A fluorine-doped long-life double afterglow carbon dot-based composite material and its preparation method

Abstract

The present invention discloses a fluorine-doped, long-life dual-afterglow carbon dot-based composite material exhibiting room-temperature phosphorescence and thermally activated delayed fluorescence, and a preparation method thereof. The composite material is prepared by solvothermally preparing the fluorine-doped carbon dots in an ethanol solvent using folic acid as a carbon source and ammonium fluoride as a dopant. Boric acid is then used as a coating matrix, and the resulting composite material is uniformly dispersed in an aqueous solution and reacted to form the composite material. The dual-afterglow carbon dot-based composite material emits blue fluorescence under 265nm ultraviolet light and produces blue delayed fluorescence after irradiation stops. It also emits blue fluorescence under 365nm ultraviolet light and produces green phosphorescence after irradiation stops. Leveraging its afterglow properties, the composite material can be used as an afterglow material in optoelectronic devices, security, and anti-counterfeiting applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of long-afterglow luminescent materials, and relates to a photoinduced long-afterglow luminescent material based on carbon dots, in particular to a dual-afterglow carbon dot-based composite material that can emit phosphorescence and delayed fluorescence at room temperature and has a long lifespan, as well as a method for preparing the carbon dot-based composite material. Background Art

[0002] Carbon dots (CDs), as a new type of nanocarbon material, not only have excellent optical properties, but also have the advantages of simple preparation, low cost and low toxicity, and have attracted widespread attention.

[0003] Due to the unique internal electronic structure and surface chemical reaction of CDs, they emit visible light after being excited by light sources, namely fluorescence and afterglow. Afterglow emission includes room temperature phosphorescence (RTP) and delayed fluorescence (DF). S 1) Transformed into triplet excitons via intersystem crossing (ISC), and then the triplet excitons radiatively transition to the ground state ( S 0), RTP is generated; the excitons are transferred from the triplet state ( T 1) to S 1 returns to the ground state through reverse intersystem crossing (RISC) to produce DF. DF materials have a small singlet-triplet energy level difference (Δ E ST ), which can theoretically achieve 100% exciton utilization, greatly improving its exciton utilization compared to fluorescence (FL) which is limited by spin exciton statistics. At the same time, its lifetime is longer than that of fluorescence, and it has the characteristic of increasing emission intensity with increasing temperature in a certain temperature range. The unique luminescence properties of this type of material give it advantages in anti-counterfeiting applications.

[0004] Currently, RTP CDs are divided into two types: matrix-based RTP CDs and matrix-free RTP CDs, which are mainly used in fields such as anti-counterfeiting and long-lasting display. For example, Zhang et al. (Zhang H, Sun L, Guo X, et al. Applied Surface Science By printing the prepared C-CDs@SA on filter paper, a green RTP visible to the naked eye for 1 second can be observed. This property can be effectively used for information encryption and anti-counterfeiting. C-CDs@SA powder also has important applications in fingerprint detection. Wu Y, Fang X, Shi J, et al. Chinese Chemical Letters, 2021, 32(12): 3907-3910.) The synthesized carbon dots with fluorescent and room temperature phosphorescent optical properties are applied to anti-counterfeiting. The directly screen-printed coded information and patterns are invisible to the naked eye under natural light. Under different wavelength excitation and removal, clear multi-color patterns with tunable FL and RTP emission are realized for anti-counterfeiting applications. Shi et al. (Shi H, Wu Yang, Xu J, et al. Chemical Engineering Journal , 2023, 476: 146524.) By forming a covalent network on the surface of AP-CDs, the vibration and rotation of the surface emitter are restricted, and the non-radiative transition of triplet excitons is suppressed, blue phosphorescence emission is achieved. The phosphorescence lifetime at the emission wavelength of 470nm is 315.73ms, and the phosphorescence quantum yield can reach 12.4%. It has been successfully used for single-modal information encryption and pattern anti-counterfeiting.

[0005] Although RTP CDs are conveniently used in low-level anti-counterfeiting in the anti-counterfeiting field, due to their single luminescence type and relatively simple functionality, they have limited performance in multi-coding anti-counterfeiting applications that require complex optical signals and are therefore easy to imitate; in the field of long-afterglow display, although RTP CDs have a long lifespan, the luminescence duration may still be insufficient to meet the needs of complex time-resolved detection or multimodal applications.

[0006] Therefore, it is very necessary to prepare a carbon dot-based composite material with dual afterglow (RTP, TADF) and a long afterglow lifetime and visible time to the naked eye. Its unique long afterglow luminescence characteristics, multimodal luminescence performance and environmental friendliness not only make it an ideal choice for the new generation of anti-counterfeiting materials, but also increase the complexity and reliability of anti-counterfeiting, and its practical application is more extensive. Summary of the Invention

[0007] The purpose of the present invention is to provide a fluorine-doped long-life double afterglow carbon dot-based composite material and a preparation method of the composite material to address the problems that the existing room temperature phosphorescent carbon dots used for anti-counterfeiting are easy to imitate and have a short afterglow lifetime.

[0008] The fluorine-doped long-life dual afterglow carbon dot-based composite material described in the present invention is a composite material obtained by reacting boric acid as a coating matrix with fluorine-doped carbon dots after being uniformly dispersed in an aqueous solution. The fluorine-doped carbon dots are prepared by a solvothermal method in an ethanol solvent using folic acid as a carbon source and ammonium fluoride as a dopant.

[0009] More specifically, the fluorine-doped long-life double-afterglow carbon dot-based composite material of the present invention is preferably coated with 1 to 1.5 wt % of fluorine-doped carbon dots.

[0010] The fluorine-doped long-life dual-afterglow carbon dot-based composite material prepared by the present invention is a light yellow powder. The fluorine-doped carbon dots are uniformly coated with a boric acid-coated matrix. The composite material exhibits dual afterglow characteristics of room temperature phosphorescence (RTP) and delayed fluorescence (DF) under different excitation wavelengths.

[0011] Specifically, the composite material emits blue fluorescence under 265nm ultraviolet light, and produces blue delayed fluorescence after the excitation light source stops irradiating, which is visible to the naked eye for 11 seconds; it emits blue fluorescence under 365nm ultraviolet light, and produces green phosphorescence after the excitation light source stops irradiating, which is visible to the naked eye for 13 seconds.

[0012] Furthermore, the present invention also provides a method for preparing the fluorine-doped long-life dual-afterglow carbon dot-based composite material, which comprises dissolving folic acid and ammonium fluoride in ethanol and conducting a solvent thermal reaction to obtain a CDs solution, mixing the solution with a boric acid solution and drying the solution to prepare the fluorine-doped long-life dual-afterglow carbon dot-based composite material.

[0013] Furthermore, in the above preparation method of the present invention, the molar mass ratio of folic acid to ammonium fluoride is preferably 1:(1-12.5).

[0014] Furthermore, in the above preparation method, the solvent thermal reaction is preferably carried out at 140 to 240° C., and the reaction time is preferably 2 to 10 hours.

[0015] The present invention further purifies the CDs solution obtained by the solvent thermal reaction by various conventional methods such as centrifugation, microporous membrane filtration, and dialysis to obtain a pure CDs solution with uniform particle size.

[0016] More specifically, in the present invention, after the CDs solution and the boric acid solution are mixed, ultrasonic means can be used to fully mix them.

[0017] The present invention preferably reacts the mixed solution at 170-180° C. and dries to prepare a fluorine-doped long-life double afterglow carbon dot-based composite material.

[0018] The present invention addresses the problems that current RTP CDs used for anti-counterfeiting are easy to imitate and have a short afterglow lifetime. By using folic acid as a carbon source, ammonium fluoride as a dopant, ethanol as a solvent, and boric acid as a coating matrix, a solvothermal method is adopted to prepare a fluorine-doped long-life double afterglow carbon dot-based composite material. The composite material has a carbon dot-matrix composite structure. On the one hand, boric acid is used as a matrix to produce a glassy state to prevent the triplet excitons of CDs from being consumed by non-radiation. On the other hand, fluorine atoms are doped to form highly polarized C-F bonds to adjust the surface electronic state and conformation of CDs, so that hydrogen bonds are formed between the carbon dots and the matrix, non-radiative transitions are suppressed, and thus afterglow emission is enhanced.

[0019] The long-life dual-afterglow carbon dot-based composite material prepared by the present invention has good dual-afterglow performance, can be used as an afterglow material, and is widely used in technical fields such as optoelectronic devices, graphic anti-counterfeiting and information encryption. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 These are actual photos of fluorine-doped long-life double afterglow carbon dot-based composite materials under irradiation with fluorescent lamps and 265 and 365nm ultraviolet lamps, as well as at different times after the ultraviolet lamps are turned off.

[0021] Figure 2 These are the TEM and HRTEM images of fluorine-doped CDs and fluorine-doped long-life double-afterglow carbon dots-based composites.

[0022] Figure 3 This is the XRD pattern of fluorine-doped long-life double afterglow carbon dot-based composite material.

[0023] Figure 4 This is the FT-IR spectrum of the fluorine-doped long-life double afterglow carbon dot-based composite material.

[0024] Figure 5 It is the XPS spectrum of fluorine-doped long-life double afterglow carbon dot-based composite material and its high-resolution C1s spectrum, B1s spectrum and O1s spectrum.

[0025] Figure 6 This is the excitation spectrum of the fluorine-doped long-life double afterglow carbon dot-based composite material.

[0026] Figure 7 The fluorescence and afterglow emission spectra of fluorine-doped long-life double afterglow carbon dot-based composite materials.

[0027] Figure 8 This is a comparison chart of the fluorescence and afterglow spectra of the fluorine-doped long-life double afterglow carbon dot-based composite material at excitation wavelengths of 265 and 365 nm.

[0028] Figure 9 This is the afterglow lifetime diagram of fluorine-doped long-life double afterglow carbon dot-based composite material under 265 and 365nm excitation.

[0029] Figure 10 This is the afterglow lifetime diagram of the undoped fluorine-containing double afterglow carbon dot-based composite material under 265 and 365 nm excitation. Implementation Method

[0030] The following embodiments are only used to more clearly illustrate the technical solutions of the present invention so that those skilled in the art can better understand and utilize the present invention, but are not intended to limit the scope of protection of the present invention.

[0031] Unless otherwise specified, the production processes, experimental methods or detection methods involved in the embodiments of the present invention are all conventional methods in the prior art, and their names and / or abbreviations are conventional names in the field and are very clear and unambiguous in the relevant fields of use. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment to implement them according to conventional conditions or the conditions recommended by the manufacturer.

[0032] The various instruments, equipment, raw materials or reagents used in the embodiments of the present invention are not particularly limited in their sources and are all conventional products that can be purchased through regular commercial channels or prepared according to conventional methods well known to those skilled in the art. Example

[0033] Example 1

[0034] 44.14 mg of folic acid and 37.04 mg of ammonium fluoride were weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 160° C. for 6 h.

[0035] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for dialyzation for 24 h to obtain a CDs solution, which was recorded as F,N-CDs.

[0036] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare fluorine-doped long-life double afterglow carbon dot-based composite material powder, which is recorded as F,N-CDs@BA.

[0037] Figure 1 Actual pictures of the above-mentioned fluorine-doped long-life double afterglow carbon dot-based composite material prepared under irradiation of fluorescent lamp and 265 and 365nm ultraviolet lamps, as well as at different times after stopping ultraviolet irradiation are given.

[0038] The figure shows that the composite material is a light yellow solid under fluorescent light, while under 265nm ultraviolet light, the composite material can emit blue fluorescence and blue delayed fluorescence, and the delayed fluorescence is visible to the naked eye for 11 seconds; under 365nm ultraviolet light, the composite material can emit blue fluorescence and green phosphorescence, and the phosphorescence is visible to the naked eye for 13 seconds.

[0039] Figure 2These are the TEM and HRTEM images (box in the upper right corner) of the CDs (a) and the fluorine-doped long-life double afterglow carbon dot-based composite material (b) prepared above.

[0040] As can be seen from the TEM image, the CDs are in the form of small single particles, evenly dispersed, and without agglomeration. In comparison, the CDs in the fluorine-doped long-life double afterglow carbon dot-based composite material are uniformly coated with a boric acid matrix, which not only makes the distribution more uniform, but also the aggregation between particles seems to be effectively suppressed, indicating that the boric acid matrix may play an isolating role and prevent the agglomeration of CDs.

[0041] Further, the HRTEM images of CDs show distinct lattice fringes with a lattice spacing of 0.21 nm, corresponding to the (100) plane of graphitic carbon, indicating that CDs have a certain degree of graphitized structure. Lattice fringes can still be observed in the HRTEM images of the coated composite material, with the lattice spacing also being 0.21 nm, indicating that the graphitized structure of CDs has not changed significantly after coating with the boric acid matrix, and that the matrix has a good protective effect on the lattice structure of CDs.

[0042] from Figure 3 The XRD spectrum of the fluorine-doped long-life double afterglow carbon dot-based composite material further shows that the diffraction peak at 2θ=23.00° corresponds to the graphite (002) crystal plane, while the diffraction peaks at 2θ=14.70°, 27.75°, and 41.58° correspond to the characteristic fingerprint peaks of B2O3, indicating the presence of B2O3 structure in the composite material. During the heating process, the BA solution gradually transforms into B2O3. The formation of the B2O3 rigid matrix can fix and rigidly protect F, N-CDs, inhibit the non-radiative vibration rotation of F, N-CDs, and isolate the F, N-CDs from external oxygen, moisture, etc. T 1 quenching, achieving F,N-CDs T 1 stabilization.

[0043] Figure 4 In the FT-IR spectrum of the fluorine-doped long-life double afterglow carbon dot-based composite material, the -1 The broad peak at 1625 cm is derived from the stretching vibration of OH. -1 The peak at 1480 cm is derived from the stretching vibration of CO. -1 The characteristic peak at 1214 cm is derived from the stretching vibration of BO. -1 The characteristic peaks at 735 and 655 cm are derived from the stretching vibration of CF, proving that the F element has been successfully incorporated into CDs. -1The characteristic peaks at 100 nm are derived from the stretching vibration of BC and the bending vibration of BOH, which further indicates that during the heating process of BA aqueous solution, BA gradually dehydrates and may form a B2O3 matrix. F, N-CDs are embedded into the matrix through the formation of BC covalent bonds. The BC covalent bonds can fix F, N-CDs and inhibit their non-radiative vibration rotation, while the inorganic glassy matrix can isolate the external oxygen and moisture from the F, N-CDs. T The quenching of 1 provides rigid protection for F,N-CDs, which is beneficial to the generation of afterglow.

[0044] Figure 5 The XPS spectra (a) and high-resolution C1s (b), B1s (c), and O1s (d) spectra of the fluorine-doped long-lifetime double-afterglow carbon dot-based composite are presented. F,N-CDs@BA is composed of C, B, O, N, and F. The characteristic peaks at 286.6, 285.7, 286.9, and 289.1 eV in the C1s high-resolution XPS spectrum originate from C-C / C=C, CO / CN, C=O / C=N, and CF bonds. The formation of CF indicates the incorporation of F into the CDs. The B1s high-resolution XPS spectrum exhibits characteristic peaks at 192.8, 193.8, and 194.7 eV attributed to BCO2, B2O3, and BO, respectively. The O1s high-resolution XPS spectrum is composed of three characteristic peaks at 532.2 eV (C=O), 533.8 eV (OH / CO), and 534.7 eV (O=CO). The above results indicate that during the heating process, BA undergoes a dehydration reaction to form a B2O3 matrix, which achieves rigid protection for F,N-CDs, which is consistent with the characterization results of XRD and FTIR.

[0045] Figure 6 It is the afterglow excitation spectrum of fluorine-doped long-life double afterglow carbon dot-based composite material, and its optimal excitation wavelengths are 265nm and 365nm.

[0046] Figure 7 Figures 1 and 2 show the fluorescence emission spectra (a) and afterglow emission spectra (b) of a fluorine-doped long-lifetime dual-afterglow carbon dot-based composite material under excitation at different wavelengths. The fluorescence emission spectrum in (a) is excitation-independent. As the excitation wavelength increases, the emission wavelength remains at 430 nm, demonstrating that the composite material has a single luminescence center. Comparing the fluorescence and afterglow emission spectra under the same excitation wavelength, if the afterglow emission wavelength is close to the fluorescence emission wavelength, it indicates delayed fluorescence emission; if the afterglow emission wavelength is red-shifted relative to the fluorescence emission wavelength, it indicates phosphorescence emission. Under excitation between 265 and 325 nm, the afterglow emission wavelength of the composite material is close to the fluorescence emission wavelength, both at 430 nm, indicating delayed fluorescence emission. Under excitation between 325 and 385 nm, the afterglow emission wavelength is red-shifted relative to the fluorescence emission wavelength, reaching 510 nm, indicating phosphorescence emission.

[0047] Figure 8 The paper also presents a comparison of the fluorescence and afterglow emission spectra of the fluorine-doped long-lifetime dual-afterglow carbon dot-based composite material at excitation wavelengths of 265 nm (a) and 365 nm (b). (a) Under 265 nm excitation, the afterglow emission wavelength is close to the fluorescence emission wavelength, demonstrating delayed fluorescence; (b) under 365 nm excitation, the afterglow emission wavelength is red-shifted relative to the fluorescence emission wavelength, demonstrating phosphorescence.

[0048] Figure 9 These are the afterglow lifetime diagrams of the fluorine-doped long-life double afterglow carbon dot-based composite material under excitation at 265nm (a) and 365nm (b), respectively. It can be seen that its delayed fluorescence lifetime is 1.21s and its phosphorescence lifetime is 0.47s.

[0049] Among the carbon dot-based dual-afterglow materials currently reported, the delayed fluorescence lifetimes are mostly concentrated around 0.1 to 1.0 seconds, with those exceeding 1 second being relatively rare. The fluorine-doped long-life dual-afterglow carbon dot-based composite material of the present invention achieves a delayed fluorescence lifetime of 1.21 seconds and also exhibits a good phosphorescence lifetime, demonstrating its excellent dual-afterglow properties and its suitability for applications in optoelectronic devices, security, and anti-counterfeiting.

[0050] Example 2

[0051] 44.14 mg of folic acid and 27.78 mg of ammonium fluoride were weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 160° C. for 6 h.

[0052] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for 24 h to obtain a CDs solution.

[0053] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare fluorine-doped long-life double afterglow carbon dot-based composite material powder.

[0054] The powdered solid obtained above was irradiated with a 265nm ultraviolet lamp for 3-5 seconds, and then the irradiation was stopped. The solid was observed to emit blue delayed fluorescence, which was visible to the naked eye for 7 seconds. The powdered solid was irradiated with a 365nm ultraviolet lamp for 3-5 seconds, and then the irradiation was stopped. The solid was observed to emit green phosphorescence, which was visible to the naked eye for 9 seconds.

[0055] Example 3

[0056] 44.14 mg of folic acid and 46.30 mg of ammonium fluoride were weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 160° C. for 6 h.

[0057] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for 24 h to obtain a CDs solution.

[0058] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare fluorine-doped long-life double afterglow carbon dot-based composite material powder.

[0059] The powdered solid obtained above was irradiated with a 265nm ultraviolet lamp for 3-5 seconds, and then the irradiation was stopped. The solid was observed to emit blue delayed fluorescence, which was visible to the naked eye for 7 seconds. The powdered solid was irradiated with a 365nm ultraviolet lamp for 3-5 seconds, and then the irradiation was stopped. The solid was observed to emit green phosphorescence, which was visible to the naked eye for 10 seconds.

[0060] Example 4

[0061] 44.14 mg of folic acid and 3704 mg of ammonium fluoride were weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 140° C. for 6 h.

[0062] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for 24 h to obtain a CDs solution.

[0063] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare fluorine-doped long-life double afterglow carbon dot-based composite material powder.

[0064] The powdered solid obtained above was irradiated with a 265nm ultraviolet lamp for 3 to 5 seconds, and then the irradiation was stopped. The solid was observed to emit blue delayed fluorescence, which was visible to the naked eye for 8 seconds; after irradiation with a 365nm ultraviolet lamp for 3 to 5 seconds, the irradiation was stopped, and the solid was observed to emit green phosphorescence, which was visible to the naked eye for 12 seconds.

[0065] Example 5

[0066] 44.14 mg of folic acid and 37.04 mg of ammonium fluoride were weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 180° C. for 6 h.

[0067] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for 24 h to obtain a CDs solution.

[0068] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare fluorine-doped long-life double afterglow carbon dot-based composite material powder.

[0069] The powdered solid obtained above was irradiated with a 265nm ultraviolet lamp for 3 to 5 seconds, and then the irradiation was stopped. The solid was observed to emit blue delayed fluorescence, which was visible to the naked eye for 11 seconds. The powdered solid was irradiated with a 365nm ultraviolet lamp for 3 to 5 seconds, and then the irradiation was stopped. The solid was observed to emit green phosphorescence, which was visible to the naked eye for 9 seconds.

[0070] Example 6

[0071] 44.14 mg of folic acid and 37.04 mg of ammonium fluoride were weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 160° C. for 2 h.

[0072] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for 24 h to obtain a CDs solution.

[0073] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare fluorine-doped long-life double afterglow carbon dot-based composite material powder.

[0074] The powdered solid obtained above was irradiated with a 265nm ultraviolet lamp for 3 to 5 seconds, and then the irradiation was stopped. The solid was observed to emit blue delayed fluorescence, which was visible to the naked eye for 9 seconds; after irradiation with a 365nm ultraviolet lamp for 3 to 5 seconds, the irradiation was stopped, and the solid was observed to emit green phosphorescence, which was visible to the naked eye for 9 seconds.

[0075] Example 7

[0076] 44.14 mg of folic acid and 37.04 mg of ammonium fluoride were weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 160° C. for 10 h.

[0077] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for 24 h to obtain a CDs solution.

[0078] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare fluorine-doped long-life double afterglow carbon dot-based composite material powder.

[0079] The powdered solid obtained above was irradiated with a 265nm ultraviolet lamp for 3-5 seconds, and then the irradiation was stopped. The solid was observed to emit blue delayed fluorescence, which was visible to the naked eye for 8 seconds. The powdered solid was irradiated with a 365nm ultraviolet lamp for 3-5 seconds, and then the irradiation was stopped. The solid was observed to emit green phosphorescence, which was visible to the naked eye for 11 seconds.

[0080] Comparative Example 1

[0081] 44.14 mg of folic acid was weighed and mixed evenly with 15 mL of ethanol to obtain a reaction solution, which was placed in a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 160° C. for 6 h.

[0082] After the reaction, the reaction solution was cooled to room temperature, centrifuged, and the supernatant was placed in a rotary evaporator. The ethanol was removed by rotary evaporation at 65°C, and 5 mL of deionized water was added to dissolve the product. The product was filtered with a 0.22 μm microporous filter membrane and transferred to a 500 Da dialysis bag for 24 h to obtain a CDs solution.

[0083] Weigh 2 g of BA powder, dissolve it in 40 mL of deionized water, and mix it evenly by ultrasonication for 30 minutes. Then add 5 mL of CDs solution and continue ultrasonication for 30 minutes. The mixed solution is placed in an oven and heated at 180°C for 5 hours. The reaction product is ground to prepare a fluorine-free double afterglow carbon dot-based composite material powder.

[0084] The powdered solid obtained above was irradiated with a 265nm ultraviolet lamp for 3 to 5 seconds, and then the irradiation was stopped. The solid was observed to emit blue delayed fluorescence, which was visible to the naked eye for 5 seconds, which was significantly shorter than that in Example 1. The powdered solid was irradiated with a 365nm ultraviolet lamp for 3 to 5 seconds, and then the irradiation was stopped. The solid was observed to emit green phosphorescence, which was visible to the naked eye for 6 seconds, which was also significantly shorter than that in Example 1.

[0085] Further testing of the afterglow lifetime of the solid under 265nm and 365nm excitation showed the following results: Figure 10 , its delayed fluorescence lifetime is 426.11ms and its phosphorescence lifetime is 196.62ms.

[0086] Comparative Example 1 shows that the delayed fluorescence lifetime of the fluorine-doped long-life double afterglow carbon dot-based composite material is 1.21s, and the phosphorescence lifetime is 0.47s, which fully demonstrates that fluorine doping can effectively prolong the life of the afterglow material, and the afterglow performance of the material prepared in Example 1 is better.

[0087] The above embodiments of the present invention do not describe all details in detail, nor do they limit the present invention to the above embodiments. Various changes, modifications, substitutions, and variations made by those skilled in the art without departing from the principles and purpose of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A fluorine-doped long-life dual-afterglow carbon dot-based composite material, comprising a composite material obtained by uniformly dispersing boric acid as a coating matrix with fluorine-doped carbon dots in an aqueous solution and then reacting the resulting composite material. The fluorine-doped carbon dots are prepared by a solvothermal method in an ethanol solvent using folic acid as a carbon source and ammonium fluoride as a dopant. The carbon dots produce blue delayed fluorescence at an excitation wavelength of 265 nm and green phosphorescence at an excitation wavelength of 365 nm.

2. The fluorine-doped long-life double afterglow carbon dot-based composite material according to claim 1, characterized in that The fluorine-doped long-life double afterglow carbon dot-based composite material is coated with 1 to 1.5 wt % of fluorine-doped carbon dots.

3. The preparation method of the fluorine-doped long-life dual afterglow carbon dot-based composite material according to claim 1 is to dissolve folic acid and ammonium fluoride in ethanol at a molar ratio of 1:7.5-12.5, carry out a solvent thermal reaction at 140-240°C to obtain a CDs solution, mix it with a boric acid solution and dry it to prepare the fluorine-doped long-life dual afterglow carbon dot-based composite material.

4. The preparation method according to claim 3, wherein The solvent thermal reaction time is 2 to 10 hours.

5. The preparation method according to claim 3, wherein The mixed reaction temperature is 170-180°C.

6. Use of the fluorine-doped long-life double afterglow carbon dot-based composite material according to claim 1 as an afterglow material in the preparation of optoelectronic devices.

7. Use of the fluorine-doped long-life double afterglow carbon dot-based composite material according to claim 1 as an anti-counterfeiting material in laser anti-counterfeiting.

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