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Title:
RED PHOSPHOR, WHITE LIGHT SOURCE, LIGHT EMITTING DEVICE, AND METHOD FOR FORMING THE RED PHOSPHOR
Document Type and Number:
WIPO Patent Application WO/2014/202311
Kind Code:
A1
Abstract:
The present invention relates to a red phosphor, which comprises an element A, magnesium (Mg), aluminum (Al), oxygen (O), and manganese (Mn) in Chemical Formula (1) that is (Α 1-x Μg x ) 4 ΑΙ 14-y 0 25 :γΜn 4+ , wherein the element A in the Chemical Formula (1) is at least one of strontium (Sr), barium (Ba), and calcium (Ca), and x and y in the Chemical Formula (1) satisfy the relational expressions 0≤x<1 and 0

Inventors:
LIU ZHONGSHI (CN)
ZHAO WENHUI (CN)
JING XIPING (CN)
Application Number:
PCT/EP2014/060269
Publication Date:
December 24, 2014
Filing Date:
May 19, 2014
Export Citation:
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Assignee:
OSRAM GMBH (DE)
International Classes:
C09K11/64
Domestic Patent References:
WO2006072919A22006-07-13
Foreign References:
CN102286281A2011-12-21
EP1073089A12001-01-31
JP2004235546A2004-08-19
US7846350B22010-12-07
US20060169998A12006-08-03
US8274215B22012-09-25
US7329371B22008-02-12
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Claims:
Patent claims

1. A red phosphor, comprising an element A, magnesium (Mg) , aluminum (Al) , oxygen (0) , and manganese (Mn) in Chemical Formula ( 1 ) ,

{A_xMgxXAlv. 025 yMn -4«+

Chemical Formula wherein the element A in the Chemical Formula (1) is at least one of strontium (Sr) , barium (Ba) , and calcium (Ca) , and 0<x<l and 0<y<l. 2. The red phosphor according to Claim 1, wherein 0<x<l and 0<y<l .

3. The red phosphor according to Claim 1 or 2, wherein the red phosphor has an emission peak with wavelength between 635 nm and 675 nm. 4. The red phosphor according to Claim 3, wherein the red phosphor has an emission peak at 652 nm.

5. A white light source, comprising: a blue light emitting diode; and a composition provided on the blue light emitting diode, which comprising a red phosphor and a yellow phosphor or a green phosphor and a red phosphor, wherein the red phosphor comprises an element A, magnesium (Mg) , aluminum (Al) , oxygen (0) , and manganese (Mn) in Chemical Formula ( 1 ) , {A_xMgxXAlv. 025 yMn-4«+

Chemical Formula wherein the element A in the Chemical Formula (1) is at least one of strontium (Sr) , barium (Ba) , and calcium (Ca) , and 0<x<l and 0<y<l. 6. The white light source according to Claim 5, wherein 0<x<l and 0<y<l.

7. A light emitting device, comprising: a light source emits light ; and a red phosphor according to Claim 1 or 2, which is excited by at least partial light to generate the excited light with a higher wavelength than that of the original light .

8. The light emitting device according to Claim 7, wherein the light source provides light with a wavelength between 450 nm and 470 nm. 9. The light emitting device according to Claim 7, wherein the light source provides light with a wavelength between 275 nm and 375 nm.

10. The light emitting device according to any of Claims 7 to 9, wherein the light source is configured as an LED. 11. The light emitting device according to Claim 7, wherein the red phosphor has an emission peak with a wavelength between 635 nm and 675 nm.

12. The light emitting device according to Claim 11, wherein the red phosphor has an emission peak at 652 nm.

13. A method for forming a red phosphor having Chemical Formula ( 1 ) ,

(A .4+

-xMgx\All4_y025 : yMn chemi ca l Fo rmu l a wherein the element A in the Chemical Formula (1) is at least one of strontium (Sr) , barium (Ba) , and calcium (Ca) , and 0≤x<l and 0<y<l; the method comprising the steps of: selecting a compound containing the element A, Al203 , Mn02 , and 4MgC03 »Mg(OH)2 »4H20 as raw materials, weighing the cor¬ responding raw materials in a molar ratio according to the Chemical Formula (1) of the phosphor, and adding a flux to form a mixture; and calcining the mixture at a temperature of 1300-1600°C for 2 to 6 hours .

14. The method according to Claim 13, wherein 0<x<l and 0<y<l.

15. The method according to Claim 13, wherein the method further comprises grinding the mixture before the calcination and grinding the calcinated product.

16. The method according to Claim 13, wherein the calcinated product is washed using water or hot water.

17. The method according to Claim 13, wherein the flux includes at least one of magnesium fluoride and calcium fluo¬ ride .

18. The method according to Claim 13, wherein the calcina¬ tion temperature increases from 1300°C to 1600°C at a rate of 5-10°C/min.

Description:
Description

Red Phosphor, White Light Source, Light Emitting Device, and

Method for Forming the Red Phosphor

Technical Field

The present invention relates to a red phosphor and a method for forming the same, and further relates to a white light source and a light emitting device. Background Art

In recent years, lighting technology is rapidly developed, particularly lighting devices adopting the technology of light emitting diodes (LED) . Lighting devices provided with LEDs have numerous advantages, such as energy saving, long lifetime, and color control etc., which advantages are much more significant, particularly compared with traditional in ¬ candescent lamps and discharge light sources. In order to realize white light utilizing LED technology, a blue LED chip can generally be used in combination with a yellow phosphor and red phosphor or a green phosphor and a red phosphor, so as to mix light to form white light. In order to realize the application of LED technology, the obtainment of a red phos ¬ phor used to form white light becomes a key topic.

A technical solution is provided according to the prior art, refer to the patent document US7846350 B2, which discloses a group of red-emitting phosphors. And the phosphor group con ¬ sists of Mg l4 (Ge (5 _ a) Mn a )0 24 , Sr(Ge (4 _ b) Mn b )O g Mg 2 (Ti (l _ c) Mn c )0 4 etc .. In addition, different maximum emission peaks can be realized through said phosphors when being respectively excited by light sources having different wavelengths , e.g. in the sys ¬ tem Zn 2 {Ti n d) Mn d )0 4 , such a phosphor can have an emission peak located at 675 nm under excitation of a light source located at 362 nm. However, These phosphors can not be excited by blue light, especially the blue light at 460-470 nm, and the emission peak locates in the deep red range which is not the most sensitive range to human eyes. Additionally, with refer ¬ ence to the patent document US2006/0169998A1, it discloses a red phosphor family, which is doped with a tetravalent manga ¬ nese ion Mn 4+ , and would have an emission peak located be ¬ tween 600 nm and 642nm under excitation of a light source having a wavelength between 450 nm and 470 nm. Although said technical solutions can achieve the effect of emitting red light, the stability of the phosphor in a high temperature environment is poor, e.g. the phosphor would decompose at 200°C, and HF acid that is highly toxic is required in the synthesis, which restrains the application of the LED having said phosphor.

In another technical solution of the prior art, an oxynitride red phosphor is provided, and is applied to LED lighting technology. With reference to the patent document

US8274215B2, said patent document discloses a red-emitting phosphor based on CaAlSiN 3 type compounds that are activated by Eu 2+ , and a phosphor of such a type can be excited by blue light and have an emission peak located at 630 nm or 640 nm. In spite of this, the raw materials required by said phosphor and the synthesis process of the nitride compounds require high costs, and a high temperature and high pressure environ ¬ ment is necessary for forming the phosphor. In addition, with reference to the patent document US7329371B2, said pa ¬ tent discloses an oxide phosphor, which can be excited by a light source having a wavelength between 350 nm and 430 nm, and emit red light. However, the phosphor of such a type cannot be excited by a blue light source, and therefore can- not be applied to blue light sources. Summary of the Invention

In order to solve the above technical problems, the present invention provides a novel red phosphor. Such a red phosphor has the advantage of environmental protection because the use of rear earth elements or heavy metal elements is avoided, and the raw materials for manufacturing said phosphor require low cost, the process of synthesizing said phosphor is also simple, and consequently, no complex instrument is necessary. Moreover, said phosphor can improve the color temperature of the white light emitted through LED lighting, enhance illumi ¬ nation intensity, and achieves hereby the requirements of R9 of color rendering index (CRI) . In addition, said red phos ¬ phor can also be excited by blue light or ultraviolet light to produce red light, without absorbing green or yellow light .

According to the present invention, the red phosphor comprises an element A, magnesium (Mg) , aluminum (Al) , oxygen (0) , and manganese (Mn) in Chemical Formula (1) that is (A-x M Sx) Al i4- y °25 y Mn r herein the element A in the Chemical Formula (1) is at least one of strontium (Sr) , barium (Ba) , and calcium (Ca) , and x and y in the Chemical Formula (1) satisfy the relational expressions 0≤x<l and 0<y<l. Said red phosphor provides the possibility of being excited by a blue light source, and the use of rear earth elements or heavy metal elements is avoided.

According to the present invention, it is provided that 0<x<l and 0<y<l in Chemical Formula (1) . Mg is introduced in the said red phosphor and provides the possibility of enhancing luminous intensity. According to the present invention, the red phosphor has an emission peak with wavelength between 635 nm and 675 nm. In this case, a possibility for improving the color of the emit ¬ ted red light is provided so as to satisfy the requirements of R9 of CRI in a better manner. Additionally, it is prefera ¬ ble that the red phosphor has an emission peak with wavelength between 650 nm and 675 nm.

In a preferable embodiment according to the present inven ¬ tion, the red phosphor has an emission peak at 652 nm. By this feature, it is provided that the red light emitting from the phosphor would be acceptable.

Another object of the present invention is achieved through a white light source, which comprises: a blue light emitting diode; and a composition that is provided on the blue light emitting diode, which comprises a red phosphor and a yellow phosphor or a green phosphor and red phosphor, wherein the red phosphor comprises an element A, magnesium (Mg) , aluminum (Al) , ox en (0), and manganese (Mn) in Chemical Formula (1) that is wherein the element A in the Chemical Formula (1) is at least one of strontium (Sr) , bari ¬ um (Ba) , and calcium (Ca) , and 0≤x<l and 0<y<l. In order to achieve proper white light, blue light source in combination with yellow phosphor and red phosphor is used, or blue light source in combination with green phosphor and red phosphor is used. Said white light can be realized through excitation of corresponding phosphors by a blue light source, such that the possibility for LED technology adopting a blue light source can be realized.

According to the present invention, it is provided that 0<x<l and 0<y<l in Chemical Formula (1) . Mg is introduced in the said white light source and provides the possibility of en ¬ hancing luminous intensity.

Further another object of the present invention is achieved through a light emitting device, which comprises a light source emits light; and the red phosphor according to the de ¬ scription, which is excited by at least partial light to gen ¬ erate the excited light with a higher wavelength than that of the original light. In this case, in combination with a blue light emitting LED, the regulation of color temperature can be realized by coating a red phosphor and a yellow phosphor or a green phosphor and a red phosphor on said LED, and the possibility of outputting white light can be achieved.

It is preferable that the light source provides light with wavelength between 450 nm and 470 nm. Light having said wavelength corresponds to a blue light source.

It is preferable that the light source provides light with wavelength between 275 nm and 375 nm. Light having said wavelength corresponds to an ultraviolet light source.

It is preferable that the light source is configured as a LED. LED light sources have advantages of energy saving and long service life etc., and stability and reliability of lighting can hereby be realized.

It is preferable that the red phosphor has an emission peak with a wavelength between 635 nm and 675 nm. In this case, the possibility of improving the color of the emitted red light can be provided, so as to satisfy the requirements of R9 of CRI in a better manner. It is preferable that the red phosphor has an emission peak at 652 nm. By this feature, it is provided that the red light emitting from the phosphor would be acceptable.

Further another object of the present invention is achieved through a method for formin a red phosphor having Chemical

Formula (1) that is wherein the element

A in the Chemical Formula (1) is at least one of strontium (Sr) , barium (Ba) , and calcium (Ca) , and 0≤x<l and 0<y<l; the method comprising the steps of: selecting a compound contain- ing the element A, Al 2 0 3 , Mn0 2 , and 4MgC0 3 •Mg(OH) 2 ·4Η 2 0 as raw materials, weighing the corresponding raw materials in a molar ratio according to the Chemical Formula (1) of the phosphor, and adding a flux to form a mixture; and calcining the mixture at a temperature of 1300-1600°C for 2 to 6 hours. According to the present invention, it is provided that 0<x<l and 0<y<l in Chemical Formula (1) . Mg is introduced in the said method and provides the possibility of enhancing lumi ¬ nous intensity.

According to the present invention, the method further com- prises grinding the mixture before calcination and grinding the calcinated product. Thus, it can be ensured that the mix ¬ ture is uniformly mixed and calcinated properly.

According to the present invention, the calcinated product is washed using water or hot water. In order to obtain the ex- pected compound after calcination, water or hot water is used to wash the calcinated product so as to provide uncontaminat- ed compound.

In a preferable embodiment according to the present inven ¬ tion, the flux includes at least one of magnesium fluoride ^

and calcium fluoride. After the use of said flux, it is easy to remove the flux by washing.

In a preferable embodiment according to the present inven ¬ tion, the calcination temperature increases from 1300°C to 1600°C at a rate of 5-10°C/min. Over-intense decomposition and loose structure as a result of rapid temperature change could be averted.

Brief Description of the Drawings

The accompanying drawings constitute a part of the present Description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention and are used to de ¬ scribe the principles of the present invention together with the Description. In the accompanying drawings, the same components are represented by the same reference numbers. As shown in the drawings :

Figure 1 is a schematic diagram showing a flow for forming a red phosphor according to an embodiment of the present inven ¬ tion; Figure 2 is a schematic diagram showing an X-ray diffraction pattern of the red phosphor according to an embodiment of the present invention; and

Figure 3 shows excitation spectrum and emission spectrum of the red phosphor having Chemical Formula (1) according to two embodiments of the present invention, wherein a curve a is obtained in case of x = 0 and y = 0.02, and a curve b is ob ¬ tained in case of x = 0.02 and y = 0.02. Detailed Description of the Embodiments

The present invention provides a novel red phosphor for LED applications; and in the invention, (Sr l x Mg x ) 4 Al l4 0 25 is selected as host, and Mn 4+ d-d energy level transition is used to re ¬ alize red emission of the phosphor. Furthermore, a bivalent magnesium ion Mg 2+ is doped in the compound, whose presence can be used in the system constructed by the chemical formula

(A_ x Mg x ) 4 Al i4 0 25 : yMn A 4+

to prevent the formation of a bivalent manganese ion Mn + , in order to avoid formation of Mn + and/or the coupling between Mn 4+ resulting in the reduction of luminous intensity, wherein the coupling between the Mn 4+ ions can also be reduced, and the luminous intensity of light emitted by said phosphor can hereby be enhanced.

Figure 1 shows a schematic diagram for steps of forming the phosphor (Sr l x Mg x ) 4 Al l4 y 0 25 : yMn 4+ according to an embodiment of the present invention. Such a phosphor can be synthesized by means of solid-state reaction, and such a chemical synthesis mode requires low costs. Moreover, in order to detect the phase of the compound, X-ray diffraction can be used to ana- lyze the phase of the powder of the compound, which will be specifically described in the following contents. The per ¬ formance of the phosphor can also be measured by emission spectrum and excitation spectrum. During the manufacturing process of said phosphor, a high purity reagent (purity over 99.999%) is used, which comprises e.g. strontium carbonate

SrCO, , . , ALO, . , Mn0 2 ,

3 , aluminum oxide 2 3 , manganese oxide 2 , and

4MgC0 3 »Mg(OH) 2 » 4H 2 0 as starting materials; for example, in order to synthesize one mole of said compound

(Sr l x Mg x ) 4 Al l4 y 0 25 : yMn 4+ , the molar ratio of the required start- mg materials SrC0 , Al ^ , Mn ° and ^gC0 3 .Mg(OH) 2 .4H 2 0 s 14 - v 4

4(l-x): (—-— ): (y) : (—x), and accordingly, when x = 0.02 and y = 0.02, the molar ratio of the above raw materials is 3.92:6.99:0.02:0.016, while said molar can be adjusted in ac ¬ cordance with specific examples. The mixture of reagents is grinded in agate mortar before calcination. During the reac- tion, strontium carbonate 3 will decompose at a high temperature so as to obtain strontium oxide SrO, and

4MgC0 3 »Mg(OH) 2 » 4H 2 0 ^ s also selected out of similar reasons. In order to accelerate said reaction process, a flux, e.g. magnesium fluoride MgF 2 and/or calcium fluoride CaF 2 , can be selected to add into and uniformly mixed with the mixture of the raw materials. As flux, magnesium fluoride and/or calci ¬ um fluoride not only will not react with the raw materials, but also accelerates the chemical reaction; moreover, the flux can be removed after the reaction by washing with e.g. water, so as to assure the purity of the obtained compound. When mixing the reagents and the flux, the corresponding raw materials are weighed in a molar ratio according to the re ¬ quirements of the chemical formula. The obtained mixture is transferred to an AI 2 O 3 crucible after being milled into pow ¬ der, and then calcined. The desired temperature for calcina ¬ tion ranges from 1300°C to 1600°C, and the temperature chang ¬ es at a rate of 5-10°C/min. Moreover, said mixture is calcined for 2 to 6 hours at said temperature to assure that the chemical reaction proceeds in accordance with the pre ¬ dicted requirements, so as to obtain the desired compound, which is then cooled to room temperature and grinded again after the calcination.

It shall be pointed out that the whole calcination process can proceed in a normal pressure environment, in which the possibility of the use of complex instruments can be avoided so as to simplify the preparing process of the desired com ¬ pound. Said compound can be washed wtih e.g. distilled water or hot distilled water after milling the obtained calcined compound, and the washing process can proceed repeatedly for at least three times so as to achieve the object of removing the flux and assuring the purity of the desired compound.

Moreover, Figure 2 shows a schematic diagram of an X-ray dif ¬ fraction pattern of the red phosphor according to an embodiment of the present invention. A pattern for X-ray diffrac- tion (XRD) of the compound (Sr l x Mg x ) 4 Al l4 y 0 25 : yMn 4+ is shown in

Figure 2, wherein x = 0.02 and y = 0.02. In said embodiment, the element A in the Chemical Formula (1) is configured as strontium Sr, and of course, elements such as calcium Ca or barium Ba can also be selected to replace the element stron- tium Sr. Moreover, a standard XRD pattern of Sr 4 Al 4 0 25 having a JCPDS card number of 74-1810 is also shown in the figure. Through the comparison of the XRD patterns of the two com ¬ pounds, it can be observed that the desired compound can be obtained through the above described preparing method, and no peak related with the flux magnesium fluoride and/or calcium fluoride is found in the XRD patterns, which indicates that no flux residual exists in the obtained compound, and the pu ¬ rity of said compound is hereby assured.

Figure 3 shows a schematic diagram of emission spectrum and excitation spectrum of the red phosphor (Sr l x Mg x ) 4 Al l4 y 0 25 : yMn 4+ according to two embodiments of the present invention, where ¬ in the curve a in the figure is obtained with x = 0 and y = 0.02, while the curve b in the figure is obtained with x = 0.02 and y = 0.02. When in the chemical formula x = 0 and y = 0.02, it means there is no magnesium element in the com ¬ pound; while when x = 0.02 and y = 0.02, it means magnesium element is introduced into said compound. And it can be ob ¬ served from the figure that due to the introduction of magne ¬ sium element, the corresponding spectrum curve indicates a significant improvement of luminous intensity of the emitted light obtained from said phosphor, compared with the spectrum curve corresponding to the compound without magnesium ele ¬ ment. Moreover, it can further be seen from the figure that there are two excitation bands in the excitation spectrum from curves a and b, wherein one center is located at 320nm, viz. in the wavelength range of ultraviolet light, while the other center is located at 450nm, viz. within the wavelength of blue light. Thus, it can be determined that said compound is suitable for ultraviolet LED and blue LED applications, and can be excited by said two wavelength ranges. Different compound can be obtained by varying x or y, and it can be seen that in excitation band the spectrum range from 450 nm to 470 nm and from 275 nm to 375 nm. In addition, it can further be seen from the excitation spectrum that the phosphor of said compound does not absorb long wavelength light, e.g. yellow light or green light, wherein the light absorption almost stops as it approaching 490nm. And the advantage lies in that e.g. if a nitride phosphor and a YAG phosphor are simultaneously applied to a blue LED, the luminescence effi ¬ ciency of the LED decreases due to absorption of the long wavelength light, e.g. yellow light, emitted by the YAG phos ¬ phor by the nitride phosphor. Accordingly, as the red phos ¬ phor according to said embodiment does not absorb the long wavelength light, e.g. yellow light, the reduction of LED luminescence efficiency due to absorption of the long wave- length light emitted by a YAG phosphor through the red phos ¬ phor can be avoided, even if said red phosphor and the YAG phosphor are simultaneously applied to a blue LED.

Additionally, it can be observed from the schematic diagram of the emission spectrum of said embodiment that the emission peak is located at 652 nm, and has two shoulder peaks respec ¬ tively located at 640 nm and 660 nm. It has an emission peak with wavelength between 635 nm and 675 nm, preferably, be- tween 650 nm and 675 nm. In addition, compared to other phosphors of Mn 4+ compounds from prior art, the emission peak of said embodiment shifts for about 4 nm, which improves R9 of CRI, so that the emitted red light is more acceptable for hu ¬ man eyes. By adjusting x or y, not only excitation spectrum and emission spectrum could be adjusted, but also luminous intensity be enhanced, tables 1-4 show the different luminous intensity achieved by different x or y.

Table 1 provides values of photometric properties of the red phosphor according to the Chemical Formula (1), wherein x = 0, and y ranges from 0.01 to 1, viz. the chemical formula of the compound is Sr 4 Al l4 _ y 0 25 : yMn 4+ , wherein said compound con ¬ tains no magnesium element, and said measured values are ob ¬ tained based on excitation light having a wavelength at 460 nm, viz. blue excitation light.

Table 1

Y relative luminous intensity (%)

1 100

2 118

3 132

4 156

5 178

6 165 7 159

8 143

9 137

10 123

50 105

60 98

80 75

100 60

Table 2 provides values of photometric properties of the red phosphor according to the Chemical Formula (1), wherein y = 0.05, and x ranges from 0 to 1, viz. the chemical formula of the compound is (Sr l x Mg x ) 4 Al l3g5 0 25 : 0.05 « 4+ , wherein said compound contains magnesium element, and said measured values are ob ¬ tained based on excitation light having a wavelength at 460 nm, viz. excitation light in blue.

Table 2 x (%) relative luminous intensity (%)

0 100

1 134

2 157

3 201

4 218

5 221

6 232

7 213

8 217

9 228 50 148

60 139

80 96

100 85

Table 3 provides values of photometric properties of the red phosphor according to the Chemical Formula (1), wherein x = 0, and y ranges from 0.01 to 1, viz. the chemical formula of the compound is Sr 4 Al l4 _ y 0 25 : yMn 4+ , wherein said compound con ¬ tains no magnesium element, and said measured values are ob ¬ tained based on excitation light having a wavelength at 320 nm, viz. excitation light in ultraviolet.

Table 3 y (%) relative luminous intensi-

1 100

2 232

3 264

4 312

5 356

6 330

7 302

8 284

9 260

10 234

50 210

60 187

80 150

100 80 Table 4 provides values of photometric properties of the red phosphor according to the Chemical Formula (1), wherein y = 0.05, and x ranges from 0 to 1, viz. the chemical formula of the compound is (Sr l x Mg x ) 4 Al l3g5 0 25 : 0.05 « 4+ , wherein said compound contains magnesium element, and said measured values are ob ¬ tained based on excitation light having a wavelength at 320 nm, viz. excitation light in ultraviolet.

Table 4

The above is merely preferred embodiments of the present in ¬ vention but not to limit the present invention. For the per ¬ son skilled in the art, the present invention may have vari ¬ ous alterations and changes. Any alterations, equivalent substitutions, improvements, within the spirit and principle of the present invention, should be covered in the protection scope of the present invention.