Preparation method and application of pure purple light oxygen-doped carbon quantum rings with 18 nm half-peak width and quantum yield close to 100%

Abstract

The present application relates to the field of fluorescent carbon nanomaterials, in particular to a method for preparing pure purple light oxygen-doped carbon quantum rings with a half-peak width of 18 nm and a quantum yield close to 100% and applications thereof. The present application uses 2,3-dihydroxynaphthalene as a carbon source precursor, and prepares narrow-band purple light carbon quantum rings with a quantum yield close to 100% through a solid-phase catalytic reaction. The carbon quantum rings prepared by the present application have a hexagonal ring structure with oxygen doping, and have a wide application prospect in the field of display devices.

Description

Technical Field

[0001] The invention relates to the field of fluorescent carbon nanomaterials, and in particular to a preparation method and application of a pure violet oxygen-doped carbon quantum ring with an emission half-peak width of 18nm and a quantum yield of nearly 100%. Background Art

[0002] Based on the type of luminescent material, self-luminous displays can be divided into organic light-emitting diodes (OLEDs), quantum dot light-emitting diodes (QLEDs), and perovskite light-emitting diodes (PeLEDs). OLEDs with narrow-band luminescence have already entered practical application in flat-panel displays such as smartphones and televisions. However, most current OLED products often use vacuum evaporation technology, which has disadvantages such as high cost, complex device structure, and low yield, which greatly hinders their further large-scale production. In contrast, QLEDs and PeLEDs have the characteristics of solution processing, high fluorescence quantum yield (PLQY), and narrow bandwidth, and can be produced on a large scale through solution processing. However, due to the toxicity of heavy metal elements (Cd, Pb, etc.), relatively poor colloidal and photothermal stability, and susceptibility to aggregation degradation and photobleaching, it is necessary to explore and develop new narrow-band luminescent quantum dots with non-toxicity, high stability, and excellent fluorescence properties for next-generation display technology.

[0003] Carbon quantum dots (CQDs), a new member of the carbon nanomaterial family, are zero-dimensional (0D) nanomaterials characterized by thin graphene sheets (typically 1-3 layers, less than 2 nm thick) with lateral dimensions typically less than 10 nm. Compared to two-dimensional graphene, CQDs offer several unique advantages, including wavelength tunability due to quantum confinement, a rich array of active centers (edges, functional groups, dopants, etc.), and excellent biocompatibility. More importantly, compared to traditional organic small molecules and semiconductor quantum dots, CQDs offer multiple advantages, including solution processability, low toxicity, and mechanical flexibility, making them promising candidates for the next generation of large-scale display devices. However, due to the irreducible π-conjugation length and strong excited-state vibrational relaxation, CQDs struggle to simultaneously achieve emission peaks with a half-width below 20 nm and a wavelength shorter than 400 nm, limiting their application in wide-color-gamut displays. Summary of the Invention

[0004] The purpose of the present invention is to provide a pure violet oxygen-doped carbon quantum ring with an emission half-peak width of 18nm and a quantum yield of nearly 100%.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned carbon quantum ring.

[0006] Another object of the present invention is to provide applications of the carbon quantum rings.

[0007] Another object of the present invention is to apply the prepared pure violet oxygen-doped carbon quantum ring material with an emission half-maximum width of 18 nm and a quantum yield of nearly 100% to electroluminescent diode devices.

[0008] According to the present invention, a pure violet oxygen-doped carbon quantum ring with an emission half-maximum width of 18 nm and a quantum yield of nearly 100% is prepared by a method comprising the following steps:

[0009] (1) 2,3-Dihydroxynaphthalene is used as a carbon source precursor, ground and thoroughly mixed with the catalyst anhydrous stannous chloride. The mixture is placed in a high-pressure reactor, heated in an oven, and reacted at 180°C for 8 hours to obtain a gray-black block solid containing carbon quantum rings.

[0010] (2) The gray-black block solid was added to dichloromethane several times, and the solid was dissolved under ultrasonic conditions to obtain a solution containing carbon quantum rings.

[0011] (3) The solution after the reaction was collected, and a mixed solvent of petroleum ether / dichloromethane was used as an eluent, and the solution was purified by column chromatography on alkaline alumina and silica gel in sequence, and finally freeze-dried to obtain a solid powder of carbon quantum rings.

[0012] The present invention will be further explained and illustrated below.

[0013] This invention addresses the current challenges of CQDs, which suffer from irreducible π-conjugation length and strong excited-state vibrational relaxation, making it difficult to simultaneously achieve a luminescence peak with a half-width below 20nm and a wavelength shorter than 400nm. The present invention provides a method for preparing and applying pure violet oxygen-doped carbon quantum rings with an emission half-width of 18nm and a quantum yield of nearly 100%.

[0014] According to the technical solution of the present invention, the catalyst anhydrous stannous chloride is crucial for preparing pure violet oxygen-doped carbon quantum rings with an emission half-width of 18nm and a quantum yield of nearly 100%. However, if the anhydrous stannous chloride is replaced with a Lewis acid such as anhydrous aluminum chloride while maintaining the same reaction conditions, the narrow-band pure violet carbon dots cannot be obtained.

[0015] According to the technical solution of the present invention, high temperature and high pressure solid-phase synthesis conditions are also crucial for preparing pure violet oxygen-doped carbon quantum rings with an emission half-width of 18nm and a quantum yield of nearly 100%. If traditional solvothermal reactions are used, it is impossible to synthesize pure violet carbon dots with narrow-band emission.

[0016] According to the technical solution of the present application, in step (1), the mass ratio of the catalyst to the carbon source precursor is 1:5 to 1:1.5. The ratio of the carbon source precursor to anhydrous stannous chloride within this range hardly affects the yield of pure violet oxygen-doped carbon quantum rings, indicating that the amount of anhydrous stannous chloride at this ratio is sufficient to support catalysis and assist dehydration.

[0017] The invention utilizes a high-temperature, high-pressure solid-phase synthesis strategy. Further optimization yields pure violet oxygen-doped carbon quantum rings with an emission half-width of 18 nm and a quantum yield of nearly 100%. The fluorescence emission peak remains unchanged with changes in excitation wavelength, and the fluorescence quantum yield reaches as high as 95%. Multiple column chromatography purification steps yield the carbon quantum rings in solid powder. The method is simple, highly controllable, and suitable for mass production.

[0018] The carbon quantum rings prepared by the present invention have a planar, oxygen-doped hexagonal ring structure consisting of 12 benzene rings and 6 embedded five-membered oxygen heterocycles. These carbon quantum rings have broad application prospects in optoelectronic devices. When applied to display electroluminescent diodes, they exhibit advantages such as high color purity, low turn-on voltage, and high brightness. They are expected to be used as low-cost, environmentally friendly, and novel luminescent materials in the display electroluminescent diode field. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a three-dimensional fluorescence spectrum of the carbon quantum ring prepared in Example 1;

[0020] Figure 2 This is the UV-visible absorption spectrum of the carbon quantum ring prepared in Example 1;

[0021] Figure 3 This is the time-resolved fluorescence spectrum of the carbon quantum ring prepared in Example 1;

[0022] Figure 4 This is a scanning tunneling microscope image of the carbon quantum ring prepared in Example 1;

[0023] Figure 5 This is the infrared spectrum of the carbon quantum ring prepared in Example 1;

[0024] Figure 6 is the X-ray photoelectron spectrum of the carbon quantum ring prepared in Example 1;

[0025] Figure 7 This is the Raman spectrum of the carbon quantum ring prepared in Example 1;

[0026] Figure 8 The device structure of the violet electroluminescent diode prepared in Example 2;

[0027] Figure 9 The current density-voltage-brightness characteristic curve of the purple light emitting diode prepared in Example 2;

[0028] Figure 10 This is a graph showing the external quantum efficiency-current density characteristic of the purple light-emitting diode prepared in Example 2;

[0029] Figure 11 The luminescence spectrum of the purple light-emitting diode prepared in Example 2 varies with voltage;

[0030] Figure 12 These are the color coordinates corresponding to the electrochromic spectrum of the purple light-emitting diode prepared in Example 2 when the voltage is 6V. DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0032] Example 1: Preparation of a pure violet oxygen-doped carbon quantum ring with an emission half-peak width of 18 nm and a quantum yield of nearly 100%

[0033] 500 mg of 2,3-dihydroxynaphthalene is used as a carbon source precursor, and it is ground to be fully mixed with 1000 mg of anhydrous stannous chloride as a catalyst. The mass ratio of the catalyst to the carbon source precursor is 1:2. Place it in a high-pressure reactor, heat it in an oven, and react at 180°C for 8 hours to obtain a gray-black block solid containing a carbon quantum ring. Add dichloromethane to the above-mentioned gray-black block solid several times, dissolve the solid under an ultrasonic environment, and obtain a solution containing a carbon quantum ring. Collect the solution after the above reaction, use a mixed solvent of petroleum ether / dichloromethane as an eluent, and purify it by column chromatography through alkaline alumina and silica gel in sequence, and finally freeze-dry to obtain a solid powder of the carbon quantum ring.

[0034] The dilute solution of carbon quantum ring emits bright purple fluorescence under a portable ultraviolet lamp (365nm), showing the excitation-independent eigenstate fluorescence characteristics ( Figure 1 ), the emission peak is at 398nm. The characteristic exciton absorption peak of the purple carbon quantum ring is at 377nm ( Figure 2 ), the smaller Stokes shift indicates a smaller ground-excited state equilibrium structure shift. Time-resolved fluorescence spectroscopy shows that the purple carbon quantum ring decays in a single exponential manner with a lifetime of 5.6ns ( Figure 3 The absolute fluorescence quantum yield was measured to be as high as 95%.

[0035] Scanning tunneling microscopy observed that the purple carbon quantum ring is a hollow regular hexagonal ring structure with uniform size distribution and an outer diameter of about 1.9nm ( Figure 4The infrared spectrum of carbon quantum rings proves the existence of CO chemical bonds in carbon dots. Combined with the results of scanning tunneling microscopy, it shows that O atoms exist in the form of oxygen-containing five-membered rings ( Figure 5 The results of X-ray photoelectron spectroscopy show that the carbon quantum ring is mainly composed of two elements, C and O, with a C:O ratio of approximately 7.09:1 ( Figure 6 ). I in Raman spectroscopy G / I D The ratio is as high as 1.7( Figure 7 ), indicating that the degree of graphitization of carbon dots is very high.

[0036] Example 2: Preparation of a purple electroluminescent diode

[0037] The above-prepared pure violet oxygen-doped carbon quantum ring is used as the active light-emitting layer in a monochromatic electroluminescent diode. Figure 8 As shown, the light-emitting diode device structure, from bottom to top, includes a transparent glass substrate (glass), an anode layer (ITO), a hole injection layer of poly (3,4-ethylenedioxythiophene):polystyrenesulfonate) (PEDOT:PSS), an electron transport layer of poly ((9,9-dioctylfluorenyl-2,7-diyl)-CO-(4,4'-(N-(p-butylphenyl))diphenyl)) (TFB), an active light-emitting layer of 1,3-di-9-carbazolylbenzene (m-CP):diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (TSPO1): carbon quantum rings, an electron transport layer of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBI), and a cathode layer (LiF / Al). The electroluminescent diode device structure is described as: ITO / PEDOT:PSS / TFB / m-CP:TSPO1:OD-CQRs / TPBI / LiF / Al.

[0038] The preparation method of the ultraviolet electroluminescent diode device is as follows:

[0039] (1) Ultrasonic cleaning of the transparent conductive substrate ITO glass was performed using acetone solution, isopropyl alcohol solution, and deionized water. After cleaning, it was blown dry with dry nitrogen. The film was then baked in an oven at 150°C for 10 minutes. The ITO film on the glass substrate served as the anode layer of the device.

[0040] (2) The dried substrate was moved into a vacuum chamber and the ITO glass was pretreated with UV ozone for 15 min under an oxygen pressure environment;

[0041] (3) Spin-coat PEDOT:PSS onto the treated ITO at 4000 rpm for 30 s to a thickness of 40 nm. Anneal in an oven at 150°C for 15 min.

[0042] (4) Spin-coat a solution of m-CP:TSPO1:OD-CQRs in o-dichlorobenzene (OD-CQRs doping mass fraction 5%) onto the PEDOT:PSS layer at 3000 rpm for 30 s to a thickness of 10 nm. Anneal in an 80°C oven for 30 min.

[0043] (5) Then ITO was transferred to a nitrogen glove box. 40 nm TPBI was vacuum-deposited at a pressure of 3 × 10 -4 Pa, the evaporation rate is 0.1 nm / s, and the evaporation rate and thickness are monitored by a film thickness meter;

[0044] (6) Then vacuum evaporate 1nm LiF, 100nm Al, and the pressure is 3×10 -4 Pa, the evaporation rate was 0.02 and 0.3 nm / s, and the evaporation rate and thickness were monitored by a film thickness meter;

[0045] (7) The device is not packaged, and the current-voltage-brightness characteristics of the device are directly tested, and the luminous spectrum parameters of the device are tested at the same time; the current density-voltage-brightness characteristic curve of the device is as follows Figure 9 The purple light emitting diode can achieve a low turn-on voltage of 3.3V and a maximum brightness of 1634cd / m 2 , the maximum external quantum efficiency is 4.4% ( Figure 10 The peak value of the violet diode is 398nm, and the half-peak width is only 24nm ( Figure 11 ), the corresponding color coordinates are (0.161, 0.017) ( Figure 12 ), showing higher color purity.

[0046] Comparative Example 1

[0047] 500 mg of 2,3-dihydroxynaphthalene was used as a carbon source precursor, ground and fully mixed with 1000 mg of anhydrous aluminum chloride (catalyst), with the mass ratio of the catalyst to the carbon source precursor being 1:2. The mixture was placed in a high-pressure reactor, heated in an oven, and reacted at 180°C for 8 hours to obtain a gray-black block solid. The gray-black block solid was added to dichloromethane several times, dissolved in an ultrasonic environment, and then purified by column chromatography on basic alumina and silica gel. No narrow-band luminescent carbon dots were obtained, and the obtained carbon dot solution was sky blue with a broad-band luminescence.

[0048] Comparative Example 2:

[0049] 500 mg of 2,3-dihydroxynaphthalene was used as a carbon source precursor, ground and thoroughly mixed with 1000 mg of anhydrous stannous chloride (catalyst), with the mass ratio of the catalyst to the carbon source precursor being 1:2. 50 mL of ethanol was added as the reaction solvent. The mixture was placed in a high-pressure reactor, heated in an oven, and subjected to a solvothermal reaction at 180°C for 8 hours. The product was purified by column chromatography on alkaline alumina and silica gel in turn, but no narrow-band luminescent carbon dots were obtained. The obtained carbon dot solution emitted broad-band sky blue and green light.

[0050] The above embodiments are implemented based on the technical solutions of the present invention, and detailed implementation methods and processes are provided. However, the protection scope of the present invention is not limited to the above embodiments.

Claims

1. A pure violet oxygen-doped carbon quantum ring with an emission half-maximum width of 18 nm and a quantum yield of nearly 100%, characterized by: The quantum ring is prepared by a method comprising the following steps: (1) 2,3-dihydroxynaphthalene was used as a carbon source precursor, ground and fully mixed with the catalyst anhydrous stannous chloride, placed in a high-pressure reactor, and heated at 180 o C conditions for 8 hours to obtain a gray-black block solid containing carbon quantum rings; (2) adding dichloromethane to the gray-black block solid several times, dissolving the solid under ultrasonic conditions to obtain a solution containing carbon quantum rings; (3) collecting the solution containing the carbon quantum rings, purifying it, and drying it to obtain a solid powder of the carbon quantum rings.

2. The pure violet oxygen-doped carbon quantum ring with an emission half-maximum width of 18 nm and a quantum yield of nearly 100% according to claim 1, characterized in that: In step (3), a mixed solvent of petroleum ether / dichloromethane is used as an eluent, and column chromatography is performed sequentially through alkaline alumina and silica gel, and freeze-dried to obtain a solid powder of the carbon quantum ring.

3. The pure violet oxygen-doped carbon quantum ring with an emission half-maximum width of 18 nm and a quantum yield of nearly 100% according to claim 1, characterized in that: In step (1), the mass ratio of the catalyst to the carbon source precursor is 1:5 to 1:1.

5.

4. A method for preparing a pure violet oxygen-doped carbon quantum ring with an emission half-maximum width of 18 nm and a quantum yield of nearly 100%, characterized in that: The method comprises the following steps: (1) 2,3-dihydroxynaphthalene was used as a carbon source precursor, ground and fully mixed with the catalyst anhydrous stannous chloride, placed in a high-pressure reactor, and heated at 180 o C conditions for 8 hours to obtain a gray-black block solid containing carbon quantum rings; (2) adding dichloromethane to the gray-black block solid several times, dissolving the solid under ultrasonic conditions to obtain a solution containing carbon quantum rings; (3) collecting the solution containing the carbon quantum rings, purifying it, and drying it to obtain a solid powder of the carbon quantum rings.

5. The method for preparing a pure violet oxygen-doped carbon quantum ring with an emission half-maximum width of 18 nm and a quantum yield of nearly 100% according to claim 4, characterized in that: In step (1), the mass ratio of the catalyst to the carbon source precursor is 1:5 to 1:1.

5.

6. Application of the pure violet oxygen-doped carbon quantum ring with an emission half-maximum width of 18 nm and a quantum yield of nearly 100% as claimed in claim 1 in display electroluminescent diodes.

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