U.S. patent application number 15/436454 was filed with the patent office on 2017-06-15 for continuous synthesis of high quantum yield inp/zns nanocrystals.
The applicant listed for this patent is Quantum Materials Corporation. Invention is credited to Werner Hoheisel, Huachang Lu, Leslaw Mleczko, Stephan Nowak.
Application Number | 20170166808 15/436454 |
Document ID | / |
Family ID | 47222115 |
Filed Date | 2017-06-15 |
United States Patent
Application |
20170166808 |
Kind Code |
A1 |
Lu; Huachang ; et
al. |
June 15, 2017 |
Continuous Synthesis Of High Quantum Yield InP/ZnS Nanocrystals
Abstract
The invention relates to a continuous-flow synthesis process for
the preparation of high quality indium phosphide/zinc sulfide
core/shell semiconduting nanocrystals in particular quantum dots
(QD) conducted in a micro-reaction system comprising at least one
mixing chamber connected to one reaction chamber.
Inventors: |
Lu; Huachang; (Koeln,
DE) ; Hoheisel; Werner; (Koeln, DE) ; Mleczko;
Leslaw; (Dormagen, DE) ; Nowak; Stephan;
(Koeln, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Quantum Materials Corporation |
San Marcos |
TX |
US |
|
|
Family ID: |
47222115 |
Appl. No.: |
15/436454 |
Filed: |
February 17, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14361862 |
May 30, 2014 |
9577149 |
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PCT/EP2012/073552 |
Nov 26, 2012 |
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15436454 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C30B 29/68 20130101;
C09K 11/703 20130101; B82Y 30/00 20130101; H01L 33/30 20130101;
C30B 29/60 20130101; Y10S 977/892 20130101; B82Y 40/00 20130101;
C30B 7/14 20130101; C30B 29/40 20130101; Y10S 977/774 20130101;
Y10S 977/824 20130101; Y10S 977/896 20130101; Y10S 977/818
20130101; B01J 13/02 20130101; C30B 7/08 20130101; C30B 29/48
20130101; Y10S 977/95 20130101; C30B 7/00 20130101; B82Y 20/00
20130101 |
International
Class: |
C09K 11/70 20060101
C09K011/70; C30B 7/14 20060101 C30B007/14; C30B 29/68 20060101
C30B029/68; C30B 29/40 20060101 C30B029/40; C30B 29/48 20060101
C30B029/48; B01J 13/02 20060101 B01J013/02; C30B 7/08 20060101
C30B007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2011 |
EP |
EP 11191589.8 |
Claims
1. (canceled) Continuous-flow method for the preparation of InP/ZnS
nanoparticles conducted in a micro-reaction system comprising at
least one mixing chamber connected to one reaction chamber and
comprising the following steps: a. Preparing an indium precursor
solution by mixing an indium salt, a fatty protic alkylamine, a
fatty alkylacid and zinc carboxylate with an inert solvent
optionally heating up to 50-200.degree. C. to get a clear solution
under water and oxygen free atmosphere, b. Preparing a phosphine
precursor solution comprising tris(trimethylsilyl) phosphine in the
inert solvent under water and oxygen free atmosphere, c. Injecting
the indium precursor solution in excess to the phosphine precursor
solution into the mixing chamber to obtain a reaction mixture,
wherein the mixing chamber is a magnetic mixing micro-chamber,
preferably at a flow rate from 0.1 ml/min to 10 ml/min, d.
Forwarding and heating the reaction mixture at a temperature from
160 to 320.degree. C., within the reaction chamber until InP core
suspension is obtained, e. Forwarding the core suspension into a
mixing chamber and injecting a shell precursor solution comprising
a Zn source and a S source to the core suspension and preferably
capping ligands into the mixing chamber, f. Forwarding and heating
the suspension at a temperature from 160 to 320.degree. C.,
preferred 200 to 280.degree. C. for shell preparation within the
reaction chamber, g. Cooling.
2. (canceled) Method according to claim 1 wherein Zn source and S
source is a single source.
3. (canceled) InP/ZnS nanoparticle obtainable by the method of
claims 1 to 2.
4. (canceled) Formulation comprising the nanoparticle of claim
3.
5. (canceled) Device comprising the nanoparticle of claim 3.
6. A InP/ZnS nanoparticle obtainable by a continuous-flow method
for preparing InP/ZnS nanoparticles conducted in a micro-reaction
system comprising at least one mixing chamber connected to one
reaction chamber, said method comprising: preparing an indium
precursor solution by mixing an indium salt, a fatty protic
alkylamine, a fatty alkylacid, and zinc carboxylate with an inert
solvent and heating up to 50-200.degree. C. to get a clear solution
under water and oxygen free atmosphere; preparing a phosphine
precursor solution comprising tris(trimethylsilyl) phosphine in the
inert solvent under water and oxygen free atmosphere; injecting the
indium precursor solution in excess to the phosphine precursor
solution into the mixing chamber to obtain a reaction mixture,
wherein the mixing chamber is a magnetic mixing micro-chamber with
a volume in the range of 10 mm.sup.3 to 10,000 mm.sup.3, and
wherein the injecting is at a flow rate from 0.1 ml/min to 10
ml/min ; forwarding and heating the reaction mixture at a
temperature from 160 to 320.degree. C., within the reaction chamber
until InP core suspension is obtained; forwarding the core
suspension into a mixing chamber and injecting a shell precursor
solution comprising a Zn source and a S source to the core
suspension and capping ligands into the mixing chamber; forwarding
and heating the suspension at a temperature from 160 to 320.degree.
C. for shell preparation within the reaction chamber; and
cooling.
7. A formulation comprising the nanoparticle of claim 6.
8. A device comprising the nanoparticle of claim 6.
Description
[0001] The invention relates to a continuous synthesis process for
the preparation of high quality indium phosphide/zinc sulfide
core/shell semiconduting nanocrystals in particular quantum dots
(QD).
[0002] Colloidal semiconductor nanocrystals have attracted intense
interest during the past two decades, owing to their unique
chemical, physical, electronic properties, which brings many
potential technological applications in biological labeling, LEDs,
lasers, photovoltaics and sensors, etc. Among all II-VI and III-V
semiconductors, InP is probably the only system which offers a
compatible, or even broader emission color range than the
CdSe-based system but eliminating intrinsic toxicity since InP
contains neither Class A elements (Cd, Hg, Pb), nor class B
elements (e.g. As, Se) (Xie et al. J.AM.CHEM.SOC., 2007, 129,
15432; Reiss et al. J.AM.CHEM.SOC., 2008, 130, 11588).
Nevertheless, synthesis of high-quality InP remains challenging.
The existing problems include among others low photoluminescence
quantum yield, poor size distribution, sensitive precursors and
poor control of the stability. The synthesis procedure of InP is
also more delicate compared to the one of CdSe-based QDs partially
due the highly sensitive phosphine precursors (Nann et al.
J.AM.CHEM.SOC., 2006, 128, 1054; Nann et al. J. Mater. Chem., 2008,
18, 2653).
[0003] Making use of the micro-reaction technique based continuous
synthesis facility; we are exploring solutions for these problems.
In recent years, micro-reaction technology has emerged as an
alternative for the synthesis of high-quality nanoparticles due to
the advantages that this technology provides: Precise control of
the reaction parameters like temperature profiles, miniaturized
reaction volume, fast reaction speed and its parallel operation
possibility may lead to a scalable process of production of various
nanoparticles (Blackmond et al. Angew. Chem. Int. Ed. 2010, 49,
2478; WO2008061632, WO2002053810). Besides, the enhanced heat
transfer and mixing efficiencies in the micro-channel allow
elevating the precursor reactant concentration above the nucleation
threshold in a very short period of time, and the burst of
nucleation can be promoted by raised temperature providing a
reliable strategy to separate the nucleation and growth phases
during the heating stage required to achieve a better particle size
distribution.
[0004] Although WO2008061632 and WO2002053810 mention the
continuous preparation of binary semi-conducting nanoparticles
using micro-reaction technique should be applicable for the
preparation of InP nanoparticles, the methods were only exemplified
with Cd-based cores and needed to be modified to solve the
particular problems of the preparation of nanoparticles comprising
InP core.
[0005] There was a need for a method for the preparation of InP
nanocrystals leading to high photoluminescence quantum yield,
narrow size distribution and enhanced stability despite the use of
sensitive precursors.
[0006] The stabilization of InP nanoparticle using a protective ZnS
shell is known to enhance environmental stability, chemical and
photochemical stability, reduced self-quenching characteristics,
and the like. In particular Peng et al. [J. Am. Chem.Soc., 2007,
12, 15432-15433] describe the "one-pot" preparation of InP/ZnS core
shell nanoparticles wherein the size range reachable for one
reaction was readily tuned by the concentration of amines, the
concentration and chain length of fatty acids in particular
myristic acid used for dissolving In(Ac).sub.3 precursor, and the
reaction temperatures (below 200.degree. C.). The most convenient
method in tuning the size was by varying the concentration of the
fatty acid.
[0007] The fluorescence properties of semiconduting nanocrystals
are known to depend on the quantity and quality of surface defects.
Surface capping ligands are known to be crucial to achieve high
quantum yield nanocrystals. A metal rich surface is also
advantageous for a good saturation of surface defects. The typical
capping ligands for II-VI semiconductor nanocrystals, such as
trioctyl phosphine oxide (TOPO) and trioctyl phosphine (TOP) have
stronger coordinating strength towards indium than for example,
cadmium. It was found that InP nanoclusters dissolve rapidly in the
presence of these ligands at temperature above 200.degree. C.,
which leads to unstable initial nuclei, more intrinsic defects and
slower crystallization process. Nann et al. teach that only weak or
non-coordinating ligands added to the core reaction mixture are
able to prevent the negative influence of strong coordinating
ligands and an excess of indium precursor is necessary to avoid
nanocrystal aggregation due to the lack of surface ligands. The
excess of indium precursor was shown not only to support rapid
nucleation, but also to provide an indium rich surface with reduced
surface defects [Nann et al. J. Mater. Chem., 2008, 18, 2653]. Nann
et al. also teach that addition of stable zinc carboxylate into the
reaction mixture does not result in lattice doping due to intrinsic
low reactivity of zinc carboxylate compared with the other reagents
involved in the synthesis but that zinc helps passivating the InP
surface by coupling to the dangling phosphine bonds, hence
enhancing the photoluminescence quantum yield of InP nanocrystals
significantly. Furthermore, the addition of zinc carboxylates was
shown to stabilize the QDs' surfaces and reduce the critical nuclei
size as shown by shift of the photoluminescence emission wavelength
to the blue observed with increasing concentration of initial zinc
carboxylate [Nann et al. J. Mater. Chem., 2008, 18, 2653].
Typically tris(trimethylsilyl) phosphine (TTSP) is used as
P-precursor for the preparation of InP core [Nann et al. J. Mater.
Chem., 2008, 18, 2653]. However TTSP is sensitive to oxidation and
requires intensive degasing under inert atmosphere before use and
throughout reaction process, so handling during batch production is
delicate, time consuming and costs are high.
[0008] There was a need for a method for the preparation of InP/ZnS
core/shell nanocrystals leading to high photoluminescence quantum
yield, narrow size distribution and enhanced stability despite the
use of sensitive precursors, wherein production costs are
reduced.
[0009] The problem was solved by a continuous-flow method for the
preparation of InP/ZnS nanoparticles conducted in a micro-reaction
system comprising at least one mixing chamber connected to one
reaction chamber and comprising the following steps: [0010] 1.
Preparing an indium precursor solution by mixing an indium salt, a
fatty protic alkyl amine and a fatty alkyl acid as weak or
non-coordinating ligands and zinc carboxylate with an inert solvent
optionally heating up to 50-200.degree. C., preferred
80-150.degree. C. to get a clear solution under water and oxygen
free atmosphere, [0011] 2. Preparing a phosphine precursor solution
comprising tris(trimethylsilyl) phosphine (TTSP) in the inert
solvent under water and oxygen free atmosphere, [0012] 3. Injecting
the indium precursor solution in excess to the phosphine precursor
solution into the mixing chamber to obtain a reaction mixture,
wherein the mixing chamber is a magnetic mixing micro-chamber,
preferably at a flow rate from 0.1 ml/min to 10 ml/min, [0013] 4.
Forwarding and heating the reaction mixture at a temperature from
160 to 320.degree. C., preferred 200 to 280.degree. C. within the
reaction chamber until InP core suspension is obtained, [0014] 5.
Forwarding the core suspension into a mixing chamber and injecting
a shell precursor solution comprising a Zn and a S source to the
core suspension and preferably capping ligands into the mixing
chamber, [0015] 6. Forwarding and heating the suspension at a
temperature from 160 to 320.degree. C., preferred 200 to
280.degree. C. for shell preparation within the reaction chamber,
[0016] 7. Cooling.
[0017] In a preferred embodiment the process of the present
invention is conducted in a microreaction system as shown in FIG.
3.
[0018] Highly efficient mixing of the precursors was found to be
advantageous and was achieved by a turbulent flow, created by the
active magnetic agitation within a miniature
polytetrafluoroethylene (PTFE) mixing chamber of 10-1000 mm.sup.3,
preferred from 30-70 mm.sup.3 volume later called mixer.
[0019] Typically the nucleation and growth of QDs is triggered in a
polytetrafluoroethylene (PTFE) capillary as a reaction chamber
connected to the mixing chamber having an inner diameter from
0.1-2.0 mm, preferred from 0.2-1.0 mm and of 0.5 to 20 meter length
set at a temperature from 20-320.degree. C., preferred from
120-280.degree. C. t. The flow rate is preferably adjusted from 0.1
ml/min to 10 ml/min.
[0020] Used micro-reaction system in particular magnetic mixing
micro-chamber was found to be particularly adapted to the
preparation of InP/Zns nanocrystals because it provides highly
efficient mixing and is easy to produce and upscale.
[0021] The heating oil provided a facile heating source to achieve
the desired temperature for different reaction stages.
Alternatively a micro-heater may be used.
[0022] Oxygen-free atmosphere is typically nitrogen or argon.
[0023] Preferred solvent is non or weakly coordinating liquid at
room temperature preferably non polar or low polar. The polarity
index can vary from 4 to 0, preferably 1.5 to 0, most preferably
0.8 to 0, based on the polarity index of water being 9, according
to the polarity scale (V. J. Barwick, Trends in Analytical
Chemistry, vol. 16, no. 6, 1997, p.293ff, Table 5). The organic
solvents, during the reaction temperature, should be stable and
degrade as little as possible.
[0024] Preferably the boiling point of organic compound is above
200.degree. C., more preferably above 240.degree. C. . Among others
suitable solvents are octadecene (ODE) or myristic acid methyl
ester, dibutyl sebacate, 1-hexadecene, 1-eicosene, paraffin wax,
diphenyl ether, benzyl ether, dioctyl ether, squalane,
trioctylamine, heat transfer fluids or any solvent mixture thereof.
Most preferred is ODE.
[0025] Indium salts are typically indium(III) chloride, indium(III)
acetate, indium(III) bromide, indium(III) nitrate, Indium(III)
sulfate, Indium(III) perchlorate or Indium(III) fluoride. Most
preferred are indium(III) chloride and indium(III) acetate.
[0026] A mixture of fatty protic alkyl amine and fatty alkyl acid
is used as weak or non-coordinating ligands to form stable
Indium-ligand complexes in the indium precursor solution. Suitable
fatty carboxylic acids are e.g. stearic acid, oleic acid, myristic
acid. Fatty alkyl amines are typically hexadecylamine, dioctylamine
or oleylamine.
[0027] Suitable zinc carboxylates for the passivation of the InP
surface are zinc undecylenate and zinc stearate.
[0028] Most preferred is a mixture of oleic acid and oleylamine and
zinc stearate.
[0029] The amount of ligands (fatty amine and fatty acid) is
carefully selected with an amine/acid ratio around 4.0-1.0 to avoid
either the oxidation or reduction of indium and form stable indium
complexes for a controllable nucleation and crystal growth process
as the effect of the concentration of the ligands is known to be
dramatic for accurate control of the reaction and preparation of
nanocrystals with distinguishable absorption peaks [Peng, X. G. et
al. Nano Lett. 2002, 2, 1027-1030].
[0030] By varying the concentration of carboxylic acid, zinc
carboxylate and/or alkyl amine, the particle size of InP was tuned
and the corresponding emission color could varied from blue to red.
In a preferred embodiment the size of InP QDs is controlled by
varying the zinc carboxylate concentration.
[0031] The Indium precursor solution is typically added to the
mixture of tris(trimethylsilyl) phosphine (TTSP) and ODE and then
heated up to 150-300.degree. C., preferred 200-260.degree. C.
[0032] The yielding product is the Zn coated InP core suspension
wherein InP quantum dots (QD) of mean diameter of 2 to 10 nm are
obtained.
[0033] In a further step a ZnS shell is deposited on Zn coated InP
core. Typically a shell precursor solution comprising either a
separate Zn precursor and S-precursor (multiple source) or a single
source precursor providing both Zn and S simultaneously is prepared
under water and oxygen free atmosphere and is directly injected
into the crude core particle suspension at reaction temperature or
previously cooled. Typically injection occurs within a second
mixing chamber, preferred a magnetic mixing micro-chamber.
[0034] Zinc diethyl dithiocarbamate (ZDC) is preferred as a single
source precursor for ZnS shell. Shell precursor solution usually
further comprises capping ligands for semiconductor nanocrystals,
such as oleic acid, oleylamine and trioctyl phosphine (TOP) in the
above mentioned inert solvent.
[0035] The reaction suspension is allowed to react at reaction
temperature until a ZnS shell with a thickness of 0.2 to 4 nm is
formed.
[0036] The obtained QDs are typically purified by adding an
anti-solvent like e.g. methanol, ethanol, isopropanol, butanol or
acetone according to procedure known in the state of the art and
characterized with e.g. UV-Vis spectroscopy, fluorescence
spectroscopy and electronic transmission spectroscopy.
[0037] InP QDs with a PL emission color ranging from blue to red
could be prepared with the method of the present invention.
[0038] Prepared QDs were characterized by the following methods:
[0039] quantum yield was measured by comparison with sulforhodamine
B according to the method described in "A Guide to Recording
Fluorescence Quantum Yields", Jobin Yvon Horiba,
[0040]
http://www.horiba.com/fileadmin/uploads/Scientific/Documents/Fluore-
scence/quantumyieldstr ad.pdf, retrieved Oct. 5, 2011. [0041] The
photoluminescence of nanoparticles were tested by UV/VIS absorption
(Jena Analytics, Specord) and photoluminescence spectroscopy
(Fluorolog 3, Jobin Yvon).
[0042] The method of the present invention has the following
advantages compared to known preparation routes: [0043] 1. New
active mixing within the microchamber generated by magnetic
stirring provided better mixing efficiency than static mixers used
in the microreaction systems of the state of the art. Better mixing
was shown to lead to higher particle quality. [0044] 2. The known
use of coordinating molecules zinc carboxylate and hexadecylamine
helps to passivate nanocrystalline surfaces, hence increasing the
quantum yield. Obtained zinc-rich nanocrystal surface helps further
growing of an additional high band-gap ZnS shell on InP cores.
[0045] Combined approaches yielded to InP/ZnS QDs with enhanced
photoluminescence and photostability. [0046] 3. The process of the
invention is a simple, fast and scalable continuous-flow method
based on capillary microreaction system for the synthesis of high
quality InP and InP/ZnS nanocrystals. [0047] 4. The present
invention is a simple continuous method for the synthesis of highly
luminescent InP and core/shell InP/ZnS with high quantum yields.
The method allows a fast synthesis of both InP core QDs as well as
overcoating of ZnS shells within much less than an hour.
[0048] The obtained InP/ZnS QDs had very good stability against
photo-bleaching over time and quantum yield of at least 40%. The
full width half maximum (FWHM) is between 60 and 150 nm. The
as-prepared core/shell InP/ZnS has very less photoluminescence
quenching after storing in a nitrogen environment for weeks till
months. FIG. 1 illustrates the schematic of core/shell structure of
InP/ZnS QDs, and different emission color of InP/ZnS QDs prepared
in this report. The color ranges from blue-green till red (500-610
nm).
[0049] A further object of the present invention is therefore an
InP/ZnS nanoparticle obtainable by the method of the present
invention.
[0050] Further objects of the present inventions are formulation or
device comprising the semiconducting core-shell nanoparticle of the
present invention, in particular electronic devices.
[0051] Experimental Section:
DESCRIPTION FIGURES
[0052] FIG. 1. illustrates the schematic of core/shell structure of
InP/ZnS QDs, and and photo of
[0053] QDs samples under UV lamp with different emission color of
InP/ZnS QDs as prepared. The color ranges from blue-green till red
(500-610 nm).
[0054] FIG. 2. UV-VIS spectra and Fluorescence spectra of InP/ZnS
core/shell QDs.
[0055] FIG. 3. scheme of capillary-based microreaction system.
[0056] FIG. 4A and 4B: structure diagram of miniature mixing
chamber.
[0057] The method of the present invention is exemplified in the
following examples without being restricted to the examples
below.
EXAMPLE 1: BATCH SYNTHESIS OF INP/ZNS NANOCRYSTALLINE
[0058] Preparation of precursor solution: Phosphine precursor stock
solution was prepared in glove-box under nitrogen atmosphere: 0.2
mmol of tris (trimethylsilyl phosphine) (TTSP) and 2 ml of
1-octadecen (ODE) were mixed in glass bottle. Zinc
diethyldithiocarbamate (ZDC) stock solution was prepared by
dispersing 0.5 g ZDC in 15 mL trioctyl phosphine (TOP) under
sonication for a few minutes until a white turbid suspension was
obtained.
[0059] Preparation of InP QDs Cores:
[0060] 22 mg (0.1 mmol) indium chloride, 28.2 mg (0.1 mmol) oleic
acid, 63.2 mg (0.1 mmol) zinc stearate and 53.5 mg (0.2 mmol)
oleylamine (OLA) were mixed with 4 ml ODE in a 50 ml three-necked
flask. The flask was repeatedly evacuated and re-filled with
nitrogen to provide a water and oxygen-free reaction atmosphere
(120.degree. C., for -30 min). Then, the solution was quickly
heated to 230.degree. C. under strong agitation. When the
temperature of the solution became stable, 0.5 ml stock TTSP-ODE
(0.2 mmol in 2 mL ODE) solution 2) as prepared above was rapidly
injected. The solution was kept at 230.degree. C. for some minutes
until desired size of InP cores was achieved. Samples were taken
after 5, 10, 15 min, etc. (0.5 mL reaction solution of each
dissolved in 2 mL toluene, and characterized by UV/Vis spectroscope
and Fluorescence spectroscope). The reaction solution was then
cooled down to room temperature for the shell overcoating step.
Nanocrystals of different size of were also obtained by adjusting
the initial concentrations of zinc stearate and HDA.
[0061] Overcoating Process for the Preparation of InP/ZnS
Core/Shell QDs:
[0062] The above InP QDs solution was cooled to room temperature. 1
mL of ZDC in TOP stock solution and 1 mL OLA were added to the
reaction mixture. The flask was repeatedly evacuated and flushed
with nitrogen to obtain a water and oxygen-free reaction
atmosphere. The solution was heated to 150.degree. C. for 20 min.
The obtained samples are also characterized by UV/Vis and
fluorescence spectroscopy. The photoluminescence of as-prepared
InP/ZnS had an increase of 3-10 times in comparison with uncoated
InP based on the estimation of intensity and fluorescence
spectroscope measurement. The photoluminescence of uncoated InP was
quenched after some days storage in normal environment, while the
photoluminescence of InP/ZnS were stable for months.
EXAMPLE 2: CONTINUOUS SYNTHESIS OF INP NANOCRYSTALLINES
[0063] Preparation of Precursor Solution
[0064] Indium-stock solution was prepared by mixing 220 mg (1 mmol)
indium chloride, 282.5 mg (1 mmol) oleic acid and 695.5 mg (2.6
mmol) Oleylamine (OLA) in a 250 ml three-necked flask with 30 ml
ODE. The flask was repeatedly evacuated and re-filled with nitrogen
to provide a water and oxygen-free reaction atmosphere. The
solution was then quickly heated to 120-150.degree. C. under strong
agitation until the solid samples were completely dispersed. The
precursor solution were then cooled down to room temperature for
the later usage. Phosphine-Stock solution was prepared in a
glove-box under nitrogen atmosphere: Tris(trimethyl silyl phoshine)
and 1-Octadecen (ODE) was mixed in glass bottle. Zinc-carbonate
stock solution was prepared by dispersing 0.5 g zinc stearate in 15
mL ODE by sonication for some minutes. The obtained mixture was a
white turbid suspension. ZDC-Stock solution (shell precursor
solution) was prepared by dispersing 0.5 g ZDC in 15 mL TOP by
ultrasonication for some minutes. The obtained mixture was also a
white turbid suspension.
[0065] Preparation of InP QDs Cores
[0066] Stock solutions for core precursor solution (e.g. 3 mL of
indium stock solution +1.2 mL of phosphine stock solution +1 mL of
zinc stearate stock solution +4.5 mL of ODE) were pumped into the
mixer of 50 mm.sup.3 volume and then through the capillary system
(4 meter of PTFE tube, heated up to 230.degree. C. in oil bath)
with a flow rate of 1.0 mL/min. The first sample with color
(fluorescence as well) appeared after several min, the InP samples
were then collected by glass bottles 1-2 min after gaining the
first color suspension. The above InP QDs solution was cooled to
room temperature. The continuous system was washed with ODE.
[0067] The other sizes of InP (other colors of photoluminescence)
were achieved by varying the amount of phosphine and/or zinc
stearate solution: increasing the amount of phosphine brought
bigger size of InP core, hence red-shifted photoluminescence;
decreasing the amount of zinc stearate brought bigger size InP
core, hence red-shifted photoluminescence.
[0068] Shelling Process for InP/ZnS QDs
[0069] For ZnS overcoating, 2.5 mL of InP rude solution and 0.75 mL
of ZDC stock solution and 4 mL ODE were pumped to the same
continuous system (mixer of 50 mm.sup.3 volume and 4 meter of PTFE
capillary tube, heated up to 220.degree. C. in oil bath) with a
flowrate of 1.0 mL/min. The obtained sample collected and also can
be characterized by UV/Vis and fluorescence spectroscopy.
[0070] FIG. 2. shows UV-VIS spectra and Fluorescence spectra of
InP/ZnS core/shell QDs obtained according to the continuous process
of example 2 by varying the amount of phosphine and/or zinc
stearate solution.
* * * * *
References