A preparation method of Na+/Cu2+ ions co-doped cesium lead bromide perovskite quantum dots, products and applications thereof

Abstract

The invention relates to a preparation method of Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide perovskite quantum dots, products and applications thereof, which belongs to the technical field of modification research of perovskite quantum dots. The invention discloses a preparation method of Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide (CsPbBr.sub.3) perovskite quantum dots, which adopts lead bromide (PbBr.sub.2), oleic acid (OA), oleylamine (OAm), sodium ion precursors and copper ion precursors for the reaction preparation in octadecene (ODE), in which copper ions (Cu.sup.2+) and sodium ions (Na.sup.+) substitute A and B crystal sites in cesium lead bromide (CsPbBr.sub.3) perovskite fluorescent quantum dots respectively. The quantum dots have been effectively improved in photoluminescence quantum yield, thermal stability, etc., and can be used as an active layer to fabricate light emitting diodes which achieve the tuning of emission color from green to blue.

Claims

1. A preparation method of Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide perovskite quantum dots, characterized in that the preparation method comprises the following steps: adding an appropriate amount of lead bromide, oleic acid, oleylamine, sodium ion precursors and copper ion precursors into octadecene, then vacuumizing and introducing nitrogen, stirring for 2030 min, heating to 100120 C., keeping for 2030 min to react, then heating up to 150160 C. and holding for 1530 min to react, then heating up to 175190 C. and injecting cesium oleate precursor to react and obtain Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide perovskite quantum dots.

2. The preparation method according to claim 1, characterized in that the molar volume ratio of the lead bromide, oleic acid and oleylamine is (0.41):2:2, mmol:mL:mL; the molar ratio of Pb.sup.2+, Na.sup.+ and Cu.sup.2+ is 0.4:(0.010.2):(0.010.2); the molar volume ratio of the lead bromide and the octadecene is 0.4:(2050), mmol:ml; the molar volume ratio of the lead bromide and the cesium oleate precursor is (0.41):1, mmol:mL.

3. The preparation method according to claim 2, characterized in that the sodium ion precursor is prepared according to the following method: dissolving sodium bromide in N,N-dimethylformamide, stirring to make it completely dissolved.

4. The preparation method according to claim 3, characterized in that the molar volume ratio of the sodium bromide and N,N-dimethylformamide is 0.1:2, mmol:mL.

5. The preparation method according to claim 2, characterized in that the copper ion precursor is prepared according to the following method: dissolving copper bromide in N,N-dimethylformamide, stirring to make it completely dissolved.

6. The preparation method according to claim 5, characterized in that the molar volume ratio of copper bromide and N,N-dimethylformamide is 0.1:2, mmol:mL.

7. The preparation method according to claim 2, characterized in that the cesium oleate precursor is prepared according to the following method: adding cesium carbonate and oleic acid to octadecene, stirring under nitrogen flow for 2030 min, then heating up to 100120 C., keeping for 2030 min to react, then heating up to 150160 C. to obtain a brown solution, keeping for 4060 min for subsequent reaction.

8. The preparation method according to claim 7, characterized in that the mass-volume ratio of the cesium carbonate and oleic acid added to octadecene is 0.8:2.6:(2032), g:mL:mL.

9. The preparation method according to any one of claim 1 to claim 8, characterized in that the preparation method prepares Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide perovskite quantum dots.

10. The Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide perovskite quantum dots according to claim 9 are used in the application of preparing active layer materials for encapsulating light-emitting diodes which achieve the tuning of emission color from green to blue.

Description

DESCRIPTION OF DRAWINGS

[0026] To enable the purpose, the technical solution and the advantages of the present invention to be clearer, the present invention will be preferably described in detail below in combination with the drawings, wherein:

[0027] FIG. 1 is the XRD pattern of CsPbBr.sub.3:Cu.sup.2+, Na.sup.+ and undoped CsPhBr.sub.3 quantum dots;

[0028] FIG. 2 is the TEM image (A) and HR-TEM image (B) of the undoped CsPhBr.sub.3 quantum dots in Embodiment 6, and the TEM image (C) and HR-TEM image (D) of the Cu.sup.2+ and Na.sup.+ ions co-doped quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) prepared in Embodiment 1;

[0029] FIG. 3 is the particle size distribution diagram (A) of the undoped CsPbBr.sub.3 quantum dots in Embodiment 6, and the particle size distribution diagram (B) of the Cu.sup.2+ and Na.sup.+ ions co-doped quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) prepared in Embodiment 1;

[0030] FIG. 4 is the emission spectrum (A) and absorption spectrum (B) of different ratios of Cu.sup.2+ and Na.sup.+ ions co-doped CsPbBr.sub.3 quantum dots and undoped CsPbBr.sub.3 quantum dots prepared by the present invention;

[0031] In FIG. 5, A is a schematic diagram of the experimental setup, B and D are emission spectra of the undoped CsPbBr.sub.3 quantum dots in Embodiment 6 and the Cu.sup.2+/Na.sup.+ co-doped quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1 in the temperature range of 20120 C., C and E are the emission intensity in the 8 thermal cycles of the undoped CsPbBr.sub.3 quantum dots in Embodiment 6 and the Cu.sup.2+/Na.sup.+ co-doped quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1;

[0032] In FIG. 6, A is the structural schematic diagram of the light-emitting diodes (PeLEDs) based on Cu.sup.2+ and Na.sup.+ co-doped and undoped CsPbBr.sub.3 QDs perovskite, and B is the normalized electroluminescence (EL) and photoluminescence (PL) spectra of the PeLEDs prepared by CsPhBr.sub.3, CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 and CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3, and the inset is the photographs of the fabricated devices on working, C is the electroluminescence (EL) spectra of PeLEDs prepared by CsPbBr.sub.3, CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 and CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3 at different voltages, D is the normalized electroluminescence (EL) and photoluminescence (PL) spectra of the PeLEDs prepared by CsPb.sub.0.954Na.sub.0.032Cu.sub.0.023Br.sub.3, CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3, and the inset is the photographs of the fabricated devices on working, E is the EL spectra of PeLEDs prepared by CsPb.sub.0.954Na.sub.0.032Cu.sub.0.023Br.sub.3, CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3 at different voltages;

[0033] In FIG. 7, the current density-brightness-voltage (J-L-V) relationship diagram of PeLEDs prepared by CsPbBr.sub.3 (A), CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 (B). CsPb.sub.0.949Na.sub.0.33Cu.sub.0.018Br.sub.3 (C), CsPb.sub.0.954Na.sub.0.032Cu.sub.0.023Br.sub.3 (D), CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 (E) and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3 (F);

[0034] In FIG. 8, A is the current density-external quantum efficiency (CE-EQE) characteristic diagram of PeLEDs prepared by undoped CsPbBr.sub.3 quantum dots, and B-F are respectively the current density-external quantum efficiency (CE-EQE) characteristic diagram of PeLEDs prepared by quantum dots CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 (B), CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3 (C) and CsPb.sub.0.954Na.sub.0.032Cu.sub.0.023Br.sub.3 (D), CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 (E) and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3 (F).

DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described below through specific embodiments. Those skilled in the art can understand other advantages and effects of the present invention easily through the disclosure of the description. The present invention can also be implemented or applied through additional different specific embodiments. All details in the description can be modified or changed based on different perspectives and applications without departing from the spirit of the present invention. It should be noted that the figures provided in the following embodiments only exemplarily explain the basic conception of the present invention, and if there is no conflict, the following embodiments and the features in the embodiments can be mutually combined.

[0036] The present invention will be further described in detail below in conjunction with the accompanying drawings:

Embodiment 1

[0037] A Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide (CsPbBr.sub.3) perovskite quantum dot is prepared according to the following method: [0038] (1) Preparation of cesium oleate precursor: put 0.8 g of cesium carbonate, 2.6 ml of oleic acid and 32 ml of octadecene in a 100 mL three-necked flask, stir under nitrogen flow for 20 min, heat to 120 C., and hold for 30 min to react, heat the mixture to 160 C. to obtain a brown solution, keep for 60 min for sufficient reaction to obtain the cesium oleate precursor, and then preheat to 100 C. for use. [0039] (2) Preparation of sodium ion precursor and copper ion precursor: add 0.1 mmol sodium bromide (NaBr) to 2 mL of DMF solution, stir well until dissolved to obtain sodium ion precursor; add 0.1 mmol copper bromide (CuBr.sub.2) to 2 ml of DMF solution, and stir well until dissolved to obtain sodium ion precursor. [0040] (3) Put 0.4 mmol of lead bromide, 2 mL of oleic acid, 2 mL of oleylamine and 40 ml of octadecene into a 100 ml three-necked flask, and then add 0.04 ml of the sodium ion precursor in step (2) and 0.08 mL of the copper ion precursor in step (2) into the three-necked flask, evacuate and then introduce with nitrogen, stir for 20 min, heat to 120 C. for 30 min for reaction, then heat to 160 C. and hold for 30 min for reaction, and then heat to 190 C. and inject into 1 ml of the cesium oleate precursor obtained in step (1) for reaction to get quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3).

Embodiment 2

[0041] A Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide (CsPbBr.sub.3) perovskite quantum dot is prepared according to the following method: [0042] (1) Preparation of cesium oleate precursor: put 0.8 g of cesium carbonate, 2.6 mL of oleic acid and 32 ml of octadecene in a 100 mL three-necked flask, stir under nitrogen flow for 20 min, heat to 120 C., and hold for 30 min to react, heat the mixture to 160 C. to obtain a brown solution, keep for 60 min for sufficient reaction to obtain the cesium oleate precursor, and then preheat to 100 C. for use. [0043] (2) Preparation of sodium ion precursor and copper ion precursor: add 0.1 mmol sodium bromide (NaBr) to 2 ml of DMF solution, stir well until dissolved to obtain sodium ion precursor; add 0.1 mmol copper bromide (CuBr.sub.2) to 2 ml of DMF solution, and stir well until dissolved to obtain sodium ion precursor. [0044] (3) Put 0.4 mmol of lead bromide, 2 mL of oleic acid, 2 ml of oleylamine and 40 ml of octadecene into a 100 ml three-necked flask, and then add 0.04 mL of the sodium ion precursor in step (2) and 0.04 ml of the copper ion precursor in step (2) into the three-necked flask, evacuate and then introduce with nitrogen, stir for 20 min, heat to 120 C. for 30 min for reaction, then heat to 160 C. and hold for 30 min for reaction, and then heat to 190 C. and inject into 1 ml of the cesium oleate precursor obtained in step (1) for reaction to get quantum dots (CsPb.sub.0.954Na.sub.0.031Cu.sub.0.012Br.sub.3).

Embodiment 3

[0045] A Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide (CsPbBr.sub.3) perovskite quantum dot is prepared according to the following method: [0046] (1) Preparation of cesium oleate precursor: put 0.8 g of cesium carbonate, 2.6 ml of oleic acid and 32 mL of octadecene in a 100 ml three-necked flask, stir under nitrogen flow for 20 min, heat to 120 C., and hold for 30 min to react, heat the mixture to 160 C. to obtain a brown solution, keep for 60 min for sufficient reaction to obtain the cesium oleate precursor, and then preheat to 100 C. for use. [0047] (2) Preparation of sodium ion precursor and copper ion precursor: add 0.1 mmol sodium bromide (NaBr) to 2 ml of DMF solution, stir well until dissolved to obtain sodium ion precursor; add 0.1 mmol copper bromide (CuBr.sub.2) to 2 ml of DMF solution, and stir well until dissolved to obtain sodium ion precursor. [0048] (3) Put 0.4 mmol of lead bromide, 2 mL of oleic acid, 2 ml of oleylamine and 40 ml of octadecene into a 100 ml three-necked flask, and then add 0.04 ml of the sodium ion precursor in step (2) and 0.12 mL of the copper ion precursor in step (2) into the three-necked flask, evacuate and then introduce with nitrogen, stir for 20 min, heat to 120 C. for 30 min for reaction, then heat to 160 C. and hold for 30 min for reaction, and then heat to 190 C. and inject into 1 ml of the cesium oleate precursor obtained in step (1) for reaction to get quantum dots (CsPb.sub.0.945Na.sub.0.032Cu.sub.0.023Br.sub.3).

Embodiment 4

[0049] A Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide (CsPbBr.sub.3) perovskite quantum dot is prepared according to the following method: [0050] (1) Preparation of cesium oleate precursor: put 0.8 g of cesium carbonate, 2.6 ml of oleic acid and 32 ml of octadecene in a 100 ml three-necked flask, stir under nitrogen flow for 20 min, heat to 120 C., and hold for 30 min to react, heat the mixture to 160 C. to obtain a brown solution, keep for 60 min for sufficient reaction to obtain the cesium oleate precursor, and then preheat to 100 C. for use. [0051] (2) Preparation of sodium ion precursor and copper ion precursor: add 0.1 mmol sodium bromide (NaBr) to 2 mL of DMF solution, stir well until dissolved to obtain sodium ion precursor; add 0.1 mmol copper bromide (CuBr.sub.2) to 2 ml of DMF solution, and stir well until dissolved to obtain sodium ion precursor. [0052] (3) Put 0.4 mmol of lead bromide, 2 mL of oleic acid, 2 ml of oleylamine and 40 ml of octadecene into a 100 mL three-necked flask, and then add 0.04 ml of the sodium ion precursor in step (2) and 0.16 ml of the copper ion precursor in step (2) into the three-necked flask, evacuate and then introduce with nitrogen, stir for 20 min, heat to 120 C. for 30 min for reaction, then heat to 160 C. and hold for 30 min for reaction, and then heat to 190 C. and inject into 1 ml of the cesium oleate precursor obtained in step (1) for reaction to get quantum dots (CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3).

Embodiment 5

[0053] A Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide (CsPhBr.sub.3) perovskite quantum dot is prepared according to the following method: [0054] (1) Preparation of cesium oleate precursor: put 0.8 g of cesium carbonate, 2.6 mL of oleic acid and 32 ml of octadecene in a 100 ml three-necked flask, stir under nitrogen flow for 20 min, heat to 120 C., and hold for 30 min to react, heat the mixture to 160 C. to obtain a brown solution, keep for 60 min for sufficient reaction to obtain the cesium oleate precursor, and then preheat to 100 C. for use. [0055] (2) Preparation of sodium ion precursor and copper ion precursor: add 0.1 mmol sodium bromide (NaBr) to 2 mL of DMF solution, stir well until dissolved to obtain sodium ion precursor; add 0.1 mmol copper bromide (CuBr.sub.2) to 2 mL of DMF solution, and stir well until dissolved to obtain sodium ion precursor. [0056] (3) Put 0.4 mmol of lead bromide, 2 ml of oleic acid, 2 ml of oleylamine and 40 ml of octadecene into a 100 ml three-necked flask, and then add 0.04 mL of the sodium ion precursor in step (2) and 0.20 mL of the copper ion precursor in step (2) into the three-necked flask, evacuate and then introduce with nitrogen, stir for 20 min, heat to 120 C. for 30 min for reaction, then heat to 160 C. and hold for 30 min for reaction, and then heat to 190 C. and inject into 1 ml of the cesium oleate precursor obtained in step (1) for reaction to get quantum dots (CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3).

Embodiment 6

[0057] A cesium lead bromide (CsPbBr.sub.3) perovskite quantum dot is prepared according to the following method: [0058] (1) Preparation of cesium oleate precursor: put 0.8 g of cesium carbonate, 2.6 ml of oleic acid and 32 ml of octadecene in a 100 ml three-necked flask, stir under nitrogen flow for 20 min, heat to 120 C., and hold for 30 min to react, heat the mixture to 160 C. to obtain a brown solution, keep for 60 min for sufficient reaction to obtain the cesium oleate precursor, and then preheat to 100 C. for use. [0059] (2) Put 0.4 mmol of lead bromide, 2 mL of oleic acid, 2 mL of oleylamine and 40 mL of octadecene into a 100 ml three-necked flask, evacuate and then introduce with nitrogen, stir for 20 min, heat to 120 C. for 30 min for reaction, then heat to 160 C. and hold for 30 min for reaction, and then heat to 190 C. and inject into 1 mL of the cesium oleate precursor obtained in step (1) for reaction to get CsPbBr.sub.3 quantum dots.

Embodiment 7

[0060] The CsPbBr.sub.3 perovskite quantum dots prepared in Embodiment 16 with different ratios of Cu.sup.2+ and Na.sup.+ ions co-doped and undoped CsPbBr.sub.3 quantum dots are used to form different products;

[0061] The CsPbBr.sub.3 perovskite quantum dots substituted with different ratios of Cu.sup.2+ and Na.sup.+ ions replacing A and B sites and the undoped CsPhBr.sub.3 quantum dots prepared in Embodiment 16 are added to 5 mL of ethyl acetate. After centrifugation at 6000 rpm for 8 min using a centrifuge, the supernatant is poured out, and the quantum dots at the bottom of the centrifuge tube are re-dispersed into n-hexane. This step is repeated three times, and then a part of the precipitate is dispersed in toluene to prepare a film sample, a part of the precipitate was dispersed in n-hexane to prepare a liquid sample, and a part of the precipitate was dried to prepare a powder sample.

Performance Testing

[0062] 1. The quantum dots prepared in Embodiment 16 were tested by X-ray diffraction, and the results are shown in FIG. 1. Since the ionic radius (79 pm) of copper ion (Cu.sup.2+) is much smaller than the ionic radius (133 pm) of lead ion (Pb.sup.2+), the ionic radius (116 pm) of sodium ion (Na.sup.+) is also much smaller than the ionic radius (167 pm) of cesium ions (Cs.sup.+), the octahedral contraction of cesium lead bromide (CsPbBr.sub.3) is induced by doping sodium ions (Na.sup.+) and copper ions (Cu.sup.2+) into cesium lead bromide (CsPbBr.sub.3). According to the Bragg's law: 2d sin =k, when part of lead ions (Pb.sup.2+) are substituted by copper ions (Cu.sup.2+) and part of cesium ions (Cs.sup.+) are replaced by sodium ions (Na.sup.+) ions, the interplanar spacing d will become smaller where A is a constant value, and the diffraction angle will become larger. [0063] 2. The liquid samples prepared from the perovskite quantum dots (CsPb.sub.0.545Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1 and the undoped quantum dots (CsPbBr.sub.3) in Embodiment 6 were analyzed by transmission electron microscopy and high-resolution transmission electron microscopy, and the results are shown in FIG. 2 (A and B are TEM and HR-TEM images of undoped CsPbBr.sub.3 quantum dots, C and D are TEM and HR-TEM images of CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3 quantum dots). It can be seen from (A) and (C) that the doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1 and the undoped quantum dots (CsPbBr.sub.3) in Embodiment 6 have similar morphologies both showing a cubic shape; from the high-resolution transmission electron microscopes (B) and (D), it can be seen that the interplanar distances (110) of the doped perovskite quantum dots (CsPb.sub.0.49Na.sub.0.033Cu.sub.0.019Br.sub.3) in Embodiment 1 and the undoped quantum dots (CsPbBr.sub.3) in Embodiment 6 are 0.401 nm and 0.412 nm, respectively. [0064] 3. The doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1 and the undoped quantum dots (CsPbBr.sub.3) in Embodiment 6 were analyzed by particle size analysis software, and the results are shown in FIG. 3. (A is the particle size distribution of undoped quantum dots (CsPbBr.sub.3), and B is the particle size distribution of the doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.019Br.sub.3). It can be seen from FIG. 3 that the average particle size of the doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1 and the undoped quantum dots (CsPbBr.sub.3) in Embodiment 6 is 9.88 mm and 9.71 nm, respectively. Lattice shrinkage of CsPbBr.sub.3 perovskite quantum dots doped with sodium ions (Na.sup.+) and copper ions (Cu.sup.2+) indicates that part of the larger lead ions (Pb.sup.2+) (133 pm) are replaced by smaller copper ions (Cu.sup.2+) (79 pm), and larger cesium ions (Cs.sup.+) (167 pm) were replaced by smaller sodium ions (Na.sup.+) (116 pm), which is consistent with the XRD results. [0065] 4. The liquid samples prepared from the CsPbBr.sub.3 perovskite quantum dots substituted with different ratios of Cu.sup.2+ and Na.sup.+ ions and the undoped perovskite quantum dots (CsPbBr.sub.3) in Embodiment 16 were subjected to ultraviolet light radiation, and the results of the absorption and emission spectrum tests are shown in FIG. 4, where A is the emission spectrum and B is the absorption spectrum. As can be seen from A, the liquid sample of undoped perovskite quantum dots (CsPbBr.sub.3) in Embodiment 6 exhibits typical exciton emission at 520 nm; the photoemission spectra of CsPbBr.sub.3 perovskite quantum dots doped with different ratios of Cu.sup.2+ and Na.sup.+ ions also show typical exciton emission, and their emission peaks gradually blue-shift 15 nm with the increase of doping concentration which indicates that the doping of Na.sup.+/Cu.sup.2+ ions will affect the local electronic configuration and energy band of cesium lead bromide perovskite quantum dots (CsPbBr.sub.3). In B, it can be seen that the band-edge absorption of Na and Cu co-doped cesium lead calcium bromide (CsPhBr.sub.3:Na.sup.+/Cu.sup.2+) quantum dots slightly shifts towards blue with increasing copper ion (Cu.sup.2+) concentration. The reason for this phenomenon is the effect of doping sodium ions (Na.sup.+) and copper ions (Cu.sup.2+) on the band gap of cesium lead bromide (CsPbBr.sub.3) perovskite quantum dots. [0066] 5. The emission spectra of thin film samples prepared from the doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1 and the undoped quantum dots (CsPbBr.sub.3) in Embodiment 6 were tested at variable temperatures in the range of 20120 C., and the results are as shown in FIG. 5 (A is a schematic diagram of the experimental setup, B and D are the temperature-dependent emission spectra of the Cu.sup.2+ and Na.sup.+ ions co-doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) in Embodiment 1 and the undoped CsPbBr.sub.3 quantum dots in Embodiment 6 in the range of 20120 C., respectively. C and E are 8 thermal cycle test charts of the undoped quantum dots (CsPbBr.sub.3) in Embodiment 6 and the Cu.sup.2+/Na.sup.+ co-doped perovskite quantum dots (CsPb.sub.0.49Na.sub.0.033Cu.sub.0.019Br.sub.3) in Embodiment 1, respectively. In B and C, it can be seen that the photoluminescence intensity of undoped quantum dots (CsPbBr.sub.3) and doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) gradually decreases with increasing temperature. At the end of the first heating cycle of undoped quantum dots (CsPbBr.sub.3), it sees a 70% emission decay but only about 50% emission attenuation occurs in the doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3). It can be seen from C and E that after 8 thermal cycles, the emission spectrum intensity of undoped perovskite quantum dots (CsPbBr.sub.3) dropped to about 10% of the initial value, but the emission intensity of the doped perovskite quantum dots (CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3) remains at about 40% of the initial value. Obviously, this phenomenon reflects the decisive effect of Na.sup.+/Cu.sup.2+ ions co-doping on improving the thermal stability of cesium lead bromide perovskite quantum dots (CsPbBr.sub.3). [0067] 6. The liquid samples prepared from the doped perovskite quantum dots substituted with different proportions of Cu.sup.2+ and Na.sup.+ ions co-doped perovskite quantum dots and the undoped perovskite quantum dots (CsPbBr.sub.3) in Embodiment 16 were used to prepare the active layer of the encapsulated light-emitting diode, and then the performance of the corresponding diode was tested. In FIG. 6. A is the schematic structural diagram of PeLED based on Cu.sup.2+ and Na.sup.+ co-doped and undoped CsPbBr.sub.3 QDs, B is the normalized electroluminescence (EL) and photoluminescence (PL) spectra of PeLEDs prepared from CsPbBr.sub.3 in Embodiment 6, CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 in Embodiment 1 and CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3 in Embodiment 2 (the inset is the photographs of the prepared device when it is working), C is the EL spectra of PeLEDs prepared from CsPbBr.sub.3 in Embodiment 6, CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 in Embodiment 1 and CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3 in Embodiment 2 at different voltages, D is the normalized EL and PL spectra of PeLEDs prepared from CsPb.sub.0.945Na.sub.0.032Cu.sub.0.023Br.sub.3. CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3 quantum dots in Embodiment 35 (the inset is the photographs of the prepared device when it works), E is the EL spectra of PeLEDs prepared from quantum dots of CsPb.sub.0.945Na.sub.0.032Cu.sub.0.023Br.sub.3. CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3 quantum dots in Embodiment 35 at different voltages. It can be seen from FIG. 6 that with the further increase of the doping concentration, the recombination of excitons and doping ions or the recombination between electrons and doping ions occurs, and a broad-band emission is formed in the EL spectrum, that is, the realization of variation from green to blue; bright blue light emission is clearly observed in the inset. [0068] 7. In FIG. 7, A is the current density-brightness-voltage (J-L-V) relationship diagram of the PeLED prepared by undoped quantum dots (CsPbBr.sub.3), and B-F are the current density-brightness-voltage (J-L-V) graph of the PeLEDs prepared by quantum dots of CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 (B), CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3 (C), CsPb.sub.0.954Na.sub.0.032Cu.sub.0.023Br.sub.3 (D), CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 (E) and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3 (F). It can be seen from FIG. 7 that the doping concentration will affect the performance of the device which can improve the turn-on voltage, circuit density and brightness of the device. When the doping concentration is further increased, the emission of excitons and doping ions will appear in the device. After the recombination of excitons and doping ions or the recombination between electrons and doping ions occurs inside the device, a new charged layer is formed, which changes the emission color. At the same time, after a large number of electrons are injected, the electrons and ions move faster which speeds up the carrier migration rate, might leading to leakage of the device or breakdown of the active layer, making the performance of the device worse. Therefore, there is an optimal doping concentration of sodium and copper ions, not the more, the better. [0069] 8. In FIG. 8, A is the current density-external quantum efficiency (CE-EQE) characteristic diagram of the PeLED prepared by undoped CsPbBr.sub.3 quantum dots, and B-F are the current density-external quantum efficiency (CE-EQE) characteristic diagram of the PeLED prepared by the quantum dots CsPb.sub.0.954Na.sub.0.034Cu.sub.0.012Br.sub.3 (B), CsPb.sub.0.949Na.sub.0.033Cu.sub.0.018Br.sub.3 (C), CsPb.sub.0.954Na.sub.0.032Cu.sub.0.023Br.sub.3 (D), CsPb.sub.0.933Na.sub.0.031Cu.sub.0.030Br.sub.3 (E) and CsPb.sub.0.918Na.sub.0.030Cu.sub.0.052Br.sub.3 (F). FIG. 8 shows the corresponding relationship between the current density and the external quantum efficiency of PeLEDs prepared by undoped and doped CsPbBr.sub.3 quantum dots with different concentrations of Cu.sup.2+ and Na.sup.+. Therefore, doping in semiconductors is an effective strategy to improve device performance due to the increase in conductivity, the decrease in electrode implantation barrier and the change in Fermi level.

[0070] In summary, the invention discloses a preparation method of Na.sup.+/Cu.sup.2+ ions co-doped cesium lead bromide (CsPbBr.sub.3) perovskite quantum dots, which adopts lead bromide (PhBr.sub.2), oleic acid (OA), oleylamine (OAm), sodium ion precursors and copper ion precursors for the reaction preparation in octadecene (ODE), in which copper ions (Cu.sup.2+) and sodium ions (Na.sup.+) co-doped cesium lead bromide (CsPbBr.sub.3) perovskite fluorescent quantum dots; the final product has been effectively improved in terms of photoluminescence quantum yield, thermal stability, etc., and can be used as an active layer to encapsulate electroluminescent diodes which achieve the emission color tuning from green to blue through electroluminescence of doped ion-exciton recombination.

[0071] The above descriptions are only examples of the invention, and are not used to limit the protection scope of the invention. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this invention shall be included in the protection scope of this invention.