CN115261022A - A single-particle dual-mode NIR excited upconversion fluorescence anti-counterfeiting material and its preparation method and application - Google Patents

Abstract

A single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material, a preparation method and application thereof, and the present invention relates to an up-conversion fluorescent anti-counterfeiting material, a preparation method and application thereof. It is to solve the technical problem of low security security level existing in the existing fluorescent anti-counterfeiting materials. The single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material of the present invention is NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ existing in the form of single-particle nanorods, nanometer The middle region of the rod is NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ , and the two end regions are NaYF ₄ :Yb ³⁺ /Er ³⁺ . Preparation method: firstly synthesize nuclear nanorods, then pickle and disperse, and then epitaxially grow to obtain single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting materials. Emits blue and green light and can be used in the field of anti-counterfeiting.

Description

A single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material and its preparation method and application

technical field

The invention relates to an up-conversion fluorescent anti-counterfeiting material, a preparation method and application thereof.

technical background

Counterfeit and shoddy goods are common in daily life. Banknotes, documents, valuables, etc. are often illegally forged. With the development of science and technology, counterfeiting methods are constantly being innovated, and even fake ones can be confused with real ones, which poses a serious security threat to individuals, society and the country. threaten. Therefore, there is an urgent need for safe and reliable anti-counterfeiting encryption and identification methods. It is a major issue to realize advanced encryption and anti-counterfeiting technology that is difficult to imitate.

Among many anti-counterfeiting technologies, fluorescent anti-counterfeiting is widely used because of its low cost, strong recognition ability, non-toxicity, and difficulty in imitation. The fluorescent materials currently used mainly include: organic fluorescent materials, carbon quantum dots, metal organic frameworks, up-conversion fluorescent materials, etc., among which up-conversion fluorescent materials have long fluorescence lifetime, large anti-anti-Stokes shift, narrow-band emission, and chemical stability. With the advantages of high stability, adjustable excitation and emission signals, etc., it has become the most ideal advanced anti-counterfeiting material. Monochromatic luminescent up-conversion nanomaterials have been widely used in various anti-counterfeiting fields, and their high anti-counterfeiting capabilities are sufficient for scenarios with low security requirements. However, for scenarios with higher anti-counterfeiting encryption requirements, a single luminescent up-conversion material is not enough to meet the anti-counterfeiting security requirements, because the monochromatic luminescent fluorescent material is easy to be imitated, and this conventional anti-counterfeiting technology uses a large number of This anti-counterfeiting method is very easy to crack.

Contents of the invention

The invention aims at the technical problems of low anti-counterfeiting technology, low level of security and easy imitation existing in the existing fluorescent anti-counterfeiting materials, and provides a single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material and its preparation method and application. The single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material has different luminescent conditions of the single particle under different laser excitations, and the middle part and both ends of the particle emit blue light and green light respectively. The particles can also be mixed with single-mode NIR excitation materials to obtain anti-counterfeiting patterns with strong fluorescence brightness, good stability and multiple protections, which have important application value in advanced anti-counterfeiting, encryption and other fields.

The single-particle dual-mode NIR excitation upconversion fluorescent anti-counterfeiting material of the present invention is NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ in the form of single-particle nanorods, wherein The middle region of the nanorod is NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ , the molar ratio of Y ³⁺ in NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ : Yb ³⁺ : Tm ³⁺ : Nd ³⁺ = (69~88.5): (10~25): (0.5~3): (1~3); the two ends of the nanorods are NaYF ₄ : Yb ³⁺ /Er ³⁺ , NaYF ₄ : Yb ³⁺ /Er ³⁺ in molar ratio Y ³⁺ : Yb ³⁺ : Er ³⁺ =(72-89):(10-25):(1-3).

In the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material of the present invention, under 808nm laser excitation, the NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ in the middle region can emit a single-particle blue fluorescent signal; Under excitation, NaYF ₄ :Yb ³⁺ /Er ³⁺ at both ends can emit green fluorescent signals, and NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ in the middle region can emit single-particle blue fluorescent signals.

The preparation method of the above-mentioned single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material is carried out according to the following steps:

1. Synthesis of NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ core nanorods:

Dissolve 0.4-0.6g NaOH in 1.2-1.6mL deionized water, add 5-8mL ethanol and 4-6mL oleic acid for stirring, then add 0.8-1.5mL NH ₄ F solution with a concentration of 2-3M, 1.5-3mL The concentration is 0.2-0.3M LnCl ₃ solution; wherein Y ³⁺ : Yb ³⁺ : Tm ³⁺ : Nd ³⁺ in LnCl ₃ solution in molar ratio = (69-88.5): (10-25): (0.5 ～3): (1～3); after the stirring is completed, transfer it to a 50mL reactor, and react at a temperature of 200～230°C for 12～24h; after the reaction is completed, it is naturally cooled to room temperature, centrifuged, and the supernatant is discarded. Add 10-15mL ethanol for sonication, repeat centrifugation and sonication 2-3 times to obtain NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ core nanorods; then wash NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ core nanorods are dispersed in 3-5ml cyclohexane for use;

2. Acid washing dispersion of NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ core nanorod single particles:

Transfer the NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ nuclear nanorods dispersed in cyclohexane to a centrifuge tube, add ethanol, and centrifuge at a speed of 10000-13500rpm for 5-10min; the supernatant Pour off the liquid, add 2M HCl and ethanol to the centrifuge tube, ultrasonically disperse for 10-15min, centrifuge at a speed of 10000-13500rpm for 10-15min to carry out pickling, repeat the pickling process 3 times, and obtain the separated NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ core nanorod particles, the separated NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ core nanorod particles were dispersed in deionized water to obtain NaYF ₄ :Yb ³⁺ / Aqueous dispersion of Tm ³⁺ /Nd ³⁺ core nanorod particles;

3. Synthesis of dual-mode NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ epitaxial structure single-particle nanorods:

Prepare 1.5-2mL EDTA-2Na·2H ₂ O solution with a concentration of 0.2-0.3M, 0.3-0.5mL LnCl ₃ solution with a concentration of 0.2-0.3M, 1.8-2.5mL NH ₄ F solution with a concentration of 2-3M, 3-5mL NaF solution with a concentration of 0.5-1M, mixed and stirred; wherein Y ³⁺ : Yb ³⁺ : Er ³⁺ in the LnCl ₃ solution in molar ratio =(72-89):(10-25):( 1～3);

Then add 0.5-1mL of HCl with a concentration of 2-3M, 0.5-1mL of HNO ₃ with a concentration of 15%-23% by mass, and 0.5-1mL of NaYF ₄ :Yb ³⁺ /Tm ³ with a concentration of 0.06-0.3M ⁺ /Nd ³⁺ aqueous dispersion of nuclear nanorod particles, stirred for 1h;

After the stirring is completed, pour it into the reaction kettle and react at a temperature of 200-230°C for 18-24 hours; cool to room temperature, discard the supernatant, and wash the remaining powder with ethanol centrifuge and dry to obtain a single-particle dual-mode NIR excitation Up-conversion fluorescent anti-counterfeiting material.

The application of the above-mentioned single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material is to use the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material in the field of anti-counterfeiting.

The anti-counterfeiting method of using single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material is carried out according to the following steps:

1. Use laser drilling technology to make uniform small holes on the surface of the anti-counterfeiting pattern mold; use single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting materials, or combine single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting materials with single-mode NIR excitation materials NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ is mixed and filled into the small holes of the anti-counterfeiting pattern; the single-mode NIR excitation material NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ is calculated by molar ratio Y ³⁺ : Yb ³⁺ : Tm ³⁺ : Nd ³⁺ =(69～88.5):(10～25):(0.5～3):(1～3);

2. Single-particle dual-mode NIR-excited up-conversion fluorescent anti-counterfeiting material exhibits blue fluorescence under excitation at 808nm, and green fluorescence under excitation at 980nm; use a laser confocal microscope for local magnification and observation, single-particle dual-mode NIR excitation up-conversion fluorescence The middle area of a single nanorod of the anti-counterfeiting material is blue light, and the two ends are green light; the single-mode NIR excitation material NaYF ₄ :Yb ^{3 +} /Tm ³⁺ /Nd ³⁺ shows blue fluorescence under excitation at 980nm. Using this characteristic, To achieve the purpose of anti-counterfeiting.

The invention prepares a single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material by modifying the single particle, which not only encrypts the fluorescence, but also encrypts the single-particle form and luminescent state, and improves the anti-counterfeiting to nanometer level. Using different wavelengths to excite single particles, and relying on the different light emission conditions of single particles in the microscopic state, greatly increases the difficulty of this kind of anti-counterfeiting cracking, and it is extremely difficult to be found. This unique single-particle dual-mode nanorod can realize advanced encryption of anti-counterfeiting patterns, which is extremely difficult to crack, making it impossible to gain insight into single-particle anti-counterfeiting information from a macro perspective.

Compared with prior art, advantage of the present invention is as follows:

The single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material can be excited at both 808nm and 980nm, realizes dual-mode excitation, and can emit visible light of different colors to achieve the purpose of dual-mode anti-counterfeiting.

Modify the single particle and improve its anti-counterfeiting by detecting the luminous state of the single particle. Unlike most fluorescent anti-counterfeiting, which only adjusts the luminous color, intensity, and life, the present invention can perform single-particle anti-counterfeiting detection in the microscopic state, imitation The difficulty has been greatly increased, and single-particle encryption at the nanometer level has been achieved.

It is a higher-level anti-counterfeiting encryption method to use the shape and color of the fluorescent anti-counterfeiting pattern on the macroscopic surface for simple anti-counterfeiting encryption, and then use the laser confocal microscope to observe the microscopic luminescence of single-particle nanorods.

The device used in the invention is simple, the cost of raw materials is low, the anti-counterfeit pattern can be obtained by filling the mold with the product, the operation process is convenient, the pattern filling can be customized independently and can be used for more complicated anti-counterfeit patterns.

The single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material of the invention can be used in the field of anti-counterfeiting.

Description of drawings

Fig. 1 is the transmission electron micrograph of NaYF ₄ : 20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorod particles obtained through step 2 in Example 1;

Fig. 2 is the transmission electron micrograph of the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained in Example 1;

Fig. 3 is the X-ray diffraction spectrum of NaYF ₄ : Yb ³⁺ /Tm ³⁺ /Nd ³⁺ nuclear nanorod particles before epitaxy in Example 1 and the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material obtained after epitaxy;

4 is a schematic diagram of the light emission of the single-particle nanorods of the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material prepared in Example 1 when they are partially enlarged and observed with a laser confocal microscope;

Fig. 5 is the NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorod particles before the epitaxy of embodiment 1 and the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material obtained after the epitaxy Emission spectrogram.

Fig. 6 is the display photo obtained under no laser excitation, 808nm laser excitation, and 980nm laser excitation of the Harbin Institute of Technology school emblem anti-counterfeiting pattern prepared in Example 1;

Fig. 7 is a luminescence display photo of the Harbin Institute of Technology school emblem anti-counterfeiting pattern prepared in Example 1, which is partially enlarged by a laser confocal microscope; where a is filled with NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ powder under 808nm excitation Obtained; b is obtained by filling NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ powder under 808nm excitation; c is filled with NaYF ₄ :Yb ³⁺ /Er ³⁺ Powder obtained under 980nm excitation; d is filled with NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ powder obtained under 980nm excitation; e is filled with NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ : Pattern obtained by Yb ³⁺ /Er ³⁺ powder under 980nm excitation.

Figure 8 shows the NaYF ₄ : 20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ nuclear nanorod particles obtained through step 2 in Example 2 and the single-particle dual-mode NIR excited up-conversion fluorescence anti-counterfeiting obtained through step 3 TEM photo of the material;

Figure 9 is the X-ray diffraction pattern of NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ nuclear nanorod particles before epitaxy in Example 2 and the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained after epitaxy;

Figure 10 is the NaYF ₄ : 20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ core nanorod particles before the epitaxy in Example 2 and the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained after the epitaxy emission spectrogram;

Fig. 11 is a photograph of the luminescence of the "8888" anti-counterfeiting pattern in Example 2 excited by different wavelengths.

Detailed ways

Use the following examples to verify the beneficial effects of the present invention.

Embodiment 1: The preparation method of the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material of this embodiment is carried out according to the following steps:

1. Synthesis of NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorods:

Dissolve 0.5g NaOH in 1.5mL of deionized water, add 5mL of ethanol and 5mL of oleic acid for stirring, then add 1.0mL of 2M NH ₄ F solution and 2mL of 0.2M LnCl ₃ solution, wherein the LnCl ₃ solution Ln=Y ³⁺ , Yb ³⁺ , Tm ³⁺ , Nd ³⁺ , the ^{molar doping ratio is Y 3+ :Yb 3+ :Tm 3+ :Nd 3+ ＝ 77.5 : 20} :0.5:2; at this time the solution Milky white, continue to stir for 45 minutes, after the stirring is completed, transfer to a 25mL reactor, and react at a temperature of 220°C for 12h; after the reaction is completed, it is naturally cooled to room temperature, and the supernatant is discarded after centrifugation, and 10mL of ethanol is added for ultrasonic dispersion treatment , repeating the above centrifugal washing and ultrasonic dispersion treatment twice to obtain NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorods; then the washed NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorods dispersed in 4mL cyclohexane, ready to use;

2. Acid washing dispersion of NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorod single particles:

The NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorods dispersed in 4mL cyclohexane were equally divided into 4 samples, and the sample operation of each part was as follows: transfer the sample to 1.5mL Add 500 μL of ethanol to the centrifuge tube, centrifuge at 13,500 rpm for 5 minutes, pour off the supernatant, then add 500 μL of 2M HCl and 750 μL of ethanol to the centrifuge tube, ultrasonically disperse for 15 minutes, and centrifuge at 13,500 rpm. Centrifuge for 15min for pickling, repeat the pickling process 3 times to obtain separated NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorod particles; 4 parts of separated NaYF ₄ :20 %Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorod particles were dispersed in 1 mL of deionized water to obtain ^NaYF ₄ : 20%Yb ^{3+ /0.5%Tm 3+} /2%Nd ³⁺ core Aqueous dispersion of nanorod particles; the microscopic appearance of single-particle core nanorods after pickling is shown in the transmission electron microscope photo of Figure 1, long ~ 1.4 μm, end face diameter ~ 200nm, and end face flat; Acidification treatment of rods, the surface of untreated nanorods is covered with a large amount of oleic acid, which makes the nanorods agglomerate and stick together, which is not conducive to the subsequent epitaxial growth of single particles, and cannot perform higher-level encryption. After acidification treatment, NaYF ₄ : 20% Yb ³⁺ /0.5% Tm ³⁺ /2% Nd ³⁺ core nanorod particles are not agglomerated and uniformly dispersed.

3. Synthesis of dual-mode NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ @NaYF ₄ :20%Yb ³⁺ /2%Er ³⁺ epitaxial structure single-particle nanorods:

Mix 1.875mL EDTA-2Na·2H ₂ O solution with a concentration of 0.2M, 0.35mL LnCl ₃ solution with a concentration of 2M, 2.0mL NH ₄ F solution with a concentration of 2M, and 4mL NaF solution with a concentration of 0.5M. 45min; wherein in the LnCl ₃ solution, Ln=Y ³⁺ , Yb ³⁺ , Er ³⁺ , the molar doping ratio is Y ³⁺ :Yb ³⁺ :Er ³⁺ =78:20:2;

Add 0.75 mL of 2M HCl, 0.75 mL of 15% HNO ₃ by mass, and 1 mL of 0.1 M NaYF ₄ : 20% Yb ³⁺ /0.5% Tm ³⁺ /2% Nd ³⁺ Aqueous dispersion of nuclear nanorod particles, stirred for 1 h;

After the stirring is completed, pour it into the reaction kettle, and react at a temperature of 220°C for 18 hours; cool to room temperature, discard the supernatant, and wash the white powder at the bottom of the reaction kettle with ethanol into a 50mL centrifuge tube, at a speed of 8000rpm Centrifuge for 5 minutes. After the centrifugation is completed, pour off the liquid, add 10 mL of ethanol for ultrasonic dispersion treatment, repeat the above washing process twice, and finally place the sample in an oven at 80°C for 8 hours to obtain single-particle dual-mode NIR-excited upconversion fluorescence. Anti-counterfeiting material.

The transmission electron microscope photo of the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained after the epitaxial growth in step 3 of Example 1 is shown in Figure 2. It can be seen from Figure 2 that the single particle after dispersion by pickling, After epitaxial growth, the end face of the nanorod has changed from the plane before epitaxy to an ellipsoid, but the diameter of the end face of the nanorod has not changed, indicating that the epitaxial growth has been carried out along the two ends of the nanorod. After epitaxial growth, the two ends of the nanorod grow With smooth epitaxial ends, dual-mode single-particle nanorods have been successfully prepared.

The X-rays of the NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ core nanorod particles before epitaxy and the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material obtained after the epitaxy The diffraction pattern is shown in Figure 3. It can be seen from Figure 3 that the diffraction peaks of the samples after epitaxy are in good agreement with the standard spectrum of β-NaYF ₄ , which proves that this method can control the synthesis of single-particle dual-mode nano Great.

In the single-particle dual-mode NIR excitation upconversion fluorescent anti-counterfeiting material of this embodiment 1, the material NaYF ₄ :Yb ^{3 +} /Er ³⁺ in the epitaxial part does not emit fluorescence under 808nm excitation, and emits green light under 980nm excitation, and the middle part NaYF ₄ : Yb ³⁺ /Tm ³⁺ /Nd ³⁺ emits blue light under the excitation of 808nm and 980nm, and the luminescent schematic diagram of the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material is shown in Figure 4. The emission spectra of NaYF ₄ : 20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ nuclear nanorod particles before epitaxy and the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained after epitaxy As shown in Figure 5, it can be seen from Figure 5 that after epitaxial growth, the overall luminous intensity of the material is significantly improved, and green light peaks appear around 520nm and 540nm. Under 980nm excitation, when observed locally with a laser confocal microscope, the middle region of the nanorods that make up the green pattern emits blue light, while the two ends emit green light. This unique single-particle dual-mode nanorod can realize advanced encryption of anti-counterfeiting patterns, which is extremely difficult to crack, making it impossible to gain insight into single-particle anti-counterfeiting information from a macro perspective.

Using the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material prepared in Example 1 for anti-counterfeiting, the specific steps are as follows:

One, adopt the school badge pattern mold of Harbin Institute of Technology to prepare anti-counterfeiting pattern, adopt laser drilling technology to punch out even small holes on the school badge pattern mold surface; the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material NaYF prepared by present embodiment ₁ : 20%Yb ³⁺ /0.5%Tm ³⁺ /2%Nd ³⁺ @NaYF ₄ :20%Yb ³⁺ /2%Er ³⁺ and single-mode NIR excitation material NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /2% Nd ³⁺ is mixed according to the mass ratio of 1:1, and applied to the small hole in the middle part of the school badge pattern; NaYF ₄ is excited by single-mode NIR: 20% Yb ³⁺ /2% Er ³⁺ is applied and filled to In the small hole of the peripheral pattern, a school badge with an anti-counterfeiting pattern is obtained.

2. The display photos of the anti-counterfeiting pattern of the school emblem of Harbin Institute of Technology under no excitation, 808nm excitation, and 980nm excitation are shown in Figure 6. It can be seen from Figure 6 that the anti-counterfeiting pattern of the school emblem of Harbin Institute of Technology is under the condition of no laser excitation. It does not emit light, and only the middle part shows blue fluorescence under 808nm excitation, and shows a green pattern under 980nm excitation, and the periphery is different from the middle color. At this time, the overall observation from the macroscopic angle is the same as that of ordinary fluorescent anti-counterfeiting.

The partial magnification of the anti-counterfeiting pattern in Figure 6 was observed with a laser confocal microscope, and the results are shown in Figure 7 . Figure 7a shows the NaYF ₄ : Yb ³⁺ /Tm ³⁺ /Nd ³⁺ single-particle luminescent photo under 808nm excitation, it can be seen that NaYF ₄ : Yb ³⁺ /Tm ³⁺ /Nd ³⁺ nanorods only emits blue light, b of Figure 7 shows the NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ single-particle luminescence photo under 808nm excitation, and it can be seen that the nanometer The rods also only emit blue light, which is consistent with the luminescence before epitaxy. Figure 7 c, d, and e show NaYF ₄ : Yb ³⁺ /Er ³⁺ monochromatic luminescent nanorods, NaYF ₄ : Yb ³ under 980nm excitation ⁺ /Tm ³⁺ /Nd ³⁺ single-color luminescent nanorods and NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ dual-color luminescent nanorods. Among them, NaYF ₄ :Yb ³⁺ /Er ³⁺ nanorods only emit green light, NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ nanorods only emit blue light, NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ nanorods emit blue light in the middle and green light in both ends. The materials involved in the anti-counterfeiting pattern of the school badge and their luminescence are listed in Table 1 below.

Table 1 The materials involved in the anti-counterfeiting pattern of the school emblem and their luminescence

Using different wavelengths to excite single particles and relying on the different luminescence conditions of single particles in the microscopic state will greatly increase the difficulty of this kind of anti-counterfeiting cracking, and it is extremely difficult to be found. Moreover, only a small hole can be filled with dual-mode NIR material, so that only a small part of the entire pattern can find the unique luminescence of dual-mode NIR single particles under microscopic observation, which greatly increases the difficulty of imitation. The luminescence of dual-mode single-particle materials is different from that of single-mode materials. The single particle of dual-mode materials emits blue light in the middle and green light at both ends, which is specific under microscopic observation, while the particles of single-mode materials only emit one kind of light, which can be used This adds another dimension by making it anti-counterfeit and encrypted. The single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material in Example 1 can realize multi-level anti-counterfeiting and protect information security.

Embodiment 2: The preparation method of the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material of this embodiment is carried out according to the following steps:

1. Synthesis of NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ core nanorods:

Weigh 0.5g NaOH into a beaker, add 1.5mL deionized water, place on a magnetic stirrer and stir to partially dissolve NaOH, add 5mL ethanol solution, stir until NaOH is completely dissolved, add 5mL oleic acid (OA), and stir for 45min;

Then add 1mL of 2M NH ₄ F and 2mL of 0.2M LnCl ₃ solution. At this time, the solution is milky white, and continue to stir for 45min; in the LnCl ₃ solution, Ln=Y ³⁺ , Yb ³⁺ , Tm ³⁺ , Nd ³⁺ , the molar doping ratio is Y ³⁺ :Yb ³⁺ :Tm ³⁺ :Nd ³⁺ ＝78.5:20:0.5:1;

Transfer the solution to a 25mL reactor and react at 220°C for 12h; after the reaction, take out the reactor and let it cool to room temperature naturally in the air, discard the supernatant, and wash the white powder at the bottom of the reactor with ethanol into a 50mL centrifuge tube , centrifuged at 8000rpm for 5min, after the centrifugation was completed, poured off the supernatant, added 10mL ethanol for ultrasonic dispersion treatment, repeated the above washing and ultrasonic dispersion process twice to obtain NaYF ₄ :Yb ³⁺ /Tm ³⁺ / Nd ³⁺ core nanorods; then disperse the washed NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ core nanorods in 4mL cyclohexane for use;

2. Acid washing dispersion of NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ core nanorod single particles:

Divide the NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ sample dispersed in 4mL cyclohexane into 4 parts, transfer it to a 1.5mL centrifuge tube, add 500μL ethanol, and Centrifuge at 13500rpm for 5min; pour off the solution, add 500μL of 2M HCl and 750μL of ethanol to the centrifuge tube, ultrasonically disperse for 15min, centrifuge at 13500rpm for 15min, repeat the above acid washing process 3 times, and finally disperse the sample in 1mL Deionized water was used for later use to obtain NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ aqueous dispersion. The particle morphology after dispersion is shown in Figure 8a.

3. Synthesis of dual-mode NaYF ₄ :20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ @NaYF ₄ :20%Yb ³⁺ /2%Er ³⁺ epitaxial structure single-particle nanorods:

Take 1.875mL of 0.2M EDTA-2Na·2H ₂ O in a 50mL beaker, add 0.35mL of 0.2M LnCl ₃ solution, 2mL of 2M NH ₄ F solution, 4mL of 0.5M NaF solution , stirred for 45min; wherein in the LnCl ₃ solution, Ln=Y ³⁺ , Yb ³⁺ , Er ³⁺ ; the molar doping ratio is Y ³⁺ :Yb ³⁺ :Er ³⁺ =78:20:2;

Add 0.75mL HCl with a concentration of 2M, 0.75mL HNO ₃ with a concentration of 15% by mass, and 1 mL of NaYF ₄ with a concentration of 0.1M: 20%Yb ³⁺ /0.5%Tm ³⁺ /1%Nd ³⁺ Water dispersion, stirred for 1h;

Then pour the mixture into a 25mL reactor and react at 220°C for 18h; after the reaction, take out the reactor and let it cool to room temperature naturally in the air, discard the supernatant, and wash the white powder at the bottom of the reactor with ethanol into a 50mL centrifuge tube , and centrifuged at 8000rpm for 5min. After the centrifugation was completed, the liquid was poured out, and 10mL of ethanol was added for ultrasonic dispersion treatment. The above washing process was repeated twice. Finally, the sample was dried in an oven at 80°C for 8h to obtain a single particle double Modular NIR excited up-conversion fluorescent anti-counterfeiting material.

The scanning electron microscope photo of the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained in Example 2 is shown in Figure 8 b. Comparing Figure 8 a and b, it can be seen that after epitaxy, smooth growth is formed on both ends of the end face. extension part.

The X-ray diffraction patterns of NaYF ₄ : Yb ³⁺ /Tm ³⁺ /Nd ³⁺ nuclear nanorod particles before epitaxy and the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained after epitaxy in Example 2 are shown in Figure 9 It can be seen that the diffraction peaks of the sample after epitaxy are in good agreement with the standard spectrum of β-NaYF ₄ , which proves that this method can control the synthesis of single-particle dual-mode nanorods with hexagonal crystal phase structure.

The emission spectra of NaYF ₄ : Yb ³⁺ /Tm ³⁺ /Nd ³⁺ nuclear nanorod particles before epitaxy in Example 2 and the single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained after epitaxy are shown in Figure 10. It can be seen from Figure 10 that after epitaxial growth, the overall luminous intensity of the material is still significantly improved, and a strong green light peak still appears.

The single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material obtained in Example 2 is used for anti-counterfeiting, and the specific steps are as follows:

1. Use the "8888" pattern mold to prepare the anti-counterfeiting pattern, and use the laser drilling technology to punch even small holes on the surface of the "8888" pattern mold; use the middle two numbers "8" and the fourth "8" as a whole The dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material obtained in Example 2 (NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ ) and the single-mode NIR excited up-conversion fluorescent anti-counterfeiting material Materials (NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ ) are mixed at a mass ratio of 1:1 and then spread to fill the small holes; other parts of the mold are filled with NaYF ₄ :Yb ³⁺ /Er ³⁺ . Excited with different wavelengths, the results are shown in Figure 11;

2. "8888" pattern, under the condition of no laser excitation, the pattern does not emit light;

"8888" pattern under 808nm laser excitation, NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ and NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ^{3 +} The material glows blue, and the pattern shows the middle two "8" parts and the fourth "8" in full view.

"8888" pattern under 980nm laser excitation, NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ and NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ The material emits blue light, the NaYF ₄ :Yb ³⁺ /Er ³⁺ material emits green light, the pattern is completely displayed, and the middle two "8" parts and the fourth "8" emit blue light as a whole, and the rest emit green light.

The present invention proposes a brand-new single-particle dual-mode up-conversion multi-color fluorescence anti-counterfeiting encryption technology for the first time. In a one-dimensional nanorod, epitaxial layers with different luminous colors are grown radially, so that multiple regions of a single nanorod Presenting different signal colors makes it impossible to identify anti-counterfeiting patterns by conventional light sources. This technology raises the level of anti-counterfeiting security to the nanometer scale. Anti-counterfeiting code words can only be identified by identifying individual particles and patterns composed of individual particles. Therefore, this encryption technology is extremely difficult to crack, which promotes the further upgrade of anti-counterfeiting technology, and can improve the security and reliability of up-conversion luminescent materials in the field of advanced anti-counterfeiting.

Claims (4)

1. A single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material is characterized in that the fluorescent anti-counterfeiting material is NaYF existing in a single-particle nano rod form ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ Wherein the middle region of the nanorod is NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ ，NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ In terms of mole ratio of Y ³⁺ ：Yb ³⁺ ：Tm ³⁺ ：Nd ³⁺ = (69 to 88.5): (10-25): (0.5 to 3): (1-3); the two end regions of the nano rod are NaYF ₄ :Yb ³⁺ /Er ³⁺ ，NaYF ₄ :Yb ³⁺ /Er ³⁺ In terms of mole ratio of Y ³⁺ ：Yb ³⁺ ：Er ³⁺ ＝(72～89)：(10～25)：(1～3)。

2. The preparation method of the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material as claimed in claim 1, which is characterized by comprising the following steps:

1. NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ And (3) synthesis of the nuclear nanorod:

dissolving 0.4-0.6 g NaOH in 1.2-1.6 mL deionized water, adding 5-8 mL ethanol and 4-6 mL oleic acid, stirring, and then adding 0.8-1.5 mL NH with the concentration of 2-3M ₄ Solution F, 1.5-3 mL LnCl with concentration of 0.2-0.3M ₃ A solution; wherein LnCl ₃ Molar ratio of Y in solution ³⁺ ：Yb ³⁺ ：Tm ³⁺ ：Nd ³⁺ = (69 to 88.5): (10-25): (0.5 to 3): (1-3); after stirring, transferring the mixture into a 50mL reaction kettle, and reacting at the temperature of 200-230 ℃ for 12-24 h; naturally cooling to room temperature after the reaction is finished, centrifugally separating, removing supernatant, adding 10-15 mL of ethanol for ultrasonic treatment, and repeating the centrifugal treatment and the ultrasonic treatment for 2-3 times to obtain NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ A core nanorod; then the washed NaYF is washed ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Dispersing the nuclear nano rod in 3-5 ml of cyclohexane for later use;

2. NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Acid washing and dispersing single particles of the nuclear nanorods:

NaYF dispersed in cyclohexane ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Transferring the nuclear nanorods into a centrifuge tube, adding ethanol, and centrifuging for 5-10 min under the condition that the rotating speed is 10000-13500 rpm; pouring out supernatant, adding 2M HCl and ethanol into a centrifuge tube, ultrasonically dispersing for 10-15 min, centrifuging at 10000-13500 rpm for 10-15 min to perform acid washing, and repeating the acid washing process for 3 times to obtain separated NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Nuclear nanorod particles of isolated NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Dispersing the nuclear nano rod particles in deionized water to obtain NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ An aqueous dispersion of core nanorod particles;

3. dual-mode NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ @NaYF ₄ :Yb ³⁺ /Er ³⁺ Synthesizing the epitaxial structure single-particle nanorod:

1.5-2 mL of EDTA-2 Na2Hl with the concentration of 0.2-0.3M ₂ O solution, 0.3-0.5 mL LnCl with concentration of 0.2-0.3M ₃ 1.8 to 2.5mL of NH with the concentration of 2 to 3M ₄ Mixing and stirring the solution F and 3-5 mL of NaF solution with the concentration of 0.5-1M; wherein LnCl ₃ Molar ratio of Y in solution ³⁺ ：Yb ³⁺ ：Er ³⁺ ＝(72～89)：(10～25)：(1～3)；

Then adding 0.5-1 mL of 2-3M HCl and 0.5-1 mL of 15-23 mass percent HNO ₃ And 0.5-1 mL of NaYF with the concentration of 0.06-0.3M ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Stirring the aqueous dispersion of the nuclear nanorod particles for 1h;

pouring the mixture into a reaction kettle after stirring, and reacting for 18-24 hours at the temperature of 200-230 ℃; and cooling to room temperature, removing supernatant, centrifugally washing the residual powder with ethanol, and drying to obtain the single-particle dual-mode NIR-excited up-conversion fluorescent anti-counterfeiting material.

3. The application of the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material as claimed in claim 1, wherein the application is that the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material is applied to the anti-counterfeiting field.

4. The application of the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material as claimed in claim 3, wherein the anti-counterfeiting method by using the single-particle dual-mode NIR excitation up-conversion fluorescent anti-counterfeiting material is carried out according to the following steps:

1. drilling uniform small holes on the surface of the anti-counterfeiting pattern die by adopting a laser drilling technology; single-particle dual-mode NIR excitation upconversion fluorescent anti-counterfeiting material, or single-particle dual-mode NIR excitation upconversion fluorescent anti-counterfeiting material and single-mode NIR excitation material NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Mixing and filling the mixture into the small holes of the anti-counterfeiting pattern; wherein the single-mode NIR excited material NaYF ₄ :Yb ³⁺ /Tm ^{3 +} /Nd ³⁺ In terms of mole ratio of Y ³⁺ ：Yb ³⁺ ：Tm ³⁺ ：Nd ³⁺ ＝(69～88.5)：(10～25)：(0.5～3)：(1～3)；

2. The single-particle dual-mode NIR excited up-conversion fluorescent anti-counterfeiting material shows blue fluorescence under the excitation of 808nm and shows green fluorescence under the excitation of 980 nm; local magnification observation is carried out by using a laser confocal microscope, the middle area of a single nanorod of the single-particle dual-mode NIR excited upconversion fluorescence anti-counterfeiting material is blue light, and the two ends of the single nanorod are green light; while single-mode NIR excited material NaYF ₄ :Yb ³⁺ /Tm ³⁺ /Nd ³⁺ Blue fluorescence is displayed under the excitation of 980nm, and the anti-counterfeiting purpose is achieved by utilizing the characteristic.

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