Light conversion material with silicon dioxide coating layer, preparation method of light conversion material and agricultural light conversion composite film containing light conversion material

Abstract

The invention belongs to the technical field of agricultural light conversion materials, and discloses a light conversion material with a silicon dioxide coating layer, a preparation method of the light conversion material and an agricultural light conversion composite film containing the light conversion material. The preparation method of the light conversion material comprises the following steps: preparing a CaS: Eu < 2 + > dispersion liquid; dropwise adding an acid solution into the first alkoxy silane to prepare a hydrolysate; adding a weakly alkaline buffer agent into the dispersion liquid, heating, dropwise adding the hydrolysate, and carrying out heat preservation reaction; after cooling, adjusting the pH value to 7.0-8.5 by using a weak base; second alkoxy silane is dropwise added, the pH value is adjusted to 8.5-10.5 after dropwise adding is completed, the temperature is increased, and a reaction is conducted; and finally, adding a silane coupling agent for reaction to prepare the light conversion material. The light conversion material provided by the invention not only can ensure the luminescence property of calcium europium sulfide, but also can improve the water and oxygen barrier ability; the agricultural light-conversion composite film prepared from the composite film can effectively block water and oxygen, the tolerance of the film to a high-humidity environment is improved, and the service life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of agricultural light conversion materials technology, specifically relating to a light conversion material with a silica coating layer, its preparation method, and an agricultural light conversion composite film containing it. Background Technology

[0002] Calcium europium sulfide (often represented by the chemical formula CaS:Eu) 2+ Calcium sulfide (CaS) is a typical rare-earth-doped sulfide luminescent material and also a highly efficient light-converting material. Its core principle is the doping of europium ions (Eu) into calcium sulfide (CaS) crystals. 2+ To achieve light conversion: It can efficiently absorb ultraviolet light (230-360nm) and blue-green light (450-560nm), and convert the light into energy through Eu. 2+ Electron transitions convert light (ultraviolet and some blue-green light) that these plants utilize less efficiently into red light at 610-750nm—a wavelength that highly matches the absorption peaks of chlorophyll a and phytochromes in plants, directly promoting photosynthesis. Currently, europium sulfide is mainly used in agricultural light-converting films to improve crop photosynthetic efficiency and increase yields. It can also be used in fields such as bioimaging and anti-counterfeiting labeling.

[0003] In practical applications, europium calcium sulfide suffers from poor chemical stability and is prone to hydrolysis and failure. To address its susceptibility to oxidation by water and oxygen, the industry often uses materials such as SiO2 and Al2O3 to coat its surface, thereby improving stability and optimizing its dispersibility in polymers. However, while existing silica or alumina coatings can temporarily block water and oxygen, they still exhibit rapid performance degradation in high-humidity environments (such as annual average humidity >70%), resulting in a significant decrease in luminescence intensity and light conversion ability during use.

[0004] Numerous publications disclose coating technologies for silica or siloxanes. For example, patent 201810933807.9 discloses a coated light-converting agent composed of an organic fluorescent agent and a siloxane. The siloxane coats the organic fluorescent agent, converting some direct light into scattered light, blocking some infrared light, and extending the lifespan of the light-converting agent. However, this low-crosslinking siloxane coating layer cannot provide adequate protection for calcium europium sulfide, making it difficult to adapt agricultural composite films containing calcium europium sulfide to high-temperature and high-humidity applications. Another patent, 201810337632.5, discloses a two-step acid-base catalytic method for assembling a dense film to coat sheet-like aluminum powder: different catalysts are used to catalyze the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) to obtain silica with different structures. These silica films are then self-assembled to form a dense silica film that coats the surface of the sheet-like aluminum powder. This allows the coated aluminum powder to remain stable under strong acid conditions and maintain good gloss, making it suitable for automotive coatings to enhance the aesthetics of car surfaces. However, aluminum powder and calcium europium sulfide have significantly different properties, and the effects of acids and alkalis on them are completely different. Furthermore, the dense passivation layer required for aluminum powder only needs to focus on indicators such as acid and alkali resistance, weather resistance, and interfacial bonding strength. On the other hand, the silica coating layer on the surface of calcium europium sulfide not only needs to ensure the coating effect, but also needs to take into account the impact on the luminescence performance of the light-converting material. It is necessary to achieve excellent water and oxygen barrier function while ensuring the efficient luminescence of the luminescent material.

[0005] Therefore, developing a silica coating method that can both preserve the luminescent properties of calcium europium sulfide and enhance its water and oxygen barrier properties is of great significance for adapting the light-converting material calcium europium sulfide to the application in greenhouse agriculture under high humidity conditions. Summary of the Invention

[0006] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a light-converting material with a silica coating, a method for preparing the same, and an agricultural light-converting composite film containing the same. The light-converting material with a silica coating provided by this invention can both ensure the luminescent properties of calcium europium sulfide and enhance its water and oxygen barrier properties; the agricultural light-converting composite film prepared using this material can effectively block water and oxygen, improve the film's tolerance to high humidity environments, and extend its service life.

[0007] This invention provides a method for preparing a light-converting material with a silica coating.

[0008] Specifically, a method for preparing a light-converting material with a silica coating layer includes the following steps:

[0009] (1) CaS:Eu 2+ The mixture is mixed with alcohol solvent and water to form a dispersion; acid solution is added dropwise to the first alkoxysilane to adjust the pH value to 3.5-5.5, and the mixture is pre-hydrolyzed to obtain the first alkoxysilane hydrolysate;

[0010] (2) After adding a weak alkaline buffer to the dispersion, heat to 40-60°C, then add the first alkoxysilane hydrolysate dropwise, and maintain the temperature for reaction to form CaS:Eu with a preliminary coating layer. 2+ reaction solution;

[0011] (3) The CaS:Eu prepared in step (2) 2+ After the reaction solution is cooled to 10-35℃, the pH value is adjusted to 7.0-8.5 with a weak base; then, dialkoxysilane is added dropwise. After the addition is complete, the pH value is adjusted to 8.5-10.5 with a weak base and the temperature is raised to 45-60℃ to carry out the reaction; finally, the product is separated to obtain the modified light-converting material.

[0012] (4) Disperse the modified light-converting material prepared in step (3) in an alcohol solvent, add a silane coupling agent, and react again to obtain a light-converting material with a silica coating layer.

[0013] The mass ratio of the first alkoxysilane to the second alkoxysilane is (1-3):1.

[0014] In some embodiments of the present invention, the mass ratio of the first alkoxysilane to the second alkoxysilane is (1-2.5):1.

[0015] In some embodiments of the present invention, the first alkoxysilane and the second alkoxysilane comprise tetramethoxysilane and / or tetraethoxysilane.

[0016] In some embodiments of the present invention, the amounts of the first alkoxysilane and the second alkoxysilane added are equal to the amounts of CaS:Eu. 2+ The mass is 1.2-2.5 times that of the first alkoxysilane and the second alkoxysilane. Preferably, the amount of the first alkoxysilane and the second alkoxysilane added is equal to the mass of CaS:Eu. 2+ It is 1.5-2.0 times the quality.

[0017] In some embodiments of the present invention, in step (1), the CaS:Eu 2+ The mass ratio of CaS:Eu to the alcohol solvent and the water is 1:(5-15):(0.5-1.2); preferably, the CaS:Eu 2+ The mass ratio of the alcohol solvent to the water is 1:(8-12):(0.5-1.0).

[0018] In some embodiments of the present invention, in step (1), a dispersant may be added during the mixing process. The dispersant may be selected from polyvinylpyrrolidone (PVP), polyethylene glycol (PEG-400 / 600), etc. The amount of the dispersant added is 0.3%-2% of the mass of CaS:Eu2+.

[0019] In some embodiments of the present invention, in step (1), acid is added dropwise to the first alkoxysilane to adjust the pH value to 3.5-5.0.

[0020] In some embodiments of the present invention, the acid solution in step (1) is acetic acid or dilute hydrochloric acid, such as a 0.05-0.20 mol / L hydrochloric acid solution. Preferably, it is a 0.08-0.15 mol / L hydrochloric acid solution.

[0021] In some embodiments of the present invention, the pre-hydrolysis time in step (1) is 10-40 min; preferably, the pre-hydrolysis time in step (1) is 15-25 min.

[0022] In some embodiments of the present invention, the weakly basic buffer in step (2) includes triethanolamine and / or diethanolamine.

[0023] In some embodiments of the present invention, the mass of the weak alkaline buffer in step (2) accounts for 0.05%-0.5% of the mass of the dispersion; preferably, the mass of the weak alkaline buffer in step (2) accounts for 0.1%-0.3% of the mass of the dispersion.

[0024] In some embodiments of the present invention, the heat preservation reaction in step (2) is carried out under stirring, with a reaction temperature of 50-60°C and a reaction time of 40-120 min. Preferably, the heat preservation reaction is carried out under stirring at a speed of 100-500 rpm, with a reaction temperature of 50-60°C and a reaction time of 70-100 min.

[0025] In some embodiments of the present invention, the dispersion is heated to 45-55°C in step (2).

[0026] In some embodiments of the present invention, the weak base in step (3) includes ammonia or triethylamine.

[0027] In some embodiments of the present invention, the temperature of the reaction in step (3) is 50-60°C and the reaction time is 40-120 min. Preferably, the temperature of the reaction in step (3) is 50-60°C and the reaction time is 70-100 min.

[0028] In some embodiments of the present invention, step (3) involves the CaS:Eu 2+ After the reaction solution is cooled to 10-35℃, the pH value is adjusted to 7.0-8.0 with a weak base; then, dialkoxysilane is added dropwise. After the addition is complete, the pH value is adjusted to 9.0-10.0 with a weak base and the temperature is raised to 45-60℃.

[0029] In some embodiments of the present invention, the alcohol solvent mentioned in steps (1) and (4) is ethanol.

[0030] In some embodiments of the present invention, the silane coupling agent in step (4) includes at least one of KH550, KH792, and A-1100.

[0031] In some embodiments of the present invention, the amount of silane coupling agent added in step (4) accounts for a certain percentage of the CaS:Eu content. 2+ The amount of the silane coupling agent added in step (4) is 0.3%-1.0% of the total mass of the first alkoxysilane and the second alkoxysilane; preferably, the amount of the silane coupling agent added in step (4) accounts for 0.3%-1.0% of the total mass of the CaS:Eu 2+ The content is 0.3%-0.8% of the total mass of the first alkoxysilane and the second alkoxysilane.

[0032] In some embodiments of the present invention, the reaction in step (4) is carried out under stirring, the temperature of the reaction is 10-35°C (room temperature), and the reaction time is 5-12h.

[0033] This invention provides a light-converting material with a silica coating.

[0034] Specifically, a light-converting material with a silica coating is prepared by the above-described method, wherein the light-converting material comprises CaS:Eu 2+ , coated on the CaS:Eu 2+ A silica layer on the surface, and a silane coupling agent located on the surface of the silica layer.

[0035] This invention provides an agricultural light-converting composite film.

[0036] Specifically, an agricultural light-converting composite film comprises the aforementioned light-converting material with a silica coating layer and PEVA resin.

[0037] In some embodiments of the present invention, the amount of the light-converting material with a silica coating is 0.5%-2.0% of the mass of the PEVA resin. Preferably, the amount of the light-converting material with a silica coating is 0.8%-1.5% of the mass of the PEVA resin.

[0038] In some embodiments of the present invention, the agricultural light-converting composite film further comprises an ultraviolet absorber and a SiO2 anti-fogging agent.

[0039] The preparation method of the above-mentioned agricultural light-converting composite film is as follows:

[0040] A light-converting composite film for agricultural use is prepared by blending a light-converting material with a silica coating layer with PEVA resin, nano-SiO2 anti-fogging agent, and ultraviolet light absorber, and then extruding the mixture into a film.

[0041] The ultraviolet absorbers include benzotriazoles, benzophenones, or triazines. Benzotriazoles include UV-531 and UV-327; benzophenones include UV-9 and UV-2000; and triazines include 2,4,6-tris(2′-hydroxy-4′-n-butoxyphenyl)triazine and 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-(octyloxy)phenol (UV-1164).

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] (1) The light-converting material with a silica coating provided by the present invention first pre-hydrolyzes a portion of alkoxysilane (TEOS) under acidic conditions, and then reacts it with CaS:Eu protected by a weak alkaline buffer. 2+ The reaction proceeds in a dispersion. Under acidic conditions, TEOS hydrolyzes rapidly, generating a large number of small-sized silanol monomers (Si-OH), which are uniformly dispersed and readily react with the optical conversion material CaS:Eu. 2+ Uniform adsorption on the surface forms a thin and continuous initial coating layer. Then, the pH is adjusted to a slightly alkaline level (especially pH 7.0-8.0), and the remaining alkoxysilane is added dropwise. Further increasing the alkalinity of the reaction solution (especially pH 9.0-10.0) accelerates the condensation rate of the silanol monomers, filling the pores of the initial layer and forming a dense, defect-free shell. By strictly controlling the temperature, pH, and the amount of TEOS added each time during the coating process, a silica coating layer with high uniformity, low porosity, tight bonding, and excellent barrier properties (preventing oxygen and moisture penetration) can be formed on the surface of the light-converting material. The light-converting material with a silica coating layer provided by this invention not only ensures the luminescent properties of calcium europium sulfide but also enhances its water and oxygen barrier capabilities. Agricultural light-converting composite films prepared using this material can effectively block water and oxygen, improve the film's tolerance to high humidity environments, and extend its service life.

[0044] (2) The present invention provides a dense SiO2 coating for calcium europium sulfide light-converting material. Through a two-step catalytic method of acid followed by alkali, the light-converting material can be prevented from being corroded by the alkaline environment and a uniform and dense shell can be formed, which significantly improves its antioxidant and water-resistant properties, laying a good foundation for its subsequent application in agricultural light-converting composite films. Detailed Implementation

[0045] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0046] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0047] Example 1

[0048] A method for preparing a light-converting material with a silica coating includes the following steps:

[0049] (1) Take 100g CaS:Eu 2+ 1000g anhydrous ethanol and 100g water were mixed and ultrasonically dispersed for 15 minutes (100W power, 40℃). 0.8g polyvinylpyrrolidone (PVP, molecular weight 10000) was added and ultrasonically dispersed for another 20 minutes to form a stable dispersion. HCl (0.1mol / L) was added to 120g TEOS (66.7% of the total amount) to adjust the pH to 4.0. The mixture was stirred and pre-hydrolyzed for 20 minutes to obtain the first alkoxysilane hydrolysate.

[0050] (2) Transfer the dispersion to a flask, install a condenser and thermometer, add triethanolamine (1% of the dispersion mass), heat in a water bath to 55°C, adjust the stirring speed to 300 rpm, and then slowly add the first alkoxysilane hydrolysate dropwise over 40 minutes. Maintain the temperature at 55°C and react for 1.5 hours to form CaS:Eu with a preliminary coating layer. 2+ Reaction solution.

[0051] (3) CaS:Eu 2+ After the reaction solution was cooled to 25°C, the pH was adjusted to 7.5 with ammonia. Then, 60g of TEOS was added dropwise over 20 minutes. After the addition was complete, the pH was adjusted to 9.5 with ammonia and the temperature was raised to 55°C. The reaction was allowed to proceed for 1.5 hours. The reaction solution was centrifuged (10,000 rpm, 10 minutes), and the supernatant was discarded. The precipitate was washed three times with anhydrous ethanol, ultrasonically dispersed for 5 minutes each time, and then centrifuged again. After the final wash, the precipitate was placed in a vacuum drying oven (60°C, 12 hours) to obtain a light-converting material with a silica coating.

[0052] (4) The light-converting material with silica coating prepared above was dispersed in 1000g of ethanol, and then 0.8g of silane coupling agent KH550 was added. The mixture was stirred at 350r / min for 12 hours at 25±2℃. During the reaction, the uniformity of the reaction was judged by observing the particle settling speed. After the reaction was completed, the mixture was centrifuged at 8000r / min for 15 minutes using a high-speed centrifuge. The lower solid particles were collected and washed three times with anhydrous ethanol to remove unreacted silane coupling agent. Finally, the product was placed in a vacuum drying oven and dried at 60℃ for 8 hours to obtain the light-converting material with silica coating.

[0053] This embodiment also provides an agricultural light-converting composite film, comprising 100g of light-converting material with a silica coating prepared by the above method, 9900g of PEVA resin, 20g of nano-SiO2 anti-fogging agent (Evonik AEROSIL® R972) and 30g of ultraviolet light absorber UV-531.

[0054] The preparation method of agricultural light-converting composite film is as follows: Weigh the light-converting material, PEVA resin (VA content 15%), Evonik AEROSIL® R972 and UV absorber UV-1164, and put them into a high-speed mixer. Premix for 20 minutes at a speed of 1000 r / min and a temperature of 90℃ to ensure that each functional additive is evenly dispersed in the resin matrix. Then feed the premixed material into a twin-screw extruder and set the temperature of each section of the barrel as follows: feeding section 145℃, compression section 165℃, melting section 180℃, and die head 185℃. Control the screw speed at 35 r / min and maintain the extrusion pressure at 10 MPa. After extrusion through the T-shaped flat die, cool and shape it through a cooling roller at a temperature of 35℃. At the same time, pull it at a traction speed of 3 m / min and adjust it in real time with an online thickness detector to finally obtain an agricultural light-converting composite film with uniform thickness (deviation ≤ ±0.005 mm) and a thickness of 0.1 mm.

[0055] Example 2

[0056] A method for preparing a light-converting material with a silica coating includes the following steps:

[0057] (1) Take 100g CaS:Eu 2+ 1100g of anhydrous ethanol and 90g of water were mixed and ultrasonically dispersed for 15 minutes (100W power, 40℃). 0.6g of polyvinylpyrrolidone (PVP, molecular weight 10000) was added and ultrasonication continued for 20 minutes to form a stable dispersion. HCl (0.1mol / L) was added to 120g of TEOS (60% of the total volume) to adjust the pH to 4.5, and the mixture was stirred for pre-hydrolysis for 15 minutes to obtain the first alkoxysilane hydrolysate.

[0058] (2) Transfer the dispersion to a flask, install a condenser and thermometer, add triethanolamine (1.5% of the dispersion mass), heat in a water bath to 50°C, adjust the stirring speed to 300 rpm, and then slowly add the first alkoxysilane hydrolysate dropwise over 50 minutes. Maintain the temperature at 50°C and react for 2 hours to form CaS:Eu with a preliminary coating layer. 2+ Reaction solution.

[0059] (3) CaS:Eu 2+After the reaction solution was cooled to 25°C, the pH was adjusted to 8.0 with ammonia. Then, 80g of TEOS was added dropwise over 25 minutes. After the addition was complete, the pH was adjusted to 10 with ammonia and the temperature was raised to 55°C. The reaction was allowed to proceed for 1.5 hours. The reaction solution was then centrifuged (10,000 rpm, 10 minutes), and the supernatant was discarded. The precipitate was washed three times with anhydrous ethanol, ultrasonically dispersed for 5 minutes each time, and then centrifuged again. After the final wash, the precipitate was placed in a vacuum drying oven (60°C, 12 hours) to obtain a light-converting material with a silica coating.

[0060] (4) The light-converting material with silica coating prepared above was dispersed in 1000g of ethanol, and then 0.7g of silane coupling agent KH550 was added. The mixture was stirred at 350r / min for 10 hours at 25±2℃. During the reaction, the uniformity of the reaction was judged by observing the particle settling speed. After the reaction was completed, the mixture was centrifuged at 8000r / min for 15 minutes using a high-speed centrifuge. The lower solid particles were collected and washed three times with anhydrous ethanol to remove unreacted silane coupling agent. Finally, the product was placed in a vacuum drying oven and dried at 60℃ for 8 hours to obtain the light-converting material with silica coating.

[0061] This embodiment also provides an agricultural light-converting composite film, comprising 100g of light-converting material with a silica coating prepared by the above method, 9900g of PEVA resin, 20g of nano-SiO2 anti-fogging agent (Evonik AEROSIL® R972) and 30g of ultraviolet light absorber UV-531.

[0062] The preparation method of agricultural light-converting composite film is as follows: Weigh the light-converting material, PEVA resin (VA content 15%), Evonik AEROSIL® R972 and UV absorber UV-1164, and put them into a high-speed mixer. Premix for 20 minutes at a speed of 1000 r / min and a temperature of 90℃ to ensure that each functional additive is evenly dispersed in the resin matrix. Then feed the premixed material into a twin-screw extruder and set the temperature of each section of the barrel as follows: feeding section 145℃, compression section 165℃, melting section 180℃, and die head 185℃. Control the screw speed at 35 r / min and maintain the extrusion pressure at 10 MPa. After extrusion through the T-shaped flat die, cool and shape it through a cooling roller at a temperature of 35℃. At the same time, pull it at a traction speed of 3 m / min and adjust it in real time with an online thickness detector to finally obtain an agricultural light-converting composite film with uniform thickness (deviation ≤ ±0.005 mm) and a thickness of 0.1 mm.

[0063] Example 3

[0064] The difference between this embodiment and Embodiment 1 is that in step (1), HCl (0.1 mol / L) is added dropwise to adjust the pH value to 5.5, and in step (3), after the addition of TEOS is completed, ammonia water is used to adjust the pH value to 8.5 and the temperature is raised to 55°C. The remaining steps are the same as in Embodiment 1.

[0065] Example 4

[0066] The difference between this embodiment and Embodiment 1 is that in step (1), HCl (0.1 mol / L) is added dropwise to adjust the pH value to 3.5, and in step (3), after the addition of TEOS is completed, ammonia water is used to adjust the pH value to 10.5 and the temperature is raised to 55°C. The remaining steps are the same as in Embodiment 1.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 is that in step (3), when CaS:Eu 2+ After the reaction solution was cooled to 25°C, the pH was adjusted to 10.0 directly using ammonia water; then 80g of TEOS was added dropwise. The remaining steps were the same as in Example 1.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that 60g of TEOS (33.3% of the total amount) was added in step (2), and 120g of TEOS (66.7% of the total amount) was added in step (3). The remaining steps are the same as in Example 1.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that triethanolamine (1% of the dispersion mass) is not added in step (2), and the first alkoxysilane hydrolysate is added dropwise after heating. The remaining steps are the same as in Example 1.

[0073] Product effectiveness test

[0074] 1. Accelerated aging test (simulating long-term use)

[0075] The light-converting materials with silica coating provided in each embodiment and comparative example were placed at 85°C and 90% relative humidity, and their light emission performance was tested at 100h and 500h, respectively.

[0076] 2. Luminescent performance test

[0077] 2.1 Instruments: Fluorescence spectrophotometer (Edinburgh FS5), constant temperature and humidity chamber (temperature control accuracy ±1℃, humidity control accuracy ±3%).

[0078] 2.2 Sample:

[0079] Uncoated CaS:Eu 2+(Uncovered sample);

[0080] The light-converting materials (coated samples) with a silica coating provided in each embodiment and comparative example;

[0081] Samples after accelerated aging (aged samples).

[0082] 2.3 Sample Preparation

[0083] Take the light-converting material powders from each batch and set aside.

[0084] 2.4 Fluorescence Spectroscopy Test

[0085] Excitation wavelength: 460nm

[0086] Emission scanning range: 600-750nm

[0087] Slit and velocity: The excitation / emission slits are both 5 nm, and the scanning speed is 200 nm / min.

[0088] Test: The emission spectra of the uncoated sample, coated sample, and aged sample were measured sequentially, and the average value was taken for each sample in 3 measurements.

[0089] 2.5 Data Comparison

[0090] Calculate the integral area of ​​the emission peak in the 600-750nm range for each sample (reflecting the total luminescence intensity).

[0091] Strength retention rate calculation:

[0092] Strength retention rate after coating = (integrated area of ​​coated sample / integrated area of ​​uncoated sample) × 100%;

[0093] Strength retention rate after aging = (integrated area of ​​aged sample / initial integrated area of ​​coated sample) × 100%.

[0094] The test results are shown in Table 1. The intensity retention rate after aging refers to the luminescence intensity retention rate of the samples after accelerated aging for 100 and 500 hours.

[0095] Table 1

[0096] Group Strength retention rate after coating / % Strength retention rate after 100 hours of aging / % Strength retention rate after 500 hours of aging / % control sample 100% / / Example 1 90.8 85.2 79.8 Example 2 90.2 84.7 77.6 Example 3 84.7 79.3 71.5 Example 4 80.5 76.4 67.2 Comparative Example 1 77.8 67.1 55.6 Comparative Example 2 75.6 62.4 52.9 Comparative Example 3 79.5 75.6 65.5

[0097] As shown in Table 1, the silica-coated light-converting material provided in this embodiment of the invention can both ensure the luminescence performance of calcium europium sulfide and improve its water and oxygen barrier capabilities. Its effect is significantly better than the comparative example. In Example 3, the pH value was slightly higher in the acidic stage, resulting in a slower TEOS hydrolysis rate and a thinner and less uniform initial coating layer; while in the alkaline stage, the final pH value was only 8.5, leading to insufficient condensation reaction, a loose shell, and high porosity. This makes the water and oxygen barrier capability of the luminescent material in Example 3 significantly weaker than that in Examples 1 and 2. In Example 4, due to the influence of the pH value in steps (1) and (3), its shell layer was too thick and uneven, CaS:Eu 2+ The core was also locally damaged, which significantly reduced the luminescence intensity retention rate of the coated sample. After accelerated aging, it did not show a superior ability to block water and oxygen. In Comparative Example 1, the weak alkaline transition step was omitted in step (3), and the pH value was directly adjusted to 10.0 before adding TEOS. Because condensation preferred adsorption, the shell layer was severely uneven. 2+ The oxidation process was also accelerated, ultimately leading to a significant decrease in luminescence performance and a deterioration in long-term stability. In Comparative Example 2, the amount of alkoxysilane used in the early stages was insufficient to form a thin, continuous, and uniform coating layer; however, the excessive amount of alkoxysilane in the later stages resulted in the stacking of thick and large shells, making it impossible to obtain a dense silica coating layer, ultimately leading to a significant decrease in luminescence performance and a deterioration in long-term stability. In Comparative Example 3, no weak alkaline buffer was used to protect CaS:Eu before adding the acidic alkoxysilane hydrolysate. 2+ Dispersion, partially CaS:Eu 2+ Dissolution not only causes severe loss of luminescent material, but also affects the coating effect in the initial stage.

[0098] 3. Accelerated aging tests were conducted on the agricultural light-converting composite films prepared in Example 1 and Comparative Examples 1, 2, and 3.

[0099] Xenon lamp aging test chamber test conditions: continuous irradiation, periodic water spray, irradiance 0.55W / m 2 @340nm, water spray cycle 18min / 102min (water spray time / no water spray time), blackboard temperature 65℃. After accelerated aging for 1200 hours, the luminescence intensity of the composite film was tested, and the luminescence intensity retention rate was calculated. The test results are shown in Table 2.

[0100] Table 2

[0101] Group Luminescence intensity retention rate after 1200 hours of accelerated aging Example 1 72.5% Comparative Example 1 56.0% Comparative Example 2 53.3% Comparative Example 3 61.4%

[0102] As shown in Table 2, the agricultural light-converting composite film prepared in Example 1 of the present invention can effectively block water and oxygen. The film has strong tolerance to high humidity environment and long service life. Its performance is particularly obvious in Comparative Examples 1-3.

[0103] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a light-converting material with a silica coating, characterized in that, Includes the following steps: (1) CaS:Eu 2+ The mixture is mixed with alcohol solvent and water to form a dispersion; acid solution is added dropwise to the first alkoxysilane to adjust the pH value to 3.5-5.5, and the mixture is pre-hydrolyzed to obtain the first alkoxysilane hydrolysate; (2) After adding a weak alkaline buffer to the dispersion, heat to 40-60°C, then add the first alkoxysilane hydrolysate dropwise, and maintain the temperature for reaction to form CaS:Eu with a preliminary coating layer. 2+ reaction solution; (3) The CaS:Eu prepared in step (2) 2+ After the reaction solution is cooled to 10-35℃, the pH value is adjusted to 7.0-8.5 with a weak base; then, dialkoxysilane is added dropwise. After the addition is complete, the pH value is adjusted to 8.5-10.5 with a weak base and the temperature is raised to 45-60℃ to carry out the reaction; finally, the product is separated to obtain the modified light-converting material. (4) Disperse the modified light-converting material prepared in step (3) in an alcohol solvent, add a silane coupling agent, and react again to obtain a light-converting material with a silica coating layer. The mass ratio of the first alkoxysilane to the second alkoxysilane is (1-3):

1.

2. The preparation method according to claim 1, characterized in that, The first alkoxysilane and the second alkoxysilane include tetramethoxysilane and / or tetraethoxysilane.

3. The preparation method according to claim 1, characterized in that, In step (1), the CaS:Eu 2+ The mass ratio of the alcohol solvent to the water is 1:(5-15):(0.5-1.0).

4. The preparation method according to claim 1 or 2, characterized in that, The weakly basic buffer in step (2) includes triethanolamine and / or diethanolamine; the mass of the weakly basic buffer accounts for 0.05%-0.5% of the mass of the dispersion.

5. The preparation method according to claim 1 or 2, characterized in that, The weak base mentioned in step (3) includes ammonia or triethylamine; the reaction temperature in step (3) is 50-60℃ and the reaction time is 40-120min.

6. The preparation method according to claim 1 or 2, characterized in that, The silane coupling agent mentioned in step (4) includes at least one of KH550, KH792, and A-1100; the amount of the silane coupling agent added accounts for a certain percentage of the CaS:Eu content. 2+ The content is 0.3%-1.0% of the total mass of the first alkoxysilane and the second alkoxysilane.

7. The preparation method according to claim 1 or 2, characterized in that, The heat preservation reaction in step (2) is carried out under stirring, the reaction temperature is 50-60℃, and the reaction time is 40-120min; the reaction in step (4) is carried out under stirring, the reaction temperature is 10-35℃, and the reaction time is 5-12h.

8. A light-converting material having a silica coating layer, characterized in that, The light-converting material is prepared by the method according to any one of claims 1-7, wherein the light-converting material comprises CaS:Eu 2+ , coated on the CaS:Eu 2+ A silica layer on the surface, and a silane coupling agent located on the surface of the silica layer.

9. An agricultural light-converting composite film, characterized in that, It comprises the light-converting material with a silica coating as described in claim 8 and PEVA resin.

10. The agricultural light-converting composite film according to claim 9, characterized in that, The amount of the light-converting material with a silica coating is 0.5%-2.0% of the mass of the PEVA resin.