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.

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 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 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 C., preferred 200 to 280 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 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 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 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

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 C., for 30 min). Then, the solution was quickly heated to 230 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 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 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 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 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 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.