Red Phosphor, White Light Source, Light-emitting Device, and Method of Forming the Red Phosphor

Technical Field

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

In recent years, the illumination technology, especially the illuminating device with use of the light-emitting diode (LED) technology, has had rapid development. The illuminating device configured with LED has various advantages, such as energy saving, long service lifetime and controllable light color, which advantages are more obvious especially compared with conventional incandescent lamp and discharge light source. In order to realize the white light using the LED technology, the blue LED chip usually can be used, in combi- nation with a yellow phosphor and a red phosphor or a green phosphor and a red phosphor, so as to mix the light and form the white light. In order to realize the application of the LED technology, to obtain the red phosphor for forming the white light becomes a key topic. It is disclosed in one prior solution a group of phosphors emitting red light, referring to the patent document 1: US 7,846,350 B2. This group of phosphor consists of

Mg _l4 (Ge ₍₅ _ _a) Mn _a )0 _: 24 Sr(Ge ₍₄ _ _b) Mn _b )0 ₉ ^ Mg ₂ (TL _c) Mn _c )0 ₄

etc. Besides, upon being respectively excitated by light sources having different wavelengths, different maximum emission peaks can be realized with this group of phosphor, for instance, in the system of ^{2 (l~d) 4} , this type of phosphor can have an emission peak of 675nm when being excited by a light source at 362nm. However, these phosphors cannot be excited by the blue light, especially the blue light having a wavelength of 460nm-470nm, and the emission peaks obtained from these phos ^¬ phors are located in the deep red range, and the human eye is not most sensitive to the red light in this range.

Besides, refer to patent document 2: US 2006/0169998 Al, which patent discloses a red phosphor family, of which family the phosphor is doped with tetravalent manganese ion Mn _r and it can be realized that the phosphor has emission peak located in the range of 600nm-642nm excited by a light source having a wavelength of 450nm-470nm. Although this solution can realize the effect of emitting red light, the stability of the phosphors is poor in high temperatures, for instance, the phosphors will be decomposed at 200°C, and the toxic hy ^¬ drofluoric acid is required during the synthesis process, and all these factors limit application of this phosphor in LED.

It is provided in another prior solution that oxynitride red phosphor is used and it is used in the LED illumination technology, referring the patent document 3: US 8,274,215 B2. This patent discloses a red light-emitting phosphor based on

CaAlSiN ₃ †-yp _e compounds excited by divalent europium Eu _{r anc} [ this type of phosphor can be excited by blue light and has an emission peak of 630nm or 640nm. Nevertheless, the cost of the raw materials required by this phosphor and the cost of synthesis of the nitride are high, the formation needs high temperature and high pressure, and some of them cannot match YAG phosphor for use at high work temperature. Summary of the Invention

In order to solve the above technical problem, the present invention provides a novel red phosphor. With addition of divalent magnesium ion, the red phosphor has higher light in- tensity than the red phosphor without addition of the diva-

CaAlr. 0, _Q : yMn ⁴⁺ . ,

lent magnesium ion, e.g. ^y . Besides, compared with the nitride red phosphor, the raw materials required for manufacturing this novel red phosphor have a lower cost, the synthesis process to be used is simpler, the manufacturing cost can be reduced, and this red phosphor can be excited by blue light.

A red phosphor according to the present invention comprises an element A, magnesium (Mg) , aluminum (Al , oxygen (0) and manganese (Mn) in a chemical formula (1)

wherein the element A in the chemical formula (1) is at least one selected from strontium (Sr) , barium (Ba) and calcium (Ca) , and 0<x<0.1 and 0<y<l. According to such configuration, the red phosphor not only can be excited by blue light, but also can realize the possibility of having stronger lumines- cence intensity than the phosphor without the magnesium ele ^¬ ment and, for instance, phosphor uniting magnesium ion and aluminum ion. Preferably, the element A in the chemical for ^¬ mula (1) is selected to be calcium (Ca) . The red phosphor ob ^¬ tained accordingly has the possibility of emitting red light with higher luminescence intensity and more acceptable to hu ^¬ man eyes.

According to the red phosphor in present invention, in the chemical formula (1), 0<y<0.1. The red phorsphor obtained ac cordingly has the possibility of emitting light with notably increased luminescence intensity. The red phosphor according to the present invention, y in chemical formula (1) is 0.025. When y is preferably selected to be 0.025, the phosphor achieved accordingly as x varies can be enhanced notably in terms of luminescence intensity. The red phosphor according to the present invention has an emission peak with a wavelength between 641nm and 664nm.

Thus, the possibility of emitting red light upon excitation of the phosphor is realized.

The red phosphor according to the present invention has emis- sion peaks with wavelengths of 641nm, 654nm and 664nm. In this way, the possibility that the red light emitted from the red phosphor meets requirements of human eyes can be real ^¬ ized. Another object of the present invention is accomplished via a white light source, comprising: a blue light-emitting diode; and a composition, disposed on the blue light-emitting diode and comprising a red phosphor and a yellow phosphor or a red phosphor and a green phosphor, wherein the red phosphor comprises an element A, magnesium (Mg) , aluminum (Al) , oxygen (0) and manganese (Mn) in a chemical formula (1) -AAh2-x- _y Mg _x O _l9 . yMn ^ wherein the element A in the chemical formula (1) is at least one selected from strontium (Sr) , barium (Ba) and calcium (Ca) , and 0<x<0.1 and 0<y<l. In order to ob ^¬ tain suitable white light, a blue light source is used in combination with a yellow phosphor and a red phosphor, or a blue light source is used in combination with a green phos ^¬ phor and a red phosphor. The white light can be realized upon excitation of corresponding phosphor by the blue light source so as to have the possibility of the LED technology using the blue light source. According to the white light source in present invention, in the chemical formula (1), 0<y<0.1. The red phosphor obtained accordingly has the possibility of emitting light with nota ^¬ bly increased luminescence intensity.

The white light source according to the present invention, y in chemical formula (1) is 0.025. When y is preferably se ^¬ lected to be 0.025, the phosphor achieved accordingly as x varies can be enhanced notably in terms of luminescence in ^¬ tensity.

Another object of the present invention is accomplished via a light-emitting device, comprising: a light source generating light output; and the red phosphor according to the preceding description, which is configured to transform at least a part of the light output to have a longer wavelength. In this way, in combination with the LED emitting blue light, the color temperature can be adjusted by coating on the LED the red phosphor and yellow phosphor or red phosphor and green phosphor, and it can output white light.

Preferably, the light source provides light with a wavelength between 450nm and470nm. Light having this wavelength is cor- responding to the blue light source, and the possibility of exciting this phosphor with the blue light source can be re ^¬ alized.

Further preferably, the light source provides light with a wavelength of 459nm. Preferably, light of this wavelength can well excite the phosphor of this light color, and it is real ^¬ ized that the emitted red light is more easily received by human eyes.

Preferably, the light source provides light with a wavelength between 300nm and400nm. Light having this wavelength is cor- responding to the ultraviolet light source, and the possibil ^¬ ity of exciting this phosphor by the ultraviolet light source can be realized.

Further preferably, the light source provides light with a wavelength of 334nm. Preferably, light of this wavelength can well excite the red phosphor and meet requirement of human eyes to red light.

Preferably, the light source is configured as an LED light source. The LED light source has the advantages of energy saving, long service lifetime, etc., and can realize illumi ^¬ nation stability and reliability.

Preferably, the red phosphor has emission peaks with a wave ^¬ length between 641nm and664nm. Thus, it can provide the possibility of improving the color of the emitted red light, and make the red light to be more easily received by human eyes so as to meet the requirement of the color rendering index R9.

Further preferably, the red phosphor has emission peaks with wavelengths of 641nm, 654nm and 664nm. Preferably, these emission peaks can provide red light more easily acceptable by human eyes.

Another object of the present invention is accomplished via a method of formin a red phosphor having a chemical formula

(1) wherein the element A in the chemical formula (1) is at least one selected from strontium (Sr) , barium (Ba) and calcium (Ca) , and 0<x<0.1 and 0<y<l, and the method comprises: taking a compound containing the element A,

AW ² , ³ , MnO _? ² and , 4MgbCO,3 al ,s, and weighing corresponding raw materials according to a molar ratio required by the chemical formula (1), and mixing a flux so as to form a mixture; and calcining the mixture at 1300- 1600°C for 2-6 hours. The method according to the present invention, in the chemical formula (1), 0<y<0.1. The red phosphor obtained accord ^¬ ingly has the possibility of emitting light with notably in ^¬ creased luminescence intensity.

The method according to the present invention, y in chemical formula (1) is 0.025. When y is preferably selected to be

0.025, the phosphor achieved accordingly as x varies can be enhanced notably in terms of luminescence intensity.

The method according to the present invention, the compound containing the element A comprises corresponding oxide, hy- droxide, carbonate or nitrate. By using the corresponding compound as raw material such as corresponding hydroxide, carbonate or nitrate, synthesis of the red phosphor can be achieved through decomposition of the compound in high temperature and obtaining the oxide. According to a preferred solution of the present invention, the method further comprises grinding the mixture prior to calcining, and grinding the calcinated product. In this way, it can be ensured that the mixture can be uniformly mixed and appropriately calcinated. According to a preferred solution of the present invention, the calcinated product is washed with water or hot water. In order to obtain expected compound after the calcination, the calcinated product is washed with water or hot water to ob ^¬ tain pollution-free compound. According to a preferred solution of the present invention, the flux comprises at least one of magnesium fluoride and calcium fluoride. After use of the flux, it can be easily re ^¬ moved by washing with water. According to a preferred solution of the present invention, a calcining temperature rises from 1300°C to 1600°C at a rate of 5-10°C/min so as to prevent loose structure of the com ^¬ pound caused by dramatic decomposition of the raw materials due to too rapid temperature change. 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 compo ^¬ nents are represented by the same reference numbers. As shown in the drawings :

Fig. 1 is a schematic diagram of process of forming a red phosphor according to the present invention;

Fig. 2 is a schematic diagram of X-ray diffraction pattern of the red phosphor according to the present invention, wherein y=0.025, and x is 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 and 0.1, respectively; Fig. 3 is excitation spectrum and emission spectrum of the red phosphor having the chemical formula (1) according to one embodiment of the present invention, wherein x=0.08 and y=0.025; and Fig. 4 is listing of luminescence intensity of the red phos ^¬ phor having the chemical formula (1) according to the present invention, wherein y=0.025 and x is 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 and 0.1, respectively. Detailed Description of the Embodiments

According to the solution of the present invention, a novel red phosphor for an LED light source is provided. With the LED light source, advantages of high efficiency, energy sav ^¬ ing and long service life can be realized. In this invention,

CaAl _l2 _ _x _ _y Mg _x O _{l9 U} sed as a host, and meanwhile, the d-d energy transition of the tetravalent manganese ion Mn j_ _{s U} sed to realize emission of red light by the phosphor. As the

CaAl _l2 _ _x _ _y Mg _x O _{l9 U} sed as the host, the charge balance of Mn in the phosphor crystal can be realized with the maganesium ion and the phosphor performance is enhanced. Besides, use of the solid state method provides a low cost method of forming or synthesizing the red phosphor. Based on this red phosphor, a white light source with good performance and illuminating device having the white light source can be manufactured so as to provide good illumination effect.

Fig. 1 shows a schematic diagram of flow of forming a red

, CaAl _n Mg _x O _l9 : yMn ⁺ ^

phosphor ^{x iy} according to the present invention. According to the solution of the present invention, this type of red phosphor is synthesized using a solid state reaction, which chemical synthesis method has a low cost, and in order to detect the phase of the compound, the phase of the compound powder can be analyzed using a method of X-ray diffraction analysis, which content will be introduced in the following. Various performances of this phosphor are also ex- hibited by the emission spectrum and excitation spectrum. During the process of manufacturing the phosphor, high-purity reactants (the purity is greater than 99.999%) are used, and these reactants comprise calcium carbonate ^ ^fl ^ , aluminum

. , ALO, . , MnO _? , 4MgCO, *Mg(OH) * 4H O oxide ^{2 3} , manganese oxide ² , and ^{& 3 &} ' ^{2 2} It is understood that the calcium carbonate can be replaced with e.g. oxide, hydroxide, carbonate or nitrite containing the element calcium, and certainly it is not limited to the above mentioned compound, any other compound containing ele ^¬ ment calcium that can achieve the similar or the same effect can be used to replace calcium carbonate, so as to obtain the oxide of the element calcium after decomposition in high temperature, to ensure the successful synthesis of the red phos ^¬ phor. Further, it is understood for the person skilled in the art that replacing the element calcium with at least one of e.g. element strontium or element barium is also plausible, so as to achieve the similar or the same photometric effect of the red phosphor containing the element calcium, e.g. similar or same spectral characteristic.

The above reactants are taken as starting reaction materials, and according to proportions of elements of the chemical for ^¬ mula of the red phosphor according to the present invention, for instance, in order to synthesize 1 mole of this compound

CaAl _{l2 x y} Mg _x O _l9 . yMn ^ molar ratio of the required starting

^ . , CaCO, ALO, MnO _? , 4MgCO, · Mg(OH) _? · 4Η _? 0 . raw materials ³ , , and ^{& 3 &} ' ^{2 2} is

12 - x - y x

1 : ( ^ ) : y : (^), and then when x=0.08 and y=0.025, for instance, the molar ratio of the above raw materials is 1:5.9475:0.025:0.016. The molar ratio could be modified cor ^¬ respondingly according to the situation of the embodiment. The mixture of the reactants is firstly milled in an agate mortar prior to calcining. During the reaction, the calcium carbonate CaC0 _{3 w} j_-|_-|_ ^ _θ decomposed at high temperature so as to obtain, for instance, calcium oxide CaO , which calcium oxide has high reactivity; moreover, to choose

4MgC0 ₃ ^» Mg(OH) ₂ ^» 4H ₂ 0 _{as raw ma} - _| -erial j_ _{s a]} _ _S o for similar reason, for example, oxide of magnesium with high reactivity can be obtained. Besides, in order to accelerate the reaction process, flux such as magnesium fluoride _anc }/or calcium fluoride CaF ² can be chosen to be added to the mixture of the raw materials and uniformly mixed. The magnesium fluoride and/or calcium fluoride as flux will not react with the raw materials, and could accelerate the chemical reaction, and be washed with, e.g., water, preferably, distilled water, after the reaction is completed so as to achieve the effect of re- moving the flux and ensuring the purity of the resulting compound obtained. When the reaction raw materials and the flux are mixed, corresponding raw materials are weighed based on the molar ratio according to requirements of the chemical formula. After the resulting mixture is grinded into powder, it is transferred to aluminum oxide crucible and starts calcining. The temperature required in the calcination is be ^¬ tween 1300°C and 1600°C with increasing rate at 5-10°C /min. Besides, the mixture is calcinated at this temperature for 2- 6 hours so as to ensure the chemical reaction to be conducted according to predetermined requirements, thus obtaining re ^¬ quired compound. The temperature can be cooled to room tem ^¬ perature after the calcination is completed for grinding again to obtain the powder, by using e.g. distilled water, the powder obtained is washed for at least three times to re- move flux, so as to ensure the obtainment of the red phosphor with few impurity or no impurity.. According to the synthesis method, the compound in chemical formula C ^a Al _n - _x - _y Mg _x O _l9 . yMn ^ _θ achieved, based on the compound, considering the difference between respective ion ra ^¬ dius, the magnesium ion and manganese ion are more suitable to unite with aluminum ion rather than uniting with calcium ion, besides, with the introduction of magnesium, the charge difference between manganese ion and aluminum ion can be bal ^¬ anced, so that a compound with large solid solution is achieved, the emission spectrum of the compound does not change with the introduction of magnesium ion, the luminescence intensity of the compound is also enhanced.

Furthermore, Fig. 2 shows a schematic diagram of X-ray dif ^¬ fraction pattern of the red phosphor according to the present invention. Fig. 2 shows the X-ray diffraction pattern of a compound obtained from the chemical formula

CaAl _l2 _ _x _ _y Mg _x O _l9 : yMn ⁴⁺ ^ _{η y= 0} ^ _{2 5 f and χ i s} ^ _Q ^ _{l f Q} ^ _{2 f}

0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 and 0.1, respective ^¬ ly. According to Fig. 2, it can be observed that, at the po ^¬ sitions indicated by the solid dots which are corresponding to the peak at respective 2-theta angle, e.g. when x is greater than 0.07, the second phase is observed in the X-ray

Al O

diffraction pattern which represents ^{2 3} . In this embodiment, the element A in the chemical formula (1) is chosen as the element calcium Ca. According to this pattern, after com-

CaAl O

paring with the standard pattern of ^{12 19} , it is understood that, the final solid-state compound can be formed by intro ^¬ ducing the divalent magnesium ion into the structure CaAl O

^{12 19} , so as to obtain the solid red phosphor. In addition, the aid of the X-ray diffraction pattern, it also can be seen that the compound of the red phosphor having a high purity can be well formed according to the above solid-phase synthe ^¬ sis method since the peak value related to magnesium fluoride or calcium fluoride is not found in this pattern.

Fig. 3 shows excitation spectrum and emission spectrum of the red phosphor having the chemical formula (1) according to one example of the present invention, wherein x=0.08 and y=0.025. It can be seen from Fig. 3 that the excitation spectrum, obtained according to the chemical formula C ^a Al _n - _x - _y Mg _x O _l9 . yMn ^ where x=0.08 and y=0.025, have two excitation bands, of which one is located at 334nm, i.e. within the ultraviolet wave ^¬ length range, and the other is located at 459nm, i.e. within the blue-light wavelength range. Based on such excitation light, emission light, for instance, having emission wave ^¬ length of 641nm, can be obtained. Thus, it can be seen that it is possible to use this compound for ultraviolet LED lamp and blue-light LED lamp, and it is excited by a light source having the two types of wavelength. Besides, it can be seen from the excitation spectrum that the phosphor of this compound does not absorb long-wavelength light, such as yellow light or green light, wherein according to Fig. 3, the light absorption stops almost at 490nm. In accordance with such configuration, for example, if the nitride phosphor and YAG phosphor in the prior art are applied simultaneously to the blue-light LED, the light-emitting efficiency of the LED will be reduced as the nitride phosphor absorbs the long- wavelength light, such as yellow light, emitted from the YAG phosphor. Therefore, according to the embodiment of the pre ^¬ sent invention, the red phosphor does not absorb the long- wavelength light, such as yellow light, and when the red phosphor and the YAG phosphor are used simultaneously on the blue-light LED, for instance, it can avoid the reduction of light-emitting efficiency of the LED caused by absorption of the long-wavelength light emitted from the YAG phosphor by the red phosphor.

It is also shown in Fig. 3 the emission spectrum of the red phosphor having the chemical formula (1) according to the em- bodiment of the present invention, wherein x=0.08 and

y=0.025, wherein the emission peak is located at 654nm, and there are two shoulder peaks, at about 641nm and 664nm, re ^¬ spectively. Such emission peaks is located in the deep red range. According to such configuration, the color rendering index applied to the LED illumination technology can be ef ^¬ fectively improved to be more acceptable to human eyes.

Fig. 4 shows listing of luminescence intensity of the red phosphor having the chemical formula (1) according to the present invention, wherein y=0.025 and x is 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 and 0.1, respective ^¬ ly. Since the emission spectrum obtained from the chemical ί i I X CaAl _n Mg _x O _l9 : yMn ⁺ . . ^ ^ .

formula (1), namely, is consistent with the emi .ssi .on spect ,rum of CaAl ^1L _q ⁹ ₇ ⁷⁵ _S 0, ¹ q ⁹ : 0.025 « ⁴⁺ , m . _Fi .g. 4„, the luminescence intensity of the compound obtained when x=0. and y=0.025, i.e. CaAl _{U 975} O _l9 . 0.025 Mn ^ ^ _{s ta} ^ _{en as} ^ _e baseline, the relative luminescence intensity when x is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 and 0.1, respective ^¬ ly, can be obtained compared with x=0. As shown in Fig. 4, when x=0.08, the compound having the maximum relative lumi- nescence intensity can be obtained, and the red phosphor ob ^¬ tained according to such compound can have greater relative luminescence intensity compared with the case where ^> is not introduced, and thus, the compound of the red phosphor according to the present invention is enabled to have better light-emitting performance due to the introduction of ^> as charge balance.

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 sub ^¬ stitutions, improvements, within the spirit and principle of the present invention, should be covered in the protection scope of the present invention.