KR100818601B1 - Red phosphor, manufacturing method thereof and white light emitting device comprising the same - Google Patents

Abstract

The present invention relates to a novel red phosphor represented by the following Chemical Formula 1, a method for manufacturing the same, and a white light emitting device including the same, wherein the red phosphor is excited by blue and UV light sources and has a high luminous efficiency. When the white light emitting device is manufactured, a white color close to natural colors can be realized.

<Formula 1>

(Ca ₁ - _x M _x ) A _a B _b S _s : Eu ²⁺ , Q

Wherein M is a divalent cation selected from the group consisting of Mg, Sr, Ba, and Zn, A is a tetravalent cation selected from the group consisting of Si, Ge, and B is Al, Ga , Sc, Y, La and Gd is characterized in that the trivalent cation selected from the group consisting of, Q is characterized in that at least one member selected from the group consisting of halogen elements, x is 0 to 0.2, a is 0 < a <0.5>, b is 0 <b <1.0 and s is 1 + 2a + 3b / 2.

Description

Red phosphor, method for manufacturing the same, and white light emitting device comprising the same {Red Phospher, method of preparation, and White Ligth Emitting Device comprising the same}

The present invention relates to a novel red phosphor, a manufacturing method thereof and a white light emitting device comprising the same.

Light Emitting Diode (LED) is a futuristic display device that is one of the most recent research fields due to its application to flat panel displays as well as various instrument panels and TVs. Known. When an electric field is applied around these LEDs, electrons injected from the cathode and holes formed in the anode combine in the light emitting layer to form a so-called “single exciton”, which emits a variety of light when it transitions to the ground state. The light emitting device of this principle is a semiconductor device with high luminous efficiency, low power consumption and good thermal stability, and has long life and good responsiveness.

Among these LEDs, white LEDs have various applicability and marketability, such as lighting for home appliances, backlights for liquid crystal display (LCD) panels, interior lights of automobiles, and are actively researched in recent years.

There are three main ways to implement white LED.

First, a combination of three LEDs emitting red, green, and blue colors is used to realize white color. This means that three LEDs must be used to make one white light source, and each LED has a different thermal or temporal characteristic, and thus the color tone is changed according to the use environment, and a uniform color mixture is not realized, and the luminance is not high. Moreover, since the color rendering property is only about 40, it is not suitable for use in general lighting or flash light sources.

The second method is to implement white by exciting a yellow phosphor using a blue LED as a light source. Such yellow phosphors include YAG or GAG-based phosphors (Nichia, U. S. Patent No. 6069440), and TAG-based phosphors (Osram, U.S. Patent No. 6504179). This strong coloring has the drawback of absorbing a part of blue light emission as white. In addition, this method is excellent in luminous efficiency, but the color rendering index (CRI) is low, the color display index is changed according to the current density, there is a disadvantage that can not obtain white light close to the sunlight.

Finally, there is a method of disposing a phosphor on a light emitting diode chip, and mixing a part of the primary light emission of the light emitting diode chip with the secondary light emission wavelength-converted by the phosphor to implement white. A white light emitting device is manufactured by using a blue light emitting diode chip and phosphors excited by blue light to emit green and red light. That is, white light having a high color rendering property of 85 or more may be realized by mixing a mixture of green light and red light excited by blue light and blue light. In this case, a thiogallate group capable of being excited by blue light and emitting light from the green to the yellow band is used as the green light emitting phosphor. The composition of a representative thiogolite group is represented by (Ca, Sr, Ba) (Al, Ga, In) ₂ S ₄ : Eu (or Ce). Among these, the SrGa 2 S 4: Eu phosphor is a green light emitting phosphor having a high light emission intensity. On the other hand, as the red light-emitting phosphor, sulfides or phosphides represented by SrS: Eu, (Sr, Ca) S: Eu, CaS: Eu or Y ₂ O ₃ : Eu, which are excited by blue light and can emit light in a red band System phosphors are used. However, the red light-emitting phosphor represented by (Sr, Ca) S: Eu has a serious problem of low emission intensity and poor chemical stability to moisture. In addition, in the case of sulfide-based or phosphide-based red phosphors, the luminous efficiency is extremely low, and due to the high reactivity of the sulfide-based or phosphorus-based red phosphors, the manufacturing process is difficult, and when applied to an ultraviolet LED chip, there is a problem of reducing the durability of the product by reacting with the LED chip. . Accordingly, the situation is limited to the application to general lighting and LCD backlighting device. Therefore, there is an urgent need for the development of a novel red light-emitting body that is relatively simple and chemically stable with a high luminous efficiency.

Therefore, the present invention provides a novel red light emitting phosphor and a method of manufacturing the same to solve the problems of the existing red light emitting phosphor. Another object of the present invention is to provide a white light emitting device having better color reproducibility and optical characteristics by using the novel red light emitting phosphor of the present invention.

In order to achieve the above object, the red phosphor of the present invention is characterized by the following formula (1).

[Formula 1]

(Ca ₁ - _x M _x ) A _a B _b S _s : Eu ^{2 +} , Q

Wherein M is a divalent cation selected from the group consisting of Mg, Sr, Ba, and Zn, A is a tetravalent cation selected from the group consisting of Si, Ge, and B is Al, Ga , Sc, Y, La and Gd is characterized in that the trivalent cation selected from the group consisting of, Q is characterized in that at least one member selected from the group consisting of halogen elements, x is 0 to 0.2, a is 0 < a <0.5>, b is 0 <b <1.0 and s is 1 + 2a + 3b / 2.

Eu is an active agent that actually plays a role of causing luminescence, and its content is included in a molar ratio of 0.001 to 0.01 with respect to mole of Ca of Chemical Formula 1.

In addition, Q is an active agent that is optionally used with the active agent, it is preferably an anion selected from a halogen element and is contained in 1 to 10% by weight of the total phosphor compound.

The red phosphor of the present invention is manufactured through the following process. Mixing each of the compounds; First calcining the mixture; Pulverizing the first calcined sample and secondary calcining by adding sulfur; The second firing step is repeated to consist of a third firing step.

In addition, a white light emitting device for achieving another object of the present invention is characterized in that it comprises the red phosphor.

The novel red phosphor of the present invention has better luminous efficiency than the conventional (Sr, Ca) S: Eu and sulfide- or phosphide-based red phosphors, and is chemically stable and has an LED chip even when applied to an ultraviolet LED chip. The reaction is insignificant and does not reduce the efficiency of the product. Therefore, when manufacturing white LED using this, it can be applied to a wide range of fields such as general lighting and LCD backlighting device.

Hereinafter, the present invention will be described in more detail.

The novel red phosphor of the present invention is represented by the following Chemical Formula 1.

<Formula 1>

(Ca ₁ - _x M _x ) A _a B _b S _s : Eu ^{2 +} , Q

Wherein M is a divalent cation selected from the group consisting of Mg, Sr, Ba, and Zn, A is a tetravalent cation selected from the group consisting of Si, Ge, and B is Al, Ga , Sc, Y, La and Gd is characterized in that the trivalent cation selected from the group consisting of, Q is characterized in that at least one member selected from the group consisting of halogen elements, x is 0 to 0.2, a is 0 < a <0.5>, b is 0 <b <1.0 and s is 1 + 2a + 3b / 2.

The method for producing a novel red phosphor according to the present invention comprises the steps of mixing a Ca-containing compound, Eu-containing compound, S-containing compound, Q-containing compound, A-containing compound, B-containing compound and M-containing compound (first step); First baking the mixture at a temperature of 700 to 1000 ° C. for 1 to 3 hours (second step); Pulverizing the first calcined sample, and adding sulfur to secondary calcining at a temperature of 2700 to 1000 ° C. for 1 hour to 3 hours (third step); And a third firing step (fourth step) of repeating the second firing step.

The first step is a step of mixing various compounds constituting the red phosphor of the present invention, specific examples of the compound are as follows.

First, the Ca-containing compounds include Ca-containing oxides, Ca-containing carbonates, Ca-containing chlorides, Ca-containing hydroxides, Ca-containing sulfates, Ca-containing fluorides, Ca-containing nitrates, Ca-containing acetates and mixtures thereof Etc. may be used, specifically CaO, CaCO ₃ , Ca (OH) ₂ , and CaSO ₄ are used.

In addition, the Eu-containing compound may be selected from Eu ₂ O ₃ , Eu (CO ₃ ) ₃ , Eu (OH) ₃ , Eu (NO ₃ ) ₃ and a compound in which a coprecipitation compound is formed from Eu metal, but is not limited thereto. Of these, Eu ₂ O ₃ is preferred.

In addition, it is preferable that S of this invention uses powder.

In addition, the Q-containing compound is a compound containing at least one halogen element selected from the group consisting of F, Cl and Br, selected from the group consisting of NH ₄ F, BaF ₂ , AlF ₃ , NH ₄ Cl and BaCl ₂ . .

Further, the A-containing compound is selected from the group consisting of Si-containing compounds and Ge-containing compounds, wherein the Si-containing compounds are Si-containing oxides, Si-containing carbonates, Si-containing chlorides, Si-containing hydroxides, Si-containing Sulfates, Si-containing fluorides, Si-containing nitrates, Si-containing acetates and mixtures thereof and the like can be used, specifically SiO ₂ and Si ₃ N ₄ .

Ge-containing compounds include Ge-containing oxides, Ge-containing carbonates, Ge-containing chlorides, Ge-containing hydroxides, Ge-containing sulfates, Ge-containing fluorides, Ge-containing nitrates, Ge-containing acetates, mixtures thereof, and the like. And specifically GeO ₂ .

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In addition, the B-containing compound is selected from the group consisting of Al-containing compounds, Ga-containing compounds, Sc-containing compounds, Y-containing compounds, Sb-containing compounds, La-containing compounds and Gd-containing compounds, wherein the Al-containing compounds are Al-containing oxides, Al-containing carbonates, Al-containing chlorides, Al-containing hydroxides, Al-containing sulfates, Al-containing fluorides, Al-containing nitrates, Al-containing acetates and mixtures thereof and the like can be used, specifically Al ₂ O ₃ .

Ga-containing compound is Ga-containing oxide, Ga-containing carbonate, Ga-containing chloride, Ga-containing hydroxide, Ga-containing sulfate, Ga-containing fluorides, Ga-containing nitrate, Ga-containing nitrate and mixtures thereof and the like may be used, specifically, the Ga ₂ O ₃ to be.

Sc-containing compounds, Sc-containing oxides, Sc-containing carbonates, Sc-containing chlorides, Sc-containing hydroxides, Sc-containing sulfates, Sc-containing fluorides, Sc-containing nitrates, Sc-containing acetates and mixtures thereof, and the like, specifically Sc ₂ O ₃ to be.

Y-containing compounds, Y-containing oxides, Y-containing carbonates, Y-containing chlorides, Y-containing hydroxides, Y-containing sulfates, Y-containing fluorides, Y-containing nitrates, Y-containing acetates and mixtures thereof, and the like, specifically Y ₂ O ₃ to be.

Sb-containing compounds, Sb-containing carbonates, Sb-containing chlorides, Sb-containing hydroxides, Sb-containing sulfates, Sb-containing fluorides, Sb-containing nitrates, Sb-containing acetates and mixtures thereof, and the like, specifically Sb ₂ O ₃ to be.

La-containing compound is La containing oxides, La-containing carbonate, La-containing chloride, La-containing hydroxide, La-containing sulfate, La-containing fluorides, La-containing nitrate, La-containing nitrate, can be used and a mixture thereof, and, specifically, La ₂ O ₃ to be.

Gd-containing oxides, Gd-containing carbonates, Gd-containing chlorides, Gd-containing hydroxides, Gd-containing sulfates, Gd-containing fluorides, Gd-containing nitrates, Gd-containing acetates, mixtures thereof, and the like, specifically, Gd ₂ Selected from O ₃ .

Meanwhile, the M-containing compound is selected from Mg, Sr, Ba, and Zn-containing compounds, and specifically Mg-containing compounds, for example, Mg-containing oxides, Mg-containing carbonates, Mg-containing chlorides, Mg-containing hydroxides, Mg-containing sulfates, and Mg-containing compounds. Fluoride, Mg-containing nitrates, Mg-containing acetates or mixtures thereof can be used, preferably MgCO ₃ .

Examples of Sr-containing compounds include Sr-containing oxides, Sr-containing carbonates, Sr-containing chlorides, Sr-containing hydroxides, Sr-containing sulfates, Sr-containing fluorides, Sr-containing nitrates, Sr-containing acetates, or mixtures thereof, preferably Is SrCO _{3 .}

Examples of Ba-containing compounds include Ba-containing oxides, Ba-containing carbonates, Ba-containing chlorides, Ba-containing hydroxides, Ba-containing sulfates, Ba-containing fluorides, Ba-containing nitrates, Ba-containing acetates or mixtures thereof, and preferably BaCO₃to be_.

Examples of Zn-containing compounds include Zn-containing oxides, Zn-containing carbonates, Zn-containing chlorides, Zn-containing hydroxides, Zn-containing sulfates, Zn-containing fluorides, Zn-containing nitrates, Zn-containing acetates or mixtures thereof, and the like. ZnCO₃to be_.

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Next, in the second step, the compounds are mixed and then first baked at a temperature of 700 to 1000 ° C. for 1 hour to 3 hours. Thereafter, in the third step, the first calcined sample is ground with a mortar and the like, and sulfur (S) is added to secondary calcining at the same temperature and time as the first calcining. The final fourth step is the third firing step and the second firing step is repeated.

The red phosphor of the present invention manufactured by the above method exhibits an excitation spectrum in the region of 460 to 490 nm. In addition, the red phosphor has been reported to exhibit an emission spectrum in the range of 600 to 740 nm.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example  One: CaSi _a Ga _{0 .4} S _s : Eu ^{2 +} , F ^-  Red phosphor manufacturing

CaCO ₃ , SiO ₂ , Ga ₂ O ₃ and S were mixed in a molar ratio of 1: a: 0.2: 2 (0 <a ≦ 0.5), where Eu ₂ O ₃ was added in an amount of 0.001 to 0.01 mole relative to CaCO ₃ . . Zirconia ball and ammonium fluoride (NH ₄ F) as a solvent are added to the mixture to 3% by weight of the total mixture and placed in a sealed teflon container in acetone or ethanol, mixed for 10 hours, and the zirconia ball and the mixture are sieved. Separated and dried in an electric oven at 90 ° C. for 12 hours.

The dried material was first calcined for 3 hours at 900 ° C. under a H ₂ / N ₂ reducing atmosphere using a tube furnace. In addition, the first calcined product was ground in a mortar and pestle. Further small amounts of sulfur were added to the pulverized product, followed by secondary firing under the same conditions as the primary firing. In addition, the final product was obtained through a third firing step of firing the secondary firing product once more.

The luminescence and excitation spectra of the prepared red phosphor were measured using a luminescence spectrometer, and the results are shown in FIGS. 1 and 2. 1 is a luminescence specification of two phosphors having Si values a of 0 and 0.05, respectively, measured by irradiation with 460 nm light. It emits red light luminescence having a peak point at 640 nm, and the luminescence size increases greatly as Si ions are added.

In addition, Figure 2 is an excitation spectrum of the peak point 640 nm, the red phosphor absorbs light in the wavelength range of 420 to 600 nm to emit red luminescence, the peak point of the excitation spectrum is 460 nm to 490 nm region Appeared in.

Example  2: ( Ca _{0 .92} Ba _{0 .08} ) Si _{0 .225} Ga _b S _s : Eu ^{2 +} , Cl ^-  Manufacture of red phosphor

CaCO₃, BaCl₂, SiO₂, Ga₂O₃ And S in a molar ratio of 1: 0.08: 0.05: b (0 <b≤0.5): 2, wherein Eu₂O₃Is the CaCO₃ Contrast was added at 0.001 to 0.01 mole. The mixture contains zirconia balls and ammonium chloride (NH) as a solvent.₄Cl) was added to 3% by weight of the total mixture and placed in a sealed Teflon container in acetone or ethanol, mixed for 10 hours, the zirconia ball and the mixture were sieved and dried in an electric oven at 90 ° C. for 12 hours. . The firing conditions of each step were changed to 1000 ° C tube furnace.₂/ N₂ 3 hours under reduced atmosphere (Ca_{0 .92}Ba_{0 .08}Si_{0 .225}Ga_bS_s: Eu^{2 +}, Cl^-A red phosphor was prepared.

Figure 3 shows the luminescence spectrum as the Ga content b is changed to 0, 0.1, 0.2, 0.8, 1.0. It can be seen that as the Ga content increases, the position of the peak point gradually moves toward the shorter wavelength. That is, the position of the peak point of the graph 1 when no Ga ions were added was 659 nm, and was 643 nm when b = 1.0 (graph 5).

Example  3: CaSi _{0 .05} Ga _{0 .One} S _s : Eu ^{2 +} , xF ^-  Manufacture of red phosphor

CaCO₃, SiO₂, Ga₂O₃ And S in a molar ratio of 1: 0.05: 0.1: 2 and here Eu₂O₃Is the CaCO₃ Contrast was added at 0.001 to 0.01 mole. In addition, the content of ammonium fluoride x is added to the CaSi in the same manner as in Example 1, except that it is added while changing to 3, 5 and 8 wt% of the total mixture, respectively._{0 .05}Ga_{0 .One}S_s: Eu^{2 +}, xF^- A red phosphor was prepared.

Next, Figure 4 shows the luminescence spectrum of the prepared phosphor, the intensity of the luminescence is greater when 5 to 8 wt% (graphs 2 and 3, respectively) than 3 wt% of NH ₄ F (graph 1). It can be seen that the increase, and the peak viscosity is moved toward the short wavelength.

Example  4: Ca ( SiGe ) _0.05 Ga _{0 .4} S _s : Eu ^{2 +} , F ^-  Manufacture of red phosphor

CaCO₃, SiO₂, GeO₂, Ga₂O₃ And S in a molar ratio of 1: 0.05: 0.05: 0.4: 2, wherein Eu₂O₃Is the CaCO₃ Contrast was added at 0.001 to 0.01 mole. NH₄F is added to Ca (SiGe) in the same manner as in Example 1, except that F is added to about 8 wt% of the total mixture._0.05Ga_{0 .4}S_s: Eu^{2 +}, F^- A red phosphor was prepared.

Next 5 is tetravalent cation Ge CaSi _{0 .05} Ga is not added is prepared the red phosphor (graph 2) and the addition of Ge was added in ^{_{0 .4 S s: Eu 2 +}} , F - in the (graph 1) As a luminescence spectrum, when the Ge ion is further added, the intensity of the luminescence does not change, but it can be seen that the position of the peak point moves toward the short wavelength.

Example  5: Eu ^{2 +} According to the quantity Ca _{0 .92} Ba _{0 .08} ) Si _{0 .225} Ga _b S _s : eEu ^{2 +} , Cl ^-  Manufacture of red phosphor

CaCO₃, BaCl₂, SiO₂, Ga₂O₃ And S in a molar ratio of 1: 0.08: 0.05: 0.4: 2, and Eu₂O₃The content of e CaCO₃0.2 to molar, respectively. (Ca) in the same manner as in Example 1, except for adding while changing to 0.5, 1.0, 2, and 5 mol_{0 .92}Ba_{0 .08}Si_{0 .225}Ga_bS_seEu^{2 +}, Cl^- A red phosphor was prepared.

The following Fig. 6 shows the luminescence spectrum was measured while variously changing the activator Eu ^{+ 2} positive. It can be seen that as the Eu ²⁺ amount increases, the position of the peak point moves toward the shorter wavelength.

Example  6: Fabrication of Light Emitting Diode Using Red Phosphor and Its Light Emission Spectrum

A white light emitting diode was manufactured using the red phosphor of Example 3. Specifically, on the sapphire substrate, a GaN nucleation layer 25 nm, n-GaN layer (metal: Ti / Al) 1.2 μm, five InGaN / GaN multiquantum well layers, InGaN layer 4 nm, GaN layer 7 nm and Blue light LEDs were manufactured by sequentially forming 0.11 μm of p-GaN layers (metal: Ni / Au), respectively. Subsequently, a red phosphor was epoxy-dispersed on the surface of the blue light LED to prepare a blue-red light emitting device.

FIG. 7 is a light emission spectrum of a light emitting diode coated with 10 wt% of the prepared epoxy, and the light emitting diode coated with a red phosphor according to the present invention has a blue luminescence having a peak point at 458 nm corresponding to a light emission band of a GaN blue LED. The main emission peak was shown in the range of 600 to 740 nm emitted from the necessity band and the red phosphor, and the color coordinates were 0.38 and 0.12, respectively. When 20% by weight was applied, the color coordinates were 0.64 and 0.24, respectively, corresponding to the red light emitting region. The color coordinates were changed from purpulish red to red according to the weight% of the phosphors relative to the epoxy.

The novel red phosphor of the present invention is excellent in luminous efficiency and chemically very stable as compared to the existing red phosphor, and also can be easily applied to various fields in the manufacture of ultraviolet chips. In particular, it is expected to be applied to the fields of home lighting, liquid crystal display (LCD) panel backlight, automobile interior, and the like.

Figure 1 is _a CaSi Ga _{0 .4} S _s of the first embodiment of the present invention: Eu ^{2 +,} F ^- is the luminous spectrum of the red phosphor. (Graphs 1 and 2 are each when a is 0.05 (λ _exn = 460 nm))

It is the excitation spectrum of the red phosphor _{^{(λ ems = 640 nm) -}} Eu 2 +, F: 2 is the first embodiment of the present invention CaSi _a Ga _{0 .4 S s.}

The luminous spectrum of the red phosphor ^- Eu ^{2 +,} Cl: Figure 3 is a second embodiment of the present invention (Ba Ca _{0 .92 0 .08) 0 .225} Si Ga _b S _s. (Graphs 1,2,3,4,5 are when b is 0,0.1,0.2,0.8,1.0 (λ _exn = 460 nm))

3 as a luminous spectrum of the red phosphor, (1, 2, and 3 are graphs each of the content of x, ^- Eu ^{2 +,} xF: Figure 4 is a third embodiment of the present invention CaSi _{0 .05} Ga _{0 .1 S s} 5,8 wt% (λ _exn = 460 nm))

5 is CaSi _{0 .05} Ga ₀ of the present invention in Example ^{_{4 .4 S s: Eu 2 +}} , F - (1) and _{Ca (SiGe) 0.05 Ga 0.4 S} s: Eu 2+, F - (2) Red Luminescence spectrum of the phosphor. (Λ _exn = 460 nm)

The luminous spectrum of the red phosphor ^- eEu ^{2 +,} Cl: Figure 6 is a fifth embodiment of the present invention (Ba Ca _{0 .92 0 .08) 0 .225} Si Ga _b S _s. (Graphs 1, 2, 3, 4, and 5 are 0.2, 0.5, 1.0, 2, and 5 mol% of the e content of Ca ions, respectively (λ _exn = 460))

Fig. 7 shows light emission spectra of the white light emitting device to which the red phosphor of Example 6 of the present invention is applied.

Claims (5)

Red phosphor having the general formula <Formula 1> (Ca ₁ - _x M _x ) A _a B _b S _s : Eu ²⁺ , Q Wherein M is a divalent cation selected from the group consisting of Mg, Sr, Ba, and Zn, A is a tetravalent cation selected from the group consisting of Si, Ge, and B is Al, It is characterized in that the trivalent cation selected from the group consisting of Ga, Sc, Y, La and Gd, Q is characterized in that at least one member selected from the group consisting of halogen elements, x is 0 to 0.2, a is 0 <a≤0.5, b is 0 <b≤1.0, and s is 1 + 2a + 3b / 2.) The red phosphor according to claim 1, wherein the content of Q is in the range of 1 to 10% by weight of the total composition of Chemical Formula 1. The red phosphor according to claim 1, wherein the red phosphor exhibits an excitation spectrum in the range of 460 to 490 nm and an emission spectrum in the range of 600 to 740 nm. A white light emitting device comprising the red phosphor according to any one of claims 1 to 3. Mixing Ca-containing compound, M-containing compound, A-containing compound, B-containing compound, Eu-containing compound, S and halogen element-containing compound; First calcining the mixture at 700 to 1000 ° C. for 1 to 3 hours; Pulverizing the first calcined sample, and adding sulfur to the second calcined sample for 1 hour to 3 hours at 700 to 1000 ° C .; Method for producing a red phosphor, characterized in that consisting of a third firing step of repeating the second firing step. (Ca, M, A, B containing compounds refer to oxides, carbonates, chlorides, hydroxides, sulfates, fluorides, nitrates, acetates and mixtures thereof containing M, M is selected from Mg, Sr, Ba, Zn Element, A is an element selected from Si, Ge, B is an element selected from Al, Ga, Sc, Y, Sb, La and Gd, Eu-containing compounds are Eu ₂ O ₃ , Eu ₂ (CO ₃ ) ₃ , Eu ( OH) ₃ , Eu (NO ₃ ) ₃ and at least one compound selected from compounds in which coprecipitation compounds are formed from Eu metal.)

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