Rare earth doped perovskite quantum dot and ligand passivation method thereof

Abstract

The invention discloses a rare earth doped perovskite quantum dot and a ligand passivation method thereof.The ligand passivation method of the rare earth doped perovskite quantum dot comprises the steps that a first perovskite quantum dot is obtained, the first perovskite quantum dot is a rare earth doped perovskite quantum dot CsPbX3: Ln with oleic acid or / and oleylamine as a surface ligand, X is a halogen element, and n is a positive integer; ln is a rare earth element; mixing the first perovskite quantum dots with a non-polar solvent, and heating and annealing to obtain second perovskite quantum dots; and mixing the second perovskite quantum with a ligand passivator for reaction to obtain the ligand passivated rare earth doped perovskite quantum dot taking the ligand passivator as a surface ligand. The luminous efficiency and the storage stability of the rare earth doped quantum dots can be considered at the same time.

Description

Technical Field

[0001] The present invention relates to the field of perovskite quantum dots, and particularly to a rare earth doped perovskite quantum dot and a ligand passivation method thereof. Background Art

[0002] All-inorganic halide perovskite quantum dots (CsPbX3, where X = Cl, Br or I) have advantages such as adjustable direct bandgap, high photoluminescence quantum yield (PLQY), high absorption coefficient, and high defect tolerance, and are receiving increasing attention in optoelectronic fields such as photovoltaics, light-emitting diodes, photodetectors, and lasers.

[0003] At the same time, rare earth ions have advantages such as rich 4f-4f and 4f-5d transition energy levels, a wide emission wavelength range, a long fluorescence lifetime, and an extremely narrow emission peak. By doping rare earth elements into perovskite, the luminescence properties of perovskite nanocrystals can be regulated and improved, further enhancing the application potential of perovskite. However, whether synthesizing undoped perovskite quantum dots or rare earth ion-doped perovskite quantum dots, during the synthesis process, oleic acid (OA) and oleylamine (OLA) are usually used as surface ligands of perovskite quantum dots to assist in dissolving synthesis raw materials and prevent perovskite quantum dots from aggregating and decomposing. For example, in a method for synthesizing rare earth doped perovskite nanocrystals disclosed in Chinese patent document CN115851273A, in order to improve solubility and yield, oleic acid (OA) and / or oleylamine (OLA) are used as surface organic ligands of perovskite quantum dots.

[0004] However, the surface bonds formed between oleic acid and / or oleylamine and perovskite quantum dots are weak and cannot well stabilize ionic perovskite quantum dots, which results in the lack of long-term stability and reproducibility of perovskite quantum dots, greatly limiting the practical application and commercial value of perovskite optoelectronic devices. To solve this problem, researchers have proposed a ligand passivation method, that is, using a strong binding ligand to replace the oleic acid and oleylamine ligands. The strong binding ligand refers to a ligand with a stronger binding force than oleic acid and oleylamine to perovskite quantum dots, and ligand passivation refers to the process of using a strong binding ligand to bind to perovskite quantum dots to reduce surface defects of perovskite, thereby improving the optoelectronic properties and stability of perovskite. There are two common ligand passivation methods. One is to directly use a strong binding ligand during the synthesis process; the other is to use a strong binding ligand to replace the oleic acid and oleylamine ligands after synthesizing rare earth doped perovskite. For example, in a method for preparing a high fluorescence quantum yield violet perovskite quantum dot disclosed in Chinese patent application CN115627163A, by replacing the functional ligand of perovskite quantum dots, the quantum dots are combined with a strong binding ligand, which can greatly improve the storage stability of perovskite quantum dots. However, for rare earth doped perovskite quantum dots, the above two methods are not applicable.

[0005] Specifically, for the first method of directly using strongly binding ligands during the synthesis of rare-earth doped perovskite quantum dots, the following problems exist: Strongly binding ligands have a strong binding force with lead but a weak binding force with rare earths. Therefore, during the synthesis of rare-earth doped perovskites, strongly binding ligands will prevent rare earths from being incorporated into the perovskite lattice, thereby preventing the improvement of luminescence performance. Therefore, oleic acid and oleylamine ligands cannot be replaced with strongly binding ligands during the synthesis process.

[0006] For the second method of replacing oleic acid and oleylamine ligands with strongly binding ligands after synthesizing rare-earth doped perovskites, the following problems exist: The reaction temperature required for synthesizing rare-earth doped perovskite quantum dots (>220 °C) is significantly higher than the synthesis temperature of perovskites in the general hot injection method (~160 °C). As the reaction temperature increases significantly, the binding force between ligands and metal ions will weaken. Therefore, more ligands need to be added during the reaction to ensure the successful synthesis of perovskite quantum dots, which will result in an excessive amount of ligands coating the surface of the finally prepared quantum dots, making it unfavorable for other ligands to recombine with the quantum dots through exchange interactions. Therefore, surface modification of the quantum dots cannot be achieved through this method.

[0007] Therefore, whether directly using strongly binding ligands during the synthesis process or applying the ligand replacement passivation method of undoped perovskite quantum dots, both will lead to problems such as a decrease in the luminescence efficiency of rare-earth doped quantum dots or even decomposition, and it is impossible to balance storage stability and luminescence efficiency. Summary of the Invention

[0008] Therefore, the object of the present invention is to solve the problem that the existing quantum dot ligand passivation methods cannot balance the luminescence efficiency and storage stability of rare-earth doped quantum dots, and to obtain a rare-earth doped perovskite quantum dot and its ligand passivation method for solving the above problems.

[0009] A ligand passivation method for rare-earth doped perovskite quantum dots, comprising:

[0010] Obtaining a first perovskite quantum dot, which is a rare-earth doped perovskite quantum dot CsPbX3:Ln with oleic acid or / and oleylamine as surface ligands, where X is a halogen element and Ln is a rare-earth element;

[0011] Mixing the first perovskite quantum dot with a non-polar solvent, and removing the surface ligand of the first perovskite quantum dot by heating and annealing to obtain a second perovskite quantum dot;

[0012] Mixing the second perovskite quantum dot with a ligand passivator and reacting to obtain a third perovskite quantum dot, which is a ligand-passivated rare-earth doped perovskite quantum dot with the ligand passivator as the surface ligand.

[0013] In the present invention, X includes any one or more of Cl, Br, and I.

[0014] In the present invention, Ln includes any one or more of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y.

[0015] The non-polar solvent in the present invention can meet the following requirements:

[0016] 1. Low polarity to avoid damaging the perovskite and be able to dissolve oleic acid and oleylamine; therefore, it is required that the structure of the solvent does not contain strongly polar groups (such as carboxylic acids, alcohols, ketones, etc.); and the non-polar solvent can meet the requirement of avoiding damaging the perovskite; among them, alkane, alkene, and aromatic hydrocarbon groups have low polarity and can generally dissolve oleic acid and oleylamine, which are suitable solvent types. 2. Since subsequent heating and annealing operations are required, it needs to remain liquid within the processing temperature range. Therefore, the non-polar solvent preferably includes non-polar solvents that are liquid at 80 °C, and most preferably, non-polar solvents that can still maintain liquid state and dissolve oleic acid and oleylamine at 130 °C; in order to meet the purpose of remaining liquid during the processing temperature and being able to dissolve oleic acid and oleylamine, alkanes, alkenes, and aromatic hydrocarbons with relatively high molecular weights are usually selected as solvents, for example: long-chain alkanes or / and long-chain alkenes; preferably, the non-polar solvent has a carbon atom number ≥ 10, that is, the non-polar solvent is a mixture of at least one or more of alkanes, alkenes, or aromatic compounds with a carbon atom number ≥ 10; preferably a mixture of at least one or more of alkanes, alkenes, or aromatic compounds with a carbon atom number of 10 - 20; for example: alkanes with 10 ≤ carbon atom number ≤ 20, or alkenes with 10 ≤ carbon atom number ≤ 20, or aromatic compounds with 10 ≤ carbon atom number ≤ 20 can be selected as the non-polar solvent mixed with the first perovskite quantum dots. Further, the non-polar solvent can be selected as at least one of dodecylbenzene, n-dodecane, and octadecene.

[0017] In the present invention, the ligand passivator includes any one or more of thiols, benzenesulfonic acids, phosphonic acids, thiocyanates, zwitterions, and alkylammonium halides. Further, the ligand passivator can be at least one of dodecylbenzenesulfonic acid, n-dodecanethiol, trihexyltetradecylphosphonium chloride, and didodecyldimethylammonium chloride.

[0018] The temperature of the heating and annealing is 80 - 130 °C; for example: the temperature of the heating and annealing is 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C;

[0019] And / or, the time of the heat annealing is 5 - 40 min, for example: 5 min, 7 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min.

[0020] And / or, the method for removing the surface ligand of the first perovskite quantum dots includes centrifugation. The conditions for centrifugation are 5000 - 8000 rpm, for example: 5000 rpm, 5500 rpm, 6000 rpm, 6500 rpm, 7000 rpm, 7500 rpm, 8000 rpm.

[0021] The concentration of the first perovskite quantum dots in the non - polar solvent is 1 - 200 mg / ml, for example: 1 mg / ml, 5 mg / ml, 10 mg / ml, 20 mg / ml, 30 mg / ml, 50 mg / ml, 70 mg / ml, 90 mg / ml, 110 mg / ml, 130 mg / ml, 150 mg / ml, 170 mg / ml, 190 mg / ml, 200 mg / ml.

[0022] The molar ratio of the second perovskite quantum dots to the ligand passivator is 1:(0.5 - 5), for example: 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5.

[0023] The second perovskite quantum dots and the ligand passivator are mixed and reacted under the conditions of shaking or stirring;

[0024] The treatment temperature during the shaking or stirring is 10 - 60 °C, and the treatment time is 1 - 30 min. For example: the treatment temperature is 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C; for example: the treatment time is 1 min, 2 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min.

[0025] The process for obtaining the first perovskite quantum dots includes: mixing and dissolving a lead source, a rare - earth halide, an organic ligand, and a solvent, and then adding a cesium - source solution to react to obtain the first perovskite quantum dots; the organic ligand is oleic acid or / and oleylamine.

[0026] The above - mentioned lead source in the present invention may refer to a compound that can provide lead elements to participate in the synthesis of perovskite, generally a lead salt; similarly, the above - mentioned cesium - source solution in the present invention refers to a compound solution that can provide cesium elements to participate in the synthesis of perovskite, generally a cesium - salt solution.

[0027] The above-mentioned mixing and dissolving process is carried out under an inert gas or vacuum condition, and it is completely dissolved by heating. The heating temperature is above 100°C, such as: 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, etc.; the temperature of the reaction is above 220°C, such as: 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, etc.

[0028] A rare-earth doped perovskite quantum dot is prepared by using the above-mentioned ligand passivation method for rare-earth doped perovskite quantum dots.

[0029] The technical solution of the present invention has the following advantages:

[0030] The ligand passivation method for rare-earth doped perovskite quantum dots provided by the present invention, first, a non-polar solvent is added to the rare-earth doped perovskite quantum dot CsPbX3:Ln with oleic acid or / and oleylamine as a surface ligand, and by heating and annealing, the rearrangement of cations in the perovskite is realized to achieve the effect of improving the crystallization of the perovskite, improve the luminescence efficiency of the rare-earth doped perovskite, and provide the possibility for subsequent sufficient removal of the excess oleic acid or / and oleylamine ligands on the surface of the perovskite; subsequently, the second perovskite quantum dot with a ligand-deficient surface can be obtained by centrifugation; finally, a ligand passivation agent is dropped into the second perovskite quantum dot, and after mixing and reacting, a ligand-passivated rare-earth doped perovskite quantum dot with the ligand passivation agent as the surface ligand can be obtained to effectively improve the stability. The present invention removes the excess oleic acid and oleylamine ligands on the surface of the perovskite through a thermal annealing process in a non-polar solvent, eliminates the factor that the oleic acid and oleylamine ligands inhibit the binding and coating of strong ligands with the perovskite, realizes the combination of the ligand passivation agent and the rare-earth doped perovskite quantum dot, and thus greatly improves the stability of the rare-earth doped perovskite; at the same time, through the thermal annealing in a non-polar solvent, the crystallinity of the rare-earth doped perovskite is improved, the number of defects in the perovskite that affect the luminescence efficiency and stability is reduced, and the reduction of the luminescence performance caused by directly replacing the oleic acid and oleylamine ligands with strong ligands is avoided, achieving the effect of improving the luminescence performance and storage stability.

[0031] Moreover, due to the method of removing the surface ligand of the first perovskite quantum dot, this operation also greatly improves the speed of ligand passivation of the rare-earth doped perovskite with a ligand passivation agent and reduces the consumption of the ligand passivation agent. Description of the Drawings

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is the fluorescence spectrum diagram of the rare earth-doped perovskite quantum dots in Example 1 and Comparative Examples 1-2 of the present invention when placed for 0 days;

[0034] Figure 2 It is the luminescence intensity diagram of the rare earth-doped perovskite quantum dots in Example 1 and Comparative Examples 1-2 of the present invention during the placement period;

[0035] Figure 3 It is the fluorescence spectrum diagram of the rare earth-doped perovskite quantum dots in Example 1 and Comparative Examples 3-4 of the present invention when placed for 0 days;

[0036] Figure 4 It is the luminescence intensity diagram of the rare earth-doped perovskite quantum dots in Example 1 and Comparative Examples 3-4 of the present invention during the placement period;

[0037] Figure 5 It is the fluorescence spectrum diagram of the rare earth-doped perovskite quantum dots in Example 1 and Comparative Example 5 of the present invention when placed for 0 days;

[0038] Figure 6 It is the luminescence intensity diagram of the rare earth-doped perovskite quantum dots in Example 1 and Comparative Example 5 of the present invention during the placement period;

[0039] Figure 7 It is the luminescence intensity diagram of the rare earth-doped perovskite quantum dots in Examples 1-9 of the present invention during the placement period. Specific Embodiments

[0040] The following embodiments are provided to better further understand the present invention, which are not limited to the best embodiments, and do not limit the content and protection scope of the present invention. Any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features that is the same as or similar to the present invention falls within the protection scope of the present invention.

[0041] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed.

[0042] Example 1

[0043] A ligand passivation method for rare earth-doped perovskite quantum dots is as follows:

[0044] (1) Synthesis of the first perovskite quantum dots: Put 0.15 mmol of lead acetate, 0.3 mmol of ytterbium chloride, 2 ml of oleic acid, 2 ml of oleylamine, and 10 ml of octadecene into a three-necked flask. Continuously stir and keep it under vacuum, heat to 120 °C and hold for 30 min. Then raise the temperature to 250 °C. Immediately inject 1 ml of 0.15 mmol / ml cesium oleate solution after reaching 250 °C. After reacting for 30 s, cool the flask to room temperature (25 °C) to obtain a coolant. Centrifuge the coolant at 5000 rpm for 5 min, and collect the white precipitate, which is the first perovskite quantum dot, specifically ytterbium-doped cesium lead chloride quantum dots with oleic acid and oleylamine as surface ligands.

[0045] (2) Perovskite heating annealing: Put 50 mg of the above first perovskite quantum dots and 10 ml of octadecene into a three-necked flask, raise the temperature to 120 °C, keep it under vacuum and continuously stir for 15 min; centrifuge at 5000 rpm for 5 min to take the precipitate, then add 10 ml of toluene for dispersion and washing, and centrifuge again at 8000 rpm to obtain the precipitate. Further disperse it in 10 ml of n-hexane to obtain the annealed second perovskite quantum dots, which are ytterbium-doped cesium lead chloride lacking ligands. The perovskite obtained in this step is in a flocculent agglomerate, indicating that the excess ligands on the perovskite surface have been fully removed.

[0046] (3) Surface modification / ligand exchange: Add 0.1 ml of dodecylbenzenesulfonic acid to the above second perovskite quantum dots to make the molar ratio of cesium lead chloride to dodecylbenzenesulfonic acid 1:2. Rotate and shake at 3000 rpm for 2 min, and the treatment temperature during shaking is room temperature. After the shaking treatment, the third perovskite quantum dots can be obtained, which are ytterbium-doped cesium lead chloride perovskite passivated by dodecylbenzenesulfonic acid. The perovskite in this step can be fully dispersed in n-hexane and no longer in a flocculent state, indicating that the surface of the perovskite quantum dots has been coated and protected by dodecylbenzenesulfonic acid ligands.

[0047] Example 2

[0048] The difference from Example 1 is that in the surface modification / ligand exchange step of this example, n-dodecyl mercaptan is used to replace dodecylbenzenesulfonic acid, and the others are the same as in Example 1.

[0049] Example 3

[0050] The difference from Example 1 is that in the surface modification / ligand exchange step of this example, trihexyltetradecylphosphonium chloride is used to replace dodecylbenzenesulfonic acid, and the others are the same as in Example 1.

[0051] Example 4

[0052] The difference from Example 1 is that in the surface modification / ligand exchange step of this example, didodecyldimethylammonium chloride is used to replace dodecylbenzenesulfonic acid, and the others are the same as in Example 1.

[0053] Example 5

[0054] A method for ligand passivation of rare earth-doped perovskite quantum dots, which is different from Example 1 in that the parameter conditions in steps (2) and (3) are different, and the details are as follows:

[0055] (2) Perovskite heating annealing: Put 10 mg of the above ytterbium-doped cesium lead chloride quantum dots and 10 ml of octadecene into a three-necked flask, heat up to 80 °C, keep vacuum pumping and continuously stir for 40 min. Centrifuge at 5000 rpm for 5 min to take the precipitate, then add 10 ml of toluene for dispersion washing, centrifuge again at 8000 rpm to obtain the precipitate, and further disperse it in 10 ml of n-hexane to obtain ytterbium-doped cesium lead chloride lacking ligands after annealing.

[0056] (3) Surface modification / ligand exchange: Take the above annealed ytterbium-doped cesium lead chloride, add 0.03 ml of dodecylbenzenesulfonic acid to make the molar ratio of cesium lead chloride to dodecylbenzenesulfonic acid 1:0.5, rotate and shake at 3000 rpm for 15 min, and the treatment temperature during shaking is 60 °C. After the shaking treatment, ytterbium-doped cesium lead chloride perovskite passivated by dodecylbenzenesulfonic acid can be obtained.

[0057] Example 6

[0058] A method for ligand passivation of rare earth-doped perovskite quantum dots, which is different from Example 1 in that the parameter conditions in steps (2) and (3) are different, and the details are as follows:

[0059] (2) Perovskite heating annealing: Put 2 g of the above ytterbium-doped cesium lead chloride quantum dots and 10 ml of octadecene into a three-necked flask, heat up to 130 °C, keep vacuum pumping and continuously stir for 5 min. Centrifuge at 5000 rpm for 5 min to take the precipitate, then add 10 ml of toluene for dispersion washing, centrifuge again at 8000 rpm to obtain the precipitate, and further disperse it in 10 ml of n-hexane to obtain ytterbium-doped cesium lead chloride lacking ligands after annealing.

[0060] (3) Surface modification / ligand exchange: Take the above annealed ytterbium-doped cesium lead chloride, add 0.1 ml of dodecylbenzenesulfonic acid to make the molar ratio of cesium lead chloride to dodecylbenzenesulfonic acid 1:5, rotate and shake at 3000 rpm for 30 min, and the treatment temperature during shaking is 40 °C. After the shaking treatment, ytterbium-doped cesium lead chloride perovskite passivated by dodecylbenzenesulfonic acid can be obtained.

[0061] Example 7

[0062] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that the non-polar solvent in step (2) is n-dodecane.

[0063] Example 8

[0064] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that the non-polar solvent in step (2) is dodecylbenzene.

[0065] Example 9

[0066] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that the non-polar solvent in step (2) is a mixed solution of n-dodecane and octadecene with a volume ratio of 1:1.

[0067] Comparative Example 1

[0068] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that this comparative example has no step (2) and step (3), and directly prepares the ytterbium-doped cesium lead chloride quantum dots obtained in step (1).

[0069] Comparative Example 2

[0070] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that this comparative example only obtains the ligand-deficient ytterbium-doped cesium lead chloride after annealing prepared in step (2).

[0071] Comparative Example 3

[0072] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that this comparative example has no heating and annealing step in step (2). Specifically, directly mix the first perovskite quantum dots with the non-polar solvent and treat them at 40 °C, and the others are the same as in Example 1.

[0073] Comparative Example 4

[0074] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that this comparative example uses the polar solvent ethyl acetate to replace the non-polar solvent octadecene in step (2), and there is no heating and annealing step in step (2), that is, directly mix the first perovskite quantum dots with the polar solvent ethyl acetate and treat them at 40 °C, and the others are the same as in Example 1.

[0075] Comparative Example 5

[0076] A ligand passivation method for rare earth-doped perovskite quantum dots, which is different from Example 1 in that this comparative example has no subsequent step (2) and step (3), and directly uses dodecylbenzenesulfonic acid as the surface ligand for the synthesis of rare earth-doped perovskite quantum dots. The specific synthesis conditions are as follows:

[0077] Synthesis of rare earth doped perovskite quantum dots: 0.15 mmol of lead acetate, 0.3 mmol of ytterbium chloride, 4 ml of dodecylbenzenesulfonic acid, and 10 ml of octadecene were put into a three-necked flask, continuously stirred and kept under vacuum, heated to 120 °C and held for 30 min. Then the temperature was raised to 250 °C, and immediately after reaching 250 °C, 1 ml of 0.15 mmol / ml cesium oleate solution was injected, and the flask was cooled after reacting for 30 s. Centrifuged at 5000 rpm for 5 min, and the white precipitate was collected, namely ytterbium-doped cesium lead chloride quantum dots.

[0078] Test examples:

[0079] The rare earth doped perovskite quantum dots prepared by the examples and comparative examples were subjected to fluorescence detection under 365 nm excitation light at 0 d, 10 d, 20 d, 30 d, 40 d, 50 d, 60 d, 70 d, 80 d, 90 d, and 100 d, respectively, and the fluorescence spectra under 365 nm excitation light were obtained. The detection results are as Figures 1 - 7 shown, where d represents the number of days (English: day).

[0080] Among them, in Figure 1 , by comparing Comparative Examples 1 and 2, it can be seen that the ytterbium-doped perovskite (Comparative Example 2) after annealing treatment has stronger rare earth luminescence intensity than before annealing (Comparative Example 1), indicating that the crystal quality of the perovskite quantum dots is improved by heating annealing, and further the efficiency of energy transfer from perovskite to rare earth is increased, thus realizing the improvement of rare earth luminescence intensity. From Example 1 and Comparative Example 2, it can be seen that the luminescence intensity of the ytterbium-doped perovskite (Example 1) treated by ligand exchange is further improved, which indicates that dodecylbenzenesulfonic acid is fully combined with the perovskite surface, thereby inhibiting the formation of perovskite surface defects, and further avoiding the dissipation of excitation energy through defects, thus improving the luminescence intensity.

[0081] In Figure 2 , the storage stability of the ytterbium-doped perovskite (Comparative Example 2) after annealing treatment is improved compared with that before annealing treatment (Comparative Example 1), which indicates that the perovskite has improved crystallization quality after solvothermal annealing, with fewer surface defects and thus better stability; however, its stability still decays by 30% at 100 d, with an obvious decay; while the ytterbium-doped perovskite (Example 1) treated by heating annealing and ligand exchange has the best stability, and the relative luminescence intensity at 100 d can reach more than 90%; this indicates that by replacing the ligands on the quantum dot surface from oleic acid oleylamine with weaker binding force to dodecylbenzenesulfonic acid with stronger binding ability, the perovskite can be effectively protected and the stability can be improved.

[0082] In Figure 3Among them, for the rare-earth doped perovskite quantum dots without annealing treatment (Comparative Example 3), after traditional direct ligand exchange treatment, the luminescence intensity decreased compared with that of Example 1. This shows that dodecylbenzenesulfonic acid not only cannot effectively perform ligand exchange with the perovskite quantum dots rich in ligands on the surface, but on the contrary, it will weaken the rare-earth luminescence due to dissolving part of the rare earth, resulting in a decrease in the product quality. As can be seen from Example 1 and Comparative Example 4, although treating perovskite quantum dots with common washing solvents such as ethyl acetate (Comparative Example 4) can also achieve the effect of eluting the excess ligands on the surface of perovskite, since these washing solvents are often polar, they will easily cause the decomposition of perovskite quantum dots and a decrease in fluorescence brightness, and the effect is inferior to that of the present invention.

[0083] In Figure 4 Among them, for the rare-earth doped perovskite quantum dots without annealing treatment (Comparative Example 3), due to the rich ligands on the surface of the quantum dots, the quantum dots cannot bind to strong ligands through the traditional ligand exchange method, so the stability is poor; for the perovskite quantum dots treated with ethyl acetate (Comparative Example 4), due to being damaged by polar solvents, the surface defects of the quantum dots increase significantly, and even after ligand exchange treatment, their stability also decreases significantly.

[0084] Therefore, through Figures 1 - 4 Comprehensively, it can be seen that through the experimental results of the present invention, it is verified that: through simple ligand exchange reaction, or ligand exchange reaction after conventional solvent washing, not only the purpose of surface modification cannot be achieved, but also the luminescence performance will be significantly reduced. In the present invention, after washing with non-polar solvents and heat annealing treatment, and then binding with strong ligands such as ligand passivators, the luminescence performance and storage stability can be significantly improved at the same time, achieving the effect of taking into account the luminescence performance and storage stability.

[0085] In Figure 5 Among them, for the rare-earth doped perovskite prepared by directly adding dodecylbenzenesulfonic acid as a ligand in the synthesis (Comparative Example 5), there is almost no rare-earth characteristic emission peak at ~980 nm, indicating that the actual doping amount of rare earth is lower than that of Example 1. This is because dodecylbenzenesulfonic acid has a strong binding ability with lead and a weak binding ability with rare earth, resulting in that directly adding these strong ligands in the synthesis will instead inhibit the incorporation of rare earth into the perovskite lattice and affect the luminescence performance of the material.

[0086] In Figure 6 Among them, for the rare-earth doped perovskite prepared by directly adding dodecylbenzenesulfonic acid as a ligand in the synthesis (Comparative Example 5), the stability is also inferior to that of Example 1; this is because the temperature for synthesizing rare-earth doped perovskite is very high (>220 °C), and at high temperatures, the binding force between ligands and metal ions will weaken, resulting in that a large amount of the added ligands do not actually bind to the perovskite sufficiently, but may instead interfere with the normal synthesis of perovskite, and the protective effect on perovskite is inferior to that of the present invention.

[0087] Through the above Figure 5 and Figure 6 The results prove that: in the present invention, after washing with a non-polar solvent and heat annealing treatment, and then binding with strong ligands such as ligand passivators; compared with directly using strong ligands in the synthesis process, it can more effectively incorporate rare earths into the perovskite lattice, significantly improving the luminescence performance and storage stability.

[0088] In Figure 7 , Examples 1-9 carried out based on the implementation method of the present invention all have good luminescence performance and fluorescence stability, and the relative luminescence intensity at 100d can reach more than 90%, fully reflecting the stability of the present invention. At the same time, doping experiments of other rare earth elements such as cerium and gadolinium were also carried out in the present invention, and technical effects basically similar to those of ytterbium doping in the present invention were obtained.

[0089] Obviously, the above examples are only for illustration and are not intended to limit the implementation methods. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A ligand passivation method for rare earth doped perovskite quantum dots, characterized in that, Comprising: Obtaining a first perovskite quantum dot, which is a rare-earth doped perovskite quantum dot CsPbX3:Ln with oleic acid or / and oleylamine as a surface ligand, where X is a halogen element and Ln is a rare-earth element; Mixing the first perovskite quantum dot with a non-polar solvent, and removing the surface ligand of the first perovskite quantum dot by heating and annealing to obtain a second perovskite quantum dot; Mixing the second perovskite quantum dot with a ligand passivator and reacting to obtain a third perovskite quantum dot, which is a ligand-passivated rare-earth doped perovskite quantum dot with the ligand passivator as a surface ligand.

2. The method according to claim 1, characterized in that, The X includes any one or more of Cl, Br, and I; And / or, the Ln includes any one or more of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; And / or, the non-polar solvent includes a non-polar solvent that is liquid at 80°C; And / or, the ligand passivator includes any one or more of thiol, benzenesulfonic acid, phosphonic acid, thiocyanate, zwitterion, and alkylammonium halide.

3. The method according to claim 2, characterized in that, The non-polar solvent is a mixture of at least one or more of alkanes, alkenes, or aromatic compounds with a carbon atom number ≥ 10; preferably a mixture of at least one or more of alkanes, alkenes, or aromatic compounds with a carbon atom number of 10-20; more preferably, the non-polar solvent includes at least one of dodecylbenzene, n-dodecane, and octadecene; And / or, the ligand passivator includes at least one of dodecylbenzenesulfonic acid, n-dodecanethiol, trihexyltetradecylphosphonium chloride, and didodecyldimethylammonium chloride.

4. The method according to any one of claims 1-3, characterized in that, The temperature of the heating and annealing is 80-130°C; And / or, the method of removing the surface ligand of the first perovskite quantum dot includes centrifugation.

5. The method according to claim 4, characterized in that, The time of the heating and annealing is 5-40 min; And / or, the conditions of the centrifugation are 5000-8000 rpm.

6. The method according to any one of claims 1-5, characterized in that, The concentration of the first perovskite quantum dot in the non-polar solvent is 1-200 mg / ml.

7. The method according to any one of claims 1-5, characterized in that, The molar ratio of the second perovskite quantum dot to the ligand passivator is 1:(0.5-5).

8. The method according to any one of claims 1-5, characterized in that, The second perovskite quantum dot and the ligand passivator are mixed and reacted under the conditions of shaking or stirring; The treatment temperature during the shaking or stirring is 10-60°C, and the treatment time is 1-30 min.

9. The method according to any one of claims 1-8, characterized in that, The process of obtaining the first perovskite quantum dot includes: mixing and dissolving a lead source, a rare-earth halide, an organic ligand, and a solvent, and then adding a cesium source solution to react to obtain the first perovskite quantum dot; the organic ligand includes oleic acid or / and oleylamine.

10. A rare earth doped perovskite quantum dot, characterized in that, Prepared by using the ligand passivation method of a rare-earth doped perovskite quantum dot according to any one of claims 1-9.

Images