KR20100099451A - Fabrication method for nitride phosphor using spark plasma sintering - Google Patents

Abstract

PURPOSE: A method for manufacturing nitride phosphors using a spark plasma sintering method is provided to obtain faster reaction time than a gas pressure sintering method, to economically manufacture the nitride phosphors at low nitrogen pressure(or a vacuum condition), and to prevent carbon contamination. CONSTITUTION: A method for manufacturing nitride phosphors uses an electric discharge plasma sintering apparatus including a carbon mold(22) and first and second carbon punches(23,24). The method comprises the following steps: providing a phosphor powder material(21) including nitride powder and an activator; coating a part of a carbon film with boron nitride; arranging the carbon film along the inner wall of the carbon mold and putting the phosphor powder material into the carbon mold; installing the carbon mold in a chamber of the electric discharge plasma sintering apparatus and removing oxygen from the chamber; sintering the phosphor powder material mixture by pressurizing the mixture; and obtaining phosphor powder by pulverizing the sintered material.

Description

Fabrication method for nitride phosphor using spark plasma sintering

The technique disclosed in the present disclosure relates to a method for producing a nitride phosphor using the discharge plasma sintering method, and more particularly, to a method for producing a nitride phosphor having low carbon contamination and excellent luminescent properties at a low speed at a high speed.

Nitride phosphors are known to exhibit excellent properties as light emitting diode phosphors used for high power illumination because they have a higher degree of covalentness than oxide phosphors and have excellent luminous efficiency, and excellent chemical and thermal stability when compared to sulfide phosphors. However, much research has not been carried out because nitrides require high temperature and high N ₂ pressure. In addition, the radius of the rare earth-based ions used as an activator is larger than that of group III ions such as Ga, In, and Al, so that it is difficult to replace the group III ion site. Therefore, thin film-type phosphors in which activator ions are introduced by sputtering or organic metal chemical vapor deposition (MOCVD) are mainly produced.

A crystalline powder type AlN phosphor was first reported by Doa et al. By doping various lanthanide oxides to AlN using a combustion method (K. Hara et al. "Combustion Synthesis of Aluminum Nitride Phosphors" Proceeding: EL2004 pp. 24-27). ). In the combustion method, AlN is formed through direct nitriding of Al. Al melting is lower than the temperature at which nitriding occurs at 660 ° C., so that Al particles are often left in the sample. Another method was reported by Hiroski et al. Of doping europium in a pressure sintering furnace (N. Hirosaki et al. "Blue-emitting AlN: Eu ²⁺ nitride phosphors for field emssion displays" Applied Physics Letters 2007. 91, 061101 , T. Takeda, N. Hirosaki, R.-J. Xie, K. Kimoto, M. Saito "Luminescence and Structure of Europium Doped Aluminum Nitride Phosphor" Proceeding: International Display Workshops 2008. pp. 2029-2030). This showed high luminescence properties and stability compared to commercially available oxide-based phosphors, but increases the manufacturing cost by requiring a long time and a large amount of nitrogen gas due to the characteristics of gas pressure sintering equipment. Therefore, there is a need for a method of synthesizing a new nitride phosphor.

According to one embodiment, there is provided a method for producing a nitride phosphor using a discharge plasma sintering apparatus comprising a carbon mold and a first carbon punch and a second carbon punch respectively positioned at both ends of the carbon mold. This method comprises the steps of providing a phosphor powder raw material comprising a nitride powder and an activator, coating boron nitride (BN) on at least a portion of the carbon film, and allowing the boron nitride coated surface to contact the phosphor powder raw material. The film is disposed along the inner wall of the carbon mold, and the phosphor powder material is introduced into the carbon mold, and a first boron nitride substrate is interposed between the phosphor powder material and the first carbon punch, and the phosphor powder material Interposing the second boron nitride substrate between the second carbon punches such that at least the phosphor powder material does not directly contact the surfaces of the carbon mold, the first carbon punch and the second carbon punch, the carbon mold Is installed in the chamber of the discharge plasma sintering apparatus and the oxygen in the chamber is , The sintering temperature was raised and the pressure to the phosphor powder, the raw material mixture, and the pressure was released and crushing the sintered product obtained by cooling a step to obtain a phosphor powder.

According to another embodiment, the step of injecting AlN phosphor powder raw material containing AlN, a photosensitizer, and an activator into a carbon mold, installing the carbon mold in a chamber of the discharge plasma sintering apparatus and removing oxygen in the chamber And sintering by heating and pressurizing the phosphor powder raw material, and sintering the sintered body obtained by removing the pressure and cooling to obtain a phosphor powder.

Hereinafter, the technology disclosed herein will be described in more detail with reference to the accompanying drawings. In the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like numbers refer to like elements throughout.

 Spark Plasma Sintering (SPS) is an ovary because it can achieve higher sintered density in a very short time than conventional atmospheric sintering as well as hot (Hot Pressing) and Hot Isotactic Pressing (HIP) sintering. It is widely applied to sintering formed materials.

 1 is a view showing an embodiment of a discharge plasma sintering apparatus used in the method for producing a nitride phosphor disclosed herein. As shown, the discharge plasma sintering apparatus may be composed of a power generating unit 10, the pressing unit 20, and the chamber 30. The power generator 10 may generate a pulsed DC current 11. The pressurizing section 20 is inserted into the carbon mold 22 and the carbon mold 22 for holding the sample, that is, the phosphor powder raw material 21, and the first carbon punch 23 and the second carbon punch for applying pressure to the sample. It may consist of (24).

2 is a view showing one cross-sectional structure of the pressing unit of the discharge plasma sintering apparatus. As shown, the carbon film 25 may be disposed on the inner wall of the carbon mold 22 in the pressing portion 20 of the discharge plasma sintering apparatus for easy release of the sintered body. The carbon film 25 is interposed between the sintered body made from the phosphor powder raw material 21 and the carbon mold 22 so that the sintered body can be easily separated from the carbon mold 22.

In the case of sintering by applying a pulsed direct current to a specimen such as a phosphor powder raw material, an excessive amount of electric current generates plasma discharge between particles in the initial stage of sintering and generates high heat of more than several thousand degrees. . This heat creates a neck at the interparticle contacts, leading to Joule heating by current. Eventually, the specimen itself may start to generate heat, and as the sintering proceeds, plasma no longer occurs, but the specimen may be more dense due to the current applied in the form of a pulse.

According to one embodiment of the method for producing a nitride phosphor using the discharge plasma sintering method, the phosphor powder raw material is first introduced into a carbon mold. As a phosphor powder raw material, an activator may be mixed and used in a nitride powder as a main raw material. The nitrides specifically include group III-V compounds such as AlN, GaN, InN, and SiAlON series such as M- α -SiAlON and β-SiAlON (M = Ca, Ba, Sr), MSi ₂ O ₂ N ₂ (M = Ca, Ba, Sr), silicon oxynitride series such as La-Si-ON (La = lanthanum element), MSi ₄ N ₇ , MSi ₅ N ₈ , MSi ₇ N ₁₀ (M = Ca, Si ₃ N ₄ series compounds such as Ba, Sr), and CASIN series compounds such as MAlSiN ₃ (M = Ca, Ba, Sr). The activator can act to receive energy and release it in the form of light. Examples of activator ions suitable for phosphor synthesis include Eu, Ce, Mn, Pr, Gd, Tb, Dy, Er, Tm, Ho and Yb, and these may be used alone or in combination. The powder raw material of the nitride phosphor may further include a photosensitizer. The photosensitizer may play a role of increasing the doping concentration of the active agent, transferring energy received from the nitride to the active agent, and increasing the conductivity of the phosphor. Si ₃ N ₄ is an example of a photosensitizer suitable for phosphor synthesis.

It is preferable to use 85 to 99% by weight of nitride, 4 to 10% by weight of photosensitive agent, and 1 to 5% by weight of active agent in the phosphor powder raw material. Outside the above range, the luminous efficiency may be reduced, or the sintered body may be difficult to be formed in powder form. For example, when preparing AlN: Eu phosphor, it is preferable to use AlN 90 to 94% by weight, Si ₃ N ₄ 4 to 8% by weight, and Eu ₂ O ₃ 1 to 3% by weight.

Next, the carbon mold is installed in a chamber of the discharge plasma sintering apparatus to remove oxygen in the chamber. The pressure in the chamber may be maintained at 50 mbar to 100 mbar at room temperature by vacuuming to remove oxygen which may act as an impurity in phosphor synthesis. Alternatively, for example, a nitrogen atmosphere may be formed by injecting nitrogen gas at 50 to 300 sccm per minute.

Subsequently, the phosphor powder raw material is heated and pressed to sinter. The temperature may be elevated at a rate of 50 to 200 ° C./min, and is preferably elevated to 1500 to 2000 ° C., more preferably 1600 to 1800 ° C., even more preferably 1700 to 1750 ° C. If the temperature is lower than the above temperature, the synthesis is not performed, and if the temperature is exceeded, a high density sintered body may be obtained. The pressure is preferably 10 to 50 MPa. After reaching the predetermined temperature, the temperature and pressure conditions are maintained for 1 to 10 minutes.

Thereafter, the pressure is removed and the sintered compact obtained by cooling is pulverized to obtain phosphor powder. In order to remove the residual carbon of the phosphor powder thus obtained, a post-heat treatment process may be further performed after heat treatment at a low temperature (600 to 1000 ° C. oxidation atmosphere) and heat treatment at a high temperature (1300 to 1500 ° C.) reducing atmosphere.

The gas pressure sintering method, which is a method for preparing powder phosphor, has to be carried out at 4 to 10 hours at a sintering temperature of about 2000 ° C. under high pressure nitrogen. It has the advantage of being economical as it has a temperature and a fast reaction time and operates at low nitrogen pressure (or vacuum conditions).

When sintering using the SPS apparatus, the sintered body may be contaminated with carbon by the carbon punch and the carbon film used, which may adversely affect the light emission characteristics of the sintered body. Therefore, when performing SPS, it is necessary to prevent the carbon contamination of the sintered compact.

According to one embodiment, there is provided a method for producing a nitride phosphor that is not carbon contamination using SPS.

Boron nitride (BN) is coated on at least a portion of the carbon film to prevent carbon contamination during the sintering process. 3 shows an example of the BN coated carbon film. BN coating may be carried out by spray coating, spin coating or dip coating the paint-type BN on the object. Coating may be performed on at least a portion in direct contact with the sample, and as shown, the carbon film may be divided into a BN-coated area and an uncoated area. When BN is coated on the carbon film, if the coating region completely covers the film surface, current may not flow between the first carbon punch, the carbon mold, and the second carbon punch by the insulating BN coating. Therefore, in order to prevent this, the part not directly contacting the phosphor powder raw material may not be BN coated.

Next, the carbon film is disposed along the inner wall of the carbon mold so that the boron nitride-coated portion may come into contact with the phosphor powder raw material. The BN-coated carbon film is rolled round and installed on the inner wall of the mold, so that the phosphor powder material to be introduced later does not come into contact with the BN-coated portion.

The phosphor powder raw material mixture is then introduced into the carbon mold. Wherein at least the phosphor powder raw material mixture is interposed between the phosphor powder raw material mixture and the first carbon punch and a second boron nitride substrate is interposed between the phosphor powder raw material mixture and the second carbon punch. Do not directly contact the surfaces of the carbon mold, the first carbon punch and the second carbon punch. The first boron nitride substrate and the second boron nitride substrate may each have a plate shape having a predetermined thickness and have durability according to temperature and pressure changes during the sintering process. 4 is a view showing examples of the form of the first boron nitride substrate and the second boron nitride substrate. The first boron nitride substrate and the second boron nitride substrate have the form of a layer coated on one end of the first carbon punch and the second carbon punch as shown in FIG. 4 (a) or in FIG. 4 (b). As shown in the drawing, it may have a pellet form separated from the first carbon punch and the second carbon punch. The pellet can be produced by maintaining the pressure of 10MPa or more for 5 minutes using the BN powder pressing mold. The thickness of the first boron nitride substrate and the second boron nitride substrate is not particularly limited as long as it is sufficient to prevent carbon penetration, but may be 2 mm to 5 mm.

5 is a cross-sectional structure of a pressurizing portion for preventing carbon penetration during sintering with a discharge plasma apparatus. As shown in the drawing, the pressurizing portion has a surface inside the first BN substrate 26, the second BN substrate 27, and the carbon film 25 in order to manufacture the nitride phosphor which does not become carbon-contaminated as described above. It is surrounded by the BN coated portion 25 ′ of, so that when the phosphor powder raw material (not shown) is introduced into the carbon mold 22, the carbon film 25 and the first carbon punch 23 having a carbon material around ) And the second carbon punch 24.

Thereafter, the carbon mold 22 is installed in the chamber to remove oxygen in the chamber, and then the phosphor powder raw material is heated and pressurized to a predetermined temperature and sintered. Then, the sintered body obtained by removing the pressure and cooling is pulverized to form phosphor powder. The step of obtaining the step, the post heat treatment step and the like are as described above. The carbon content in the phosphor powder thus produced may be 1 wt% or less.

Using the above-described discharge plasma sintering method, it is possible to produce a nitride phosphor having excellent luminescence properties at a low temperature faster than the conventional gas pressure sintering method. In addition, the use of BN pellets during sintering can prevent the penetration of carbon into the phosphor, thereby improving the luminescence properties.

Hereinafter, the present disclosure will be described with reference to specific embodiments, but the disclosed technique is not limited thereto.

[Example]

Characteristics of AlN Phosphors with and without Boron Nitride in SPS Sintering

(Example 1)

1 g of phosphor by mixing 91% by weight of AlN powder, 7% by weight of Si ₃ N ₄ as a photosensitizer, and 2% by weight of Eu ₂ O ₃ as an activator to prepare an Al-doped AlN phosphor using a discharge plasma sintering method Powder raw material was prepared. The carbon film was spray coated with a solution of boron nitride and then rolled round and placed along the inner wall of the carbon mold with the coated side facing inward. Place the BN pellet on the carbon punch under the carbon mold and inject the phosphor powder raw material, and then place another BN pellet on it and cover it with the carbon punch on the carbon mold, and then discharge plasma sintering (SPS) apparatus (SPS, Eltech co.) Installed in the chamber. Next, rotary pump the inside of the chamber of the SPS device to create a vacuum of about 80 mbar to 100 mbar, then increase the temperature to 100 ° C./min while applying a pressure of 30 MPa, hold for 5 minutes at a temperature of 1700 ° C., remove the pressure and cool at room temperature. I was. The BN powder remaining in the synthesized pellet sintered compact was removed by grinding and the sintered compact was pulverized. In order to remove the remaining carbon and reduce surface defects, AlN phosphors were prepared by heat treatment in a low temperature oxidizing atmosphere and heat treatment in a high temperature reducing atmosphere.

(Comparative Example 1)

 An AlN phosphor was prepared under the same conditions as in Example 1 except that a carbon film not coated with boron nitride was used and no BN pellets were used.

In order to measure the degree of contamination by carbon infiltration of the powders prepared in Example 1 and Comparative Example 1, the carbon content was analyzed by a carbon analyzer (Leco Co., WC600, MI, USA.). As a result, the carbon content in the AlN phosphor of Example 1 was 0.987% by weight, whereas the carbon content in the AlN phosphor of Comparative Example 1 was 1.960% by weight, and the AlN phosphor manufactured by using BN pellets had a half degree of carbon contamination. It can be seen that the decrease.

6 is a graph showing photoluminescence spectra of AlN phosphors of Example 1 and Comparative Example 1. FIG. As shown, each AlN phosphor has a maximum emission wavelength at 480 nm which is blue, and since the phosphor produced using BN pellets is less contaminated by carbon infiltration, it is about compared with the phosphor prepared without BN pellets. It represents 92 times the intensity.

Crystal Phase and Luminescence Characteristics of AlN Phosphors by Mixing Ratio of Phosphor Powder Raw Materials

AlN phosphors of Examples 2 to 6 were synthesized to evaluate the physical properties of the phosphors according to the change in the amount of Si ₃ N ₄ photosensitizer used as the photosensitizer. A phosphor was prepared in the same manner as in Example 1 except that the reaction mixture was prepared at a reaction temperature of 1750 ° C. according to the mixing ratio of Table 1.

Table 1: Mixing ratio of powder raw materials (unit: weight%)

Example AlN Si ₃ N ₄ Eu ₂ O ₃ 2 94 4 2 3 93 5 2 4 92 6 2 5 91 7 2 6 90 8 2

7 is an X-ray diffraction pattern of the powder synthesized in Examples 2 to 6. Referring to FIG. 7, a single AlN single phase could be observed regardless of the amount of Si ₃ N ₄ mixed. If Si ^4+, which has a smaller ion size than Al ³⁺ , is substituted for Al ³⁺ , the distance between atoms (d) will be closer to 2θ, but it is expected that there will be no significant change in 2θ. Could. This is because the stacking fault is formed by replacing Si ⁴⁺ with Al ³⁺ sites, which does not seem to inherently change the distance between AlN atoms.

8 is a photoluminescence spectrum of the powder synthesized in Examples 2 to 6 measured using an excitation wavelength of 340 nm at room temperature. Referring to FIG. 8, the strongest light emission intensity was shown at 480 nm, and the light emission intensity increased as the content of Si ₃ N ₄ increased. In the case of the emission spectrum of the phosphor of Example 6, in which 8 wt% of Si ₃ N ₄ was incorporated, its half width was 68.8 nm, which emitted light in a wide region. When Si ⁴⁺ is substituted, a stacking defect is formed to form a polytypoid structure, so that the emission intensity increases as the content of Si ₃ N ₄ increases.

Luminescence Characteristics of AlN Phosphors with Variation of Sintering Temperature

The AlN phosphors of Examples 7 to 10 were synthesized according to the temperatures shown in Table 2 using the luminescent plasma sintering method, and other synthesis conditions were the same as those of Example 1.

Table 2: Sintering temperature during luminescent plasma sintering

Example Sintering Temperature (℃) 7 1650 8 1700 9 1750 10 1800

9 is an AlN powder and the field emission electron microscope (FE-SEM) photograph of Examples 7 to 10 before the reaction. As shown, the size of the AlN particles synthesized by the discharge plasma sintering method is about 1 μm, with little difference from the particle size of the AlN powder before the reaction, and as the synthesis temperature increases, the size of the particles does not change significantly, but the particle surface It can be seen that the roughness.

10 and 11 are photoluminescence spectra and cathodoluminescence spectra of the AlN phosphors of Examples 7 to 10, respectively. The excitation wavelength of the photoluminescence spectrum is 340 nm, and the excitation source of the cathode emission spectrum is a cathode ray having an acceleration voltage of 1 keV and a current of 200 mA / cm ² per unit area. 10 and 11, the photoluminescence spectrum has a maximum emission intensity at 1700 ° C. (Example 8) and the cathode emission spectrum at 1750 ° C. (Example 9).

1 is a view showing an embodiment of a discharge plasma sintering apparatus used in the method for producing a nitride phosphor disclosed herein.

2 is a view showing one cross-sectional structure of the pressing unit of the discharge plasma sintering apparatus.

3 shows an example of a BN coated carbon film.

4 is a view showing examples of the form of the first boron nitride substrate and the second boron nitride substrate.

5 is a cross-sectional structure of a pressurizing portion for preventing carbon penetration during sintering with a discharge plasma apparatus.

6 is a graph showing photoluminescence spectra of AlN phosphors of Example 1 and Comparative Example 1. FIG.

7 is an X-ray diffraction pattern of the powder synthesized in Examples 2 to 6.

8 is a photoluminescence spectrum of the powder synthesized in Examples 2 to 6 measured using an excitation wavelength of 340 nm at room temperature.

9 is an AlN powder and the field emission electron microscope (FE-SEM) photograph of Examples 7 to 10 before the reaction.

10 and 11 are photoluminescence spectra and cathodoluminescence spectra of the AlN phosphors of Examples 7 to 10, respectively.

Claims (10)

In the method of manufacturing a nitride phosphor using a discharge plasma sintering apparatus comprising a carbon mold and a first carbon punch and a second carbon punch respectively positioned at both ends of the carbon mold, Providing a phosphor powder comprising a nitride powder and an active agent; Coating boron nitride (BN) on at least a portion of the carbon film; The carbon film is disposed along the inner wall of the carbon mold so that the boron nitride-coated surface contacts the phosphor powder raw material, and the phosphor powder raw material is introduced into the carbon mold, wherein the phosphor powder raw material and the first By interposing a first boron nitride substrate between the carbon punches and interposing a second boron nitride substrate between the phosphor powder material and the second carbon punch, at least the phosphor powder raw material is formed in the carbon mold, the first carbon punch, and the Preventing direct contact with the surface of the second carbon punch; Installing the carbon mold in a chamber of the discharge plasma sintering apparatus and removing oxygen in the chamber; Sintering the phosphor powder raw material mixture by heating and pressing; And A method for producing a nitride phosphor comprising the step of pulverizing the sintered body obtained by removing the pressure and cooling to obtain a phosphor powder. According to claim 1, After the heat treatment in the oxidation atmosphere of 600 to 1000 ℃ to remove the remaining carbon of the phosphor powder, and further comprising a post heat treatment step of heat treatment in a reducing atmosphere of 1300 to 1500 ℃. According to claim 1, The nitride phosphor powder raw material is AlN 90 to 94% by weight, Si ₃ N ₄ 4 to 8% by weight, and Eu ₂ O ₃ 1 to 3% by weight manufacturing method of the nitride phosphor. According to claim 1, The step of sintering by raising the temperature and pressure is carried out at a temperature of 1500 to 2000 ℃ and a pressure of 10 to 50 MPa at a temperature rising rate of 50 to 200 ℃ / min. The method according to any one of claims 1 to 4, The carbon content in the phosphor powder is 1 wt% or less method for producing a nitride phosphor. Injecting AlN phosphor powder raw material including AlN, a photosensitizer, and an activator into a carbon mold; Installing the carbon mold in a chamber of a discharge plasma sintering apparatus and removing oxygen in the chamber; Sintering the phosphor powder by heating and pressurizing it; And Method of producing an AlN phosphor comprising the step of pulverizing the sintered body obtained by removing the pressure and cooling to obtain a phosphor powder. The method according to claim 6, After the heat treatment in the oxidation atmosphere of 600 to 1000 ℃ to remove the remaining carbon of the phosphor powder, and further comprising a post heat treatment step of heat treatment in a reducing atmosphere of 1300 to 1500 ℃. The method according to claim 6, The AlN phosphor powder raw material comprises 90 to 94% by weight of AlN, 4 to 8% by weight of the photosensitizer, and 1 to 3% by weight of the active agent. The method according to claim 6, The step of sintering by heating and pressurizing is performed at a temperature of 1500 to 2000 ° C. and a pressure of 10 to 50 MPa at a temperature rising rate of 50 to 200 ° C./min. The method according to any one of claims 5 to 9, The carbon content in the phosphor powder is 1% by weight or less manufacturing method of AlN phosphor.

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