Boron-nitrogen co-doped long-life high-quantum-yield dual-mode afterglow carbon dot as well as preparation method and application thereof

Abstract

The invention relates to a boron-nitrogen co-doped long-life high-quantum-yield dual-mode afterglow carbon dot and a preparation method thereof.The boron-nitrogen co-doped long-life high-quantum-yield dual-mode afterglow carbon dot is a yellow-green afterglow carbon dot prepared by taking fluorescein sodium as a precursor and boric acid and L-asparaginic acid as a boron source and a nitrogen source through a reaction at 140-220 DEG C. The macroscopic duration of the afterglow carbon dot is not less than 10 s, the photoluminescence quantum yield is not less than 60%, and the afterglow carbon dot has a good application prospect. The afterglow quantum yield is not less than 50%, and the material can be used as a long-afterglow luminescent material to be applied to the field of traffic safety.

Description

Technical Field

[0001] This invention belongs to the field of luminescent materials technology, and relates to a kind of afterglow carbon dot, particularly to a boron-nitrogen co-doped long-lifetime, high-quantum-yield dual-mode afterglow carbon dot with white light excitation, as well as its preparation method and application. Background Technology

[0002] Afterglow carbon dots are a specific subclass of carbon dots (CDs), inheriting the basic characteristics of CDs such as good dispersibility, quasi-spherical zero-dimensional structure with a size typically less than 10 nm, excellent biocompatibility and water solubility, low toxicity, and relatively low preparation cost. However, the core feature and unique advantage of afterglow CDs lies in their characteristic long-lifetime luminescence behavior, mainly including room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF). These two mechanisms endow afterglow CDs with superior optical properties that significantly distinguish them from ordinary fluorescent CDs, such as high exciton utilization, long luminescence lifetime (down to the second level), and large Stokes shift. Based on these unique advantages, afterglow CDs show broad application prospects in cutting-edge fields such as bioimaging, optical sensing, fingerprint recognition, and information encryption and anti-counterfeiting.

[0003] Current research on afterglow CDs mainly focuses on the ultraviolet band (UVC). λ ex The excitation system is <380nm). However, such ultraviolet excitation sources have significant limitations, including certain phototoxicity, short afterglow CDs emission wavelength, and low afterglow luminescence quantum yield. In contrast, visible white light excitation (400-700nm) is not only easier to obtain, but also has strong penetrating power and is safer to use, making it more valuable for practical applications.

[0004] In recent years, although significant breakthroughs have been made in the research of white light-excited afterglow CDs in terms of application expansion and performance optimization, the literature shows that their visually visible duration is generally less than 10 s, their photoluminescence quantum yield (PLQY) is generally less than 60%, and their afterglow QY is generally less than 50%.

[0005] For example, Wu et al. (Hectogram-Scale Synthesis of Visible Light Excitable RoomTemperature Phosphorescence Carbon Dots. Small(2024, 20(46): 2402796) Using diethylenetriamine as a precursor and boron, nitrogen and phosphorus as dopants, afterglow CDs were prepared for use as long afterglow luminescent materials for traffic. By utilizing the auxiliary partial phosphorescence resonance energy transfer, a stable white afterglow was achieved between complementary colors. By doping heteroatoms to regulate the electronic structure and surface states of CDs, their luminescence performance and quantum yield were improved. However, their visual visibility time was only 5s, which was difficult to meet the long-term requirements of long afterglow luminescent materials for traffic.

[0006] Lin et al. (Visible-Light Excited Multicolor Room TemperaturePhosphorescence of Boron and Nitrogen Co-Doped Carbon Dots. ACS Applied Optical Materials (2025, 3(3): 712-719) The luminescence performance and QY of afterglow CDs were improved by heteroatom doping, but the visible duration was only 8s and the afterglow QY was 16.78%, resulting in insufficient luminescence intensity.

[0007] Despite the efforts made by scientists, key performance characteristics such as the visible duration and QY of white light-excited permeable CDs still need to be improved. Developing white light-excited permeable CDs with long visible duration and high QY is crucial for expanding their practical applications. Summary of the Invention

[0008] The purpose of this invention is to provide a boron-nitrogen co-doped, long-lifetime, high-quantum-yield, dual-mode afterglow carbon dot to improve the problems of short lifetime, low quantum yield, and limited application range of traditional white-light excited afterglow carbon dots.

[0009] Providing a method for preparing and applying the dual-mode afterglow carbon dots is another objective of this invention.

[0010] To achieve the above-mentioned objectives, the boron-nitrogen co-doped long-lifetime, high-quantum-yield dual-mode afterglow carbon dots provided by this invention are yellow-green afterglow CDs prepared by reacting sodium fluorescein as a precursor, boric acid and L-aspartic acid as boron and nitrogen sources, respectively, at 140–220 °C.

[0011] The boron-nitrogen co-doped long-lifetime, high-quantum-yield, dual-mode afterglow carbon dots have a visual duration of not less than 10 s, a PLQY of not less than 60%, and an afterglow QY of not less than 50%.

[0012] The application further provides a preparation method of the boron and nitrogen co-doped long-lifetime high-quantum-yield dual-mode afterglow carbon dots.

[0013] Further, in the preparation method, the molar ratio of the boronic acid to the L-aspartic acid is preferably 1-20:1.

[0014] Further, the amount of the fluorescein sodium is preferably 0.1-0.3% of the mass of the L-aspartic acid.

[0015] Further, in the preparation method, the reaction time is preferably 4-8 hours.

[0016] Further, the preparation method is more preferably that the reaction is carried out at 180 DEG C for 5 hours.

[0017] Further, the preparation method further comprises a grinding treatment of the reaction product, including a conventional mortar grinding treatment.

[0018] The fluorescein sodium is used as a reaction raw material, the benzene ring structure with a large conjugation degree is introduced, which is beneficial to form a rigid structure, protect the triplet exciton, promote intersystem crossing (ISC) and reverse intersystem crossing (RISC), thereby facilitating dual-mode afterglow emission, and the contained carbonyl is beneficial to improve the luminescence intensity of the CDs. E ST The L-aspartic acid also contains a luminescent group C=O and -NH2, and the triplet exciton is stabilized by constructing a covalent bond or a hydrogen bond, the energy level difference (Delta

[0019] The application utilizes a simple reaction to prepare white-light-excited yellow-green afterglow carbon dots with long naked-eye visible time and high quantum yield characteristics, and the carbon dots are used as long-afterglow luminescent materials, which exhibit excellent application potential in the field of traffic safety.

[0020] For example, the afterglow carbon dots can be coated on the surface of a traffic control device such as a speed bump, and after irradiation by a light source, a high-brightness yellow-green afterglow is continuously released in a dark environment, and the light emission can still continue for a period of time after the light source disappears, realizing passive long-acting warning.

[0021] Further, the afterglow carbon dots of the present application can also be applied in the field of visual safety warning clothes, integrated into the reflective tape of the clothes through silk screen printing technology, to improve the visibility of the wearer in low light environment and prevent accidents. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a transmission electron microscope image and a high-resolution transmission electron microscope image (inset) of the bimodal afterglow CDs prepared in Example 1.

[0023] Figure 2 is an X-ray diffraction pattern of the bimodal afterglow CDs prepared in Example 1.

[0024] Figure 3 is an infrared spectrum of the bimodal afterglow CDs prepared in Example 1.

[0025] Figure 4 is an afterglow photo of the bimodal afterglow CDs prepared in Example 1 under white light excitation.

[0026] Figure 5 is an afterglow spectrum and a fluorescence spectrum of the bimodal afterglow CDs prepared in Example 1 under different excitation wavelengths.

[0027] Figure 6 is a variable-temperature afterglow spectrum of the bimodal afterglow CDs prepared in Example 1 under 425 nm excitation.

[0028] Figure 7 is a normalized curve of the fluorescence spectrum and the afterglow spectrum of the bimodal afterglow CDs prepared in Example 1 under 425 nm excitation at 77 K.

[0029] Figure 8 is an afterglow decay curve of the bimodal afterglow CDs prepared in Example 1 under 425 nm excitation at 485 and 555 nm emissions.

[0030] Figure 9 is the integral area of the PL spectrum and the afterglow spectrum of the bimodal afterglow CDs prepared in Example 1 under 425 nm excitation.

[0031] Figure 10 is an ultraviolet absorption spectrum of the bimodal afterglow CDs prepared in Example 1.

[0032] Figure 11 is an afterglow photo of the bimodal afterglow CDs prepared in Examples 2-5 under white light excitation.

[0033] Figure 12 is the afterglow emission plot of FLS-180, BA-180 and ASP-180 prepared in Comparative Example 1 under white light excitation.

[0034] Figure 13 is the afterglow photos of B-CDs and N-CDs prepared in Comparative Examples 2 and 3 under white light excitation.

[0035] Figure 14 is the afterglow spectra and lifetime decay curves of B-CDs prepared in Comparative Example 3.

[0036] Figure 15 is the afterglow spectra and infrared spectra comparison of B-CDs and N-CDs with B,N-CDs prepared in Comparative Examples 2 and 3.

[0037] Figure 16 is the application illustration of the speed bump prepared with the dual-mode afterglow CDs prepared in Example 1 under white light source excitation and after turning off.

[0038] Figure 17 is the application illustration of the reflective strip prepared with the dual-mode afterglow CDs prepared in Example 1 under white light source excitation and after turning off. Embodiment

[0039] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present application, so that those skilled in the art can well understand and utilize the present application, rather than limiting the protection scope of the present application.

[0040] The production process, experimental method or detection method involved in the embodiments of the present application, if not specifically stated, are all conventional methods in the prior art, and their names and / or abbreviations all belong to conventional names in the art, which are very clear and explicit in the related application field. Those skilled in the art can understand the conventional process steps and apply the corresponding equipment according to the conventional conditions or the conditions recommended by the manufacturer.

[0041] The various instruments, equipment, raw materials or reagents used in the embodiments of the present application do not have special restrictions on the source, and are all conventional products that can be purchased through normal commercial channels, or can be prepared according to the conventional methods well known to those skilled in the art.

[0042] The dual-mode afterglow CDs with long visible length and high QY emission in the following specific embodiments of the present application are prepared according to the following steps:

[0043] S1: Place fluorescein sodium, L-aspartic acid and boric acid in a beaker, then add deionized water, and ultrasonically treat at room temperature to fully dissolve;

[0044] S2: The beaker was placed in an oven for heating reaction, and after the reaction was completed, it was cooled to room temperature, and the solid sample was taken out;

[0045] S3: The solid sample was placed in a mortar and ground to obtain yellow-green solid powder B, N-CDs. Example

[0046] Example 1

[0047] 7 mg of fluorescein sodium, 4.6 g of boric acid and 1 g of L-aspartic acid were weighed into a 100 mL beaker, 40 mL of deionized water was added, and ultrasonic treatment was carried out at room temperature for 15 min in a 59 KHz high-frequency ultrasonic cleaner to make it fully dissolved.

[0048] The beaker was covered with tin foil and placed in an oven, heated to 180°C for 5h, and cooled to room temperature to obtain a solid sample.

[0049] The solid sample was ground with a mortar to obtain yellow-green solid powder B, N-CDs.

[0050] A small amount of prepared B, N-CDs powder was taken and dispersed in deionized water for related physicochemical property testing.

[0051] Figure 1 The TEM and high-resolution TEM images of B, N-CDs (inset) can be seen from the figure that B, N-CDs present uniformly dispersed nanospheres, and the high-resolution transmission electron microscope image presents a clear crystal structure, and the lattice fringe spacing is 0.21 nm, corresponding to the (100) crystal face diffraction of graphite.

[0052] Figure 2 The XRD pattern of B, N-CDs is shown in FIG. 5, and B, N-CDs has a diffraction peak near 2 θ =23.5° and 41°, respectively, corresponding to the (002) crystal face and (100) crystal face of graphite, confirming that the B, N-CDs composite material has a typical CDs structure.

[0053] Figure 3 The FTIR pattern of B, N-CDs is shown in FIG. 6, and it can be seen from the figure that the surface of B, N-CDs is rich in N-H, C=O, C-N and B-C.

[0054] Figure 4 The afterglow photo of B, N-CDs under white light excitation is shown in FIG. 7, and it can be seen from the figure that the yellow-green afterglow emission is visible to the naked eye for 15 s.

[0055] Figure 5are the afterglow spectra and fluorescence spectra of B, N-CDs under different excitation wavelengths, the optimal excitation and emission of B, N-CDs fluorescence are 445 and 485 nm, respectively, and the optimal excitation and emission of afterglow are 425 and 485 nm, respectively.

[0056] Figure 6 is the variable-temperature afterglow spectrum of B, N-CDs under 425 nm excitation, when the temperature rises from 77 K to 345 K, the RTP intensity (555 nm) l em continuously decreases, the afterglow emission center is blue-shifted, and the afterglow intensity (485 nm) l em continuously increases with the increase of temperature.

[0057] Figure 7 is the normalized curve of the fluorescence spectrum and the afterglow spectrum of B, N-CDs under 425 nm excitation at 77 K, the fluorescence peak (495 nm) and the phosphorescence peak (555 nm) of B, N-CDs at low temperature (425 nm) at 77 K determine the lowest S 1and T 1between the ∆ E ST is 0.271 eV, such a small ∆ E ST can enhance the SOC, stabilize the triplet exciton, and then realize the dual-mode afterglow emission.

[0058] Figure 8 is the afterglow decay curve of B, N-CDs at 425 nm excitation, 485 nm emission and 555 nm emission, under the condition of 425 nm excitation, the lifetime of RTP at 555 nm is 877 ms; while under the condition of 425 nm excitation, the lifetime of TADF at 485 nm is 778 ms.

[0059] Figure 9 is the integral area of the PL spectrum and the afterglow spectrum of B, N-CDs under 425 nm excitation, under the condition of 425 nm excitation, the PLQY is 87.91%, and the afterglow QY is 57.59%.

[0060] Figure 10 is the UV absorption spectrum of B, N-CDs, there are absorption peaks at 249 and 444 nm, respectively, corresponding to the π→π* transition of C=C and the n→π* transition of C=O / C=N, which is conducive to ISC and RISC, and realizes long-lifetime dual-mode afterglow emission; the weak band at 480 nm can be attributed to sp 2 hybrid carbon.

[0061] Example 2

[0062] Take 7 mg of sodium fluorescein, 0.46 g of boric acid and 1 g of L-aspartic acid into a 100 mL beaker, add 40 mL of deionized water, and ultrasonically treat at room temperature for 15 min in a 59 KHz high-frequency ultrasonic cleaner to fully dissolve.

[0063] Cover the beaker with tin foil and place it in an oven, heat to 180℃ for 5h, cool to room temperature to obtain a solid sample.

[0064] Grind the solid sample with a mortar to obtain a yellow-green solid powder B, N-CDs.

[0065] Example 3

[0066] Take 7 mg of sodium fluorescein, 2.3 g of boric acid and 1 g of L-aspartic acid into a 100 mL beaker, add 40 mL of deionized water, and ultrasonically treat at room temperature for 15 min in a 59 KHz high-frequency ultrasonic cleaner to fully dissolve.

[0067] Cover the beaker with tin foil and place it in an oven, heat to 180℃ for 5h, cool to room temperature to obtain a solid sample.

[0068] Grind the solid sample with a mortar to obtain a yellow-green solid powder B, N-CDs.

[0069] Example 4

[0070] Take 7 mg of sodium fluorescein, 6.9 g of boric acid and 1 g of L-aspartic acid into a 100 mL beaker, add 40 mL of deionized water, and ultrasonically treat at room temperature for 15 min in a 59 KHz high-frequency ultrasonic cleaner to fully dissolve.

[0071] Cover the beaker with tin foil and place it in an oven, heat to 180℃ for 5h, cool to room temperature to obtain a solid sample.

[0072] Grind the solid sample with a mortar to obtain a yellow-green solid powder B, N-CDs.

[0073] Example 5

[0074] Take 7 mg of sodium fluorescein, 9.2 g of boric acid and 1 g of L-aspartic acid into a 100 mL beaker, add 40 mL of deionized water, and ultrasonically treat at room temperature for 15 min in a 59 KHz high-frequency ultrasonic cleaner to fully dissolve.

[0075] Cover the beaker with tin foil and place it in an oven, heat to 180℃ for 5h, cool to room temperature to obtain a solid sample.

[0076] Grind the solid sample with a mortar to obtain a yellow-green solid powder B, N-CDs.

[0077] Figure 11 The afterglow photos of different boronic acids with L-aspartic acid molar ratio B, N-CDs prepared in Examples 2-5 under white light excitation, all have yellow-green afterglow emission, and the length of time when visible by naked eye is 10s, 12s, 13s and 13s respectively.

[0078] Comparative Example 1

[0079] 7mg of fluorescein sodium, 4.6g of boric acid and 1g of L-aspartic acid were weighed and placed in a 100mL beaker, 40mL of deionized water was added, and ultrasonic treatment was carried out at room temperature in a 59KHz high-frequency ultrasonic cleaner for 15min to make it fully dissolved.

[0080] The beaker was covered with tin foil and placed in an oven, heated to 180℃ for 5h, and cooled to room temperature to obtain a solid sample. After grinding with a mortar, solid powder samples FLS-180, BA-180 and ASP-180 were obtained respectively.

[0081] From the test results of Figure 12 It can be seen that the afterglow emission intensity of FLS-180, BA-180 and ASP-180 under white light excitation is close to 0, and there is no afterglow phenomenon in the three samples.

[0082] Comparative Example 2

[0083] 7mg of fluorescein sodium, 4.6g of boric acid were weighed and placed in a 100mL beaker, 40mL of deionized water was added, and ultrasonic treatment was carried out at room temperature in a 59KHz high-frequency ultrasonic cleaner for 15min to make it fully dissolved.

[0084] The beaker was covered with tin foil and placed in an oven, heated to 180℃ for 5h, and cooled to room temperature to obtain a solid sample.

[0085] The solid sample was ground with a mortar to obtain a yellow-green solid powder B-CDs.

[0086] Comparative Example 3

[0087] 7mg of fluorescein sodium, 1g of L-aspartic acid were weighed and placed in a 100mL beaker, 40mL of deionized water was added, and ultrasonic treatment was carried out at room temperature in a 59KHz high-frequency ultrasonic cleaner for 15min to make it fully dissolved.

[0088] The beaker was covered with tin foil and placed in an oven, heated to 180℃ for 5h, and cooled to room temperature to obtain a solid sample.

[0089] The solid sample was ground with a mortar to obtain a solid powder N-CDs.

[0090] Figure 13The test results show that the B-CDs and N-CDs have strong solid-state fluorescence performance at room temperature, under white light excitation, the B-CDs emit yellow-green fluorescence and green afterglow emission, which can be observed by naked eye for 10s; the N-CDs emit white-brown fluorescence and no afterglow phenomenon.

[0091] Figure 14 In the B-CDs, the optimal excitation and emission of afterglow are 285 and 490 nm respectively, and the afterglow lifetime is 191 ms, and the time length observed by naked eye and the afterglow lifetime are both weakened compared with the B, N-CDs composite material.

[0092] Further, Figure 15 By comparing the afterglow spectra of B, N-CDs, B-CDs and N-CDs, it can be known that the N-CDs have no afterglow phenomenon, the intensity of B, N-CDs is increased compared with B-CDs, and the absorption peak is slightly red-shifted.

[0093] And by comparison of FTIR in Figure 15 , it can be known that the N-CDs and B-CDs have no luminescent group C=O, the B-CDs contain B-C covalent bond, which can form rigid structure, promote the process of ISC and RISC between singlet state and triplet state, effectively protect triplet excitons, inhibit non-radiative transition, and realize afterglow emission. But for B, N-CDs, there are both luminescent group C=O and B-C covalent bond, the C=O is beneficial to increase QY, and the B-C bond stretching vibration peak is enhanced, thereby promoting long afterglow emission.

[0094] Application Example 1

[0095] The B, N-CDs prepared by using the application example 1 are used to make traffic speed control facilities, i.e. speed reduction belt.

[0096] Figure 16 is an application diagram of the speed reduction belt coated with B, N-CDs after white light source excitation and turn-off. When the car passes through the speed reduction belt at night, the speed reduction belt will emit afterglow; and after the vehicle passes through the speed reduction belt, the sign will continue to emit light for a short time and can be captured by the next vehicle.

[0097] Application Example 2

[0098] The B, N-CDs prepared by using the application example 1 are used to make reflective strips, instead of traditional fluorescent reflective strips.

[0099] Figure 16 is an application diagram of the reflective strips prepared by B, N-CDs after white light source excitation and turn-off. It can be seen that these reflective strips are pasted on the clothes and hats of sanitation workers, which improves the visibility of night work.

[0100] The above embodiments of the present application do not describe all the details and do not limit the present application to the above described embodiments. Various changes, modifications, substitutions and variations of these embodiments, which are made without departing from the principles and spirit of the present application, should be included in the scope of protection of the present application.

Claims

1. A boron-nitrogen co-doped long-lifetime, high-quantum-yield dual-mode afterglow carbon dopants are prepared by reacting sodium fluorescein as a precursor, boric acid and L-aspartic acid as boron and nitrogen sources, respectively, at 140-220℃. The resulting yellow-green afterglow CDs have a visual visibility duration of not less than 10s, a PLQY of not less than 60%, and an afterglow QY of not less than 50%.

2. The method for preparing boron-nitrogen co-doped long-lifetime, high-quantum-yield dual-mode afterglow carbon dots according to claim 1 is to use sodium fluorescein as a precursor, and boric acid and L-aspartic acid as boron and nitrogen sources respectively, dispersed in water, and react at 140-220°C to prepare yellow-green solid CDs powder.

3. The preparation method according to claim 2, characterized in that: The molar ratio of boric acid to L-aspartic acid is 1 to 20:

1.

4. The preparation method according to claim 2, characterized in that: The amount of sodium fluorescein used is 0.1% to 0.3% of the mass of L-aspartic acid.

5. The preparation method according to claim 2, characterized in that: The reaction time is 4 to 8 hours.

6. The preparation method according to claim 2, characterized in that: The reaction was carried out at 180℃ for 5 hours.

7. The preparation method according to claim 2, characterized in that: The reaction products were ground.

8. The application of the boron-nitrogen co-doped long-lifetime, high-quantum-yield dual-mode afterglow carbon dots as long-afterglow luminescent materials in the field of traffic safety as described in claim 1.

9. The application according to claim 8, characterized in that it is... The afterglow carbon dots are used as long afterglow luminescent materials for the speed bumps of traffic speed control devices.

10. The application of the boron-nitrogen co-doped long-lifetime, high-quantum-yield dual-mode afterglow carbon dots as a long-afterglow luminescent material for reflective strips in visual safety warning clothing as described in claim 1.

Images