Preparation method of high-quantum-efficiency coated fluorescent powder

Abstract

This invention discloses a method for preparing high-quantum-efficiency coated phosphors, belonging to the field of material surface treatment. By coating phosphors with hafnium oxide, coated phosphors with higher quantum efficiencies than the phosphors themselves are prepared. Furthermore, by optimizing the process parameters of the atomic layer deposition scheme, the problems of bubbling, delamination, and porosity caused by the reaction of traditional alumina film coating of fluoride phosphor particles, resulting in uneven film coating and a decrease in quantum efficiency, are solved. This invention achieves the goal of coating the surface of fluoride phosphor particles with a highly uniform and stable hafnium oxide film using atomic layer deposition technology, thereby improving the water resistance and quantum efficiency of the fluoride phosphors.

Description

Technical Field

[0001] This invention relates to a method for preparing a high quantum efficiency coated phosphor, belonging to the field of material surface treatment. Background Technology

[0002] LEDs possess core advantages such as energy saving, long lifespan, environmental friendliness, and small size, and have been widely used in the global lighting and display fields. Phosphor-converted white LEDs (pc-wLEDs) are currently the mainstream white LED technology in general lighting, display backlighting, and other fields. Traditional pc-wLEDs use blue InGaN chips with yellow YAG:Ce LEDs. 3+ Phosphors achieve white light, but these LEDs lack red light components, have a high color temperature, and a low color rendering index. Therefore, it is crucial to develop a red phosphor with high stability and good luminous performance. Currently, the mainstream red phosphors are Mn... 4+ Doping with fluorides and Eu 2+ Doped nitrides, wherein Mn 4+ Fluoride-doped phosphors have narrow emission spectra (Mn) 4+ Fluoride doping has a full width at half maximum (FWHM) of 2-5 nm, Eu 2+ Doped nitrides (with a full width at half maximum (FWHM) of 80-90 nm) have attracted widespread attention, and their application in the display field is extremely beneficial for improving display color gamut performance. However, Mn... 4+ Fluoride-doped phosphors have poor stability and are prone to decomposition when exposed to moisture. Once decomposed, they will lead to the formation of Mn. 4+ Deactivation destroys the luminescent centers, resulting in a significant reduction in the luminescence intensity of the phosphor. Furthermore, the decomposition products (such as dark brown manganese oxides) adhere to the surface of the phosphor particles, hindering the absorption of excitation light and the emission of fluorescence, leading to a decrease in luminescence efficiency (quantum efficiency) and color purity. Therefore, the development of highly stable fluoride phosphors is of great significance.

[0003] Coating phosphor particles with a protective film has been proven to effectively improve phosphor stability. Atomic layer deposition (ALD) technology is widely used in various fields due to its ability to control film thickness and uniformity at the atomic scale. Therefore, researchers have used ALD to coat phosphor particles with alumina films. The precursor trimethylaluminum used in ALD is easily decomposed and can form alumina with oxygen or carboxyl groups over a wide temperature window, thus preparing a powder coating layer. For example, patent CN110343518A discloses a method for coating fluoride phosphors based on ALD technology. The method adjusts the reactant purging time according to the number of cycles, controlling the total reaction time to no more than 2 hours, and successfully coats alumina onto the surface of fluoride phosphors using trimethylaluminum and ozone as precursors. Patent CN105038776A discloses a method for preparing highly stable manganese-doped potassium fluorosilicate using ALD technology. By setting the window temperature to 185°C and controlling the airflow speed and flow rate, ALD is performed for 48 hours. Using oxygen as a precursor, alumina was successfully coated onto the surface of fluoride phosphors. However, while the method of coating alumina onto the surface of fluoride phosphors disclosed in the two patents solves the waterproofing problem to some extent, the trimethylaluminum precursor involved in atomic layer deposition undergoes a ligand exchange reaction with the surface of fluoride phosphors to form volatile AlF3. This causes blistering, porosity, and delamination in the alumina coating layer, resulting in incomplete coating. Water vapor can pass through the pores, leading to surface deterioration. Therefore, this solution does not completely solve the problem of improving the waterproofing performance of phosphors and also brings the additional problem of reducing the quantum efficiency of phosphors.To further improve the waterproof performance of fluorescent powders, the paper "Stabilizing FluoridePhosphors: Surface Modification by Atomic Layer Deposition[J]. Chemistry of Materials, 2019, 31(18):7192-7202.DOI:10.1021 / acs.chemmater.9b01491" proposes a method of coating titanium dioxide to enhance its waterproof performance. However, in practical applications, due to the high activity of titanium dioxide and the presence of a large number of Ti-OH bonds (surface hydroxyl groups) on its surface, these hydroxyl groups can trap photogenerated electrons, leading to nonradiative recombination and reducing quantum efficiency. Simultaneously, titanium dioxide has a high refractive index (n ≈ 0.05). (2.5-2.9) On the one hand, the Fresnel reflection of the incident excitation light at the interface between the coating layer and the phosphor increases, resulting in a lower excitation efficiency. On the other hand, the light emitted by the phosphor particles is more likely to form total internal reflection due to the large difference in refractive index between the coating layer and air. The light is confined within the coating layer, and the propagation path in the titanium dioxide coating film becomes longer, causing photons to undergo multiple reflections before escaping the material, which also leads to a further reduction in quantum efficiency. Therefore, it is necessary to develop a coating phosphor solution that improves quantum efficiency while ensuring its waterproof performance. Summary of the Invention

[0004] To further improve the quantum efficiency of phosphors and enable their application in high-quantum-efficiency scenarios (high efficiency means less light is converted into heat, saving energy; it also reduces the thermal quenching effect of phosphors and allows excitation chips, such as blue LED chips, to operate at lower temperatures, resulting in higher efficiency and longer lifespan. This is particularly suitable for enclosed environments where heat dissipation is difficult, such as automotive headlights), this invention proposes a hafnium oxide-coated phosphor scheme. Combining the characteristics of hafnium oxide precursors, the properties of hafnium oxide itself, and the impact of hafnium oxide coating on the phosphor surface, the atomic layer deposition process parameters for hafnium oxide-coated phosphor were specifically investigated. A method for preparing high-quantum-efficiency coated phosphors was developed, and its waterproof performance was further improved, providing more possibilities for its applications.

[0005] A method for preparing a high quantum efficiency coated phosphor, using an atomic layer deposition apparatus, the method comprising: Step 1: Place the fluoride phosphor into the deposition chamber inside the cavity; Step 2: Set the cavity temperature and pipeline temperature; Step 3: Using nitrogen as the carrier gas, tetrakis(dimethylamino)hafnium is introduced into the deposition chamber to purge the phosphor. Step 4: Stop loading tetra(dimethylamino)hafnium, introduce nitrogen gas into the deposition chamber, and purge the phosphor. Step 5: Stop the nitrogen flow and introduce ozone into the deposition chamber to purge the phosphor. Step 6: Stop the ozone supply and introduce nitrogen into the deposition chamber to purge the phosphor. Step 7: Flip the phosphor, and then repeat steps 3 to 6 N times. Step 8: Stop the nitrogen gas supply and allow the deposition chamber to cool naturally to obtain fluoride phosphor with a hafnium oxide film coating on the particle surface.

[0006] Optionally, the fluoride phosphor includes manganese-doped potassium fluorosilicate K2SiF6:Mn and manganese-doped potassium fluorotitanate K2TiF6:Mn, wherein the molar percentage of Mn is 0.5%-10%; the phosphor particle size is 10nm–100μm; and the hafnium oxide coating thickness is 2nm–100nm.

[0007] Optionally, in step 2, the cavity temperature is set to 80~130℃ and the pipeline temperature is set to 50~100℃.

[0008] Optionally, in step 3, the tetra(dimethylamino)hafnium purging time is 50~500ms.

[0009] Optionally, in steps 4 and 6, the nitrogen purging time is 10~30s.

[0010] Optionally, in step 5, the ozone purging time is 100~300ms.

[0011] Optionally, in step 7, N is 200 to 500 times; the flipping method includes manual flipping and automatic machine flipping.

[0012] The present invention also provides a high quantum efficiency coated phosphor, which is prepared by the above method.

[0013] The present invention also provides a method for improving the quantum efficiency of coated phosphors, wherein the method involves coating a hafnium oxide thin film onto the surface of a fluoride phosphor using an atomic layer deposition method.

[0014] Optionally, the method includes: Step 1: Place the fluoride phosphor into the deposition chamber inside the cavity; Step 2: Set the cavity temperature and pipeline temperature; Step 3: Using nitrogen as the carrier gas, tetrakis(dimethylamino)hafnium is introduced into the deposition chamber to purge the phosphor. Step 4: Stop loading tetra(dimethylamino)hafnium, introduce nitrogen gas into the deposition chamber, and purge the phosphor. Step 5: Stop the nitrogen flow and introduce ozone into the deposition chamber to purge the phosphor. Step 6: Stop the ozone supply and introduce nitrogen into the deposition chamber to purge the phosphor. Step 7: Flip the phosphor, and then repeat steps 3 to 6 N times. Step 8: Stop the nitrogen gas supply and allow the deposition chamber to cool naturally to obtain fluoride phosphor with a hafnium oxide film coating on the particle surface.

[0015] The beneficial effects of this invention are: By using hafnium oxide to coat phosphors, a coated phosphor with higher quantum efficiency than the phosphor itself was prepared. Furthermore, by optimizing the process parameters of the atomic layer deposition scheme, the problems of bubbling, delamination, and pores caused by the reaction of traditional alumina film coating of fluoride phosphor particles, as well as uneven film coating and subsequent decrease in quantum efficiency, were solved. This enabled the atomic layer deposition technology to coat the surface of fluoride phosphor particles with a highly uniform and stable hafnium oxide film, thereby improving the water resistance and quantum efficiency of the fluoride phosphor. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating the process of coating fluoride phosphors into nanoscale thin films using atomic layer deposition technology, as described in this invention.

[0018] Figure 2 This is a quantum efficiency graph of the phosphor in the comparative sample of Example 2 of the present invention.

[0019] Figure 3 This is a quantum efficiency diagram of the encapsulated phosphor prepared in Example 2 of the present invention.

[0020] Figure 4 This is a quantum efficiency diagram of the encapsulated phosphor prepared in Example 3 of the present invention.

[0021] Figure 5 This is a quantum efficiency diagram of the encapsulated phosphor prepared in Example 4 of the present invention.

[0022] Figure 6 This is a diagram showing the state of the coated phosphor prepared by the method provided in this invention immersed in a glass bottle containing deionized water.

[0023] Figure 7This is a photograph of the phosphor coating prepared by the method of this invention, after being immersed in deionized water for one week, and then irradiated with 460nm blue light of the same intensity. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] Example 1 This embodiment provides a method for preparing a high quantum efficiency coated phosphor, which is prepared using an atomic layer deposition (ALD) device. See [link to relevant documentation]. Figure 1 The method includes: Step 1: Place the fluoride phosphor into the deposition chamber inside the cavity; The fluoride phosphor used in this solution is commercially available.

[0026] Step 2: Set the cavity temperature and pipeline temperature; The cavity temperature is set to 80~130℃, and the pipeline temperature is set to 50~100℃.

[0027] In some embodiments of the present invention, the cavity temperature is preferably 120°C; in some embodiments of the present invention, the pipeline temperature is preferably 70°C.

[0028] Step 3: Using nitrogen as the carrier gas, tetrakis(dimethylamino)hafnium is introduced into the deposition chamber to purge the phosphor. Tetra(dimethylamino)hafnium is placed in a steel cylinder, which is heated with a metal wire mesh bag to a temperature of 70°C to generate vapor pressure so that vapor can be ejected. The purging time of tetra(dimethylamino)hafnium is 50~500ms; in some embodiments of the present invention, the purging time of tetra(dimethylamino)hafnium is preferably 200ms.

[0029] Step 4: Stop loading tetra(dimethylamino)hafnium, introduce nitrogen gas into the deposition chamber, and purge the phosphor. The nitrogen purging time is 10-30 seconds. In some embodiments of the present invention, the nitrogen purging time is preferably 20 seconds.

[0030] Step 5: Stop the nitrogen flow and introduce ozone into the deposition chamber to purge the phosphor. The ozone purging time is 100~300ms, and in some embodiments of the present invention, the ozone purging time is preferably 200ms.

[0031] Step 6: Stop the ozone supply and introduce nitrogen into the deposition chamber to purge the phosphor. The nitrogen purging time is 10-30 seconds. In some embodiments of the present invention, the nitrogen purging time is preferably 20 seconds.

[0032] Step 7: Remove the phosphor and disperse it on the wire mesh covering the metal disc, allowing the phosphor to disperse, agitate, and deposit at the bottom of the disc. Place the disc containing the phosphor into the cavity. Figure 1 As shown, steps 3 through 6 are then repeated. Steps 3 to 6 are repeated 200 to 500 times. In one embodiment of the present invention, the number of repetitions is preferably 200 times, and the coating thickness is 9.4 nm, that is, the thickness of each cycle is approximately 0.047 nm. In another embodiment of the present invention, the number of repetitions is preferably 300 times. In another embodiment of the present invention, the number of repetitions is preferably 400 times. In practical applications, different numbers of repetitions can be set according to the actual required coating thickness, and different coating thicknesses can also be achieved by changing other deposition parameters. The present invention does not limit this.

[0033] Step 8: Stop the nitrogen gas supply and allow the deposition chamber to cool naturally to obtain fluoride phosphor with a hafnium oxide film coating on the particle surface.

[0034] Example 2 This embodiment provides a method for preparing a high-quantum-efficiency coated phosphor using an atomic layer deposition (ALD) apparatus. Based on Example 1, this embodiment sets specific ALD process parameters to obtain a hafnium oxide thin film-coated phosphor. To verify the quantum efficiency improvement effect of this method, an uncoated fluoride phosphor is selected as a control sample for comparison with the quantum efficiency of the coated phosphor prepared using this method.

[0035] Specifically, the fluoride phosphor K2SiF6:Mn obtained from commercial purchases 4+ (The grain size varies from 10nm to 100μm, with an average size of about 1μm.) Weigh 1.5g of fluoride phosphor and place it into the deposition chamber of the atomic layer deposition equipment. Then open all the gas valves of the atomic layer deposition equipment, set the deposition parameters, turn on the high-purity nitrogen gas of the atomic layer deposition equipment as the carrier gas, set the deposition temperature to 120℃, the nitrogen flow rate to 15ml / min, the ozone flow rate to 50ml / min, the chamber temperature to 120℃, the pipeline temperature to 70℃, the precursor tetra(dimethylamino)hafnium purging time to 200ms, the ozone purging time to 200ms, and the nitrogen purging time to 20s.

[0036] Atomic layer deposition begins and ends after 200 cycles, yielding a hafnium oxide thin film-coated sample, denoted as 200Hf.

[0037] The quantum efficiency of the control sample and the 200 Hf sample prepared using the method described in this application were determined using a Horiba Aqualog fluorescence spectrometer. Figure 2 As shown, the quantum efficiency of the comparative sample is 86.27%; Figure 3 As shown, the quantum efficiency of the 200Hf sample prepared using the scheme of this application is 90.9%.

[0038] Depend on Figure 2 and Figure 3 It is known that after applying the hafnium oxide coating to fluoride phosphors using the scheme provided in this application, their quantum efficiency is higher than that of uncoated fluoride phosphors. This is in stark contrast to the results of existing methods that reduce the quantum efficiency after coating with alumina or titanium oxide (for an explanation of the quantum efficiency of fluoride phosphors after coating with alumina or titanium oxide, please refer to the comparative patent CN110343518A and the article "Stabilizing Fluoride Phosphors: Surface Modification by Atomic Layer Deposition[J]").

[0039] The reason why the quantum efficiency of fluoride phosphors is higher than that of uncoated fluoride phosphors after being coated with hafnium oxide is that the present application can passivate the dangling bonds on the phosphor surface after coating, reduce the probability of recombination of phosphor surface defects, and thus improve the quantum efficiency. Therefore, the quantum efficiency of the coated phosphors is higher than that of the uncoated fluoride phosphors themselves.

[0040] Example 3 This embodiment provides a method for preparing a high quantum efficiency coated phosphor using an atomic layer deposition (ALD) device. Based on Example 1, this embodiment sets specific ALD process parameters to obtain a hafnium oxide thin film coated phosphor. Uncoated fluoride phosphor is used as a comparative sample.

[0041] The difference between this embodiment and Embodiment 2 is that the number of cycles in the deposition process is 300.

[0042] Specifically, the fluoride phosphor K2SiF6:Mn obtained from commercial purchases 4+Weigh 1.5g of fluoride phosphor and place it into the deposition chamber of the atomic layer deposition equipment. Then, open all the gas valves of the atomic layer deposition equipment, set the deposition parameters, turn on the high-purity nitrogen gas of the atomic layer deposition equipment as the carrier gas, set the deposition temperature to 120℃, the nitrogen flow rate to 15ml / min, the ozone flow rate to 50ml / min, the chamber temperature to 120℃, the pipeline temperature to 70℃, the precursor tetra(dimethylamino)hafnium purging time to 200ms, the ozone purging time to 200ms, and the nitrogen purging time to 20s.

[0043] Atomic layer deposition begins, and the deposition ends after 300 cycles, yielding a hafnium oxide thin film-coated sample, denoted as 300.

[0044] like Figure 4 As shown, the quantum efficiency of sample 300, measured using a Horiba Aqualog fluorescence spectrometer, was 91.62%, which is also higher than... Figure 2 The quantum efficiency of the comparative samples is shown.

[0045] Example 4 This embodiment provides a method for preparing a high quantum efficiency coated phosphor using an atomic layer deposition (ALD) device. Based on Example 1, this embodiment sets specific ALD process parameters to obtain a hafnium oxide thin film coated phosphor. Uncoated fluoride phosphor is used as a comparative sample.

[0046] The difference between this embodiment and Embodiment 2 is that the number of cycles in the deposition process is 400.

[0047] Specifically, the fluoride phosphor K2SiF6:Mn obtained from commercial purchases 4+ Weigh 1.5g of fluoride phosphor and place it into the deposition chamber of the atomic layer deposition equipment. Then, open all the gas valves of the atomic layer deposition equipment, set the deposition parameters, turn on the high-purity nitrogen gas of the atomic layer deposition equipment as the carrier gas, set the deposition temperature to 120℃, the nitrogen flow rate to 15ml / min, the ozone flow rate to 50ml / min, the chamber temperature to 120℃, the pipeline temperature to 70℃, the precursor tetra(dimethylamino)hafnium purging time to 200ms, the ozone purging time to 200ms, and the nitrogen purging time to 20s.

[0048] Atomic layer deposition begins, and the deposition ends after 400 cycles, yielding a hafnium oxide thin film-coated sample, denoted as 400.

[0049] like Figure 5 As shown, the quantum efficiency of sample 400, measured using a Horiba Aqualog fluorescence spectrometer, was 91.08%, which is also higher than... Figure 2 The quantum efficiency of the comparative samples is shown.

[0050] To further verify the coating performance of the method of this application on fluoride phosphors, samples 200 Hf, 300, and 400 were immersed in glass bottles containing deionized water, respectively. Figure 6 As shown, after standing for one week, the fluorescence power of the phosphor at the same location was measured using an optical power meter under the same intensity of 460nm blue light. The luminescence characteristics are as follows. Figure 7 As shown, the phosphors still emit light after being soaked for a week, demonstrating their good waterproof performance. Sample 300 exhibits the highest fluorescence power retention rate, at 95.2% of the initial value, indicating that its fluorescence power remains good even after a week of soaking. In contrast, existing phosphors coated with alumina show that their optimal fluorescence power drops to 87% of the initial value after immersion in water for 2 hours (see Table 1 of comparative patent CN110343518A). Therefore, the phosphors coated with hafnium oxide film in this application have superior waterproof performance.

[0051] Some steps in the embodiments of the present invention can be implemented using software, and the corresponding software program can be stored in a readable storage medium, such as an optical disc or a hard disk.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high quantum efficiency coated phosphor, comprising using an atomic layer deposition apparatus, characterized in that, The method includes: Step 1: Place the fluoride phosphor into the deposition chamber inside the cavity; Step 2: Set the cavity temperature and pipeline temperature; Step 3: Using nitrogen as the carrier gas, tetrakis(dimethylamino)hafnium is introduced into the deposition chamber to purge the phosphor. Step 4: Stop loading tetra(dimethylamino)hafnium, introduce nitrogen gas into the deposition chamber, and purge the phosphor. Step 5: Stop the nitrogen flow and introduce ozone into the deposition chamber to purge the phosphor. Step 6: Stop the ozone supply and introduce nitrogen into the deposition chamber to purge the phosphor. Step 7: Flip the phosphor, and then repeat steps 3 to 6 N times. Step 8: Stop the nitrogen gas supply and allow the deposition chamber to cool naturally to obtain fluoride phosphor with a hafnium oxide film coating on the particle surface.

2. The method according to claim 1, characterized in that, The fluoride phosphor comprises manganese-doped potassium fluorosilicate K2SiF6:Mn and manganese-doped potassium fluorotitanate K2TiF6:Mn, wherein the molar percentage of Mn is 0.5%-10%; the phosphor particle size is 10nm–100μm; and the hafnium oxide coating thickness is 2nm–100nm.

3. The method according to claim 1, characterized in that, In step 2, the temperature of the atomic layer deposition chamber is set to 80~130℃, and the temperature of the gas pipeline is set to 50~100℃.

4. The method according to claim 1, characterized in that, In step 3, tetra(dimethylamino)hafnium is placed in a steel cylinder, which is heated with a metal wire mesh bag to a temperature of 70°C to generate vapor pressure and release steam; the steam purging time is 50~500ms.

5. The method according to claim 1, characterized in that, In steps 4 and 6, the nitrogen purging time is 10-30 seconds.

6. The method according to claim 1, characterized in that, In step 5, the ozone purging time is 100~300ms.

7. The method according to claim 1, characterized in that, In step 7, N is 200 to 500 times.

8. A high quantum efficiency coated phosphor, characterized in that, The coated phosphor is prepared using any one of the methods described in claims 1-7.

9. A method for improving the quantum efficiency of coated phosphors, characterized in that, The method involves coating a hafnium oxide thin film onto the surface of a fluoride phosphor using atomic layer deposition.

10. The method according to claim 9, characterized in that, The method includes: Step 1: Place the fluoride phosphor into the deposition chamber inside the cavity; Step 2: Set the cavity temperature and pipeline temperature; Step 3: Using nitrogen as the carrier gas, tetrakis(dimethylamino)hafnium is introduced into the deposition chamber to purge the phosphor. Step 4: Stop loading tetra(dimethylamino)hafnium, introduce nitrogen gas into the deposition chamber, and purge the phosphor. Step 5: Stop the nitrogen flow and introduce ozone into the deposition chamber to purge the phosphor. Step 6: Stop the ozone supply and introduce nitrogen into the deposition chamber to purge the phosphor. Step 7, flipping, including manual flipping and automatic machine flipping of phosphor, then repeating steps 3 to 6 N times; Step 8: Stop the nitrogen gas supply and allow the deposition chamber to cool naturally to obtain fluoride phosphor with a hafnium oxide film coating on the particle surface.

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