 in both figures)
for "Impregnated ALD-a/c, air" which are in fact a continuation in
time of the same samples indicated in the same graphs,
respectively, as "Impregnated ALD-a/c, N2". Only the starting point
is again at 0 seconds. Note that the end intensity of the N2-curve
(curves 3) is about equal to these starting intensity of the
air-curves (curves 4). This is also the reason that the air curves
do not show the above-mentioned photobrightening. FIG. 6D shows the
curve (curve 4) "Impregnated ALD-c, air" which is obtained after
the impregnated ALD particles are directly subjected to
photoluminescence measurements under air conditions (thus without
an earlier measurement of the PL as function of time under N2).
Here, again the initial photobrightening is perceived.
[0198] As indicated above, it is concluded that also a thermal ALD
coating is very effective in keeping water/air outside the porous
silica particles. Hence, an alumina ALD coating was applied to the
particulate porous inorganic material, to allow a good analysis of
the shell by EDX after coating (an alumina coating on the silica
particle may be easier analyzed than a silica coating on the silica
particles). However, a silica coating can be applied by an exact
same ALD procedure.
[0199] The HR-SEM images also show that there is hardly any
contamination of acrylics on the outside of the particles. The
shell and ALD coating are fairly smooth. Here, a stationary ALD
coating technique (powder on a wafer) has been used, which already
gives very promising results. Powder coating using eg fluidized bed
ALD should give at least similar, if not better results. In
addition, powder coating ALD should also enable the coating of
larger amounts of powder. Coating of multi-gram powder batches are
known in the field.
[0200] Note that the invention is not limited to coatings (or
shells) on the cores obtained by the ALD process. Also other
processes may be applied.
Example 5: Example Impregnation of Trisoperl Particles with Low
Molecular Weight Silicone
[0201] Commercial QDs from crystalplex were modified with a
siloxane ligand as described in PCT/IB2013/059577, which is herein
incorporated by reference). The ligand used was a 5000 Mw siloxane
molecule (AB109373, viscosity .about.100 cSt.) with an amine
functional group in the side chain, where the amine group was first
converted into a carboxylic acid as described in PCT/IB2013/059577
before ligand exchange. The ligands bind to the QD surface through
the carboxylic acid, and the siloxane ligands make the QDs miscible
into low molecular weight silicones (below 100 cSt.).
[0202] After ligand exchange the QDs were purified once by adding 1
ml heptane and 2 ml of ethanol to 500 ul of QD-ligand mixture
(.about.1% wt QDs). The QD pellet was redispersed in 250 ul
heptanes (hence 2% wt QDs). The 250 ul purified QDs in heptane was
added to 0.5 gram of AB109380 (25-35%
Methylhydrosiloxane-dimethylsiloxane copolymer; viscosity 25-35
cSt.) which gave a transparent mixture (not possible without the
siloxane ligand).
[0203] To 2 gram of AB109356 (Polydimethylsiloxane,
vinyldimethylsiloxy terminated; viscosity 100 cSt.), 4 ul of a 100
times diluted solution of a platinum catalyst in xylene (AB146697
(Platinum-divinyltetramethyldisiloxane complex; (2.1-2.4% Pt)) was
added. The QD-AB109380 mixture and the Pt-109356 mixture were
combined and vigorously stirred for a few minutes, resulting in a
clear and transparent curable QD-silicone mixture (0.2% wt
QDs).
[0204] To the mixture, 0.5 gram of triosperl particles were added,
and mixed for 1 minute to allow impregnation. The
QD-silicone-trisoperl mixture was put on the filter of a Buchner
funnel, and evacuated for 5 minutes. The excess QD-silicone liquid
was removed in this manner, and a fairly dry but slightly sticky
powder remained on the Buchner funnel. The resulting impregnated
powder was investigated under the microscope, and from the bright
field image it was concluded that the particles were properly
impregnated with the QD-silicone liquid (not a black but shiny
appearance). In fluorescence microscopy, bright fluorescence from
the impregnated particles is observed.
[0205] Next, the triosperl particles impregnated with the
QD-silicone mixture were cured. It can be observed that the shiny
appearance in the bright field image partly disappears after 5
minutes curing, and completely disappears after 90 minutes curing.
After 90 minutes curing the particles have a black appearance,
which is attributed to shrinkage of the silicones upon curing
(which is more pronounced for low molecular weight silicones as
compared to high molecular weight silicones), which results in
"cracking" within in the pores. The cracks cause scattering of the
light, giving the black appearance (also observed for acrylate
filled particles).
[0206] Finally, the cured impregnated triosperl particles were
brought mixed into toluene and sonicated for 2 minutes. The
ultrasonic treatment caused the particles to de-agglomerate into a
fine dispersion of impregnated particles in toluene. After the
ultrasonic treatment the particles were brought into Ebecryl 150 (a
high viscous acrylate). Bright field microscopy images of the cured
impregnated triosperl particles showcase a black appearance, which
remained. In other words, no re-filling of the porous particles is
observed (which causes the particles to become non-scattering). For
non-impregnated particles, re-filling is observed within tens of
seconds. For the silicone impregnated particles this was not the
case.
[0207] Fluorescence microscopy of the impregnated and cured
triosperl shows uniform luminescence over the particle for all
particles. In summary, it is also shown that the triosperl
particles can impregnated with a curable QD-silicone mixture,
cured, and washed with the ultrasonic treatment in toluene
resulting in a fine de-agglomerated powder.
[0208] AB109356 refers to Polydimethylsiloxane, vinyldimethylsiloxy
terminated; viscosity 100 cSt.; AB109380 refers to 25-35%
Methylhydrosiloxane-dimethylsiloxane copolymer; viscosity 25-35
cSt; AB146697 refers to Platinum-divinyltetramethyldisiloxane
complex in xylene; (2.1-2.4% Pt). These chemicals were purchased
from ABCR.
* * * * *