JP2009280773A - Phosphor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a red phosphor for a PDP, which has high color purity. <P>SOLUTION: The red phosphor for a PDP is a trivalent europium (Eu<SP>3+</SP>) activated rare earth borate phosphor, which is represented by YBO<SB>3</SB>:Eu<SP>3+</SP>or (Y, Gd)BO<SB>3</SB>:Eu<SP>3+</SP>with at least a neodymium (Nd) compound attached thereto. The attachment of a neodymium (Nd) compound such as neodymium vanadate (NdVO<SB>4</SB>) brings about a phosphor with high emission luminance, a long life, and high color purity. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a phosphor suitable for applications requiring excellent color reproducibility such as a flat display, particularly a plasma display panel.

  Phosphors are used in lighting devices such as fluorescent lamps (FL), cold cathode fluorescent lamps (CCFL), xenon lamps, vacuum ultraviolet lamps, light emitting diodes (LEDs), etc., CRTs, plasma display panels (PDPs). ), A field emission display (FED) or the like, or a light source such as CCFL, FED or LED in a backlight of a color liquid crystal display (LCD).

Among these, light sources used particularly for display devices and LCD backlights are required to have high color reproducibility as displays in addition to high light emission luminance and long life.
In order to realize high color reproducibility, the color purity of the three primary colors of red, green, and blue light is required to be high. Light with high color purity is ultimately light that is composed of only a single wavelength, such as monochromatic light, that is, laser light. Difficult to get into. For example, in the case of light emission from a phosphor, there is a light emission peak having different widths or having a plurality of light emission peaks depending on the type of the phosphor, so that it is difficult to obtain light with an arbitrary emission color and high color purity.

Depending on the type of phosphor, there is a phosphor having relatively excellent color purity, but it is rare that the phosphor simultaneously has excellent characteristics such as high emission luminance and long life.
For example, in a phosphor used for PDP, ZnSiO ₄ : Mn ²⁺ phosphor that emits green light, BaMgAl ₁₀ O ₁₇ : Eu ²⁺ phosphor that emits blue light, and (Y , Gd) BO ₃ : Eu ³⁺ is typically used, and these PDP phosphors are efficiently excited by irradiation with light in the vacuum ultraviolet (VUV) region and exhibit good luminance. Has suitable life characteristics. However, the emission spectrum of the (Y, Gd) BO ₃ : Eu ³⁺ phosphor of the red phosphor has strong emission peaks near 592 nm, 610 nm, and 626 nm as shown in Comparative Example 1 in FIG. Since it has a strong emission peak at 592 nm, the chromaticity is (x = 0.539, y = 0.360) and orange-red, which is not preferable in terms of the color gamut.

In order to improve the emission color of the red phosphor for PDP, for example, other phosphors such as Y ₂ O ₃ : Eu ³⁺ , YVO ₄ : Eu ³⁺ , Y (P, V) O ₄ : Eu ³⁺ are proposed. (For example, refer to Patent Document 1). However, these phosphors such as Y ₂ O ₃ : Eu ³⁺ , YVO ₄ : Eu ³⁺ , and Y (P, V) O ₄ : Eu ³⁺ improve the chromaticity of the emission color, but have a luminance for PDP use. There was a problem in practicality such as a decrease in life and a short life.
In addition, a technique for improving the contrast by using a colorant such as a pigment for the phosphor for PDP is disclosed (for example, see Patent Document 2). However, it does not improve the emission color.

JP 50-67782 A (first page) JP-A-8-287835 (2nd and 4th pages)

  An object of the present invention is to provide a phosphor for PDP with higher color purity without impairing characteristics such as high light emission luminance and long life in view of the above-described conventional technology.

  As a result of various studies and experiments to solve the above problems, the present inventors have found that the trivalent europium-activated rare earth borate phosphor, which is the red phosphor for PDP, has a specific rare earth. It has been found that the color purity of the obtained emission color is improved by attaching the compound to the phosphor surface.

The phosphor according to claim 1 is a trivalent europium (Eu ³⁺ ) -activated rare earth borate phosphor, and is characterized in that at least a neodymium (Nd) compound is attached.
Then, by attaching a neodymium (Nd) compound to the trivalent europium (Eu ³⁺ ) -activated rare earth borate phosphor, the emission color of the phosphor is adjusted, and the phosphor is further improved in color purity.

The phosphor according to claim 2 is the phosphor according to claim 1, wherein the trivalent europium (Eu ³⁺ ) -activated rare earth borate phosphor is YBO ₃ : Eu ³⁺ or (Y, Gd) BO ₃ : It is characterized by being represented by Eu ³⁺ .
Then, by attaching a neodymium (Nd) compound to the phosphor represented by YBO ₃ : Eu ³⁺ or (Y, Gd) BO ₃ : Eu ³⁺ , the emission color of the phosphor is adjusted, and the color purity is further improved. The resulting phosphor.

The phosphor according to claim 3 is the phosphor according to claim 1 or 2, wherein the neodymium (Nd) compound is composed of vanadate, tungstate, molybdate, aluminate, oxysulfide, oxide. It is characterized by comprising at least one or more.
By attaching these neodymium (Nd) compounds to a trivalent europium (Eu ³⁺ ) activated rare earth borate phosphor, the emission color of the phosphor is adjusted, and a phosphor with improved color purity Become.

The phosphor according to claim 4 is the phosphor according to claim 1, wherein the neodymium (Nd) compound is NdVO ₄ , Nd ₂ W ₃ O ₁₂ , KNdW ₂ O ₈ , Nd ₂ Mo ₃ O ₁₂ , KNdMo. It is characterized by comprising a compound represented by at least one of ₂ O ₈ , NdAlO ₃ , Nd ₂ O ₂ S, and Nd ₂ O ₃ .
By attaching these neodymium (Nd) compounds to a trivalent europium (Eu ³⁺ ) activated rare earth borate phosphor, the emission color of the phosphor is adjusted, and a phosphor with improved color purity Become.

The phosphor according to claim 5 is the phosphor according to claims 1 to 4, characterized in that the neodymium (Nd) compound is fine particles having an average particle diameter D50 of 0.05 μm or more and 1 μm or less. .
Further, by making the particle size of the neodymium (Nd) compound attached to the trivalent europium (Eu ³⁺ ) activated rare earth borate phosphor into fine particles having an average particle size D50 of 0.05 μm or more and 1 μm or less, it is more effective. Thus, the emission color of the phosphor is adjusted, resulting in a phosphor with improved color purity.

According to the phosphor of claim 1, at least a neodymium (Nd) compound is attached to the trivalent europium (Eu ³⁺ ) activated rare earth borate phosphor, thereby adjusting the emission color of the phosphor. A phosphor with improved color purity can be obtained.

According to the phosphor of claim 2, in the phosphor of claim 1, the trivalent europium (Eu ³⁺ ) activated rare earth borate phosphor is YBO ₃ : Eu ³⁺ or (Y, Gd) BO. ₃ : By making Eu ³⁺ , the emission color of the phosphor is adjusted, and a phosphor with improved color purity can be obtained.

  According to the phosphor according to claim 3, in the phosphor according to claim 1 or 2, the neodymium (Nd) compound is converted into vanadate, tungstate, molybdate, aluminate, oxysulfide, oxidation By adopting a configuration composed of at least one of the objects, the emission color of the phosphor is adjusted, and a phosphor with improved color purity can be obtained.

According to the phosphor of claim 4, in the phosphor of claims 1 to 2, the neodymium (Nd) compound is NdVO ₄ , Nd ₂ W ₃ O ₁₂ , KNdW ₂ O ₈ , Nd ₂ Mo ₃ O _12. , KNdMo ₂ O ₈ , NdAlO ₃ , Nd ₂ O ₂ S, and Nd ₂ O ₃ , the emission color of the phosphor is adjusted, and the color purity is improved. An improved phosphor can be obtained.

  According to the phosphor of claim 5, in the phosphor of claims 1 to 4, the neodymium (Nd) compound is a fine particle having an average particle diameter D50 of 0.05 μm or more and 1 μm or less. The emission color of the phosphor is effectively adjusted, and a phosphor with improved color purity can be obtained.

  Hereinafter, the process for producing the phosphor according to one embodiment of the present invention will be described. The phosphor according to the present invention can be obtained by mixing compounds containing component elements in a predetermined ratio, firing the obtained mixture under predetermined conditions, and further attaching a specific compound.

Examples of the trivalent europium-activated rare earth borate phosphor of the red phosphor for PDP include YBO ₃ : Eu ³⁺ and (Y, Gd) BO ₃ : Eu ^3+. ) BO ₃ : Eu ^{3+ A} phosphor will be used for explanation.
Since this (Y, Gd) BO ₃ : Eu ³⁺ phosphor has a strong orange emission peak in the vicinity of 592 nm in addition to the red emission in the vicinity of 610 nm and 626 nm, the emission color has a chromaticity of, for example, x = 0. 639, y = 0.360, which is orange-red and has poor color purity, and the red light source for PDP is not preferable because of its large orange component.

Here, as the neodymium (Nd) compound, for example, neodymium vanadate (NdVO ₄ ), neodymium aluminate (NdAlO ₃ ), neodymium tungstate (Nd ₂ W ₃ O ₁₂ ) is used as a filter material, and the above (Y, Gd) The fine particles of these filter materials are adhered to the surface of the BO ₃ : Eu ³⁺ activated phosphor to obtain a fine filter material-attached phosphor. These fine particles of Nd compound filter material have high reflectivity in the visible light region as a whole, but have absorption wavelength regions in the vicinity of 460 nm to 480 nm, 510 nm to 530 nm, 580 nm to 610 nm, and the like.
By attaching the Nd compound filter material fine particles to the surface of the Eu ³⁺ activated phosphor, the peak around 592 nm is absorbed and suppressed by the filter effect of the Nd compound filter material fine particles, but the remaining around 610 nm and 630 nm. Since the nearby peak is hardly absorbed, the color purity is increased without substantially impairing the light emission luminance, and the phosphor becomes a preferable phosphor for PDP.

The filter effect of the filter material fine particles depends on the particle size. Fine particles having an average particle diameter D50 of about 0.05 μm to 1 μm are preferable. When it exceeds 1 μm, the filter effect on the light emission of the phosphor becomes small, and when it is less than 0.05 μm, the body color of the filter material fine particles themselves becomes extremely thin, and the filter effect is also reduced, which is not preferable.
The filter material fine particles of the Nd compound are reduced in particle size by means such as a ball mill or a bead mill.

There are various methods for attaching the filter material fine particles to the phosphor surface. For example, a suspension in which fine particles of the filter material are dispersed in water at a predetermined ratio is prepared, and the target is put in this suspension. Filter material fine particles are adhered to the surface of the phosphor by adding the phosphor and stirring and mixing.
At this time, an inorganic binder such as a water glass system may be added for effective adhesion. As an alternative, a colloidal hydroxide such as zinc hydroxide or aluminum hydroxide may be used, and in addition, an adhesive organic substance such as gelatin or gum arabic may be used.
After the phosphor is sufficiently stirred in the suspension, stirring is stopped and the phosphor is allowed to settle. After removing the supernatant, washing, filtration, drying, and sieving are performed to obtain a phosphor having filter material fine particles attached to the surface.
The phosphor having the fine particles adhered thereto thus obtained can be handled in the same manner as a normal phosphor to which filter material fine particles or the like are not adhered.

In addition, as the neodymium compound, KNdW ₂ O ₈ , Nd ₂ Mo ₃ O ₁₂ , KNdMo ₂ O ₈ , Nd ₂ O ₂ S, Nd ₂ O _{3 and the} like can be preferably used.
Moreover, you may substitute a part of neodymium element among these neodymium compounds with an erbium (Er) element. At this time, the amount to be substituted with the erbium element is preferably up to about 50 mol%. At this time, if the substitution amount exceeds 50 mol%, there is a problem that absorption characteristic of neodymium is weakened.
In addition, as long as it is a substance that does not inhibit the characteristic absorption of the neodymium compound, such as erbium, other substances may be simultaneously contained in the filter material fine particles.

  Next, as an example of the above embodiment, the filter material fine particle-adhered phosphor of the present invention and its characteristics will be described.

^First , the characteristics of the (Y, Gd) BO ₃ : Eu ³⁺ phosphor with the filter material fine particles attached as the red phosphor for PDP will be described.

First, a (Y, Gd) BO ₃ : Eu ³⁺ phosphor is synthesized.
As raw materials, 77.7 g of yttrium oxide (Y ₂ O ₃ ) (0.688 mol as Y), 46.6 g of gadolinium oxide (Gd ₂ O ₃ ) (0.257 mol as Gd), 9.7 g of oxidation Europium (Eu ₂ O ₃ ) (0.055 mol as Eu) and 74.1 g of boric acid (H ₃ BO ₃ ) (1.2 mol as B) were mixed well, and then filled into a quartz crucible, Baking at 1060 ° C. for 3 hours, and then removing the excess boric acid, the obtained fired body was washed several times with warm water and subjected to a ball mill process to obtain (Y, Gd) BO ₃ : Eu ³⁺ phosphor. It was. The (Y, Gd) BO ₃ : Eu ³⁺ phosphor has a composition represented by (Y _0.688 , Gd _0.257 ) BO ₃ : Eu ³⁺ _0.055 .

Neodymium vanadate neodymium (NdVO ₄ ) was selected as filter material fine particles to be attached to the (Y, Gd) BO ₃ : Eu ³⁺ phosphor.
The NdVO ₄ fine particles have a sufficient amount of 336.5 g neodymium oxide (Nd ₂ O ₃ ) (2 mol as Nd) and 181.9 g vanadium pentoxide (V ₂ O ₅ ) (2 mol as V) as raw materials. After mixing, the mixture was filled in a quartz crucible and baked at 1200 ° C. for 4 hours, followed by washing and ball milling to obtain fine particles.
When the particle size distribution of the obtained NdVO ₄ fine particles was measured with a laser diffraction particle size distribution analyzer (model: SALD-2100, manufactured by Shimadzu Corporation), the average particle size D50 was 0.75 μm, and the maximum particle size D100 was 4. It was 45 μm.

Next, the process of attaching the filter material fine particles will be described.
3 g of the obtained NdVO ₄ fine particles are added to 500 ml of pure water, and dispersed by stirring to form a suspension. To 500 ml of this suspension, 100 g of (Y, Gd) BO ₃ : Eu ^{3 +} phosphor (average particle diameter D50 is 2.6 μm) is added and mixed with stirring, and further 10 ml of 1M zinc chloride (ZnCl ₂ ) aqueous solution is added and stirred. Mix. After mixing well, dilute aqueous ammonia (about 14%) is added little by little to adjust to pH 9. Thereafter, stirring is stopped and the phosphor is allowed to settle. After removing the supernatant, it is washed with pure water several times, and after filtration, through a drying step and a sieving step, a phosphor having 3% by mass of the target NdVO ₄ fine particles attached thereto is obtained. The obtained NdVO ₄ fine particle-attached phosphor was designated as Example 1.

For comparison, a (Y, Gd) BO ₃ : Eu ³⁺ phosphor without NdVO ₄ fine particles was used as Comparative Example 1. Furthermore, instead of the NdVO ₄ fine particles, “Bengara” (ferric oxide pigment) is used in the same manner as the above NdVO ₄ fine particles as a pigment used for improving contrast in the conventional cathode ray tube, Patent Document 2, etc. A (Y, Gd) BO ₃ : Eu ³⁺ phosphor adhered at a rate of 0.1% by mass with respect to the phosphor was prepared. The obtained red pepper-attached phosphor was designated as Comparative Example 2.

Next, the light emission characteristics of Example 1, Comparative Example 1 and Comparative Example 2 were measured. Luminance was measured using a luminance meter (model: LS-110, manufactured by Konica Minolta). The reflection spectrum and emission spectrum were measured using a fiber multichannel spectrometer (model: USB2000 Ocean Optics). In the reflection spectrum measurement, a 40 W bulb was used as the irradiation light source, and the relative value when the reflection of a standard white plate (Tokyo Denshoku No.57992) was set to 1 was obtained as the reflectance. The emission spectrum was irradiated with 146 nm vacuum ultraviolet light as excitation light using a vacuum ultraviolet excimer light irradiation device (manufactured by USHIO INC.). The results are shown in FIG. 1 for the reflection spectra of Example 1, Comparative Example 1 and Comparative Example 2, and in FIG. 2 for the emission spectra of Example 1 and Comparative Example 1.
In addition, Table 1 shows the relative peak ratio together with the luminance when the peak intensity of Comparative Example 1 is set to 1 from the emission spectrum.

As shown in FIG. 1, compared with the reflection spectrum of Comparative Example 1, the reflection spectrum of Example 1 has a large peak in the vicinity of 580 nm to 600 nm, and effectively absorbs light in the vicinity of this wavelength. Recognize. On the other hand, the reflection spectrum of Comparative Example 2 greatly absorbs light having a wavelength of about 580 nm or less, but does not absorb much light having a wavelength near 590 nm.
Further, as shown in FIG. 2 and Table 1, it can be seen that in Example 1, the emission peak at 592 nm is effectively suppressed, while the influence on the other emission peaks at 610 nm and 626 nm is small. However, in Comparative Example 2, all the emission peaks are uniformly suppressed.
That is, it can be seen that Example 1 of the phosphor of the present invention has a remarkable filter effect with respect to the peak at 592 nm. On the other hand, Comparative Example 2, that is, fluorescent light having a conventional red pigment attached thereto. The three emission peak intensities of 592 nm, 610 nm, and 626 nm are uniformly smaller than the phosphor of Comparative Example 1 without pigment, and the specific filter effect on the 592 nm peak is almost the same. I understand that there is no.

The chromaticity at this time is (x = 0.646, y = 0.360) in Comparative Example 1, whereas Example 1 (x = 0.646, y = 0.353). It was found that the chromaticity was also improved. However, Comparative Example 2 (x = 0.661, y = 0.359) was almost unchanged from Comparative Example 1.
Next, examples in which various filter material fine particles are used for the (Y, Gd) BO ₃ : Eu ³⁺ phosphor will be described.

(Y, Gd) BO ₃ : Eu ^{3+ The} phosphor ₃ was applied to the phosphor in the same manner as in Example 1 except that neodymium tungstate (Nd ₂ W ₃ O ₁₂ ) was used as the filter material fine particles. Fine particles were adhered at a ratio of mass% to obtain a phosphor with Nd ₂ W ₃ O ₁₂ fine particles attached. This was designated Example 2.
At this time, Nd ₂ W ₃ O ₁₂ fine particles were 168.3 neodymium oxide (Nd ₂ O ₃ ) (1 mol as Nd) and 347.8 g of tungsten trioxide (WO ₃ ) (1.5 as W) as raw materials. The mixture was sufficiently mixed, and then filled into a quartz crucible, fired at 1000 ° C. for 4 hours, and then finely divided through a washing and ball mill process. The particle size distribution was measured in the same manner as in Example 1. The average particle diameter D50 was 0.50 μm, and the maximum particle diameter D100 was 1.28 μm.

Other than using (Nd _0.5 Er _0.5 ) VO _{4 in} which a part of neodymium vanadate of Example 1 was substituted with erbium as filter material fine particles in (Y, Gd) BO ₃ : Eu ³⁺ phosphor Were adhered to the phosphor at a ratio of 3% by mass in the same manner as in Example 1 to obtain a (Nd _0.5 Er _0.5 ) VO ₄ particulate-attached phosphor. This was designated as Example 3.
At this time, the fine particles of (Nd _0.5 Er _0.5 ) VO ₄ are 168.3 g of neodymium oxide (Nd ₂ O ₃ ) (1 mol as Nd) and 191.3 g of erbium oxide (Er ₂ O ₃ ) as raw materials. ) (1 mol as Er) and 181.9 g of vanadium pentoxide (V ₂ O ₅ ) (2 mol as V) were mixed well, filled in a quartz crucible and fired at 1200 ° C. for 4 hours, and then washed. The particle size distribution was measured in the same manner as in Example 1, and the average particle size D50 was 0.63 μm, and the maximum particle size D100 was 1.93 μm.

A ratio of 3% by mass with respect to the phosphor in the same manner as in Example 1 except that neodymium aluminate (NdAlO ₃ ) was used as the filter material fine particles for the (Y, Gd) BO ₃ : Eu ³⁺ phosphor. Then, fine particles were adhered to obtain an NdAlO ₃ fine particle-adhered phosphor. This was designated Example 4.
At this time, the NdAlO ₃ fine particles sufficiently contain 336.5 g of neodymium oxide (Nd ₂ O ₃ ) (2 mol as Nd) and 102.0 g of alumina (Al ₂ O ₃ ) (2 mol as Al) as raw materials. After mixing, the quartz crucible was filled and baked at 1420 ° C. for 5 hours, and then the particles were obtained by washing and ball milling. The particle size distribution was measured in the same manner as in Example 1. The maximum particle diameter D100 was 0.81 μm and 3.61 μm.

  The light emission characteristics of Examples 2 to 4 thus obtained were evaluated in the same manner as Example 1. The results are shown in Table 2.

  As shown in Table 2, in Examples 2 to 4 of the phosphors of the present invention, the peak intensity at 592 nm is remarkably suppressed as compared with other peaks (610 nm, 626 nm), and 592 nm. It turns out that the specific filter effect with respect to the peak of is remarkable.

Next, characteristics of the YBO ₃ : Eu ³⁺ phosphor to which the filter material fine particles are attached will be described.
As raw materials, 106.7 g of yttrium oxide (Y ₂ O ₃ ) (0.945 mol as Y), 9.7 g of europium oxide (Eu ₂ O ₃ ) (0.055 mol as Eu) and 74.1 g of boron The acid (H ₃ BO ₃ ) (1.2 moles as B) was mixed well, then filled into a quartz crucible, fired at 1060 ° C. for 3 hours, and then removed to remove excess boric acid. The fired body was washed several times with warm water, and YBO ₃ : Eu ³⁺ phosphor was obtained through a ball mill process. This _{YBO 3} : Eu ³⁺ phosphor has a composition represented by Y _0.945 BO ₃ : Eu ³⁺ _0.055 .

As a filter material fine particle to be attached to this YBO ₃ : Eu ³⁺ phosphor, neodymium vanadate neodymium (NdVO ₄ ) is selected and fine particles are added at a ratio of 4% by mass with respect to the phosphor in the same manner as in Example 1. attached to, NdVO ₄ particles adhering _YBO 3: give the ^{Eu 3+} phosphor. This was designated as Example 5.
The light emission characteristics of the obtained Example 5 were evaluated in the same manner as in Example 1, and the results are shown in Table 3. Note that the luminance and relative peak ratio at this time are expressed as relative values based on YBO ₃ : Eu ³⁺ phosphor on which fine particles are not attached.

  As shown in Table 3, in Example 5 of the phosphor of the present invention, the peak intensity at 592 nm is remarkably suppressed as compared with the other peaks (610 nm, 626 nm), and the specificity for the peak at 592 nm is unique. It can be seen that the filter effect is remarkable.

  In addition, when attaching filter material fine particles to the trivalent europium activated rare earth borate phosphor as described above, the filter material is attached depending on the target phosphor, the target emission intensity, chromaticity, and other conditions. The filter effect can be adjusted by adjusting the amount appropriately.

The PDP filter material fine particle-adhered phosphor of the present invention has high emission luminance, long life, and high color purity, so that it has high color reproducibility without using a special filter or the like on the panel surface, for example. An excellent PDP can be configured.
In addition, the present invention can also be suitably used for applications such as a xenon (Xe) lamp that emits light with vacuum ultraviolet light excitation and for which improvement in color purity is desired.

It is a graph showing the reflection spectrum of the fluorescent substance of one embodiment of this invention. It is a graph showing the emission spectrum of the fluorescent substance of one embodiment of this invention.

Claims (5)

A trivalent europium (Eu ³⁺ ) -activated rare earth borate phosphor characterized in that at least a neodymium (Nd) compound is adhered. The fluorescence according to claim 1, wherein the trivalent europium (Eu ³⁺ ) -activated rare earth borate phosphor is represented by YBO ₃ : Eu ³⁺ or (Y, Gd) BO ₃ : Eu ^3+. body.   3. The fluorescence according to claim 1, wherein the neodymium (Nd) compound is composed of at least one of vanadate, tungstate, molybdate, aluminate, oxysulfide, and oxide. body. The neodymium (Nd) compound includes at least NdVO ₄ , Nd ₂ W ₃ O ₁₂ , KNdW ₂ O ₈ , Nd ₂ Mo ₃ O ₁₂ , KNdMo ₂ O ₈ , NdAlO ₃ , Nd ₂ O ₂ S, and Nd ₂ O ₃ . 3. The phosphor according to claim 1, comprising a compound represented by one or more.   5. The phosphor according to claim 1, wherein the neodymium (Nd) compound is fine particles having an average particle diameter D50 of 0.05 μm or more and 1 μm or less.

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