CN114891506A - Multi-modal down-conversion nanocrystalline based on energy transfer regulation and control as well as preparation method and application thereof - Google Patents

Abstract

A multi-modal down-conversion nanocrystalline based on energy transfer regulation and control, a preparation method and application thereof relate to a multi-modal down-conversion core-shell nanocrystalline, a preparation method and application thereof. The method aims to solve the problems of harsh requirements and low anti-counterfeiting level of the existing rare earth doped down-conversion nanocrystalline excitation light source. The down-conversion nanocrystalline of the invention is beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ The nanocrystalline is taken as the core and Ce is taken ³⁺ And Mn ²⁺ Doped NaGdF ₄ The core-shell structure nanocrystal is an outer layer; and X is Eu, Tb or Sm. The preparation method comprises the following steps: firstly preparing a nanocrystalline inner core, and then coating NaGd on the outer surface of the core _0.75 F ₄ :Ce _0.25 ³⁺ Form coreShell nanocrystals; introducing Mn into the shell ²⁺ To obtain the nano-crystal. The nanocrystalline is formed into a film on a substrate, after laser excitation, anti-counterfeiting is realized through the emission wave bands and the luminous colors of different activator particles and the fluorescent color change characteristics expressed along with time after excitation is closed, and the nanocrystalline is used for the anti-counterfeiting field.

Description

Multi-modal down-conversion nanocrystalline based on energy transfer regulation and control as well as preparation method and application thereof

Technical Field

The invention relates to a multimode down-conversion core-shell nanocrystal and a preparation method and application thereof.

Background

With the rapid development of economic society, people gradually realize the importance of information authenticity and safety storage, the demand for developing novel anti-counterfeiting materials and anti-counterfeiting technologies is more urgent, and in order to solve the problem of anti-counterfeiting safety at present, a series of multi-color luminous down-conversion nano materials are prepared and developed, and the application of the down-conversion materials in optical anti-counterfeiting is further expanded by designing corresponding core-shell structures and realizing expected energy transfer. The preparation and performance of the rare earth doped nano material are attracted wide attention in recent years, wherein the rare earth doped NaGdF ₄ The nano material has low phonon energy, high luminous efficiency and stable physicochemical properties, and has wide application potential in the field of optical display. Current rare earth doped NaGdF ₄ The research on materials mainly focuses on the multifunctional design of non-radiative energy transfer, but the design faces the bottlenecks of too short energy transfer distance between ions, existence of reverse energy transfer and the like. Therefore, the method has very important significance for solving the problem of the limitation of the current energy transmission path by constructing a core-shell structure and changing the doping elements.

Gd(4f ⁷ ) The elements are due to having half-full 4f ⁿ The number of configuration electrons, the energy state of stable electrons, especially the excited state energy level thereof are very high (>3×10 ⁴ cm ^-1 ) And thus is often used as a host material for rare earth luminescence. The matrix material of Gd is Gd ₂ O ₃ 、KGdF ₄ 、GdF ₃ 、NaGdF ₄ 、BaGdF ₅ And so on. Due to NaGdF ₄ The crystals have low phonon energy and stable optical properties, making them one of the ideal down-conversion matrix materials. Gd (Gd) ³⁺ Lowest excited state of ion ⁶ P _7/2 To the ground state ⁸ S _7/2 The difference in energy level between them is about 32258cm ^-1 Far greater than the commonly used activator (Er) ³⁺ 、Ho ³⁺ 、Tb ³⁺ Etc.) has a very small effect on the luminescence of the activator. In Yb ³⁺ /Er ³⁺ Systems are exemplified in which Sm is incorporated ³⁺ 、Nd ³⁺ Severe energy quenching of the ion occurs but incorporation of Gd ³⁺ This situation can be effectively avoided. On the other hand in NaGdF ₄ In the crystal, Gd can be utilized ³⁺ The energy transfer of the ions transfers the excitation energy to the excitant. This "bridging" effect of energy transfer can be combined with zone-division doping to minimize excitation energy loss, and this effect can be used to realize various lanthanide-series active activators (including Eu) even at extremely low activator concentrations ³⁺ 、Tb ³⁺ 、Sm ³⁺ ) To adjustable down-conversion transmission. Up to now, NaGdF ₄ Fluorescent materials for substrates have been widely used for anti-counterfeiting purposes.

Yuan et al published in Advanced materials 32 of 2020, entitled "rare earth Doped Dual-Mode luminescent Core-Shell Nanoparticles based on Energy regulation and application thereof in Advanced Anti-Counterfeiting (Energy management in Lanthanide-Doped Core-Shell Nanoparticles for Tunable Dual-Mode Luminescence-coupling security) prepares NaGdF ₄ :Yb ³⁺ /Ho ³⁺ /Ce ³⁺ @NaYF ₄ :X ³⁺ (X is Eu, Tb, Sm, Dy) nanocrystals using Gd ³⁺ -mediated interfacial energy transfer and Ce ³⁺ -efficient up-and down-conversion of different mode luminescence by assisted cross-relaxation and by adding Ce ³⁺ The concentration realizes that the up-conversion luminescence color can be adjusted from green light to red light; NaGdF ₄ :Yb ³⁺ /Ho ³⁺ /Ce ³⁺ @NaYF ₄ :X ³⁺ X of the core-shell nano structure under the excitation of 254nm ultraviolet light and 980nm laser ³⁺ (X＝Eu、TbSm and Dy) can simultaneously observe high-efficiency and multi-color adjustable dual-mode emission, and finally the material is applied to 2D coding to realize encryption. However, the anti-counterfeiting of the research needs to be realized by matching up and down conversion, and more activator particles are involved in the preparation process, so that the mutual influence is generated, and the luminescence is weak. On the other hand, the anti-counterfeiting mode is limited, and the 980nm laser can be obtained only in a laboratory and cannot meet the light source requirement of multi-mode display in practical application.

The existing materials are limited by single-mode anti-counterfeiting, the selectivity of the materials to an excitation light source is high, and the fluorescent anti-counterfeiting materials cannot meet the anti-counterfeiting requirements of higher level, more modes and wider popularization.

Disclosure of Invention

The invention aims to solve the problems of harsh requirements on an excitation light source and low anti-counterfeiting level caused by narrow-band absorption of the existing rare earth doped down-conversion nanocrystalline, and provides the multi-mode down-conversion nanocrystalline based on energy transfer regulation and control and the preparation method thereof.

The multimode down-conversion nanocrystalline based on energy transfer regulation is beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ The nanocrystalline is taken as the core and Ce is taken ³⁺ And Mn ²⁺ Doped NaGdF ₄ The core-shell structure nanocrystal is an outer layer; wherein X is Eu, Tb or Sm.

The preparation method of the multi-modal down-conversion nanocrystalline based on energy transfer regulation comprises the following steps:

firstly, preparing beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ A nanocrystalline core; wherein X is Eu, Tb or Sm;

di, in beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ The nanocrystalline is coated with NaGd _0.75 F ₄ ：Ce _0.25 ³⁺ Forming core-shell nanocrystals;

thirdly, by ion exchange method, in beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ ：Ce _0.25 ³⁺ Is introduced into the shell of ²⁺ To obtain an energy baseAnd transmitting the regulated multi-modal down-conversion nanocrystalline.

Further, the beta-NaGd described in step one _0.60 F ₄ :X _0.40 ³⁺ The method for preparing the nanocrystalline inner core comprises the following steps:

(1) firstly, according to beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ Weighing gadolinium chloride hexahydrate (GdCl) according to stoichiometric ratio ₃ ·6H ₂ O)、NaOH、NH ₄ Chlorides of F and X; wherein the total amount of rare earth ions is 1mmol, and X is Eu, Tb or Sm;

(2) NaOH and NH ₄ F is added into methanol to be dissolved to obtain NaOH and NH ₄ A methanol solution of F; wherein NH ₄ The mass ratio of the F to the volume of the methanol is 1g (60-70) mL;

(3) adding chloride of gadolinium chloride hexahydrate and X into a reactor with a condensing device, adding oleic acid and octadecylene, introducing argon as reaction protective gas, heating to 140-160 ℃, stirring at constant temperature for 30-60 min, dissolving metal chloride in a solvent, and removing water in the solution; cooling to 50-55 ℃, and adding NaOH and NH ₄ Stirring the methanol solution of F for 30-40 min at 50-55 ℃ for nucleation; after nucleation is finished, heating to 100-105 ℃ and keeping to remove methanol, after the methanol is removed, heating to 295-300 ℃ and keeping to react for 1-1.5 h to finish epitaxial growth; after the reaction is finished, the heating device is closed, stirred and cooled to room temperature to obtain a mixed solution;

(4) transferring the mixed solution into a centrifuge tube, adding absolute ethyl alcohol for centrifugal separation, and then adding cyclohexane for ultrasonic washing treatment; the operations of anhydrous ethanol centrifugal separation and cyclohexane ultrasonic washing are repeated for 2 to 3 times to obtain the beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ Nanocrystalline, beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ The nanocrystals were dispersed in cyclohexane for storage.

Furthermore, the ratio of the amount of the chloride hexahydrate in the step one (3) to the volume of the oleic acid is 1mol (3-4) mL;

furthermore, the ratio of the amount of the chloride hexahydrate to the volume of the octadecene in the step one (3) is 1mol (16-17) mL;

further, in step two, the beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ The nanocrystalline is coated with NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The method for forming the core-shell nanocrystal comprises the following steps:

(1) according to NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Weighing gadolinium chloride hexahydrate (GdCl) according to stoichiometric ratio ₃ ^. 6H ₂ O), cerium chloride hexahydrate (CeCl) ₃ ^. 6H ₂ O), NaOH and NH ₄ F; measuring beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ A cyclohexane solution of nanocrystals; wherein gadolinium chloride hexahydrate and beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ beta-NaGd in nanocrystalline cyclohexane solutions _0.60 F ₄ :X _0.40 ³⁺ The molar ratio of (1) to (1.4-1.6);

(2) NaOH and NH ₄ F is added into methanol to be dissolved to obtain NaOH and NH ₄ A methanol solution of F; wherein NH ₄ The mass ratio of the F to the volume of the methanol is 1g (60-70) mL;

(3) gadolinium chloride hexahydrate and cerium chloride hexahydrate (CeCl) ₃ ^. 6H ₂ O) and beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ Adding a cyclohexane solution of the nanocrystalline into a reactor with a condensing device, adding oleic acid and octadecylene, introducing argon as reaction protective gas, heating to 155-160 ℃, stirring at a constant temperature for 30-60 min, and removing water and cyclohexane in the solution; cooling to 50-55 ℃, and adding NaOH and NH ₄ Stirring the methanol solution of F at the constant temperature of 50-55 ℃ for 30-40 min to form new crystal nuclei; after nucleation is finished, heating to 90-100 ℃ and keeping to remove methanol, after the methanol is removed, heating to 295-300 ℃ and keeping reacting for 1h to finish epitaxial growth; after the reaction is finished, the heating device is closed, stirred and cooled to room temperature to obtain a mixed solution;

(4) transferring the mixed solution to a centrifuge tube, and adding excessive anhydrous ethanolCarrying out centrifugal separation on alcohol, and then adding cyclohexane for ultrasonic washing treatment; the operations of anhydrous ethanol centrifugal separation and cyclohexane ultrasonic washing are repeated for 2 to 3 times to obtain the beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Core-shell structure nanocrystalline, and dispersing it in cyclohexane for storage.

Further, the compound described in step three is beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Outer layer of (2) is doped with Mn ²⁺ The method comprises the following steps:

(1) beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Dispersing core-shell structure nanocrystal in cyclohexane, and adding into Nitroso (NOBF) tetrafluoroborate ₄ ) Then oscillating for half an hour at constant temperature at 37 ℃ until the solution is layered, taking the lower layer solution, and putting the lower layer solution into a centrifugal separator to separate out solid phase substances, thus obtaining hydrated nano-crystals;

(2) dissolving the solid phase substance in a mixed solution of toluene and cyclohexane, washing to remove DMF, and then carrying out centrifugal separation to obtain nano particles; the volume ratio of the toluene to the cyclohexane in the mixed solution of the toluene and the cyclohexane is 1: 1;

(3) addition of nanoparticles to MnCl ₂ And ultrasonically mixing the solution, then heating to 60-100 ℃, keeping the temperature for 10-40 min for exchange, cooling, adding ethanol for washing, and then carrying out centrifugal separation to obtain the multi-modal down-conversion nanocrystalline based on energy transfer regulation. Energy transfer regulation-based beta-NaGd available for multi-modal down-conversion nanocrystals _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ /Mn ²⁺ And (4) showing.

Further, in step three (1), β -NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Ratio of core-shell structure nanocrystal to nitroso-tetrafluoroborate1mol of: (10-15) mL.

The application of the multi-modal down-conversion nanocrystalline based on energy transfer regulation is to apply the multi-modal down-conversion nanocrystalline based on energy transfer regulation to anti-counterfeiting detection.

The method for applying the multimode down-conversion nanocrystalline to the anti-counterfeiting based on the energy transfer regulation comprises the following steps:

(1) coating cyclohexane dispersion liquid of multi-modal down-conversion nanocrystalline based on energy transfer regulation on a substrate film, and drying to obtain an anti-counterfeiting film;

(2) exciting the anti-counterfeiting film by 254nm laser to obtain an emission spectrum of the anti-counterfeiting film;

(3) the deep anti-counterfeiting is realized by reflecting the emission wave bands and the light-emitting colors of different activator particles through an emission spectrum spectrogram and showing the change characteristic of the fluorescence color along with the time lapse after the excitation is closed. The key of the material in anti-counterfeiting is to apply the change of the life modality to anti-counterfeiting, so that the anti-counterfeiting safety is greatly improved.

The multi-modal down-conversion nanocrystalline based on energy transfer regulation has structural advantages, and firstly selects beta-NaGd _0.60 F ₄ :Eu _0.40 ³⁺ The inner core and the outer shell are made of chemically inert NaGdF ₄ The substrate protective layer spatially isolates the surface quenching center from the internal active luminescent ions, thereby better protecting Eu ³⁺ Higher down-converted fluorescence intensity is achieved and fluorescence emission intensity is increased by preventing energy transfer to surface quenching centers.

The multi-modal down-conversion nanocrystalline based on energy transfer regulation and control also has the advantages in principle, namely, firstly, the multi-modal down-conversion nanocrystalline is prepared by Ce ³⁺ Has built up Ce ³⁺ →Gd ³⁺ → activator ion X ³⁺ (X ═ Eu, Tb, Sm) energy transfer process using Ce ³⁺ A wide range of excitation wave band corresponding to 4f-5d transition to indirectly realize Eu ³⁺ The emission of the activator ion makes up the inherent narrow-band absorption defect of the activator ion and expands the pumping wave band of the activator ion. And by changing the kind of activator ion (Eu) ³⁺ 、Tb ³⁺ 、Sm ^{3 +} ) The method realizes the multiband regulation and control of down-conversion fluorescence, realizes the regulation and control of luminous color, and lays a solid foundation for anti-counterfeiting application.

The invention discloses application of multi-modal down-conversion nanocrystalline based on energy transfer regulation in the field of anti-counterfeiting, and the key is to use long-life ions Mn ²⁺ By hydration and ion exchange, Mn is realized in the shell ²⁺ Doping of Mn ²⁺ By the addition of the luminescent ion Mn ²⁺ And the life difference of the activator ions realizes that the color of the single particle is changed in the time dimension in the excitation state and after the excitation is closed, and the application of the change of the life mode to the anti-counterfeiting is the key of the application of the material to the anti-counterfeiting.

The invention designs the energy transfer process of the material by combining the energy level of the converted ions under the rare earth, thereby realizing the expansion of the excitation wave band, the regulation and control of the emission wave band and the color change of the service life dimension, so that when the multi-mode nanocrystalline is applied to anti-counterfeiting, the multi-mode nanocrystalline can have higher-level encryption, and the limitation of starting anti-counterfeiting only from the emission wave band, namely photoluminescence color at present is broken through. The invention provides a simple and feasible method for expanding the application of the down-conversion nano particles in anti-counterfeiting.

The invention uses beta-NaGdF ₄ As a down-conversion substrate material, a core-shell down-conversion nano material with a unique energy transfer way is controllably synthesized by adopting a thermal cracking method, so that the expansion of an excitation light source is realized, the multicolor adjustability is realized by changing the species and the concentration of doped rare earth ions, and the color adjustability of the material is realized in a time dimension by doping elements with long service life. The anti-counterfeiting method can be used for anti-counterfeiting under different scenes, and can greatly improve the anti-counterfeiting safety. Can be used in the anti-counterfeiting field.

Drawings

FIG. 1 is NaGd obtained in the first step of example 1 _0.60 F ₄ :Eu _0.40 ³⁺ A transmission electron microscope photograph of the nanocrystalline core;

FIG. 2 is a graph showing the core-shell ratio obtained in step two of example 1 as 1: 1.5 NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ A transmission electron microscope photograph of the core-shell structure nanocrystal;

FIG. 3 shows NaGd obtained in step three of example 1 _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ A transmission electron microscope photograph of the core-shell structure nanocrystal;

FIG. 4 is NaGd in example 1 _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ X-ray diffraction spectrograms of different samples in the preparation stage of the nanocrystalline;

FIG. 5 shows NaGd in example 1 _0.60 F ₄ :Eu _0.40 ³⁺ An emission spectrum of a nuclear nanocrystal sample under 395nm laser excitation;

FIG. 6 shows NaGd in example 1 _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ An emission spectrum of a nuclear nanocrystal sample under 254nm laser excitation;

FIG. 7 shows NaGd prepared according to step two in example 1 _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ NaGd prepared in example 2 _0.80 F ₄ :Tb _0.20 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ And NaGd prepared in example 3 _0.90 F ₄ :Sm _0.10 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ And a photograph of the emission color in the cuvette used.

FIG. 8 shows NaGd prepared according to step two in example 1 _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ NaGd prepared in example 2 _0.80 F ₄ :Tb _0.20 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ And NaGd prepared in example 3 _0.90 F ₄ :Sm _0.10 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Schematic energy transfer under 254nm uv excitation.

FIG. 9 shows Mn doping in example 1 ²⁺ NaGd of (A) _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ The emission spectrum of the sample under the excitation of 254nm laser;

FIG. 10 shows NaGd in example 1 _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ The sample is excited by 254nm laser, Eu is at 615nm ³⁺ And Mn at 531nm ²⁺ A fluorescence attenuation spectrum;

FIG. 11 shows NaGd in example 1 _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ Time resolved spectroscopy after the end of the 254nm excitation.

Detailed Description

The technical solutions of the present invention are described in detail below with reference to the drawings and examples, but the present invention is not limited to the scope of the examples.

Example 1: the preparation method of the multi-modal down-conversion nanocrystal based on energy transfer regulation and control comprises the following steps:

firstly, preparing beta-NaGd _0.60 F ₄ :Eu _0.40 ³⁺ The specific method of the nanocrystalline core is as follows:

(1) firstly, according to beta-NaGd _0.60 F ₄ :Eu _0.40 ³⁺ Weighing 0.6mmol gadolinium chloride hexahydrate (GdCl) ₃ ^. 6H ₂ O)、0.1g NaOH、0.148g NH ₄ F and 0.4mmol of europium chloride hexahydrate (EuCl) ₃ ^. 6H ₂ O)；

(2) NaOH and NH ₄ Adding F into 10mL of methanol for ultrasonic treatment for 20min to obtain NaOH and NH ₄ A methanol solution of F;

(3) gadolinium chloride hexahydrate and europium chloride hexahydrate are added into a three-neck flask with a condensing device, 4mL of Oleic Acid (OA) and 17mL of Octadecene (ODE) are added, and argon is introduced to serve as a reaction holderProtecting gas, heating to 155 ℃, stirring at constant temperature for 30min to dissolve the metal chloride in the solvent and removing water in the solution; cooling to 55 ℃, adding NaOH and NH ₄ Stirring the methanol solution of F at 55 ℃ for 30min to nucleate; after nucleation is finished, heating to 100 ℃, blowing argon gas into the mixed solution for 30min under the argon gas atmosphere to fully remove methanol in the reaction system, heating to 295 ℃ after methanol is removed, keeping reaction for 1h, and finishing epitaxial growth; after the reaction is finished, the heating device is closed, stirred and cooled to room temperature to obtain a mixed solution;

(4) transferring the mixed solution into a centrifuge tube, adding 40mL of absolute ethyl alcohol, performing centrifugal separation at the rotating speed of 8000rpm, and then adding 40mL of cyclohexane for ultrasonic washing treatment; the operations of anhydrous ethanol centrifugal separation and cyclohexane ultrasonic washing are repeated for 2 times to obtain the beta-NaGdF ₄ :Eu ³⁺ Nanocrystals, i.e. beta-NaGdF ₄ :Eu ³⁺ Dispersing the inner core in 10mL of cyclohexane to obtain beta-NaGdF ₄ :Eu ³⁺ A cyclohexane dispersion of nanocrystals;

di, in beta-NaGd _0.60 F ₄ :Eu _0.40 ³⁺ The surface of the nanocrystal is coated with NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The method for forming the core-shell nanocrystal comprises the following steps:

(1) according to NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Weighing 0.5625mmol of gadolinium chloride hexahydrate (GdCl) ₃ ·6H ₂ O), 0.1875mmol of cerium chloride hexahydrate (CeCl) ₃ ·6H ₂ O), 0.075g NaOH and 0.111g NH ₄ F; then, the sample containing 0.5mmol of beta-NaGd _0.60 F ₄ :Eu _0.40 ³⁺ beta-NaGd of (4) _0.60 F ₄ :Eu _0.40 ³⁺ A cyclohexane dispersion;

(2) NaOH and NH ₄ Adding F into 10mL of methanol for ultrasonic treatment for 10min to obtain NaOH and NH ₄ A methanol solution of F;

(3) gadolinium chloride hexahydrate and cerium chloride hexahydrate (CeCl) ₃ ^. 6H ₂ O) and beta-NaGd _0.60 F ₄ :Eu _0.40 ³⁺ CyclohexaneAdding the dispersion into a three-neck flask with a condensing device, adding 4mL of Oleic Acid (OA) and 17mL of Octadecene (ODE), introducing argon as a reaction protective gas, heating to 155 ℃, stirring at a constant temperature for 30min, and removing water and cyclohexane in the solution; cooling to 55 ℃, adding NaOH and NH ₄ Stirring the methanol solution of F at 55 ℃ for 30min to nucleate; after nucleation is finished, heating to 100 ℃ and keeping, blowing argon into the mixed solution for 30min under the argon atmosphere to fully remove methanol in the reaction system, heating to 295 ℃ after methanol is removed, keeping reaction for 1h, and finishing epitaxial growth; after the reaction is finished, the heating device is closed, stirred and naturally cooled to room temperature to obtain a mixed solution;

(4) transferring the mixed solution into a centrifuge tube, adding 40mL of absolute ethyl alcohol, performing centrifugal separation at the rotating speed of 8000rpm, and then adding 40mL of cyclohexane for ultrasonic washing treatment; the operations of anhydrous ethanol centrifugal separation and cyclohexane ultrasonic washing are repeated for 2 times to obtain NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Nanocrystal dispersed in 10mL cyclohexane to obtain NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ A cyclohexane dispersion of nanocrystals;

thirdly, by ion exchange method, in beta-NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Mn is introduced into the shell layer of the nano crystal ²⁺ The method comprises the following specific steps:

(1) 10mL of NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The cyclohexane dispersion of the nanocrystals was added to 10mL of Nitrosotetrafluoroborate (NOBF) ₄ ) Mixing in 0.01M DMF solution, and hydrating to remove the oleic acid end capping of the nanocrystal and change it into water phase, which is favorable to Mn ²⁺ Is put in a constant temperature oscillation box and oscillated for 2 hours at the temperature of 30 ℃ tillLayering the solution;

(2) adding 6mL of toluene and 6mL of cyclohexane into the layered mixed solution, continuing to oscillate for 1h, then putting the mixed solution into a centrifuge, and centrifuging for 10min at 11000rpm, wherein the process aims to wash off DMF solution attached to the nanocrystal, placing the obtained nanocrystal in a 100mL volumetric flask, and using deionized water to perform constant volume for later use;

(3) taking 10mL of nano particle aqueous solution with the concentration of 0.05mmol/mL and 10mL of MnCl with the concentration of 15 mu mol/mL ₂ .4H ₂ Mixing and ultrasonically treating the O solution for 30min, adding the O solution into a three-necked bottle, heating to 90 ℃, continuously stirring for 30min, then cooling, respectively filling the solution in the three-necked bottle into two 50mL centrifuge tubes, respectively adding 20mL ethanol, oppositely placing the centrifuge tubes filled with the liquid into a centrifugal machine, centrifuging at 11000rpm for 10min to obtain a shell layer doped with Mn ²⁺ Core-shell nanocrystals of (1) with NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ The nanocrystalline is a multi-modal down-conversion nanocrystalline based on energy transfer regulation.

NaGd obtained in step one of example 1 _0.60 F ₄ :Eu _0.40 ³⁺ The transmission electron microscope photograph of the nanocrystal core is shown in figure 1, and NaGd obtained in the second step _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The TEM micrograph of the core-shell nanocrystal is shown in FIG. 2, and the NaGd obtained in step three _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ A transmission electron micrograph of the core-shell structured nanocrystals is shown in FIG. 3. As can be seen from FIGS. 1 to 3, NaGd synthesized in example 1 _0.75 F ₄ :Eu _0.25 ³⁺ Nanocrystalline core, NaGd _0.75 F ₄ :Eu _0.25 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Core-shell structured nanocrystals and NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ The core-shell structure nanocrystals are uniform hexagonal nanoparticles, NaGd _0.75 F ₄ :Eu _0.25 ³⁺ The average particle diameter of the nanocrystalline inner core is 10.5nm, and NaGd _0.75 F ₄ :Eu _0.25 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The average grain diameter of the core-shell structure nanocrystal is increased to 14nm, and NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ The average particle size of the core-shell structure nanocrystal is also 14 nm.

NaGd obtained in step one of example 1 _0.60 F ₄ :Eu _0.40 ³⁺ Nanocrystalline inner core and NaGd obtained in the second step _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The X-ray diffraction spectrum of the core-shell structure nanocrystal is shown in FIG. 4, and from FIG. 4, NaGd _0.60 F ₄ :Eu _0.40 ³⁺ Nanocrystalline, NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Core-shell structure nanocrystal and NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ The XRD spectrogram of the core-shell structure nanocrystalline sample is matched with the standard spectrogram, and the ion Ce is doped ³⁺ The original crystal structure of the sample is not changed.

NaGd obtained in step one of example 1 under 395nm excitation _0.60 F ₄ :Eu _0.40 ³⁺ The emission spectrum of the nanocrystal is shown in FIG. 5, and NaGd obtained in step two of example 1 is excited at 254nm _0.60 F ₄ :Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The emission spectrum of the core-shell structure nanocrystal is shown in FIG. 6, and 5 and 6 show that Ce is introduced ³⁺ Realizes the luminescence of the nanocrystalline under the illumination of 254nm and finally realizes the Eu ³⁺ The widening of the excitation band increases the application possibility.

Practice ofExample 2: in this example, europium chloride hexahydrate (EuCl) from step one of example 1 was added ₃ ^. 6H ₂ O) was replaced by terbium chloride hexahydrate (TbCl) ₃ ^. 6H ₂ O), other parameters in step one were the same as in example 1, to prepare NaGd _0.80 F ₄ :Tb _0.20 ³⁺ A nanocrystalline core; the shell was prepared using the same parameters as in step two of example 1 to obtain NaGd _0.80 F ₄ :Tb _0.20 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Core-shell nanocrystals.

Example 3: in this example, europium chloride hexahydrate (EuCl) from step one of example 1 was added ₃ ^. 6H ₂ O) is replaced by samarium chloride hexahydrate (SmCl) ₃ ^. 6H ₂ O), other parameters in step one were the same as in example 1, to prepare NaGd _0.90 F ₄ :Sm _0.10 ³⁺ A nanocrystalline core; the shell was prepared using the same parameters as in step two of example 1 to obtain NaGd _0.90 F ₄ :Sm _0.10 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Core-shell nanocrystals.

Example 1 NaGd prepared via step two _0.60 F ₄ ：Eu _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ NaGd prepared in example 2 _0.80 F ₄ :Tb _0.20 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ And NaGd prepared in example 3 _0.90 F ₄ :Sm _0.10 ³⁺ @NaGd _0.75 F ₄ ：Ce _0.25 ³⁺ The spectrum of (a) is shown in FIG. 7. From the spectrum of FIG. 7, it can be seen that by doping with Ce ³⁺ Can be expanded to include Eu ³⁺ A series of down-conversion rare earth ion excitation wave band expansion. Ce is given by analyzing the energy level relation of the down-conversion ions of the rare earth ³⁺ →Gd ³⁺ →X ³⁺ The energy transfer between energy levels is schematically illustrated in fig. 8.

Example 1 Long-lived ions Mn ²⁺ Of (2)Hetero, by hydration and ion exchange, in NaGd _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ Mn is realized in a shell layer ²⁺ Doping of Mn ²⁺ By the addition of the luminescent ion Mn ²⁺ And Eu ³⁺ The life difference of the material realizes that the color of a single particle is changed in the time dimension in the excitation state and after the excitation is closed, and the application of the change of the life mode to the anti-counterfeiting is the key of the application of the material to the anti-counterfeiting.

Mn is shown in FIG. 4 ²⁺ The original crystal structure of the sample is not changed by introducing the ions. As can be seen from FIG. 9, Mn ²⁺ Doping of (2) finally realizes Mn ²⁺ The emission at 531nm emits fluorescent signals with multiple wave bands under the excitation of 254nm laser, the emission wavelengths of the fluorescent signals are respectively located at 531nm, 595nm, 615nm and 695nm, and the nanocrystal obtained in the embodiment 3 has a multi-mode light emitting function.

10mL of the down-conversion anti-counterfeiting nanocrystalline NaGd prepared in the embodiment 1 and having the multi-modal luminescent function _0.60 F ₄ ：Eu _0.40 ³⁺ @NaGdF ₄ ：Ce ³⁺ /Mn ²⁺ Adding the cyclohexane dispersion liquid into a clean four-way cuvette; irradiating the nanocrystalline by using an excitation light source of 254nm to obtain an emission spectrum; then measuring Eu at 531nm and 615nm respectively ³⁺ And Mn ²⁺ The fluorescence lifetime of (a); fitting the fluorescence attenuation curves at 531nm and 615nm respectively to obtain Eu ³⁺ And Mn ²⁺ The fluorescence lifetime of (2) was analyzed by comparison, and the analysis results are shown in FIG. 10. From the comparison, it is found that Eu ³⁺ And Mn ²⁺ FIG. 11 shows the relationship between the lifetime of NaGd after cessation of excitation at 254nm _0.60 F ₄ :Eu _0.40 ³⁺ @NaGdF ₄ :Ce ³⁺ /Mn ²⁺ Time-resolved spectroscopy, and analysis shows that Eu in the nanocrystal is 20ms later after the laser is turned off in the time dimension ³⁺ The luminous intensity approaches zero, and Mn is present ²⁺ And has a certain luminous intensity, so that when the exciting light is switched off in a very short time, the change from red to green exists, the service life mode of the nanocrystal is realized, and thus, the multimode effect is realizedThe state nanocrystalline is successfully prepared and verified.

The invention combines the energy level of the converted ions under the rare earth to design the energy transfer process, thereby realizing the expansion of the excitation wave band, the regulation and control of the emission wave band and the color change of the service life dimension, and leading the multimode nanocrystal to have higher-level encryption when being applied to anti-counterfeiting.

Claims (10)

1. The multimode down-conversion nanocrystalline based on energy transfer regulation is characterized in that the down-conversion nanocrystalline is beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ The nanocrystalline is taken as the core and Ce is taken ³⁺ And Mn ²⁺ Doped NaGdF ₄ The core-shell structure nanocrystal is an outer layer; wherein X is Eu, Tb or Sm.

2. The method for preparing the multi-modal down-conversion nanocrystal based on energy transfer modulation as claimed in claim 1 is characterized in that the method is carried out according to the following steps:

firstly, preparing beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ A nanocrystalline core; wherein X is Eu, Tb or Sm;

di, in beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ The nanocrystalline is coated with NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Forming core-shell nanocrystals;

thirdly, by ion exchange method, in beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ ：Ce _0.25 ³⁺ Is introduced into the shell of ²⁺ And obtaining the multi-modal down-conversion nanocrystalline based on energy transfer regulation.

3. The method for preparing the multi-modal down-conversion nanocrystal based on energy transfer regulation and control as claimed in claim 2, wherein the β -NaGd is used as the first step _0.60 F ₄ :X _0.40 ³⁺ The method for preparing the nanocrystalline inner core comprises the following steps:

(1) firstly, according to beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ Weighing gadolinium chloride hexahydrate, NaOH and NH according to the stoichiometric ratio ₄ Chlorides of F and X; wherein the total amount of rare earth ions is 1mmol, and X is Eu, Tb or Sm;

(2) NaOH and NH ₄ F is added into methanol to be dissolved to obtain NaOH and NH ₄ A methanol solution of F; wherein NH ₄ The ratio of the mass of F to the volume of methanol was 1g: (60-70) mL;

(3) adding chloride of gadolinium chloride hexahydrate and X into a reactor with a condensing device, adding oleic acid and octadecylene, introducing argon as reaction protective gas, heating to 140-160 ℃, stirring at constant temperature for 30-60 min, dissolving metal chloride in a solvent, and removing water in the solution; cooling to 50-55 ℃, and adding NaOH and NH ₄ Stirring the methanol solution of F for 30-40 min at 50-55 ℃ for nucleation; after nucleation is finished, heating to 100-105 ℃ and keeping to remove methanol, after the methanol is removed, heating to 295-300 ℃ and keeping to react for 1-1.5 h to finish epitaxial growth; after the reaction is finished, the heating device is closed, stirred and cooled to room temperature to obtain a mixed solution;

(4) transferring the mixed solution into a centrifuge tube, adding absolute ethyl alcohol for centrifugal separation, and then adding cyclohexane for ultrasonic washing treatment; the operations of anhydrous ethanol centrifugal separation and cyclohexane ultrasonic washing are repeated for 2 to 3 times to obtain the beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ Nanocrystalline, beta-NaGd obtained _0.60 F ₄ :X _0.40 ³⁺ The nanocrystals were dispersed in cyclohexane for storage.

4. The method for preparing multi-modal down-conversion nanocrystals based on the energy transfer modulation as claimed in claim 3, wherein the ratio of the amount of the substance of chloride hexahydrate to the volume of oleic acid in step (3) is 1mol: (3-4) mL.

5. The method for preparing multi-modal down-conversion nanocrystals based on the energy transfer modulation as claimed in claim 3 or 4, characterized in that the ratio of the amount of the substance of chloride hexahydrate to the volume of octadecene in step (3) is 1mol: (16-17) mL.

6. The method for preparing the multi-modal down-conversion nanocrystal based on energy transfer regulation and control as claimed in claim 2, wherein the step two is performed by using beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ NaGd is coated outside the nanocrystal _0.75 F ₄ :Ce _0.25 ³⁺ The method for forming the core-shell nanocrystal comprises the following steps:

(1) according to NaGd _0.75 F ₄ ：Ce _0.25 ³⁺ Weighing gadolinium chloride hexahydrate (GdCl) according to stoichiometric ratio ₃ ·6H ₂ O), cerium chloride hexahydrate (CeCl) ₃ ^. 6H ₂ O), NaOH and NH ₄ F; measuring beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ A cyclohexane solution of nanocrystals; wherein gadolinium chloride hexahydrate and beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ beta-NaGd in nanocrystalline cyclohexane solutions _0.60 F ₄ :X _0.40 ³⁺ In a molar ratio of 1: 1.5;

(2) NaOH and NH ₄ F is added into methanol to be dissolved to obtain NaOH and NH ₄ A methanol solution of F; wherein NH ₄ The ratio of the mass of F to the volume of methanol was 1g: (60-70) mL;

(3) gadolinium chloride hexahydrate, cerium chloride hexahydrate and beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ Adding a cyclohexane solution of the nanocrystalline into a reactor with a condensing device, adding oleic acid and octadecylene, introducing argon as reaction protective gas, heating to 155-160 ℃, stirring at a constant temperature for 30-60 min, and removing water and cyclohexane in the solution; cooling to 50-55 ℃, and then adding NaOH and NH ₄ Stirring the methanol solution of F at the constant temperature of 50-55 ℃ for 30-40 min to form new crystal nuclei; after nucleation is finished, heating to 90-100 ℃ and keeping to remove methanol, after the methanol is removed, heating to 295-300 ℃ and keeping reacting for 1h to finish epitaxial growth; after the reaction is finished, the heating device is closed, stirred and cooled to room temperature to obtain a mixed solution;

(4) will be mixed withTransferring the mixed solution into a centrifugal tube, adding absolute ethyl alcohol for centrifugal separation, and then adding cyclohexane for ultrasonic washing treatment; the operations of anhydrous ethanol centrifugal separation and cyclohexane ultrasonic washing are repeated for 2 to 3 times to obtain the beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Core-shell structure of nanocrystalline prepared from beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The core-shell structure nanocrystals are dispersed in cyclohexane for storage.

7. The method for preparing the multi-modal down-conversion nanocrystal based on energy transfer regulation and control as claimed in claim 2, characterized in that the step three is performed by beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Outer layer of (2) is doped with Mn ²⁺ The method comprises the following steps:

(1) beta-NaGd _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ Dispersing core-shell structure nanocrystal in cyclohexane, and adding into Nitroso (NOBF) tetrafluoroborate ₄ ) Then oscillating for half an hour at constant temperature at 37 ℃ until the solution is layered, taking the lower layer solution, and putting the lower layer solution into a centrifugal separator to separate out solid phase substances, thus obtaining hydrated nano-crystals;

(2) dissolving the solid phase substance in a mixed solution of toluene and cyclohexane, washing to remove DMF, and then carrying out centrifugal separation to obtain nano particles; the volume ratio of the toluene to the cyclohexane in the mixed solution of the toluene and the cyclohexane is 1: 1;

(3) addition of nanoparticles to MnCl ₂ And ultrasonically mixing the solution, then heating to 60-100 ℃, keeping the temperature for 10-40 min for exchange, cooling, adding ethanol for washing, and then carrying out centrifugal separation to obtain the multi-modal down-conversion nanocrystalline based on energy transfer regulation.

8. The energy-based of claim 7The preparation method of the transfer-regulated multi-mode down-conversion nanocrystal is characterized in that the beta-NaGd in the step (1) _0.60 F ₄ :X _0.40 ³⁺ @NaGd _0.75 F ₄ :Ce _0.25 ³⁺ The ratio of the core-shell structure nanocrystal to the nitroso-tetrafluoroborate is 1mol: (10-15) mL.

9. The application of the multi-modal down-conversion nanocrystal based on energy transfer regulation and control as claimed in claim 1, characterized in that the application is to apply the multi-modal down-conversion nanocrystal based on energy transfer regulation and control in anti-counterfeiting detection.

10. The application of the multi-modal down-conversion nanocrystal based on energy transfer regulation and control as claimed in claim 9, wherein the method for applying the multi-modal down-conversion nanocrystal based on energy transfer regulation and control to anti-counterfeiting is as follows:

(1) coating cyclohexane dispersion liquid of multi-modal down-conversion nanocrystalline based on energy transfer regulation on a substrate film, and drying to obtain an anti-counterfeiting film;

(2) exciting the anti-counterfeiting film by 254nm laser to obtain an emission spectrum of the anti-counterfeiting film;

(3) the anti-counterfeiting is realized by reflecting the emission wave bands and the light-emitting colors of different activator particles through an emission spectrum spectrogram and by showing the change characteristic of the fluorescence color along with the time lapse after the excitation is closed.

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