Up-conversion luminescent material, preparation method thereof and film

Abstract

The invention relates to the technical field of up-conversion luminescent materials, in particular to an up-conversion luminescent material, a preparation method thereof and a thin film. The up-conversion luminescent material provided by the invention is prepared by the following steps: adding yttrium chloride, ytterbium chloride and erbium chloride into H2O, adding a nitrilotriacetic acid solution and a sodium fluoride solution, and adjusting pH; carrying out hydrothermal reaction; cooling, centrifugally separating, washing and drying; when the upconversion material is synthesized under the assistance of the nitrilotriacetic acid, the product obtained under an acidic condition has stronger luminous capacity, a precursor (namely, a raw material) is not easy to settle in an acidic medium, and the formed final product has better uniformity; meanwhile, the beta-NaYF4 up-conversion microcrystal is successfully synthesized by adopting a hydrothermal synthesis method, the steps are simple, the operation is simple, the cost is low, and the preparation is easy; the film provided by the invention has excellent luminescence performance, and can be used in occasions with high sensitivity, low background noise and special spectral response.

Description

Technical Field

[0001] The invention relates to the technical field of up-conversion luminescent materials, and in particular to an up-conversion luminescent material and a preparation method and a film thereof. Background Art

[0002] Upconversion luminescence refers to the phenomenon of emitting short-wavelength high-energy photons by absorbing long-wavelength low-energy photons. It is a typical nonlinear anti-Stokes luminescence phenomenon. The upconversion luminescence mechanism is mainly through the luminescence center successively absorbing two or more low-energy photons, reaching the excited state energy level after radiationless decay, and then returning from the excited state to the ground state and releasing a high-energy photon. In short, upconversion luminescence is the process of converting long-wavelength excitation light into short-wavelength emission light through a two-photon or multi-photon mechanism.

[0003] Upconversion luminescent materials are usually composed of optically active rare earth ions (activators and sensitizers) and optically inert matrix crystals. The matrix material is very important for the upconversion luminescence process. The matrix material itself does not emit light, but it can provide a suitable crystal field for the activation ions. The research focus of upconversion luminescent materials is to find matrix materials with high chemical stability, low phonon energy, good matching between the lattice and rare earth ions, and low absorption of incident light. Commonly used matrix materials are: oxides, fluorides, fluoride oxides and sulfides.

[0004] There is a close correlation between luminescence properties and structural morphology, so the preparation of upconversion luminescent materials with uniform particle size and morphology has always been the focus of attention. At present, the methods for synthesizing upconversion luminescent materials mainly include: coprecipitation method, microemulsion, sol-gel method, hydrothermal synthesis method, thermal decomposition method, etc. Among them, the hydrothermal synthesis method is widely used because of its simple operation and low cost. This method provides sufficient temperature and corresponding pressure, which is conducive to the crystallization and growth of upconversion luminescent materials. During the reaction process, the addition of appropriate capping agents can effectively regulate the particle size, morphology and crystal phase of upconversion luminescent materials. Commonly used capping agents include trisodium citrate and ethylenediaminetetraacetic acid. They have a significant effect on the morphology, crystal phase and luminescence properties of β-NaYF4 upconversion luminescent materials, and can produce microcrystalline materials with a variety of morphologies and sizes. However, its luminescence performance needs to be further improved.

[0005] In view of this, the present application aims to provide an up-conversion luminescent material and a preparation method and a film thereof to achieve better luminescent properties. Summary of the invention

[0006] In order to solve the above problems, the present invention provides an up-conversion luminescent material, a preparation method thereof and a thin film. When the up-conversion material is synthesized with the assistance of nitrilotriacetic acid, the product obtained under acidic conditions (pH 2) has a stronger luminescent ability, and the final product formed has better uniformity. At the same time, β-NaYF4 up-conversion microcrystals are successfully synthesized by a hydrothermal synthesis method. The microcrystals with large size and high crystallinity have stronger luminescent properties and can better meet application requirements.

[0007] The technical solution adopted by the present invention is:

[0008] A method for preparing an upconversion luminescent material comprises the following steps:

[0009] S1. Add yttrium chloride, ytterbium chloride and erbium chloride to H2O and stir magnetically until the solution is clear and transparent;

[0010] S2. Add nitrilotriacetic acid solution and sodium fluoride solution, and while stirring continuously, add a small amount of hydrochloric acid or sodium hydroxide solution to adjust the pH to 1.5-2.0;

[0011] S3. The mixed solution is added to a hydrothermal reactor to react;

[0012] S4. After the solution is cooled to room temperature, the product is separated by centrifugation, washed with water and ethanol respectively, and then dried in an oven to obtain upconversion microcrystals.

[0013] Furthermore, the molar ratio of nitrilotriacetic acid to lanthanide ions is 1 to 2.5:1.

[0014] Here, the molar ratio of nitrilotriacetic acid / lanthanide ions refers to the molar ratio of nitrilotriacetic acid to the sum of "yttrium chloride, ytterbium chloride, and erbium chloride".

[0015] Furthermore, in step S2, the concentration of the added nitrilotriacetic acid solution is 2.50 mM, and the concentration of the added sodium fluoride solution is 16 mM.

[0016] Furthermore, in step S2, the concentration of the added hydrochloric acid / sodium hydroxide solution is 1M.

[0017] Furthermore, in step S3, the temperature of the hydrothermal reaction is 175-185° C., and the time of the hydrothermal reaction is 19-21 h.

[0018] Furthermore, in step S4, the rotation speed of the centrifugal separation is 7500-8500 r / min.

[0019] Furthermore, in step S4, washing is performed with water and ethanol at least twice respectively.

[0020] Furthermore, in step S4, the drying temperature of the oven is set to 75-85°C.

[0021] Based on the same inventive concept, the present application also provides an up-conversion luminescent material prepared using the above-mentioned preparation method.

[0022] Based on the same inventive concept, the present application also provides a thin film made of the above-mentioned up-conversion luminescent material.

[0023] Furthermore, the specific preparation steps of the film are: adding upconversion luminescent material to H2O, heating and reflux at 90°C for 3h until the solution is clear and transparent, cooling the solution to room temperature, and drying in an oven at 60°C to obtain a transparent, flexible and transparent film of nitrilotriacetic acid-upconversion microcrystals / polyvinyl alcohol.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1. The upconversion luminescent material provided in the present application comprises the following steps: S1. adding yttrium chloride, ytterbium chloride and erbium chloride to H2O, and stirring magnetically until the solution is clear and transparent; S2. adding nitrilotriacetic acid solution and sodium fluoride solution, and adding a small amount of hydrochloric acid or sodium hydroxide solution to adjust the pH to 1.5-2.0 while stirring continuously; S3. adding the mixed solution to a hydrothermal reactor to react; S4. cooling the solution to room temperature, centrifuging the product, washing it with water and ethanol respectively, and then drying it in an oven to obtain upconversion microcrystals; when nitrilotriacetic acid is used to assist in the synthesis of upconversion microcrystals, the product obtained under acidic conditions (pH 2) has a stronger luminescence ability, and in an acidic medium, the precursor (i.e., the raw material) is not easy to precipitate, and the final product formed has better uniformity, while most of the upconversion microcrystals (UCMCs) are currently prepared at pH 3-4, at which time rare earth hydroxide precipitation has appeared in the raw material, and the purity and morphology uniformity of the final product formed are poor;

[0026] 2. The up-conversion luminescent material provided in this application uses a hydrothermal synthesis method to successfully synthesize β-NaYF4 up-conversion microcrystals, which has simple steps, simple operation, low cost and easy preparation;

[0027] 3. The film provided by the present application uses the up-conversion microcrystals with high luminescence intensity prepared by the present application, so the film prepared at a lower addition amount can still have a strong luminescence ability. The lower addition amount also ensures the transparency and concealment of the film. Therefore, the fluorescent film provided by the present application has excellent luminescence performance and can be used in occasions with high sensitivity, low background noise and special spectral response. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the preparation process in an embodiment of the present invention;

[0029] Figure 2is a SEM image in an embodiment of the present invention;

[0030] Figure 3 TEM images in an embodiment of the present invention;

[0031] Figure 4 Graph showing the fluorescence intensity of up-conversion microcrystals prepared in the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0032] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively by way of examples, and preferred embodiments of the present invention are given below. However, the present invention can be implemented in a variety of different forms and is not limited to the embodiments described herein. Any other implementation schemes obtained by modifying or equivalently replacing the technical scheme of the present invention without creative results are within the protection scope of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0034] The numerical values ​​disclosed in the embodiments of the present invention are approximate values, not definite values. When the error or experimental conditions permit, all values ​​within the error range may be included without being limited to the specific numerical values ​​disclosed in the embodiments of the present invention.

[0035] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0036] Example 1

[0037] This embodiment provides a method for preparing an upconversion luminescent material, comprising the following steps:

[0038] Add 0.80mmol yttrium chloride, 0.18mmol ytterbium chloride, and 0.02mmol erbium chloride to 5mL H2O and stir magnetically until the solution is clear and transparent;

[0039] Then, 5 mL of 2.50 mM nitrilotriacetic acid solution and 5 mL of 16 mM sodium fluoride solution were added.

[0040] While stirring continuously, adjust the pH to 2 by adding a small amount of 1 M hydrochloric acid or 1 M sodium hydroxide solution;

[0041] Then the mixed solution was added into a hydrothermal reactor lined with polytetrafluoroethylene and heated at 180 °C for 20 h;

[0042] After the solution was cooled to room temperature, the product was separated by centrifugation at 8000 r / min, washed twice with water and ethanol respectively, and dried in an oven at 80° C. to obtain upconversion microcrystals.

[0043] It should be noted that in this embodiment, the optimal embodiment is obtained by setting the molar ratio of nitrilotriacetic acid / lanthanide ions to (0 / 1, 1 / 1, 2 / 1, 2.5 / 1); setting the molar ratio of sodium fluoride / lanthanide ions to (4 / 1, 8 / 1, 12 / 1, 16 / 1, 20 / 1); and setting the pH to (2, 5, 8, 11), and testing and optimizing the conditions respectively.

[0044] Comparative Example 1

[0045] This comparative example provides a Na3Cit-upconversion microcrystal, which is prepared in the same manner as in Example 1 except that 5 mL of 2.00 mM Na3Cit solution and 5 mL of 12 mM sodium fluoride solution are added.

[0046] Comparative Example 2

[0047] This comparative example provides an EDTA-upconversion microcrystal, which is prepared in the same manner as in Example 1 except that 5 mL of 1.50 mM Na3Cit solution and 5 mL of 12 mM sodium fluoride solution are added and heated at 200°C for 24 h.

[0048] Performance Testing

[0049] The upconversion microcrystals prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to fluorescence testing. The test structure is detailed in the attached Figure 4 As shown in the figure, it can be seen that the up-conversion microcrystalline material prepared in the embodiments of the present application has a better fluorescence intensity and can better meet the application requirements.

[0050] In summary, when the up-conversion microcrystal material provided by the present application is synthesized with the aid of nitrilotriacetic acid, the product obtained under acidic conditions (pH 2) has a stronger luminescence ability. In the acidic medium, the precursor (i.e., the raw material) is not easy to precipitate, and the final product formed has better uniformity. However, most of the up-conversion microcrystals (UCMCs) are prepared at pH 3 to 4 are used for preparation. At this time, rare earth hydroxide precipitation has appeared in the raw materials, and the purity and morphology uniformity of the final product are poor; the up-conversion luminescent material is successfully synthesized into β-NaYF4 up-conversion microcrystals by hydrothermal synthesis, which has simple steps, simple operation, low cost and easy preparation; it is used to prepare thin films. Since the up-conversion microcrystals with large luminescence intensity prepared by the present application are used, the film obtained under the condition of lower addition amount can still have strong luminescence ability, and the lower addition amount can ensure the transparency and concealment of the film. Therefore, the fluorescent film provided by the present application has excellent luminescence performance, which can meet the needs of high sensitivity, low background noise and special spectral response. For example, the flexible transparent film that can emit green fluorescence in a near-infrared light environment provided by the present application is used in special fields such as customs anti-smuggling or concealed anti-counterfeiting marks.

[0051] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing an upconversion luminescent material, characterized in that: The steps include: S1. Add yttrium chloride, ytterbium chloride and erbium chloride to H2O and stir magnetically until the solution is clear and transparent; S2. Add nitrilotriacetic acid solution and sodium fluoride solution, and while stirring continuously, add a small amount of hydrochloric acid or sodium hydroxide solution to adjust the pH to 1.5-2.0; S3. The mixed solution is added to a hydrothermal reactor to react; S4. After the solution is cooled to room temperature, the product is separated by centrifugation, washed with water and ethanol respectively, and then dried in an oven to obtain upconversion microcrystals.

2. The method for preparing an upconversion luminescent material according to claim 1, characterized in that: The molar ratio of nitrilotriacetic acid to lanthanide ions is 1 to 2.5:

1.

3. The method for preparing an upconversion luminescent material according to claim 2, characterized in that: In step S2, the concentration of the added nitrilotriacetic acid solution is 2.50 mM, and the concentration of the added sodium fluoride solution is 16 mM.

4. The method for preparing an upconversion luminescent material according to claim 1, characterized in that: In step S2, the concentration of the added hydrochloric acid / sodium hydroxide solution is 1M.

5. The method for preparing an up-conversion luminescent material according to claim 1, characterized in that: In step S3, the temperature of the hydrothermal reaction is 175-185° C., and the time of the hydrothermal reaction is 19-21 h.

6. The method for preparing an up-conversion luminescent material according to claim 1, characterized in that: In step S4, the rotation speed of centrifugal separation is 7500-8500 r / min.

7. The method for preparing an up-conversion luminescent material according to claim 1, characterized in that: In step S4, washing is performed at least twice with water and ethanol respectively.

8. The method for preparing an up-conversion luminescent material according to claim 1, characterized in that: In step S4, the drying temperature of the oven is set to 75-85°C.

9. An up-conversion luminescent material prepared according to the preparation method according to any one of claims 1 to 8.

10. A thin film made of the up-conversion luminescent material according to claim 9.

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