A method for preparing fluorescent carbon dots with high fluorescence quantum efficiency and narrow emission peak half-width and its application

Abstract

This invention provides a method for preparing fluorescent carbon dots with high fluorescence quantum efficiency and narrow emission peak half-width, and its applications. The method includes the following steps: using 1,5-naphthyldiamine and aromatic aldehyde as precursors, adding them to a certain volume of alcohol solvent, with or without an acid catalyst, ultrasonically mixing, and then transferring to a reaction vessel with a polytetrafluoroethylene liner for a solvothermal reaction. After the reaction, the product is centrifuged, and the supernatant is collected to obtain fluorescent carbon dots; the fluorescent carbon dots are blue fluorescent carbon dots and / or blue-green fluorescent carbon dots. This preparation method has a simple synthesis process and high reproducibility. The obtained fluorescent carbon dots have high fluorescence quantum efficiency and extremely narrow half-width, giving them excellent optical properties. They can be widely used in fields such as ultra-high-definition display backlights and lighting with wide color gamut and high color purity.

Description

Technical Field

[0001] This invention belongs to the fields of chemistry and carbon nanomaterials technology, specifically including a method and application for preparing fluorescent carbon dots with high fluorescence quantum efficiency and narrow emission peak half-width. Background Technology

[0002] Carbon dots are zero-dimensional carbon nanoparticles with a size less than 10 nm. In 2004, Xu et al. accidentally discovered fluorescent carbon dots while separating and purifying single-walled carbon nanotubes using electrophoresis [J. Am. Chem. Soc., 2004, 126, 12736], but their fluorescence quantum efficiency was very low. With the continuous development of materials science, research on carbon dots has deepened, and their effects have become increasingly significant. Carbon dots possess advantages such as environmental friendliness, wide availability of raw materials, high chemical and photochemical stability, and high luminescence efficiency, and have been widely applied and researched in numerous fields, including cell imaging, sensitivity detection of chemical and biological species, optoelectronic devices, solar energy conversion, and pollution control.

[0003] The International Telecommunication Union (ITU) stated at REC2020 that the full width at half maximum (FWHM) of backlights for ultra-high-definition displays (UHD displays) with a wider color gamut and better color reproduction should be less than 20 nm; the peak positions of the red, green, and blue primary colors should be as close as possible to 637 nm, 532 nm, and 467 nm, respectively. Currently reported high-purity blue and blue-green fluorescent materials with high luminous efficiency and narrow emission (FWHM < 30 nm) are mostly II-VI group semiconductor quantum dots, lead-containing perovskite quantum dots, or nanocrystals. In comparison, carbon dots do not contain highly toxic heavy metal ions, resulting in less environmental hazard and cytotoxicity. Furthermore, carbon dots have better environmental stability, making them a promising candidate for use as luminescent materials in UHD display backlights. However, most blue and blue-green fluorescent carbon dots synthesized by commonly used top-down and bottom-up methods typically have a fluorescence peak FWHM above 60 nm, with very few below 40 nm, let alone below 20 nm, which is insufficient to meet the requirements of carbon dots in the field of ultra-high-definition display backlights. Yuan et al. used 1,5-naphthyldiamine and citric acid as precursors and obtained deep blue fluorescent carbon dots with a fluorescence quantum efficiency of up to 70% through solvothermal treatment, high-temperature post-treatment with ammonia-hydrazine solution, and complex column chromatography separation techniques. However, the emission peak position was at 433 nm and the FWHM was 35 nm. The entire synthesis process was cumbersome and complex and the yield of the target carbon dots was very low [Nature Photonics, 2020, 14(3): 171-176]. Yoshinaga et al. obtained blue fluorescent carbon dots (481 nm) with an FWHM of 30 nm and blue-green fluorescent carbon dots (511 nm) with an FWHM of 27 nm by open heating of a 1,2-butanediol solution of phloroglucinol at 180 °C, combined with 2 days of dialysis and high-speed centrifugation washing at 16,000 rpm / min [7, ACS Omega, 2021, 6, 1741-1750]. However, their results did not meet the application requirements. Therefore, it is crucial to study a simple and rapid method to prepare high-brightness, high-color-purity blue and blue-green fluorescent carbon dots with an FWHM less than 50 nm, especially to prepare high-brightness, high-color-purity blue and blue-green fluorescent carbon dots with an FWHM ≤ 20 nm, for their application in the field of ultra-high-definition displays. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, the first objective of this invention is to provide a method for preparing fluorescent carbon dots with high fluorescence quantum efficiency and narrow emission peak half-width. This preparation method is simple, fast, time-saving, highly efficient, lossless, and highly reproducible.

[0005] The second objective of this invention is to provide a fluorescent carbon dot obtained by the above-described preparation method. This fluorescent carbon dot exhibits high color purity, high brightness, high fluorescence quantum efficiency, and an extremely narrow emission peak half-width, which better meets the application requirements of ultra-high-definition display backlights in the prior art.

[0006] A third objective of this invention is to provide an application of fluorescent carbon dots as described above in the fabrication of backlights or lighting elements for ultra-high-definition displays.

[0007] To achieve the first objective mentioned above, the technical solution adopted by this invention includes:

[0008] This invention discloses a method for preparing fluorescent carbon dots with high fluorescence quantum efficiency and narrow emission peak half-width, comprising the following steps:

[0009] Using 1,5-naphthyldiamine and aromatic aldehyde as precursors, a certain volume of alcohol solvent was added, with or without an acid catalyst. After ultrasonic mixing, the mixture was transferred to a reaction vessel with a polytetrafluoroethylene liner for solvothermal reaction. After the reaction was completed, the product was centrifuged and the supernatant was collected to obtain fluorescent carbon dots.

[0010] The fluorescent carbon dots are blue fluorescent carbon dots and / or blue-green fluorescent carbon dots.

[0011] To address the stringent requirements for luminescence efficiency and emission peak half-width in existing technologies, this invention presents a novel route for preparing fluorescent carbon dots. Specifically, based on the Schiff base reaction process, using 1,5-naphthyldiamine (containing an amino group) and an aromatic aldehyde (containing an aldehyde group) as common carbon sources, a one-step solvothermal method successfully prepares blue and / or blue-green fluorescent carbon dots with high color purity, high brightness, high fluorescence quantum efficiency, and extremely narrow emission peak half-width. The entire preparation process is simple, rapid, efficient, and lossless. By precisely controlling the amounts of 1,5-naphthyldiamine and aromatic aldehyde, as well as the solvothermal reaction conditions, high-purity blue or blue-green fluorescent carbon dots can be obtained. Of course, to further improve the purity of the fluorescent carbon dots, column chromatography purification is added to obtain pure blue or blue-green fluorescent carbon dots. Testing revealed that when the fluorescent carbon dots are blue, their emission peak position is around 480 nm, with a half-width at half-maximum (WHM) of ≤25 nm, optimally controllable at 18 nm, and a fluorescence quantum efficiency ≥80%. This is currently the blue fluorescent carbon dot with the narrowest FWHM and highest color purity reported in the literature. When the fluorescent carbon dots are blue-green, their emission peak position is around 490 nm, with a WHM of <50 nm, optimally controllable at 20 nm, and a fluorescence quantum efficiency ≥65%. Due to the excellent optical properties of the obtained fluorescent carbon dots, they can be widely used in the fabrication of backlights or lighting elements for ultra-high-definition displays with wide color gamut and high color purity.

[0012] Furthermore, the mass ratio of the 1,5-naphthyldiamine, aromatic aldehyde, and acid catalyst is 100:60-200:0-300; exemplaryly, the mass ratio of the 1,5-naphthyldiamine, aromatic aldehyde, and organic acid can also be 100:100-200:100-300, 100:100-150:200-300, 100:100-200:200-300, 100:100-150:250-300, 100:60-200:0-150, 100:60-200:200-300, etc.

[0013] Furthermore, the aromatic aldehydes include, but are not limited to, one or more combinations of benzaldehyde, terephthalaldehyde, or salicylaldehyde;

[0014] Furthermore, the alcohol solvent includes, but is not limited to, one or more combinations of methanol, ethanol, isopropanol, or ethylene glycol;

[0015] Furthermore, the mass-to-volume ratio of the 1,5-naphthyldiamine to the alcohol solvent is 0.1g:15-30mL; exemplaryly, the mass-to-volume ratio of the 1,5-naphthyldiamine to the alcohol solvent can also be 0.1g:15-17.5mL, 0.1g:15-20mL, 0.1g:15-25mL, 0.1g:20-25mL, 0.1g:20-30mL, 0.1g:25-30mL, etc.

[0016] Furthermore, the acid catalyst includes, but is not limited to, one or more combinations of acetic acid, formic acid, and benzenesulfonic acid.

[0017] Furthermore, the temperature of the solvothermal reaction is 100–200°C, and the reaction time is 100–720 min.

[0018] Furthermore, the ultrasonic treatment time is 5 to 30 minutes.

[0019] Furthermore, to further improve the purity of the fluorescent carbon dots, those skilled in the art can introduce some commonly used purification methods, such as column chromatography, according to experimental needs; in one specific embodiment, the separation and purification of the supernatant is introduced, and the specific steps are as follows:

[0020] The supernatant was added to a silica gel chromatography column, and a mixed solution of ethanol and ethyl acetate was used as the eluent to separate and collect different batches of the separated products, yielding a pure fluorescent carbon dot eluent.

[0021] Furthermore, the eluent was prepared with ethanol and ethyl acetate in a volume ratio of 5:4.

[0022] To achieve the second objective mentioned above, the technical solution adopted by the present invention includes:

[0023] This invention discloses a fluorescent carbon dot prepared by the above method, wherein the particle size of the fluorescent carbon dot is 1-5 nm.

[0024] Furthermore, when the fluorescent carbon dots are blue fluorescent carbon dots, their emission peak position is around 480 nm, and the half-width at half-maximum (WHM) of the emission peak is ≤25 nm. When excited by 460 nm light, the fluorescence quantum efficiency is ≥80%. The emission exhibits wavelength-independent characteristics when the excitation wavelength is between 350 and 465 nm. It is particularly important to emphasize that, by controlling the reaction temperature, reaction time, and raw material dosage, the WHM can be as narrow as 18 nm.

[0025] Furthermore, when the fluorescent carbon dots are blue-green fluorescent carbon dots, their emission peak position is around 490 nm, and the half-width at half-maximum (WHM) of the emission peak is <50 nm. When excited by 460 nm light, the fluorescence quantum efficiency is ≥65%. The emission exhibits excitation wavelength independence when the excitation wavelength is between 350 and 465 nm. It is particularly important to emphasize that, by controlling the reaction temperature, reaction time, and raw material dosage, the WHM can be as narrow as 20 nm.

[0026] To achieve the third objective mentioned above, the technical solution adopted by this invention includes:

[0027] This invention discloses an application of fluorescent carbon dots as described above in the fabrication of backlights or lighting elements for ultra-high-definition displays.

[0028] Beneficial effects of this invention:

[0029] This invention utilizes 1,5-naphthyldiamine and aromatic aldehydes as precursors, employing a one-step solvothermal method via a Schiff base reaction to prepare high-purity blue and blue-green fluorescent carbon dots with a fluorescence peak half-width (HWHM) of less than 50 nm. The blue and blue-green fluorescent carbon dots prepared by this invention exhibit wavelength-independent emission characteristics, with emission positions around 480 nm and 490 nm, respectively, and HWHMs less than 50 nm. Notably, when excited by 460 nm light, the fluorescence quantum efficiency of the blue fluorescent carbon dots exceeds 80%, and the HWHM can be as narrow as 18 nm, the smallest reported value to date. This invention features a simple and low-cost preparation process, and the high-purity fluorescent carbon dots prepared have broad application prospects in display and lighting fields. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the synthesis technology of high-color-purity fluorescent carbon dots in Example 1 of the present invention.

[0031] Figure 2 This is a TEM image of the high-purity blue fluorescent carbon dots obtained in Example 1 of the present invention;

[0032] Figure 3The absorption and excitation spectra of the high-purity blue fluorescent carbon dot ethanol solution obtained in Example 1 of this invention are shown.

[0033] Figure 4 This is a graph showing the fluorescence spectrum of the high-purity blue fluorescent carbon dot ethanol solution obtained in Example 1 of the present invention as a function of excitation wavelength.

[0034] Figure 5 The graph shows the relative fluorescence quantum efficiency of the high-purity blue fluorescent carbon dot ethanol solution obtained in Example 1 of this invention under light excitation at 460 nm.

[0035] Figure 6 This is a graph showing the fluorescence spectrum of the high-purity blue-green fluorescent carbon dot ethanol solution obtained in Example 1 of the present invention as a function of excitation wavelength.

[0036] Figure 7 The fluorescence spectra of the fluorescent carbon dot ethanol solutions prepared in Examples 2, 3, and 4 of this invention under light excitation at 460 nm are shown.

[0037] Figure 8 The fluorescence spectra of the fluorescent carbon dot ethanol solutions prepared in Examples 5, 6, and 7 of this invention under light excitation at 460 nm are shown.

[0038] Figure 9 The fluorescence spectrum of the high-purity fluorescent carbon dot ethanol solution prepared in Example 10 of this invention under light excitation at 460 nm.

[0039] Figure 10 This is a graph showing the fluorescence spectrum of the fluorescent carbon dot ethanol solution prepared in Comparative Example 1 of this invention as a function of excitation wavelength.

[0040] Figure 11 The graph shows the fluorescence spectrum of the fluorescent carbon dot ethanol solution prepared in Comparative Example 2 of this invention as a function of excitation wavelength.

[0041] Figure 12 This is a graph showing the fluorescence spectrum of the fluorescent carbon dot ethanol solution prepared in Comparative Example 3 of this invention as a function of excitation wavelength.

[0042] Figure 13 This is a graph showing the fluorescence spectrum of the fluorescent carbon dot ethanol solution prepared in Comparative Example 4 of this invention as a function of excitation wavelength. Detailed Implementation

[0043] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] 0.1 g of 1,5-naphthyldiamine, 0.153 g of benzaldehyde, and 0.210 g of acetic acid were added to 15 mL of ethanol and ultrasonically dispersed for 30 min. The mixture was then transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and reacted at 200 °C for 200 min. After natural cooling to room temperature, the mixture was centrifuged at 12000 r / min for 15 min, and the supernatant was collected. Using a 5:4 mixture of ethanol and ethyl acetate as the eluent, the supernatant was separated by silica gel column chromatography to obtain high-purity blue fluorescent carbon dots with an FWHM of 18 nm and high-purity blue-green fluorescent carbon dots with an FWHM of 20 nm.

[0046] The synthesis route diagram of the high-color-purity fluorescent carbon dots obtained in this embodiment is as follows: Figure 1 As shown.

[0047] The TEM image of the high-purity blue fluorescent carbon dots obtained in this embodiment is as follows. Figure 2 As shown.

[0048] The optical properties of the high-purity blue fluorescent carbon dots prepared in this embodiment are as follows: Figures 3-5 As shown, the UV-Vis absorption spectrum indicates that this carbon point has two distinct absorption peaks at approximately 440 nm and 469 nm. Figure 3 When the excitation wavelength varies between 350 and 465 nm, the emission spectrum of this blue fluorescent carbon dot exhibits a characteristic where the emission position is independent of the excitation wavelength. The corresponding emission peak position is 479 nm, while the FWHM is only 18 nm. Figure 4 Using fluorescein as a reference, the relative fluorescence quantum efficiency of this carbon dot was 84.8% when excited by light at 460 nm. Figure 5 This demonstrates that ultra-bright, high-purity blue fluorescent carbon dots can indeed be obtained through this invention.

[0049] The fluorescence spectrum of the high-purity blue-green fluorescent carbon dots prepared in this embodiment is shown in the figure below. Figure 6 As shown, when the excitation wavelength varies between 350 and 465 nm, the emission spectrum of this blue-green fluorescent carbon dot also exhibits a characteristic where the emission position is independent of the excitation wavelength. The corresponding emission peak position is 490 nm, and the FWHM is only 20 nm. Using fluorescein as a reference, the relative fluorescence quantum efficiency of this carbon dot was measured to be 67.5% when excited by light at 460 nm. This demonstrates that ultra-bright, high-purity blue-green fluorescent carbon dots can indeed be obtained through this invention.

[0050] Example 2

[0051] Add 0.1 g of 1,5-naphthyldiamine, 0.1 g of terephthalaldehyde, and 0.210 g of acetic acid to 15 mL of methanol. After sonicating for 30 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 100 °C for 360 min, then allow to cool naturally to room temperature. Centrifuge at 12000 rpm for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0052] The FWHM of the carbon dot fluorescence emission peak obtained in this embodiment is 22 nm, and the fluorescence peak is located at 490 nm.

[0053] Example 3

[0054] Add 0.1 g of 1,5-naphthyldiamine, 0.1 g of terephthalaldehyde, and 0.263 g of acetic acid to 15 mL of ethylene glycol. After sonicating for 15 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 150 °C for 150 min, then allow to cool naturally to room temperature. Centrifuge at 12000 rpm for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0055] The FWHM of the carbon dot fluorescence emission peak obtained in this embodiment is 23 nm, and the fluorescence peak is located at 491 nm.

[0056] Example 4

[0057] Add 0.1 g of 1,5-naphthyldiamine, 0.067 g of benzaldehyde, and 0.131 g of acetic acid to 15 mL of isopropanol. After sonicating for 15 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 150 °C for 150 min, then allow to cool naturally to room temperature. Centrifuge at 12000 rpm for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0058] The FWHM of the carbon dot fluorescence emission peak obtained in this embodiment is 22 nm, and the fluorescence peak is located at 488 nm.

[0059] Example 5

[0060] Add 0.1 g of 1,5-naphthyldiamine, 0.163 g of salicylaldehyde, and 0.210 g of acetic acid to 15 mL of ethanol. After sonicating for 30 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 200 °C for 200 min, then allow to cool naturally to room temperature. Centrifuge at 12000 r / min and collect the supernatant to obtain fluorescent carbon dots.

[0061] The FWHM of the carbon dot fluorescence emission peak obtained in this embodiment is 22 nm, and the fluorescence peak is located at 495 nm.

[0062] Example 6

[0063] Add 0.1 g of 1,5-naphthyldiamine, 0.153 g of benzaldehyde, and 0.210 g of acetic acid to 15 mL of methanol. After sonication for 5 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 100 °C for 360 min, then allow to cool naturally to room temperature. Centrifuge at 12000 rpm for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0064] The FWHM of the carbon dot fluorescence emission peak obtained in this embodiment is 20 nm, and the fluorescence peak is located at 489 nm.

[0065] Example 7

[0066] Add 0.1 g of 1,5-naphthyldiamine, 0.2 g of terephthalaldehyde, and 0.131 g of acetic acid to 15 mL of methanol. After sonication for 5 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 100 °C for 540 min, then allow to cool naturally to room temperature. Centrifuge at 12000 rpm for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0067] The FWHM of the carbon dot fluorescence emission peak obtained in this embodiment is 21 nm, and the fluorescence peak is located at 491 nm.

[0068] Example 8

[0069] Add 0.1 g of 1,5-naphthyldiamine, 0.067 g of benzaldehyde, and 0.210 g of acetic acid to 15 mL of ethanol. After ultrasonic dispersion for 30 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 200 °C for 200 min, then allow to cool naturally to room temperature. Centrifuge at 12000 r / min for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0070] Example 9

[0071] Add 0.1 g of 1,5-naphthyldiamine, 0.164 g of benzaldehyde, and 0.105 g of acetic acid to 15 mL of ethanol. After sonicating for 10 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 100 °C for 720 min, then allow to cool naturally to room temperature. Centrifuge at 12000 rpm for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0072] Example 10

[0073] 0.1 g of 1,5-naphthyldiamine and 0.153 g of benzaldehyde were added to 15 mL of ethanol. After sonication for 30 min, the mixture was transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). The reaction was carried out at 200 °C for 200 min, and then allowed to cool naturally to room temperature. The supernatant was collected after centrifugation at 12000 r / min. Using a mixture of ethanol and ethyl acetate (5:4) as the eluent, the supernatant obtained by separation by silica gel column chromatography was dissolved in ethanol after rotary evaporation to obtain high-purity fluorescent carbon dots.

[0074] The high-purity carbon dot fluorescence emission peak obtained in this embodiment has an FWHM of 37 nm and a fluorescence peak at 490 nm.

[0075] Example 11

[0076] Add 0.1 g of 1,5-naphthyldiamine, 0.157 g of benzaldehyde, and 0.131 g of acetic acid to 30 mL of ethanol. After sonicating for 30 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 200 °C for 100 min, then allow to cool naturally to room temperature. Centrifuge at 12000 r / min and collect the supernatant to obtain fluorescent carbon dots.

[0077] Comparative Example 1

[0078] Add 0.1 g of 1,8-naphthyldiamine, 0.127 g of benzaldehyde, and 0.105 g of acetic acid to 15 mL of ethanol. After sonicating for 10 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 100 °C for 720 min, then allow to cool naturally to room temperature. Centrifuge at 12000 r / min and collect the supernatant to obtain fluorescent carbon dots.

[0079] The FWHM of the carbon dot fluorescence emission peak obtained in this comparative example is 96 nm, and the fluorescence peak is located at 463 nm.

[0080] Comparative Example 2

[0081] Add 0.1 g of 1,5-naphthyldiamine to 15 mL of ethanol, sonicate for 30 min, then transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene. React at 200 °C for 100 min, then allow to cool naturally to room temperature. Centrifuge at 12000 r / min and collect the supernatant to obtain fluorescent carbon dots.

[0082] The FWHM of the carbon dot fluorescence emission peak obtained in this comparative example is 57 nm, and the fluorescence peak is located at 388 nm.

[0083] Comparative Example 3

[0084] Add 0.135 g of benzaldehyde to 15 mL of ethanol, sonicate for 10 min, then transfer the mixture to a 100 mL PTFE-lined autoclave. React at 200 °C for 200 min, then allow to cool naturally to room temperature. Centrifuge at 12000 r / min and collect the supernatant to obtain fluorescent carbon dots.

[0085] The FWHM of the carbon dot fluorescence emission peak obtained in this comparative example is 53 nm, and the fluorescence peak is located at 475 nm.

[0086] Comparative Example 4

[0087] Add 0.1 g of 1,8-naphthyldiamine, 0.067 g of benzaldehyde, and 0.131 g of acetic acid to 15 mL of isopropanol. After sonicating for 15 min, transfer the mixture to a 100 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE). React at 150 °C for 150 min, then allow to cool naturally to room temperature. Centrifuge at 12000 rpm for 15 min and collect the supernatant to obtain fluorescent carbon dots.

[0088] The FWHM of the carbon dot fluorescence emission peak obtained in this comparative example is 103 nm, and the fluorescence peak is located at 500 nm.

[0089] Based on the data from Comparative Examples 1-4, it is impossible to obtain fluorescent carbon dots with a single luminescent center, characterized by high brightness and ultra-narrow emission peaks, when the raw material is a single 1,5-naphthyldiamine / aromatic aldehyde, or when other amines are used to replace the naphthyldiamine at a different position, such as using 1,8-naphthyldiamine instead of 1,5-naphthyldiamine.

[0090] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing fluorescent carbon dots with high fluorescent quantum efficiency and narrow full width at half maximum of the emission peak, characterized in that, It comprises the following steps: 1,5-naphthalene diamine and aromatic aldehyde are added to a certain volume of alcohol solvent, an acid catalyst is added, and the mixture is ultrasonically mixed and then transferred to a reaction kettle containing a polytetrafluoroethylene lining to perform a solvothermal reaction; after the reaction, the product is centrifuged, the supernatant is collected, and fluorescent carbon dots are obtained; The fluorescent carbon dots are blue fluorescent carbon dots and / or blue-green fluorescent carbon dots; The mass ratio of 1,5-naphthalene diamine, aromatic aldehyde and acid catalyst is 100:100-200:100-300; The mass-volume ratio of 1,5-naphthalene diamine to alcohol solvent is 0.1g:15-30 mL; The temperature of the solvothermal reaction is 100-200℃, and the reaction time is 100-720 min; The aromatic aldehyde is one or a combination of benzaldehyde, p-xylylformaldehyde or salicylaldehyde; The alcohol solvent is one or a combination of methanol, ethanol, isopropanol or ethylene glycol; The acid catalyst is acetic acid.

2. The method of claim 1, wherein, The ultrasonic treatment time is 5-30 min.

3. The method of claim 1, wherein, The preparation process also includes separation and purification treatment of the supernatant, and the specific steps are: The supernatant is added to a silica gel chromatography column, a mixed solution of ethanol and ethyl acetate is used as the eluent, and different batches of separated products are separated and collected to obtain a pure color fluorescent carbon dot eluent.

4. The method of claim 3, wherein, The eluent is prepared according to a volume ratio of ethanol to ethyl acetate of 5:

4.

5. The fluorescent carbon dots prepared by the method according to any one of claims 1-4, wherein, The particle size of the fluorescent carbon dots is 1-5 nm. 6.The fluorescent carbon dot of claim 5, wherein, When the fluorescent carbon dots are blue fluorescent carbon dots, the full width at half maximum of the emission peak is ≤25 nm, and the fluorescence quantum efficiency is ≥80% when excited by 460 nm light. 7.The fluorescent carbon dot of claim 5, wherein, When the fluorescent carbon dots are blue-green fluorescent carbon dots, the full width at half maximum of the emission peak is <50 nm, and the fluorescence quantum efficiency is ≥65% when excited by 460 nm light.

8. Use of the fluorescent carbon dots according to any one of claims 5-7 in the preparation of an ultra-high-definition display backlight or a lighting element.

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