U.S. patent application number 12/841032 was filed with the patent office on 2010-11-11 for nanoparticle synthesis by solvothermal process.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Jesse Dan Froehlich, Sheng Li, Amane Mochizuki, Toshitaka Nakamura.
Application Number | 20100283377 12/841032 |
Document ID | / |
Family ID | 40445157 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100283377 |
Kind Code |
A1 |
Li; Sheng ; et al. |
November 11, 2010 |
NANOPARTICLE SYNTHESIS BY SOLVOTHERMAL PROCESS
Abstract
An optical film capable of converting blue light to yellow light
and a while light emitting device comprising the optical film are
described. The optical film comprises a layer of YAG nanoparticles,
wherein the layer of YAG nanoparticles has a size distribution of
between about 2 nm to about 200 nm
Inventors: |
Li; Sheng; (Vista, CA)
; Froehlich; Jesse Dan; (Vista, CA) ; Nakamura;
Toshitaka; (Oceanside, CA) ; Mochizuki; Amane;
(San Diego, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
NITTO DENKO CORPORATION
Osaka
JP
|
Family ID: |
40445157 |
Appl. No.: |
12/841032 |
Filed: |
July 21, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12032590 |
Feb 15, 2008 |
|
|
|
12841032 |
|
|
|
|
Current U.S.
Class: |
313/483 ;
428/325 |
Current CPC
Class: |
C01P 2002/72 20130101;
Y02B 20/00 20130101; Y10T 428/252 20150115; C09K 11/7774 20130101;
C01F 17/34 20200101; C01P 2004/64 20130101; Y02B 20/181 20130101;
C01P 2004/04 20130101; Y10S 977/81 20130101; B82Y 30/00 20130101;
C01P 2002/84 20130101 |
Class at
Publication: |
313/483 ;
428/325 |
International
Class: |
H01J 1/62 20060101
H01J001/62; B32B 5/16 20060101 B32B005/16 |
Claims
1. An optical film capable of converting blue light to yellow
light, comprising a layer of YAG nanoparticles, wherein the layer
of YAG nanoparticles has a size distribution of between about 2 nm
to about 200 nm.
2. The optical film of claim 1, wherein the layer of YAG
nanoparticles comprises cerium doped YAG phosphor.
3. A white light emitting device comprising at least one optical
film of claim 1.
4. A white light emitting device comprising: a light source capable
of emitting blue light; and a Ce.sup.3+-YAG phosphor comprising
Ce.sup.3+-YAG nanoparticles having a size distribution of between
about 2 nm to about 200 nm.
Description
PRIORITY APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/032,590, filed Feb. 15, 2008, the entire disclosure of
which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to the solvothermal synthesis of
yttrium aluminium garnet (YAG). Specifically, this invention
relates to a cost effective and novel means of producing high
yields of nano-sized (<30 nm) YAG particles via a solvothermal
synthesis process.
[0004] 2. Description of the Related Art
[0005] Yttrium aluminum garnet (Y.sub.3Al.sub.5O.sub.12), or YAG,
has many potential commercial applications due to its good optical
properties..sup.1-2 Ce.sup.3+-doped YAG phosphor (Ce.sup.3+-YAG),
combined with blue light emitting diode (LED), is widely used for
the white solid state LED.
[0006] There are several methods to synthesize YAG particles. For
example, the conventional solid-state reaction.sup.2-4 is a fairly
simple process, but it typically requires high temperature
(>1,600.degree. C.) and long reaction time. Furthermore, the YAG
particles produced by this method tend to be larger than about 1
.mu.m. The sol-gel method.sup.5-7 makes YAG by direct
crystallization from amorphous precursor at a lower temperature
(.about.700.degree. C.), but it requires a more complicated process
and an additional thermal treatment at high temperature (>800
.degree. C.). The hydrothermal synthesis .sup.8-11 also typically
requires both high temperature (>400 .degree. C.) and high
pressure (>30 MPa) to overcome the supercritical condition of
water (Tc=374.degree. C., Pc=22.4 MPa).
[0007] The organic solvothermal process.sup.12-13 has also been
used to synthesize YAG powder at lower temperature and pressure.
The YAG powder synthesized by the earlier method consists of the
aggregates of irregular grains. Although the later solvothermal
process.sup.14-18 was capable of making monodispersed spherical YAG
powder, it still lacked the ability to synthesize Ce.sup.3+-doped
YAG phosphor at low temperature. Recently, a glycothermal
method.sup.18-19 has been developed to synthesize Ce.sup.3+-doped
YAG Nano-phosphors, and the method incorporates a luminescent
cerium center into YAG nanoparticles without post heat treatment at
high temperatures. However, the glycothermal process affords little
control of the inner pressure, along with low recovery ceramic
yield and relatively low internal quantum efficiency (IQE).
[0008] The embodiments of present invention are directed to an
improved solvothermal method for making inorganic nanoparticles
that not only allows the interior pressure to be preset prior to
the reaction as well as to be adjusted freely throughout the
reaction, but also dramatically simplifies the work-up process with
high recovery yield. The present invention also makes nanometer
sized YAG particles with high internal quantum efficiency (IQE)
value.
REFERENCES
[0009] 1. M. Veith, S. Mathur, A. Kareiva, M. Jilari, M. Zimmer, V.
Huch, J. Mater. Chem., 9, 3069, 1999. 2. S. M. Sim, K. A. Keller,
J. Mater. Sci., 35, 713, 2000. 3. D. R. Messier, G. E. Gazza, Am.
Ceram. Soc. Bull. 51 (1972) 692. 4. K. Ohno and T. Abe, J.
Electrochem. Soc., 1986, 133, 638.
5. D. Hreniak, W. Strek, J. Alloys Compd. 341 (2002) 183.
[0010] 6. G. Gowda, J. Mater. Sci. Lett. 5 (1986) 1029. 7. Y. Liu,
Z. F. Zhang, B. King, J. Halloran, R. M. Laine, J. Am. Ceram. Soc.
79 (1996) 385. 8. B. V. Mill, Sov. Php-Crystallogr. (Engl.
Transl.), 12 [1] 137-35, (1969). 9. R. C. Puttbach, R. R. Monchamp,
and J. W. Nielsen, "Hydrothermal Growth of Y3AI50'; pp. 569-71 in
Crystal Growth, Proceedings of the International Conference on
Crystal Growth (Boston, Mass., 1966). Edited by H. S. Peiser.
Pergamon Press, Oxford, U. K., 1967. 10. E. D. Kolb and R. A.
Laudise, J. Cryst. Growth, 29 [I] 29-39 (1975). 11. T. Takamori and
L. D. David, Am. Ceram. SUC. Bull., 65[9] 1282-86 (1986). 12. M.
Inoue, H. Kominami, and T. Inui, J. Am. Ceram. Soc., 73 [4] 1100-02
(1990). 13. M. Inoue, H. Otsu, H. Kominami, and T. Inui, J. Am.
Ceram. Soc., 74 [6] 1452-54 (1991). 14. M. Inoue, H. Kominami, and
T. Inui, J. Chem. Soc. Dalton Trans. 3331-3336 (1991).
15. M. Inoue, H. Otsu, H. Kominami, T. Inui, J. Alloys Compd. 1995,
226, 146-151.
[0011] 16. Y. Hakuta, K. Seino, H. Ura, T. Adschiri, H. Takizawa,
and K. Aari, J. Mater. Chem. 1999, 9, 2671-2674.
17. X. Zhang, H. Liu, W. He, J. Wang, X. Li, R. Boughton, J. Alloys
Compd. 2004, 372, 300-303.
[0012] 18. R. Kasuya, T. Isobe, H. Kuma, and J. Katano, J. Phys.
Chem. B 2005, 109, 22126-22130.
19. R. Kasuya, T. Isobe, and H. Kuma, J. Alloys Compd. 2006,
408-412, 820-823.
SUMMARY OF THE INVENTION
[0013] One embodiment provides a solvothermal process for making
inorganic nanoparticles, comprising forming a suspension or
solution comprising at least one group II-IV and lanthanide metal
inorganic salt in a first medium, disposing the suspension or
solution in a sealed chamber having an interior pressure, heating
the suspension or solution to a peak temperature higher than the
normal boiling point of the first medium, elevating the interior
pressure of the sealed chamber to an initial interior pressure
prior to the heating, optionally adding a second medium to the
suspension or solution after the heating, and forming a plurality
of inorganic nanoparticles, wherein 80% of the plurality of
inorganic nanoparticles has a diameter less than 100 nm.
[0014] Another embodiment provides a solvothermal process for
making yttrium aluminum garnet (YAG) nanoparticles, comprising
forming a suspension or solution comprising a at least one group
II-IV and lanthanide metal inorganic salt in a first medium,
disposing the suspension or solution in a sealed chamber having an
initial interior pressure that is higher than the atmospheric
pressure, heating the suspension or solution in the sealed chamber
to a peak temperature higher than the normal boiling point of the
first medium, and precipitating the YAG nanoparticles. Another
embodiment provides a plurality of Ce.sup.3+-YAG nanoparticles
produced by such solvothermal process.
[0015] One embodiment provides an optical film capable of
converting blue light to yellow light, comprising a layer of YAG
nanoparticles, wherein the layer of YAG nanoparticles has a size
distribution of between about 2 nm to about 200 nm. Another
embodiment provides a white light emitting device comprising at
least one such optical film.
[0016] One embodiment provides A white light emitting device
comprising a light source capable of emitting blue light, and a
Ce.sup.3+-YAG phosphor comprising Ce.sup.3+-YAG nanoparticles
having a size distribution of between about 2 nm to about 200
nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic showing a solvothermal process for
making inorganic nanoparticles.
[0018] FIG. 2 is shows a schematic of a white light emitting device
(LED) comprising a blue LED chip encapsulated by a Ce.sup.3+-YAG
phosphor.
[0019] FIG. 3 is an X-ray diffraction spectrum of YAG nanoparticles
made by the solvothermal process.
[0020] FIG. 4 shows the TEM micrograph of the YAG nanoparticles
made by the solvothermal process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0021] Although certain preferred embodiments and examples are
disclosed below, it will be understood by those skilled in the art
that the invention extends beyond the specifically disclosed
embodiments and/or uses of the invention and obvious modifications
and equivalents thereof. Thus, it is intended that the scope of the
invention herein disclosed should not be limited by the particular
disclosed embodiments described below.
[0022] Cerium-doped yttrium aluminum garnet (Ce.sup.3+-YAG) is used
as a phosphor and a scintillator. It emits yellow light when
subject to blue or ultraviolet light, or x-ray. It is also used in
white light-emitting diodes as it is capable of covert blue light
into yellow, which appears as white. Although Ce.sup.3+-YAG may be
made in many different ways, the reaction conditions are generally
harsh for many syntheses. A low temperature solvothermal method for
synthesizing YAG was first reported in 1990's. Solvothermal
synthesis is a technique in which the reaction occurs in a sealed
vessel that allows certain solvents such to be heated to
temperatures far in excess of their normal boiling points.
[0023] Solvothermal synthesis is a technique in which the reaction
occurs in a pressure vessel that allows normal solvents such as
water or alcohols to be heated to temperatures far in excess of
their normal boiling points. Most solvothermal synthesis of YAG
powder or glycothermal synthesis of Ce.sup.3+-YAG involve the use
of either 1,4-butanediol or in a mixture of 1,4-butanediol and
polyethylene glycol (PEG), and the pressure can go up to 5.5 MPa.
The 1,4-butanediol is a restricted solvent, therefore the cost is
high and it's difficult to obtain. The workup process of the
product colloidal solution is also time-consuming, requiring
several washes before the precipitates can be recover. This further
contributes to the inefficient and noneconomical large scale
process.
[0024] An improved solvothermal method that not only allows the
inner pressure to be preset as well as to be adjusted freely
throughout the reaction, but also dramatically simplifies the
work-up process with high recovery yield. In addition, a new
solvent, 1,5-pentanediol, was used in place of conventional
1,4-butanediol which is now a highly restricted material. The
present invention also makes nanometer sized YAG particles with
high IQE value.
[0025] Some embodiments provide a solvothermal process for making
inorganic nanoparticles. With reference to FIG. 1, process 100 is a
solvothermal process wherein inorganic nanoparticles may be made
under relatively low temperature and elevated pressure conditions.
Examples of inorganic nanoparticles that may be made by process 100
include, but not limited to, Y.sub.3Al.sub.5O.sub.12:Ce,
BaAl.sub.2O.sub.4:Eu, MgAl.sub.2O.sub.4:Eu, SrTiO.sub.3:Pr,
Y.sub.3A1.sub.5O.sub.12:Eu, Y.sub.3Al.sub.5O.sub.12:Tb,
Y.sub.2O.sub.3:Eu, Y.sub.2O.sub.3:Ce, ZnO:Ga. The term
"nanoparticles" includes all shapes of nano-sized materials, such
as nanorods, nanowires, nanospheres, etc. The process 100 begins at
step 110 by forming a suspension or solution comprising a metal
oxide precursor in a first medium. In some embodiments, the metal
oxide precursor may comprise a group II-IV and lanthanide metal
inorganic salt (including but not limited to: aluminum
isopropoxide, aluminum t-butoxide, aluminum ethoxide, aluminum
lactate, aluminum oxide, aluminum nitrate, aluminum sulfate,
aluminum phosphate, alumatrane, aluminum acetylacetonate, yttrium
acetate, yttrium acetylacetonate, yttrium butoxide, yttrium
isopropoxide, yttrium nitrate, yttrium oxide, yttrium phosphate,
yttrium sulfate, cerium acetate, cerium acetylacetonate, cerium
butoxide, cerium isopropoxide, cerium nitrate, cerium oxide, cerium
phosphate, cerium sulfate, titanium oxide, zinc oxide, zirconium
oxide). In some embodiments, the metal precursor may comprise at
least one of the yttrium source, aluminum source, and cerium
source. For example, aluminum isopropoxide, aluminum t-butoxide,
aluminum ethoxide, aluminum lactate, aluminum oxide, aluminum
nitrate, aluminum sulfate, aluminum phosphate, alumatrane, aluminum
acetylacetonate, yttrium acetate, yttrium acetylacetonate, yttrium
butoxide, yttrium isopropoxide, yttrium nitrate, yttrium oxide,
yttrium phosphate, yttrium sulfate, cerium acetate, cerium
acetylacetonate, cerium butoxide, cerium isopropoxide, cerium
nitrate, cerium oxide, cerium phosphate, and cerium sulfate.
[0026] The first medium may comprise at least one
low-molecular-weight alcohol. A low-molecular-weight alcohol
typically weighs less than 500 u. In some embodiments, suitable
metal oxide are suspended or dissolved in a low-molecular-weight
alcohol. Examples of low-molecular-weight alcohol include, but not
limited to, butanol, isopropanol, propanol, ethanol, methanol,
1,5-pentanediol, 1,4-butanediol, 1,3-propanediol, 1,2-propanediol,
ethylene glycol. In some embodiments, the alcohol may include alkyl
alcohol or substituted alkyl alcohol. In some embodiments, the
low-molecular-weight alcohol may comprise low-molecular-weight
glycol. The term "low-molecular-weight aliphatic glycol" refers to
compounds containing non-aromatic carbons and two hydroxyl groups.
In some embodiments, a mixture of water and at least one
low-molecular-weight alcohol may also be used as the first
medium.
[0027] The suspension or solution is disposed in a sealed chamber
having an interior pressure. In some embodiments, the sealed
chamber is a reaction vessel with an adjustable and/or controllable
pressure. In some embodiments, the sealed chamber may be configured
to have controllable or adjustable pressure by connecting a
pressurized gas cylinder to the chamber. The pressurized gas
cylinder may contain an inert gas (e.g., nitrogen, argon, XeF.sub.2
or XeF.sub.4, etc.) or air. A sealed chamber in gas communication
with a pressurized gas or air source would allow the interior
pressure (i.e., the pressure inside the sealed chamber) to be
preset or adjusted throughout the reaction or heating process,
thereby provide control over the experimental or reaction
condition. In some embodiments, the sealed chamber may be an
autoclave or any sealed vessel that can withstand an elevated
pressure and/or elevated temperature to at least the highest
pressure and the highest temperature to be reached in a particular
reaction.
[0028] The process 100 continues to step 120 by elevating the
interior pressure of the sealed chamber to an initial interior
pressure that is higher than the atmospheric pressure. In other
words, the initial interior pressure may be preset prior to the
reaction taking place in the chamber, and may also be controlled or
adjusted during and after the reaction. In some embodiments, the
initial pressure inside the sealed chamber may be preset to an
elevated pressure prior to heating the suspension or solution. The
elevated pressure may be any pressure that is higher than the
atmospheric pressure. In some embodiments, the initial pressure may
be set to be between about 50 to about 600 psi (pounds per inch).
In some embodiments, the initial pressure may also be about 100 to
about 500 psi, about 200 to about 400 psi, about 250 to about 350
psi, or about 300 psi. In some embodiments, the initial pressure
may be about 100 to about 3000 psi, about 100 to about 2500 psi,
about 200 to about 2000 psi, about 300 to about 1500 psi, or about
400 to about 1000 psi.
[0029] The process 100 continues to step 130 by heating the
suspension or solution in a sealed chamber to a peak temperature.
The peak temperature is higher than the normal boiling point of the
first medium. The normal boiling point of the first medium refers
to the boiling point of the first medium under normal atmospheric
pressure. In some embodiment, the peak or optimal temperature may
be between about 100 to about 600.degree. C., about 200 to about
400.degree. C., about 250 to about 350.degree. C., or about
300.degree. C. In some embodiments, the heating process may
comprise applying heat so that a certain temperature increment or
step up is exerted on the suspension or solution. In some
embodiments, the temperature increment or step up may be between,
for example, about 1 to about 15.degree. C./min, about 2 to about
10.degree. C./min, or about 2 to about 8.degree. C./min.
[0030] As the temperature inside the chamber increases during the
reaction or the heating of suspension or solution, the interior
pressure may also increase. In some embodiments, the interior
pressure may also be maintained relatively constant by releasing
the pressure buildup by venting or release the gas or air inside
the chamber. In some embodiments, the interior pressure may also be
adjusted so it does not reach an excessive pressure according to
the reaction carried out in the sealed chamber. In some
embodiments, additional inert gas or air may be introduced into the
sealed chamber during or after the reaction to increase the
interior pressure. In some embodiments, the final pressures reached
inside of the sealed chamber may be between 100 to about 3,000 psi.
In some embodiments, the final pressure can also be between 200 to
about 2000 psi, about 300 to about 1000 psi, about 400 to about 900
psi, or about 500 to about 700 psi.
[0031] In some embodiments, once the peak or optimal temperature is
reached, the reaction is maintained at the peak temperature for a
period of time before allowing the suspension or solution to cool
down to room temperature. In some embodiments, the interior
pressure of the sealed chamber may also be maintained at a certain
level. The period of time wherein the temperature and/or pressure
is to be maintained may range from, for example, about 10 min to 24
hours, about 30 min to about 20 hours, about 1 to about 10 hours,
and about 1 to about 5 hours.
[0032] The process 100 continues to step 140 by forming a plurality
of inorganic nanoparticles from the cooled suspension, solution or
colloidal solution. The inorganic nanoparticles may comprise
nanotubes, nanowires, nanospheres, nanorods or any combination
thereof. In some embodiments, the inorganic nanoparticles may
comprise YAG. In some embodiments, the inorganic nanoparticles may
also comprise Ce.sup.3+-YAG powders. In some embodiments, a second
medium may be used to facilitate the precipitation. In some
embodiments, the nanoparticles are precipitated in the second
medium. Examples of suitable second medium include, but not limited
to, acetonitrile, propiononitrile, butyronitrile, acetone,
butanone, pentanone, cyclopentanone, byclohexanone, ethanol,
propanol, isopropanol, butanol, diethyl ether, and tetrahydrofuran.
The collected nanoparticles may be dried in a vacuum oven or in
air. In some embodiments, the dimension of the nanoparticles may be
on the order of about 2 to about 200 nm, about 5 to about 150 nm,
about 10 to about 100 nm, about 15 to about 75 nm, about 20 to
about 50 nm or less than about 30 nm. In some embodiments, 80% of
the plurality of inorganic nanoparticles has a diameter less than
200 nm, preferably less than 150 nm or less than 100 nm.
[0033] The solvothermal process is capable of providing a ceramic
yield of over 60%, more preferably over 80%, and the YAG
nanoparticles made by such process are capable of having an
internal quantum efficiency of over 25%.
[0034] In some embodiments, an optical film that is capable of
converting blue light to yellow light may be made using the YAG
nanoparticles described above. The optical film may comprise a
layer of YAG nanoparticles having a size distribution of between
about 2 nm to about 200 nm. In some embodiments, the YAG
nanoparticle size distribution may be about 10 nm to about 150 nm,
about 20 nm to about 100 nm or about 30 nm to about 100 nm. In one
embodiment, the layer of YAG nanoparticles may comprise cerium
doped YAG phosphor.
[0035] Some embodiments also provide a light emitting device (LED)
comprising cerium doped YAG phosphor. FIG. 2 shows a schematic of a
LED comprising a blue LED chip 22 encapsulated by a Ce.sup.3+-YAG
phosphor 23. In some embodiments, the Ce.sup.3+-YAG phosphor 23
comprises Ce.sup.3+-YAG nanoparticles dispersed in an encapsulant
resin. The Ce.sup.3+-YAG phosphor is capable of absorbing a portion
of blue light 24 emitted by the blue LED chip 22 and convert to
yellow light 25. The yellow light 25 and a portion of blue light 24
not absorbed by the Ce.sup.3+-YAG phosphor will result in white
light emission 26. The Ce.sup.3+-YAG phosphor of a conventional
white LED may contain Ce.sup.3+-YAG particle size greater then 1
.mu.m. In this case, the emitted blue and yellow lights can be back
scattered by the large particle size and result in the loss of
emitted light or lowered emission. Utilizing the small
nanoparticles made by the solvothermal process discussed herein
would eliminate the back scattering and increase the overall light
output or intensity.
[0036] In some embodiments, the optical film comprising YAG
nanoparticles described above may also be incorporated in a LED,
either stand alone or in combination with the Ce.sup.3+-YAG
phosphor to reduce back scattering of emitted light and to improve
emission.
EXAMPLE
[0037] Aluminium isopropoxide (1.934 g, 9.47 mmol), yttrium(III)
acetate tetrahydrate (1.903 g, 5.63 mmol), and cerium(III) acetate
monohydrate (19 mg, 0.056 mmol) at Ce/(Y+Ce)=1.0 wt. % were
suspended in a mixture of 1,5-pentanediol and water (30 ml, volume
ratio=10/1) in a glass inner vessel. Then the vessel was placed in
a 100 mL autoclave (additional solvent 1,5-pentanediol (2 mL) was
poured into the gap between the autoclave wall and the glass
vessel) and purged with Ar for 15 min. The autoclave was then
pre-charged with N.sub.2 to reach 300 psi, and heated to
300.degree. C. at a rate of .about.3.degree. C./min with stirring
at 300 rpm. During the heating, the interior pressure gradually
increased so a combination of apply/release N.sub.2 are to be
applied to adjust the pressure to be about 600 psi. After heating
at 300.degree. C. and 600 psi for about 3 hours, the reaction was
allowed to cool to room temperature. The yellowish colloidal
solution was poured into acetonitrile (400 ml) under vigorous
stirring, and allowed to settle down. After centrifuge, the
collected solid was dried in vacuum oven at room temperature for
overnight to obtain 1.2 g yellowish powder.
[0038] X-ray diffraction spectrum of YAG nanoparticles is shown in
FIG. 3. The TEM micrograph of the YAG nanoparticles is shown in
FIG. 4. Internal quantum efficiency (IQE) is about 37.9%.
* * * * *