Preparation method of all-inorganic fluorescent film for solid-state illumination

Abstract

The invention relates to a preparation method of an all-inorganic fluorescent film for solid-state illumination. According to the method, a full-inorganic bonding solvent prepared from sodium silicate (16-22%), aluminum oxide (2-6%), potassium hydroxide (6-12%) and pure water is adopted, a substrate is sequentially coated with the bonding solvent and one or more kinds of fluorescent powder, and standing and curing are conducted for 6-24 hours at the room temperature (15-30 DEG C) to form the film. By adopting an all-inorganic system and a room-temperature curing process, the technical problems that a traditional fluorescent film is poor in thermal stability and fluorescent powder performance is damaged due to high-temperature preparation are effectively solved, and the prepared fluorescent film is good in thermal stability and excellent in luminescence performance.

Description

Technical Field

[0001] This invention relates to the field of solid-state lighting technology, and more specifically to a method for preparing an all-inorganic fluorescent thin film. Background Technology

[0002] Laser lighting, with its advantages of strong directionality, high brightness, long illumination distance, and long lifespan, has been rapidly adopted in high-end applications such as automotive headlights, rail transit signal lights, stage performance lighting, deep-sea / high-altitude searchlights, and high-power industrial and scientific research light sources. As a crucial component of laser lighting, fluorescent conversion materials face greater challenges in key performance aspects such as resistance to high blue laser irradiation and high luminous efficiency. Traditional organic fluorescent thin films suffer from low thermal conductivity and poor thermal stability, making it difficult to meet the high brightness and high luminous efficiency requirements of laser lighting. This invention utilizes all-inorganic materials and prepares a phosphor thin film under room temperature conditions to address the aforementioned problems.

[0003] First, traditional fluorescent conversion materials often lack sufficient thermal stability when subjected to high-power laser irradiation. This not only accelerates material aging for high luminous flux output but also limits the reliability of laser illumination systems. Second, existing fluorescent conversion materials also have significant shortcomings in thermal conductivity. Due to the low intrinsic thermal conductivity of the matrix material, heat cannot dissipate rapidly, leading to excessively high local temperature rises, which can cause fluorescence quenching or even surface carbonization, severely affecting luminous efficiency and lifetime. This problem is particularly prominent in applications requiring high power. Furthermore, existing fluorescent conversion materials generally rely on high-temperature sintering to achieve densification, but high temperatures can cause irreversible thermal damage to phosphor particles, potentially resulting in lattice defects, surface roughening, and local phase transitions, leading to a decrease in quantum efficiency and emission intensity.

[0004] To address the thermal stability issues of organic materials, the industry has developed various all-inorganic fluorescent conversion materials, including fluorescent single crystals, fluorescent ceramics, and fluorescent glasses. However, these materials typically require high-temperature sintering processes (500-1000°C) for preparation, leading to the following problems: firstly, high temperatures can cause thermal damage to phosphor particles, reducing quantum efficiency; secondly, high-temperature processes involve large investments in equipment, high energy consumption, and high costs. Therefore, developing a method for preparing fluorescent thin films that combines the advantages of all-inorganic materials with room-temperature preparation processes is of great significance. Consequently, preparing inorganic bulk materials with high quantum efficiency and resistance to high-power laser excitation has become a major challenge for high-power laser illumination.

[0005] To address the aforementioned issues, this study proposes a simple and feasible method for preparing all-inorganic fluorescent thin films for solid-state lighting. This invention improves the thermal stability of the fluorescent thin film through the selection of all-inorganic components. Simultaneously, the room-temperature preparation conditions effectively preserve the original luminescent properties of the phosphor particles. This invention provides an innovative method for preparing fluorescent thin films for laser lighting. Summary of the Invention

[0006] This invention provides a method for preparing an all-inorganic fluorescent thin film for solid-state lighting, aiming to solve the problems of thermal damage and poor thermal stability caused by high-temperature sintering in traditional phosphor thin film preparation. To achieve this goal, this invention eliminates the high-temperature sintering step and adopts a sinter-free process, avoiding high-temperature thermal damage to phosphor particles and fully preserving their original luminescent properties. Simultaneously, it uses an all-inorganic material system to replace organic matrices such as silicone, significantly reducing preparation costs and process complexity, ensuring excellent luminescent performance and long-term stability of the thin film. This invention provides a solution for the preparation of fluorescent thin films for laser lighting and has broad application prospects.

[0007] The technical solution of this invention is as follows: A method for preparing an all-inorganic fluorescent thin film for solid-state lighting, the method using an all-inorganic raw material system, including phosphor, all-inorganic bonding solvent and substrate; the core process is to sequentially coat the bonding solvent and phosphor onto the substrate at room temperature, and the bonding solvent undergoes hydration etching and polymerization reactions with the substrate and phosphor, and the final fluorescent thin film is formed by static curing.

[0008] A method for preparing an all-inorganic fluorescent thin film for solid-state lighting includes the following steps: (1) Prepare a substrate, one or more phosphors and an all-inorganic bonding solvent; the all-inorganic bonding solvent is composed of sodium silicate, alumina, potassium hydroxide and pure water; wherein the mass percentage of sodium silicate is 16-22%, the mass percentage of alumina is 2-6%, the mass percentage of potassium hydroxide is 6-12%, and the remainder is pure water. (2) The inorganic bonding solvent can be coated onto the substrate by spin coating, drop coating or spray coating. The spin coating parameters are: acceleration 300-400 rpm / s, rotation speed 150-200 rpm, and time 60-180 s, so that the bonding solvent and the substrate can be in full contact and form a preliminary bonding process between the bonding solvent and the substrate. (3) Apply the fluorescent powder by scraping, using a 900-1100 mesh stainless steel screen, with a scraper pressure of 0.1-0.5 MPa, and control the thickness of a single scraping to 0.1-0.3 mm; (4) The substrate coated with the bonding solvent and the phosphor is statically cured at a temperature of 15-30°C for 6-24 hours. The curing process involves the following chemical reaction: sodium silicate is hydrolyzed under alkaline conditions to generate silanol groups (Si–OH), which undergo a condensation reaction with hydroxyl groups (–OH) on the substrate surface (such as sapphire or quartz glass) to form Si–O–Al / Si covalent bonds; at the same time, nano-alumina partially dissolves in the alkaline environment and participates in the formation of an aluminosilicate three-dimensional network, which encapsulates and anchors the phosphor particles in the inorganic network, thereby achieving chemical bonding at room temperature and forming the all-inorganic fluorescent film.

[0009] Preferably, the mass ratio of the all-inorganic bonding solvent to the phosphor is 1:0.5 to 1:5.

[0010] Preferably, the preparation method is carried out in a mold, in which the substrate is placed and the mold is made of silicone, epoxy resin or polyethylene.

[0011] Preferably, steps (2) and (3) are repeated at least once, and after each repetition, the film is left to stand at 15-30°C for 20-40 minutes to form an all-inorganic fluorescent film with a multilayer composite structure.

[0012] Preferably, the phosphor is selected from one or more of YAG-based phosphors, aluminate-based phosphors, nitride-based phosphors, and silicate-based phosphors.

[0013] Preferably, step (3) involves coating the phosphor onto the bonding solvent using a sieve with a mesh size of 900 to 1100. The all-inorganic bonding solvent is prepared by adding sodium silicate, nano-alumina (average particle size 20–100 nm), and potassium hydroxide in pure water at a mass percentage of 16–22%:2–6%:6–12%, and stirring in a water bath at 70–90°C for 1–3 hours until a homogeneous solution with a transparent or translucent appearance, a viscosity of 50–500 mPa·s (25°C), and a pH of 10–13 is obtained. The solution is then cooled to room temperature before use.

[0014] The substrate material can be glass or sapphire, the surface must be flat and smooth, and it must be a substrate material that can undergo hydrogen-oxygen catalytic bonding. The mold material can be silicone, epoxy resin or polyethylene, with length, width and height dimensions between 1cm and 5cm, and the mold must match the length and width dimensions of the substrate. The spin coater used in the preparation method consists of a vacuum tray, a vacuum pump, a feed cylinder, a spin coating chamber, and a control panel.

[0015] The phosphor and substrate material used in the preparation method can be firmly bonded by a bonding solvent. This is achieved through hydrogen-oxygen catalytic bonding technology, which involves hydration etching and polymerization reactions. The substrate and phosphor particles react with the bonding solvent at room temperature, ultimately forming a network structure composed of chemical bonds on their surface.

[0016] The sieve used in the preparation method is between 800 and 1200 mesh.

[0017] The resulting fluorescent film is tightly bonded to the substrate material and can be changed according to the shape of the substrate.

[0018] This invention provides a method for preparing an all-inorganic fluorescent thin film for solid-state lighting, which has at least the following beneficial effects: 1. By using an all-inorganic bonding solvent composed of sodium silicate, alumina, and potassium hydroxide to replace the traditional organic silicone matrix, the technical problems of poor thermal stability and low thermal conductivity of organic materials are solved. In the background technology, organic silicone matrices are prone to thermal aging and carbonization under high-power laser irradiation. However, the all-inorganic material system of this invention forms a dense inorganic network structure with chemical bonds between phosphor particles and the substrate through a hydrogen-oxygen catalytic bonding mechanism. This allows the fluorescent film to maintain structural stability under high-power laser irradiation, achieving effective heat dissipation and improving the reliability and lifespan of solid-state lighting devices.

[0019] 2. This invention employs a room-temperature static curing process without sintering. The entire preparation process is carried out at a temperature of 15-30°C, solving the technical problem of thermal damage to the phosphor lattice structure caused by traditional high-temperature sintering processes (typically requiring 500-1000°C). High-temperature sintering in the background technology leads to lattice defects, surface roughening, and local phase transitions in phosphors, resulting in a decrease in quantum efficiency and emission intensity. This invention, however, preserves the original lattice structure of the phosphor completely through room-temperature curing, maintaining the phosphor's high quantum efficiency and luminescence intensity, and improving light conversion efficiency and brightness.

[0020] 3. This invention employs a simple process of sequential coating and room temperature curing, replacing the traditional complex high-temperature sintering or hot pressing process, thus solving the technical problems of high equipment investment, high energy consumption, and high cost in the prior art. This invention eliminates the need for high-temperature equipment and energy consumption, simplifies the production process, reduces equipment and manufacturing costs, and is suitable for large-scale industrial production. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the fabrication process of an all-inorganic fluorescent thin film for solid-state lighting; Figure 2 This is a photoluminescence spectrum of an all-inorganic fluorescent thin film with a sapphire substrate prepared according to an embodiment 1 of the present invention; Figure 3This is the electroluminescence spectrum of an all-inorganic fluorescent thin film with a sapphire substrate prepared according to an embodiment 1 of the present invention after being packaged into a light source; Figure 4 This is a cross-sectional SEM image of an all-inorganic fluorescent thin film with a sapphire substrate, prepared according to an embodiment 1 of the present invention. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0023] Preparation example: Preparation of bonding solvents Dissolve 5.0 g sodium silicate, 0.5 g nano alumina (average particle size 50 nm), and 1.5 g potassium hydroxide in 17.0 g pure water. Stir in a constant temperature water bath at 80°C for 2 hours until a homogeneous, transparent solution is formed with a viscosity of 200 mPa·s (measured at 25°C) and a pH of 12. Cool to room temperature for later use.

[0024] Example 1: Single-layer YAG fluorescent film on sapphire substrate Step 1: Substrate preparation Select a sapphire substrate with dimensions of 20mm×20mm×2mm, and ultrasonically clean it sequentially with acetone and anhydrous ethanol for 10 minutes each time. Rinse with deionized water and dry with nitrogen. Place the cleaned substrate into a silicone mold with dimensions of 20mm×20mm×20mm.

[0025] Step 2: Bonding solvent coating (see...) Figure 1 ) Weigh 0.2 g of the bonding solvent prepared in the preparation example and place it in the feed cylinder of the spin coater. The spin coater parameters are set as follows: first stage acceleration 360 rpm / s, second stage uniform speed 180 rpm, third stage stop, total spin coat time 120 s. After spin coating, allow it to stand for 30 minutes at room temperature (22°C) and relative humidity 50% to allow the bonding solvent to fully contact the sapphire substrate.

[0026] Step 3: Phosphor Coating Weigh 0.6g YAG:Ce 3+ Phosphor (particle size D50 = 15 μm, provided by ×× company) was uniformly coated onto the bonding solvent through a 1000-mesh stainless steel sieve with a scraper pressure of 0.3 MPa, forming a phosphor layer with a thickness of approximately 0.2 mm. The coating was then left to stand for 30 minutes under the same environmental conditions.

[0027] Step 4: Curing into a film The entire structure (fluorescent film, mold, and sapphire substrate) was placed in a 22°C environment and allowed to cure for 10 hours until the bonding solvent was completely cured. After curing, the film was removed from the mold.

[0028] Step 5: Performance Testing (1) Thickness test: The average thickness of the final inorganic fluorescent film was 0.52 mm, measured with a micrometer.

[0029] (2) Bonding strength test: The tape peeling method (ASTM D3359 standard) was used. The film and the substrate were firmly bonded and there was no peeling. The grade was 5B.

[0030] (3) Photoluminescence test (see Figure 2 The results were measured using an Edinburgh FLS980 fluorescence spectrometer, with a 450nm blue laser as the excitation source and an excitation power of 10mW. Figure 2 As shown, the excitation peak of the fluorescent film is located at 455 nm, and the emission peak is located at 560 nm. The peak wavelengths are consistent with those of the original YAG phosphor, indicating that the preparation process did not damage the phosphor's luminescence properties. The quantum efficiency is 92.5%.

[0031] (4) Packaging and testing (see) Figure 3 The prepared fluorescent film was encapsulated onto a blue LED light source (wavelength 450nm, power 3W). The measured white light output parameters were: color temperature 4282K, luminous flux 9884 lm, color rendering index Ra=61.2, and color coordinates CIE(0.3754, 0.3998). Figure 3 As shown, the electroluminescence spectrum shows a blue peak at 450 nm and a yellow peak at 560 nm, which together produce white light.

[0032] (5) Microstructure testing (see Figure 4 The cross-section of the thin film was observed using a scanning electron microscope (SEM, model JEOL JSM-7800F). Figure 4 As shown, the phosphor layer and the sapphire substrate are tightly bonded together by a bonding solvent layer, with no obvious pores or cracks at the interface. The bonding solvent layer is approximately 5-10 μm thick, and the phosphor particles are uniformly distributed within the inorganic network.

[0033] Example 2: Single-layer YAG fluorescent film on a quartz glass substrate The difference between this embodiment and Embodiment 1 is that the substrate material is quartz glass (20mm×20mm×2mm), while the other parameters and steps are the same as in Embodiment 1.

[0034] Test results: average film thickness 0.51 mm, bonding strength grade 5B, quantum efficiency 91.8%, white light output color temperature 4315 K, luminous flux 9756 lm.

[0035] Example 3: Fluorescent thin film with high phosphor ratio The difference between this embodiment and Embodiment 1 is that the mass ratio of the bonding solvent to the phosphor is 1:5, that is, 0.12g of bonding solvent and 0.6g of phosphor are weighed. Other parameters and steps are the same as in Embodiment 1.

[0036] Test results: The average film thickness is 0.48 mm, the bonding strength is 4B, the quantum efficiency is 88.3%, the white light output color temperature is 4156 K, and the luminous flux is 10521 lm (the luminous flux increases with the increase in phosphor content).

[0037] Example 4: Multilayer composite fluorescent thin film This embodiment prepares a fluorescent thin film with a bilayer composite structure, corresponding to claim 4.

[0038] A 20mm × 20mm × 2mm sapphire substrate was selected, and a first layer of bonding solvent (0.2g) and phosphor (0.6g) was coated according to the method in Example 1. The substrate was then allowed to stand at 22°C for 30 minutes. A second layer of bonding solvent (0.2g) and phosphor (0.6g) was then coated, and the substrate was allowed to stand for another 30 minutes. Finally, the substrate was allowed to cure at 22°C for 12 hours.

[0039] Test results: The total thickness of the film is 1.05 mm, containing two phosphor layers, each approximately 0.5 mm thick. The bonding strength is 5B, the quantum efficiency is 90.1%, and the white light output luminous flux is 15328 lm (due to the double-layer structure, the luminous flux is significantly improved).

[0040] Example 5: Using aluminate phosphor This embodiment verifies the applicability of other types of phosphors, corresponding to claim 5.

[0041] The method of Example 1 was used, but the phosphor was replaced with green aluminate phosphor SrAl2O4:Eu. 2+ ,Dy 3+ (Particle size D50 = 12 μm). The mass ratio of bonding solvent to phosphor is 1:3.

[0042] Test results: The average film thickness is 0.50 mm, and the bonding strength is grade 5B. Under 450 nm blue light excitation, the emission peak is located at 520 nm (green light), and the quantum efficiency is 85.6%.

[0043] Example 6: Mixed Phosphor System This embodiment uses a mixture of two phosphors.

[0044] The method of Example 1 was used, but the phosphor was changed to YAG:Ce. 3+ (Yellow powder) and CaAlSiN3:Eu 2+ A mixture of (red powder) in a mass ratio of 2:1, with a total mass of 0.6g.

[0045] Test results: The average thickness of the film is 0.53 mm, the emission spectrum includes a 560 nm yellow peak and a 650 nm red peak, the white light output color temperature is 3250 K (warm white light), and the color rendering index Ra=78.5 (improved color rendering).

[0046] Example 7: Different curing temperatures This embodiment verifies the upper limit of the temperature range.

[0047] The method of Example 1 was used, but the curing temperature was changed to 28°C and the curing time was 8 hours.

[0048] Test results: The average film thickness is 0.51 mm, the bonding strength grade is 5B, and the quantum efficiency is 91.2%. The curing temperature is relatively high, resulting in a faster curing speed; curing can be completed in 8 hours.

[0049] Example 8: Different curing temperatures (lower limit) This embodiment verifies the lower limit of the temperature range.

[0050] The method of Example 1 was used, but the curing temperature was changed to 16°C and the curing time was 18 hours.

[0051] Test results: The average film thickness is 0.50 mm, the bonding strength grade is 5B, and the quantum efficiency is 91.5%. The curing temperature is relatively low, and the curing speed is slow, requiring 18 hours to complete curing.

[0052] Comparative Example 1: Organosilicon matrix Fluorescent films were prepared using a traditional silicone encapsulation process.

[0053] 0.6g of YAG phosphor was mixed evenly with 2.0g of silicone rubber (methyl silicone rubber), coated onto a sapphire substrate, and cured at 120°C for 2 hours to obtain a fluorescent film with a thickness of about 0.5mm.

[0054] Test results: The initial quantum efficiency was 93.2%, but after irradiation with a high-power laser (5W blue laser) for 30 minutes, the quantum efficiency dropped to 68.5%, and yellowing and local carbonization appeared on the surface of the film.

[0055] Comparative Example 2: High-Temperature Sintered Ceramics YAG ceramic fluorescent sheets were prepared using a high-temperature sintering process.

[0056] YAG phosphor was sintered at 850°C for 4 hours to obtain a ceramic sheet with a thickness of about 0.5 mm.

[0057] Test results: Due to lattice damage caused by high-temperature sintering, the quantum efficiency was only 76.3%, which is 16.2 percentage points lower than that of the original phosphor (92.5%).

[0058] Performance comparison between the examples and comparative examples

[0059] As can be seen from the table above, the all-inorganic fluorescent thin film of the present invention maintains high quantum efficiency while exhibiting excellent thermal stability and low preparation cost.

Claims

1. A method for preparing an all-inorganic fluorescent thin film for solid-state lighting, comprising using an all-inorganic bonding solvent to solidify phosphor onto a substrate to form a fluorescent thin film, characterized in that, Includes the following steps: a) Prepare a substrate, one or more phosphors, and an all-inorganic bonding solvent, wherein the all-inorganic bonding solvent is composed of sodium silicate, alumina, potassium hydroxide, and pure water, wherein the mass percentage of sodium silicate is 16-22%, the mass percentage of alumina is 2-6%, the mass percentage of potassium hydroxide is 6-12%, and the balance is pure water. b) The all-inorganic bonding solvent is coated onto the substrate by spin coating, drop coating or spray coating. The parameters for spin coating are: acceleration 300-400 rpm / s, rotation speed 150-200 rpm, time 60-180 s. After coating, the substrate is left to stand at 15-30°C for 20-40 minutes to allow the bonding solvent to fully contact the substrate. c) The phosphor is applied by a scraping method using a 900–1100 mesh stainless steel screen, with a scraper pressure of 0.1–0.5 MPa and a single scraping thickness controlled at 0.1–0.3 mm. d) The substrate coated with the all-inorganic bonding solvent and the phosphor is statically cured at 15-30°C for 6-24 hours. The phosphor is anchored in the inorganic network by the condensation reaction of the silanol groups formed by the hydrolysis of sodium silicate and the hydroxyl groups on the substrate surface, and by the aluminosilicate three-dimensional network formed by the participation of alumina, thus forming the all-inorganic fluorescent film.

2. The method according to claim 1, characterized in that, The mass ratio of the inorganic bonding solvent to the phosphor in step a) is 1:0.5 to 1:

5.

3. The method according to claim 1 or 2, characterized in that, The substrate is placed inside the mold, which is made of silicone, epoxy resin or polyethylene.

4. The method according to any one of claims 1 to 3, characterized in that, Repeat steps b) and c) at least once, and after each repetition, let stand at 15-30°C for 20-40 minutes. Finally, perform step d) for final curing to form an all-inorganic fluorescent film with a multilayer composite structure.

5. The method according to any one of claims 1 to 4, characterized in that, The phosphor is selected from one or more of YAG-based phosphors, aluminate-based phosphors, nitride-based phosphors, and silicate-based phosphors.

6. The method according to any one of claims 1 to 5, characterized in that, Step c) involves coating the phosphor onto the bonding solvent using a sieve with a mesh size of 900 to 1100.

7. A fully inorganic fluorescent thin film for solid-state lighting, characterized in that, include: substrate; A bonding solvent layer is coated on the substrate. The bonding solvent layer is composed of a mixture of sodium silicate, alumina, potassium hydroxide, and pure water, wherein the mass percentage of sodium silicate is 16-22%, the mass percentage of alumina is 2-6%, the mass percentage of potassium hydroxide is 6-12%, and the balance is pure water. A phosphor layer is coated on the bonding solvent layer; The phosphor layer is bonded to the substrate via the bonding solvent layer through a hydrogen-oxygen catalytic bonding mechanism, and the all-inorganic fluorescent film is cured and formed at room temperature.

8. The all-inorganic fluorescent thin film according to claim 7, characterized in that, The phosphor is selected from one or more of YAG-based phosphors, aluminate-based phosphors, nitride-based phosphors, and silicate-based phosphors.

9. The all-inorganic fluorescent thin film according to claim 7 or 8, characterized in that, The all-inorganic fluorescent film has a multilayer composite structure.

10. The all-inorganic fluorescent thin film according to any one of claims 7 to 9, characterized in that, The substrate is an inorganic material rich in hydroxyl groups (–OH), preferably sapphire, quartz glass, fused silica, or silicon wafers treated with plasma or acid and alkali. The substrate surface should be clean and free of oil, and the water contact angle should be less than 30° to ensure effective condensation with silanol groups in the bonding solvent.

Images