CN1631793A - Synthetic method of cadmium selenide and cadmium telluride quantum dots - Google Patents

Abstract

The invention belongs to a method for synthesizing cadmium selenide and cadmium telluride quantum dots by a solvothermal method. The method uses cadmium carboxylate or cadmium oxide as a cadmium source, and selenium powder and tellurium powder are respectively The molar ratio of selenium source and tellurium source, cadmium source and selenium source or tellurium source is 5:1-1:5, and trioctylphosphine is used to dissolve selenium powder and tellurium powder, oleic acid, hexadecylamine or trioctylamine Phosphine oxide is used as coating agent, the molar ratio of cadmium source and coating agent is 1:2-1:6, benzene, toluene, cyclohexane, n-hexane or n-heptane are used as solvent, and the concentration of cadmium source is 0.001-0.015M The reaction is completed by heating in an autoclave under the condition of 140-180°C for 0.8-16 hours, and the cadmium selenide and cadmium telluride quantum dots of different sizes are obtained by changing the reaction time. The synthesized cadmium selenide and cadmium telluride quantum dots have a narrow size distribution, showing a narrow fluorescence emission. Half width is 29-35nm.

Description

Synthetic method of cadmium selenide and cadmium telluride quantum dots

technical field

The invention belongs to a synthesis method of cadmium selenide and cadmium telluride quantum dots.

Background technique

Inorganic semiconductor nanocrystals differ from bulk materials in many physical properties. For example, due to the quantum confinement effect, II-VI semiconductor quantum dots (Semiconductor Quantum Dots), that is, semiconductor nanocrystals with three-dimensional dimensions smaller than their exciton Bohr diameter, exhibit size-dependent optical properties, and this property It can be applied to the preparation of light-emitting diodes, solar cells, single-electron lasers, biological labels and other fields. Therefore, the synthesis of size-controllable semiconductor quantum dots has become the focus of extensive research in recent years. In the synthesis of II-VI semiconductor quantum dots, the method of thermal decomposition of metal organic compound precursors developed by the Bawendi group is one of the methods widely used to synthesize high-quality semiconductor quantum dots (J.Am.Chem.Soc .1993, 115, 8706). However, the raw materials used in this method are highly toxic substances, which are easy to pollute the environment, and the experimental operation is complicated, which is not conducive to large-scale industrial production. For example, dimethyl cadmium used as a cadmium source is a highly toxic substance, which is easily decomposed when exposed to water, and is prone to explosion during operation. Therefore, the reaction must be completed under anaerobic and anhydrous conditions. In addition, in the method of preparing semiconductor quantum dots by thermal decomposition of metal-organic compounds, the nucleation and growth reactions of quantum dots need to be controlled at different temperatures, and the temperature is relatively high, at least above 250°C. It is not easy to control; and at least one of the reaction monomers in the reaction needs to be injected into the hot solution at a higher temperature in a very short time, which is difficult to achieve for large-scale industrial production. Since then, Peng et al. have improved the above experiments, using more stable cadmium sources such as cadmium oxide, cadmium carbonate, cadmium acetate, etc. to replace dimethyl cadmium, which is easy to decompose and explode at room temperature, and has high toxicity to prepare semiconductor quantum dots. (J. Am. Chem. Soc. 2001, 123, 183; Nano Lett. 2001, 1, 333). However, the nucleation and growth reactions of quantum dots in the reaction still need to be controlled at different high temperatures, and at least one reaction monomer still needs to be quickly injected into the hot solution with a higher nucleation temperature in a very short time . Therefore, this method is still not conducive to large-scale industrial production. There are also attempts to synthesize semiconductor quantum dots by solvothermal method (Chem.Commun.2001, 629-630), but the size distribution of the obtained products is relatively wide, showing a broad fluorescence emission spectrum. Therefore, it is highly necessary to explore new synthetic methods for semiconductor quantum dots that are conducive to large-scale industrial production.

Contents of the invention

The purpose of the present invention is to provide a synthesis method of cadmium selenide and cadmium telluride quantum dots.

In the method for preparing semiconductor nanocrystals by thermal decomposition of metal organic compounds, the nucleation and growth stages of nanocrystals are separated by selecting different temperatures. Generally, the nucleation temperature is higher than the growth temperature, and the purpose is to make the nanocrystal nucleus grow slowly after the rapid formation of the nanocrystal nucleus. Because small-sized nanocrystals are unstable, have high surface energy, and grow faster than large-sized nanocrystals, in the reaction using the solvothermal method, the autoclave provides a high enough temperature and pressure for the reaction, which is conducive to the perfection of the structure. the formation of single crystals. The temperature of the reaction in the autoclave is gradually increased from room temperature to the set reaction temperature. Although the two stages of nucleation and growth cannot be separated directly by adjusting the temperature, when the temperature rises to a certain value, a single When the monomer concentration is reduced below a critical value, the nucleation reaction will become the main process. The reaction monomer selected by the present invention has sufficient chemical stability, only a part of the monomer is consumed in the nucleation stage, and the remaining monomer is enough to provide the growth of the crystal nucleus, so the resulting nanocrystal will have a narrow size distribution .

The present invention selects the alkyl carboxylate cadmium or cadmium oxide containing 2 to 18 carbon atoms as the cadmium source, the selenium powder and the tellurium powder as the selenium source and the tellurium source respectively, and uses trioctylphosphine (TOP) to dissolve the selenium powder and the tellurium powder. Tellurium powder, oleic acid, hexadecylamine or trioctylphosphine oxide (TOPO) as coating agent, the molar ratio of cadmium source and selenium source or tellurium source is 5:1-1:5, the concentration of cadmium source is 0.001 -0.015M, the molar ratio of cadmium source and coating agent is 1:2-1:6, benzene, toluene, cyclohexane, n-hexane or n-heptane are solvents, and the reaction is carried out in an autoclave at a temperature of 140-180°C completed within.

In the preparation process, first heat the cadmium source, encapsulant and solvent at a certain temperature, such as 90±10°C, until it is colorless and transparent, and after cooling to below 40°C, mix it with newly prepared selenium or tellurium Trioctylphosphine (TOP) solutions are mixed and added to an autoclave lined with polytetrafluoroethylene. Seal the autoclave and put it into the furnace to heat at 140-180°C for 0.8-16 hours. After cooling, cadmium selenide will appear. Or cadmium telluride quantum dot generation.

The cadmium selenide and cadmium telluride quantum dots synthesized by the invention have a narrower size distribution, showing a narrower fluorescence emission peak. For example, the half-value width of the fluorescence emission peak of cadmium selenide quantum dots is 22-33 nm, and the half-value width of the fluorescence emission peak of cadmium telluride quantum dots is 29-35 nm. The required reaction temperature of this method is low, which is beneficial to reduce energy consumption; the operation is simple and does not require expensive and complicated equipment, so it is more suitable for industrial production.

A feature of the method of the present invention is that different sizes of cadmium selenide or cadmium telluride quantum dots can be obtained with different reaction times.

Description of drawings

Accompanying drawing 1 is that cadmium tetradecyl carboxylate and selenium powder mol ratio are 2: 1, and the concentration of cadmium tetradecyl carboxylate is 0.005M, and cadmium tetradecyl carboxylate and oleic acid mol ratio are 1: 4. The ultraviolet-visible (UV-Vis) spectrum and fluorescence (PL) spectrum of cadmium sulfide quantum dots of different sizes obtained under the condition of reaction temperature of 180°C for different reaction times, and the half-maximum width of the fluorescence emission peak is 22-31nm .

Accompanying drawing 2 is the transmission electron micrograph of the cadmium selenide quantum dot with diameter about 3.0nm.

Accompanying drawing 3 is that cadmium tetradecyl carboxylate and tellurium powder mol ratio are 2: 1, the concentration of cadmium tetradecyl carboxylate is 0.005M, and cadmium tetradecyl carboxylate and oleic acid mol ratio are 1: 4. The ultraviolet-visible (UV-Vis) spectrum and fluorescence (PL) spectrum of cadmium telluride quantum dots of different sizes obtained under the condition of reaction temperature of 180°C and different reaction times, the half-maximum width of the fluorescence emission peak is 29- 35nm

Detailed ways

Example 1:

Heat the mixture of 0.1mmol (0.0235g) cadmium acetate, 0.6mmol (0.2320g) TOPO and 20ml benzene at a temperature of 90±10°C until it is colorless and transparent. After cooling down to below 40°C, mix the solution with The solution of 0.05mmol (0.004g) selenium and 0.06g TOP is mixed and then added to a 30ml autoclave with Teflon lining. Seal the autoclave and put it in the furnace to heat at 160°C for 1 hour. After cooling, there will be selenium. Cadmium oxide quantum dot generation. The fluorescence emission peak position of its benzene solution at room temperature is around 521nm, and the half-maximum width is 31nm.

Example 2:

Heat a mixture of 1.0mmol (0.5671g) cadmium tetradecyl carboxylate, 3.2mmol (0.891g) oleic acid and 70ml toluene at a temperature of 90±10°C until it is colorless and transparent, and after cooling to below 40°C, Then this solution was mixed with a solution containing 5.0mmol (0.3948g) selenium and 4.3g TOP, and then they were added to a 100ml autoclave with a polytetrafluoroethylene lining, and the autoclave was sealed and heated at 180°C for 10 hours in a furnace. , after cooling, cadmium selenide quantum dots are formed. The fluorescence emission peak position of its toluene solution at room temperature is around 643nm, and the half-peak width is 26nm.

Example 3:

Heat the mixture of 0.6mmol (0.4071g) cadmium stearate, 1.2mmol (0.4640g) TOPO and 40ml cyclohexane at a temperature of 90±10°C until it is colorless and transparent, and after cooling to below 40°C, put This solution is mixed with a solution containing 0.6mmol (0.0474g) of selenium and 0.32g of TOP, and is added to a 50ml autoclave with a Teflon liner. After that, cadmium selenide quantum dots are formed. The fluorescence emission peak position of its cyclohexane solution at room temperature is around 494nm, and the half-peak width is 30nm.

Example 4:

Heat a mixture of 1.0mmol (0.1285g) cadmium oxide, 6.0mmol (1.4488g) HDA and 70ml n-hexane at a temperature of 90±10°C until it is colorless and transparent, and after cooling down to below 40°C, mix the solution with A solution containing 0.2mmol (0.0158g) of selenium and 0.15g of TOP is mixed and then added to a 100ml autoclave with a polytetrafluoroethylene liner. Cadmium Selenide Quantum Dot Generation. The fluorescence emission peak position of its n-hexane solution at room temperature is around 530nm, and the half-peak width is 33nm.

Example 5:

Heat the mixture of 0.02mmol (0.0114g) cadmium tetradecyl carboxylate, 3.2mmol (0.891g) oleic acid and 20ml n-heptane at a temperature of 90±10°C until it is colorless and transparent, and wait until it is cooled to below 40°C Then, mix this solution with a solution containing 0.04mmol (0.0032g) of selenium and 0.05g of TOP, and then add them together to a 30ml autoclave with a polytetrafluoroethylene lining, seal the autoclave and put it into a furnace to heat at 140°C After cooling for 5 hours, cadmium selenide quantum dots were formed. The fluorescence emission peak position of its n-heptane solution at room temperature is around 554nm, and the half-peak width is 32nm.

Embodiment 6:

Heat a mixture of 0.5mmol (0.0643g) cadmium oxide, 2.0mmol (0.5650g) oleic acid and 40ml toluene at a temperature of 90±10°C until it is colorless and transparent, and after cooling to below 40°C, mix the solution with The solution containing 0.25mmol (0.0319g) of tellurium and 0.5g of TOP is mixed and put into a 50ml autoclave with Teflon liner. Seal the autoclave and put it into the furnace and heat it at 180°C for 4 hours. After cooling, there will be Cadmium telluride quantum dot generation. The fluorescence emission peak position of its toluene solution at room temperature is around 648nm, and the half-peak width is 33nm.

Embodiment 7:

Heat the mixture of 0.02mmol (0.0136g) cadmium stearate, 0.04mmol (0.0155g) TOPO and 20ml n-hexane at a temperature of 90±10°C until it is colorless and transparent. The solution was mixed with a solution containing 0.1mmol (0.0128g) tellurium and 0.35g TOP, and then they were added to a 30ml autoclave with a polytetrafluoroethylene liner. There are cadmium telluride quantum dots generated. The fluorescence emission peak position of its n-hexane solution at room temperature is around 658nm, and the half-peak width is 35nm.

Embodiment 8:

Heat the mixture of 1.2mmol (0.6804g) cadmium tetradecyl carboxylate, 0.04mmol (0.0155g) TOPO and 80ml cyclohexane at a temperature of 90±10°C until it is colorless and transparent, and wait until it is cooled below 40°C , then mix this solution with a solution containing 0.24mmol (0.0307g) tellurium and 0.5g TOP, and add them together into a 100ml autoclave with a polytetrafluoroethylene lining, seal the autoclave and put it into the furnace to heat at 160°C for 5 Hours, cadmium telluride quantum dots are formed after cooling. The fluorescence emission peak position of its cyclohexane solution at room temperature is around 647nm, and the half-peak width is 33nm.

Embodiment 9:

Heat the mixture of 0.3mmol (0.0705g) cadmium acetate, 1.2mmol (0.4642g) TOPO and 20ml n-heptane at a temperature of 90±10°C until it is colorless and transparent, and then cool the solution below 40°C Mix it with a solution containing 0.15mmol (0.0192g) tellurium and 0.3g TOP, and add it together into a 50ml autoclave with a Teflon liner, seal the autoclave and put it into the furnace to heat at 140°C for 3 hours, and then it will be ready after cooling There are cadmium telluride quantum dots generated. The fluorescence emission peak position of its n-heptane solution at room temperature is around 622nm, and the half-peak width is 34nm.

Example 10:

Heat a mixture of 0.1mmol (0.0567g) cadmium tetradecyl carboxylate, 0.4mmol (0.1130g) oleic acid and 20ml toluene at a temperature of 90±10°C until it is colorless and transparent, and after cooling to below 40°C, Then this solution was mixed with a solution containing 0.05mmol (0.0064g) tellurium and 0.15gTOP, and then they were added to a 30ml autoclave with a polytetrafluoroethylene liner. The autoclave was sealed and heated at 180°C for 16 hours in a furnace. After cooling, cadmium telluride quantum dots are formed. The fluorescence emission peak position of its toluene solution at room temperature is around 661nm, and the half-peak width is 35nm.

Claims (3)

1, a kind of method for preparing cadmium selenide and cadmium telluride quantum dot, the alkyl carboxylic acid cadmium or the Cadmium oxide that it is characterized in that selecting containing 2～18 carbon atoms are the cadmium source, selenium powder and tellurium powder are respectively selenium source and tellurium source, and use tri octyl phosphine to dissolve selenium powder and tellurium powder, oleic acid, hexadecylamine or trioctyl phosphine oxide are coating agent, benzene, toluene, hexanaphthene, normal hexane or normal heptane are solvent, are reflected under 140-180 ℃ the temperature to finish in autoclave.

2, the method for preparing cadmium selenide and cadmium telluride quantum dot according to claim 1 is characterized in that the cadmium source: the mol ratio in selenium source or tellurium source is 5: 1-1: 5, and the concentration in cadmium source is 0.001-0.015M, the mol ratio of cadmium source and coating agent is 1: 2-1: 6.

3, the method for preparing cadmium selenide and cadmium telluride quantum dot according to claim 1 is characterized in that controlling the differential responses time to make the quantum dot of different size.

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