Blue fluorescent powder, preparation method and application thereof
By using phosphate-based blue phosphors co-doped with Li+ and Eu2+, the problems of low thermal stability and low luminous efficiency of existing blue phosphors have been solved, enabling the application of high color rendering index white LEDs with excellent thermal stability and luminous intensity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANCHANG RES INST OF SUN YAT SEN UNIV
- Filing Date
- 2024-09-23
- Publication Date
- 2026-04-17
AI Technical Summary
Existing blue phosphors have poor thermal stability, low luminous efficiency, and poor matching between their excitation bands and near-ultraviolet chips, making it difficult to meet the needs of high color rendering index white LEDs.
A phosphate-based blue phosphor co-doped with Li+ and Eu2+ is used, with the chemical formula Na3Rb0.97Li0.97xMg7(PO4)6:0.03Eu2+. By introducing Li+ to optimize the crystal structure, the luminous efficiency and thermal stability of Eu2+ are improved, and the emission peak position can be tuned by different Li+ contents.
It improves the luminous intensity of blue phosphor and the actual doping concentration of Eu2+ ions, enhances the tunability of the emitted color, has excellent thermal stability, and is suitable for white LEDs with high color rendering index.
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Figure CN119193157B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of luminescent materials, and more specifically, to a blue phosphor, its preparation method, and its application. Background Technology
[0002] Currently, the main approach to fabricating white light-emitting diodes (WLEDs) is "fluorescence conversion" technology. This technology uses blue or near-ultraviolet light emitted from a semiconductor chip to excite the fluorescent material encapsulated on it, and white light is obtained through the mixing of multiple colors. Near-ultraviolet LED chips can achieve full-spectrum white light by combining three-color phosphors, which not only achieves a high color rendering index and adjustable color temperature, but also effectively avoids the harmful blue light emission of blue LEDs, meeting the current societal demand for "healthy lighting." However, due to problems such as the mismatch between the absorption position of phosphors and ultraviolet chips, low luminous efficiency, and poor thermal stability, truly high-quality blue phosphors that can be combined in UV-LED devices to obtain WLEDs are still lacking. Although commercially available blue phosphors (BAM) have high luminous efficiency, the excitation band of BAM is mainly located in the 245nm–325nm range, which does not match the optimal excitation range of near-ultraviolet chips (340nm–400nm). Furthermore, the synthesis temperature of commercial BAM powder is as high as 1600℃, requiring advanced equipment and consuming a large amount of energy. Therefore, it is urgent to study blue phosphors with a wide ultraviolet absorption region, excellent thermal stability, and low energy consumption for synthesis that can be excited by near-ultraviolet light.
[0003] Bohnisch et al. (DOI: 10.1039 / c9tc00482c) discovered Eu 2+ Doped alkaline earth diorophores exhibit similarity to blue powder BAM:Eu 2+ It exhibits almost identical blue emission, but with a wider excitation band. This demonstrates that this alkaline earth bis(orthophosphate) has significant advantages as a matrix material compared to other matrix materials. However, this Eu... 2+ The luminous efficiency of doped alkaline earth bis-orthophosphate phosphors still needs to be improved, and the phosphors cannot achieve tunable luminous color. Summary of the Invention
[0004] The primary objective of this invention is to overcome the problems of poor thermal stability and insufficient luminous efficiency of existing blue phosphors, and to provide a Li + Eu 2+ Co-doped phosphate-based blue phosphor. The chemical formula of this blue phosphor is: Na3Rb 0.97 Li 0.97x Mg7(PO4)6: 0.03Eu 2+ Where 0.4 ≤ x ≤ 4. A certain amount of Li was introduced into this blue phosphor. +This effectively improved the luminescence intensity of the blue phosphor and Eu. 2+ The actual doping concentration of ions is reduced, and the full width at half maximum (FWHM) of its emission peak is decreased; it can also effectively absorb ultraviolet light, making it applicable to white LEDs, especially high color rendering index white LEDs. Furthermore, different Li... + The introduction of certain concentrations can cause varying degrees of blue shift in the optimal emission peak position of the blue phosphor, thereby allowing the optimal emission peak position to shift within the 430–450 nm range, which is beneficial for achieving tunable emission color. Furthermore, the blue phosphor of this invention exhibits excellent thermal stability.
[0005] A further objective of this invention is to provide a method for preparing blue phosphor.
[0006] Another object of the present invention is to provide an application of the above-mentioned blue phosphor in the fields of lighting and display.
[0007] The above-mentioned objective of the present invention is achieved through the following technical solution:
[0008] A blue phosphor with the following formula: Na3Rb 0.97 Li 0.97x Mg7(PO4)6: 0.03Eu 2+ , where 0.4≤x≤4.
[0009] The inventors of this invention discovered that in Na3Rb 0.97 Mg7(PO4)6: 0.03Eu 2+ Introducing a specific amount of Li + This helps optimize the crystal structure of materials and reduce surface defects. On the one hand, Li + Entering the matrix will bring the luminescent center Eu 2+ The increased spacing between ion pairs reduces energy relaxation between them and improves Eu. 2+ On the one hand, lithium ions can improve the luminescence efficiency of phosphors, thereby increasing the luminescence intensity of blue phosphors. On the other hand, lithium ions may interact with defect sites in the crystal lattice, thereby repairing or filling these defects, reducing the loss of energy that may be dissipated in the form of heat or other non-radiative forms due to defects, and helping to form a more stable crystal structure, which is conducive to the radiative recombination of photons, allowing more photons to be released through radiative recombination, thereby improving the internal quantum efficiency of phosphors.
[0010] Furthermore, the inventors of this invention have also discovered that introducing a specific amount of Li + This helps to improve the rigidity of the crystal structure, thereby suppressing lattice vibrations, reducing Stokes displacement and the loss of excitation energy, which in turn helps to improve the luminescence intensity of the phosphor.
[0011] In addition, the blue phosphor of the present invention has good thermal stability and exhibits high luminescence intensity in the temperature range of 300-450K.
[0012] Furthermore, the blue phosphor of the present invention can be calcined at a temperature of 900–930°C during preparation, resulting in low energy consumption.
[0013] In this invention, x represents Li + Relative to Rb + The percentage of moles accounted for.
[0014] In this invention, x can specifically be 0.4, 0.8, 0.92, 1.6, 2, 2.4, 2.8 or 4.
[0015] Preferably, 0.8 ≤ x ≤ 2.8.
[0016] More preferably, 2 ≤ x ≤ 2.8. Blue phosphors in this range exhibit higher internal quantum yields.
[0017] A method for preparing the above-mentioned blue phosphor includes the following steps:
[0018] S1. Weigh the raw material components; the raw material components include sodium source, rubidium source, magnesium source, phosphorus source, lithium source and europium source;
[0019] S2. Mix the raw material components and calcine them in a reducing atmosphere to obtain the blue phosphor.
[0020] Preferably, in step S1, the molar ratio of sodium in the sodium source, rubidium in the rubidium source, magnesium in the magnesium source, phosphorus in the phosphorus source, lithium in the lithium source, and europium in the europium source is:
[0021] (3~3.16): (0.96~1.17): 7: 6: (0.40~4.08): 0.03.
[0022] More preferably, in step S1, the molar ratio of sodium in the sodium source, rubidium in the rubidium source, magnesium in the magnesium source, phosphorus in the phosphorus source, lithium in the lithium source, and europium in the europium source is:
[0023] (3.029~3.060): (1.017~1.070): 7: 6: (0.40~4.08): 0.03.
[0024] Excess rubidium and sodium sources may form certain defect structures during calcination, and these defects may serve as new luminescent or energy transfer centers. Furthermore, excess rubidium and sodium sources can contribute to the formation of more regular, highly crystalline crystal structures and can also enhance the properties of Eu. 2+The phosphor is more evenly distributed within the phosphor matrix, reducing the concentration quenching effect. The combined effect of these factors results in higher phosphor luminescence intensity.
[0025] Preferably, in step S1, the lithium source is lithium carbonate.
[0026] Preferably, in step S1, the sodium source is at least one of Na2CO3 or NaHCO3.
[0027] Preferably, in step S1, the rubidium source is Rb2CO3.
[0028] Preferably, in step S1, the magnesium source is at least one of 4MgCO3·Mg(OH)2 or MgO.
[0029] Preferably, in step S1, the phosphorus source is NH4H2PO4.
[0030] Preferably, in step S1, the europium source is Eu2O3.
[0031] Preferably, in step S2, the mixing method is grinding.
[0032] More preferably, a grinding medium is added during the grinding process.
[0033] More preferably, the grinding medium is at least one of ethanol or acetone.
[0034] Preferably, in step S2, the calcination temperature is 900–930°C.
[0035] More preferably, the calcination temperature is increased at a rate of 5°C to 10°C / min.
[0036] Preferably, in step S2, the calcination time is 12-13 hours.
[0037] Preferably, in step S2, after calcination, the process further includes cooling and grinding.
[0038] Preferably, in step S2, the calcination is carried out in a tubular furnace.
[0039] Preferably, in step S2, the reducing atmosphere is one of a mixture of hydrogen and nitrogen or a mixture of hydrogen and argon; in the reducing atmosphere, the volume percentage of hydrogen is 5-20%.
[0040] This invention particularly protects the application of the aforementioned blue phosphor in the fields of lighting or display.
[0041] Preferably, the blue phosphor is used in the preparation of LEDs.
[0042] More preferably, the LED is a near-ultraviolet LED.
[0043] More preferably, the near-ultraviolet LED includes a near-ultraviolet chip and a light-emitting material, wherein the light-emitting material includes red phosphor, green phosphor and blue phosphor.
[0044] Compared with the prior art, the beneficial effects of the present invention are:
[0045] This invention is based on Na3Rb 0.97 Mg7(PO4)6: 0.03Eu 2+ Introducing a certain amount of Li + This effectively improved the luminescence intensity of the blue phosphor and Eu. 2+ The actual doping concentration of ions is reduced, and the full width at half maximum (FWHM) of its emission peak is decreased; it can also effectively absorb ultraviolet light, making it applicable to white LEDs, especially high color rendering index white LEDs. Furthermore, different Li... + The introduction of certain concentrations can cause varying degrees of blue shift in the optimal emission peak position of the blue phosphor, thereby allowing the optimal emission peak position to shift within the 430–450 nm range, which is beneficial for achieving tunable emission color. Furthermore, the blue phosphor of this invention exhibits excellent thermal stability. Attached Figure Description
[0046] Figure 1 The X-ray diffraction patterns are those of the blue phosphors prepared in Examples 1-7.
[0047] Figure 2 The excitation spectrum (monitoring wavelength 450 nm) and emission spectrum (excitation wavelength 350 nm) of the blue phosphors prepared in Examples 1-7 and Comparative Example 1 are shown.
[0048] Figure 3 The emission spectra of the blue phosphors of Examples 1, 8 and Comparative Example 1 under 350 nm light excitation are shown.
[0049] Figure 4 The emission spectra of the blue phosphors prepared in Examples 5 and 9-11 under 350 nm light excitation are shown.
[0050] Figure 5 The X-ray diffraction patterns are of the blue phosphors prepared in Examples 5 and 9-11.
[0051] Figure 6 The graph shows the internal quantum yield (IQY) data of the blue phosphors prepared in Examples 1, 7 and Comparative Example 1 under 350 nm excitation.
[0052] Figure 7The emission spectrum of the phosphor in Example 1 is temperature-dependent in the range of 300–450 K.
[0053] Figure 8 This is a normalized curve of the temperature-dependent integral luminescence intensity of the phosphor in Example 1 within the range of 300–450 K as a function of temperature.
[0054] Figure 9 The emission spectrum of the LED package sample prepared in Example 1, which is combined with commercial red and green phosphors, is shown under a 50mA current drive. Detailed Implementation
[0055] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.
[0056] Example 1
[0057] This embodiment provides a blue phosphor, the preparation method of which includes the following steps:
[0058] S1. Weigh the raw materials Na2CO3, Rb2CO3, 4MgCO3·Mg(OH)2, NH4H2PO4, Li2CO3, and Eu2O3: according to the chemical formula Na3Rb 0.97 Li 2.716 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 2.8) and the amounts of sodium in Na2CO3 and rubidium in Rb2CO3 were weighed in excess by 1% and 5%, respectively.
[0059] The weighing quantities of each raw material are shown in Table 1;
[0060] S2. After grinding the raw material from S1 into ethanol in an agate mortar until uniform, transfer it to a corundum crucible and place it in a tube furnace. In a reducing atmosphere of 5% H2-95% N2, heat the material from 30°C to 900°C at a rate of 5°C / min. Calcinate the material at 900°C for 12 hours, then allow it to cool naturally to room temperature. Grind the material thoroughly into powder to obtain blue fluorescent powder.
[0061] Example 2
[0062] This embodiment provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Li 2.328 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 2.4). The weighing quantities of each raw material are shown in Table 1.
[0063] Example 3
[0064] This embodiment provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Li 0.388 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 0.4). The weighing quantities of each raw material are shown in Table 1.
[0065] Example 4
[0066] This embodiment provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Li 0.776 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 0.8). The weighing quantities of each raw material are shown in Table 1.
[0067] Example 5
[0068] This embodiment provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Li 0.89 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 0.92). The weighing quantities of each raw material are shown in Table 1.
[0069] Example 6
[0070] This embodiment provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Li 1.552 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 1.6). The weighing quantities of each raw material are shown in Table 1.
[0071] Example 7
[0072] This embodiment provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Li 1.94 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 2). The weighing quantities of each raw material are shown in Table 1.
[0073] Example 8
[0074] This embodiment provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Li 3.88 Mg7(PO4)6: 0.03Eu 2+(Equivalent to x = 4). The weighing quantities of each raw material are shown in Table 1.
[0075] Example 9
[0076] This embodiment provides a blue phosphor, which differs from Example 5 in that the amounts of rubidium in Rb2CO3 and sodium in Na2CO3 are not excessive. The weighing amounts of each raw material are shown in Table 1.
[0077] Example 10
[0078] This embodiment provides a blue phosphor, which differs from Example 5 in that the amount of rubidium in Rb2CO3 and sodium in Na2CO3 is 10% and 2% excess, respectively. The weighing amounts of each raw material are shown in Table 1.
[0079] Example 11
[0080] This embodiment provides a blue phosphor, which differs from Example 5 in that the amount of rubidium in Rb2CO3 and sodium in Na2CO3 is 20% and 5% excess, respectively. The weighing amounts of each raw material are shown in Table 1.
[0081] Comparative Example 1
[0082] This comparative example provides a blue phosphor, which differs from Example 1 in that its chemical formula is Na3Rb. 0.97 Mg7(PO4)6: 0.03Eu 2+ (Equivalent to x = 0). The weighing quantities of each raw material are shown in Table 1.
[0083] Table 1. Raw material consumption of the examples and comparative examples
[0084]
[0085]
[0086] Performance testing
[0087] 1. Luminescent properties
[0088] Examples 1-7 were subjected to XRD characterization, and the results are as follows: Figure 1 As shown. From Figure 1 The X-ray diffraction pattern shows that, compared with the standard card ICSD#253861 (Na3RbMg7(PO4)6), the X-ray diffraction peaks of each blue phosphor are basically consistent with those of the standard card.
[0089] The blue phosphors from each example and Comparative Example 1 were subjected to fluorescence spectroscopy tests, and the results are as follows: Figures 2-4 As shown. Figure 2 The excitation and emission spectra of the blue phosphors in Examples 1-7 and Comparative Example 1 are shown. Figure 3 The emission spectra of the blue phosphors in Examples 1, 8, and Comparative Example 1 are shown below. Figure 4 Table 2 shows the emission spectra of the blue phosphors in Examples 5, 9-12. Table 2 also shows the emission integral intensity, full width at half maximum (FWHM), and optimal emission peak position of the blue phosphors in each example and comparative example. As can be seen from Table 2, compared to Comparative Example 1, Li... + The introduction of [Li] (in various embodiments) can enhance the luminescence intensity of the blue phosphor. Specifically, with the addition of Li... + With increasing concentration, the emission integral intensity of the blue phosphor first increases and then decreases. The reason for the decrease is that Li + Excessive amounts can easily cause Eu 2+ The luminescence quenching phenomenon and lattice distortion were observed; among them, the blue phosphor of Example 1 exhibited the strongest emission integral intensity, demonstrating excellent luminescence performance. Furthermore, the luminescence intensity of the blue phosphor of this invention is higher than that of the phosphor provided in the literature (DOI: 10.1039 / c9tc00482c).
[0090] Combined with Table 2, Figure 2 and Figure 3 It can be seen that Li + The introduction of Li caused a blue shift in the optimal emission peak position of the blue phosphor, enabling tunable emission color. Specifically, with the introduction of Li... + With increasing concentration, the degree of blue shift at the optimal emission peak position first increases and then decreases.
[0091] As can be seen from Table 2, Li + The introduction of Li can reduce the full width at half maximum (FWHM) of blue phosphors, and gradually narrow the emission band. A narrower emission band means that the phosphor's luminescence intensity is more concentrated within a specific wavelength range, reducing the influence of stray light and resulting in purer light emission, which is beneficial for obtaining more accurate color representation. Among these, with the introduction of Li... + As the concentration increases, the degree to which the half-peak width of the blue phosphor decreases increases and then decreases.
[0092] Figure 5 X-ray diffraction patterns of the blue phosphors prepared in Examples 5 and 9-11. Figure 4 , Figure 5 As shown in Table 2, compared to Example 9, the addition of excess Rb₂CO₃ and Na₂CO₃ (Examples 5, 10-11) increased the luminescence intensity of the blue phosphor. Among them, the blue phosphor in Example 5 exhibited the highest luminescence intensity and the highest crystallinity. Increased crystallinity signifies enhanced rigidity of the crystal structure, which can suppress lattice vibrations and reduce the loss of excitation energy, thereby improving luminescence intensity.
[0093] Figure 6The graph shows the internal quantum yield (IQY) data of the blue phosphors prepared in Examples 1, 7, and Comparative Example 1 under 350 nm excitation. Figure 6 It is clearly visible that, compared to the version without Li, + Compared to Comparative Example 1, Example 7, and Example 1, the blue phosphors of these two examples exhibit higher internal quantum yields, and Li + Example 1 with higher doping concentration has IQY compared to Li + The high doping level in Example 7 (with lower doping concentration) indicates that Li + Doping helps improve Eu 2+ The actual doping concentration of ions is increased, thereby improving the quantum yield of the phosphor. Furthermore, the internal quantum yield of the blue phosphor of this invention is higher than that of the phosphor provided in the literature (DOI: 10.1039 / c9tc00482c).
[0094] Figure 7 and Figure 8 The figures show the temperature-dependent emission spectrum of the phosphor in Example 1 within the range of 300–450 K and its normalized integral luminescence intensity as a function of temperature. The luminescent thermal stability of the phosphor is crucial for its practical application in white LEDs. Figure 8 It can be clearly seen that the integrated luminescence intensity of the phosphor prepared in Example 1 gradually decreases with increasing temperature. Nevertheless, the integrated luminescence intensity at 400K (125℃) is still 90% of that at 300K (25℃), indicating that the phosphor has excellent thermal stability.
[0095] Table 2. Emission integral intensity and full width at half maximum (FWHM) of each embodiment and comparative example.
[0096]
[0097]
[0098] 2. LED luminous performance
[0099] Commercial red phosphor (K2SiF6:Mn) was used. 4+ The blue phosphor from Example 1 was mixed with green phosphor (Silicate S525 green phosphor) and blue phosphor in a mass ratio of approximately 6:2:1, and then packaged with a near-ultraviolet chip (365nm) to prepare a white LED. The emission spectrum of the packaged white LED at a drive current of 50mA is shown below. Figure 9 As shown. From Figure 9It is known that the spectrum contains a sufficient number of color components, and the intensity distribution of these color components is relatively uniform. Measurements show that the prepared white LED has color coordinates of (0.302, 0.358), a color purity of 0.095, a correlated color temperature of 6803K, and a color rendering index of 85.84. These optical performance parameters indicate that this phosphor can be used to prepare a white LED with good performance. Furthermore, due to its high color temperature, it emits cool white light, which is bright and suitable for places requiring high-brightness lighting, such as hospital operating rooms or factories.
[0100] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A method for preparing a blue fluorescent powder, characterized by, Includes the following steps: S1. According to the chemical formula Na3Rb 0.97 Li 0.97x Mg7(PO4)6: 0.03Eu 2+ The raw materials are weighed in such a ratio as 0.92 ≤ x ≤ 2.8; the raw material components include Na2CO3, Rb2CO3, 4MgCO3·Mg(OH)2, NH4H2PO4, Li2CO3 and Eu2O3, and the amount of sodium in Na2CO3 and rubidium in Rb2CO3 are weighed in excess by 1% and 5% respectively. S2. The raw material components are mixed and calcined in a reducing atmosphere to obtain the blue phosphor.
2. The preparation method according to claim 1, characterized in that, 2≤x≤2.8。 3. The preparation method according to claim 1, characterized in that, In step S2, the calcination temperature is 900~930℃.
4. The preparation method according to claim 1, characterized in that, In step S2, the calcination time is 12-13 h.
5. A blue phosphor with tunable emission color, characterized in that It is prepared by any of the preparation methods described in claims 1 to 4.
6. The application of the blue phosphor according to any one of claims 4 to 5 in the fields of lighting or display.