A type of Mn 4+ Surface treatment method for fluoride-doped red phosphor
By constructing a Mn4+-depleted layer on the surface of K2SiF6:Mn4+ phosphor, the problem of phosphor hydrolysis in humid environments was solved, achieving high-efficiency luminescence performance under high temperature and high humidity conditions and improving the stability of white LED devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTHEAST UNIV
- Filing Date
- 2024-03-11
- Publication Date
- 2026-05-12
AI Technical Summary
K2SiF6:Mn4+ red phosphor is easily hydrolyzed into dark brown manganese oxide in humid environments, which leads to a sharp decrease in luminous performance and limits the performance improvement and application promotion of white LED devices.
Phosphors were treated with niobium oxide and potassium hydrofluoride in hydrofluoric acid solution, combined with hydrothermal reaction, to construct a Mn4+-depleted layer, modify surface defects, reduce water molecule diffusion channels, and passivate [MnF6]2-, thereby improving the moisture resistance of the phosphor.
It significantly improves the moisture resistance of phosphors, enabling them to maintain an internal quantum efficiency of 92.56% and an initial luminous intensity of 100.64% under high temperature and high humidity conditions, thus ensuring the long-term stability of white LED devices.
Smart Images
Figure CN118291129B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a Mn 4+ Surface treatment method for fluoride-doped red phosphor. Background Technology
[0002] Phosphor-converting white LEDs offer advantages such as energy efficiency, environmental friendliness, high brightness, long lifespan, and simple manufacturing processes, making them a mainstream lighting source in the lighting and display industries. White LEDs are primarily manufactured by combining blue LED chips with multi-color phosphors. Among these, red phosphors play a crucial role in optimizing and improving the color rendering index, color temperature, color gamut, and other light color parameters of the lighting source. Currently, commercially available red phosphors for LEDs mainly include Eu... 2+ Activated nitride phosphors and Mn 4+ There are two main categories of activated fluoride phosphors. Among them, the fluoride-type red phosphor K2SiF6:Mn 4+ It possesses unique advantages such as narrow-band red light emission around 630nm, high luminous efficiency, and high thermal stability, making it highly suitable for the demands of high-quality wide color gamut backlight displays. However, K2SiF6:Mn 4+ The key technical challenge of red phosphors lies in their poor moisture resistance; the [MnF6] on the phosphor surface... 2- The fluorinated groups readily hydrolyze into dark brown manganese oxides in humid environments, which adhere to the surface, severely hindering the excitation of excitation light and the emission process of the phosphor. This leads to a sharp decrease in luminescence performance, limiting the performance improvement and application of display and lighting devices. The high operating temperature of white LED devices further exacerbates the degradation effect of the aforementioned fluoride phosphors. To overcome this problem, there is an urgent need to develop a method to improve the luminescence performance of K2SiF6:Mn. 4+ This technology improves the moisture and heat resistance of red phosphors, thereby enhancing their long-term stability.
[0003] Currently regarding K2SiF6:Mn 4+ Methods to improve the moisture resistance of red phosphors mainly include constructing organic coating shells, inorganic heterogeneous shells, and inorganic homogeneous shells. Organic coatings effectively improve the water resistance of phosphors by utilizing the hydrophobic properties of organic materials, but they suffer from poor thermal stability and are easily penetrated by water molecules, thus eroding the internal phosphor. Inorganic heterogeneous shells utilize the density of oxides, etc., to prevent water vapor from contacting the internal phosphor; however, because they are different from the matrix material and opaque, they inevitably lead to a decrease in luminescence performance while improving the phosphor's water resistance. Inorganic homogeneous shells possess the same physicochemical properties as the internal phosphor and can act as a surface shielding layer to prevent water molecules from hydrolyzing K2SiF6:Mn. 4+ [MnF6] inside the phosphor 2-Furthermore, it has a relatively small impact on the luminescence performance of phosphors, but the degree of improvement is still limited to the inherent properties of the matrix itself. There is still room for improvement in the luminescence performance and luminescence stability of the modified phosphors. Summary of the Invention
[0004] Purpose of the invention: The purpose of this invention is to provide a Mn 4+ A surface treatment method for doped fluoride red phosphors, which can significantly improve the surface treatment efficiency of Mn. 4+ Fluoride-doped red phosphors improve moisture resistance without affecting their initial luminescence performance, thus maintaining high luminescence performance even in extreme humid and hot environments, thereby improving the long-term stability of white LED devices.
[0005] Technical solution: The Mn described in this invention 4+ A surface treatment method for fluoride-doped red phosphors includes the following steps:
[0006] (1) Niobium oxide was dissolved in an aqueous solution of hydrofluoric acid under constant temperature water bath to obtain a fluoroniobic acid solution; Mn 4+ Fluoride-doped red phosphor was added to a fluoroniobic acid solution and stirred thoroughly in a constant temperature water bath. The phosphor after reaction was washed and dried to obtain a preliminarily modified phosphor.
[0007] (2) Dissolve potassium hydrofluoride and thiourea in hydrofluoric acid aqueous solution to obtain hydrothermal mixed solution; add the preliminarily modified phosphor to hydrothermal mixed solution and carry out hydrothermal reaction at high temperature; wash and dry the phosphor after reaction to obtain modified fluoride red phosphor.
[0008] In step (1), the Mn 4+ The chemical formula of the fluoride-doped red phosphor is K₂SiF₆:Mn. 4+ .
[0009] In steps (1) to (2), the mass fraction of the hydrofluoric acid aqueous solution is 49%.
[0010] In step (1), the concentration of fluoroniobic acid in the fluoroniobic acid solution is 0.25 to 2 mol / L.
[0011] In step (1), niobium oxide and Mn 4+ The molar ratio of fluoride-doped red phosphor is 2.5 to 20:10.
[0012] In step (1), the stirring conditions are: temperature of 80℃, speed of 150-200 rpm, and stirring time of 20-40 min.
[0013] In step (2), the concentration of potassium hydrofluoric acid in the hydrothermal mixed solution is 1-8 mol / L; the concentration of thiourea is 0.01 g / mL.
[0014] In step (2), the hydrothermal reaction conditions are: reaction temperature of 150-200℃ and reaction time of 8-16h.
[0015] In step (1), the washing and drying conditions are as follows: the reaction product is washed 3 to 5 times with anhydrous ethanol and then dried at 80°C for no less than 2 hours.
[0016] In step (2), the washing and drying conditions are as follows: the reaction product is washed repeatedly 3 to 5 times with 0.02 g / mL thiourea aqueous solution and anhydrous ethanol, and then dried at 80°C for 2 hours.
[0017] The method of this invention first involves K2SiF6:Mn 4+ In Nb 5+ -In HF solution, the surface dissolves and ionizes to release free K+. + and [SiF6] 2- [MnF6] 2- The group is also constantly recrystallizing; when dissolution and crystallization reach dynamic equilibrium, Nb 5+ With free [MnF6] 2- A disproportionation reaction occurs, changing its valence to Mn. 2+ It cannot be doped into the phosphor again, thus creating a Mn-poor environment on the phosphor surface. 4+ Layer. Second step K2SiF6:Mn 4+ Under the high temperature and high pressure environment of hydrothermal treatment, phosphors undergo vigorous dissolution and recrystallization on their surface, promoting surface atomic rearrangement, modifying surface defects, resulting in better surface crystallinity, reducing water molecule diffusion channels, and decreasing the degree of water molecule reaction with the surface; simultaneously, under the action of reducing thiourea, the dissolved [MnF6] can be further dissolved. 2- Passivation reinforces the surface Mn-poor 4+ The layers are made denser, thus significantly improving the K2SiF6:Mn content. 4+ Moisture resistance of fluorescent powder.
[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the Mn obtained by the method of the present invention 4+ Fluoride-doped red phosphor materials exhibit significantly improved water resistance with almost no impact on the initial luminescence performance of the phosphor. Even after 6 days of degradation under high temperature and high humidity conditions, they still maintain an internal quantum efficiency of 92.56% and an initial luminescence intensity of 100.64%, thus enabling the long-term stable use of white LED devices. Attached Figure Description
[0019] Figure 1 The graph shows the comparison of the internal quantum efficiency of the surface-modified red phosphor materials prepared in Examples 1-8 of this invention before and after degradation for 6 days in a high temperature and high humidity (85℃ / 85%RH) environment.
[0020] Figure 2 The graph shows the comparison of the internal quantum efficiency of the surface-modified red phosphor materials prepared in Examples 9-13 of this invention before and after degradation for 6 days in a high temperature and high humidity (85℃ / 85%RH) environment.
[0021] Figure 3 The following are excitation and emission spectra of the phosphors in Examples 4 and 11 of the present invention and the phosphors without surface modification.
[0022] Figure 4 These are actual images of the phosphors from Examples 4 and 11 of the present invention and the phosphors without surface modification before and after degradation for 6 days in a high temperature and high humidity (85℃ / 85%RH) environment;
[0023] Figure 5 The graph shows the changes in internal quantum efficiency of the phosphors in Examples 4 and 11 of this invention and the phosphors without surface modification under high temperature and high humidity (85℃ / 85%RH) conditions.
[0024] Figure 6 Normalized luminescence intensity variation graphs of Example 4, Example 11 and unmodified phosphors of the present invention under high temperature and high humidity (85℃ / 85%RH) environment;
[0025] Figure 7 The fluorescence lifetimes of the phosphors in Examples 4 and 11 of this invention and the phosphors without surface modification treatment;
[0026] Figure 8 The fluorescence lifetime of the phosphors in Examples 4 and 11 of the present invention and the phosphors without surface modification after 6 days of degradation in a high temperature and high humidity (85℃ / 85%RH) environment;
[0027] Figure 9 The images show actual photos and normalized luminescence intensity changes of the phosphors from Examples 4 and 11 of this invention, as well as the unmodified phosphors, after immersion in deionized water for 360 minutes. Detailed Implementation
[0028] Example 1
[0029] Prepare raw materials: 2.5 mmol Nb₂O₅, phosphor K₂SiF₆:Mn 4+10 mmol of HF (49 wt%) aqueous solution in 20 mL; first, 2.5 mmol of Nb₂O₅ was fully dissolved in 20 mL of hydrofluoric acid aqueous solution (49 wt%) in an 80 °C constant temperature water bath to obtain a fluoroniobic acid solution with a concentration of 0.25 mol / L, and then 10 mmol of phosphor K₂SiF₆:Mn 4+ The phosphor was placed in the above fluoroniobic acid solution and stirred at a constant temperature of 200 rpm for 30 min. After the reaction, the phosphor was washed with anhydrous ethanol 3 to 5 times and then dried at 80°C for 2 h to obtain the phosphor after surface passivation treatment.
[0030] Example 2
[0031] Example 2 was prepared in the same way as Example 1, except that the amount of raw material Nb2O5 added was 5 mmol, which yielded a fluoroniobic acid solution with a concentration of 0.50 mol / L, and finally obtained a phosphor with surface passivation treatment.
[0032] Example 3
[0033] Example 3 was prepared in exactly the same way as Example 1, except that the amount of raw material Nb2O5 added was 7.5 mmol, which yielded a fluoroniobic acid solution with a concentration of 0.75 mol / L, and finally obtained a phosphor with surface passivation treatment.
[0034] Example 4
[0035] Example 4 was prepared in the same way as Example 1, except that the amount of raw material Nb2O5 added was 10 mmol, which yielded a fluoroniobic acid solution with a concentration of 1.0 mol / L, and finally obtained a phosphor with surface passivation treatment.
[0036] Example 5
[0037] Example 5 was prepared in exactly the same way as Example 1, except that the amount of raw material Nb2O5 added was 12.5 mmol, which yielded a fluoroniobic acid solution with a concentration of 1.25 mol / L, and finally obtained a phosphor with surface passivation treatment.
[0038] Example 6
[0039] Example 6 was prepared in the same way as Example 1, except that the amount of raw material Nb2O5 added was 15 mmol, which yielded a fluoroniobic acid solution with a concentration of 1.50 mol / L, and finally obtained a phosphor with surface passivation treatment.
[0040] Example 7
[0041] Example 7 was prepared in exactly the same way as Example 1, except that the amount of raw material Nb2O5 added was 17.5 mmol, which yielded a fluoroniobic acid solution with a concentration of 1.75 mol / L, and finally obtained a phosphor with surface passivation treatment.
[0042] Example 8
[0043] Example 8 was prepared in the same way as Example 1, except that the amount of raw material Nb2O5 added was 20 mmol, which yielded a fluoroniobic acid solution with a concentration of 2.0 mol / L, and finally obtained a phosphor with surface passivation treatment.
[0044] The K2SiF6:Mn obtained in Examples 1-8 4+ The internal quantum efficiency of the phosphor before and after degradation for 6 days in a high temperature and high humidity (85℃ / 85%RH) environment is as follows: Figure 1 As shown, the phosphors after surface passivation treatment all maintained high internal quantum efficiencies, indicating that the surface passivation treatment has almost no effect on the luminescence performance of the phosphors themselves. After 6 days of treatment in an extreme humid and hot environment, the untreated K2SiF6:Mn 4+ The internal quantum efficiency of the phosphor decreased from 92.90% to 14.62%, essentially losing its luminescent properties. In contrast, the internal quantum efficiencies of the phosphors in Examples 1-8 all remained above 50%, indicating that the phosphors were not completely degraded and maintained a certain level of luminescent performance. Example 4 exhibited better moisture resistance, maintaining an internal quantum efficiency of 82.73%.
[0045] Example 9
[0046] Prepare the following raw materials: 20 mmol KHF2, 0.02 g thiourea, and 20 mL of HF (49 wt%) aqueous solution; dissolve 20 mmol KHF2 and 0.02 g thiourea completely in 20 mL of hydrofluoric acid aqueous solution (49 wt%) under constant temperature water bath to obtain KHF2 with a concentration of 1 mol / L. + -HF solution; 10 mmol of the surface-passivated phosphor obtained in Example 4 was placed in the above K... + The sample was placed in a hydrothermal reactor in an HF solution and hydrothermally treated at 180°C for 12 hours. The sample was then removed and washed repeatedly with 0.02 g / mL thiourea aqueous solution and anhydrous ethanol 3 to 5 times, and then dried at 80°C for 2 hours to obtain the surface-modified phosphor.
[0047] Example 10
[0048] Example 10 was prepared using the same method as Example 9, the only difference being that the amount of raw material KHF2 added was 40 mmol, resulting in a KHF2 concentration of 2 mol / L. + -HF solution; finally, surface-modified phosphor is obtained.
[0049] Example 11
[0050] The preparation method of Example 11 is exactly the same as that of Example 9, the only difference being that the amount of raw material KHF2 added is 80 mmol, resulting in a KHF2 concentration of 4 mol / L. + -HF solution; finally, surface-modified phosphor is obtained.
[0051] Example 12
[0052] Example 12 was prepared in exactly the same way as Example 9, except that the amount of raw material KHF2 added was 120 mmol, resulting in a KHF2 concentration of 6 mol / L. + -HF solution; finally, surface-modified phosphor is obtained.
[0053] Example 13
[0054] The preparation method of Example 13 is exactly the same as that of Example 9, the only difference being that the amount of raw material KHF2 added is 160 mmol, resulting in a KHF2 concentration of 8 mol / L. + -HF solution; finally, surface-modified phosphor is obtained.
[0055] The modified K2SiF6:Mn prepared in Examples 9-13 4+ The internal quantum efficiency of the phosphor before and after degradation for 6 days in a high temperature and high humidity (85℃ / 85%RH) environment is as follows: Figure 2 As shown, the phosphors after hydrothermal treatment all maintained high internal quantum efficiency, indicating that hydrothermal treatment had almost no effect on the luminescence performance of the phosphors themselves. After being treated in an extreme humid and hot environment for 6 days, the internal quantum efficiency of Examples 9 to 13 remained high. Among them, the internal quantum efficiency of the phosphor in Example 11 changed from 92.04% to 92.56% after 6 days of degradation, with almost no decrease in luminescence performance, indicating that its moisture resistance was excellent.
[0056] Depend on Figure 3 It can be seen that the excitation and emission peak positions of the untreated phosphor, the phosphors of Example 4 and Example 11 are completely consistent. The luminescence intensity of the phosphors of Example 4 and Example 11 is only slightly reduced, about 95.6% of that of the untreated fluoride phosphor, thus constructing a surface-depleted Mn phosphor. 4+ During the layering process, some Mn, which serves as the luminescent center, is lost from the phosphor surface. 4+ However, under the high temperature and high pressure environment of hydrothermal treatment, the phosphor surface undergoes drastic dissolution and recrystallization, promoting surface atomic rearrangement, modifying surface defects, and resulting in better phosphor surface crystallinity. This effectively compensates for some of the Mn lost from the phosphor surface. 4+ This leads to a decrease in luminous intensity.
[0057] Depend on Figure 4 , Figure 5 and Figure 6 It can be seen that with the extension of the damp heat treatment time, the untreated phosphor deteriorated rapidly, changing from bright orange to brownish-black, and the luminescence intensity decreased significantly. In contrast, the intensity of Example 4 decreased slowly, while Example 11 showed almost no change, retaining 100.64% of the initial luminescence intensity, and both examples essentially maintained their initial bright orange color, indicating that Example 11 had excellent moisture resistance. Table 1 shows the internal quantum efficiency (IQY), external quantum efficiency (EQY), absorptivity (AE), relative intensity, and normalized intensity of the untreated phosphor, Example 4, and Example 11 before and after 6 days of degradation under high temperature and high humidity (85℃ / 85%RH) conditions.
[0058] Table 1. Luminescent performance data of untreated phosphor, phosphors of Example 4 and Example 11 before and after damp heat degradation.
[0059]
[0060] Depend on Figure 7 , Figure 8 The fluorescence lifetime calculation formula, I(t)=I0exp(-t / T), shows that the fluorescence lifetimes (τ) of the untreated phosphor, Example 4, and Example 11 are 8.521ms, 8.529ms, and 8.547ms, respectively, indicating that the surface is Mn-poor. 4+ The construction of the layer did not affect K2SiF6:Mn 4+ Mesoluminescent center Mn 4+ The intrinsic luminescent properties of the phosphor were observed. After humid heat treatment, the lifetimes of the three phosphors were 8.374 ms, 8.456 ms, and 8.492 ms, respectively. The lifetime of the untreated phosphor decreased significantly by approximately 0.147 ms, while the lifetime decreases after degradation in Examples 4 and 11 were extremely small, at 0.073 ms and 0.055 ms, respectively. This indicates that the modified Mn phosphor exhibits good intrinsic luminescence properties. 4+ The luminescent center is almost undamaged and does not produce excessive crystal defects in humid and hot environments, exhibiting excellent moisture resistance.
[0061] Depend on Figure 9As shown in (ad), to further determine the moisture resistance of the modified fluoride red phosphor, the untreated phosphor, and the phosphors of Example 4 and Example 11 were immersed in deionized water for 360 min, and their luminescence performance was compared. The untreated phosphor, when immersed in water under natural light, immediately changed from bright orange to brownish-black, and after 360 min, its luminescence intensity was only 49.93% of the initial value. In stark contrast, the phosphors of Example 4 and Example 11, even after immersion in water for 360 min, did not show significant color change, and their luminescence intensities remained at 79.79% and 98.86% of their initial values, respectively, indicating that the modified phosphors have excellent moisture resistance.
Claims
1. A type of Mn 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that, Includes the following steps: (1) Niobium oxide was dissolved in an aqueous solution of hydrofluoric acid under constant temperature water bath to obtain a fluoroniobic acid solution; Mn 4+ Fluoride-doped red phosphor was added to a fluoroniobic acid solution and stirred thoroughly in a constant temperature water bath. The reacted phosphor was then washed and dried to obtain a preliminarily modified phosphor; the Mn... 4+ The chemical formula of the fluoride-doped red phosphor is K₂SiF₆:Mn. 4+ ; (2) Dissolve potassium hydrofluoride and thiourea in hydrofluoric acid aqueous solution to obtain hydrothermal mixed solution; add the preliminarily modified phosphor to hydrothermal mixed solution and carry out hydrothermal reaction at high temperature; wash and dry the phosphor after reaction to obtain modified fluoride red phosphor.
2. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In steps (1) to (2), the mass fraction of the hydrofluoric acid aqueous solution is not less than 49%.
3. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In step (1), the concentration of fluoroniobic acid in the fluoroniobic acid solution is 0.25~2 mol / L.
4. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In step (1), niobium oxide and Mn 4+ The molar ratio of fluoride-doped red phosphor is 2.5 to 20:
10.
5. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In step (1), the stirring conditions are: temperature not lower than 80℃, speed of rotation 150~200rpm, and stirring time 20~40min.
6. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In step (2), the concentration of potassium hydrofluoric acid in the hydrothermal mixed solution is 1~8 mol / L; the concentration of thiourea is 0.01 g / mL.
7. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In step (2), the hydrothermal reaction conditions are: reaction temperature of 150~200℃ and reaction time of 8~16h.
8. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In step (1), the washing and drying conditions are as follows: the reaction product is washed 3 to 5 times with anhydrous ethanol and then dried at a temperature of not less than 80°C for not less than 2 hours.
9. The Mn according to claim 1 4+ A surface treatment method for fluoride-doped red phosphors, characterized in that: In step (2), the washing and drying conditions are as follows: the reaction product is washed repeatedly 3 to 5 times with 0.02 g / mL thiourea aqueous solution and anhydrous ethanol, and then dried at a temperature not lower than 80°C for 2 hours.