WO2012168279A1

WO2012168279A1 - Method for synthesizing core/shell nanoparticles and their solution

Info

Publication number: WO2012168279A1
Application number: PCT/EP2012/060661
Authority: WO
Inventors: Huachang Lu; Leslaw Mleczko; Min FU; Tao Liu; Heinz Dieter
Original assignee: Bayer Intellectual Property Gmbh; Bayer Technology And Engineering (Shanghai) Co. Ltd.
Priority date: 2011-06-07
Filing date: 2012-06-06
Publication date: 2012-12-13
Also published as: CN103582690B; WO2012167398A8; WO2012167398A1; CN103582690A

Abstract

The present invention provides a method for synthesizing core/shell nanoparticles and their solution. A method for synthesizing a core/shell nanoparticles solution, comprising the steps of: adjusting the temperature of a semiconductor nanoparticles solution to a predetermined coating temperature; adding a shell precursor solution into the semiconductor nanoparticles solution and reacting at the predetermined coating temperature, the shell precursor solution being mixed with components comprising zinc salt, alkanethiol and nonpolar organic solvent; after a predetermined reaction time, obtaining the core/shell nanoparticles solution. The core/shell nanoparticles obtained in this invention are characterized by a high quantum yield, a low toxicity, a low production cost and a simple process.

Description

Method for synthesizing core/shell nanoparticles and their solution

Field of the invention

The present i n vent ion relates to a method for synthesizing core shell nanoparticles and their solution.

Description of the Related Art

inorganic semiconductor nanoparticles demonstrate several advantages over the organic luminescent materials, including stable performance, wide excitation spectrum, narrow photolumincscence peak as well as excellent stabilit with different surroundings. A 11 the above features make these nanoparticles widely used in solar cells, LEDs, luminescent probes, bio tagging, security labels, functional films, lasers and electronic communications etc.

Most of the inorganic semiconductor nanoparticles comprise of Cd, As, Pb and Se etc. The intrinsic toxicity of these elements pollutes the environmental, and sheds a doubt on the commercial applicability of these nanoparticles. As the result, non-toxic or low-toxic semiconductor nanoparticles (e.g. iB-l 11 A-VIA and IIB-IB-IIIA-VIA group nanoparticles) with a high solar absorption coefficient and good photolumincscence stability have attracted intensive research.

However, the surface defects and by-products formed during the preparation led to fluorescence quenching centers, and then decrease the quantum yield of the semiconductor nanoparticles. According to the researchers, coating semiconductor nanoparticles with a higher-band-gap inorganic semiconducting material to form core shell nanoparticles can passivate the surface defects, resulting in the improved quantum yield and photoiuminescence stability of semiconductor nanopart icles.

Normally, the coating of a shell of semiconductor nanoparticles is achieved by the dropwise or pouring addition of shell precursor solution into a solution of core semiconductor nanoparticles under a predetermined coating temperature. The shell precursor solution comprises of metal salt, sulfur source, organic ligand and solvent. Several factors can infect the luminescent property, size, morphology as well as the crystallization of the core/shell nanoparticles, such as type of sulfur source, type of ligand and ligand concentration, coating temperature, coating reaction time as well as adding method of shell precursor addition.

Several reports disclosed the coating process of a ZnS shell precursor solution on the surface of semiconductor nanoparticles, so as to improve their quantum yield. For example, enguo Xie et al. prepared CuInS: ZnS core/shell nanoparticles at 180^°C. I n their case, a mixture of zinc stearate as the zinc salt, sulfur powder as the sulfur source, and oleylaminc as the organic ligand, and a quantum yield up to 30 % was achieved. The similar methodology has been adopted by the same research group to prepare AginS: ZnS core/shell nanoparticles. ( enguo Xie, et al, JACS, 2009, 131, 5691-5697)

Thomas Pons et al. prepared CuinS: ZnS core shell nanoparticles by using the mixture f zinc stearate as the zinc salt, zinc diethyl dithiocarbamate as the sulfur source, trioctylphosphine and o Icy I a mine as organic ligand. In their case, a quantum yield up to 30 % was achieved. (Thomas Pons, et al., ACS Nano, 2010, 4 (5), 2531-2538)

Liang Li et al. used the mixture of zinc stearate as the zinc salt, zinc ethyl xanthate as the sulfur source, octadecene, toluene, and dimethylformamide, and the CuinS: ZnS core/shell nanoparticles were obtained by the dropwise addition of the mixture into a solution f CuinS: nanoparticles. In their case, a high quantum yield up to 60 % was achieved, which was 10 times f that for CuinS: nanoparticles. ( Liang Li, et al., Chem. Mater.2009, 21, 2422-2429)

The research group of Victor I. Klimov used the mixture of zinc stearate as the zinc salt or cadmium leate as the cadmium salt, trioctylphosphine as the ligand and octadecene, and the CuinS: ZnS core shell nanoparticles or CuInS2/CdS core shell nanoparticles were obtained by the dropwise addition of the mixture into a solution of CuinS: nanoparticles at 210 ^°C. In their case, a respective high quantum yield up to 67 % f

core/shell nanoparticles and 86 % f CuInS2/CdS core/shell nanoparticles was achieved. (Liang Li, et a I., JACS, 2011, 133(5), 1176-1179)

Summery of the Invention

According to an example of the present invention, the present invention provides a method for synthesizing a core/shell nanoparticles solution, comprising the steps of:

a) adjusting the temperature of a semiconductor nanoparticles solution to a predetermined coating temperature;

b) adding a shell precursor solution into the semiconductor nanoparticles solution and reacting at the predetermined coating temperature; the shell precursor solution being mixed with components comprising zinc salt, alkanethiol and nonpolar organic solvent; and

c) after a predetermined reaction time, obtaining the core shell nanoparticles solution. Semiconducting material is selected from the group consisting f ΙΒ-ΙΙΙΑ-ΥΊΑ group compound and IIB-IB-IIIA-VIA group compound.

ΙΒ-ΙΙΙΑ-ΥΊΑ group compound according to this invention, wherein IB is selected from the group consisting of Cu and Ag, IIIA is selected from the group consisting f In and Ga, VIA is selected from the group consisting of Se and S.

IB-IIIA-VIA group compound is preferably selected from the group consisting of CuinS:, AgliiS.:. C^'LilnSc:. AglnSc.% CuGaS₂, CuGaSe₂, AgGaS:, AgGaSc:, CuInGaS, CuAglnS, CuInGaSe, CuAglnSe, AglnGaS, AglnGaSe, CuAgGaS, CuAgGaSc, CuInSeS, AglnSeS and CuAgGaScS.

IB-IIIA-VIA group compound is more preferably selected from the group consisting o C^'uInS , AgInS₂, CuInSe₂, AglnSe¾ CuGaS₂, CuInGaS, CuAglnS and AglnGaS.

IIB-IB-IIIA-VIA group compound according to this invention, wherein IB is selected from the group consisting of Cu and Ag, IIIA is selected from the group consisting of In and Ga, VIA is selected from the group consist ing of Sc and S, 11 B is Zn.

IIB-IB-IIIA-VIA group compound is preferably selected from the group consisting of ZnCuInS:, ZnAglnS , ZnCuInSe¾ ZnAginSc:. ZnCuGaS₂, ZnCuGaSe.:. ZnAgGaS₂, ZnAgGaSc;, ZnCuInGaS, ZnCuAglnS, ZnCuInGaSe, ZnCuAglnSe, ZnAglnGaS, ZnAglnGaSe, ZnCuAgGaS, ZnCuAgGaSe, ZnCulnSeS, ZnAglnScS and ZnCuAgGaSeS.

IIB-IB-IIIA-VIA group compound is more preferably selected from the group consisting of ZnCulnS:, ZnAglnS2, ZnCuInSe¾ ZnAginSc: and ZnAglnScS.

Addition method can be direct pouring or dropwise.

Shell precursor solution comprises zinc salt, alkanethiol and nonpolar organic solvent, which is obtained by heating the mixture until the zinc salt dissolved.

Alternatively, other organic ligand can be added during the preparation of shell precursor solution. Organic ligand is selected from the group consisting of phosphate ester and fatty amine.

The molar concentration of alkanethiol is higher than of zinc salt.

The molar ratio between alkanethiol and zinc salt is preferred (2—80): 1 , more preferred (2-50): 1, and most preferred (4-20): 1.

Zinc salt is selected from the group consisting of zinc acetate, zinc chloride, zinc sulphate, zinc diethyl dithiocarbamate, zinc dihexy dithiocarbamate, zinc stearate, zinc oleate, zinc zinc myristate, zinc palmitate. zinc laurate and zinc decanoate.

Alkanethiol is select from the group consisting of an alkanethiol with one or more sulfhydryl functional groups.

Alkanethiol is selected from the group consisting of I -octanethiol, iso-octanethiol, dodecanethiol, 1 -tetradecanethiol, 1 -hexadecanethiol, 1 -octadecanethiol, 1,8-dioctylthiol and 1,6-dioctylthiol.

Nonpolar organic solvent is selected from the group consisting of octadecene, dodecane, hexadecane, octadecane, Diphyl DT, Diphyl THT, paraffin, dipenyl ether, dioctyl ether and dibenzyl ether.

Phosphate ester is selected from the group consisting of trioctyl phosphate and tributyl phosphate. Fatty amine is selected from the group consisting of 1 -hexadecanamine, octadecylamine, n-tetradecylamine and oleyiamine.

The molar ratio between zinc salt and phosphate ester is 1 :(1 :80), preferred 1 :(2 : 50), and more preferred 1 : (4 : 20).

The molar ratio between zinc salt and fatty amine is 1 :(1 : 80), preferred 1 :(2 : 50), and more preferred 1 : (4 : 20).

Coating temperature is from 150 ^°C to 290 ^°C , preferably from 200 ^°C to 260 ^°C , and more preferably from 220 ^°C to 250 ^°C .

Reaction time is from 1 min to 4 h, preferably from 5 min to 3 h, and more preferably from 15 min to 2 h.

According t an example of the present invention, the present invention provides a method for synthesizing core shel l nanoparticles, comprising the steps of:

mixing a core shell nanoparticles solution prepared by any method according to the above description with an organic solvent to obtain a suspension; and

separating core shell nanoparticles from the suspension.

The method further comprises a step of: core/shell nanoparticles are washed at least for one t ime to remove the impurities.

Organic solvent is selected from the group consisting of methanol, ethanoi, isopropanoi, 1 -butanol, methyl ethyl ketone and acetone.

The core composition of the core shel l nanoparticles is se l ect e d according to t he composition of semiconductor nanoparticles. ZnS is selected as the shell composition of core/shell nanoparticles. Accordingly, the core shel l nanoparticles obtained from different semiconductor nanoparticles are marked as semiconductor nanopart icles Zn S, f r example: AglnS ZnS, AgCii InS ZnS, ZnCu l nS - ZnS and ZnAgl nS ? ZnS etc. The surface of core composition of the core/shell nanoparticles can cither completely covered or part ial ly covered with shell composition.

The core she l l nanoparticles prepared according to this invent ion can be applied in LEDs, lasers, solar cells, electronic communications, security labels and bio tagging etc.

I n this invention, alkanethiol is not only as the organic ligand, but also as the sulfur source. I n one hand, during the dissolusion of zinc salt, the chelat ion of alkanethiol with zinc salt leads to the formation of organometallic zinc compound, which improves the solubi lity of zinc salt in the nonpolar organic solvent. On the other hand, sulfur slowly released at a coating temperature reacts with organometallic zinc compound, and the homogeneous ZnS shell formed on the surface of semiconductor nanoparticles, which passivates the surface defects of semiconductor nanoparticles and improves quantum yield of core/shell nanoparticles. Furthermore, the slow released of alkanethiol avoids the discrete nucleation of ZnS, and the formation of by-products is decreased, resulting in the further increase of the quantum yield of the core/shell nanoparticles.

Compared with the conventional preparation method, the method according to this invention is advantageous in the following aspects:

1. The alkanethiol applied in this invention passivates the surface defects of semiconductor nanoparticles, and reduces the formation of by-products. As a result, the significant improvement of quantum yield up to 75 % is achieved.

2. The feed stocks and solvent used in this invention are cheap and easily available, resulting in a low preparation cost. Furthermore, the feed stocks and solvent are low toxicity or nontoxicity.

3. In this invention, the alkanethiol is used both as sulfur source and organic ligand, which reduces the feed stocks for the reaction. Furthermore, the shell precursor solution can be introduced by direct addition. As a result, the simplicity, controllability, and reproducibility of the process are significantly improved, which facilitates the commercial production of the core/shell nanoparticles.

Brief description of the Drawings

Figure 1 . UV-Vis absorption and photoluminescence spectra of CuInSivZnS core/shell nanoparticles prepared in examples.

Figure 2. Photoluminescence spectra CulnS2 ZnS core/shell nanoparticles prepared in examples.

Figure 3. TEM picture of CulnS;/ZnS core/shell nanoparticles prepared in an example.

Figure 4. X RD spectrum of Cu l nS nanoparticles and Cu lnS ; ZnS core shell nanoparticles prepared in an example.

Figure 5. TEM picture of CulnS - nanopart icles prepared in an example.

The figures are subject to use for the further description of the examples and methods according to the present invention. The figures and the descriptions are used for exemplification purpose, but not restrict the application field of this invent ion. Description of the preferred embodiment

Some examples are used for the further description of the present invention. It should be understood that these examples are only used for exemplification purpose, but not restrict the application field of this invention. It should also be understood that those skilled in the art can modify or change the present invention after referring to this invention. But all these equivalent changes or modification also fall into the claims defined in the present invention.

Adjusting the temperature of a semiconductor nanoparticles solution to a predetermined coating temperature, adding (e.g., by direct pouring) a shell precursor solution into the semiconductor nanoparticles solution and reacting at the predetermined coating temperature. The core/shell nanoparticles solution is obtained after a predetermined reaction time. After cooling to a low temperature (e.g. room temperature), core/shell nanoparticles solution is mixed with a polar solvent to obtain a suspension, and separating the core/shell nanoparticles from the suspension. During the addition of shell precursor solution into the semiconductor nanoparticles solution, it is preferred to select a method that can ensure the fast mixing of the two solutions, e.g. the shell precursor solution can be poured into the semiconductor nanoparticles solution.

The semiconductor nanoparticles can be obtained eiher by the separation from the solution of semiconductor nanoparticles, or by other processes.

For example, the solution of semiconductor nanoparticles can be prepared by the following steps:

Into a nonpoiar organic solvent, the metal salt, indium salt, alkanethiol are added with one or more compounds from CS, sulfur powder and thiourea. Under a flow of an inert gas and with vigorous stirring, the mixture is heated to 200 ^°C~290 ^°C . At the same temperature, the stirring is continued for 1 mm- 6 h to ensure the complete dissolution of all the components and finally obtain the solution of semiconductor nanoparticles. During synthesizing the solution of semiconductor nanoparticles, the stirring temperature and stirring time show influence on the size, and furtherly affect the luminescent properties of the core/shell nanoparticles.

In the solution of I B- I l l A- VI A group compound, the molar ratio between IB group metal salt and I I IA group metal salt is 1 - 2 : 2- 1 , wherein the I B group metal salt can be mixed with IIIA group metal salt in any proportions.

Furthermore, the molar amount of VIA group compound is not less than the total molar amount of I B and I I IA group metal salts.

I n the solution of I I B- I B- I I IA-V I A group compound, the molar ratio between I B group metal salt and I I IA group metal salt is 1 - 2 : 2 - 1 , wherein the I B metal salt can be mixed with IIIA group metal salt in any proportions. Furthermore, the molar amount of VIA group compound is not less than the total molar amount of IB and II IA group metal salts, and the ratio between the molar amount of I IB group metal salt and the total molar amount of IB and II IA group metal salts is 1—20 : 20-1.

IB group metal salt is selected from the group consisting of cuprous acetate, cop er acetate, copper chloride, cuprous chloride, cuprous sulphate, cuprous nitrate, copper nitrate, cuprous iodide, cuprous stearate, cuprous oleate, cuprous myristate, cuprous palmitate, cuprous laurate, cuprous decanoate, silver nitrate, silver sulphate, silver acetate and silver stearate.

IIIA group metal salt is selected from the group consisting of indium acetate, indium chloride, indium sulphate, indium nitrate, indium iodide, indium stearate, indium oleate, indium myristate, indium palmitate, i ndium laurate, i ndi m decanoate, gall iiim chloride, gallium sulphate, gallium stearate, gallium acetate and gallium nitrate.

IIB group metal salt is selected from the group consisting of zinc acetate, zinc chloride, zinc sulphate, zinc diethyl dithiocarbamate, zinc dihexyi clithiocarbamate, zinc stearate, zinc oleate, zinc myristate, zinc palmitate, zinc laurate, and zinc decanoate.

VIA group compound is selected from the group consisting of Se powder and bis(trimethylsilyl) seienide.

Alkanethiol is selected from the group consisting of 1 -octanethiol, iso-octyl thiol, dodecanethiol, 1 -tetradecanethiol, I -hexadecanethiol, I -octaclecanethiol. 1,8-octanedithiol and 1,6- octanedithiol.

Nonpolar organic solvent is selected from the group consisting of octadecene. dodecane, hexadecane, ottadecane, diphyl DT, diphyl THT, pafaffin, diphenyl ether, dioctyl ether and dibenzyl ether.

The solution of semiconductor nanoparticles can also be obtained by dispersing the semiconductor nanoparticles into one or more organic solvents.

Organic solvent is selected from the group consisting of octadecene, dodecane, hexadecane, octadecane, diphyl DT, diphyl THT, paraffin, dipheny l ether, dioctyl ether, alkyl sulfhydryl comprises of one or more sulfydry I groups, triocty I phosphate, tributyl p hosphate, hexadecylamine, octadecylamine, n-tetradecylamine and oleylaminc.

For experimental details that are not indicated in the following examples, the regular experimental conditions are applied (e.g. the conditions indicated in handbook of operation in catalytic chemistry, or the suggestions given by the equipment suppliers).

The following methods are applied to characterize the core shell nanoparticles:

1) UV-Vis and photoluminescence (PL) spectra Before the optical test, the obtained core shell nanoparticles are di luted by toluene. A Gary 50 (Varian, USA) UV-visiblc spectrophotometer was used to record the absorption spectra of the core/shell nanoparticles. Using the same solution of core/shell nanoparticles, the PL spectra were collected a Cary Eclipse (Varian, USA) photoluminescence spectrometer. During the measurement of PL spectra, the PMT voltage was set as 600 V, and the excitation wavelength and the width of emission slice were set as 485 nm and 5.0 nm respectively. During the dilut ion of core/shell nanoparticles, the absorption intensity at 485 nm was adjusted below 0.05, so as to avoid the influence of reabsorption on the following data analysis.

2) Quantum yield

The quantum yield of core/shell nanoparticles was obtained by comparing the integrated emission from Rhodamine B (with a quantum yi eld o f 97 % in ethanol) in ethanol and that f core shell nanoparticles dispersed in hexane. Concentrations of both were adjusted to provide the same optical densities (below 0.05) at the excitation wavelength. Quantum yield of sample is determined accordin to the following equation,

Wherein,

YQ is the quantum yield of core/shell nanoparticles to be measured,

Ys is the quantum yield of Rhodamine B in ethanol,

FQ, FS is the integrated emission f core shell nanoparticles in toluene and Rhodamine B in ethanol respectively.

AQ and As is the optical density of core shell nanoparticles in toluene and Rhodam ine in ethanol at the excitation wavelength respect iv ely.

DQ and Ds is the diffraction coefficient of toluene and ethanol respectively.

3) X-ray diffraction ( XRD )

Powder XRD measurements were performed on a D/max2200 X-ray diffraction system

(Rigaku. Japan). Samples for XRD measurements were prepared by dropping a colloidal suspension f core/shell nanoparticles in toluene on a glass wafer and evaporating the solvent. During the measurement, Cu/Κ-α was used as the irradiation source, applying the operation voltage and current of 40 KV and 30 niA respectiv ely. The sample was scanned from 20-70 ° with a scanni ng rate f 67min.

4) Transmission electron microscopy (TEM )

A Philips CM 20 transm ission electron m icroscope (HRTEM) was used to ev aluate the microstructures of the prepared core/shell nanoparticles, and the sample was prepared by dipping an amorphous carbon copper grid in a dilute toluene dispersed core/shell nanoparticles solution, then the sample was left to evaporate at room temperature.

Example 1 : Influence o f react ion t i me on the properties of CulnS; ZnS core shell nanoparticles.

0.293 g zinc acetate was mixed with 3 ml dodecanethiol and 6 ml octadecene. The mixture was heated to 100 ^°C , and the temperature was maintained until the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.051 g cuprous acetate, 0.120 g indium acetate and 1.03 ml dodecanethiol were mixed with 10.3 ml octadecene to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min. Then the mixture was stirred at 240 ^°C for a predetermined stirring time (as shown in Table 1), and the solution of CuInS2 nanoparticles was formed.

The shell precursor solution was poured into the solution of CulnS; nanoparticles, and the solution of CulnS · ZnS core/shell nanoparticles was obtained after a predetermined reaction time (as shown in Table 1) at 240 ^°C . The solution of CulnS: ZnS core/ shell nanoparticles was cooled to room temperature.

The CulnS; ZnS core/ shell nanoparticles were precipitated out by adding three equivalents of acetone, isopropanol mixture (1 :4 by volume. ). The mixture was then centrifuged. After removal of supernatant , the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume.) were added to wash the precipitate, and the core/shell nanoparticles were obtained by the centrifugation. The above washing procedure is repeated for 2 times. The CulnS: ZnS sample was finally re-dispersed in toluene and stored under N2 atmosphere.

Table 1 shows the preparation conditions and properties of CulnS; ZnS core/shell nanoparticles. Figure 1 and Figure 2 demonstrate the absorption and PL spectra of sample Y 1 , Y . Y5 , Y6 , Y8-10 and Y 16 respectively. Figure 3 shows the TEM images of sample Y7.

Table I : Preparation conditions and the properties of CulnS; ZnS core/shell nanoparticles

Y6 60 240 90 75.3 589

Y7 60 240 180 72.1 580

Υ8 90 240 30 41 .4 611

Υ9 120 240 5 18.2 675

Y10 120 240 30 25.2 648

As shown in Table 1 , the PL wavelength of CulnS 2/ZnS core shell nanoparticles could be controlled by varying the stirring time for the preparation o CulnS; nanoparticles and the reaction time for the growth of shell. As a result, core/shell nanoparticles with photoliiminescence in different colors could be obtained. By the process optimization, orange luminescent core/shell nanoparticles with a PL wavelength of 589 mil and a high quantum yield of 75 % were obtained.

Example 2: Influence of zinc salt amount on the properties of CulnS: ZnS core/shell nanoparticles.

A certain amount of zinc acetate (as shown in Table 2) was mixed with 3 ml dodecanethiol and 6 m 1 octadecene. The mixture was heated to 100 ^°C , and the temperature was maintained until the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.036 g cuprous acetate. 0.084 g indium acetate and 0.72 ml dodecanethiol were mixed with 7.2 ml octadecene to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 inin. Then the mixture was stirred at 240 ^°C for 60 in in, and the solution f CulnS: nanoparticles was formed and cooled to 220 ^°C .

The shell precursor solution was poured into the solution of CulnS: nanoparticles, and the solution of CulnS: ZnS core/shell nanoparticles was obtained after a predetermined reaction time (as shown in Table 2) at 220 ^°C . The solution of CulnS: ZnS core shell nanoparticles was cooled to room temperature.

The CulnS: ZnS core/ shell nanoparticles were precipitated out by adding three equivalents of acetone isopropanol mixture (1 :4 by volume. ). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume. ) were added to wash the precipitate, and the core shell nanoparticles were obtained by the ccntrifugation. The above washing procedure is repeated for 2 times, and the final core, shell nanoparticles were dispersed in toluene and stored under N2. Table 2 shows the preparation conditions and properties f CulnS: ZnS core, shell nanoparticles. Figure 4 shows the X D pattern of sample Yl 1, Y13 and Y 1 . Figure 5 shows the TEM images of sample Y 1 1. Table 2: Preparation conditions and the properties of Cu lnS: ZnS core shell nanoparticles

Example3 : Influence of stirring temperature on the properties of CulnS 2/ZnS core/shell nanoparticles.

0.440 g zinc acetate was mixed with 3 ml dodccanetliiol and 6 ml octadecene. The mixture was heated to 100 ^°C , and the temperature was maintained unt i l the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.075 g cuprous acetate, 0. 1 75 g indium acetate and 1 .5ml dodccanetliiol were mixed with 1 5 ml octadecene to form a mixture. Under a flow of N2, the mixture was degassed and st irred for 30 min. Then the mixture was stirred at 260 ^°C for 30 min, and the solution of CulnS; nanoparticles was formed and cooled to 240 ^°C .

The shell precursor solution was poured into the solution of Cul nS; nanoparticles, and the solution of core/shell CulnS; ZnS nanoparticles was obtained after a predetermined reaction time (as shown in Table 3) at 240 ^°C . The solution of Cu lnS; ZnS core shell nanoparticles was cooled to room temperature.

The CulnS; ZnS core/shell nanoparticles were precipitated out by adding three equivalents of acetone isopropanol mixture (1 :4 by volume.). The mixture was then ccntri fugcd. After removal f supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume.) were added to wash the precipitate, and the core /shell nanoparticles were obtained by the centrifugation. The above washing procedure is repeated for 2 times, and the final core/shell nanoparticles were dispersed in toluene and stored under N2. Tab le 3 shows the preparation conditions and properties of the CulnS: ZnS core/shell nanoparticles.

Table 3 : Preparation conditions and the properties of CulnS; ZnS core/shell nanoparticles Stirring

Stirring

time during Coating

temperature Reaction Quantu

Sample CuInS: temperatur PL wavelength during CuInS; time m y i e 1 d

number nanoparticles e (nm)

nanoparticles (min) (%)

synthesis fC)

synthesis(^°C)

(min)

Y 16 260 30 240 15 1 0.8 671

Y17 260 30 240 60 10.5 659

Example 4: Influence of nonpolar organic solvent on the properties of Cu InS: ZnS core/shell nanoparticles

0.440 g zinc acetate was mixed with 3 ml dodecanethiol and 6 ml octadecene. The mixture was healed to 100 ^°C , and the temperature was maintained unti l the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.074 g cuprous acetate, 0. 1 75 g indium acetate and 1 .5 ml dodecanethiol were mixed with 1 5 ml dip Ivy I DT t form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min. Then the mixture was stirred at 240 ^°C for 60 min, and the solution f CuInS; nanoparticles was formed and cooled to 220 ^°C .

The shell precursor solution was poured into the solution of CuI nS: nanoparticles, and the solution of CuInS ZnS core/shell nanoparticles was obtained after the react ion at 220 ^°C for 180 min. The solution of CuInS: ZnS core/shell nanoparticles was cooled to room temperature.

The Cu InS; ZnS core/shell nanoparticles were precipitated out by adding three equivalents of acetone/ isopropanol mixture (1 :4 by volume. ). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume.) were added to wash the precipitate, and the core shell nanoparticles were obtained by the centrifugation. The above washing procedure is repeated for 2 times, and the final core shell nanoparticles were dispersed in toluene and stored under N2. The obtained core shell nanoparticles showed a quantum yield of 53 % with a PL wavelength of 587 nm.

Example 5: Influence of zinc precursor solution on the properties of CulnSv^'ZnS core/shell nanoparticles

0.8662 g z i nc d i et hy l d i th i ocarba matc was mixed wi th 3 m 1 dodecanethiol and 6 m I octadecene. The mixture was heated to 100 ^°C , and the temperature was mai nta ined unt i l the zinc salt was completely dissolv ed. The obtained homogeneous solut ion was used as the shell precursor solution. 0.074 g cuprous acetate, 0.175 g indium acetate and 1.5 ml dodecanethiol were mixed with 1 ml diphyl DT to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min. Then the mixture was stirred at 240 ^°C for 60 min, and the solution f CulnS; nanoparticles was formed and cooled to 220 ^°C .

The shell precursor solution was poured into the solution of CulnS; nanoparticles, and the solution f CulnS; ZnS core/shell nanoparticles was obtained after the reaction at 220 ^°C for 120 min. The solution of CiilnS; ZnS core/shell nanoparticles was cooled to room temperature.

The CulnS; ZnS core/shell nanoparticles were precipitated out by adding four equivalents of acetone isopropanol mixture (1 :4 by volume.). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and t hree equivalents of acetone isopropanol mixture (1 :4 by volume.) were added to wash the precipitate, and the core shell nanoparticles were obtained by the centriiugation. The above washing procedure is repeated for 2 times, and the final core shell nanoparticles were dispersed in toluene and stored under N2. The obtained core shell nanoparticles showed a quantum yield of 53.7 % with a PL wavelength of 605 nm.

Example 6: Influence of 0 ley I amine n the properties of CulnS: ZnS core shell nanoparticles 0.2205 g zinc acetate was mixed with 3 m I dodecanethiol, 3 m I 0 Icy I am i ne and 6 m 1 octadecenc. The mixture was heated to 100 ^°C , and the temperature was maintai ned unt i l the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.074 g cuprous acetate, 0. 1 75 g indium acetate and 1 .5 ml dodecanethiol were mixed with 15 ml diphyl DT to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min. Then the mixture was stirred at 240 ^°C for 60 min, and the solution of CulnS; nanoparticles was formed and cooled to 220 ^°C .

The shell precursor solution was poured into the solution f CulnS - nanoparticles, and the solution of CulnS: ZnS core/shell nanoparticles was obtained after the reaction at 240 ^°C for 60 min. The solution of C lnS; ZnS core/shell nanoparticles was cooled to room temperature.

The CulnS - ZnS core/shell nanoparticles were precipitated out by adding four equiv alents f acetone/ isopropanol mixture ( 1 :4 by volume.). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume.) were added to wash the precipitate, and the core shell nanoparticles were obtained by the centrifugation. The above operation was repeated twice, and the final core. shell nanoparticles were dispersed in toluene and stored under N2. The obtained core/shell nanoparticles showed a quantum yield of 20.9 % with a PL wavelength of 576 nm. Example 7: Influence of octadecylamine on the properties of CuInS:/ZnS core/shell nanoparticles.

0.2205 g zinc acetate was mixed with 3 ml dodecanethioi, 3 ml octadecylamine and 6 ml octadecene. The mixture was heated to 100 ^°C , and the temperature was maintained until the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.074 g cuprous acetate, 0.175 g indium acetate and 1.5 ml dodecanethioi were mixed with 15 ml diphyl DT to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min. Then the mixture was stirred at 240 ^°C for 60 min, and the solution of CulnS; nanoparticles was formed.

The shell precursor solution was poured into the solution of Cul nS; nanoparticles, and the solution of CuinS; ZnS core/shell nanoparticles was obtained after the reaction at 240 ^°C for 60 min. The solution of CulnS: ZnS core/shell nanoparticles was cooled to room temperature.

The Cu inS: ZnS core/shell nanoparticles were precipitated out by adding four equivalents of acetone isopropanol mixture (1 :4 by volume.). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone/isopropanol mixture (1 :4 by volume.) were added to wash the precipitate, and the core shell nanoparticles were obtained by the centrifugation. The above operation was repeated twice, and the final core/shell nanoparticles were dispersed in toluene and stored under N;. The obtained core/shell nanoparticles showed a quantum yield of 42 % with a PL wavelength of 582 ran.

Example 8 : Influence of trioctyl phosphate on the properties of CulnS: ZnS core/shell nanoparticles.

0.2205 g zinc acetate was mixed with 3 ml dodecanethioi, 5 ml trioctyl phosphate and 3 ml octadecene. The mixture was heated to 100 ^°C , and the temperature was maintained unt i l the zinc salt was completely dissolved. The obtained homogeneous solut ion was used as the shell precursor solution.

0.074 g cuprous acetate, 0.175 g indium acetate and 1 .5 ml dodecanethioi were mixed with 1 ml diphyl DT to form a mixture. Under a flow of N2, the mixture was degassed and st irred f r 30 min. Then the mixture was st irred at 230^°C for 60min, and the solut ion f Cu l nS; nanoparticles was formed.

The shell precursor solution was poured into the solut ion f Cul nS: nanoparticles, and the solution of Cu lnS: ZnS core/shell nanoparticles was obtained after the reaction at 230 ^°C for 60 min. The solution of CulnS; ZnS core/shell nanopart icles was cooled to room temperature.

The Cu lnS - ZnS core shel l nanoparticles were precipitated out by adding four equivalents of acetone isopropanol mixture (1 :4 by volume. ). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume. ) were added to wash the precipitate, and the core shell nanoparticles were obtained by the centrifugation. The above washing procedure is repeated for 2 times. The above operation was repeated twice, and the final core shell nanoparticles were dispersed in toluene and stored under N2. The obtained core shell nanoparticles showed a quantum yield of 38 % with a PL wavelength of 594 nm.

Example 9: Preparation of AglnS: ZnS core shell nanoparticles.

0.220 g zinc acetate was mixed with 3 ml dodecanethiol, and 6 ml octadecenc. The mixture was heated to 100 ^°C , and the temperature was maintained unti l the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.085 g silver nitrate, 0. 1 75 g indium acetate and 1 .5 ml dodecanethiol were mixed with 1 5 ml octadecenc to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min. Then the mixture was stirred at 240 ^°C for 15min, and the solution of AglnS: nanoparticles was formed.

The shell precursor solution was poured into the solution of AglnS - nanoparticles, and the solution of AglnS; ZnS core- shell nanoparticles was obtained after the reaction at 220 ^°C for 60 min. The solution of AglnS: ZnS core/shell nanoparticles was cooled to room temperature.

The AglnS: ZnS core/shell nanoparticles were precipitated out by adding four equivalents of acetone isopropanol mixture ( 1 :4 by volume. ). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equiv alents of acetone isopropanol mixture (1 :4 by v olume. ) were added to wash the precipitate, and the core/shell nanoparticles were obtained by the centrifugation. The above operation was repeated twice, and the final core shel l nanoparticles were dispersed in toluene and stored under N2.

Example 10: Preparation of ZnCulnS; ZnS core shell nanoparticles.

0.220 g zinc acetate was mixed with 3 ml dodecanethiol, and 6 ml octadecenc. The mixture was heated to 100^°C , and the temperature was maintained unti l the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shell precursor solution.

0.076 g cuprous acetate, 0. 1 75 g indium acetate, 0.109 g zinc acetate and 1 .5 m 1 dodecanethiol were mixed with 1 5 ml octadecenc to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min. Then the mixture was stirred at 230 ^°C for 90 min, and the solution of ZnC lnS; nanoparticles was formed.

The shell precursor solution was poured into the solution of ZnCulnS: nanoparticles, and the solution of ZnCulnS: ZnS core, shell nanoparticles was obtained after the reaction at 220 ^°C for 60 min. The solution of ZnCulnS: ZnS core/shell nanoparticles was cooled to room temperature.

The ZnCulnS: ZnS core shell nanoparticles were precipitated out by adding four equivalents of acetone/isopropanol mixture (1 :4 by volume.). The mixture was then centrifuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume. ) were added to wash the precipitate, and the core/shell nanoparticles were obtained by the centrifugat ion. The abov e operation was repeated twice, and the fina l core/shell nanopart icles were dispersed in toluene and stored under N2. Example 1 I : Preparation of Cul nS: ZnS core shel l nanoparticles.

0.293 g zinc acetate was mixed with 3 ml dodecanethiol, and 6 ml octadecene. The mixture was heated to 100 ^°C , and the temperature was maintained unt i l the zinc salt was completely dissolved. The obtained homogeneous solution was used as the shel l precursor solution.

0.051 g cuprous acetate, 0.120 g indium acetate and 1.03 ml dodecanethiol were mixed with 10.3 ml octadecene to form a mixture. Under a flow of N2, the mixture was degassed and stirred for 30 min, and the solution of Cu l nS nanoparticles was obtained after 60 min at 240 ^°C . When the nanopart icles solution was cooled to room temperature, 33 ml acetone as added to precipitate the nanopart icles, and the precipitated C l nS: nanoparticles were col lected by centrifugation and the removal of supernatant.

The CulnS nanoparticles were dispersed in 5 ml toluene, and 20 ml acetone was added to wash the nanoparticles, and the CulnS: nanoparticles were obtai ned by centrifugation. The abov e operation was repeated twice, and the final CulnS: nanoparticles were dispersed in 1 1 ml octadecene. Under a flow of N2, the solution was stirred and degassed for 30 min. Then the temperature of the solution was fastly increased to 240 ^°C , and the shell precursor solution was fastly poured. The mixture was stirred at 240 ^°C for 60 min, and the solution of CulnS: ZnS nanoparticles was formed and cooled to room temperature, =

The C lnS: ZnS core shel l nanoparticles were precipitated out by adding four equivalents of acetone/ isopropanol mixture (1 :4 by volume. ). The mixture was then centriiuged. After removal of supernatant, the precipitate was re-dispersed in toluene, and three equivalents of acetone isopropanol mixture (1 :4 by volume. ) were added to wash the precipitate, and the core/ shell nanoparticles were obtained by the centrifugation. The above operation was repeated twice, and the final Cu lnS; ZnS core/shell nanoparticles were dispersed in toluene and stored under N2. The obtained nanopart icles showed a quantum yield of 70 % with a PL wavelength of 561 ran.

Claims

1. A method for synthesizing a core shell nanopart icles solution, comprising the steps of:

c) after a predetermined reaction time, obtaining the core shell nanopart icles solution.

2. The method according to claim 1 , wherein, the molar rat i o f alkanethiol is higher t han f zinc salt.

3. The method according to one f the claim 1 or 2 , wherein, the molar rat io between alkanethiol and zi nc salt is (2-80) : I .

4. The method according to claim 1 , wherein, the alkanethiol is select from the group consisti ng f an a lkanethiol with one or more sulfhydryl funct iona l groups.

5. The method according to claim 4, wherein, the a lkanethiol is selected from t he group consisting of 1 -octancthiol, iso-octanethiol. dodecanethiol, 1 -tetradecanethiol, 1 -hexadecanethiol, 1 -octadecanethiol, 1 ,8-dioctyithiol and 1 ,6-dioctylthiol.

6. The method according to one of the claim 1 , 2 or 4, wherein, the nonpolar organic s lv nt is selected from the group consist ing of octadecene, dodecane, hexadecane, octadecane, diphyl DT, diphyl THT, paraffin, dipenyl ether, clioctyl ether and dibenzyl ether.

7. The method according to one f the claim 1 , 2 or 4, wherein, the coating temperature is from 150 ^°C to 290 ^°C .

8. The method according to claim 7, wherein, the coating temperature is from 200 ^°C to 260 ^°C .

9. The method according to one f the claim 1 , 2 or 4, wherein, the reaction t ime is fr m 1 mi n to 4 h.

1 0. The method according to claim 9, wherein, the react ion time is from 15 min to 2 h.

11. The method for synthesizing core shel l nanopart icles, comprising the steps of:

mixing a core/shell nanoparticles solution prepared according to one of claim 1 to 10 with an organic solvent to obtain a suspension; and

separating the core/shell nanoparticles from the suspension.

12. The met hod according to claim 1 1 , wherein, washi ng the core/shell nanoparticles at least one time t remove the impurit ies.

13. The method according to one f the claim 1 1 r 1 2 , wherein, the organic solv ent is selected from the group consisting of methanol, ethanol, acetone, isopropyl alcohol and but a no I.