CN100497517C - Method for preparing core-shell quantum point of semiconductor in II VI families capable of adjusting and controlling wavelength of fluorescence - Google Patents

Abstract

The invention discloses a method for preparing II-VI semiconductor core-shell quantum dots with adjustable fluorescence wavelength. The method is to coat the CdSe quantum dots with alternate ion implantation technology, and then prepare the prepared CdSe nuclear quantum dots. Expose to air at high temperature, adjust the fluorescence of nuclear quantum dots according to the exposure time, and then achieve coating in an anhydrous and oxygen-free reaction atmosphere. Under certain temperature conditions, the longer the nuclear CdSe sample is in contact with the atmosphere, the shorter the fluorescence wavelength of the nuclear quantum dots. The advantages of the present invention are: the preparation of nuclear quantum dots is simplified, and only a single red-emitting quantum dot core is used as a raw material to coat core-shell quantum dots emitting red, yellow, and green fluorescence respectively; although nuclear quantum dots are fluorescent blue After shifting, the defect state luminescence appears, but after coating CdS, the defect state luminescence can be basically eliminated.

Description

Preparation method of II-VI semiconductor core-shell quantum dots with adjustable fluorescence wavelength

technical field

The invention relates to a preparation method of II-VI group semiconductor core-shell quantum dots, in particular to a preparation method of CdSe/CdS/ZnS core-shell quantum dots, which can regulate the luminescent fluorescence wavelength.

Background technique

In the past two decades, due to the special physical properties of semiconductor quantum dots, they have been favored by many scholars, and their preparation methods have been developed rapidly. One of the hotspots, the preparation methods of II-VI group CdSe quantum dots are emerging in an endless stream, because CdSe quantum dots have many unique properties: only need to control the particle size of CdSe, you can get the emission wavelength almost covering the entire visible light band. Fluorescence; the full width at half maximum (FWHM) of the fluorescence peak is very narrow, generally around 20nm-30nm; after coating the same family of quantum dots with a wider band gap such as ZnS or CdS, the fluorescence efficiency can be increased to 60%-80%, And the ability to resist fluorescence decay has been greatly enhanced; it has a large surface-to-volume ratio, and the fluorescence is extremely sensitive to the chemical environment. Therefore, CdSe/ZnS core-shell quantum dots have very attractive development prospects in many fields such as light-emitting diodes, nano-lasers, solar cells, nano-biological probes, and life coding.

Using alternate ion implantation (SILAR) method to realize CdSe/ZnS core-shell quantum dots, compared with the traditional method of slowly dropping (wise drop), its advantages are: the thickness of the cladding layer can be precisely controlled; Layer cladding, such as CdSe/CdS/Cd _0.5 Zn _0.5 S/ZnS, minimizes the effects of lattice mismatch. However, there are two disadvantages in this method: first, the coating temperature requirement is relatively high, and the smaller quantum dots will grow again before reaching this temperature, and the fluorescence will be red-shifted, so it is difficult to achieve coating of smaller quantum dots Another shortcoming is that core-shell quantum dots that emit different colors of fluorescence require correspondingly different core quantum dot raw materials.

Contents of the invention

Based on the above-mentioned defects in the prior art, the purpose of the present invention is to propose a single quantum dot CdSe that emits red light as the core, and the outer coating of CdS/ZnS can realize the core that emits red, yellow, and green fluorescence respectively. Preparation method of shell quantum dots.

In order to achieve the above object, the technical solution of the present invention is: on the basis of using alternate ion implantation technology to coat CdSe quantum dots, the prepared CdSe nuclear quantum dots are exposed to the air at high temperature, and the nuclear quantum dots are aligned according to the exposure time. Adjust the fluorescent point, and then realize the coating in an anhydrous and anaerobic reaction atmosphere. The preparation steps are as follows:

A. Preparation of cadmium precursor solution. Cadmium oxide and oleic acid are dissolved in octadecene at 240-260°C under the condition of argon, and the amounts of cadmium oxide, oleic acid and octadecene added are 0.62-1.56% and 16.4% by mass percentage respectively. —27.0%, 82.98—71.44%, stored in a water bath at 80—90°C.

B. Preparation of zinc precursor solution. Zinc oxide and oleic acid are dissolved in octadecene at 300-310°C under the condition of argon, and the amounts of zinc oxide, oleic acid and octadecene added are 0.4-1.0% and 16.5% by mass percentage respectively. -27.1%, 83.1-71.9%, stored in a water bath at 80-90°C.

C. Preparation of sulfur precursor solution. Under the condition of argon, the sulfur powder is dissolved in octadecene at 160-180°C, and the amount of sulfur powder and octadecene added is 0.2-0.4% and 99.6-99.8% respectively by mass percentage. Store at room temperature.

D. Preparation of core CdSe. Put cadmium oxide, oleic acid and octadecene into a reaction vessel, such as a three-neck flask. The mass percentages of cadmium oxide, oleic acid and octadecene added are 1.13-1.3%, 10.5-12.7% and 88.37-86% respectively. Stir and heat under the condition of argon to 240-260°C until the cadmium oxide is completely dissolved, and then cool down to room temperature, and use it as a cadmium stock solution for later use.

In a sealed container bottle, dissolve the selenium powder in a mixture of tri-n-butylphosphine and octadecene. The mass percentages of the added selenium powder, tri-n-butylphosphine and octadecene are respectively 4.1-8.2%, 28.3-32.7%, 67.3-59.1%, which are used as the selenium stock solution for later use.

In the above cadmium stock solution, add octadecylamine and tri-n-octylphosphine oxide, the mass percentage of octadecylamine added is 33.3-41.6%, and the mass percentage of tri-n-octylphosphine oxide is 8.3%- 16.6%. Under the condition of argon, heat the reaction vessel to 280-300°C, then inject the selenium stock solution into it, keep it at 240-270°C for 3-10min, remove the heating device and cool the product to 80°C , Inject acetone for precipitation 2-3 times, and centrifuge to collect the precipitate.

Put the precipitate collected by centrifugation into an airtight container, and add octadecene and octadecylamine. The amount of octadecene and octadecylamine added is respectively 50-66.6% and 33.3-50% by mass percentage, because the amount of precipitate added is about 10% of the total mass of octadecene and octadecylamine One-thousandth, so it is ignored. Then, under the condition of argon, heat to 180-220 ℃. After the temperature is stabilized, open the reaction vessel to expose the sample to the atmosphere, take out the samples in batches within 2-30 minutes, put them into different reaction vessels, and restore the argon gas flow.

E. Coating CdS/ZnS on core CdSe samples exposed to the atmosphere for different times. Calculate the volume of precursor solution needed for coating according to the amount of core CdSe. First coat the first layer of CdS: inject the cadmium precursor liquid, after 5-10 minutes, inject the sulfur precursor liquid, anneal for 10-30 minutes, the annealing temperature is 230-240 ° C; then coat the second layer of ZnS, coating conditions and The first layer is the same, so reciprocating, and finally obtain the CdSe/CdS/ZnS core-shell structure quantum dots with the required number of coating layers.

The present invention regulates the fluorescence basket shift of nuclear quantum dots by adjusting the contact time between the nuclear CdSe sample and the atmosphere: under a certain temperature condition, the longer the nuclear CdSe sample is in contact with the atmosphere, the shorter the fluorescence wavelength of the nuclear quantum dots is, and the defect state emits light appear. According to the number of layers of coated CdS or ZnS, the fluorescence red shift of core-shell quantum dots can be adjusted.

The advantages of the present invention are:

1: The preparation of nuclear quantum dots is simplified. Only a single red-emitting quantum dot core is used as a raw material to coat core-shell quantum dots that emit red, yellow, and green fluorescence respectively, and quantum dots with larger sizes that emit red light The reproducibility of nuclei preparation is very good,

2: Although the defect state luminescence occurs after the blue shift of nuclear quantum dot fluorescence, after coating CdS, the defect state luminescence can be basically eliminated, and the full width at half maximum and fluorescence efficiency are still acceptable.

Description of drawings

Fig. 1 is the fluorescence spectrogram of embodiment 1. Numbers 1-9 are the fluorescence spectra of the nuclear CdSe samples after 0 minutes, 2 minutes, 5 minutes, 8 minutes, 11 minutes, 16 minutes, 20 minutes, 25 minutes and 30 minutes respectively.

The No. 9 spectrum in Figure 2 is the No. 9 spectrum in Figure 1, the No. 10 fluorescence spectrum is the spectrum of a layer of CdS sample coated on the No. 9 sample, and the No. 11 is continued coating on the No. 10 sample Spectra of a layer of ZnS sample.

Figure 3 is a layer of coating outside the core CdSe quantum dots The trend diagram of the fluorescence peak wavelength of CdSe/CdS/ZnS core-shell quantum dots changing with the time when the core CdSe quantum dots are exposed to the atmosphere.

Detailed ways

Example 1

A. Preparation of cadmium precursor solution. Cadmium oxide and oleic acid are dissolved in octadecene at 250°C under the condition of argon, and the amounts of cadmium oxide, oleic acid, and octadecene added are 1.3%, 21.7%, and 77.0% by mass percentage, respectively. , stored in a water bath at 80°C;

B. Preparation of zinc precursor solution. Zinc oxide and oleic acid are dissolved in octadecene at 300°C under the condition of argon, and the amounts of zinc oxide, oleic acid and octadecene added are 0.8%, 21.82%, and 77.38% by mass percentage, respectively. , stored in a water bath at 80°C;

C. Preparation of sulfur precursor solution. Under the same argon gas condition, the sulfur powder is dissolved in octadecene at 170°C, the amount of sulfur powder and octadecene added is 0.32% and 99.68% respectively by mass percentage, and it is stored at room temperature;

D. Preparation of core CdSe. The specific process is as follows: Weigh 0.3mmol cadmium oxide, put it into a three-necked bottle with argon gas with 0.5ml oleic acid and 3.8ml octadecene, stir and heat to 260°C until the cadmium oxide is completely dissolved, stop heating after completion, as The stock solution of cadmium is ready for use.

Dissolve 1.8 mmol of selenium powder in a mixed solution of 0.7 ml of tri-n-butylphosphine and 1.3 ml of octadecene in an anhydrous and oxygen-free glove box to obtain a stock solution of selenium and put it into a sealed pear-shaped bottle for use.

After the stock solution of cadmium is lowered to room temperature, add 2.5g of octadecylamine and 0.5g of tri-n-octylphosphine oxide, and immediately inject the stock solution of selenium after heating to 280°C, keep it at 255°C for 5min, then remove After the heating device was cooled to 80°C, acetone was injected twice for sedimentation, and the precipitate was collected by centrifugation.

Put the precipitate collected by centrifugation into an airtight container, and add octadecene and octadecylamine. The amounts of octadecene and octadecylamine added are respectively 60% and 40% by mass percentage, and then heated to 200° C. under the condition of argon. After the temperature is stabilized, open the reaction vessel to expose the samples to the atmosphere. Take out the samples in nine batches at 0 minutes, 2 minutes, 5 minutes, 8 minutes, 11 minutes, 16 minutes, 20 minutes, 25 minutes, and 30 minutes. In the reaction vessel, and restore the argon.

CdSe/CdS/ZnS核壳结构量子点荧光峰波长随着核CdSe量子点接触大气时间变化的趋势图。E. CdS/ZnS were respectively coated on the core CdSe samples exposed to the atmosphere for different times. First coat the first layer of CdS: inject the cadmium precursor liquid, and after 7 minutes, inject the sulfur precursor liquid, anneal for 20 minutes, and the annealing temperature is 235°C; then coat the second layer of ZnS, the coating conditions are the same as the first layer, so reciprocating, Figure 3 is the core CdSe quantum dots and cladding

The trend diagram of the fluorescence peak wavelength of CdSe/CdS/ZnS core-shell quantum dots changing with the time when the core CdSe quantum dots are exposed to the atmosphere.

Claims (1)

1. A method for preparing II-VI group semiconductor core-shell quantum dots capable of regulating fluorescence wavelength, characterized in that the preparation steps are as follows: A. Preparation of cadmium precursor solution Cadmium oxide and oleic acid are dissolved in octadecene at 240-260°C under the condition of argon, and the amount of cadmium oxide, oleic acid and octadecene is added in mass percentage Measured at 0.62-1.56%, 16.4-27.0%, 82.98-71.44%, respectively, stored in a water bath at 80-90°C; B. Preparation of zinc precursor solution Zinc oxide and oleic acid are dissolved in octadecene at 300-310°C under the condition of argon, and the amount of zinc oxide, oleic acid and octadecene is added in mass percentage Measured at 0.4-1.0%, 16.5-27.1%, 83.1-71.9%, respectively, stored in a water bath at 80-90°C; C. Preparation of sulfur precursor solution Under the condition of argon, sulfur powder is dissolved in octadecene at 160-180°C, and the amount of sulfur powder and octadecene added is 0.2- 0.4%, 99.6-99.8%, stored at room temperature; D. Preparation of nuclear CdSe Put cadmium oxide, oleic acid and octadecene into the reaction vessel, and the mass percentages of cadmium oxide, oleic acid and octadecene added are 1.13-1.3%, 10.5-12.7%, 88.37-86%, stirring and heating to 240-260°C under the condition of argon until the cadmium oxide is completely dissolved, then lowered to room temperature, and used as a cadmium stock solution for later use; In a sealed container bottle, dissolve the selenium powder in the mixed solution of tri-n-butylphosphorus and octadecene, and the mass percentages of selenium powder, tri-n-butylphosphorus and octadecene are 4.1-8.2% respectively , 28.3-32.7%, 67.3-59.1%, stand-by as the stock solution of selenium; In the above cadmium stock solution, add octadecylamine and tri-n-octylphosphine oxide, the mass percentage of octadecylamine added is 33.3-41.6%, and the mass percentage of tri-n-octylphosphine oxide is 8.3%- 16.6%, under the condition of argon, heat the reaction vessel to 280-300°C, then inject the stock solution of selenium into it, keep it at the temperature of 240-270°C for 3-10min, remove the heating device to cool the product to After 80°C, inject acetone for precipitation 2-3 times, and centrifuge to collect the precipitate; Put the precipitate collected by centrifugation into a closed container, add octadecene and octadecylamine, the amount of octadecene and octadecylamine added is 50-66.6% by mass percentage , 33.3-50%, and then heated to 180-220°C under the condition of argon, and opened the reaction vessel after the temperature stabilized, so that the samples were in contact with the atmosphere, and the samples were taken out in batches within 2-30min, and put into different reaction chambers. In the container, and restore argon; E. Coat CdS/ZnS on core CdSe samples that have been in contact with the atmosphere for different times. Calculate the volume of precursor solution that needs to be coated according to the amount of core CdSe. First, coat the first layer of CdS: inject cadmium precursor liquid, After 5-10 minutes, inject the sulfur precursor liquid, anneal for 10-30 minutes, the annealing temperature is 230-240 ℃; then coat the second layer of ZnS, the coating conditions are the same as the first layer, and so on, finally get the desired coating CdSe/CdS/ZnS core-shell quantum dots with clad layers.

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