CN111154480B

CN111154480B - Long-afterglow material and preparation method and application thereof

Info

Publication number: CN111154480B
Application number: CN201811314890.8A
Authority: CN
Inventors: 刘应亮; 周婉; 庄健乐; 胡超凡; 雷炳富; 张浩然; 张学杰
Original assignee: South China Agricultural University
Current assignee: South China Agricultural University
Priority date: 2018-11-06
Filing date: 2018-11-06
Publication date: 2021-07-23
Anticipated expiration: 2038-11-06
Also published as: CN111154480A

Abstract

The invention provides a long afterglow material and a preparation method and application thereof. The long afterglow material is formed by compounding carbon dots into a matrix, is in a glass state, and has the properties of fluorescence, delayed fluorescence and phosphorescence; the material has longer service life, higher phosphorescence quantum efficiency and better stability, and the metal-free afterglow material is successfully prepared from the heteroatom-free carbon dots, the service life is up to 2682ms, and the phosphorescence quantum efficiency is up to 17.5 percent. The invention also provides a preparation method of the long afterglow material, the glassy state is formed by carrying out one-step heat treatment on the carbon dots and the matrix, the method has universal adaptability, the obtained material has better phosphorescence effect, the operation is simple, the cost is low, the green environment-friendly effect is realized, the application range is wide, and the mass production can be realized. Meanwhile, the long afterglow material has good effect in the aspects of three-mode anti-counterfeiting technology and information encryption, and has wide application prospect in the field of optoelectronics, particularly in the field of anti-counterfeiting and information encryption technology.

Description

Long-afterglow material and preparation method and application thereof

Technical Field

The invention belongs to the field of composite functional materials, and particularly relates to a long afterglow material, and a preparation method and application thereof.

Background

The afterglow material includes room phosphorescence, persistent luminescence and delayed fluorescence material. Phosphorescence has led to widespread use in optoelectronics, photodynamic therapy, sensing, data recording, bioscience technology, and security systems due to its long lifetime and broad stokes shift. However, Room Temperature Phosphorescent (RTP) materials have heretofore typically been inorganic or metal complexes, and these materials typically contain toxic heavy metals, are expensive, and are unstable. Therefore, it is very important to research and develop a metal-free RTP material having low cost, multi-purpose, excellent performance, and environmental friendliness.

Carbon Dots (CDs) become a research hotspot of the RTP material without metal at present due to simple preparation, low cost and easy regulation and control of composition and structure. However, the method is only limited to be suitable for single or a few specific CDs, and the problems of low phosphorescence quantum efficiency, short lifetime and the like exist in the RTP materials based on the CDs generally. This greatly limits the research and practical application of CDs-based RTP materials. Further summary and analysis may reveal that the present phosphorescent-producing CDs are almost exclusively heteroatom CDs, in particular all containing nitrogen atoms. Since nitrogen-doped CDs contain not only aromatic carbonyl groups but also heterocyclic nitrogen, they all have a certain degree of spin-orbit coupling. However, the heteroatom-free CDs contain only three elements, carbon, hydrogen and oxygen, and their energy level structures are single, and therefore occupy fewer energy level structures in which electronic transitions can occur. Thereby making it more difficult to obtain RTP by providing CDs without heteroatoms with a larger energy band gap between singlet and triplet states. The phenomenon of RTP with virtually heteroatom-free CDs has never been reported, let alone Delayed Fluorescence (DF) properties. More notably, the phosphorescence emission band of the RTP material based on CDs, which has been reported at present, is mainly concentrated on the green band, which also hinders the wide application prospect of the material. It is therefore of great importance to find a universally applicable and efficient method to obtain RTP materials with excellent properties.

With the development of economy, counterfeit and shoddy products circulating in the market become a non-competitive fact that hinders the development of society. The current anti-counterfeiting means comprises: magnetic anti-counterfeiting, liquid crystal anti-counterfeiting, fluorescent anti-counterfeiting, nano-luminescent anti-counterfeiting and the like. Among them, the fluorescence anti-counterfeiting is the most spotlighted means. Phosphorescence-based security offers significant advantages over fluorescence security. The phosphorescent anti-counterfeiting mark has the characteristic of emitting fluorescence under the excitation of an ultraviolet lamp, so that the identification degree of the mark can be improved by adopting a phosphorescent material as the anti-counterfeiting mark; secondly, there are many materials which emit fluorescence under an ultraviolet lamp at present, but the RTP has less materials, so that the difficulty of counterfeiting is increased when the phosphorescent material is used as an anti-counterfeiting mark; most importantly, the duration of phosphorescence of different phosphorescent materials is different with naked eyes, and when the difference between the phosphorescence duration of the mark of a certain fake and the standard time is too large, the fake can be easily judged to be forged. Information encryption is the most basic and most core technical measure and theoretical foundation for guaranteeing information security. The security of information transmission can be improved to a certain extent through the encryption technology, and the method plays an important role in hiding information.

Therefore, how to obtain an RTP material with longer service life, higher phosphorescence quantum efficiency and better stability, how to solve the technical problem that the RTP material is difficult to obtain by carbon dots without heteroatoms, and how to solve the technical problem remain to be researched and solved.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a long-afterglow material which has the advantages of longer service life, higher phosphorescence quantum efficiency, better stability and fluorescence, delayed fluorescence and phosphorescence properties.

The invention also aims to provide the preparation method of the long afterglow material, which has universal adaptability, simple preparation process, environmental protection, high efficiency, abundant and easily obtained raw materials and can realize mass production.

The invention also aims to provide application of the long afterglow material.

The purpose of the invention is realized by the following technical scheme:

the long afterglow material comprises Carbon Dots (CDs) and a matrix, wherein the carbon dots are compounded into the matrix, and the long afterglow material is in a glass state.

The glassy state is preferably formed by a one-step heat treatment.

The long afterglow material is preferably a long afterglow material without heavy metals; further preferred is a long afterglow material containing no metal.

The carbon dots and the matrix are preferably mixed according to the mass ratio of (0.001-0.08) to (1-3). Along with the continuous increase of the carbon dot content, the luminous intensity is gradually increased and then slowly reduced, and can be adjusted as required.

The substrate is at least one of boron-containing inorganic substance or aluminum-containing inorganic substance; further preferred are Boric Acid (BA) and boron oxide (B)₂O₃) At least one of borate, aluminate, aluminum chloride and aluminate.

The preparation method of the long afterglow material comprises the following steps:

mixing carbon points with the substrate uniformly, carrying out heat treatment at the temperature of at least 140 ℃ to ensure that the mixture forms a molten state, and cooling to obtain the long afterglow material.

The temperature of the heat treatment is preferably 140-1000 ℃, and the structure of the carbon dots can be damaged when the temperature is too high; more preferably 140 to 500 ℃.

The time of the heat treatment is preferably 2-10 hours; more preferably 4 to 7 hours.

The carbon dots can be heteroatom-free carbon dots or doping element-containing carbon dots; the doping element comprises N, S, B at least one.

The carbon dots are preferably heteroatom-free carbon dots, that is, the carbon dots contain only three elements of carbon, hydrogen and oxygen.

The carbon dots can be prepared by a conventional method, such as a hydrothermal method, a microwave method, a solvothermal method, a pyrolysis method and the like; the reaction system can be a macromolecule (such as polyvinyl alcohol) and amino compound system, an organic acid and amino compound system, an amino acid and hydrogen peroxide system, an organic amine and organic alcohol system, an organic amine compound and inorganic acid system, an organic sugar compound system (such as glucose), an organic amine compound (such as m-phenylenediamine) and the like.

The reaction temperature for preparing the carbon dots is preferably 160-240 ℃, the reaction time is preferably 6-24 hours, and the reaction is preferably carried out in a high-pressure reaction kettle.

The carbon dots are preferably carbon dots obtained through a pretreatment step, wherein the pretreatment step mainly comprises separation and purification, including dialysis, centrifugation, filtration, drying and the like.

The mixing method comprises the steps of grinding through a mortar or stirring and uniformly mixing after dissolving.

The long afterglow material is applied to optoelectronics.

Preferably, the application in the anti-counterfeiting technology and the information encryption field further improves the security quality by using the fluorescence property, the RTP property and the delayed fluorescence property of the long afterglow material and the different properties of the long afterglow materials with different compositions.

The action mechanism of the invention is as follows:

the invention innovatively designs a new idea of awakening the afterglow of CDs by a universally applicable and very effective method, and discloses the afterglow mechanism of CDs: CDs have absorption peak in ultraviolet region and are derived from aromatic sp²The present invention perfectly reduces the energy band gap between singlet and triplet states by introducing electron-withdrawing boron atoms through one-step heat treatment of CDs and matrix to form a glassy state, while the glassy state can effectively protect excited triplet states from energy loss due to rotation or vibrational processes. Successfully overcomes the defect that no heteroatom-free CDs can not obtain afterglow due to occupying less energy level structures, and breaks through the bottleneck that the afterglow emission is limited in a green band. The research shows that the long afterglow material of the present invention can form new bond energy, for example, boric acid and carbon point can form new boron-carbon bond energyThe electron transition energy level is reduced, and the energy band gap between the lowest singlet state and the triplet state is reduced.

Compared with the prior art, the invention has the following advantages and effects:

(1) the metal-free long afterglow material based on the composite material of CDs has long service life and high phosphorescence quantum efficiency, the longest service life is 2682ms, and the highest phosphorescence quantum efficiency is 17.5%. More particularly, the metal-free long afterglow material shows dual-emission afterglow property, contains both yellow persistent room temperature phosphorescence and blue persistent delayed fluorescence, has fluorescence, delayed fluorescence and phosphorescence properties, not only successfully overcomes the defect that in the prior art, no heteroatom-containing CDs cannot obtain afterglow due to occupying less energy level structures, but also breaks through the bottleneck that afterglow emission is limited in a green band.

(2) In addition to heteroatom-free CDs, the present invention also provides a series of excellent metal-free long afterglow materials, such as the highest phosphorescence quantum yield (17.5%) N-CDs/BA composite and blue, green, yellow and orange red RTP found in c-CDs/BA, B, N-CDs/BA and S, N-CDs/BA composites, respectively.

(3) Compared with RTP materials in the prior art, the long afterglow material has the advantages of abundant and easily obtained raw materials, simple synthesis process, green and environment-friendly whole process, no after-treatment pollutants and capability of realizing industrial production.

(4) The invention also provides a one-step heat treatment preparation method of the long afterglow material, the method is simple to operate, low in cost, environment-friendly and wide in application range, and the prepared long afterglow material is long in service life, high in phosphorescence quantum efficiency and capable of being produced in large scale. The method for obtaining the RTP property by the one-step heat treatment of the mixed solution of CDs and boron-containing inorganic substances (such as BA and the like) has universality. Not only one kind of CDs shows RTP property in the BA matrix, but also other CDs (including CDs without heteroatoms and CDs doped with heteroatoms) show RTP property in the BA matrix, and not only has universality, but also is very effective, and has stronger RTP than CDs in other matrices; and the longest life CDs composites so far were obtained.

(5) The method for obtaining the long afterglow material not only breaks through the phenomenon that no heteroatom CDs can not obtain RTP, but also overcomes the defect that phosphorescent emission is only limited to green light.

(6) The metal-free RTP material prepared by the invention not only has efficient fluorescence, but also shows excellent dual-emission afterglow property, and simultaneously shows RTP and delayed fluorescence property, so that the metal-free RTP material serving as a security material applied to anti-counterfeiting and information encryption technology can improve the security quality, and has wide application prospect.

Drawings

FIG. 1 is a contour fluorescence spectrum of an excitation-emission matrix of an aqueous solution of heteroatom-free carbon dots a-CDs at room temperature.

FIG. 2 is a graph of the emission spectrum of the composite material a-CDs/BA with dual afterglow emission at different excitation wavelengths under room temperature.

FIG. 3 is a photograph of a real digital photograph of a dual afterglow emitting composite a-CDs/BA captured under natural light, under UV light (254nm or 365nm) and after UV light is turned off (254nm or 365nm) at intervals of 1s, respectively.

FIG. 4 is a graph of phosphorescence lifetime results of a dual afterglow emitting composite material a-CDs/BA at an emission wavelength of 430nm at an excitation wavelength of 250nm and an emission wavelength of 530nm at an excitation wavelength of 360nm, respectively, wherein the table at the upper right corner is corresponding lifetime fitting data.

FIG. 5 is an X-ray diffraction pattern of BA, a-CDs and composite a-CDs/BA at room temperature.

FIG. 6 is B₂O₃a-CDs/B obtained by compounding a-CDs without heteroatom carbon points₂O₃Phosphorescence emission spectra of the composite material under excitation of different wavelengths.

FIG. 7 shows a-CDs/B₂O₃The X-ray diffraction pattern of the composite material.

FIG. 8 is the X-ray diffraction pattern of the dual-emission afterglow composite material a-CDs/BA obtained at different temperatures.

FIG. 9 is a phosphorescence emission spectrum of a composite material b-CDs/BA obtained by compounding a heteroatom-free carbon site b-CDs with BA under excitation of different wavelengths.

FIG. 10 is the phosphorescence emission spectrum of the composite material c-CDs/BA obtained by compounding the non-heteroatom carbon sites c-CDs with BA under different wavelength excitation.

FIG. 11 is a phosphorescence emission spectrum of the composite material N-CDs/BA obtained by compounding nitrogen-doped carbon dots N-CDs with BA under excitation of different wavelengths.

FIG. 12 is a phosphorescence emission spectrum of a composite material B, N-CDs/BA obtained by compounding BA with boron-nitrogen co-doped atomic carbon dots B, N-CDs under excitation of different wavelengths.

FIG. 13 is a phosphorescence emission spectrum of a composite material S, N-CDs/BA obtained by compounding the sulfur and nitrogen co-doped atomic carbon sites S, N-CDs with BA under excitation of different wavelengths.

FIG. 14 is a photograph of the real digital images captured at intervals of 1S for B-CDs/BA, c-CDs/BA, N-CDs/BA, B, N-CDs/BA and S, N-CDs/BA composite material obtained by compounding different CDs with BA under natural light, under the irradiation of 365nm ultraviolet lamp and after the 365nm ultraviolet lamp is turned off, respectively.

FIG. 15 is an X-ray diffraction pattern of composite materials B-CDs/BA, c-CDs/BA, N-CDs/BA, B, N-CDs/BA and S, N-CDs/BA obtained by compounding different CDs with BA at room temperature.

FIG. 16 is a graph of the effect of a three-mode security application in which a panda pattern is neatly hidden within a square pattern that is a digital photograph of the actual pattern exhibited under natural light, under UV light, after 365nm UV light is turned off, and after 254nm UV light is turned off, respectively.

Fig. 17 is a diagram of the effects of an information encryption application, wherein (a) a digital photograph of a "TFRAULSE" pattern, which is composed of capital letters of "true" and "false" english words, exhibited by a real pattern after natural light, 365nm and 254nm ultraviolet lamps, respectively, were turned off; (b) the three-mode information encrypted "SCAU" pattern is a digital photograph of the real pattern exhibited after natural light, ultraviolet lamp irradiation, 365nm and 254nm ultraviolet lamp irradiation were turned off, respectively.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.

Example 1

The preparation method of the metal-free RTP material CDs/BA composite material comprises the following specific steps:

(1) preparation of CDs: the a-CDs are prepared by adopting an organic acid system, specifically, the raw material is anhydrous citric acid, and the synthesis method is a solvothermal method. The method is roughly divided into the following two steps: first, 1g of anhydrous citric acid was weighed and dissolved in 20mL of distilled water, and the resulting solution was transferred to a large beaker. And then, heating the large beaker in a heating cover at 180 ℃ until the solution turns brown, naturally cooling the large beaker to room temperature, taking out a sample, separating and purifying the sample to obtain the required a-CDs without heteroatoms, and refrigerating the a-CDs in a refrigerator for later use.

(2) Preparation of a-CDs/BA composite material: firstly, 3g of BA is weighed and transferred into a beaker, dissolved by 40mL of deionized water, added with 1mL of 20mg/mL a-CDs and stirred for 30min by a magnetic stirrer to be fully and uniformly mixed. Wrapping the beaker with tinfoil prevents the water in the mixture from evaporating too quickly. And placing the composite material into an oven with the temperature of 180 ℃ for heat treatment for 5 hours, and naturally cooling the composite material to room temperature to obtain the amorphous glassy a-CDs/BA composite material. The final product was ground to a powder and pressed into a round shape.

(3)a-CDs/B₂O₃Preparing a composite material: first, 1g of B is weighed₂O₃Transferring into mortar, adding 20mg of solid obtained by freeze drying the a-CDs obtained in step (1), and mixing the a-CDs and B₂O₃Grind with a mortar for 30 minutes to mix well. The well mixed mixture was transferred to a beaker and the beaker was wrapped with tinfoil to prevent the water in the mixture from evaporating too quickly. Placing the mixture into an oven with the temperature of 180 ℃ for heat treatment for 5 hours, and naturally cooling the mixture to the room temperature to obtain the amorphous glassy a-CDs/B₂O₃A composite material. The final product was ground to a powder and pressed into a round shape.

(4) According to the preparation method of the step (2), respectively adding 0.2mL, 0.5mL, 2mL and 4mL of a-CDs with the concentration of 20mg/mL to obtain a-CDs/BA composite materials with different a-CDs contents;

according to the preparation method of step (3), 4mg, 10mg, 40mg and 80mg of a-CDs, obtaining a-CDs/B with different a-CDs content₂O₃A composite material.

And (3) carrying out RTP property research on the obtained a-CDs/BA composite materials with different a-CDs contents, and after ultraviolet irradiation, turning off the ultraviolet lamp light to ensure that the composite material can still emit light, wherein the light emitting color after the ultraviolet lamp is turned off is different from the light emitting color under the ultraviolet lamp irradiation. The RTP property of the a-CDs/BA composite material is gradually increased and then slowly reduced along with the increase of the concentration of the a-CDs, wherein the RTP strength of the composite material prepared by adding 2mL of the a-CDs is strongest.

(5) And (3) respectively preparing the a-CDs/BA composite material according to the step (2) at different heat treatment temperatures (100 ℃, 120 ℃, 140 ℃, 160 ℃, 180 ℃, 200 ℃, 250 ℃, 300 ℃ and 400 ℃).

FIG. 1 is a contour fluorescence spectrum of the excitation-emission matrix of the heteroatom-free carbon dot a-CDs aqueous solution prepared in step (1) at room temperature. The excitation-emission contour spectrum shows that the aqueous solution of the a-CDs has an excitation dependence phenomenon, and the emission wavelength changes along with the change of the excitation wavelength.

FIG. 2 is a phosphorescence emission spectrum of the dual afterglow emission composite material a-CDs/BA prepared in step (2) under room temperature conditions and at different excitation wavelengths. Two emission peak positions can be seen from the phosphorescence emission spectrum of the composite material a-CDs/BA, wherein the emission peak of the blue light emission band is basically kept unchanged, and the emission peak of the green light emission band is gradually red-shifted with the increase of the excitation wavelength.

FIG. 3 is a real digital photograph of the dual afterglow emitting composite material a-CDs/BA obtained in step (2) captured at intervals of 1s under natural light, under ultraviolet lamp irradiation (254nm or 365nm) and after the ultraviolet lamp irradiation is turned off (254nm or 365nm), respectively. From the digital photographs, it can be seen that the composite material a-CDs/BA has no obvious difference under natural light and ultraviolet lamp, but shows yellow-green RTP property when the 365nm ultraviolet lamp is turned off, and shows bright blue delayed fluorescence property when the 254nm ultraviolet lamp is turned off.

FIG. 4 shows phosphorescence lifetimes of a dual afterglow emitting composite a-CDs/BA at an emission wavelength of 430nm at an excitation wavelength of 250nm and an emission wavelength of 530nm at an excitation wavelength of 360nm, respectively, and corresponding lifetime fitting data are shown in the table at the top right corner. The phosphorescence lifetime of the composite material a-CDs/BA under the excitation wavelength of 360nm and the emission wavelength of 530nm is up to 1567ms, and the phosphorescence lifetime under the excitation wavelength of 250nm and the emission wavelength of 430nm is longer and up to 2682 ms. This 2682ms lifetime is much longer than the lifetime of currently reported CDs composites (less than 1s), which is also the longest lifetime of CDs composites to date.

FIG. 5 is an X-ray diffraction pattern of BA, a-CDs and a-CDs/BA composites at room temperature. Wherein a-CDs shows only amorphous characteristic peaks, and a-CDs/BA shows boron oxide and amorphous glassy state characteristic peaks.

FIG. 6 shows B obtained in step (3)₂O₃a-CDs/B obtained by compounding a-CDs without heteroatom carbon points₂O₃Phosphorescence emission spectra of the composite material under excitation of different wavelengths. Composite material a-CDs/B₂O₃Mainly concentrated around 550nm, and shows a yellow RTP phenomenon.

FIG. 7 shows a-CDs/B₂O₃X-ray diffraction pattern of the composite. The XRD pattern shows that a-CDs/B₂O₃The composite material contains boron oxide and amorphous characteristic peaks.

FIG. 8 is an X-ray diffraction pattern of the dual-emission afterglow composite material a-CDs/BA obtained at different temperatures. The XRD pattern shows that the characteristic peak of boron oxide phase gradually strengthening amorphous glass state becomes more and more obvious with the increase of reaction temperature (heat treatment temperature), and only the sample obtained above 140 ℃ shows RTP property. And the composite material without the occurrence of amorphous characteristic peaks cannot exhibit RTP properties. This demonstrates that the glass state is indeed an indispensable factor in the RTP properties of wake-up CDs.

Example 2

The preparation method of the metal-free RTP material b-CDs/BA composite material comprises the following specific steps:

(1) preparation of CDs: the preparation of CDs adopts an organic compound system, particularly takes polyvinyl alcohol as a raw material to synthesize CDs by a one-step hydrothermal method, and comprises the following steps: first, 0.5g of polyvinyl alcohol was weighed out and dissolved in 20mL of deionized water, and the resulting solution was transferred to a reaction vessel. Secondly, the reaction kettle is placed in an oven at 200 ℃ for reaction for 10 hours, and the reaction kettle is naturally cooled to room temperature. Separating and purifying the reacted solution to obtain the required b-CDs without heteroatoms, and refrigerating the b-CDs in a refrigerator for later use.

(2) b-preparation of CDs/BA composite material: firstly, 3g of BA is weighed and transferred into a beaker, dissolved by 40mL of deionized water, and then 1mL of b-CDs with the concentration of 0.01g/mL is added, and stirred by a magnetic stirrer for 30min to be fully and uniformly mixed. Wrapping the beaker with tinfoil prevents the water in the mixture from evaporating too quickly. Putting the composite material into an oven with the temperature of 180 ℃ for heat treatment for 5 hours, and naturally cooling the composite material to the room temperature to obtain the amorphous glassy b-CDs/BA composite material. The final product was ground to a powder and pressed into a round shape.

(3) As in step (4) in example 1, the amount of b-CDs added in step (2) may not be fixed, and for example, 0.5mL, 1mL, 2mL, etc. may be added as required.

FIG. 9 is a phosphorescence emission spectrum of the composite material b-CDs/BA obtained by compounding the heteroatom-free carbon sites b-CDs with BA in the step (2) under excitation of different wavelengths. The phosphorescence emission of the composite material b-CDs/BA is mainly concentrated at about 550nm, and the RTP phenomenon of yellow is shown.

Example 3

The preparation method of the metal-free RTP material c-CDs/BA composite material comprises the following specific steps:

(1) preparation of CDs: the preparation of CDs adopts an organic saccharide compound system, and specifically uses glucose as a raw material to synthesize CDs by a microwave method, and the preparation method specifically comprises the following steps: first, 0.22g of glucose was weighed out and dissolved in 2.5mL of deionized water, respectively, and the resulting solutions were transferred to glass bottles. Secondly, the glass bottle is placed in a microwave oven to react for 10min under a certain power (for example 800W), and the glass bottle is naturally cooled to the room temperature. And separating and purifying the solution after reaction to finally obtain the required c-CDs without heteroatoms, and refrigerating the c-CDs in a refrigerator for later use.

(2) Preparation of c-CDs/BA composite material: firstly, 3g of BA is weighed and transferred into a beaker, dissolved by 40mL of deionized water, and then 1mL of c-CDs with the concentration of 0.01g/mL is added, and stirred by a magnetic stirrer for 30min to be fully and uniformly mixed. Wrapping the beaker with tinfoil prevents the water in the mixture from evaporating too quickly. Putting the composite material into an oven with the temperature of 180 ℃ for heat treatment for 5 hours, and naturally cooling the composite material to room temperature to obtain the amorphous glassy c-CDs/BA composite material. The final product was ground to a powder and pressed into a round shape.

(3) Different amounts of c-CDs may be added in step (2) as required.

FIG. 10 is a phosphorescence emission spectrum of the composite material c-CDs/BA obtained by compounding the heteroatom-free carbon sites c-CDs with BA in the step (2) under excitation of different wavelengths. The phosphorescence emission spectrum of the composite material c-CDs/BA has a red shift phenomenon along with the increase of the excitation wavelength, and the phosphorescence emission peak is presented in a blue light region.

Example 4

The preparation method of the metal-free RTP material N-CDs/BA composite material comprises the following specific steps:

(1) preparation of CDs: the preparation of CDs adopts an organic amine compound, specifically synthesizes CDs by using m-phenylenediamine as a raw material through a one-step hydrothermal method, and specifically comprises the following steps: first, 0.9g of m-phenylenediamine was weighed out and dissolved in 90mL of ethanol, respectively, and then the solution was transferred to a polytetrafluoroethylene-lined autoclave and heated at 180 ℃ for 12 hours. After natural cooling to room temperature, a grey suspension was obtained and the crude product was purified by silica column chromatography. Finally, after removal of the solvent and further drying in vacuo at 60 ℃, N-CDs are finally obtained. N-CDs are prepared into a solution with the concentration of 1mg/mL by deionized water and are stored in a refrigerator for later use.

(2) Preparation of N-CDs/BA composite material: firstly, 3g of BA is weighed and transferred into a beaker, dissolved by 40mL of deionized water, and then 1mL of N-CDs is added and stirred for 30min by a magnetic stirrer to be fully and uniformly mixed. Wrapping the beaker with tinfoil prevents the water in the mixture from evaporating too quickly. Putting the glass-ceramic composite material into an oven with the temperature of 180 ℃ for heat treatment for 5 hours, and naturally cooling the glass-ceramic composite material to room temperature to obtain the amorphous glassy N-CDs/BA composite material. The final product was ground to a powder and pressed into a round shape.

(3) Different amounts of N-CDs may be added in step (2) as required.

FIG. 11 is a phosphorescence emission spectrum of the composite material N-CDs/BA obtained by compounding nitrogen-doped carbon dots N-CDs with BA in the step (2) under excitation of different wavelengths. The phosphorescence emission peak of the composite material N-CDs/BA does not change along with the change of the excitation wavelength, the emission peak is concentrated at about 545nm, and the yellow RTP phenomenon is shown.

Example 5

The preparation method of the metal-free RTP material B, N-CDs/BA composite material comprises the following specific steps:

(1) preparation of CDs: organic amine compounds and inorganic acid are adopted for preparing CDs, and particularly, the CDs are synthesized by a one-step hydrothermal method by taking ethylenediamine and BA as raw materials, and the method comprises the following specific steps: first, 1g of BA was weighed out and dissolved in 25mL of deionized water and 1mL of ethylenediamine was added. The solution was then transferred to a teflon lined autoclave. After heating at 240 ℃ for 8 hours, natural cooling to room temperature gives a brown product. The obtained brown solution is centrifugally separated to obtain pure B, N-CDs, and the pure B, N-CDs are stored in a refrigerator for later use.

(2) B, preparation of N-CDs/BA composite material: firstly, 3g of BA is weighed and transferred into a beaker, dissolved by 40mL of deionized water, then 1mL of B, N-CDs with the concentration of 0.01g/mL is added, and stirred by a magnetic stirrer for 30min to be fully and uniformly mixed. Wrapping the beaker with tinfoil prevents the water in the mixture from evaporating too quickly. Putting the composite material into an oven with the temperature of 180 ℃ for heat treatment for 5 hours, and naturally cooling the composite material to room temperature to obtain the amorphous glassy B, N-CDs/BA composite material. The final product was ground to a powder and pressed into a round shape.

(3) Different amounts of B, N-CDs may be added in step (2) as required.

FIG. 12 is a phosphorescence emission spectrum of the composite material B, N-CDs/BA obtained by compounding boron-nitrogen co-doped atomic carbon dots B, N-CDs in the step (2) with BA under excitation of different wavelengths. The phosphorescence emission of the composite material B, N-CDs/BA shows excitation independence, the phosphorescence emission peak is concentrated at about 500nm, and the green RTP phenomenon is shown.

Example 6

The preparation method of the metal-free RTP material S, N-CDs/BA composite material comprises the following specific steps:

(1) preparation of CDs: organic amine compounds and inorganic acid are adopted for preparing CDs, and specifically, m-phenylenediamine and concentrated sulfuric acid are used as raw materials to synthesize the CDs by a one-step hydrothermal method, and the method specifically comprises the following steps: first, 0.2g of m-phenylenediamine was weighed out and dissolved in 30mL of ethanol, and then 1mL of concentrated sulfuric acid was added. This mixture was then transferred to a teflon lined reactor and allowed to cool to room temperature after heating at 200 ℃ for 10 hours. Taking out the dark green crude product, centrifuging at high speed to remove large-particle precipitate, dialyzing for 24 hours to obtain pure S, N-CDs, and refrigerating in a refrigerator for later use.

(2) Preparing an S, N-CDs/BA composite material: firstly, 3g of BA is weighed and transferred into a beaker, 40mL of deionized water is used for dissolving, 1mL of S with the concentration of 0.01g/mL is added, and N-CDs is stirred for 30min by a magnetic stirrer to be fully and uniformly mixed. Wrapping the beaker with tinfoil prevents the water in the mixture from evaporating too quickly. Putting the glass-ceramic composite material into an oven with the temperature of 180 ℃ for heat treatment for 5 hours, and naturally cooling the glass-ceramic composite material to room temperature to obtain the S, N-CDs/BA composite material with amorphous glass state. The final product was ground to a powder and pressed into a round shape.

(3) Different amounts of S, N-CDs may be added in step (2) as required.

FIG. 13 is a phosphorescence emission spectrum of the composite material S, N-CDs/BA obtained by the composite sulfur-nitrogen co-doped atomic carbon sites S, N-CDs of the BA in the step (2) under excitation of different wavelengths. The phosphorescence emission of the composite material S, N-CDs/BA basically has no excitation dependence phenomenon, the emission peak is mainly concentrated at about 580nm, and the RTP phenomenon of orange red is shown.

FIG. 14 is a real digital photograph of the composite materials B-CDs/BA, c-CDs/BA, N-CDs/BA, B, N-CDs/BA and S, N-CDs/BA captured at intervals of 1S after natural light, 365nm UV light and 365nm UV light are turned off, respectively. The composite materials obtained by one-step heat treatment of various CDs and BA show bright RTP phenomenon after ultraviolet and the like are turned off. And the phosphorescent emission is significantly red-shifted compared to the fluorescent emission. Moreover, the composite material shows a relatively durable and stable RTP phenomenon, and still shows the super-strong RTP after the ultraviolet lamp is turned off after the composite material is placed for 10 months.

FIG. 15 shows X-ray diffraction patterns of composite materials B-CDs/BA, c-CDs/BA, N-CDs/BA, B, N-CDs/BA and S, N-CDs/BA obtained by compounding different CDs with BA at room temperature. The X-ray diffraction patterns of the five samples showed that the five CDs/BA composites all had characteristic peaks for amorphous glassy boron oxide. This further demonstrates that the glassy state is one of the important factors in RTP for waking up CDs, and that the glassy state can effectively stabilize the triplet excited state of the system.

Example 7

The preparation method of the a-CDs/silica composite material comprises the following specific steps:

first, 10mL of tetraethyl orthosilicate (TEOS) was weighed into a round-bottom flask, dissolved in 40mL of deionized water, and then 1mL of 20mg/mL a-CD was added and stirred with a magnetic stirrer for 30min to mix well. Condensing and refluxing for 5 hours at 180 ℃ in an oil bath, and naturally cooling to room temperature to obtain the a-CDs/silica composite material.

Example 8

The triple anti-counterfeiting technology and the information encryption application comprise the following specific steps:

(1) triple anti-counterfeiting technology: we smear a square pattern by using a-CDs/BA with ultra-long dual emission afterglow obtained in example 1, N-CDs/BA with persistent RTP obtained in example 4, and B, N-CDs/BA with persistent RTP obtained in example 5. Wherein, a panda pattern smeared by a-CDs/BA and a bamboo shape smeared by B, N-CDs/BA are ingeniously hidden in the square pattern, and N-CDs/BA is smeared at other blank positions, thus achieving triple anti-counterfeiting effect.

(2) Information encryption application: the anti-counterfeiting pattern 'TFRAULSE' is a mixture of 'true' and 'false' English capital letters. Wherein the TRUE information 'TRUE' is formed by smearing a-CDs/BA composite material with double afterglow, and the interference information 'FALSE' is formed by smearing N-CDs/BA. We also obtained another dual-mode information encryption scheme using a-CDs/BA and N-CDs/BA. We delineate the true stored information "S" with the a-CDs/BA material with dual emission long persistence, while the three interference information "C", "A", and "U" with silica, N-CDs/BA, and a-CDs/silica, respectively.

Fig. 16 shows a three-mode anti-counterfeiting application, wherein a panda pattern is skillfully hidden in a square pattern. Under the sunlight, the anti-counterfeiting pattern is only a simple square pattern, and a white panda pattern is displayed under the irradiation of an ultraviolet lamp (254nm or 365 nm). When the 365nm ultraviolet lamp was turned off, a yellow-green panda pattern with bamboo patterns appeared again, but when the 254nm ultraviolet lamp was turned off, a blue skeleton pattern appeared.

Fig. 17 shows an information encryption application, (a) a "TFRAULSE" pattern combined by capital letters of "TRUE" and "false", showing the "TFRAULSE" pattern under natural light, exhibiting the combined "TFRAULSE" pattern after 365nm uv lamp illumination is turned off, but showing only "TRUE" after 254nm uv lamp is turned off. (b) The 'SCAU' pattern encrypted for the three-mode information respectively shows the 'SCAU' pattern under natural light and the 'SAU' pattern under the irradiation of an ultraviolet lamp (254nm or 365nm), the 'SA' pattern is shown after the irradiation of the 365nm ultraviolet lamp is turned off, and the final real information 'S' is only displayed after the 254nm ultraviolet lamp is turned off. This information encryption technique can only decrypt hidden information if a particular excitation wavelength is turned off, otherwise the wrong information will be transmitted.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A long afterglow material comprises carbon dots and a matrix, and is characterized in that:

the carbon dots are compounded into the matrix, and the long afterglow material is in a glass state; the glass state is formed by one-step heat treatment;

the substrate is at least one of boric acid and boron oxide;

the long afterglow material has fluorescence property, RTP property and delayed fluorescence property;

the long afterglow material is a metal-free long afterglow material.

2. The long persistent material of claim 1, wherein:

the carbon dots and the matrix are mixed according to the mass ratio of (0.001-0.08) to (1-3).

3. The method for preparing a long-afterglow material as defined in any one of claims 1 to 2, comprising the steps of:

4. The method for preparing a long afterglow material of claim 3, wherein:

the carbon dots can be heteroatom-free carbon dots or doping element-containing carbon dots;

the temperature of the heat treatment is 140-1000 ℃;

the time of the heat treatment is 2-10 hours.

5. The method for preparing a long afterglow material of claim 4, wherein:

the doping element comprises N, S, B;

the temperature of the heat treatment is 140-500 ℃;

the time of the heat treatment is 4-7 hours.

6. The method for preparing a long afterglow material of claim 3, wherein:

the carbon points are carbon points without heteroatoms;

the carbon dots can be prepared by a conventional method;

the carbon dots are obtained by a pretreatment step,

the pretreatment comprises separation and purification.

7. The method for preparing a long afterglow material of claim 6, wherein:

the separation and purification comprises dialysis, centrifugation, filtration and drying;

the reaction temperature for preparing the carbon dots is 160-240 ℃, and the reaction time is 6-24 hours.

8. Use of the long afterglow material of any of claims 1 to 2 in optoelectronics.

9. The use of a long persistent material according to claim 8 in optoelectronics, wherein:

the long afterglow material is applied to the fields of anti-counterfeiting technology and information encryption.