A synthesis process of green-emitting Cs3MnBr5 quantum dots

Abstract

The present invention relates to a synthesis process of green-light-emitting Cs3MnBr5 quantum dots, which comprises the following steps: 1) drying CsBr, MnBr2, and Cs2CO3; 2) dissolving Cs2CO3 in an organic acid to obtain a ligand solution; 3) ball-milling and mixing CsBr and MnBr2 in a molar ratio of 1:1, then adding the ligand solution obtained in step 2), further ball-milling, dispersing with an organic solvent immiscible with water, centrifuging, and taking the supernatant to obtain a precursor solution; 4) taking the precursor solution, adding distilled water, ultrasonically dispersing, and separating the upper solvent layer by liquid separation to obtain a quantum dot colloidal solution containing Cs3MnBr5; 5) centrifuging the quantum dot colloidal solution, separating the lower solid, and drying it under vacuum to obtain Cs3MnBr5 quantum dot powder. The whole process of the present invention is simple, fast, green, and low-cost, and is convenient for industrial synthesis.

Description

Technical Field

[0001] The present invention relates to the technical field of metal halide luminescent materials, and specifically to a synthesis process of green-emitting Cs3MnBr5 quantum dots. Background Art

[0002] LEDs have developed rapidly due to their long service life, environmental friendliness, energy conservation and emission reduction, etc., and are widely used in displays. Such displays generally consist of LEDs that emit red, green, and blue (RGB) light. This type of display has characteristics such as high brightness, low heat generation, long life, accurate color, and wide color gamut. Therefore, people have been looking for new fluorescent and phosphorescent materials that may be used in RGB-emitting LEDs to optimize and improve the production screen in terms of color temperature, color gamut, color reproducibility, energy consumption, etc. Quantum dot materials have received extensive attention in the research of new high-performance LEDs due to their unique optoelectronic properties such as flexible bandgap width adjustment (by controlling crystal composition and size), high charge generation and transport rates, narrow full width at half maximum, high luminous efficiency, and wide color gamut coverage. In the field of LEDs, the most studied quantum dot materials are all-inorganic lead halide perovskite quantum dots and Cd-based wurtzite or zinc blende quantum dots. These two QD materials have advantages such as high luminous intensity, high quantum yield, and adjustable spectra. In particular, all-inorganic lead halide perovskite QDs can be adjusted in the emission range throughout the visible light band of 410 - 700 nm, the full width at half maximum of the emission peak is less than 50 nm, the quantum yield can reach more than 90%, and the external quantum efficiency (EQE) of the fabricated LEDs reaches 28.9%. It is the most promising material in new display devices that meet the requirements of high-performance displays in recent years. However, due to the toxicity of Pb and Cd ions and the poor stability of the two types of quantum dots, it has hindered their development in practical applications, which has also prompted researchers to turn their attention to new directions. One method is to replace Pd and Cd ions with another non-toxic ion to reduce the content of Pd and Cd ions in the quantum dots, and at the same time use ligand engineering and surface encapsulation to enhance the stability of the quantum dots. But these methods cannot fundamentally solve the toxicity problem of heavy metal ions. In addition, there have also been many studies on lead-free metal halide perovskite nanocrystals such as CsGeBr3, Cs2AgBiX6, Cs2SnI6, etc. However, these perovskite nanocrystals are far less efficient and monochromatic than all-inorganic lead halide perovskite quantum dots in terms of luminescence, seriously affecting the color purity and performance of LEDs. Therefore, we urgently need to find new lead-free phosphors with high quantum yield and narrow full width at half maximum as the electron-hole recombination layer of high-performance LED devices.

[0003] Mn 2+ and Mn 4+It has a unique optoelectronic charm. The luminescence of the Mn ion emission center is affected by the Mn ion coordination environment and the distance between the emission centers, which realizes that the luminescence color range of Mn ions covers from the blue band to the near infrared, and the luminescence behavior of Mn ions can also be adjusted by methods similar to perovskite materials. At the same time, when Mn ions are used as doping ions, some unexpected luminescence behaviors appear, namely the new "cocktail effect", such as the red-blue shift of the emission peak, the change of photoluminescence lifetime, multi-peak emission, cathode luminescence, temperature quenching and mechanical luminescence; different doping concentrations of Mn ions cause different degrees of magnetic coupling (Mn-Mn) between Mn ions, making the luminescence of Mn ions different from that of isolated Mn ions. At present, manganese ions are widely used as activators for orange-red phosphors as doping elements. Mn 2+ Due to its low toxicity, excellent luminescence performance and easy synthesis, manganese halides have been widely studied as a new generation of optoelectronic materials. Among them, manganese ion metal halide Cs3MnBr5 is an all-inorganic, lead-free Mn ion with a narrow half-width green luminescence. 2+ Halide, the luminescent center is Mn 2+ With Br - Formed MnBr4 2- The tetrahedral structure has a PLQY of up to 74.9% and a narrow half-peak width of 39nm. Therefore, the quantum dot material of this crystal is expected to be used as the electron-hole recombination layer of a new type of high-performance LED.

[0004] There are many methods for synthesizing Cs3MnBr5 crystals, including evaporation crystallization, freeze-drying assisted recrystallization, and hot injection. At present, the most mature and effective method for synthesizing Cs3MnBr5 quantum dot materials is hot injection. However, the hot injection process is complex and the synthesis conditions are harsh. It requires a series of steps such as precursor dissolution, heating, vacuum degassing, further heating reaction under nitrogen atmosphere, cooling to terminate the reaction, centrifugation, washing, and drying to obtain quantum dot powder. The reaction time required in the heating reaction stage is extremely short, and the reaction system needs to be quickly transferred for cooling. This process is difficult to achieve precise control and is not suitable for large-scale industrial production. At the same time, the hot injection method has low resource utilization and is environmentally unfriendly. The reaction process consumes a lot of resources, including the inert gas consumed, the energy consumed by the heating source, and the organic reagents used in large quantities during the reaction. Therefore, a new, green, efficient, and simple process is needed to synthesize Cs3MnBr5 quantum dot materials. Summary of the invention

[0005] In view of the above problems, the present invention discloses a green light emitting Cs3MnBr5 quantum dot synthesis process, the specific scheme is:

[0006] A green light emitting Cs3MnBr5 quantum dot synthesis process comprises the following steps:

[0007] 1) Dry CsBr, MnBr2, and Cs2CO3.

[0008] 2) Dissolve Cs2CO3 in an organic acid to obtain a ligand solution.

[0009] 3) Ball-mill and mix CsBr and MnBr2 in a molar ratio of 1:1, then add the ligand solution obtained in step 2), further ball-mill, disperse with an organic solvent immiscible with water, centrifuge, and take the supernatant to obtain a precursor solution.

[0010] 4) Take the precursor solution, add distilled water, ultrasonically disperse it, and then separate the upper solvent layer by liquid separation to obtain a quantum dot colloidal solution containing Cs3MnBr5.

[0011] 5) Centrifuge the quantum dot colloidal solution, separate the lower solid, and dry it under vacuum to obtain Cs3MnBr5 quantum dot powder.

[0012] Preferably, in step 1), the drying method is to freeze at -70 °C and then dry under vacuum.

[0013] Preferably, in step 2), the Cs2CO3 powder is dissolved in the organic acid at a ratio of 5 mmol / 10 mL.

[0014] Preferably, in step 2), the organic acid is selected from at least one of carboxylic acids and organic sulfonic acids.

[0015] Preferably, in step 2), the organic acid is selected from at least one of capric acid, oleic acid, 1,6 - hexanedioic acid, 1,10 - decanedioic acid, ethyl sulfonic acid, and benzenesulfinic acid.

[0016] Preferably, in step 3), the solvent is selected from at least one of cyclohexane, toluene, and n - hexane.

[0017] This patent designs a green, simple, and efficient process for preparing Cs3MnBr5 quantum dot materials: By an acid - base reaction, a new cesium source / ligand system is designed, and this system is introduced into a ball - mill jar containing CsBr and MnBr2 in different molar ratios and ground by high - energy ball - milling (using a CsBr:MnBr2 less than the stoichiometric ratio to form a Cs - deficient + system, and then the missing Cs in the precursor solution is supplemented by adding the synthesized organic cesium salt and long - chain organic acid ligand system. +, while introducing a ligand into the precursor system to passivate the defects of the quantum dots), followed by dispersion and centrifugation in an organic solvent (such as cyclohexane), and our precursor solution (supernatant) was quickly obtained. Adding water, a polar solvent insoluble in the organic solvent, to the precursor solution and performing ultrasonic treatment can generate Cs3MnBr5 quantum dots in a short time. Subsequently, after centrifugation, vacuum drying, and grinding, Cs3MnBr5 quantum dot powder is obtained.

[0018] The features of the present invention are: (1) Using CsBr:MnBr2 with a ratio less than the stoichiometric ratio to form a Cs-deficient + system, and then supplementing the missing Cs in the precursor solution by adding a synthesized organic cesium salt and a long-chain organic acid ligand system + , while introducing a ligand into the precursor system to passivate the defects of the quantum dots. (2) Using an organic reagent immiscible with water as the solvent of the precursor solution; (3) Using a small amount of water can induce the formation of Cs3MnBr5 quantum dots without the need for other additional operations.

[0019] The advantages of the present invention are: (1) The synthesis process can be carried out at room temperature and in an air atmosphere without the need to use inert gas protection or a heating source; (2) A high-energy ball mill and an ultrasonic cleaner can be used to assist in the synthesis, and the operation is simple; (3) Only a small amount of organic reagent is used in the process, and Cs3MnBr5 quantum dots are induced to form by water subsequently, without introducing additional organic reagents, and the synthesis process has a lower dependence on organic reagents; (4) The entire process is simple, fast, green, low-cost, convenient for industrial synthesis, and has a high energy utilization rate. Brief Description of the Drawings

[0020] The present invention will be further described below in conjunction with the drawings and embodiments.

[0021] Figure 1 is the technical route diagram for synthesizing Cs3MnBr5 quantum dots of the present invention.

[0022] Figure 2 is the schematic diagram of the synthesis process of Cs3MnBr5 quantum dots synthesized in Example 1.

[0023] Figure 3 is the X-ray diffraction pattern (XRD) of Cs3MnBr5 quantum dots synthesized in Example 1.

[0024] Figure 4 is the emission spectrum (PL), excitation spectrum (PLE), and ultraviolet absorption spectrum (Abs) of Cs3MnBr5 quantum dots synthesized in Example 1.

[0025] Figure 5Transmission electron microscopy (TEM) images of the Cs3MnBr5 quantum dots synthesized in Example 1 at different magnifications. Detailed implementation manners

[0026] The present invention will be clearly described below in conjunction with specific embodiments of the present invention. The description here is only used to explain the present invention, but not to limit the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative efforts, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

[0027] Example 1

[0028] As Figure 1 and Figure 2 shown in the process, the following operations are carried out:

[0029] 1. Preparation of Cs3MnBr5 quantum dots (taking the oleic acid / cesium oleate system as an example for the ligand system, a CsBr:MnBr2 feed ratio (taking 1:1 as an example for this time) and cyclohexane as the solvent (dispersant)):

[0030] (1) First, pre-treat the raw materials and the ball milling tank: Freeze the used CsBr, MnBr2, and Cs2CO3 powders at -70 °C for 6 h, then vacuum dry for 48 h for standby; ultrasonically clean the ball milling tank for 10 min, then clean it with a superclean cleaner for 20 min, take out the ball milling tank, and carry out vacuum drying treatment at 100 °C for standby.

[0031] (2) Preparation of the oleic acid / cesium oleate system: Prepare raw materials of oleic acid (OA) / cesium carbonate (Cs2CO3) according to a ratio of 5 mmol / 10 mL. Add OA to a beaker, add Cs2CO3 to OA under rapid stirring, slowly raise the temperature to 80 °C, stir at 80 °C until the solution becomes clear and transparent, and store the solution refrigerated at 2 - 6 °C for standby. The main idea of the ligand system in this process route is to use organic acid alkanes to react with cesium carbonate or cesium hydroxide to generate organic cesium salts to introduce Cs + and ligands, so as to induce the formation of a cesium-rich phase Cs3MnBr5 and passivate the surface defects of quantum dots. The organic acids that can be used include carboxylic acids (R-COOH) such as: monounsaturated fatty acids: capric acid, monounsaturated fatty acids: oleic acid, dibasic saturated fatty acids: 1,6-hexanedioic acid, 1,10-decanedioic acid, etc.; organic sulfonic acids (R-SO3H) such as: ethyl sulfonic acid, etc.; sulfinic acids (R-SOOH) such as: benzenesulfinic acid, etc. Oleic acid is selected in this example.

[0032] (3) Preparation of precursor solution: Take CsBr and MnBr₂ prepared in (1) in a molar ratio of 1:1, load them into the pre-treated ball mill tank in (1), perform pre-ball milling for 8 minutes using a high-energy ball mill, then add 500 μL of the ligand solution prepared in (2), and further ball mill for 17 minutes to obtain a brownish mud-like substance; disperse it with 50 mL of cyclohexane, then centrifuge at 10000 rpm / min for 10 min, and take the supernatant to obtain the precursor solution.

[0033] (4) Ultrasonic-assisted water-induced synthesis of Cs₃MnBr₅ quantum dots: Take 2 mL of the precursor solution obtained in (3), add 20 μL of distilled water, place it in an ultrasonic cleaner and ultrasonicate at 50% power for 5 minutes, separate the liquid and take out the upper cyclohexane layer to obtain a colloidal solution containing Cs₃MnBr₅ quantum dots.

[0034] (5) Obtaining Cs₃MnBr₅ quantum dot powder: Centrifuge the colloidal solution of quantum dots obtained in (4) at 12500 rpm / min for 30 minutes, then separate the lower solid, and dry it under vacuum to obtain Cs₃MnBr₅ quantum dot powder.

[0035] Example 2

[0036] Replace oleic acid with capric acid and cyclohexane with toluene, and the rest of the process is the same as in Example 1.

[0037] Example 3

[0038] Replace oleic acid with 1,6-hexanedioic acid and cyclohexane with n-hexane, and the rest of the process is the same as in Example 1.

[0039] Example 4

[0040] Replace oleic acid with ethylsulfonic acid, and the rest of the process is the same as in Example 1.

[0041] Green-emitting Cs₃MnBr₅ quantum dots were obtained in Examples 1-4, and they have good luminescence properties.

[0042] Perform XRD detection on the material synthesized in Example 1, and the results are as Figure 3 , proving that the Cs₃MnBr₅ quantum dots synthesized by the method of the present invention have high phase purity and low impurity content.

[0043] As Figure 4 is the emission spectrum (PL) and excitation spectrum (PLE) of the Cs₃MnBr₅ quantum dots synthesized in Example 1. It shows that they have high ultraviolet absorption ability and luminescence properties.

[0044] As Figure 5, a-c are transmission electron microscopy (TEM) images of the Cs3MnBr5 quantum dots synthesized in Example 1 at different magnifications. The results show that Cs3MnBr5 quantum dot crystals with a size of about 40 nm were synthesized.

Claims

1. A synthesis process of green-light-emitting Cs3MnBr5 quantum dots, characterized in that, Including the following steps: 1) Dry CsBr, MnBr2, and Cs2CO3; 2) Dissolve Cs2CO3 in an organic acid to obtain a ligand solution; the organic acid is selected from at least one of capric acid, oleic acid, 1,6 - hexanedioic acid, 1,10 - nonanedioic acid, ethylsulfonic acid, and benzenesulfinic acid; 3) Ball - mill and mix CsBr and MnBr2 in a molar ratio of 1:1, then add the ligand solution obtained in step 2), further ball - mill, then disperse with an organic solvent immiscible with water, centrifuge, and take the supernatant to obtain a precursor solution; the solvent is selected from at least one of cyclohexane, toluene, and n - hexane; 4) Take the precursor solution, add distilled water, ultrasonically disperse it, and then separate the upper solvent layer by liquid separation to obtain a quantum dot colloidal solution containing Cs3MnBr5; 5) Centrifuge the quantum dot colloidal solution, separate the lower solid, and dry it under vacuum to obtain Cs3MnBr5 quantum dot powder.

2. The synthesis process of green-light-emitting Cs3MnBr5 quantum dots according to claim 1, characterized in that: In step 1), the drying method is to freeze at - 70 °C and then dry under vacuum.

3. The synthesis process of green-light-emitting Cs3MnBr5 quantum dots according to claim 1, characterized in that: In step 2), the Cs2CO3 powder is dissolved in the organic acid at a ratio of 5 mmol / 10 mL.

Images