High-temperature-resistant organic fluorescent powder and preparation method thereof

Abstract

The invention discloses high-temperature-resistant organic fluorescent powder and a preparation method thereof. The organic fluorescent powder comprises a fluorescent seed and a silicon dioxide aerogel layer, wherein the fluorescent seed is formed by coating a Sm < 0.4 > Yb < 0.2 > Er < 0.4 > (HTTA) < 3 > Phen fluorescent material with polymethyl methacrylate and has an up-down light conversion function, and the surface of the fluorescent seed is coated with the silicon dioxide aerogel layer. During preparation, the organic fluorescent seeds are firstly prepared, then the fluorescent seeds are introduced during preparation of the silicon dioxide aerogel, and finally the high-temperature-resistant organic fluorescent powder with the core-shell structure is synthesized. According to the high-temperature-resistant light conversion powder, the vertical light conversion effect can be achieved; meanwhile, through comprehensive coating of the PMMA and the silicon dioxide aerogel, the high-temperature resistance and the optical performance of the light conversion powder are improved, the optical loss is reduced, the mechanical performance is improved, and the light conversion powder can adapt to preparation modes of downstream products such as high-temperature extrusion.

Description

Technical Field

[0001] The present invention belongs to the field of high-temperature resistant fluorescent materials and their preparation methods, and particularly relates to a high-temperature resistant organic fluorescent powder and its preparation method. Background Art

[0002] Light conversion materials are a type of functional materials that can convert ultraviolet light or near-infrared light in sunlight into blue light, green light, and red light that can be utilized by plant photosynthesis. These materials have important applications in fields such as agriculture and solar cells.

[0003] Light conversion materials are divided into two categories: inorganic materials and organic materials; in the actual industrialization process, inorganic light conversion materials have strong temperature resistance and aging resistance, but poor compatibility with various systems, and are likely to cause a decline in the optical properties of the final product when combined with other systems. Moreover, most importantly, the fluorescence converted by inorganic materials is weak and the efficiency is not high. To achieve the required fluorescence intensity, it is often necessary to add an excessive amount of inorganic materials, resulting in a high cost. Organic light conversion materials have high luminous intensity, low addition amount, and good compatibility with various organic solvents and resins. However, organic light conversion materials have poor high-temperature resistance and weak aging resistance. In actual use, after high-temperature treatment, the organic light conversion materials have been damaged, and the fluorescence of the final product has almost disappeared.

[0004] In the prior art, most of the light conversion agents used have a single light conversion effect and can only achieve single down-conversion or up-conversion. For example, in the patent publication text with the patent application number 2018107000301, it is mentioned that by using europium ions as the luminescent body, triphenylphosphine oxide (TPPO) and 2-thiophenecarbonyltrifluoroacetone (TTA) as organic ligands, and using calcium carbonate as the matrix, a europium complex composite fluorescent material is prepared under set conditions. This method can only obtain a single down-conversion fluorescent material. Moreover, the composite fluorescent material of rare earth ion organic ligands and inorganic substances is not tightly bonded. Although inorganic substances have good high-temperature resistance, due to the poor bonding effect between the composite fluorescent material of rare earth ion organic ligands and inorganic substances, rare earth ion organic ligands will fall off from the inorganic substances during the high-temperature preparation process, and some rare earth ion organic ligands will be damaged at high temperatures.

[0005] Furthermore, through organic and inorganic material coating, although the high-temperature resistance can be improved to a certain extent, coating one or more layer structures will significantly reduce the luminous intensity of the fluorescent material. In this case, when applied to the subsequent preparation process, most of the fluorescent composite materials have lost their fluorescence effect.

[0006] Therefore, there is a need to research a light conversion powder that can achieve high-temperature resistance and both up-conversion and down-conversion, and does not affect the fluorescence intensity of the light conversion powder itself. Summary of the Invention

[0007] Objective of the Invention: The technical problem to be solved by the present invention is to provide an organic phosphor with a core-shell structure, which can not only achieve up-conversion and down-conversion of light, but also has high temperature resistance, and can effectively avoid the problem of luminescence loss caused by the formation of the core-shell structure.

[0008] Technical Solution: The high temperature resistant organic phosphor of the present invention comprises a phosphor seed formed by polymethyl methacrylate coating the Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material, and a silica aerogel layer coated on the surface of the phosphor seed.

[0009] The Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material of the present invention is obtained by simultaneously doping Yb 3+ , Er 3+ and Sm 3+ ions on the HTTA and phen ligands to obtain a light conversion powder capable of up-conversion and down-conversion of light. The preparation process and light conversion mechanism are as follows:

[0010]

[0011] I. Down-conversion process

[0012] 1. Absorbing excitation light: When the Sm(TTA)3Phen phosphor is excited by light of a specific wavelength, for example, in the ultraviolet or blue light region, the ligands HTTA (2-thenoyltrifluoroacetone) and phen (1,10-phenanthroline) in its molecules will absorb the energy of photons.

[0013] 2. Energy transfer: The absorbed energy will be transferred to the central Sm³⁺ ions. Due to the good antenna effect of HTTA and phen, the absorbed energy can be effectively concentrated on the Sm³⁺ ions, causing the Sm³⁺ ions to transition from the ground state to the excited state.

[0014] 3. Emission process: Energy level transition of Sm³⁺ ions: Sm³⁺ ions have abundant 4f-4f transition energy levels. The Sm³⁺ ions in the excited state will undergo a non-radiative relaxation process, transferring energy from high energy levels to lower energy levels, and finally returning to the ground state. In this process, energy will be released in the form of light, generating fluorescence emission.

[0015] 4. Characteristic Emission Peaks: The characteristic emission peaks of Sm³⁺ ions are mainly concentrated in the visible light region, such as 564 nm (green light), 602 nm (orange light), and 645 nm (red light), etc. These emission peaks correspond to the transitions of Sm³⁺ ions such as 4G5 / 2→6H5 / 2, 4G5 / 2→6H7 / 2, and 4G5 / 2→6H9 / 2.

[0016] II. Upconversion Light Process

[0017] The phosphor co-doped with Yb³⁺ and Er³⁺ exhibits upconversion luminescence characteristics, that is, under the excitation of light with lower energy (such as infrared light), it emits visible light with higher energy. The specific luminescence mechanism is as follows:

[0018] The upconversion green light emission changes slowly with the increase of the concentration of Yb³⁺ ions, while the upconversion red light emission increases with the increase of the concentration of Yb³⁺ ions. The luminescence color of the phosphor can be regulated by changing the doping concentration of Yb³⁺ ions. With the increase of the concentration of Yb³⁺ ions, the luminescence of the phosphor gradually changes from green to red.

[0019] Luminescence Mechanism: Both the upconversion green light and red light emissions belong to two-photon processes. The cross-relaxation process plays a dominant role in the upconversion red light emission process. The green light emissions at 533 nm and 557 nm and the red light emission at 688 nm are all two-photon processes. Under the excitation of a 980 nm laser, Yb³⁺ is excited from the ground state 2F7 / 2 to the excited state 2F5 / 2, and then through the energy transfer processes ET1 and ET2, the population of the 4F7 / 2 energy level of Er³⁺ is formed. Then, through the non-radiative relaxation processes NR1 and NR2, the populations of the 2H 11 / 2 and 4S3 / 2 energy levels are formed, and finally through the radiative transition processes 2H 11 / 2→4I 15 / 2 and 4S3 / 2→4I 15 / 2, the emitted light (green light) is obtained, 4 F 9 / 2 →4I 15 / 2 (red light).

[0020] Based on the above fluorescent materials, in the present invention, a PMMA coating is first formed, and then a silica aerogel layer is formed on the basis of this PMMA coating. By virtue of forming the PMMA coating first, not only the uniform coating of the silica aerogel layer on the fluorescent material is realized, but also the high-temperature resistance of the prepared organic phosphor is improved. At the same time, a silica aerogel layer with a refractive index closer to that of the atmosphere is coated on the outermost layer to construct a more effective double-layer dielectric structure and reduce the luminescence loss of the prepared organic phosphor.

[0021] Furthermore, for the organic phosphor of the present invention, the Sm 0.4 Yb0.2 Er 0.4 (HTTA)3Phen fluorescent material is prepared by the following steps:

[0022] (1) Dissolve the rare earth metal salt mixture containing Yb 3+ , Er 3+ and Sm 3+ ions, α-thienoyltrifluoroacetone and 1,10-phenanthroline in ethanol respectively; wherein, the molar ratio of Yb 3+ , Er 3+ and Sm 3+ ions in the rare earth metal salt mixture is 1:2:2, the molar ratio of α-thienoyltrifluoroacetone to the total molar amount of Yb 3+ , Er 3+ and Sm 3+ is 3:1, and the molar ratio of 1,10-phenanthroline to α-thienoyltrifluoroacetone is 1:3;

[0023] (2) Stir the α-thienoyltrifluoroacetone solution in a water bath at 60 - 65 °C, and add the rare earth metal salt mixture solution and 1,10-phenanthroline solution to obtain a mixed reaction solution;

[0024] (3) Adjust the pH value of the mixed reaction solution to 6 - 7, and react for 6 - 7 h to obtain a precipitate, which is washed and dried to obtain Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material.

[0025] The method for preparing the above high-temperature resistant organic fluorescent powder according to the present invention includes the following steps:

[0026] (1) Prepare fluorescent seeds: Mix methyl methacrylate and Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material according to a mass ratio of 40:(1 - 2), add cross-linking agent ethylene glycol di(methacrylate) accounting for 1 - 3% of the mass of methyl methacrylate, and ultrasonically stir for 3 - 5 min to obtain a mixture; then add the mixture to ethanol, stir and react for 2 - 4 h, and then obtain PMMA-Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent seeds through centrifugation and drying;

[0027] (2) Preparation of organic fluorescent powder: Prepare fluorescent seeds, alcohol solvent and water according to the mass ratio of 1:(20 - 35):(8 - 16); Mix the alcohol solvent and water evenly, add tetraethyl orthosilicate to obtain a sol, and the mass ratio of tetraethyl orthosilicate to fluorescent seeds is (1 - 4):2; Add an acid catalyst to the sol to adjust the pH to 3 - 4, and stir for 2 - 4 h at 1000 - 1600 rpm for hydrolysis reaction; Reduce the stirring speed to 300 - 500 rpm, add an alkali catalyst to adjust the pH to 9 - 10, and carry out a condensation reaction to obtain a wet gel. Subsequently, add fluorescent seeds to the wet gel, stir evenly, and age at room temperature for 24 - 36 h, and then obtain the organic fluorescent powder with a silica aerogel layer coated on the surface by atmospheric drying.

[0028] When preparing the organic fluorescent powder of the present invention, by introducing fluorescent seeds during the preparation of silica aerogel, so that under alkaline catalytic conditions, the groups on the surface of PMMA react with the hydroxyl groups of the synthesized silica aerogel formed by hydrolysis - condensation, which not only improves the binding force between PMMA and the silica aerogel layer, but also can effectively reduce the hydroxyl groups in the silica aerogel network, reduce capillary action, prevent the collapse of the aerogel, and improve the structural mechanical properties of the aerogel layer, so as to finally form an organic fluorescent powder that not only has high - temperature resistance, but also has excellent mechanical properties and can reduce luminescence loss.

[0029] Furthermore, the preparation of the organic fluorescent powder of the present invention also includes step (3) surface modification: Mix secondary alkyl sulfonate, BYK - 190 polyurethane dispersion aid, and BYK - 358 acrylic leveling aid according to the mass ratio of (5 - 7):(3 - 5):1, and then add them to the alcohol solvent of the organic fluorescent powder according to the proportion of 5 - 8% of the mass of the organic fluorescent powder, and stir for 40 - 60 min to complete the surface modification of the light - converting powder.

[0030] Furthermore, in step (2) of preparing the organic fluorescent powder of the present invention, the alcohol solvent is methanol, ethanol or isopropanol.

[0031] Furthermore, in step (2) of preparing the organic fluorescent powder of the present invention, the acid catalyst is citric acid, tartaric acid or acetic acid; the alkali catalyst is ammonia water or sodium hydroxide.

[0032] Furthermore, in step (2) of preparing the organic fluorescent powder of the present invention, the atmospheric drying is carried out by drying at 70 - 80 °C for 2 - 3 h and then drying at 90 - 120 °C for 5 - 7 h in sequence.

[0033] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are as follows: The high-temperature-resistant photoconversion powder of the present invention can not only achieve the up-conversion and down-conversion photoconversion effects; at the same time, through the comprehensive coating of PMMA and silica aerogel, the high-temperature resistance performance and optical performance of the photoconversion powder are improved, the light loss is reduced, the mechanical performance is improved, and it can adapt to the preparation methods of downstream products such as high-temperature extrusion. Brief description of the drawings

[0034] Figure 1 For SA@PMMA-Sm in Example 2 0.4 Yb 0.2 Er 0.4 SEM scanning electron micrograph of (HTTA)3Phen organic fluorescent powder;

[0035] Figure 2 For SA@Sm in Comparative Example 2 0.4 Yb 0.2 Er 0.4 SEM scanning electron micrograph of (HTTA)3Phen organic fluorescent powder. Detailed description of the specific embodiments

[0036] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments.

[0037] It should be noted that the raw materials used in the present invention can all be purchased commercially. Among them, the CAS numbers of some of the raw materials used are shown in Table 1 below.

[0038] Table 1 CAS numbers of some raw materials

[0039] Serial number Raw material CAS number 1 α-Thienoyltrifluoroacetone 326-91-0 2 1,10-Phenanthroline 66-71-7 3 Methyl methacrylate 80-62-6 4 Ethylene glycol dimethacrylate 97-90-5 5 Tetraethyl orthosilicate 78-10-4

[0040] Example 1

[0041] The high-temperature-resistant organic fluorescent powder of this Example 1 was prepared by the following steps:

[0042] (1) Preparation of Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material:

[0043] ① Dissolve a mixture of 1 mol of YbCl3·6H2O, 2 mol of SmCl3·6H2O and 2 mol of ErCl3·6H2O (the molar ratio of Yb 3+ , Er 3+ and Sm 3+ is 1:2:2), 15 mol of α-thienoyltrifluoroacetone (HTTA) and 5 mol of 1,10-phenanthroline (phen) in ethanol respectively.

[0044] ② Add the ethanol solution of HTTA into a three-necked flask, stir and reflux it in a water bath at 60 °C; successively add the mixed solution of YbCl3·6H2O, SmCl3·6H2O and ErCl3·6H2O and the ethanol solution of phen into the three-necked flask to obtain a mixed reaction solution.

[0045] ③ Adjust the pH value of the reaction mixture to 6 by dropping 1 mol / L sodium hydroxide ethanol solution; then control the reaction time of the mixture at 6 h at a water bath temperature of 60 °C; after the reaction is completed, centrifuge the mixture at a speed of 10,000 r / min to obtain a precipitate; centrifuge the precipitate, wash it with water and ethanol, repeat this process three times, and then dry it in a vacuum oven at 60 °C for 12 h to obtain Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen powder.

[0046] (2)Preparation of fluorescent seeds:

[0047] Mix methyl methacrylate (MMA) and Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen powder in a mass ratio of 40:1, add 1% (by mass of methyl methacrylate) of the cross-linking agent ethylene glycol di(methacrylate) (EGDMA), and ultrasonically stir for 5 min; then drop the mixture into a three-necked flask filled with ethanol at a speed of 5 ml / min, with a water bath temperature of 60 °C and a stirring speed of 800 rpm, and react for 2 h; after the dropping is completed, centrifuge at 10,000 rpm using a centrifuge and dry in a vacuum oven at 60 °C for 4 h to obtain PMMA-Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent seeds.

[0048] (3)Preparation of organic fluorescent powder:

[0049] ① Prepare the fluorescent seeds, ethanol and water in a mass ratio of 1:20:8; after mixing ethanol and water evenly, add tetraethyl orthosilicate to obtain a sol, the mass ratio of tetraethyl orthosilicate to the fluorescent seeds is 3:2, add citric acid to the sol to adjust the pH to 3, and carry out a hydrolysis reaction for 2 h under stirring at 1000 rpm;

[0050] ② Reduce the rotation speed to 300 rpm, add ammonia water to adjust the pH to 9 for a condensation reaction to obtain a wet gel;

[0051] ③ Add fluorescent seeds to the wet gel. After stirring evenly, age at room temperature for 30 h, then dry the wet gel at 70 °C for 3 h, and then continue to dry at 100 °C for 7 h. Finally, an organic fluorescent powder coated with a silica aerogel layer on the surface is obtained.

[0052] Comparative Example 1

[0053] Compared with Example 1, the difference in this Comparative Example 1 is that silica is used for coating, and the specific steps are as follows:

[0054] (1)Prepare PMMA-Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent seeds: the same as in Example 1;

[0055] (2)Prepare the organic fluorescent powder: Add the fluorescent seeds to a mixed solvent of ethanol and water (volume ratio of the two is 2:1), stir evenly as component A; Stir water, ethanol and ammonia water in a volume ratio of 20:60:10 for 30 min to mix evenly as component B; Stir tetraethyl orthosilicate and ethanol in a mass ratio of 10:90 for 30 min to mix evenly as component C. Subsequently, pour component B into a three-neck flask reactor and stir at a speed of 800 rpm / min, and the water bath temperature is 60 - 65 °C; At this time, quickly add component A to component B while keeping the stirring speed unchanged. After 1 min, drip component C into the three-neck flask at a speed of 30 - 60 ml / min, and at the same time slowly reduce the stirring speed to 500 rpm / min, and keep the reaction going for 2 h. Finally, centrifuge at a speed of 8000 rpm / min to separate SiO2@PMMA-Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen microspheres, and wash three times with ethanol.

[0056] Example 2

[0057] The high-temperature resistant organic fluorescent powder of this Example 2 is prepared by the following steps:

[0058] (1)Prepare Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material:

[0059] ① Mix 1 mol of YbCl3·6H2O, 2 mol of SmCl3·6H2O and 2 mol of ErCl3·6H2O (Yb 3+ 、Er 3+ and Sm 3+A mixture with a molar ratio of 1:2:2), 15 mol of α - thenoyltrifluoroacetone (HTTA) and 5 mol of 1,10 - phenanthroline (phen) were respectively dissolved in ethanol.

[0060] ② The ethanol solution of HTTA was added into a three - necked flask and stirred and refluxed in a water bath at 60 °C; the mixed solution of YbCl3·6H2O, SmCl3·6H2O and ErCl3·6H2O and the ethanol solution of phen were successively added into the three - necked flask to obtain a mixed reaction solution.

[0061] ③ The pH value of the reaction mixture was adjusted to 7 by dropping 1 mol / L sodium hydroxide ethanol solution; then the mixture was controlled at a reaction time of 6 h at a water bath temperature of 60 °C; after the reaction was completed, the mixture was centrifuged at a speed of 10000 r / min to obtain a precipitate; the precipitate was centrifuged, washed with water and ethanol, and this process was repeated three times, and then dried in a vacuum oven at 60 °C for 12 h to obtain Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen powder.

[0062] (2)Preparation of fluorescent seeds:

[0063] Methyl methacrylate (MMA) and Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen powder were mixed in a mass ratio of 20:1, and ethylene glycol bis(methacrylate) (EGDMA) accounting for 1% of the mass of methyl methacrylate was added, and ultrasonic stirring was carried out for 5 min; then the mixture was dropped into a three - necked flask filled with ethanol at a speed of 5 ml / min, the water bath temperature was 60 °C, and the stirring speed was 800 rpm, and the reaction was carried out for 2 h; after the dropping was completed, centrifugation was carried out at 10000 rpm using a centrifuge, and drying was carried out in a vacuum oven at 60 °C for 4 h to obtain PMMA - Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent seeds.

[0064] (3)Preparation of organic fluorescent powder:

[0065] ① Prepare the fluorescent seeds, ethanol and water in a mass ratio of 1:35:16; after mixing ethanol and water evenly, tetraethyl orthosilicate was added to prepare a sol, the mass ratio of this tetraethyl orthosilicate to the fluorescent seeds was 1:2, citric acid was added to the sol to adjust the pH to 4, and hydrolysis reaction was carried out for 4 h under stirring at 1000 rpm;

[0066] ②Reduce the rotation speed to 300 rpm, add ammonia water to adjust the pH to 10, and carry out a condensation reaction to obtain a wet gel;

[0067] ③Add fluorescent seeds to the wet gel, stir evenly, age at room temperature for 36 h, then dry the wet gel at 80 °C for 2 h, and then continue to dry at 120 °C for 5 h. Finally, an organic fluorescent powder coated with a silica aerogel layer on the surface is obtained.

[0068] Comparative Example 2

[0069] The difference between this Comparative Example 2 and Example 2 is that instead of wrapping it with PMMA, it is directly wrapped with silica aerogel, and the specific steps are as follows:

[0070] (1) Prepare Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material:

[0071] ①Dissolve a mixture of 1 mol of YbCl3·6H2O, 2 mol of SmCl3·6H2O, and 2 mol of ErCl3·6H2O (the molar ratio of Yb 3+ , Er 3+ and Sm 3+ is 1:2:2), 15 mol of α-thienoyltrifluoroacetone (HTTA), and 5 mol of 1,10-phenanthroline (phen) in ethanol respectively.

[0072] ②Add the ethanol solution of HTTA to a three-necked flask, stir and reflux in a water bath at 60 °C; add the mixed solution of YbCl3·6H2O, SmCl3·6H2O, and ErCl3·6H2O and the ethanol solution of phen to the three-necked flask in sequence to obtain a mixed reaction solution.

[0073] ③Adjust the pH value of the reaction mixture to 7 by dropping 1 mol / L sodium hydroxide ethanol solution; then control the reaction time of the mixture at 60 °C in a water bath for 6 h; after the reaction is completed, centrifuge the mixture at a rotation speed of 10000 r / min to obtain a precipitate; centrifuge the precipitate, wash it with water and ethanol, repeat this process three times, and then dry it in a vacuum oven at 60 °C for 12 h to obtain Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen powder.

[0074] (2) Prepare organic fluorescent powder:

[0075] ①According to the mass ratio of 1:35:16, Sm 0.4 Yb0.2 Er 0.4 (HTTA)3Phen powder, ethanol and water were prepared; after mixing ethanol and water evenly, tetraethyl orthosilicate was added to obtain a sol. The mass ratio of the tetraethyl orthosilicate to the fluorescent seeds was 1:2. Citric acid was added to the sol to adjust the pH to 4, and a hydrolysis reaction was carried out for 4 h under stirring at 1000 rpm.

[0076] ② The rotation speed was reduced to 300 rpm, and ammonia water was added to adjust the pH to 10 for a condensation reaction to obtain a wet gel.

[0077] ③ Fluorescent seeds were added to the wet gel. After stirring evenly, it was aged at room temperature for 36 h, then the wet gel was dried at 80 °C for 2 h, and then continued to be dried at 120 °C for 5 h. Finally, an organic fluorescent powder coated with a silica aerogel layer on the surface was prepared.

[0078] Performance test 1: Optical intensity test

[0079] The up and down conversion performance of the high-temperature resistant organic fluorescent powders prepared in Example 1 and Comparative Example 1 of the present invention was tested, and the obtained results are shown in Table 2 and Table 3 below. It can be seen from Table 2 and Table 3 that the high-temperature resistant organic fluorescent powders prepared in Example 1 and Comparative Example 1 of the present invention show characteristic emission peaks at 520, 600, and 640 nm under a 300 - 400 nm ultraviolet light source, presenting an overall down conversion characteristic; under 980 nm laser excitation, the fluorescent powder shows characteristic emission peaks at 520, 540, and 654 nm, presenting an overall up conversion characteristic. Thus, it was verified that the Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen powder has up and down conversion performance.

[0080] However, compared with Example 1, the optical intensity of the high-temperature resistant organic fluorescent powder in Comparative Example 1 is reduced by about 30% compared with the Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material, while the high-temperature resistant organic fluorescent powder prepared in Example 1 of the present invention compared with Sm 0.4 Yb 0.2 Er 0.4The optical intensity of the (HTTA)3Phen fluorescent material only decreases by about 10%. That is, under ultraviolet excitation, the fluorescence powder of the aerogel emits strong light, while the fluorescence intensity of the silica-coated one is slightly weaker. The reason is that there are more air pores and less hindrance to the light propagation in them, with a lower refractive index (close to that of air), so the transmittance is higher and the fluorescence intensity is stronger. When the fluorescent particles emit light, by constructing a transition layer of PMMA and fumed silica, the refractive index gradually approaches that of air, reducing the interface loss during the light emission process, resulting in a strong fluorescence intensity. In Comparative Example 1, the refractive index difference between pure silica and air refractive index is large, leading to large interface reflection loss.

[0081] Compared with Example 1, in Comparative Example 2, the high-temperature resistant organic fluorescent powder compared with Sm 0.4 Yb 0.2 Er 0.4 The optical intensity of the (HTTA)3Phen fluorescent material decreases by about 50%. That is, under ultraviolet excitation, the fluorescence intensity of the non-PMMA-coated fluorescent powder is lower than that of the silica-coated one. The reasons are as follows: on the one hand, without PMMA coating, there is inhomogeneity during the formation of the silica aerogel coating; on the other hand, the silica aerogel collapses during the forming process, further leading to inhomogeneity of the coating, resulting in a greatly increased coating thickness and an increased interface loss during the light emission process, thus the fluorescence intensity is smaller.

[0082] Table 2 Down-conversion fluorescence intensity of the organic fluorescent powders of Example 1, Comparative Example 1 and Comparative Example 2

[0083] (Ultraviolet 300 - 400 nm light source)

[0084] Example Embodiment Strength (cps) Characteristic wavelength 560nm 600nm 640nm <![CDATA[Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material]]> <![CDATA[0.3×10 5 > <![CDATA[6×10 5 > <![CDATA[1.65×10 6 > Example 1 - Organic phosphor <![CDATA[0.27×10 5 > <![CDATA[5.5×10 5 > <![CDATA[1.5×10 6 > Comparative Example 1 - Organic phosphor <![CDATA[0.19×10 5 > <![CDATA[3.8×10 5 > <![CDATA[1.1×10 6 > Comparative Example 2 - Organic phosphor <![CDATA[0.14×10 5 > <![CDATA[3×10 5 > <![CDATA[0.85×10 6 >

[0085] Table 3 Down-conversion fluorescence intensity of the organic fluorescent powders of Example 1, Comparative Example 1 and Comparative Example 2

[0086] (980 nm laser)

[0087] Example Embodiment Strength (cps) Characteristic wavelength 520nm 540nm 654nm <![CDATA[Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material]]> <![CDATA[3×10 3 > <![CDATA[7×10 3 > <![CDATA[5×10 3 > Example 1 - Organic phosphor <![CDATA[2.8×10 3 > <![CDATA[6×10 3 > <![CDATA[4.5×10 3 > Comparative Example 1 - Organic phosphor <![CDATA[2.1×10 3 > <![CDATA[5×10 3 > <![CDATA[3.5×10 3 > Comparative Example 2 - Organic phosphor <![CDATA[1.42×10 3 > <![CDATA[3.1×10 3 > <![CDATA[2.5×10 3 >

[0088] Performance test 2: Structure characterization

[0089] The organic fluorescent powders prepared in Example 2 and Comparative Example 2 of the present invention were subjected to structure characterization, and the obtained results are as follows Figure 1 and Figure 2 shown. Combining Figure 1 and Figure 2 it can be known that by doping Sm 0.4 Yb 0.2 Er 0.4When the (HTTA)3Phen fluorescent material is encapsulated with silica aerogel to improve its high-temperature resistance, pre-encapsulation with PMMA or without PMMA directly affects whether the silica aerogel layer used can form a uniform encapsulation of the fluorescent material. Figure 1 A uniform encapsulation was formed. Figure 2 Particle agglomeration occurred.

[0090] For the application of organic fluorescent powders, most are processed into products. To improve the dispersibility of organic fluorescent powders in subsequent processing, the following method is used to modify the surface of the above-mentioned organic fluorescent powders: Sodium secondary alkyl sulfonate, BYK-190 polyurethane dispersing aid, and BYK-358 acrylic leveling aid are mixed in a mass ratio of (5-7):(3-5):1, and then added to the alcohol solvent of the organic fluorescent powder according to a ratio of 5-8% of the mass of the organic fluorescent powder, and stirred for 40-60 min to complete the surface modification of the light conversion powder.

[0091] Performance Test 3: Haze Detection of PE Film

[0092] The organic fluorescent powders prepared in Example 2 and Comparative Example 2 were made into PE films. The specific preparation method is as follows:

[0093] (1) Surface modification: The organic fluorescent powder was added to an ethanol solution and dispersed evenly to obtain an organic fluorescent powder dispersion. Then, sodium secondary alkyl sulfonate, BYK-190 polyurethane dispersing aid, and BYK-358 acrylic leveling aid were mixed evenly in a mass ratio of 5:3:1 to obtain a modified solvent. The modified solvent was added to the organic fluorescent powder dispersion, and the mass of the modified solvent was 8% of the organic fluorescent powder. After stirring for 40 min, modified organic light conversion powder was obtained.

[0094] (2) Film formation: The modified organic light conversion powder was evenly mixed with PE particles to obtain a mixture; then the mixture was processed at an extrusion pressure of 5 Mpa, a rotation speed of 150 rpm, and a temperature of 180 °C to obtain an 80-μm-thick agricultural composite PE film.

[0095] The composite PE films respectively prepared from the organic fluorescent powders of Example 2 and Comparative Example 2 were subjected to haze detection, and the obtained results are shown in Table 4 below.

[0096] Table 4 Optical Performance Detection of PE Films in Example 2 and Comparative Example 2

[0097] Example Haze Example 2 0.8 Comparative Example 2 1.4

[0098] As can be seen from Table 4, through Sm 0.4 Yb 0.2 Er 0.4(HTTA)3Phen fluorescent material is first wrapped with PMMA, which can effectively improve the uniformity of the prepared organic fluorescent powder, and then effectively reduce the haze of the prepared PE film and improve the optical properties of the prepared PE film.

[0099] In addition to the above embodiments, adopting the preparation process steps and the defined process parameters of the present invention can achieve the technical effects claimed above in the present invention, and thus no further experimental verification is carried out one by one.

Claims

1. A high-temperature resistant organic fluorescent powder, characterized in that, The organic fluorescent powder comprises a fluorescent seed formed by a (HTTA)3Phen fluorescent material of Sm 0.4 Yb 0.2 Er 0.4 with up-conversion and down-conversion functions coated with polymethyl methacrylate, and a silica aerogel layer coated on the surface of the fluorescent seed.

2. The high-temperature resistant organic fluorescent powder according to claim 1, wherein The Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material is prepared by the following steps: (1) Dissolve a rare earth metal salt mixture containing Yb 3+ , Er 3+ and Sm 3+ ions, α-thienoyltrifluoroacetone and 1,10-phenanthroline in ethanol respectively; wherein, the molar ratio of Yb 3+ , Er 3+ and Sm 3+ ions in the rare earth metal salt mixture is 1:2:2, the molar ratio of α-thienoyltrifluoroacetone to the total molar amount of Yb 3+ , Er 3+ and Sm 3+ is 3:1, and the molar ratio of 1,10-phenanthroline to α-thienoyltrifluoroacetone is 1:3; (2) Stir the α - thenoyltrifluoroacetone solution in a water bath at 60 - 65 °C, and add the rare earth metal salt mixture solution and 1,10 - phenanthroline solution to obtain a mixed reaction solution; (3) Adjust the pH value of the mixed reaction solution to 6-7, and react for 6-7 h to obtain a precipitate, which is washed and dried to obtain Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material.

3. A method for preparing the high-temperature resistant organic fluorescent powder according to claim 1, characterized in that, It includes the following steps: (1) Preparation of fluorescent seeds: Methyl methacrylate and Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent material are mixed in a mass ratio of 40:(1 - 2), and ethylene glycol di(methacrylate), which is a cross-linking agent accounting for 1 - 3% of the mass of methyl methacrylate, is added. After ultrasonic stirring for 3 - 5 min, a mixture is obtained; subsequently, the mixture is dissolved in ethanol, and after stirring and reacting for 2 - 4 h, PMMA-Sm 0.4 Yb 0.2 Er 0.4 (HTTA)3Phen fluorescent seeds are obtained through centrifugation and drying. (2) Prepare the organic fluorescent powder: Prepare the fluorescent seeds, alcohol solvent and water according to the mass ratio of 1:(20 - 35):(8 - 16); Mix the alcohol solvent and water evenly, and add tetraethyl orthosilicate to obtain a sol. The mass ratio of tetraethyl orthosilicate to the fluorescent seeds is (1 - 4):2; Add an acid catalyst to the sol to adjust the pH to 3 - 4, and stir for 2 - 4 h at 1000 - 1600 rpm for hydrolysis reaction; Reduce the stirring speed to 300 - 500 rpm, add an alkali catalyst to adjust the pH to 9 - 10, and carry out a condensation reaction to obtain a wet gel. Subsequently, add the fluorescent seeds to the wet gel, stir evenly, and age at room temperature for 24 - 36 h, and then obtain the organic fluorescent powder coated with a silica aerogel layer by atmospheric drying.

4. The method for preparing the high-temperature resistant organic fluorescent powder according to claim 3, characterized in that, This method also includes the following steps: (3) Surface modification: Mix sodium secondary alkyl sulfonate, BYK - 190 polyurethane dispersing aid, and BYK - 358 acrylic leveling aid according to the mass ratio of (5 - 7):(3 - 5):1, and then add them to the alcohol solvent of the organic fluorescent powder according to the proportion of 5 - 8% of the mass of the organic fluorescent powder, and stir for 40 - 60 min to complete the surface modification of the light conversion powder.

5. The method for preparing the high-temperature resistant organic fluorescent powder according to claim 3, wherein, In step (2), the alcohol solvent is methanol, ethanol or isopropanol.

6. The method for preparing the high-temperature resistant organic fluorescent powder according to claim 3, characterized in that, In step (2), the acid catalyst is citric acid, tartaric acid or acetic acid; the alkali catalyst is ammonia water or sodium hydroxide.

7. The method for preparing the high-temperature resistant organic fluorescent powder according to claim 3, wherein, In step (2), the atmospheric drying is carried out by drying at 70 - 80 °C for 2 - 3 h and then at 90 - 120 °C for 5 - 7 h in sequence.

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