Blue fluorescent powder as well as preparation method and application thereof

Abstract

The invention relates to blue fluorescent powder as well as a preparation method and application thereof. The chemical composition formula of the blue fluorescent powder is Na3Rb0. 97Li0. 97xMg7 (PO4) 6: 0.03 Eu < 2 + >, and x is more than or equal to 0.4 and less than or equal to 4. A certain amount of Li < + > is introduced into the blue fluorescent powder, so that the luminous intensity of the blue fluorescent powder and the actual doping concentration of Eu < 2 + > ions are effectively improved, and the half-peak width of an emission peak of the blue fluorescent powder is reduced; the fluorescent powder can effectively absorb ultraviolet light, and can be applied to white light LEDs, especially white light LEDs with high color rendering indexes. Besides, due to the introduction of different Li < + > contents, different degrees of blue shift can be realized at the optimal emission peak position of the blue fluorescent powder, so that the optimal emission peak position of the blue fluorescent powder can move within the range of 430-450 nm, and the realization of tunable light emitting color is facilitated. In addition, the blue fluorescent powder provided by the invention has excellent thermal stability.

Description

Technical Field

[0001] The present invention relates to the field of luminescent materials, and more specifically, to a blue phosphor and a preparation method and application thereof. Background Art

[0002] At present, the main way to prepare white light emitting diodes (WLEDs) is the "fluorescence conversion" technology, which uses blue light or near-ultraviolet light emitted by semiconductor chips to excite the fluorescent materials encapsulated thereon, and obtains white light by mixing multi-color light. Among them, near-ultraviolet LED chips can obtain full-spectrum white light by combining three-color phosphors, which can not only achieve high color rendering index and adjustable color temperature, but also effectively avoid the damage to human eyes caused by excessive blue light emission of blue LEDs, and meet the current social demand for "healthy lighting". However, due to the problems of mismatch between the absorption position of phosphors and ultraviolet chips, low luminous efficiency and poor thermal stability, there is still a lack of blue phosphors that can be combined with each other in UV-LED devices to obtain high-quality W-LEDs. Although the commercial blue powder BAM has high luminous efficiency, the excitation band of BAM is mainly located at 245nm~325nm, which is not well matched with the excitation range of the best near-ultraviolet chip of 340nm~400nm; in addition, the synthesis temperature of commercial BAM powder needs to be as high as 1600℃, which has high equipment requirements and high energy consumption. Therefore, it is urgent to study near-UV-excited blue phosphors with a wide UV absorption region, excellent thermal stability, and low synthesis energy consumption.

[0003] Bohnisch et al. (DOI: 10.1039 / c9tc00482c) found that Eu 2+ Doped alkaline earth bis-orthophosphate has the same properties as blue powder BAM:Eu 2+ Almost the same blue emission, but with a wider excitation band. It can be seen that compared with other matrix materials, the alkaline earth bis orthophosphate has great advantages as a matrix material. 2+ The luminous efficiency of doped alkaline earth bis-orthophosphate phosphors still needs to be improved, and the luminescent color of the phosphors cannot be tuned. Summary of the invention

[0004] The primary purpose of the present invention is to overcome the problems of poor thermal stability and luminous efficiency of the above-mentioned existing blue phosphors, and to provide a Li + 、Eu 2+ Co-doped phosphate-based blue phosphor. The chemical composition formula of the 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 +, effectively improving the luminous intensity of blue phosphor and Eu 2+ The actual doping concentration of Li ions is reduced, and the half-peak width of its emission peak is reduced; it can also effectively absorb ultraviolet light and can be used in white light LEDs, especially white light LEDs with high color rendering index. + The introduction of the content can make the optimal emission peak position of the blue phosphor achieve different degrees of blue shift, and then the optimal emission peak position of the blue phosphor can be moved within the range of 430-450nm, which is conducive to achieving tunable luminescent color. In addition, the blue phosphor of the present invention has excellent thermal stability.

[0005] A further object of the present 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 blue phosphor in the field of lighting and display.

[0007] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0008] A blue phosphor, the composition formula of which is: Na3Rb 0.97 Li 0.97x Mg7(PO4)6:0.03Eu 2+ , where 0.4≤x≤4.

[0009] The inventors of the present invention have found that in Na3Rb 0.97 Mg7(PO4)6:0.03Eu 2+ A specific amount of Li is introduced into + , which helps to optimize the crystal structure of the material and reduce surface defects. On the one hand, Li + Entering the matrix will emit the luminescent center Eu 2+ The distance between them increases, which reduces the energy relaxation between ion pairs and improves Eu 2+ The luminous efficiency of the blue phosphor can be improved, thereby increasing the luminous intensity of the blue phosphor; on the other hand, lithium ions may interact with defect sites in the crystal lattice to repair or fill these defects, reducing the loss of energy that may be dissipated in the form of heat or other non-radiative forms caused by defects, while helping to form a more stable crystal structure, which is beneficial to the radiative recombination of photons, allowing more photons to be released in the form of radiative recombination, thereby improving the internal quantum efficiency of the phosphor.

[0010] In addition, the inventors of the present invention have also found that the introduction of a specific amount of Li + It helps to improve the rigidity of the crystal structure, thereby suppressing lattice vibration, reducing Stokes shift and excitation energy loss, and thus helps to improve the luminous intensity of the phosphor.

[0011] In addition, the blue phosphor of the present invention has good thermal stability and exhibits high luminous intensity at a temperature ranging from 300 to 450K.

[0012] In addition, the calcination temperature of the blue phosphor of the present invention during the preparation process can be 900-930° C., and the energy consumption is low.

[0013] In the present invention, x is Li + Relative Rb + The mole percentage coefficient.

[0014] In the present invention, x may 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. The internal quantum yield of the blue phosphor within this range is higher.

[0017] A method for preparing the above-mentioned blue phosphor comprises the following steps:

[0018] S1. Weigh the raw material components; the raw material components include a sodium source, a rubidium source, a magnesium source, a phosphorus source, a lithium source and a 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 the sodium element in the sodium source, the rubidium element in the rubidium source, the magnesium element in the magnesium source, the phosphorus element in the phosphorus source, the lithium element in the lithium source and the europium element 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 the sodium element in the sodium source, the rubidium element in the rubidium source, the magnesium element in the magnesium source, the phosphorus element in the phosphorus source, the lithium element in the lithium source and the europium element in the europium source is:

[0023] (3.029~3.060):(1.017~1.070):7:6:(0.40~4.08):0.03.

[0024] Excessive rubidium source and excessive sodium source may form certain defect structures during the calcination process, and these defects may serve as new luminescence centers or energy transfer centers; in addition, excessive rubidium source and excessive sodium source can also help to form a more regular and higher crystal structure, and can also make Eu 2+The distribution of phosphor in the phosphor matrix is ​​more uniform, reducing the concentration quenching effect. The combined effect of these factors can make the luminescence intensity of phosphor higher.

[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, grinding media is added during the grinding process.

[0033] Further 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 temperature is raised to the calcining temperature at a rate of 5°C to 10°C / min.

[0036] Preferably, in step S2, the calcination time is 12 to 13 hours.

[0037] Preferably, in step S2, after the calcination, a cooling and grinding step is also included.

[0038] Preferably, in step S2, the calcination is carried out in a tube furnace.

[0039] Preferably, in step S2, the reducing atmosphere is one of a mixed gas of hydrogen and nitrogen and a mixed gas of hydrogen and argon; in the reducing atmosphere, the volume proportion of hydrogen is 5-20%.

[0040] The present invention particularly protects the use of the above blue phosphor in the field 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] Further preferably, the near-ultraviolet LED comprises a near-ultraviolet chip and a luminescent material, and the luminescent material comprises a red phosphor, a green phosphor and the blue phosphor.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention is Na3Rb 0.97 Mg7(PO4)6:0.03Eu 2+ A certain amount of Li is introduced into + , effectively improving the luminous intensity of blue phosphor and Eu 2+ The actual doping concentration of Li ions is reduced, and the half-peak width of its emission peak is reduced; it can also effectively absorb ultraviolet light and can be used in white light LEDs, especially white light LEDs with high color rendering index. + The introduction of the content can make the optimal emission peak position of the blue phosphor achieve different degrees of blue shift, and then the optimal emission peak position of the blue phosphor can be moved within the range of 430-450nm, which is conducive to achieving tunable luminescent color. In addition, the blue phosphor of the present invention has excellent thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The X-ray diffraction patterns of the blue phosphors prepared in Examples 1 to 7 are shown.

[0047] Figure 2 The excitation spectra (monitoring wavelength is 450 nm) and emission spectra (excitation wavelength is 350 nm) of the blue phosphors prepared in Examples 1 to 7 and Comparative Example 1 are shown.

[0048] Figure 3 The emission spectra of the blue phosphors of Example 1, Example 8 and Comparative Example 1 under 350nm light excitation.

[0049] Figure 4 The emission spectra of the blue phosphors prepared in Examples 5 and 9 to 11 under 350nm light excitation.

[0050] Figure 5 The X-ray diffraction patterns of the blue phosphors prepared in Examples 5 and 9-11 are shown.

[0051] Figure 6 The internal quantum yield (IQY) data of the blue phosphors prepared in Example 1, Example 7 and Comparative Example 1 under 350nm excitation are shown in FIG.

[0052] Figure 7This is a temperature-dependent emission spectrum diagram of the phosphor of Example 1 in the range of 300 to 450K.

[0053] Figure 8 This is a normalized curve diagram of the temperature-dependent integrated luminous intensity of the phosphor in Example 1 in the range of 300 to 450 K versus temperature.

[0054] Fig. 9 This is an emission spectrum of an LED package sample in which the blue phosphor prepared in Example 1 is packaged in combination with commercial red phosphor and green phosphor under 50 mA current driving. DETAILED DESCRIPTION

[0055] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0056] Example 1

[0057] This embodiment provides a blue phosphor, and the preparation method thereof comprises the following steps:

[0058] S1. Weigh the raw materials Na2CO3, Rb2CO3, 4MgCO3·Mg(OH)2, NH4H2PO4, Li2CO3 and Eu2O3: according to the chemical composition formula Na3Rb 0.97 Li 2.716 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=2.8) and the amounts of the sodium element of Na2CO3 and the rubidium element of Rb2CO3 are weighed in excess of 1% and 5% respectively.

[0059] The weighing amount of each raw material is shown in Table 1;

[0060] S2. Add ethanol to the raw materials in S1 and grind them evenly in an agate mortar. Then transfer them to a small corundum crucible and place it in a tubular furnace. Raise the temperature from 30°C to 900°C at a rate of 5°C / min in a reducing atmosphere of 5% H2-95% N2. Keep calcining at 900°C for 12 hours, then cool naturally to room temperature, and grind them thoroughly into powder to obtain blue phosphor.

[0061] Example 2

[0062] This embodiment provides a blue phosphor, which is different from the embodiment 1 in that: the chemical composition formula is Na3Rb 0.97 Li 2.328 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=2.4). The weighing amount of each raw material is shown in Table 1.

[0063] Example 3

[0064] This embodiment provides a blue phosphor, which is different from the embodiment 1 in that: the chemical composition formula is Na3Rb 0.97 Li 0.388 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=0.4). The weighing amount of each raw material is shown in Table 1.

[0065] Example 4

[0066] This embodiment provides a blue phosphor, which is different from the embodiment 1 in that: the chemical composition formula is Na3Rb 0.97 Li 0.776 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=0.8). The weighing amount of each raw material is shown in Table 1.

[0067] Example 5

[0068] This embodiment provides a blue phosphor, which is different from the embodiment 1 in that: the chemical composition formula is Na3Rb 0.97 Li 0.89 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=0.92). The weighing amount of each raw material is shown in Table 1.

[0069] Example 6

[0070] This embodiment provides a blue phosphor, which is different from the embodiment 1 in that: the chemical composition formula is Na3Rb 0.97 Li 1.552 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=1.6). The weighing amount of each raw material is shown in Table 1.

[0071] Example 7

[0072] This embodiment provides a blue phosphor, which is different from the embodiment 1 in that: the chemical composition formula is Na3Rb 0.97 Li 1.94 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=2). The weighing amount of each raw material is shown in Table 1.

[0073] Example 8

[0074] This embodiment provides a blue phosphor, which is different from the embodiment 1 in that: the chemical composition formula is Na3Rb 0.97 Li 3.88 Mg7(PO4)6:0.03Eu 2+(equivalent to x=4). The weighing amount of each raw material is shown in Table 1.

[0075] Example 9

[0076] This embodiment provides a blue phosphor, which is different from Embodiment 5 in that the amount of the rubidium element in Rb2CO3 and the sodium element in Na2CO3 is not excessive. The weighed amount of each raw material is shown in Table 1.

[0077] Example 10

[0078] This embodiment provides a blue phosphor, which is different from Embodiment 5 in that the amount of rubidium in Rb2CO3 and sodium in Na2CO3 are in excess of 10% and 2% respectively. The weighed amount of each raw material is shown in Table 1.

[0079] Embodiment 11

[0080] This embodiment provides a blue phosphor, which is different from Embodiment 5 in that the amount of rubidium element in Rb2CO3 and sodium element in Na2CO3 are in excess of 20% and 5% respectively. The weighed amount of each raw material is shown in Table 1.

[0081] Comparative Example 1

[0082] This comparative example provides a blue phosphor, which is different from Example 1 in that: the chemical composition formula is Na3Rb 0.97 Mg7(PO4)6:0.03Eu 2+ (equivalent to x=0). The weighed amounts of each raw material are shown in Table 1.

[0083] Table 1 Raw material dosage of Examples and Comparative Examples

[0084]

[0085]

[0086] Performance Testing

[0087] 1. Luminescence properties

[0088] Take Examples 1 to 7 and perform XRD characterization. The results are as follows Figure 1 As shown. Figure 1 It can be seen from the X-ray diffraction pattern that, compared with the standard card ICSD#253861 (Na3RbMg7(PO4)6), the X-ray diffraction peaks of each blue phosphor are basically consistent with the standard card.

[0089] The blue phosphors of each embodiment and comparative example 1 were tested for fluorescence spectrum. The results are as follows: Figures 2 to 4 shown. Figure 2 The excitation spectra and emission spectra of the blue phosphors of Examples 1 to 7 and Comparative Example 1 are shown; Figure 3 The emission spectra of the blue phosphors of Example 1, Example 8 and Comparative Example 1 are shown; Figure 4 The emission spectra of the blue phosphors of Examples 5, 9 to 12 are shown in Table 2. The emission integrated intensity, half-peak width and optimal emission peak position of the blue phosphors of each Example and Comparative Example are shown in Table 2. + The introduction of (each embodiment) can improve the luminous intensity of the blue phosphor. + As the concentration increases, the emission integrated intensity of the blue phosphor increases first and then decreases. The reason for the decrease is that Li + Too high a dose can easily cause Eu 2+ The luminescence quenching phenomenon and lattice distortion caused by the blue phosphor of Example 1 are eliminated; among them, the emission integrated intensity of the blue phosphor of Example 1 is the strongest, showing excellent luminescence performance. In addition, the luminescence intensity of the blue phosphor of the present 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 + With the introduction of Li + With the increase of concentration, the blue shift degree of the optimal emission peak position first increases and then decreases.

[0091] From Table 2, we can see that Li + The introduction of can reduce the half-peak width of blue phosphor and gradually narrow the emission band. The narrow emission band means that the luminous intensity of the phosphor in a specific wavelength range is more concentrated, making the phosphor less affected by stray light and emitting purer light color, which is conducive to obtaining more accurate color expression. + With the increase of concentration, the half-width of the blue phosphor decreases and then decreases.

[0092] Figure 5 The X-ray diffraction patterns of the blue phosphors prepared in Examples 5 and 9 to 11 are shown in FIG. Figure 4 , Figure 5 As can be seen from Table 2, relative to Example 9, the addition of excess Rb2CO3 and Na2CO3 (Examples 5, Examples 10-11) increases the luminous intensity of the blue phosphor, among which the luminous intensity of the blue phosphor in Example 5 is the highest and the crystallinity is the highest. The increase in crystallinity means the enhancement of the rigidity of the crystal structure, which can suppress lattice vibration, and is conducive to reducing the loss of excitation energy, thereby increasing the luminous intensity.

[0093] Figure 6The internal quantum yield (IQY) data of the blue phosphor prepared in Example 1, Example 7 and Comparative Example 1 under 350nm excitation is shown in FIG. Figure 6 It can be clearly seen that compared with the + The internal quantum yield of the blue phosphors of Example 7 and Example 1 is higher than that of Comparative Example 1, and Li + The IQY of Example 1 with a higher doping amount is higher than that of Li + The doping amount of Example 7 is relatively low, indicating that Li + Doping helps to increase Eu 2+ The actual doping concentration of the ions is increased, thereby improving the quantum yield of the phosphor. In addition, the internal quantum yield of the blue phosphor of the present invention is higher than that of the phosphor provided in the literature (DOI: 10.1039 / c9tc00482c).

[0094] Figure 7 and Figure 8 The temperature-dependent emission spectrum of the phosphor in Example 1 in the range of 300-450K and the normalized graph of its integrated luminous intensity changing with temperature are shown respectively. The thermal stability of the luminous flux of the phosphor is crucial to its practical application in white light LEDs. Figure 8 It can be clearly seen that the integrated luminous intensity of the phosphor prepared in Example 1 gradually decreases with increasing temperature. Nevertheless, the integrated luminous intensity at 400K (125°C) is still 90% of that at 300K (25°C), indicating that the phosphor has excellent thermal stability.

[0095] Table 2 Emission integrated intensity and half peak width of each embodiment and comparative example

[0096]

[0097]

[0098] 2.LED luminous performance

[0099] Using commercial red phosphor (K2SiF6: Mn 4+ ) and green phosphor (silicate S525 green powder) were mixed with the blue phosphor of Example 1 at a mass ratio of about 6:2:1, and then packaged with a near-ultraviolet chip (365nm) to prepare a white light LED. The emission spectrum of the packaged white light LED at a driving current of 50mA is as follows Fig. 9 As shown. Fig. 9It can be seen that the spectrum contains enough color components, and the intensity distribution of these color components is relatively uniform. After measurement, it can be seen that the color coordinates of the prepared white light LED are (0.302, 0.358), the color purity is 0.095, the correlated color temperature is 6803K, and the color rendering index is 85.84. From these optical performance parameters, it can be seen that the phosphor can prepare white light LEDs with good performance, and because of its high color temperature, the light emitted is cold white light with bright light color, which is 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 embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A blue phosphor, characterized in that: The chemical composition formula of the blue phosphor is: 3B 0.97 Li 0.97x Mg7(PO4)6:0.03Eu 2+ , where 0.4≤x≤4.

2. The blue phosphor according to claim 1, characterized in that: 0.8≤x≤2.8。 3. The blue phosphor according to claim 2, characterized in that: 2≤x≤2.8。 4. A method for preparing the blue phosphor according to any one of claims 1 to 3, characterized in that: The steps include: S1. Weigh the raw material components; the raw material components include a sodium source, a rubidium source, a magnesium source, a phosphorus source, a lithium source and a europium source; S2. Mix the raw material components and calcine them in a reducing atmosphere to obtain the blue phosphor.

5. The preparation method according to claim 4, characterized in that: In step S1, the molar ratio of the sodium element in the sodium source, the rubidium element in the rubidium source, the magnesium element in the magnesium source, the phosphorus element in the phosphorus source, the lithium element in the lithium source and the europium element in the europium source is: (3-3.16): (0.97-1.17): 7: 6: (0.40-4.08): 0.

03.

6. The preparation method according to claim 5, characterized in that: In step S1, the molar ratio of the sodium element in the sodium source, the rubidium element in the rubidium source, the magnesium element in the magnesium source, the phosphorus element in the phosphorus source, the lithium element in the lithium source and the europium element in the europium source is: (3.029-3.060): (1.017-1.070): 7: 6: (0.40-4.08): 0.

03.

7. The preparation method according to claim 4, characterized in that: In step S1, the lithium source is lithium carbonate.

8. The preparation method according to claim 4, characterized in that: In step S2, the calcination temperature is 900-930°C.

9. The preparation method according to claim 4, characterized in that: In step S2, the calcination time is 12 to 13 hours.

10. Use of the blue phosphor according to any one of claims 1 to 3 in the field of lighting or display.

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