A dual-mode thermochromic anti-counterfeiting material and its preparation method and application

Abstract

The present invention discloses a dual-mode thermochromic anti-counterfeiting material, its preparation method, and application. The material comprises upconversion nanocrystals and lead halide perovskite quantum dots; the chemical formula of the upconversion nanocrystals is NaLnF4:Yb,Tm, where Ln is one of Y, Gd, Sc, Lu, and La; the chemical formula of the perovskite quantum dots is CsPbX3, where X is one of Br and I; the particle size of the upconversion nanocrystals is 10 to 30 nm, and the particle size of the perovskite quantum dots is 2 to 10 nm. Under the excitation of a 980 nm infrared laser, the luminescence color of the material changes with increasing temperature; under the excitation of a 365 nm ultraviolet light, the luminescence intensity decreases with increasing temperature. When used in the anti-counterfeiting field, it has dual anti-counterfeiting functions, solving the problem of the single anti-counterfeiting technology of traditional anti-counterfeiting materials. Furthermore, its anti-counterfeiting effect relies on the unique physical and chemical properties of the material, making it difficult to imitate.

Description

Technical Field

[0001] The present invention belongs to the technical field of luminescent materials, and in particular relates to a dual-mode thermochromic anti-counterfeiting material and a preparation method and application thereof. Background Art

[0002] In recent years, the growing problem of counterfeiting and substandard products has caused immeasurable economic losses to society. To protect the legitimate rights and interests of businesses and consumers, governments and businesses have developed various anti-counterfeiting technologies, such as watermarking, laser holography, barcoding, and fluorescent anti-counterfeiting technologies, to combat these increasingly common counterfeiting methods. Fluorescent anti-counterfeiting technology has garnered widespread attention due to its high efficiency, ease of implementation, low cost, and ease of large-scale production.

[0003] Rare earth ion-doped upconversion nanomaterials offer advantages such as narrow emission bands, long fluorescence lifetimes, and large Stokes shifts, making them widely used fluorescent anti-counterfeiting materials. However, the emission color of traditional upconversion materials typically changes only with the excitation power density, resulting in a limited anti-counterfeiting mode and the risk of counterfeiting.

[0004] Lead halide perovskite quantum dots (CsPbX3, X=Cl, Br, I) have the advantages of large absorption coefficient, high luminescence quantum efficiency, adjustable luminescence wavelength and covering the entire visible light band. They are also an ideal choice as fluorescent anti-counterfeiting materials. Summary of the Invention

[0005] In order to improve the singleness of the anti-counterfeiting mode of fluorescent materials, the present invention provides a dual-mode thermochromic anti-counterfeiting material, a preparation method thereof, and an application thereof in optical anti-counterfeiting.

[0006] The present invention leverages the excellent optical properties of both rare earth upconversion nanomaterials and lead halide perovskite quantum dots. The dual-mode thermochromic anti-counterfeiting material is a composite nanomaterial of rare earth upconversion nanomaterials and lead halide perovskite quantum dots. Under 980nm infrared laser excitation, energy transfer occurs between the rare earth upconversion nanomaterial and the lead halide perovskite quantum dots, resulting in dual luminescence from both the upconversion material and the perovskite quantum dots, with the luminescence color changing with increasing temperature. Under 365nm ultraviolet light excitation, the material exhibits the characteristic emission peak of the perovskite quantum dots, and the luminescence intensity decreases with increasing temperature. Therefore, the material provided by the present invention exhibits dual-mode anti-counterfeiting functionality and has practical application value in the field of anti-counterfeiting.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] On the one hand, the present invention provides a dual-mode thermochromic anti-counterfeiting material, which includes upconversion nanocrystals and lead halide perovskite quantum dots; the chemical formula of the upconversion nanocrystals is NaLnF4:Yb,Tm, wherein Ln is one of Y, Gd, Sc, Lu, and La; the chemical formula of the perovskite quantum dots is CsPbX3, wherein X is one of Br and I; the particle size of the upconversion nanocrystals is 10 to 30 nm, and the particle size of the perovskite quantum dots is 2 to 10 nm.

[0009] Another aspect of the present invention provides a method for preparing the dual-mode thermochromic anti-counterfeiting material, the method comprising the following steps:

[0010] 1) mixing a rare earth chloride, oleic acid, and 1-octadecene, introducing an inert gas, stirring at 120° C. to 150° C. for 0.5 to 1 hour, then heating to 150° C. to maintain for 0.5 to 1.5 hours to obtain a mixed solution A, and finally cooling the mixed solution A to room temperature; the total amount of the rare earth chloride is 1 mole, comprising 0.795 to 0.899 mole parts of LnCl3, 0.1 to 0.2 mole parts of YbCl3, and 0.001 to 0.005 mole parts of TmCl3, wherein Ln is Y, Gd, Sc, Lu, or La;

[0011] 2) mixing sodium hydroxide, ammonium fluoride, and methanol, adding the mixture to the mixed solution A prepared in step 1), heating to 35-55° C. and maintaining for 0.5-1 hour to remove the methanol to obtain a mixed solution B, heating the mixed solution B to 100-120° C., introducing an inert gas, and stirring for 10-30 minutes to remove water and air, then heating the mixed solution B to 280-310° C. and maintaining under an inert gas atmosphere for 1-2 hours, finally cooling the mixed solution B to room temperature and washing it by centrifugation with ethanol to obtain upconversion nanocrystals;

[0012] 3) mixing cesium carbonate, oleic acid, and 1-octadecene, introducing an inert gas, and stirring at 120° C. to 150° C. until the solution becomes clear to obtain a cesium oleate precursor solution;

[0013] 4) PbX3 and 1-octadecene are mixed, wherein X is Br or I, an inert gas is introduced, and the mixture is heated to 100-150°C and maintained for 0.5-1 hour to obtain a mixed solution C, and then the upconversion nanocrystals prepared in step 2) are added to the mixed solution C. After PbX3 is completely dissolved, the temperature is raised to 150-190°C, and the cesium oleate precursor solution prepared in step 3) is added. After reacting for 10-60 seconds, the mixture is placed in an ice water bath for cooling and centrifuged to obtain the composite nanomaterial.

[0014] In the above technical solution, further, in the step 1), the molar ratio of rare earth chloride to oleic acid is 1:(10-20); the molar ratio of rare earth chloride to 1-octadecene is 1:(20-50).

[0015] In the above technical solution, further, in the step 2), the molar ratio of sodium hydroxide to ammonium fluoride is (1-3):(2-5); the molar ratio of sodium hydroxide to methanol is 1:(200-300).

[0016] In the above technical solution, further, in the step 3), the molar ratio of cesium carbonate to oleic acid is 1:(2-4); the molar ratio of cesium carbonate to 1-octadecene is 1:(25-70).

[0017] In the above technical solution, further, in the step 4), the molar ratio of PbX3 to 1-octadecene is 1:(60-200); the molar ratio of PbX3 to cesium in the cesium oleate precursor solution is 1:(0.25-0.75).

[0018] In the above technical solution, further, in the step 4), the molar ratio of the upconversion nanocrystals to PbX3 is 1:(1-5).

[0019] In another aspect, the present invention provides a use of the dual-mode thermochromic anti-counterfeiting material in optical anti-counterfeiting.

[0020] In the above technical solution, further, the dual-mode thermochromic anti-counterfeiting material is dispersed in a mixture of toluene and polystyrene to prepare ink for outputting invisible fluorescent anti-counterfeiting patterns.

[0021] Beneficial effects of the present invention:

[0022] 1. This dual-mode thermochromic anti-counterfeiting material, when excited by 980nm infrared laser light, changes color as temperature increases; under 365nm ultraviolet light excitation, its luminescence intensity decreases with increasing temperature. This dual-mode thermochromic anti-counterfeiting material offers dual anti-counterfeiting capabilities, resolving the single-technology issue of traditional anti-counterfeiting materials. Furthermore, its effectiveness relies on the material's unique physical and chemical properties, making it difficult to imitate.

[0023] 2. The multi-mode anti-counterfeiting materials in the prior art can achieve color changes under light of different wavelengths. The present invention can not only achieve color changes under light of different wavelengths, but also achieve richer color changes under light of different wavelengths by heating with a hair dryer, and the anti-counterfeiting mode is more complex. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a transmission electron microscope photograph of the material obtained in Example 1;

[0025] Figure 2 The emission spectrum of the material prepared in Example 1 changes with temperature under 980nm excitation;

[0026] Figure 3 The emission spectrum of the material prepared in Example 1 changes with temperature under 365nm excitation;

[0027] Figure 4 For Application Example 1, luminescent photos of printed images at different temperatures are taken under irradiation of 980nm infrared laser and 365nm ultraviolet light. DETAILED DESCRIPTION

[0028] The following examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0029] Example 1

[0030] The preparation of the dual-mode thermochromic anti-counterfeiting material NaGdF4:Yb,Tm / CsPbBr3 includes the following steps:

[0031] (1) 0.798 mmol of gadolinium chloride, 0.2 mmol of ytterbium chloride, 0.002 mmol of thulium chloride, 6 mL of oleic acid, and 15 mL of 1-octadecene were mixed, introduced with inert gas, and stirred at 120°C for 1 hour. The mixture was then heated to 160°C and maintained for 1 hour to obtain a clear and transparent mixed solution A. The mixed solution A was then cooled to room temperature.

[0032] (2) 2.5 mmol of sodium hydroxide, 4 mmol of ammonium fluoride and 10 mL of methanol were mixed and added to the mixed solution A prepared in step 1), and heated to 40° C. and maintained for 0.5 hour to remove methanol to obtain a mixed solution B. The mixed solution B was heated to 100° C., introduced into an inert gas and stirred for 20 minutes to remove water and air. The solution was then heated to 290° C. and maintained under an inert gas atmosphere for 1 hour. Finally, the solution was cooled to room temperature and centrifuged and washed with ethanol to obtain upconversion nanocrystals.

[0033] (3) 0.4 g of cesium carbonate, 1.25 mL of oleic acid, and 20 mL of 1-octadecene were mixed, introduced with inert gas, and stirred at 120° C. until the solution became clear, thereby obtaining a cesium oleate precursor solution;

[0034] (4) 0.2 mmol of lead bromide was mixed with 5 mL of 1-octadecene, inert gas was introduced, and the mixture was heated to 120 ° C and maintained for 0.5 hours to obtain a mixed solution C. Then, 0.1 mmol of the upconversion nanocrystals prepared in step 2) was added to the mixed solution C. After PbBr3 was completely dissolved, the temperature was raised to 160 ° C, and 0.4 mL of the cesium oleate precursor solution prepared in step 3) was added. After reacting for 20 seconds, the mixture was placed in an ice water bath for cooling and centrifuged to obtain a dual-mode thermochromic anti-counterfeiting material NaYF4:Yb,Tm / CsPbBr3.

[0035] Figure 1 This is a transmission electron microscope photograph of the material prepared in Example 1. It can be seen that 11-13 nm perovskite nanocrystals grow on the surface of 40 nm upconversion nanocrystals.

[0036] Figure 2 This is the emission spectrum of the material under 980nm excitation as the temperature changes (30-150℃). It can be seen that at 30℃, the green light emission intensity is higher than the red light emission in its upconversion luminescence spectrum. As the temperature increases, the green light emission weakens and the red light emission strengthens.

[0037] Figure 3 This is the emission spectrum of the material under 365nm excitation as the temperature changes (30-150°C). It can be seen that at 30°C, the material exhibits green emission, and as the temperature increases, the emission intensity gradually decreases.

[0038] Application Example 1

[0039] The NaYF4:Yb,Tm / CsPbBr3 nanocomposite prepared in Example 1 is used for anti-counterfeiting. The specific operation steps are as follows: 0.1g of the nanocomposite prepared in this example, 2.5mL of toluene, and 7.5mL of polystyrene are mixed to form ink, which is added to the ink cartridge of an inkjet printer to print out the designed anti-counterfeiting pattern.

[0040] like Figure 4 As shown in the figure, under 980nm infrared laser irradiation, the printed image exhibits green → white → pink luminescence at 30℃, 60℃, 80℃, 90℃, and 210℃. Under 365nm ultraviolet light irradiation, the luminescence color appears bright green at 30℃, gradually weakens with increasing temperature, and disappears completely when the temperature exceeds 90℃.

[0041] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the scope defined in the claims. Other variations or modifications may be made based on the above description. Obvious variations or modifications derived therefrom shall remain within the scope of protection of the present invention.

Claims

1. An application of an upconversion / perovskite composite nanomaterial in optical anti-counterfeiting, characterized in that: The application uses a hair dryer to heat the material to achieve color changes under light of different wavelengths; The composite nanomaterial includes upconversion nanocrystals and lead halide perovskite quantum dots. The chemical formula of the upconversion nanocrystals is NaLnF4:Yb,Tm, where Ln is Y, Gd, Sc, Lu or La; the perovskite quantum dots are CsPbX3, where X is Br or I; the particle size of the upconversion nanocrystals is 10-30 nm, and the particle size of the perovskite quantum dots is 2-10 nm. The preparation method of the material comprises the following steps: 1) mixing a rare earth chloride, oleic acid, and 1-octadecene, introducing an inert gas, stirring at 120° C. to 150° C. for 0.5 to 1 hour, then heating to 150° C. to maintain the temperature for 0.5 to 1.5 hours to obtain a mixed solution A, and finally cooling the mixed solution A to room temperature; the total amount of the rare earth chloride is 1 mole, comprising 0.795 to 0.899 mole parts of LnCl3, 0.1 to 0.2 mole parts of YbCl3, and 0.001 to 0.005 mole parts of TmCl3, wherein Ln is Y, Gd, Sc, Lu, or La; 2) Sodium hydroxide, ammonium fluoride, and methanol are mixed and added to the mixed solution A prepared in step 1), and the mixture is heated to 35-55° C. and maintained for 0.5-1 hour to obtain a mixed solution B. The mixed solution B is heated to 100-120° C., an inert gas is introduced, and stirred for 10-30 minutes. Subsequently, the mixed solution B is heated to 280-310° C. and maintained under an inert gas atmosphere for 1-2 hours. Finally, the mixed solution B is cooled to room temperature and centrifuged and washed with ethanol to obtain upconversion nanocrystals; 3) Cesium carbonate, oleic acid, and 1-octadecene are mixed, introduced with inert gas, and stirred at 120°C to 150°C until the solution becomes clear to obtain a cesium oleate precursor solution; 4) PbX2 and 1-octadecene are mixed, wherein X is Br or I, an inert gas is introduced, and the mixture is heated to 100-150°C and maintained for 0.5-1 hour to obtain a mixed solution C, and then the upconversion nanocrystals prepared in step 2) are added to the mixed solution C. After PbX2 is completely dissolved, the temperature is raised to 150-190°C, and the cesium oleate precursor solution prepared in step 3) is added. After reacting for 10-60 seconds, the mixture is placed in an ice water bath for cooling and centrifuged to obtain the composite nanomaterial.

2. The use according to claim 1, characterized in that In the step 1), the molar ratio of rare earth chloride to oleic acid is 1:(10-20); the molar ratio of rare earth chloride to 1-octadecene is 1:(20-50).

3. The use according to claim 1, characterized in that In the step 2), the molar ratio of sodium hydroxide to ammonium fluoride is (1-3):(2-5); the molar ratio of sodium hydroxide to methanol is 1:(200-300).

4. The use according to claim 1, characterized in that In the step 3), the molar ratio of cesium carbonate to oleic acid is 1:(2-4); the molar ratio of cesium carbonate to 1-octadecene is 1:(25-70).

5. The use according to claim 2, characterized in that In the step 4), the molar ratio of PbX2 to 1-octadecene is 1:(60-200); the molar ratio of PbX2 to cesium in the cesium oleate precursor solution is 1:(0.25-0.75).

6. The use according to claim 1, characterized in that In the step 4), the molar ratio of the upconversion nanocrystals to PbX2 is 1:(1-5).

7. The use according to claim 1, characterized in that The upconversion / perovskite composite nanomaterial is dispersed in a mixed solution of toluene and polystyrene to prepare ink for outputting invisible fluorescent anti-counterfeiting patterns.

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