A self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties, its preparation method, and its application in anti-counterfeiting.

Abstract

This invention relates to a self-protected carbonized polymer dot with near-infrared room-temperature phosphorescence properties, its preparation method, and its application in anti-counterfeiting, belonging to the field of luminescent carbon nanomaterial preparation technology. Phenothiazine is dissolved in water with pyromellitic acid, 1,2,3,4-butanetetracarboxylic acid, methylfumaric acid, or diethylenetriaminepentaacetic acid. The pH of the reaction system is adjusted to 2-13 before a hydrothermal reaction is carried out. After the reaction, the mixture is cooled, filtered, dialyzed, concentrated, and freeze-dried under vacuum to obtain a solid powder of self-protected carbonized polymer dots with near-infrared room-temperature phosphorescence properties. The obtained carbonized polymer dots can achieve stable near-infrared room-temperature phosphorescence emission in air without the need for an external rigid matrix, and have advantages such as simple preparation method, readily available raw materials, and suitability for mass production. This invention expands the types of near-infrared room-temperature phosphorescent carbonized polymer dot materials and provides a new material system for their application in anti-counterfeiting, information encryption, and bioimaging.

Description

Technical Field

[0001] This invention belongs to the field of luminescent carbon nanomaterial preparation technology, specifically relating to a self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties, its preparation method, and its application in anti-counterfeiting. Background Technology

[0002] The triplet excitons in room-temperature phosphorescent materials are highly susceptible to quenching due to environmental factors such as oxygen and moisture. Near-infrared (NIIR) room-temperature phosphorescent materials, with their long emission wavelengths and low background interference, have attracted widespread attention in recent years due to their potential applications in bioimaging, anti-counterfeiting, and information encryption. However, near-infrared emission typically corresponds to a small excited-state bandgap. According to the bandgap law, excited states are more likely to dissipate energy through non-radiative pathways such as vibrational coupling. Therefore, achieving stable and efficient NIIR room-temperature phosphorescence emission is generally more challenging than visible light emission. Existing NIIR room-temperature phosphorescent materials include inorganic heavy metal compounds (such as platinum, palladium, and iridium complexes), which suffer from high cost, high toxicity, and demanding synthesis requirements. While purely organic materials avoid the heavy metal problem, they still often face challenges such as complex synthesis steps, strong dependence on crystals or added rigid matrices, and limited processing applicability. Therefore, developing a novel material that is readily available, simple to prepare, requires no matrix assistance, and can produce stable NIIR room-temperature phosphorescence is of great significance.

[0003] Carbonized polymer dots, as an emerging zero-dimensional carbon-based nanomaterial, possess advantages such as low cost, simple and green preparation methods, and tunable optical properties, and have shown promising application prospects in the field of room-temperature phosphorescence in recent years. However, the room-temperature phosphorescence emission wavelengths of existing carbonized polymer dots are mostly concentrated in the visible light region (<600 nm), and they rely on matrix assistance (such as polyacrylamide, cyanuric acid, molecular sieves, etc.), and mostly exist in the form of bulk phase materials or film materials, which is not conducive to subsequent modification and application. Currently, self-protected near-infrared room-temperature phosphorescent carbonized polymer dot materials that can achieve intrinsic emission wavelengths greater than 700 nm, do not require matrix assistance, and are easy to modify are still extremely scarce. Carbonized polymer dots are usually prepared from organic molecules containing functional groups such as amino, hydroxyl, and carboxyl groups. Their surfaces have abundant functional groups and highly cross-linked nanostructures, which are beneficial for suppressing non-radiative transition processes through self-immobilization. Therefore, introducing specific small organic molecules into carbonized polymer dots through cross-linking confinement is expected to generate triplet excitons with narrow-band emission energy levels, thereby realizing near-infrared room-temperature phosphorescence emission. Summary of the Invention

[0004] The purpose of this invention is to provide a self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties, its preparation method, and its application in the field of anti-counterfeiting. The carbonized polymer dot is prepared from phenothiazine and various organic carboxylic acids.

[0005] The "self-protected" nature of this invention refers to the fact that the carbonized polymer dots themselves can form a rigid cross-linked network structure, stably emitting near-infrared room-temperature phosphorescence in an air environment without the need for any external matrix (such as polyacrylamide, cyanuric acid, molecular sieves, etc.). Its core mechanism lies in the cross-linking polymerization between phenothiazine and organic carboxylic acid molecules during the hydrothermal reaction, forming a highly cross-linked carbonized polymer dot framework that tightly confines the phenothiazine or its derived luminescent units within the polymer dots. This confined structure, on the one hand, suppresses molecular vibration and rotation through spatial constraint, reducing non-radiative energy dissipation; on the other hand, it stabilizes triplet excitons through the amide-related cross-linking structure and rigid network, while simultaneously isolating them from the quenching effects of oxygen and moisture. In contrast, traditional matrix-assisted room-temperature phosphorescent materials must rely on an external rigid matrix (such as crystals, polymer films, molecular sieves, etc.) to protect the luminescent molecules. Their luminescence performance is highly dependent on the choice of matrix and preparation conditions, and they are often difficult to process in solution or repeatedly dissolve. The self-protected carbonized polymer dots of this invention do not require an external matrix and have the significant advantage of structural self-support.

[0006] The preparation method of this invention overcomes the drawbacks of existing methods, such as high cost, complex preparation, and limited material types. This invention uses a one-step hydrothermal method to prepare an aqueous solution of carbonized polymer dots, which, after separation and purification, yields a solid powder of carbonized polymer dots with near-infrared room-temperature phosphorescence properties. Even with changes in the type of raw materials, this invention can still prepare carbonized polymer dots with near-infrared room-temperature phosphorescence properties. The method is simple, easy to implement, and low in cost, and the resulting product has excellent performance, making it suitable for mass synthesis and possessing broad application prospects in the field of anti-counterfeiting.

[0007] This invention first utilizes a mixed solution of phenothiazine and pyromellitic acid in a high-temperature reactor to conduct a hydrothermal reaction, preparing an aqueous solution of carbonized polymer dots. Then, through filtration, dialysis, concentration, and freeze-drying, a high-yield carbonized polymer dot powder with near-infrared room-temperature phosphorescence properties is obtained. Furthermore, this invention also explores other organic carboxylic acid molecules besides pyromellitic acid. Experiments show that suitable organic carboxylic acid molecules can be selected from one or more of the following compounds: pyromellitic acid, 1,2,3,4-butanetetracarboxylic acid, methylfumaric acid, and diethylenetriaminepentaacetic acid. Hydrothermal reactions of the above organic carboxylic acid molecules with phenothiazine can all produce carbonized polymer dots with near-infrared room-temperature phosphorescence properties.

[0008] The present invention discloses a method for preparing a self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties, comprising the following steps:

[0009] (1) Weigh 0.2~2.0 mmol of phenothiazine and 0.1~0.5 mmol of organic carboxylic acid molecules and dissolve them in 9~10 mL of deionized water. Then add sodium hydroxide solution to adjust the pH of the reaction system to 2~13. Mix thoroughly and stir evenly. Then, perform a hydrothermal reaction at 120~220℃ for 2~12 hours.

[0010] (2) After the solution in step (1) has cooled naturally to room temperature, filter it to remove large particles of impurities and obtain a pale yellow aqueous solution of carbonized polymer dots. The solution exhibits yellow-green fluorescence under a handheld ultraviolet lamp.

[0011] (3) The polymer spot aqueous solution obtained in step (2) is placed into a dialysis bag with a molecular weight cutoff of 500~1000 Da for dialysis. The dialysis solution is concentrated to remove impurities, and then vacuum freeze-dried to obtain carbonized polymer spot solid powder with near-infrared room temperature phosphorescence.

[0012] Further, in step (1), the organic carboxylic acid molecule is one or more of 1,2,3,4-butanetetracarboxylic acid, methyltrans-butenedioic acid, diethylenetriaminepentaacetic acid, or pyromellitic acid.

[0013] Furthermore, in step (1), the pH value of the reaction system is adjusted using a 2.0 mol / L sodium hydroxide solution.

[0014] Furthermore, in step (2), a 0.22 μm water filter head is used for filtration.

[0015] Furthermore, in step (3), the pressure of vacuum freeze drying is 1~10 Pa, the freeze drying temperature is -30~-10℃, and the freeze drying time is 24~48 h.

[0016] The carbonized polymer dot solid powder prepared by this invention exhibits excellent and stable near-infrared room temperature phosphorescence properties and good solubility in water (more than 100 g per 10 mL of water at room temperature). Furthermore, the near-infrared room temperature phosphorescence properties of the solid powder are well recoverable after repeated dissolution and freeze-drying. This method effectively overcomes the shortcomings of existing near-infrared room temperature phosphorescent materials, such as the need for a rigid matrix, complex synthesis, and limited material types. It enables the simple and large-scale preparation of various carbonized polymer dots with near-infrared room temperature phosphorescence, and the prepared materials have broad application prospects in fields such as bioimaging, anti-counterfeiting, and information encryption. Attached Figure Description

[0017] Figure 1 Transmission electron microscopy (TEM) images and particle size distribution of carbonized polymer spot 1;

[0018] Figure 2Fluorescence spectra of the aqueous solution of carbonized polymer point 1 under different wavelengths of light excitation;

[0019] Figure 3 Fluorescence spectra of carbonized polymer dot 1 solid powder under different wavelengths of light excitation;

[0020] Figure 4 : Phosphorus spectrum of carbonized polymer point 1 solid powder after irradiation with a 365 nm UV lamp is stopped;

[0021] Figure 5 : Luminescence intensity decay curve of solid powder of carbonized polymer point 1;

[0022] Figure 6 : UV-Vis absorption spectrum of aqueous solution of carbonized polymer point 1;

[0023] Figure 7 Fourier transform infrared absorption (FT-IR) spectrum of carbonized polymer at point 1;

[0024] Figure 8 X-ray photoelectron spectroscopy (XPS) of carbonized polymer point 1; where, XPS full spectrum (a), high-resolution XPS spectrum of carbon (b), high-resolution XPS spectrum of nitrogen (c), and high-resolution XPS spectrum of sulfur (d).

[0025] Figure 9 : Room temperature phosphorus spectra of carbonized polymer at point 1 with different feed ratios;

[0026] Figure 10 : Room temperature phosphorus spectra of carbonized polymer at different reaction times at point 1;

[0027] Figure 11 : Room temperature phosphorus spectra of carbonized polymer at different reaction temperatures at point 1;

[0028] Figure 12 : Room temperature phosphorus spectra of carbonized polymer point 1 synthesized at different pH values;

[0029] Figure 13 Thermogravimetric analysis (TGA) curve of carbonized polymer at point 1;

[0030] Figure 14 Time-resolved room-temperature phosphorescence spectrum of point 1 of the carbonized polymer;

[0031] Figure 15 The anti-counterfeiting mark constructed from carbonized polymer dot 1 is shown in photos after exposure to sunlight, irradiation with a 365nm ultraviolet lamp, and after the irradiation with the 365nm ultraviolet lamp has stopped. Detailed Implementation

[0032] The present invention will be further described below with reference to embodiments. The purpose of referring to the embodiments is to illustrate the present invention in detail, and not to limit the present invention. It should be noted that the technical solutions summarized in the present invention can be reasonably modified and extended within the scope of the following embodiments.

[0033] Example 1: Preparation of carbonized polymer point 1

[0034] 39.85 mg (0.2 mmol) of phenothiazine and 25.42 mg (0.1 mmol) of pyromellitic acid were weighed and dissolved in 9.7 mL of water. 0.3 mL of 2.0 mol / L sodium hydroxide was added to adjust the pH of the reaction system to 11.6, and the mixture was stirred thoroughly with a glass rod. The solution was transferred to a 25 mL stainless steel reactor lined with polytetrafluoroethylene (PTFE), and the lid was tightened. The reactor was subjected to hydrothermal reaction at 180 °C for 8 h. After the reactor cooled naturally to room temperature, the solution was removed and filtered through a 0.22 μm aqueous filter to obtain an aqueous solution of carbonized polymer dots. Under 360 nm UV light, this aqueous solution exhibited weak yellow fluorescence. The obtained aqueous solution of carbonized polymer dots was placed in a dialysis bag with a molecular weight cutoff of 1000 Da and allowed to dialyze for 36 h. The collected dialysis liquid was concentrated to 2 mL using a rotary evaporator to remove impurities, and then vacuum freeze-dried (pressure 5 Pa; temperature -25℃; drying time 24 h) to obtain a solid powder of carbonized polymer point 1 with near-infrared room temperature phosphorescence properties. The product mass was 20.6 mg, and the yield was approximately 23%.

[0035] The carbonized polymer dots 1 obtained in the above steps exhibit a dot-like nanostructure in transmission electron microscopy images, demonstrating good dispersibility with a size distribution ranging from 2.0 to 6.0 nm and an average particle size of 4.03 nm. Figure 1 The aqueous solution of carbonized polymer point 1 exhibits weak yellow fluorescence under 360 nm UV light irradiation, with a quantum yield of 2.98%. Its emission peak is broad and shows some excitation dependence. Figure 2 The optimal excitation wavelength is 320 nm, and the optimal emission wavelength is 487 nm. Furthermore, carbonized polymer point 1 exhibits a broad fluorescence emission peak in the solid state at 450–650 nm. Figure 3 The solid-state phosphorescence exhibits a quantum efficiency of 2.15%, an optimal excitation wavelength of 365 nm, and an optimal emission wavelength of 730 nm. Room temperature phosphorescence spectrum ( Figure 4 This indicates that the carbonized polymer point 1 exhibits strong near-infrared room-temperature phosphorescence emission, with a phosphorescence peak at 717 nm and a phosphorescence lifetime of ( Figure 5 The wavelength was 54.62 ms. The UV-Vis absorption spectrum ( Figure 6This indicates that it exhibits absorption in the 320–400 nm range, corresponding to the characteristic absorption peak of n→π* for C=O. Furthermore, the infrared spectrum ( Figure 7 The presence of amide bands (I / II) in the carbonized polymer spots indicates the presence of carbonyl, amino, and hydroxyl groups. X-ray photoelectron spectroscopy analysis (…) Figure 8 The results indicate that the obtained carbonized polymer dots are mainly composed of four elements: C, N, O, and S. The presence of nitrogen and sulfur in the carbonized polymer dots suggests that these two elements have been introduced into the interior of the carbonized polymer dots, and they play an important role in regulating the phosphorescence properties of the carbonized polymer dots. Placing the solid powder of carbonized polymer dot 1 in liquid nitrogen resulted in a longer phosphorescence lifetime and enhanced brightness.

[0036] Example 2: Effect of experimental conditions on the properties of carbonized polymer point 1

[0037] Raw material feeding ratio: Different masses of phenothiazine (39.85, 39.85, 39.85, 39.85, 199.27, 398.5 mg, equivalent to 0.2, 0.2, 0.2, 0.2, 1.0, 2.0 mmol, respectively) and pyromellitic acid (120.07, 63.53, 50.83, 25.42, 50.83, 50.83 mg, corresponding to 0.5, 0.25, 0.2, 0.1, 0.2, 0.2 mmol, respectively) were weighed and dissolved in 9.7 mL of deionized water. 0.3 mL of 2 mol / L sodium hydroxide was added to adjust the pH of the reaction system to 2.4, 2.8, 3.2, 3.9, 5.0, and 9.0, respectively. The mixture was stirred evenly with a glass rod. The subsequent preparation process was the same as in Example 1, to investigate the effect of different feeding ratios on the luminescence properties of carbonized polymer dots under the same time and temperature conditions.

[0038] Reaction time: 39.85 mg (0.2 mmol) of phenothiazine and 25.42 mg (0.1 mmol) of pyromellitic acid were dissolved in 9.7 mL of deionized water. 0.3 mL of 2 mol / L sodium hydroxide was added to adjust the pH of the reaction system to 11.6. The mixture was stirred thoroughly with a glass rod, and the subsequent preparation process was the same as in Example 1. Hydrothermal treatment was performed at 180℃ for different times (2, 4, 6, 8, 10, and 12 h) to investigate the effect of reaction time on the luminescent properties of the carbonized polymer dots.

[0039] Reaction temperature: 39.85 mg (0.2 mmol) of phenothiazine and 25.42 mg (0.1 mmol) of pyromellitic acid were dissolved in 9.7 mL of deionized water. 0.3 mL of 2 mol / L sodium hydroxide was added to adjust the pH of the reaction system to 11.6. The mixture was stirred thoroughly with a glass rod, and the subsequent preparation process was the same as in Example 1. Hydrothermal reactions were carried out at 120, 140, 160, 180, 200, and 220 °C for 8 h, respectively, to investigate the effect of reaction temperature on the luminescent properties of the carbonized polymer.

[0040] pH of the reaction system: 39.85 mg (0.2 mmol) of phenothiazine and 25.42 mg (0.1 mmol) of pyromellitic acid were weighed and dissolved in different volumes of deionized water (10, 9.9, 9.7, 9.5, 9.2, 9.0 mL); then 2 mol / L sodium hydroxide (0, 0.1, 0.3, 0.5, 0.8, 1.0 mL) was added to adjust the pH of the reaction system to 2.3, 2.7, 3.9, 11.6, 12.3, and 12.7. The mixture was stirred evenly with a glass rod, and the subsequent preparation process was the same as in Example 1. The reaction was hydrothermally heated at 180℃ for 8 h to investigate the effect of the pH of the reaction system on the luminescent properties of the carbonized polymer dots.

[0041] The results showed that the feed ratio, reaction time, reaction temperature, and pH of the reaction system all had a significant impact on the properties of the product. The highest near-infrared phosphorescence quantum yield was obtained when the phenothiazine concentration was 39.85 mg (0.2 mmol) and the pyromellitic acid concentration was 25.42 mg (0.1 mmol) (Figure 9). The luminescence properties of the product showed an increasing trend after 8 h of reaction, and the effect of extending the reaction time after 8 h was relatively small; therefore, 8 h is considered a reasonable reaction time. Figure 10 The phosphorescence properties of the product are poor when the reaction temperature is between 120 and 180℃. When the reaction temperature is between 180 and 220℃, the quantum yield increases with increasing temperature. However, compared to 180℃, the quantum yield increases further at 200℃, 220℃, and higher reaction temperatures, but this can easily cause deformation of the reaction vessel. Therefore, 180℃ is a more reasonable reaction condition. Figure 11 When 0.3 mL of sodium hydroxide was added (the pH of the reaction system was 11.6), the product exhibited the highest near-infrared room-temperature phosphorescence performance. Figure 12 Therefore, by optimizing experimental conditions according to actual needs, carbonized polymer dots with excellent near-infrared phosphorescence properties can be obtained.

[0042] Example 3: Investigation of the stability of carbonized polymer point 1

[0043] The preparation process was as described in Example 1. The obtained carbonized polymer spot 1 was subjected to thermogravimetric analysis to determine its thermal stability. The results showed that ( Figure 13 The carbonized polymer at point 1 hardly decomposes below 200℃, indicating that it has good thermal stability.

[0044] The preparation process was as described in Example 1. The time-resolved room-temperature phosphorescence spectrum of the obtained carbonized polymer spot 1 was tested under conditions where the delay time was increased from 1 ms to 200 ms to determine its near-infrared phosphorescence stability. The results showed that ( Figure 14 As the delay time increases, point 1 of the carbonized polymer still maintains a near-infrared room temperature phosphorescence emission peak of 717 nm, without interference from other emission peaks.

[0045] The preparation process is as described in Example 1. The obtained carbonized polymer dots were placed at room temperature for 6 months, and the powder still maintained its near-infrared room temperature phosphorescence properties. The powder was dissolved, freeze-dried, and repeated multiple times. The results showed that the near-infrared room temperature phosphorescence properties of carbonized polymer dots 1 had good consistency. Therefore, the near-infrared room temperature phosphorescence of the carbonized polymer dot powder prepared by this invention has good recoverability and reproducibility, and is expected to achieve mass production.

[0046] Example 4: Verification of the method's universality

[0047] To verify the universality of this invention, we selected several structurally different acids (1,2,3,4-butanetetracarboxylic acid, methylfumaric acid, and diethylenetriaminepentaacetic acid) to replace the pyromellitic acid in Example 1, prepared carbonized polymers at points 2-4, and characterized their near-infrared phosphorescence properties at room temperature. The results are shown in Table 1. The experimental results indicate that the amide-related crosslinking structure may play an important role in near-infrared room-temperature phosphorescence emission. Simultaneously, the presence of nitrogen and sulfur heteroatoms in the phenothiazine structure is beneficial for improving the intersystem crossing efficiency of the system, thereby promoting the generation of near-infrared room-temperature phosphorescence. Compared to carbonized polymer spot 1, carbonized polymer spots 2 and 3 exhibit weaker near-infrared room-temperature phosphorescence due to the lack of benzene ring structures in their raw materials, 1,2,3,4-butanetetracarboxylic acid and methylfurenediaic acid. This lack of benzene rings hinders phosphorescence formation during their formation process. In contrast, carbonized polymer spot 4, with its raw material diethylenetriaminepentaacetic acid containing more carboxyl and nitrogen atoms, provides more potential crosslinking sites, resulting in a product exhibiting stronger near-infrared room-temperature phosphorescence. Carbonized polymer spots 1-4 all exhibit near-infrared phosphorescence at 715–717 nm at room temperature, indicating that near-infrared room-temperature phosphorescence is prevalent in this system.

[0048] Table 1: Experimental data for carbonized polymer spots 1-4

[0049]

[0050] Note: Strong indicates that obvious near-infrared phosphorescence can be observed after the 365 nm ultraviolet lamp stops irradiating; Weak indicates that a weaker phosphorescence can be observed after the 365 nm ultraviolet lamp stops irradiating.

[0051] Example 5: Application - Design of Anti-counterfeiting Labels

[0052] Figure 15 These are photographs of the carbonized polymer dot 1 powder in anti-counterfeiting applications. The left image (under sunlight) shows the pattern does not emit light under natural light, revealing the yellowish-white color of the powder itself. The middle image (with UV lamp on) shows the pattern emitting yellowish-green fluorescence under 365 nm UV excitation. The right image (with UV lamp off) shows the pattern emitting room-temperature phosphorescent afterglow in the red to near-infrared region after the UV lamp is turned off. This demonstrates that the self-protective near-infrared room-temperature phosphorescent carbonized polymer dots prepared by this invention are suitable for anti-counterfeiting applications.

Claims

1. A method for preparing self-protected carbonized polymer dots with near-infrared room temperature phosphorescence properties, comprising the following steps: (1) Weigh 0.2~2.0 mmol of phenothiazine and 0.1~0.5 mmol of organic carboxylic acid molecules and dissolve them in 9~10 mL of deionized water. Then add sodium hydroxide solution to adjust the pH of the reaction system to 2~13. Mix thoroughly and stir evenly. Then, perform a hydrothermal reaction at 120~220℃ for 2~12 hours. (2) After the solution in step (1) has cooled naturally to room temperature, filter it to remove large particles of impurities and obtain a pale yellow aqueous solution of carbonized polymer dots, which has yellow-green fluorescence under a handheld ultraviolet lamp. (3) The polymer spot aqueous solution obtained in step (2) is placed into a dialysis bag with a molecular weight cutoff of 500~1000 Da for dialysis. The obtained dialysis liquid is concentrated to remove impurities and then freeze-dried under vacuum to obtain carbonized polymer spot solid powder with near-infrared room temperature phosphorescence.

2. The method for preparing a self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties as described in claim 1, characterized in that: In step (1), the organic carboxylic acid molecule is one or more of 1,2,3,4-butanetetracarboxylic acid, methyltrans-butenedioic acid, diethylenetriaminepentaacetic acid, or pyromellitic acid.

3. The method for preparing a self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties as described in claim 1, characterized in that: In step (1), the pH value of the reaction system is adjusted using a 2.0 mol / L sodium hydroxide solution.

4. The method for preparing a self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties as described in claim 1, characterized in that: In step (2), a 0.22 μm water filter head is used for filtration.

5. The method for preparing a self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties as described in claim 1, characterized in that: In step (3), the pressure of vacuum freeze drying is 1~10 Pa, the freeze drying temperature is -30~-10℃, and the freeze drying time is 24~48 h.

6. A self-protected carbonized polymer dot with near-infrared room-temperature phosphorescent properties, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 5.

7. The application of the self-protected carbonized polymer dot with near-infrared room temperature phosphorescence properties as described in claim 6 in the field of anti-counterfeiting.

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