Cadmium selenide core-shell quantum dot as well as preparation method and application thereof

Abstract

The invention discloses a cadmium selenide core-shell quantum dot as well as a preparation method and application thereof, a thermal injection method is adopted as a synthetic preparation scheme, and the preparation method is divided into a nucleation stage and a cladding stage. Compared with a one-pot method, the method has the advantages that the repeatability is high, and the size of the cadmium selenide core quantum dot can be accurately screened. In the nucleation process, a mixed surfactant nucleation strategy is adopted, the cadmium selenide quantum dots with more uniform size distribution are grown by regulating and controlling the amount of the two surfactants, and the crystallinity of the cadmium selenide quantum dots is further improved. Due to the fact that cadmium selenide has a large number of unsaturated key positions, the cadmium selenide generates surface defects, the core-shell structure of the cadmium selenide / zinc cadmium sulfide core-shell quantum dot is designed to passivate the surface of the cadmium selenide core, and the cadmium selenide / zinc cadmium sulfide core-shell quantum dot has higher luminous efficiency and narrower half-wave width. The cadmium selenide quantum dots with the quantum yield larger than 75% and the half-wave width smaller than 30 nanometers can be stably prepared through the thermal injection method, and the cadmium selenide quantum dots can be stably used for large-scale industrial production of photoelectric devices.

Description

Technical Field

[0001] The present invention belongs to the field of fluorescent materials, and in particular relates to a high-performance cadmium selenide core-shell quantum dot and a preparation method and application thereof. Background Art

[0002] Semiconductor quantum dots are semiconductor nanoparticles with diameters ranging from 2 to 10 nanometers. Leveraging the quantum size effect, their fluorescence wavelength can be tuned by precisely controlling their size, resulting in a narrow emission spectrum. These unique properties give quantum dots enormous potential for applications in optoelectronic displays, solar cells, and bioluminescent probes. As quantum dot devices become increasingly common in various applications, their safety and the feasibility of large-scale production have become key research priorities.

[0003] In the current market, cadmium-based quantum dots represented by cadmium selenide quantum dots (CdSe QDs) are widely recognized for their excellent luminescence performance. However, they still face problems such as imprecise control of nucleation reactions and high complexity of surfactant systems, which seriously restrict the further improvement of their optical properties and the stability of industrial preparation. Therefore, it is necessary to further explore the mechanism of their nucleation reaction and optimize the preparation process of CdSe QDs.

[0004] Cadmium selenide quantum dots (CdSe) are typical II-VI semiconductors with direct band gap properties of approximately 1.74 eV. The conduction band of CdSe QDs is formed by Cd 5s orbitals, resulting in high electron mobility. The valence band is dominated by Se 4p orbitals, giving electrons a strong ability to be excited. The core of CdSe QDs is often coated with a shell material, such as zinc sulfide or cadmium sulfide. The shell layer primarily reduces surface defects, inhibits photobleaching, protects the QDs from environmental influences, and improves their photostability and chemical stability. The shell can also optimize the QDs' optical properties, such as enhancing fluorescence intensity and quantum efficiency. The shell thickness significantly influences the performance of CdSe QDs. A thinner shell helps maintain high fluorescence efficiency, while a thicker shell further improves the QDs' stability and corrosion resistance. Therefore, optimizing the core-shell structure and designing a simpler preparation process are currently the main research directions for CdSe QDs.

[0005] The conventional method for preparing CdSe quantum dots is hot injection. Research on hot injection method can help to obtain higher quality CdSe quantum dots. This method involves rapidly injecting cadmium precursor and selenium source into organic solvent at high temperature. By precisely controlling the temperature and injection rate, CdSe quantum dots with uniform particle size and excellent optical properties can be synthesized. The advantage of this method is that it can control particle size, morphology and fluorescence properties. Among the reported methods for preparing cadmium selenide quantum dots, there are still many challenges, such as size uniformity control, surface defect suppression and the feasibility of large-scale preparation. During the preparation process, stearic acid is often used as a surfactant, but the synthesis process of stearic acid usually requires a higher temperature, resulting in low synthesis efficiency and may also affect the long-term dispersibility of quantum dots. Oleic acid is also another commonly used surfactant with a faster reaction rate but poor stability. As a result, during the synthesis process, quantum dots appear agglomerate or unevenly dispersed, affecting their optical properties and stability. Therefore, oleic acid is not suitable as a single surfactant for the nucleation of quantum dots. The long-chain alkyl and phosphate groups of octadecylphosphonic acid can form a stable self-assembled layer on the surface of cadmium selenide quantum dots, which is particularly suitable for application fields such as optoelectronic devices and sensors.

[0006] Therefore, based on the existing technology, by combining the nucleation of oleic acid and octadecylphosphonic acid, the size of the cadmium selenide quantum dot core can be precisely controlled, and quantum dots with better size uniformity can be obtained, thereby making the optical properties of cadmium selenide quantum dots better. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide high-performance cadmium selenide / cadmium zinc sulfide core-shell quantum dots (CdSe / CdZnS QDs) with strong repeatability and narrow half-wavewidth and a preparation method thereof, so that they have a half-wavewidth of less than 30 nanometers and a quantum yield of greater than 70%, so as to meet the needs of large-scale commercial production of quantum dots.

[0008] One of the purposes of the present invention is to provide a cadmium selenide / cadmium zinc sulfide core-shell quantum dot with strong repeatability and narrow half-wave width, comprising a cadmium selenide quantum dot core and a cadmium zinc sulfide core-shell coated on the surface of the cadmium selenide quantum dot core.

[0009] The present invention adopts different temperatures, different heating times, different ratios and the like during nucleation, thereby making the cadmium selenide quantum dots have higher quality, higher quantum efficiency and better stability after being coated with a shell layer.

[0010] The present application uses a hot injection method to prepare cadmium selenide cores and cadmium selenide core-shell quantum dots. The embodiment provides a method for preparing the above-mentioned cadmium selenide quantum dots, comprising: reacting a cadmium precursor, a selenium precursor, an organic solvent 1, a surfactant 1, and a surfactant 2 at a nucleation temperature for a certain time to form a cadmium selenide quantum dot core. The cadmium selenide quantum dot core is then shell-coated, and a cadmium shell precursor, a zinc shell precursor, a surfactant 1, and an organic solvent 2 are added to a reaction vessel, reacted at the shelling temperature, and the cadmium selenide quantum dots are injected. When the temperature stabilizes, a sulfur source is injected, and the reaction is carried out for a certain time. After the reaction is completed, the cadmium selenide / cadmium zinc sulfide core-shell quantum dots are obtained by purification.

[0011] Preferably, the cadmium precursor is cadmium oxide.

[0012] Preferably, the selenium precursor is tri-n-octylphosphine selenide, which is a mixture of selenium powder and tri-octylphosphine.

[0013] Preferably, the organic solvent 1 is trioctylamine.

[0014] Preferably, the surfactant 1 is oleic acid, and the surfactant 2 is octadecylphosphonic acid.

[0015] Preferably, the first temperature is 310 degrees Celsius, which can ensure the normal formation of nanoseeds. If the temperature is lower than this, the reactants will not react or the reaction speed will be too slow. If the temperature is higher than this, the nanoseeds will quickly generate cadmium selenide nuclei.

[0016] Preferably, the first temperature reaction time is 5-20 minutes, which is sufficient to ensure the normal formation of the nano seeds. If the time is shorter than this, the reactants will not react significantly. If the time is longer than this, the size of the nano seeds will be too large.

[0017] Those skilled in the art can select any appropriate pre-reaction and substitution reaction conditions according to any method for preparing cadmium selenide quantum dots disclosed in the prior art, depending on the different reaction products and actual needs.

[0018] Preferably, the zinc-containing shell precursor is zinc acetate.

[0019] Preferably, the cadmium-containing shell precursor is cadmium acetate dihydrate.

[0020] Preferably, the sulfur-containing shell precursor is tri-n-octylphosphine sulfide, which is a mixture of sulfur powder and tri-octylphosphine.

[0021] Preferably, the organic solvent 2 is isotriacontane.

[0022] Preferably, the surfactant 1 of the shelling reaction is oleic acid. This temperature can ensure that the shell layer is coated layer by layer. If it is lower than this temperature, the reaction speed is too slow. If it is higher than this temperature, the cadmium selenide core continues to grow.

[0023] Preferably, the reaction temperature of the shelling reaction is 290 degrees, which can ensure that the shell layers are covered layer by layer. If the temperature is lower than this, the reaction speed is too slow, and if the temperature is higher than this, the cadmium selenide core continues to grow.

[0024] Preferably, the reaction time of the coating reaction is 5-20 minutes.

[0025] The second object of the present invention is to provide a use of the cadmium selenide / cadmium zinc sulfide core-shell quantum dots with high repeatability and narrow half-wave width, that is, the cadmium selenide / cadmium zinc sulfide core-shell quantum dots with high repeatability and narrow half-wave width are used to prepare light-emitting devices, fluorescent probes or QLEDs.

[0026] The numerical range described in the present invention includes not only the point values ​​exemplified above, but also any point values ​​between the above numerical ranges that are not exemplified. Due to space limitations and for the sake of simplicity, the present invention does not list the specific point values ​​included in the range.

[0027] This invention uses a hot injection method to prepare CdSe core-shell quantum dots with high repeatability and a narrow half-wavelength width. Using low-cost cadmium oxide as a cadmium precursor and tri-n-octylphosphine selenide as a selenium precursor, the CdSe core is prepared using a mixed surfactant strategy. This allows for precise control of the CdSe core size and significantly optimizes the core synthesis process. Furthermore, the simple experimental steps offer enhanced repeatability. This method, which produces CdSe core-shell quantum dots with high repeatability and a narrow half-wavelength width, is expected to enable the commercial large-scale production of quantum dots in the QLED field, demonstrating high production value and potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the UV-visible absorption spectrum of cadmium selenide quantum dots 1 prepared by adding a fixed amount of octadecylphosphonic acid and different amounts of oleic acid obtained in Example 1 of the present invention.

[0029] Figure 2 The luminous efficiency of cadmium selenide quantum dots 1 prepared by adding a fixed amount of octadecylphosphonic acid and different amounts of oleic acid obtained in Example 1 of the present invention is shown.

[0030] Figure 3 This is the UV-visible absorption spectrum of cadmium selenide quantum dots 1 prepared by adding a fixed amount of oleic acid and different amounts of octadecylphosphonic acid obtained in Example 1 of the present invention.

[0031] Figure 4 This is the fluorescence emission spectrum of cadmium selenide quantum dots 1 prepared by adding a fixed amount of oleic acid and different amounts of octadecylphosphonic acid obtained in Example 1 of the present invention.

[0032] Figure 5 This is the UV-visible absorption spectrum of cadmium selenide quantum dots 3 prepared by adding only a fixed amount of oleic acid obtained in Comparative Example 1 of the present invention.

[0033] Figure 6 This is the UV-visible absorption spectrum of cadmium selenide quantum dots 4 prepared by adding only a fixed amount of octadecylphosphonic acid obtained in Comparative Example 2 of the present invention.

[0034] Figure 7The luminous efficiency of the cadmium selenide quantum dots prepared in Example 1 and Comparative Examples 1 and 2 of the present invention is shown. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0036] In the present invention, the quantum yield of the cadmium selenide quantum dots obtained in each embodiment and the comparative example was obtained according to the calculation formula of the quantum yield described in the literature. The reference substance used for calculating the quantum yield was a sulfuric acid solution of quinine, which had a quantum yield of 88% under 365 nm excitation.

[0037] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example 1

[0038] Cadmium selenide quantum dots 1 were prepared by the following steps: Step (1), in a three-necked flask, different amounts of octadecylphosphonic acid and oleic acid are added to 10 ml of trioctylamine, and then 0.5 mmol of cadmium oxide is added. After the temperature is raised to 310 degrees, 0.25 ml of tri-n-octylphosphine selenide precursor solution is injected and reacted for 5 minutes to obtain cadmium selenide quantum dots 1.

[0039] Step (2) is to add 5 ml of isotriacontane and zinc and cadmium shell precursors to a three-necked flask, and then add 1 ml of oleic acid. At 290 degrees, the cadmium selenide quantum dot core obtained in step (1) is added, and then the tri-n-octylphosphine sulfur precursor solution is injected and reacted for 10 minutes. After purification, a core-shell structured cadmium selenide / cadmium zinc sulfide quantum dot solution with a quantum yield of 88%, a fluorescence peak position of 645 nm, and a half-wave width of 30 nm is obtained.

[0040] Comparative Example 1 Cadmium selenide quantum dots 2 were prepared by the following steps: The only difference from Example 1 is that in step (1), only different amounts of oleic acid are added to obtain cadmium selenide quantum dots 2, and then step 2 is performed to obtain a cadmium selenide / cadmium zinc sulfide quantum dot solution.

[0041] Comparative Example 2 Cadmium selenide quantum dots 3 were prepared by the following steps: The only difference from Example 1 is that in step (1), only different amounts of octadecylphosphonic acid are added to obtain cadmium selenide quantum dots 3, and then step 2 is performed to obtain a cadmium selenide / cadmium zinc sulfide quantum dot solution.

[0042] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cadmium selenide core-shell quantum dot, characterized in that The cadmium selenide core-shell quantum dots have a core-shell structure, in which cadmium selenide serves as the core and cadmium zinc sulfide serves as the epitaxial layer.

2. The cadmium selenide core-shell quantum dots according to claim 1, wherein The half-wave width of the cadmium selenide core-shell quantum dots is 25-35 nanometers.

3. The cadmium selenide core-shell quantum dots according to claim 2, wherein The luminous efficiency of the cadmium selenide quantum dots is 70-90%.

4. A method for preparing cadmium selenide core-shell quantum dots as claimed in claim 3, characterized in that: The preparation method comprises the following steps: A cadmium source, an organic solvent 1, a surfactant 1, and a surfactant 2 are added to a reaction vessel, and the reaction is first carried out at a nucleation temperature, and a selenium source is injected. The reaction time is 5-20 minutes to preliminarily form nanoseeds. After the reaction is completed, cadmium selenide quantum dots are obtained by purification. A cadmium shell precursor, a zinc shell precursor, a surfactant, and an organic solvent 2 are added to a reaction vessel, and the reaction is carried out at a shelling temperature, and cadmium selenide quantum dots are injected. When the temperature stabilizes, a sulfur source is injected. The reaction time is 5-20 minutes. After the reaction is completed, cadmium selenide core-shell quantum dots are obtained by purification.

5. The preparation method according to claim 4, characterized in that When preparing cadmium selenide quantum dots, the cadmium source is cadmium oxide; the organic solvent 1 is trioctylamine; the selenium source is tri-n-octylphosphine selenide, which is a mixture of selenium powder and trioctylphosphine; the surfactant 1 is oleic acid, with a main carbon chain length of 18 carbon chains; the surfactant 2 is octadecylphosphonic acid, also known as n-octadecylphosphonate; the reaction vessel is a three-necked round-bottom flask; the reaction temperature of the nucleation reaction is 310 degrees, and the reaction time is 5-20 minutes; the nucleation reaction and the shelling reaction are carried out under an inert gas atmosphere.

6. The preparation method according to claim 5, characterized in that When preparing cadmium selenide core-shell quantum dots, the zinc-containing zinc precursor is zinc acetate; the cadmium-containing cadmium precursor is cadmium acetate dihydrate; the organic solvent 2 is isotriacontane, also known as squalane; the sulfur-containing sulfur precursor is tri-n-octylphosphine sulfide, which is a mixture of sulfur powder and trioctylphosphine; and the surfactant 1 is oleic acid with a main carbon chain length of 18 carbon chains. The reaction temperature of the shelling reaction is 290 degrees Celsius, and the reaction time of the shelling reaction is 5-20 minutes.

7. Use of the cadmium selenide core-shell quantum dots according to any one of claims 1 to 3 for preparing light-emitting devices, fluorescent probes or fluorescent detectors.

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