Preparation method of indium phosphide nanocrystal with high fluorescence quantum yield

Abstract

The invention discloses a preparation method of indium phosphide nanocrystals with high fluorescence quantum yield, and belongs to the field of semiconductor materials and nanotechnology. The method comprises the following steps: taking hypophosphite as a phosphorus source for synthesizing the indium phosphide nanocrystals, heating and purifying gas generated by the hypophosphite to obtain pure phosphine gas, introducing the phosphine gas into a fatty acid indium octadecene solution with the molar concentration of 0.05-0.2, and reacting for 10-30 minutes at the temperature of 160-300 DEG C to obtain the indium phosphide nanocrystals. And after the reaction is finished, alternately cleaning by adopting a first solvent and a second solvent to obtain the monodisperse indium phosphide nanocrystal. The indium phosphide nanocrystal synthesized by the invention has the advantages of narrow size distribution, adjustable absorption and emission peak positions, high fluorescence quantum yield (up to 96%) and the like. According to the method, the use of an expensive traditional organic phosphorus source, the dependence on inert gas and a low-temperature environment and the risk of generation and explosion of toxic gas are avoided, the technological process is safe and convenient, and the synthesis cost is low.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor materials and nanotechnology, and specifically relates to a green, safe and controllable synthesis method of indium phosphide nanocrystals with high fluorescence quantum yield. Background Art

[0002] Semiconductor nanocrystals, due to their unique band structure, exhibit excellent optical properties such as wide spectral absorption, narrow emission and high fluorescence quantum yield, and have broad application prospects in lighting display, laser devices, biomedicine, energy and photocatalysis. At present, the material system that has developed relatively mature and achieved certain commercial applications is II-VI semiconductor nanocrystals containing heavy metals such as cadmium and lead. However, heavy metal elements pose a serious threat to human health and the ecological environment, and also create obstacles to their industrial production and commercial applications. Therefore, it is of great significance to develop semiconductor nanocrystals that do not contain heavy metal elements.

[0003] Non-heavy metal III-V group InP semiconductors have a relatively narrow band gap (1.35 eV) and a large exciton Bohr radius (~10 nm), which allows their fluorescence emission peak to cover the blue to near-infrared band, thus having great development potential. However, the chemical synthesis of indium phosphide nanocrystals is difficult, mainly due to the lack of green, safe and controllable phosphorus sources. Currently, the phosphorus sources used for the synthesis of indium phosphide nanocrystals can be divided into two categories. The first type of phosphorus source is a compound containing negative trivalent phosphorus, such as tri(trimethylsilyl)phosphine (J.Phys.Chem.,1994,98(19):4966-4969.Nature,2019,575,634-638), tri(trimethylgermyl)phosphine (Angew.Chem.,Int.Ed.Engl,2015,54(48):14299-303.) and calcium phosphide (Mater.chem.phys.2006,96,494-497.). This type of phosphorus source has high reactivity, and negative trivalent phosphorus can directly react with positive trivalent indium precursor to form indium phosphide nanocrystals. Among them, tri(trimethylsilyl)phosphine is currently the most commonly used phosphorus precursor for the synthesis of indium phosphide nanocrystals. However, this phosphorus source is expensive, and because negative trivalent phosphorus has a strong reducibility, it must be stored and operated in a low-temperature environment of an inert gas atmosphere, otherwise it will produce flammable and explosive highly toxic gases, which is extremely dangerous. Therefore, this type of phosphorus source is difficult to apply to large-scale industrial production. The second type is compounds containing higher valence phosphorus elements, such as white phosphorus (Chem. Mater. 2017, 29, 4236), tri(dimethylamino)phosphine (Chem. Mater., 2015, 27 (13): 4893-4898), phosphorus trichloride (Angew. Chem., Int. Ed. 2008, 47, 3540), etc. The valence state of the phosphorus element in this type of phosphorus source is higher than negative trivalent, and it must be pre-reacted to produce negative trivalent phosphorus elements before it can react with indium precursors to generate indium phosphide nanocrystals. This results in its generally low reactivity, and some precursors also need to add highly dangerous reducing agents (such as metallic sodium) to assist the reduction of phosphorus elements to negative trivalent. The most studied one is tri(dimethylamino)phosphine, which is more stable than tri(trimethylsilyl)phosphine, but still has the risk of inhalation poisoning and requires inert gas atmosphere for storage and operation. At the same time, due to its low activity, it is difficult to obtain uniform size distribution of indium phosphide nanocrystals synthesized using tri(dimethylamino)phosphine.

[0004] The high cost, high risk and unsatisfactory reactivity of the above-mentioned phosphorus sources have greatly increased the difficulty of R&D and production cost of InP nanocrystals, becoming an obstacle to the industrial production and commercial application of InP nanocrystals. Therefore, developing new phosphorus sources with low cost and high safety, and designing a simple synthesis route, are of vital importance to achieve green and controllable synthesis of InP nanocrystals. Summary of the invention

[0005] In view of the challenges of high cost, high risk and unsatisfactory reaction activity of the currently commonly used phosphorus sources in the synthesis of indium phosphide nanocrystals, the present invention designs a green, safe and controllable synthesis method of indium phosphide nanocrystals.

[0006] The present invention is achieved through the following technical scheme: a method for preparing indium phosphide nanocrystals with high fluorescence quantum yield, specifically comprising the following steps:

[0007] (1) placing anhydrous indium acetate and a long-chain fatty acid in a molar ratio of 1:2 to 1:4 in a four-necked flask, heating, stirring, and degassing to obtain fatty acid indium; adding octadecene to obtain an indium precursor solution with a concentration of 0.05 to 0.2 molarity, and keeping it warm at 100 to 120° C. for later use;

[0008] (2) placing hypophosphite and octadecene in a three-necked flask, stirring, and degassing to obtain a phosphorus precursor; the molar ratio of hypophosphite to fatty acid indium is 1:1 to 4:1;

[0009] (3) The phosphorus precursor is heated to 300° C. to 320° C., and the hypophosphite is decomposed to release phosphine gas, which is then passed into the indium precursor solution after passing through a calcium chloride drying tube and kept warm for 5 to 10 minutes. The temperature in the three-necked flask is then lowered to room temperature and the valve is closed;

[0010] (4) raising the temperature of the indium precursor to 160-300° C., keeping the temperature for 10-30 minutes, stopping the reaction, and lowering the temperature in the four-necked flask to room temperature;

[0011] (5) adding the first solvent, centrifuging the reaction solution, repeating the centrifugation with the second solvent and the first solvent, and then dissolving the indium phosphide nanocrystals in the second solvent to obtain a solution;

[0012] (6) Add 10% to 15% by mass of hydrofluoric acid acetone solution and react under ultraviolet light for 30 minutes to 50 minutes to passivate the surface defects of indium phosphide nanocrystals and improve the fluorescence quantum yield. Furthermore, one of the three-necked flasks containing hypophosphite is connected to a rubber hose with a valve and leads to a drying tube filled with anhydrous calcium chloride. The outlet end of the drying tube is connected to a rubber hose with a Luer connector, and the Luer connector is connected to a stainless steel needle. The needle is inserted into the four-necked flask of indium precursor, and the needle tip is placed below the liquid surface.

[0013] Further, the hypophosphite is one of ammonium hypophosphite, sodium hypophosphite, potassium hypophosphite, zinc hypophosphite or calcium hypophosphite;

[0014] Further, the long-chain fatty acid is one of caprylic acid, lauric acid, palmitic acid, myristic acid, stearic acid or oleic acid;

[0015] Furthermore, the first solvent is one of ethanol, isopropanol, acetonitrile or acetone; the second solvent is one of n-hexane, n-octane, chloroform, dichloromethane or toluene. The beneficial effects of the present invention are:

[0016] (1) Using hypophosphite as a phosphorus precursor to synthesize indium phosphide nanocrystals is safer and more convenient than traditional synthesis methods. The synthesis cost is reduced by three orders of magnitude, which is conducive to large-scale production.

[0017] (2) The size distribution of synthesized indium phosphide nanocrystals is narrow and the absorption peak position can be controlled.

[0018] The invention adopts hypophosphite as a phosphorus source to synthesize indium phosphide nanocrystals, and synthesizes indium phosphide nanocrystals with narrow size distribution, adjustable absorption and emission peaks and high fluorescence quantum yield (96%). Hypophosphite is cheap and easy to store, thereby reducing the synthesis cost and improving the safety and operability of the experiment, especially the synthesis cost is reduced to one thousandth of that of using a traditional phosphorus source. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the reaction device for synthesizing indium phosphide nanocrystals from hypophosphite.

[0020] Figure 2 is the absorption spectrum of the indium phosphide nanocrystals in Examples 1-5.

[0021] Figure 3 This is an electron micrograph of indium phosphide nanocrystals synthesized by hypophosphite in Example 3.

[0022] Figure 4 It is the photoluminescence emission spectra of the indium phosphide nanocrystals synthesized by hypophosphite and the indium phosphide nanocrystals synthesized by tri(dimethylamino)phosphine in the comparative example. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the following detailed description of the present invention. Those skilled in the art can fully understand the present invention without the description of these details.

[0025] A method for preparing indium phosphide nanocrystals with high fluorescence quantum yield comprises the following steps:

[0026] (1) Anhydrous indium acetate and a long-chain fatty acid are placed in a four-necked flask at a molar ratio of 1:2 to 1:4, heated, stirred, and degassed to obtain fatty acid indium, and octadecene is added to obtain an indium precursor solution with a concentration of 0.05 to 0.2 molar, which is kept warm at 100 to 120° C. for later use; the long-chain fatty acid is one of caprylic acid, lauric acid, palmitic acid, myristic acid, stearic acid, or oleic acid.

[0027] (2) Hypophosphite and octadecene are placed in a three-necked flask, stirred, and degassed to obtain a phosphorus precursor; the molar ratio of hypophosphite to fatty acid indium is 1:1 to 4:1; for example, 1:1, 2:1, 3:1, 4:1, etc.; the hypophosphite is one of ammonium hypophosphite, sodium hypophosphite, potassium hypophosphite, zinc hypophosphite, or calcium hypophosphite.

[0028] (3) The phosphorus precursor is heated to 300° C. to 320° C., and the hypophosphite is decomposed to release phosphine gas, which is then passed into the indium precursor solution after passing through a calcium chloride drying tube and kept warm for 5 to 10 minutes. The temperature in the three-necked flask is then lowered to room temperature and the valve is closed;

[0029] In certain specific embodiments, one of the three-necked flasks containing hypophosphite is connected to a rubber hose with a valve and leads to a drying tube filled with anhydrous calcium chloride. The gas outlet of the drying tube is connected to a rubber hose with a Luer connector, and the Luer connector is connected to a stainless steel needle. The needle is inserted into a four-necked flask containing an indium precursor, with the needle tip placed below the liquid surface.

[0030] (4) raising the temperature of the indium precursor to 160-300° C., keeping the temperature for 10-30 minutes, stopping the reaction, and lowering the temperature in the four-necked flask to room temperature;

[0031] (5) adding a first solvent, centrifuging the reaction solution, repeating the centrifugation with a second solvent and the first solvent, and then dissolving the indium phosphide nanocrystal solution in the second solvent; the first solvent is one of ethanol, isopropanol, acetonitrile or acetone; the second solvent is one of n-hexane, n-octane, chloroform or toluene.

[0032] (6) adding 10% to 15% by mass of a hydrofluoric acid acetone solution and reacting under ultraviolet light for 30 to 50 minutes to passivate surface defects of the indium phosphide nanocrystals and improve the fluorescence quantum yield.

[0033] Example 1

[0034] 0.5 mmol of anhydrous indium acetate and 2 mmol of myristic acid are placed in a four-necked flask, heated, stirred, and degassed to obtain indium myristic acid; 10 ml of octadecene is added to obtain a 0.05 mol indium precursor solution, which is kept warm at 110°C for standby use. 0.5 mmol of ammonium hypophosphite and 10 ml of octadecene are placed in another three-necked flask, stirred, and degassed to obtain a phosphorus precursor. One of the three-necked flasks is connected to a rubber hose with a valve, and leads to a drying tube filled with anhydrous calcium chloride. The outlet end of the drying tube is connected to a rubber hose with a Luer connector, and the Luer connector is connected to a stainless steel needle tube. Insert the needle tube into the four-necked flask of the indium precursor, and place the needle tip below the liquid surface. The phosphorus precursor is heated to 300°C, and the ammonium hypophosphite decomposes to release phosphine gas. Open the valve to allow the phosphine gas to pass through the drying tube and enter the indium precursor solution. Keep warm for 5 minutes, lower the temperature in the three-necked flask to room temperature and close the valve. The indium precursor was heated to 160°C and kept warm for 10 minutes to stop the reaction, and the temperature in the four-necked flask was lowered to room temperature. Acetonitrile was added, the reaction solution was centrifuged, and then centrifuged repeatedly with acetonitrile and toluene, and then dissolved in toluene to obtain an indium phosphide nanocrystal solution.

[0035] Table 1 Absorption peak position and diameter of nanocrystals

[0036]

[0037] Example 2

[0038] Place 1 mmol of anhydrous indium acetate and 2 mmol of palmitic acid in a four-necked flask, heat, stir, and degas. Add 10 ml of octadecene to obtain a 0.1 mol indium precursor solution, and keep it warm at 110°C for use. Place 2 mmol of sodium hypophosphite and 10 ml of octadecene in another three-necked flask, stir, and degas to obtain a phosphorus precursor. One of the three-necked flask mouths is connected to a rubber hose with a valve, and leads to a drying tube filled with anhydrous calcium chloride. The outlet end of the drying tube is connected to a rubber hose with a Luer connector, and the Luer connector is connected to a stainless steel needle tube. Insert the needle tube into the four-necked flask of the indium precursor, and place the needle tip below the liquid surface. Heat the phosphorus precursor to 310°C, and the sodium hypophosphite decomposes to release phosphine gas. Open the valve to allow the phosphine gas to pass through the drying tube and enter the indium precursor solution. Keep warm for 5 minutes, lower the temperature in the three-necked flask to room temperature and close the valve. The indium precursor was heated to 200°C, kept warm for 15 minutes, the reaction was stopped, and the temperature in the four-necked flask was lowered to room temperature. Ethanol was added, the reaction solution was centrifuged, and then centrifuged repeatedly with ethanol and hexane, and then dissolved in hexane to obtain an indium phosphide nanocrystal solution. A 10% mass fraction of hydrofluoric acid acetone solution was added to the nanocrystal solution, and the reaction was allowed to react under ultraviolet light for 30 minutes.

[0039] Table 2 Absorption peak, fluorescence emission peak, fluorescence quantum yield and diameter of nanocrystals

[0040]

[0041]

[0042] Example 3

[0043] 1.5 mmol of anhydrous indium acetate and 3 mmol of lauric acid are placed in a four-necked flask, heated, stirred, and degassed. 10 ml of octadecene is added to obtain a 0.15 mol indium precursor solution, which is kept warm at 110°C for use. 4.5 mmol of zinc hypophosphite and 10 ml of octadecene are placed in another three-necked flask, stirred, and degassed to obtain a phosphorus precursor. One of the three-necked flasks is connected to a rubber hose with a valve, and leads to a drying tube filled with anhydrous calcium chloride. The outlet end of the drying tube is connected to a rubber hose with a Luer connector, and the Luer connector is connected to a stainless steel needle tube. Insert the needle tube into the four-necked flask of the indium precursor, and place the needle tip below the liquid surface. Heat the phosphorus precursor to 320°C, and the zinc hypophosphite decomposes to release phosphine gas. Open the valve to allow the phosphine gas to pass through the drying tube and enter the indium precursor solution. Keep warm for 5 minutes, lower the temperature in the three-necked flask to room temperature and close the valve. The indium precursor was heated to 240°C, kept warm for 20 minutes, the reaction was stopped, and the temperature in the four-necked flask was lowered to room temperature. Isopropanol was added, the reaction solution was centrifuged, and the centrifugation was repeated with isopropanol and n-octane, and then dissolved in n-octane to obtain an indium phosphide nanocrystal solution. A 10% mass fraction of hydrofluoric acid acetone solution was added to the nanocrystal solution, and the reaction was allowed to react under ultraviolet light for 30 minutes.

[0044] Table 3 Absorption peak, fluorescence emission peak, fluorescence quantum yield and diameter of nanocrystals

[0045]

[0046] Example 4

[0047] 2 mmol of anhydrous indium acetate, 4 mmol of oleic acid and 2 mmol of octanoic acid are placed in a four-necked flask for heating, stirring and degassing. 10 ml of octadecene is added to obtain a 0.2 mol indium precursor solution, which is kept warm at 110°C for use. 8 mmol of potassium hypophosphite and 10 ml of octadecene are placed in another three-necked flask for stirring and degassing to obtain a phosphorus precursor. One of the three-necked flask mouths is connected to a rubber hose with a valve and leads to a drying tube filled with anhydrous calcium chloride. The outlet end of the drying tube is connected to a rubber hose with a Luer connector, and the Luer connector is connected to a stainless steel needle tube. Insert the needle tube into the four-necked flask of the indium precursor, and place the needle tip below the liquid surface. Heat the phosphorus precursor to 310°C, and the potassium hypophosphite decomposes to release phosphine gas. Open the valve to allow the phosphine gas to pass through the drying tube and enter the indium precursor solution. Keep warm for 5 minutes, lower the temperature in the three-necked flask to room temperature and close the valve. The indium precursor was heated to 280°C, kept warm for 25 minutes, the reaction was stopped, and the temperature in the four-necked flask was lowered to room temperature. Acetone was added, the reaction solution was centrifuged, and then centrifuged repeatedly with acetone and chloroform, and then dissolved in chloroform to obtain an indium phosphide nanocrystal solution. A 10% mass fraction of hydrofluoric acid acetone solution was added to the nanocrystal solution, and the reaction was allowed to react under ultraviolet light for 30 minutes.

[0048] Table 4 Absorption peak, fluorescence emission peak, fluorescence quantum yield and diameter of nanocrystals

[0049]

[0050] Example 5

[0051] 2 mmol of anhydrous indium acetate, 2 mmol of stearic acid and 4 mmol of octanoic acid were placed in a four-necked flask for heating, stirring and degassing. 10 ml of octadecene was added to obtain a 0.2 mol indium precursor solution, which was kept warm at 110°C for use. 8 mmol of calcium hypophosphite and 10 ml of octadecene were placed in another three-necked flask for stirring and degassing to obtain a phosphorus precursor. One of the three-necked flasks was connected to a rubber hose with a valve and led to a drying tube filled with anhydrous calcium chloride. The outlet end of the drying tube was connected to a rubber hose with a Luer connector, and the Luer connector was connected to a stainless steel needle tube. The needle tube was inserted into the four-necked flask of the indium precursor, and the needle tip was placed below the liquid surface. The phosphorus precursor was heated to 320°C, and the calcium hypophosphite decomposed to release phosphine gas. The valve was opened to allow the phosphine gas to pass through the drying tube and enter the indium precursor solution. Keep warm for 5 minutes, lower the temperature in the three-necked flask to room temperature and close the valve. The indium precursor was heated to 300°C, kept warm for 30 minutes, the reaction was stopped, and the temperature in the four-necked flask was lowered to room temperature. Acetone was added, the reaction solution was centrifuged, and then centrifuged repeatedly with acetone and dichloromethane, and then dissolved in dichloromethane to obtain an indium phosphide nanocrystal solution. A 10% mass fraction of hydrofluoric acid acetone solution was added to the nanocrystal solution, and the reaction was allowed to react under ultraviolet light for 30 minutes.

[0052] Table 5 Absorption peak, fluorescence emission peak, fluorescence quantum yield and diameter of nanocrystals

[0053]

[0054] Comparative Example

[0055] In order to compare the superiority of the present invention using hypophosphite to synthesize indium phosphide nanocrystals, a comparative example uses tri(dimethylamino)phosphine to synthesize indium phosphide nanocrystals, and compares it with the synthesis of indium phosphide nanocrystals by hypophosphite (taking Example 3 as an example). The preparation process of indium phosphide nanocrystals synthesized by tri(dimethylamino)phosphine is referred to Example 3, except that fatty acid indium is replaced with indium chloride, 10 ml of octadecene is replaced with oleylamine, and hot injection of tri(dimethylamino)phosphine is used for synthesis. The results show that compared with the synthesis of indium phosphide nanocrystals by tri(dimethylamino)phosphine, the size distribution of indium phosphide nanocrystals synthesized by the present invention using hypophosphite is narrower, and the fluorescence quantum yield is higher, because the phosphine produced by the decomposition of hypophosphite has higher reactivity, which promotes the uniform nucleation of indium phosphide nanocrystals and improves the crystal quality.

[0056] Table 6 Fluorescence quantum yield and diameter of nanocrystals

[0057]

[0058] Although several embodiments of the present invention have been given herein, those skilled in the art should understand that the embodiments herein may be modified without departing from the spirit of the present invention. The above embodiments are merely exemplary and should not be used as a limitation on the scope of the claims of the present invention.

Claims

1. A method for preparing indium phosphide nanocrystals with high fluorescence quantum yield, characterized in that: The specific steps include: (1) Anhydrous indium acetate and long-chain fatty acid are placed in a four-necked flask at a molar ratio of 1:2 to 1:4, heated, stirred, and degassed to obtain fatty acid indium; octadecene is added to obtain an indium precursor solution with a concentration of 0.05 to 0.2 molarity, and the solution is kept warm at 100 to 120° C. for later use; (2) placing hypophosphite and octadecene in a three-necked flask, stirring and degassing to obtain a phosphorus precursor; the molar ratio of hypophosphite to fatty acid indium is 1:1 to 4:1; (3) Raise the temperature of the phosphorus precursor to 300°C~320°C, and the hypophosphite decomposes to release phosphine gas, which is then passed into the indium precursor solution after passing through a calcium chloride drying tube. Keep the temperature for 5~10 minutes, lower the temperature in the three-necked flask to room temperature, and close the valve; (4) Raise the temperature of the indium precursor to 160-300°C, keep it warm for 10-30 minutes, stop the reaction, and lower the temperature in the four-necked flask to room temperature; (5) Adding the first solvent, centrifuging the reaction solution, repeating the centrifugation with the first solvent and the second solvent, and then dissolving the indium phosphide nanocrystal into the second solvent to obtain an indium phosphide nanocrystal solution.

2. The method for preparing indium phosphide nanocrystals with high fluorescence quantum yield according to claim 1, characterized in that: The hypophosphite is one of ammonium hypophosphite, sodium hypophosphite, potassium hypophosphite, zinc hypophosphite or calcium hypophosphite.

3. The method for preparing indium phosphide nanocrystals with high fluorescence quantum yield according to claim 1, characterized in that: The long-chain fatty acid is one of caprylic acid, lauric acid, palmitic acid, myristic acid, stearic acid or oleic acid.

4. The method for preparing indium phosphide nanocrystals with high fluorescence quantum yield according to claim 1, characterized in that: The first solvent is one of ethanol, isopropanol, acetonitrile or acetone.

5. The method for preparing indium phosphide nanocrystals with high fluorescence quantum yield according to claim 1, characterized in that: The second solvent is one of n-hexane, n-octane, chloroform, toluene or dichloromethane.

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