Multifunctional composite luminescent material capable of realizing bimodal fluorescence temperature sensing and multicolor anti-counterfeiting and preparation method thereof

Abstract

The invention belongs to the field of solid luminescent materials, and discloses a multifunctional composite luminescent material capable of realizing bimodal fluorescence temperature sensing and multicolor anti-counterfeiting and a preparation method thereof, the chemical formula of the multifunctional composite luminescent material is Ln < 3 + >: A2M3O12 / g-C3N4, the combination of Ln and A is one of the following two: (1) Ln = Er, and A = Yb; (2) Ln = Er / Yb, and A = Sc; and M is one of W or Mo. Under the excitation of 980 nm, green up-conversion luminescence of transition emission from 2H11 / 2 to 4I15 / 2 and from 4S3 / 2 to 4I15 / 2 shows a thermal enhancement phenomenon, and the composite luminescent material can be applied to ratio type temperature sensing; under 365 nm excitation, 465 nm blue down-conversion luminescence shows a thermal quenching phenomenon, and the material is suitable for fluorescence intensity type temperature sensing; in addition, by means of switching of a 980 nm excitation light source and a 365 nm excitation light source, the light emitting color can be reversibly converted between green and blue, and therefore dynamic fluorescent anti-counterfeiting is achieved.

Description

Technical Field

[0001] This invention belongs to the field of solid-state luminescent materials, and in particular relates to a multifunctional composite luminescent material that realizes fluorescence temperature sensing and multicolor anti-counterfeiting, and its preparation method. Background Technology

[0002] Rare-earth ion-doped luminescent materials have been widely used in lighting displays, biomedicine, lasers, sensing, anti-counterfeiting, and information storage due to their advantages such as high luminescence efficiency, good physicochemical stability, and strong tunability of luminescence characteristics. Among them, fluorescence temperature sensing technology based on these materials has unique advantages in real-time temperature sensing of moving objects or micro / nano-scale targets due to its characteristics such as remote monitoring, fast response speed, and resistance to electromagnetic interference, thus becoming a current research hotspot.

[0003] Currently, commonly used fluorescence temperature sensing schemes can be mainly divided into two types according to excitation method and emission mechanism. The first type is based on 980nm or 808nm near-infrared light excitation, and the fluorescence temperature is measured according to Er... 3+ Ho 3+ Tm 3+ 、Nd 3+ The relationship between the upconversion luminescence intensity ratio of plasma and temperature change is used for thermometry. For example, Runowski et al. reported the use of β-NaYF4:Yb under 980 nm excitation. 3 + Er 3+ @Er in SiO2 phosphor 3+ Ionic 2 H 11 / 2 → 4 I 15 / 2 and 4 S 3 / 2 → 4 I 15 / 2 The upconversion luminescence intensity ratio can be used to detect the temperature of chicken breast (DOI: 10.1021 / acsami.9b00445). However, due to the generally low upconversion luminescence efficiency, a strong fluorescence signal is usually obtained under laser excitation, which limits its flexible application in various practical scenarios. Furthermore, increasing the laser power to enhance the upconversion luminescence signal intensity can easily cause a laser heating effect, leading to incorrect temperature readings. The second method utilizes ultraviolet light excitation, Eu... 3+ 、Tb 3+Temperature sensing is achieved by varying the intensity, lifetime, or fluorescence intensity ratio of downconversion fluorescence peaks in plasma as a function of temperature. Since downconversion luminescence is a single-photon process, it typically exhibits a much higher luminous efficiency than upconversion luminescence. However, ultraviolet light has weak penetration in biological organisms and is prone to causing tissue damage, failing to meet the requirements of biomedical applications. To date, both of these approaches have been extensively studied and have achieved some progress. However, most developed fluorescent temperature sensing materials rely on single-wavelength excitation, limiting their flexible application in various practical scenarios. Therefore, it is necessary to develop a luminescent material capable of simultaneously utilizing near-infrared excitation for upconversion luminescence and ultraviolet excitation for downconversion luminescence for dual-modal temperature sensing. This design not only adapts to the excitation light requirements of different application environments but also provides a self-calibration mechanism between the two modes, further improving the accuracy of temperature measurement.

[0004] On the other hand, rare-earth ion-doped luminescent materials also possess unique value and advantages in the field of fluorescent anti-counterfeiting. Traditional single-emission modes are easily counterfeited due to their limited signal characteristics. Therefore, developing multi-color luminescent materials whose emission color can be flexibly controlled by external conditions such as excitation wavelength, temperature, or pressure has become crucial for preparing highly concealed and difficult-to-counterfeit anti-counterfeiting labels. For example, Zhou et al. reported that the NaYF4:Gd@NaYbF4:Tm@NaYF4 material can achieve multi-level, high-efficiency anti-counterfeiting by controlling the emission color of the material through changing the 980nm laser pulse width and using multi-wavelength excitation (DOI: 10.1002 / adma.202310524). Unfortunately, current research is mostly limited to developing single-function materials. However, with the rapid development of industries such as biotechnology, precision electronics manufacturing, and high-end logistics chains, the market demand for functionally integrated materials is increasingly urgent. Taking the vaccine cold chain as an example, it is necessary to monitor the temperature accurately in real time to ensure vaccine activity, and also to equip the materials with anti-counterfeiting labels that are difficult to counterfeit, thereby ensuring safety and efficacy. Therefore, multifunctional luminescent materials that combine precise fluorescence temperature sensing with efficient anti-counterfeiting properties have great application prospects. However, the design and development of such materials still face challenges, and related research needs to be strengthened. Summary of the Invention

[0005] The purpose of this invention is to provide a multifunctional luminescent material that can achieve dual-mode fluorescence temperature sensing under different wavelength excitation and can also be used for multicolor fluorescence anti-counterfeiting. Another purpose of this invention is to provide a method for preparing the above-mentioned material.

[0006] The multifunctional luminescent material proposed in this invention has the chemical formula Ln 3+ :A2M3O 12 / g-C3N4 (M = Mo, W), specifically Er 3+ :Yb2M3O 12 / g-C3N4 and Er 3+ / Yb 3+ :Sc2M3O 12 / g-C3N4; where, in Er 3+ :Yb2M3O 12 In / g-C3N4, Er 3+ The doping concentration is 4 mol%-6 mol%; in Er 3+ / Yb 3+ :Sc2M3O 12 In / g-C3N4, Er 3+ Doping concentration of 1 mol%-3 mol% Yb 3+ The doping concentration is 9 mol%-12 mol%.

[0007] The preparation method of the above-mentioned multifunctional luminescent material includes the following steps: (1) Take Ln(NO3)3, A(NO3)3 and ammonium molybdate or ammonium tungstate solution and mix them; add organic complex to the mixed solution at 100℃ and stir continuously; then add ammonia water to adjust the pH of the mixed solution to 7, stir to form a transparent suspension, transfer to a constant temperature environment of 90-100℃ and keep warm for 12-15h to obtain wet gel; then raise the temperature to 120-150℃ and keep warm for 18-24h to obtain dry gel; put the obtained dry gel into a crucible and keep warm at 500-600℃ to obtain amorphous precursor powder; grind the precursor powder and calcine it at 1000-1200℃ for 3-5h to obtain luminescent powder; after the obtained luminescent powder is fully ground and dispersed, mix it with anhydrous ethanol and ultrasonically disperse it for 30-60min to obtain phosphor suspension; (2) Mix and grind urea and melamine, put them in a crucible, heat to 520-550℃, keep warm for 3-4h, and cool to room temperature with the furnace to obtain g-C3N4 powder; grind and disperse the obtained g-C3N4 powder, mix it with deionized water (preferably ultrasonically dispersed for 4-6h) to form a suspension, and then mix it with gelatin solution to obtain g-C3N4 suspension; (3) Keep stirring (the phosphor suspension can be stirred for 5-10 min beforehand), add the g-C3N4 suspension obtained in step (2) to the phosphor suspension obtained in step (1), transfer the mixture obtained by stirring to a hydrothermal reactor, keep it at 160-190℃ for 18-30 h; after the reactor is cooled to room temperature at a rate of 3-5℃ / min, the obtained product is centrifuged and washed several times with anhydrous ethanol and deionized water respectively, and dried to obtain the final product.

[0008] In the above technical solution, the organic complexing agent is either glycine or citric acid.

[0009] Furthermore, the molar ratio of the amount of the organic complex added to the total amount of metal cations in the solution is (1-3):1, and the mass ratio of the luminescent powder to the volume of anhydrous ethanol is (0.04-0.06) g:10 ml.

[0010] Furthermore, in step (2), the mass ratio of urea to melamine is 3:1, the ratio of g-C3N4 to deionized water is (0.01-0.02) g:10 ml, the volume ratio of the suspension to the gelatin solution is (4-6):1, and the concentration of the gelatin solution is 70-90 mg / mL.

[0011] Furthermore, in step (3), the volume ratio of the phosphor suspension to the g-C3N4 suspension is 1:(2-4).

[0012] Compared with the prior art, the beneficial effects of the present invention are: 1. Under 980nm excitation, when the temperature is increased from room temperature to 100℃, the Ln content in the material of this invention... 3+ :A2M3O 12 The kernel emits 2 H 11 / 2 → 4 I 15 / 2 and 4 S 3 / 2 → 4 I 15 / 2 The green upconversion fluorescence intensity gradually increases, and the luminescence returns to its initial state during cooling, demonstrating good repeatability. This is because A2M3O 12 As a negative thermal expansion matrix, when the temperature rises, the matrix lattice contracts, causing the activation ions Er to... 3+ With sensitized ion Yb 3+ The reduced distance effectively promoted Er 3+ →Yb 3+ The energy transfer process increases Er 3+ The electronic layout number of the excited state of an ion and its upconversion luminescence intensity. According to Boltzmann's law, Er... 3+ ion 2 H 11 / 2 → 4 I 15 / 2 and 4 S 3 / 2 → 4 I 15 / 2 The fluorescence intensity ratio (LIR) of the transition changes with temperature to perform ratiometric temperature sensing, and its fluorescence thermal enhancement effect helps to improve the accuracy of temperature measurement at high temperatures.

[0013] The material of this invention passes through Ln 3+ :A2M3O 12The core is coated with g-C3N4, which, under 365nm excitation, emits broadband blue light with a wavelength of 465nm (g-C3N4: δ*→LP). As the temperature increases, the intensity of this emission band gradually decreases due to the increased activity of thermally activated nonradiative transitions, following the Arrhenius law. Based on the Arrhenius fitting equation, temperature sensing can be performed by observing the relationship between the g-C3N4 emission intensity and temperature. Therefore, based on Ln... 3+ :A2M3O 12 When combined with g-C3N4, this composite material can simultaneously achieve fluorescence temperature sensing under 980nm near-infrared excitation and 365nm ultraviolet excitation, effectively improving its detection accuracy and adaptability to different environments.

[0014] 2. By mixing the material of this invention with epoxy resin or silicone, multi-color anti-counterfeiting patterns can be drawn. Under 980nm excitation, the anti-counterfeiting pattern exhibits green fluorescence; when the excitation wavelength is changed to 365nm, the anti-counterfeiting pattern emits blue light. Compared with the previous single-mode emission, the flexible and adjustable emission color of this material can effectively improve the security of anti-counterfeiting, and the emission is stable and durable, demonstrating outstanding practical value.

[0015] 3. Due to A2M3O 12 The crystal structure is an open framework structure formed by the common vertex connection of octahedrons and tetrahedrons, with a large number of cavities and one-dimensional channels inside. Therefore, it easily absorbs water at room temperature and transforms into A2M3O. 12 The formation of nH₂O (n = 2-3) hydrate causes it to lose its negative thermal expansion properties and affects the luminescence efficiency of the doped rare earth ions. The material of this invention utilizes Ln... 3+ :A2M3O 12 Surface coating with hydrophobic g-C3N4 can improve Ln 3+ :A2M3O 12 The intrinsic water absorption of negative thermal expansion materials, and reduce Ln 3+ :A2M3O 12 The surface quenching centers effectively improve Ln 3+ Upconversion of luminous intensity helps improve the signal-to-noise ratio during temperature sensing and ensures clear display of anti-counterfeiting marks.

[0016] 4. This invention achieves the coating of A2M3O by g-C3N4 nanosheets with ultrasonic dispersion pretreatment combined with a hydrothermal in-situ coating process. 12 Firm coating of particles. First, ultrasonic dispersion is used to initially remove the interlayer van der Waals forces of the bulk g-C3N4 powder prepared by high-temperature thermal polymerization, providing sufficient active sites for the subsequent coating process. Further, by adding gelatin polymer, the hydroxyl and amino functional groups on its molecular chain are utilized to assist in the subsequent hydrothermal treatment process, ensuring the adhesion of Ln...3+ :A2M3O 12 Hydrogen bonds are formed between surface hydroxyl groups and surface groups of g-C3N4. Subsequently, in a hydrothermal environment at 160-190℃, the interlayer forces of g-C3N4 are further disrupted through solvent intercalation, allowing it to be fully exfoliated into small-sized nanosheets. Furthermore, the high-temperature and high-pressure reaction environment promotes the growth of Ln... 3+ :A2M3O 12 Electrostatic adsorption between g-C3N4 nanosheets and Ln was finally achieved. 3+ :A2M3O 12 Dense coating on the particle surface. Attached Figure Description

[0017] Figure 1 The bulk g-C3N4 powder prepared in Example 1 and 5 mol% Er 3+ Yb2W3O 12 X-ray diffraction pattern of / g-C3N4 composite material; Figure 2 The 5 mol% Er prepared in Example 1 3+ Yb2W3O 12 Transmission electron microscopy image of / g-C3N4 and corresponding energy dispersive spectroscopy elemental distribution map; Figure 3 The 5 mol% Er prepared in Example 1 3+ Yb2W3O 12 Thermogravimetric curve of / g-C3N4; Figure 4 a and Figure 4 b represents excitation at 980 nm, and the 5 mol% Er prepared in Example 1... 3+ Yb2W3O 12 Upconversion temperature-varying spectrum of / g-C3N4 composite material and its corresponding CIE color coordinate diagram; Figure 4 c and Figure 4 d represents the 5 mol% Er prepared in Example 1. 3+ Yb2W3O 12 / g-C3N4 of Er 3+ Upconversion fluorescence intensity ratio (LIR= 2 H 11 / 2 / 4 S 3 / 2 The graph showing the relationship between temperature and relative sensitivity, and the corresponding graph showing the change in relative sensitivity; Figure 5 a and Figure 5 b represents the excitation at 365 nm, as shown in the Er prepared in Example 1. 3+ Yb2W3O12 Downconversion temperature spectrum of / g-C3N4 composite material and its corresponding CIE chromaticity coordinates; Figure 5 c and Figure 5 d represents the 5 mol% Er prepared in Example 1. 3+ Yb2W3O 12 The graph showing the relationship between the fluorescence intensity of g-C3N4 and temperature, and the corresponding change in relative sensitivity; Figure 6 The 5 mol% Er prepared using Example 1 3+ Yb2W3O 12 Photographs showing the luminescence changes of anti-counterfeiting patterns made with / g-C3N4 under different excitation wavelengths; Figure 7 5 mol% Er was prepared for Comparative Example 1 3+ Yb2W3O 12 Thermogravimetric curve; Figure 8 a and Figure 8 b shows the upconversion emission spectrum of the materials prepared in Example 1 and Comparative Example 1 under 980 nm excitation and the downconversion emission spectrum under 365 nm excitation. Detailed Implementation

[0018] The technical solutions of the present invention will be thoroughly reviewed and described below with reference to the embodiments of the present invention, thereby further explaining the invention. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort, based on the embodiments of the present invention, are within the scope of protection of the present invention.

[0019] Example 1 Weigh out 2 ml, 38 ml, and 14.7 ml of 0.05 mol / L Er(NO3)3, Yb(NO3)3, and 0.017 mol / L ammonium tungstate aqueous solutions, respectively, and place them in a beaker. Mix and stir for 30 min. At 100 °C, while maintaining stirring, add 1.9212 g of citric acid to the mixed solution and continue stirring for 30 min. Then, add ammonia water dropwise to adjust the pH of the mixed solution to 7 and stir for another 30 min to form a transparent suspension. Place the suspension in a 90 °C oven for 15 h to obtain a wet gel, and then heat to 140 °C for 20 h to obtain a dry gel. Place the obtained dry gel in a corundum crucible and calcine at 600 °C for 2 h to obtain a black precursor powder. After grinding and dispersing, the obtained black powder is heated at 1100 °C for 4 h to obtain a white fluorescent powder. Grind and disperse the obtained powder, weigh out 0.05 g of fluorescent powder and mix it with 10 ml of anhydrous ethanol in a beaker. Stir and disperse the mixture ultrasonically for 60 minutes. min yielded 5 mol%Er 3+ Yb2W3O 12 spare.

[0020] 3g and 1g of urea and melamine were weighed separately, mixed and ground in a mortar for 10 min, then placed in a crucible and heated to 530℃ at a rate of 3℃ / min for 3.5 h. After cooling, yellow g-C3N4 powder was obtained. The powder was ground and dispersed for 30 min. 0.03g of g-C3N4 powder was weighed and mixed with 20ml of deionized water. After ultrasonic dispersion for 5 h, 20ml of g-C3N4 suspension was further mixed with 4ml of 80mg / mL gelatin solution and stirred for another 30 min to obtain g-C3N4 suspension for later use. After stirring the phosphor suspension for 10 min, while maintaining the stirring state, 24 ml of g-C3N4 suspension was slowly added, and stirring was continued at room temperature for 12 h. The mixture was then placed in a hydrothermal reactor and reacted at 180 °C for 24 h. After cooling to room temperature, the resulting product was centrifuged and washed several times with anhydrous ethanol and deionized water, and dried at 80 °C to finally obtain 5 mol% Er. 3+ :Yb2W3O 12 / g-C3N4 composite luminescent material.

[0021] Figure 1 The prepared bulk g-C3N4 powder and 5 mol% Er are shown. 3+ :Yb2W3O 12 X-ray diffraction pattern of g-C3N4 composite material. As shown in the figure, two characteristic peaks appear in the diffraction pattern of the bulk g-C3N4 powder, corresponding to the (100) and (002) crystal planes of g-C3N4, respectively, proving the successful synthesis of g-C3N4. (5mol%Er) 3+ :Yb2W3O12 Diffraction pattern of / g-C3N4 composite material and orthorhombic Yb2W3O 12 The standard diffraction peaks were basically matched, and there were no obvious diffraction peaks originating from g-C3N4, proving that the thin g-C3N4 coating layer had a significant effect on the Yb2W3O4 content. 12 The crystal structure of the core is not significantly affected. Figure 2 The transmission electron microscope images and energy dispersive spectroscopy (EDS) results demonstrate that, after hydrothermal treatment, the bulk g-C3N4 was successfully exfoliated into nanosheets and coated onto Yb2W3O. 12 The outer layer of the particle. Figure 3 The thermogravimetric curve of the sample shows that the weight change of the material is less than 1% during the temperature rise from room temperature to 673 K, indicating that the material absorbs very little water and exhibits a certain degree of hydrophobicity. Figure 4 As can be seen, under 980 nm excitation, when the temperature increases from room temperature to 373 K, the material emits Er. 3+ Ionic 2 H 11 / 2 → 4 I 15 / 2 (523nm) and 4 S 3 / 2 → 4 I 15 / 2 The green upconversion fluorescence intensity at 548 nm was increased by 2.4 and 1.5 times, respectively. Figure 4 As can be seen, temperature changes have no significant effect on the upconversion emission color of the material. Based on the Boltzmann relation, the ratio of 523nm to 548nm emission intensity can be used to determine the maximum relative sensitivity of 0.81%K. -1 Fluorescent temperature sensing ( Figure 4 c and Figure 4 d). By Figure 5 As can be seen, when the excitation wavelength is changed to 365 nm, the material emits blue light with wavelengths ranging from 400 nm to 600 nm, with the emission peak located at 465 nm. The variation of the emission peak intensity with temperature can be fitted by the Arrhenius equation, thereby realizing temperature sensing based on emission intensity, with a maximum relative sensitivity of 1.43% K. -1 After thoroughly mixing the material with silicone, an anti-counterfeiting pattern is drawn. Figure 6 It can be seen that the anti-counterfeiting mark emits green and blue light when excited at 980nm and 365nm respectively. The multi-color emission with wavelength modulation can effectively improve the anti-counterfeiting security.

[0022] Comparative Example 1 To compare the effects of g-C3N4, 5 mol% Er was prepared using the sol-gel method. 3+ Yb2W3O 12Powder. The specific preparation process conditions are the same as those for the 5 mol% Er prepared in Example 1. 3+ Yb2W3O 12 The powders are the same.

[0023] Depend on Figure 7 It can be seen that the prepared 5mol%Er 3+ Yb2W3O 12 Due to its strong water absorption, the powder exhibited significant weight loss in the K range of 313-387 K, with a loss of 8.6 wt%. Figure 3 and Figure 7 The comparison shows that coating with hydrophobic g-C3N4 can improve Er 3+ Yb2W3O 12 Its water absorption properties. (By...) Figure 8 It is evident that, under 980 nm excitation, the luminescence intensity of this powder is weaker than that of the 5 mol% Er synthesized in Example 1. 3+ Yb2W3O 12 / g-C3N4 composite material, therefore g-C3N4 coating can effectively improve the upconversion luminescence intensity of the material. When excited at 365nm, 5mol%Er 3+ Yb2W3O 12 There is no obvious luminescence. Therefore, this material cannot achieve dual-mode temperature sensing under different excitation wavelengths or multicolor fluorescent anti-counterfeiting.

[0024] Example 2 Weigh out 0.8 ml, 4.8 ml, 34.4 ml, and 14.7 ml of 0.05 mol / L Er(NO3)3, Yb(NO3)3, Sc(NO3)3, and 0.017 mol / L ammonium tungstate aqueous solutions, respectively, and place them in a beaker. Mix and stir for 30 min. At 100 °C, while maintaining stirring, add 1.729 g of citric acid to the mixed solution. Continue stirring for another 30 min. Then, add ammonia water dropwise to adjust the pH of the mixed solution to 7. After stirring for 30 minutes, a transparent suspension was formed. This suspension was then placed in a 100℃ oven and kept at that temperature for 12 hours to obtain a wet gel. The temperature was then raised to 120℃ and kept at that temperature for 24 hours to obtain a dry gel. The obtained dry gel was placed in a corundum crucible and calcined at 550℃ for 2 hours to obtain a black precursor powder. After grinding and dispersing, the resulting powder was kept at 1200℃ for 3 hours. The obtained luminescent powder was then ground and dispersed. 0.04 g of phosphor was weighed and mixed with 10 ml of anhydrous ethanol in a beaker, stirred evenly, and ultrasonically dispersed for 60 minutes to obtain 2% Er. 3+ / 12%Yb 3+ :Sc2W3O 12 Granules are ready for use; 3g and 1g of urea and melamine were weighed separately, mixed and ground in a mortar for 10 min, then placed in a crucible and placed in a pit furnace. The temperature was increased to 550℃ at 3℃ / min and kept at a constant temperature for 4 h. After cooling, yellow g-C3N4 powder was obtained. The powder was ground and dispersed for 30 min. 0.03g of g-C3N4 powder was weighed and mixed with 30ml of deionized water. After ultrasonic dispersion for 6 h, the g-C3N4 suspension was further mixed with 5ml of gelatin solution (80mg / mL) and stirred for another 30 min to obtain g-C3N4 suspension for later use. After stirring 10 ml of phosphor suspension for 5 min, 30 ml of g-C3N4 suspension was slowly added while maintaining stirring, and the mixture was stirred continuously at room temperature for 12 h. The mixture was then placed in a hydrothermal reactor and reacted at 160 °C for 30 h. After cooling to room temperature, the resulting product was centrifuged and washed several times with anhydrous ethanol and deionized water, and dried at 80 °C to finally obtain 2% Er. 3+ / 12%Yb 3+ :Sc2Mo3O 12 / g-C3N4 composite luminescent material.

[0025] Under excitation at 980 nm and 365 nm, the prepared material emitted green upconversion luminescence and blue downconversion luminescence, respectively. Under 980 nm excitation, as the temperature increased from room temperature to 373 K, Er... 3+ Ionic 2 H 11 / 2 → 4 I 15 / 2 (527nm) and 4 S 3 / 2 → 4 I 15 / 2 The green upconversion transition at 554 nm was enhanced by 2.0 and 1.1 times, respectively; when temperature sensing was performed based on the intensity ratio of 527 nm and 554 nm, its highest relative sensitivity was 0.76% K. -1 When the excitation wavelength was changed to 365 nm, the blue emission band of g-C3N4 exhibited thermal quenching with increasing temperature; when the relationship between this emission intensity and temperature was used for temperature measurement, the maximum relative sensitivity was 1.23% K. -1 The anti-counterfeiting labels made from this material emit green and blue light when excited at 980nm and 365nm respectively, thus possessing multi-color anti-counterfeiting functionality.

[0026] Example 3 Weigh 1.6 ml, 38.4 ml, and 14.8 ml of 0.05 mol / L Er(NO3)3, Yb(NO3)3, and 0.029 mol / L ammonium molybdate aqueous solutions, respectively, and place them in a beaker. Mix and stir for 30 min. While stirring at 100℃, add 0.6759 g of glycine to the mixture. Continue stirring for 30 min, then add ammonia to adjust the pH to 7. Stir for another 30 min to form a transparent suspension. Place the suspension in a 95℃ oven for 13 h to obtain a wet gel, then heat to 150℃ and hold for 18 h to obtain a dry gel. Place the dry gel in a crucible and calcine at 500℃ for 2 h to obtain a precursor powder. After grinding and dispersing, the powder is heated to 1000℃ for 5 h to obtain a white powder. Grind and disperse the powder. Weigh 0.06 g of phosphor and mix with 10 ml of anhydrous ethanol in a beaker, and ultrasonically disperse for 60 minutes. min yielded 4 mol%Er 3+ Yb2MoO 12 Granules are available for later use.

[0027] 3g and 1g of urea and melamine were weighed separately, mixed and ground in a mortar for 10 min, and then placed in a crucible. The temperature was increased to 520℃ at 3℃ / min and kept at 4h. After cooling, yellow g-C3N4 powder was obtained. The powder was ground and dispersed for 30 min. 0.06g of g-C3N4 powder was weighed and mixed with 30ml of deionized water. After ultrasonic dispersion for 5h, the g-C3N4 suspension was further mixed with 7.5ml of 80mg / mL gelatin solution and stirred for another 30 min to obtain g-C3N4 suspension for later use. After stirring 10 ml of phosphor suspension for 8 min, 30 ml of g-C3N4 suspension was slowly added while maintaining stirring, and the mixture was stirred continuously at room temperature for 12 h. The mixture was then placed in a hydrothermal reactor and reacted at 190 °C for 18 h. After cooling to room temperature, the resulting product was centrifuged and washed several times with anhydrous ethanol and deionized water, and dried at 80 °C to finally obtain 4 mol% Er. 3+ :Yb2Mo3O 12 / g-C3N4 composite luminescent material.

[0028] The obtained product was subjected to upconversion temperature-varying spectroscopy under 980 nm excitation. As the temperature increased from room temperature to 373 K, Er... 3+ Ionic 2 H 11 / 2 → 4 I 15 / 2 (524nm) and 4 S 3 / 2 → 4 I 15 / 2The green upconversion transition at 550 nm was enhanced by 3.0 and 1.6 times, respectively. When temperature sensing was performed based on the intensity ratio of 524 nm and 550 nm, the highest relative sensitivity was 0.73% K. -1 When the excitation wavelength was changed to 365 nm, the maximum relative sensitivity for temperature measurement based on the relationship between the intensity of the blue emission band of g-C3N4 and temperature was 1.31% K. -1 The anti-counterfeiting labels made from this material emit green and blue light when excited at 980nm and 365nm respectively, thus possessing multi-color anti-counterfeiting functionality.

Claims

1. A multifunctional composite luminescent material capable of realizing dual-mode fluorescent temperature sensing and multicolor anti-counterfeiting, characterized in that, The chemical formula is Ln 3+ : A2M3O 12 / g-C3N4, the material is Ln 3+ : A2M3O 12 The fluorescent particles are the core, and g-C3N4 is the outer shell layer; wherein M is one of W or Mo, and simultaneously: Ln is Er, and A is Yb; or Ln is Er and Yb, and A is Sc.

2. The composite luminescent material according to claim 1, wherein When A = Yb 3+ , Ln 3+ is Er 3+ ion, and the doping concentration is 4mol%-6mol%; when A = Sc 3+ , Ln 3+ is Er 3+ combined with Yb 3+ ion, and the doping concentration of Er 3+ is 1mol%-3mol%, and the doping concentration of Yb 3+ is 9mol%-12mol%.

3. The method of claim 1, wherein the composite light emitting material is prepared by mixing the phosphor and the light emitting material. Comprising: (1) taking Ln(NO3)3, A(NO3)3 and ammonium molybdate or ammonium tungstate solution mixed; at 100℃, the mixed solution was added to the organic complex, continuous stirring; again drop into ammonia water to adjust the pH value of the mixed solution to 7, stirring to form a transparent suspension, then transferred to 90-100℃ constant temperature environment for 12-15h to obtain wet gel; then heated to 120-150℃, 18-24h to obtain dry gel; the dry gel obtained was put into a crucible, and the amorphous precursor powder was obtained by heating at 500-600℃; the precursor powder was ground, and calcined at 1000-1200℃ for 3-5h to obtain the luminescent powder; the luminescent powder was fully ground and dispersed, mixed with anhydrous ethanol to obtain a fluorescent powder suspension; (2) urea and melamine were mixed and ground, put into a crucible, heated to 520-550℃, and kept for 3-4h, then cooled to room temperature to obtain g-C3N4 powder; the g-C3N4 powder was ground and dispersed, mixed with deionized water to form a suspension, and then mixed with a gelatin solution to obtain a g-C3N4 suspension; (3) under stirring, the g-C3N4 suspension obtained in step (2) was added to the fluorescent powder suspension obtained in step (1), and the mixed solution was transferred to a hydrothermal reaction kettle and kept at 160-190℃ for 18-30h; after the reaction kettle was cooled to room temperature at a rate of 3-5℃ / min, the product was centrifuged and washed several times with anhydrous ethanol and deionized water respectively, and dried to obtain the final product.

4. The method of claim 3, wherein the composite light emitting material is prepared by mixing the phosphor and the light emitting material. In step (1), the organic complexing agent is any one of glycine or citric acid.

5. The method of claim 3, wherein the composite light emitting material is prepared by mixing the phosphor and the light emitting material. In step (1), the molar ratio of the amount of organic complex added to the total amount of metal cations in the solution is (1-3):1, and the mass to volume ratio of the luminescent powder to anhydrous ethanol is (0.04-0.06)g:10ml.

6. The method for preparing the composite luminescent material according to claim 3, characterized in that: In step (2), the mass ratio of urea to melamine is 3:1, the ratio of g-C3N4 to deionized water is (0.01-0.02)g:10ml, and the volume ratio of the suspension to the gelatin solution is (4-6):1, and the concentration of the gelatin solution is 70-90mg / mL.

7. The method of claim 3, wherein the composite light emitting material is prepared by mixing the phosphor and the light emitting material. In step (3), the volume ratio of the fluorescent powder suspension to the g-C3N4 suspension is 1:(2-4).

8. The composite light emitting material of claim 1, wherein, Under 980 nm excitation, when the temperature is increased from room temperature to 373 K, Ln 3+ :A2M3O 12 Er in the kernel 3+ Ion emission 2 H 11 / 2 → 4 I 15 / 2 and 4 S 3 / 2 → 4 I 15 / 2 The intensity of upconversion green light continues to increase. Under 365nm excitation, the g-C3N4 coating layer emits strong blue light with a wavelength peak at 465nm, which originates from the δ*→LP transition of g-C3N4. This emission gradually weakens as the temperature increases.

9. A dual modality fluorescent temperature sensor, characterized in that, The composite luminescent material as claimed in claim 1 is used to realize bimodal fluorescence temperature sensing, specifically: under 980 nm excitation, the fluorescence intensity ratio between the Er 3+ ions 2 H 11 / 2 → 4 I 15 / 2 and 4 S 3 / 2 → 4 I 15 / 2 transitions in the composite luminescent material is used to realize ratio temperature sensing according to the change rule of the fluorescence intensity ratio with temperature; when the excitation wavelength is changed to 365 nm, fluorescence intensity type temperature sensing is realized according to the relationship between the blue light integral intensity of g-C3N4 and temperature, and the working range of the above two temperature measurement modes is 293-373 K.

10. Use of the composite luminescent material according to claim 1 in multicolor security against forgery, characterized in that, The composite luminescent material emits green light under 980nm excitation and blue light under 365nm excitation, and is used for preparing multi-color anti-counterfeiting marks for anti-counterfeiting and encryption.

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