Method for preparing β-sialon fluorescent material

Abstract

The present invention provides a method for preparing a β-sialon fluorescent material having excellent emission intensity. The method for preparing the β-sialon material comprises providing a silicon nitride-containing composition containing aluminum, oxygen atoms, and europium, heat-treating the composition, and contacting the heat-treated composition with an alkaline substance.

Description

[0001] This application is a divisional application of the invention application with an application date of December 15, 2016, an international application number of PCT / JP2016 / 005147, a Chinese national phase application number of 201680043777.3, and an invention name of "Method for preparing β-sialon fluorescent material".

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of Japanese Patent Application No. 2015-244160, filed December 15, 2015, and Japanese Patent Application No. 2016-238927, filed December 9, 2016, the disclosures of which are hereby incorporated by reference herein in their entireties. Technical Field

[0004] The present disclosure relates to a method for preparing a β-sialon fluorescent material. Background Art

[0005] Some types of light-emitting devices can emit light of various hues based on the principle of additive color mixing, using a combination of a light source and a fluorescent material, wherein the fluorescent material is excited by light from the light source to emit light of a hue different from the hue of the light source. In particular, light-emitting devices that combine light-emitting diodes (hereinafter referred to as "LEDs") and fluorescent materials are used for backlighting of liquid crystal displays, lighting systems, and the like. By constructing a light-emitting device using multiple fluorescent materials (for example, a fluorescent material that emits green light in combination with a fluorescent material that emits red light), the color reproduction range of a liquid crystal display can be increased, or the color rendering properties of a lighting system can be improved.

[0006] As such a fluorescent material, for example, a fluorescent material containing sialon (a solid solution of silicon nitride) has been proposed, and as such sialons, α-sialon and β-sialon having different crystal structures are generally known. Among these sialons, a fluorescent material containing β-sialon (hereinafter also referred to as a "β-sialon fluorescent material") is a green fluorescent material that is excited in a wide range from near-ultraviolet light to blue light and emits light with a peak wavelength in the range of 520 nm to 560 nm.

[0007] β-sialon fluorescent material is composed of, for example, the formula Si 6-z Al z O z N 8-z: Eu (0<z≤4.2). β-sialon fluorescent materials are obtained as a calcined product by mixing silicon nitride (Si3N4), aluminum nitride (AlN) and aluminum oxide (Al2O3) together with europium oxide (Eu2O3) as an activator in a specified molar ratio and calcining the mixture at about 2000°C. It has been disclosed that a β-sialon fluorescent material with high emission intensity can be obtained by heat-treating this calcined product in an inert gas and then treating it with an acid (see, for example, JP 2005-255895 A and JP2011-174015A). Another known approach to providing higher emission intensity is to perform heat treatment in two steps at a high temperature and use the β-sialon fluorescent material obtained by calcination as part of the raw material (see, for example, JP 2007-326981 A and JP 2013-173868 A). Summary of the Invention

[0008] A method for preparing a β-sialon fluorescent material includes providing a silicon nitride-containing composition containing aluminum, oxygen atoms, and europium, heat-treating the composition, and contacting the heat-treated composition with an alkaline substance.

[0009] According to one embodiment of the present disclosure, the method can prepare a β-sialon fluorescent material with excellent emission intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Shown is an emission spectrum showing the relative emission intensity of β-sialon fluorescent materials according to some embodiments of the present disclosure plotted against wavelength.

[0011] Figure 2 is an exemplary SEM image of a β-sialon fluorescent material of a comparative example.

[0012] Figure 3 is an exemplary SEM image of a β-sialon fluorescent material according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0013] From a practical point of view, there is a constant demand for higher emission intensity of β-sialon fluorescent materials. In one embodiment of the present disclosure, an object is to provide a method for preparing a β-sialon fluorescent material having excellent emission intensity.

[0014] The present inventors have conducted intensive studies in view of the above circumstances. As a result, the present inventors have found that high emission intensity can be obtained by heat-treating a β-sialon fluorescent material and bringing the heat-treated fluorescent material into contact with an alkaline substance.

[0015] Hereinafter, embodiments of the present disclosure will be described. However, the following embodiments are merely examples of some specific aspects such as preparation methods, which are intended to give a specific form of the technical concept of the present invention and are not intended to limit the scope of the present invention to such embodiments.

[0016] Relationships such as the relationship between color names and chromaticity coordinates and the relationship between the wavelength of light and the color name of monochromatic light conform to JIS Z8110.

[0017] In this specification, the term "step" is understood to include not only independent steps but also combinations of steps that are not different from each other, as long as such combined steps meet the desired purpose. In addition, unless otherwise specified, when multiple substances belong to any component in a specific composition, the content of such component in the composition means the total content of the multiple substances present in the composition.

[0018] The average particle size is the volume median diameter (Dm) and is measured by a pore resistance method based on the Coulter principle. Specifically, the particle size distribution is measured using a particle size distribution analyzer (e.g., Multisizer manufactured by BECKMAN COULTER), and the volume median diameter (Dm) is determined as the particle size at which 50% of the volume is accumulated from the smaller particle region.

[0019] (Method for preparing β-sialon fluorescent material)

[0020] The method for preparing a β-sialon fluorescent material includes providing a silicon nitride-containing composition containing aluminum, oxygen atoms and europium (hereinafter also referred to as the "providing step"), heat-treating the composition (hereinafter also referred to as the "first heat treatment step"), and contacting the heat-treated composition with an alkaline substance (hereinafter also referred to as the "alkaline treatment step").

[0021] The composition provided in the providing step is, for example, particles of the β-sialon fluorescent material itself. After heat treatment, unstable phases such as low crystalline parts present in the fluorescent material particles may be pyrolyzed to produce pyrolyzates such as silicon. Subsequent contact of the fluorescent material particles containing the pyrolyzate with an alkaline substance causes, for example, a reaction between the pyrolyzate and the alkaline substance, and thus the pyrolyzate is likely to be converted into a highly light-transmitting soluble compound such as an alkali metal silicate. This is likely to be the reason why the emission intensity can be high. The resulting soluble compound can be easily dissolved and removed by, for example, cleaning with a liquid medium. In addition, compared with acid treatment using hydrofluoric acid, contact with an alkaline substance will cause less damage to the particles of the β-sialon fluorescent material, and it is believed that such a characteristic is one of the reasons why the emission intensity tends to become higher.

[0022] (Provide steps)

[0023] In the providing step, a silicon nitride-containing composition containing aluminum, oxygen atoms, and europium is provided. The composition to be provided is, for example, a solid solution of silicon nitride containing aluminum, oxygen atoms, and europium, and has a composition represented by the following formula (I):

[0024] Si 6-z Al z O z N 8-z :Eu (I)

[0025] In formula (I), z satisfies 0<z≤4.2.

[0026] For example, the composition can be provided by selecting a desired composition from commercial products, or can be provided by preparing a desired composition by heat-treating a mixture of raw materials according to a conventional method.

[0027] When the composition is prepared in the providing step, the desired composition can be obtained by, for example, heat-treating a mixture containing an aluminum compound, a europium compound, and silicon nitride (hereinafter also referred to as "raw material mixture").

[0028] The raw material mixture preferably contains at least one aluminum compound, at least one europium compound and at least one silicon nitride. Examples of aluminum compounds include oxides, hydroxides, nitrides, oxynitrides, fluorides and chlorides containing aluminum. At least a portion of the aluminum compound can be replaced by elemental aluminum metal or an aluminum alloy. Specific examples of aluminum compounds include aluminum nitride (AlN), aluminum oxide (Al2O3) and aluminum hydroxide (Al(OH)3), and it is preferred to use at least one selected from the group consisting of these compounds. The aluminum compound can be used alone or in combination of two or more.

[0029] The average particle size of the aluminum compound used as a raw material is, for example, not less than 0.01 μm and not more than 20 μm, and preferably not less than 0.1 μm and not more than 10 μm. The purity of the aluminum compound is, for example, not less than 95 wt %, and preferably not less than 99 wt %.

[0030] Examples of europium compounds include oxides, hydroxides, nitrides, oxynitrides, fluorides and chlorides containing europium. At least a portion of the europium compound may be substituted by elemental europium metal or europium alloy. Specific examples of europium compounds include europium oxide (Eu2O3), europium nitride (EuN) and europium fluoride (EuF3), and it is preferred to use at least one selected from the group consisting of these compounds. The europium compound may be used alone or in combination of two or more.

[0031] The average particle size of the europium compound used as a raw material is, for example, not less than 0.01 μm and not more than 20 μm, and preferably not less than 0.1 μm and not more than 10.0 μm. The purity of the europium compound is, for example, not less than 95 wt %, and preferably not less than 99.5 wt %.

[0032] Silicon nitride is a silicon compound containing nitrogen atoms and silicon atoms, and may be silicon nitride containing oxygen atoms. When silicon nitride contains oxygen atoms, the oxygen atoms may be present as silicon oxide or silicon oxynitride. The content of oxygen atoms in silicon nitride is, for example, less than 2% by weight, and preferably not more than 1.5% by weight. The content of oxygen atoms is, for example, not less than 0.3% by weight, and preferably not less than 0.4% by weight. The purity of silicon nitride is, for example, not less than 95% by weight, and preferably not less than 99% by weight.

[0033] The average particle size of silicon nitride is, for example, not less than 0.01 μm and not more than 15 μm, and preferably not less than 0.1 μm and not more than 5.0 μm.

[0034] In the raw material mixture, at least a portion of the silicon nitride may be replaced by elemental silicon or another silicon compound such as silicon oxide. That is, the raw material mixture may contain elemental silicon or a silicon compound such as silicon oxide in addition to silicon nitride, or may contain elemental silicon or a silicon compound such as silicon oxide in place of silicon nitride. Examples of silicon compounds include silicon oxide, silicon oxynitride, and silicates.

[0035] The aluminum compound, europium compound, and silicon nitride are mixed together to form a raw material mixture in the following ratios. For example, the molar ratio of silicon atoms to aluminum atoms in the raw material mixture is (6-z):z (0 < z ≤ 4.2), and preferably 0.01 < z < 1.0. For example, the molar ratio of the sum of silicon atoms plus aluminum atoms to europium atoms is 6:0.001 to 6:0.05, and preferably 6:0.003 to 6:0.02.

[0036] If necessary, the raw material mixture may also contain a separately provided β-sialon fluorescent material. When the raw material mixture contains the β-sialon fluorescent material, its content may be, for example, not less than 1 wt% and not more than 50 wt% of the total weight of the raw material mixture.

[0037] If necessary, the raw material mixture may contain a flux, such as a halide. The addition of a flux to the raw material mixture further promotes the reaction between the raw materials and allows the solid phase reaction to proceed more uniformly, so that the obtainable fluorescent material achieves large particle size and higher emission characteristics. For example, the reason for this effect is likely to be because the temperature of the heat treatment in the providing step is substantially equal to or higher than the temperature at which the flux (such as a halide) forms a liquid phase. Examples of halides include chlorides and fluorides of rare earth metals, alkaline earth metals, and alkali metals. The flux can be added as a supplementary compound to control the element ratio of the cation to the target ratio, or it can be added after the raw materials have been added to the target ratio. When the raw material mixture contains a flux, its content is, for example, not higher than 20% by weight of the raw material mixture, and preferably not higher than 10% by weight. This content is, for example, not less than 0.1% by weight.

[0038] The raw material mixture can be obtained by weighing the desired starting compounds in the desired ratio and mixing the starting compounds together using a ball mill or the like, a mixer (such as a Henschel mixer) or a double-tube mixer, or a mortar and pestle. The mixing can be dry mixing or can be wet mixing involving a medium (such as a solvent).

[0039] The temperature for heat treatment of the raw material mixture is, for example, not less than 1850°C and not more than 2100°C, preferably not less than 1900°C and not more than 2050°C, more preferably not less than 1920°C and not more than 2050°C, and still more preferably not less than 2000°C and not more than 2050°C. Heat treatment at a temperature of 1850°C or higher allows efficient formation of the β-sialon fluorescent material while accelerating the incorporation of europium into the crystal, resulting in the desired β-sialon fluorescent material. Heat treatment temperatures of 2100°C or lower tend to prevent decomposition of the resulting β-sialon fluorescent material.

[0040] The atmosphere during the heat treatment of the raw material mixture preferably includes nitrogen, and more preferably is essentially a nitrogen atmosphere. When the atmosphere used for the heat treatment of the raw material mixture contains nitrogen, other gases such as hydrogen, oxygen, and ammonia may be present in addition to nitrogen. The nitrogen content in the atmosphere used for the heat treatment of the raw material mixture is, for example, not less than 90% by volume, and preferably not less than 95% by volume.

[0041] The pressure during the heat treatment of the raw material mixture may be, for example, normal pressure to 200 MPa. In order to prevent decomposition of the formed β-sialon fluorescent material, a higher pressure is more preferred, and a pressure of not less than 0.1 MPa and not more than 200 MPa is preferred, and a pressure of not less than 0.6 MPa and not more than 1.2 MPa is even more preferred because of fewer restrictions on industrial facilities.

[0042] During the heat treatment, the raw material mixture is heated from, for example, room temperature to a predetermined temperature. The temperature is raised for, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 24 hours, and more preferably not less than 3 hours and not more than 20 hours. If the temperature is raised for 1 hour or longer, the fluorescent material particles tend to grow sufficiently, and the incorporation of europium into the crystals of the fluorescent material particles tends to be accelerated.

[0043] During the heat treatment of the raw material mixture, the mixture may be maintained at a prescribed temperature for a prescribed time, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 30 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0044] In the heat treatment of the raw material mixture, the cooling time in which the material that has been heated to the specified temperature is cooled to room temperature is, for example, not less than 0.1 hours and not more than 20 hours, preferably not less than 1 hour and not more than 15 hours, and more preferably not less than 3 hours and not more than 12 hours. During the cooling period from the specified temperature to room temperature, the material can be kept at an appropriate temperature for an appropriate holding time. The holding time is controlled so that, for example, the emission intensity of the β-sialon fluorescent material will become higher. The holding time at the specified temperature during the cooling period is, for example, not less than 0.1 hours and not more than 20 hours, and preferably not less than 1 hour and not more than 10 hours. The temperature of the material is maintained, for example, not less than 1000°C and less than 1800°C, and preferably not less than 1200°C and not higher than 1700°C.

[0045] The heat treatment of the raw material mixture can be performed, for example, in a boron nitride crucible.

[0046] After the heat treatment of the raw material mixture, the resulting composition can be subjected to a size adjustment step, which carries out a combination of processes such as crushing, pulverizing and classification. The size adjustment step obtains a powder with a desired particle size. Specifically, after coarse pulverization, a conventional pulverizer (such as a ball mill, a jet mill or a vibrating mill) can be used to pulverize the composition to a specified particle size. Excessive pulverization may cause defects on the surface of the fluorescent material particles and may cause the emission intensity to decrease. When the pulverized particles are a mixture of various sizes, they can be classified to adjust the particle size. The final adjustment of the particle size can be carried out even after a downstream step (such as the first heat treatment step or the alkali treatment step described later).

[0047] (First Heat Treatment Step)

[0048] In the first heat treatment step, the composition obtained in the providing step is heat-treated to obtain a first heat-treated product. During the first heat treatment step, for example, unstable crystals (such as amorphous materials present in the β-sialon fluorescent material) are likely to at least partially decompose. From the perspective of achieving higher emission intensity, the atmosphere during the first heat treatment step is preferably a rare gas atmosphere or a vacuum, and more preferably a rare gas atmosphere.

[0049] The rare gas atmosphere in the first heat treatment step includes at least one of a rare gas such as helium, neon, and argon, and preferably includes at least argon. The rare gas atmosphere may contain other gases in addition to the rare gas, such as oxygen, hydrogen, and nitrogen. The content of the rare gas in the rare gas atmosphere is, for example, not less than 95% by volume, and preferably not less than 99% by volume.

[0050] When the first heat treatment step is performed in a rare gas atmosphere, the pressure may be, for example, in the range of normal pressure to 1 MPa, and preferably normal pressure to 0.2 MPa.

[0051] The first heat treatment step can be carried out under reduced pressure below normal pressure, and is particularly preferably carried out in a vacuum. When the heat treatment is carried out in a vacuum, the pressure is, for example, not higher than 10 kPa, preferably not higher than 1 kPa, and more preferably not higher than 100 Pa. Here, the term "reduced pressure" or "vacuum" does not exclude the possibility of the presence of any gas. Examples of gases that may be present include rare gases, nitrogen, hydrogen, and oxygen.

[0052] The heat treatment temperature of the first heat treatment step is, for example, not less than 1300°C and not more than 1600°C, and preferably not less than 1350°C and not more than 1500°C. The temperature of the first heat treatment step is preferably lower than the temperature of the heat treatment of the raw material mixture. With this configuration, unstable crystals present in the fluorescent material particles are likely to be pyrolyzed more efficiently, and the resulting fluorescent material particles will achieve higher stability and higher crystallinity. The pyrolyzed products formed in the first heat treatment step include, for example, elemental silicon and can be removed by downstream steps (such as the alkali treatment step described later).

[0053] The heat treatment time of the first heat treatment step is, for example, not less than 1 hour and not more than 48 hours, and preferably not less than 2 hours and not more than 20 hours.

[0054] In the first heat treatment step, the composition is heat-treated by raising the temperature from, for example, room temperature to a predetermined temperature. The time for raising the temperature is, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 24 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0055] In the first heat treatment step, the composition may be maintained at a predetermined temperature for a predetermined time, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 30 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0056] In the first heat treatment step, the cooling time for the composition that has been heated to the specified temperature to cool to room temperature is, for example, not less than 0.1 hours and not more than 20 hours, preferably not less than 1 hour and not more than 15 hours, and more preferably not less than 3 hours and not more than 12 hours. During the cooling from the specified temperature to room temperature, the mixture can be kept at an appropriate temperature for an appropriate holding time. The holding time is controlled so that, for example, the emission intensity of the β-sialon fluorescent material will become higher. The holding time at the specified temperature during the cooling period is, for example, not less than 0.5 hours and not more than 20 hours, and preferably not less than 1 hour and not more than 10 hours. The temperature at which the composition is maintained is, for example, not less than 800°C and less than 1600°C, and preferably not less than 1000°C and not higher than 1400°C.

[0057] In the first heat treatment step, the composition obtained in the providing step can be heat treated in the presence of a europium compound. In this case, the heat treatment is preferably carried out in a rare gas atmosphere. When the composition obtained in the providing step is heat treated in a rare gas atmosphere in the presence of a europium compound, a β-sialon fluorescent material with excellent emission intensity can be efficiently prepared. For example, the explanation of this effect is likely to be as follows. When the first heat treatment step is carried out in a rare gas atmosphere in the presence of a europium compound, at least a portion of the europium compound is reduced to form a gas derived from the europium compound. It is possible that the gas contacts the composition provided in the providing step and therefore the europium present in the composition is easily reduced to a divalent state. It is also possible that the gas produced by the reduction of the europium compound is incorporated into the composition. The higher emission intensity is likely to be attributed to a combination of these mechanisms.

[0058] The example of the europium compound used in the first heat treatment step includes oxides, hydroxides, nitrides, oxynitrides, fluorides and chlorides containing europium. At least a portion of the europium compound can be replaced by elemental europium metal or europium alloy. Specific examples of europium compounds include europium oxide (Eu2O3), europium nitride (EuN) and europium fluoride (EuF3), and it is preferred to use at least one selected from the group consisting of these compounds. Europium oxide is more preferred. The europium compound can be used alone, or two or more can be used in combination.

[0059] The average particle size of the europium compound used in the first heat treatment step is, for example, not less than 0.01 μm and not more than 20 μm, and preferably not less than 0.1 μm and not more than 10.0 μm. The purity of the europium compound is, for example, not less than 95 wt %, and preferably not less than 99.5 wt %.

[0060] When a europium compound is used in the first heat treatment step, the weight ratio of the europium compound to the composition (100 wt %) obtained in the providing step is not less than 0.01 wt %, preferably not less than 0.05 wt %, and more preferably not less than 0.1 wt %. The weight ratio is not more than 50 wt %, preferably not more than 20 wt %, more preferably not more than 15 wt %, and still more preferably not more than 10 wt %.

[0061] When using a europium compound in the first heat treatment step, heat treatment is carried out in such a way that the gas produced by the europium compound can be in contact with the composition obtained in the providing step. For example, a mixture of the composition obtained in the providing step and the europium compound can be heat treated in a single container. Alternatively, the composition obtained in the providing step and the europium compound can be heat treated in a single container or a separate container without mixing with each other. Still alternatively, a part of the europium compound can be mixed with the composition obtained in the providing step, and the remainder of the resulting mixture and the compound can be heat treated in a single container or a separate container without mixing with each other. When the composition obtained in the providing step and the europium compound are mixed together, the mixing is preferably carried out as uniformly as possible.

[0062] The method for preparing a β-sialon fluorescent material may include a step in which the first heat-treated product produced by the first heat-treatment step is treated after the first heat-treatment step by crushing, pulverizing, etc. Treatments such as crushing and pulverizing can be performed by the methods described above.

[0063] (Alkali treatment step)

[0064] In the alkali treatment step, the composition heat-treated in the first heat treatment step (the product after the first heat treatment) is contacted with an alkaline substance to obtain an alkali-treated product. The contact with the alkaline substance enables a higher emission intensity to be obtained, which is probably because the components (such as pyrolyzates) present in the product after the first heat treatment that may be harmful to the emission characteristics react with the alkaline substance and are converted into compounds having a lower impact on the emission characteristics.

[0065] Examples of the alkaline substance include alkali metal hydroxides such as LiOH, NaOH, KOH, RbOH, and CsOH; alkali metal carbonates such as Li2CO3, Na2CO3, K2CO3, Rb2CO3, and Cs2CO3; hydroxides of elements of Group 2 of the periodic table such as Mg(OH)2, Ca(OH)2, Sr(OH)2, and Ba(OH)2; ammonia (NH3); hydrazine; ethylenediaminecatechol (EDP); and quaternary ammonium compounds such as tetramethylammonium hydroxide and tetraethylammonium hydroxide. Those alkaline substances that are soluble in water are preferred. More preferably, the alkaline substance includes at least one selected from the group consisting of LiOH, NaOH, KOH, RbOH, CsOH, Li2CO3, Na2CO3, K2CO3, Rb2CO3, Cs2CO3, ammonia (NH3) and tetraethylammonium hydroxide, still more preferably includes at least one selected from the group consisting of LiOH, NaOH, KOH, RbOH, CsOH and NH3, and particularly preferably includes at least NaOH or KOH.

[0066] The amount of the alkaline substance contacted with the first heat-treated product can be appropriately selected according to factors such as the type of alkaline substance. For example, the weight ratio of the alkaline substance to the heat-treated product is not less than 0.5 weight %, preferably not less than 1 weight %, more preferably not less than 5 weight %, and even more preferably not less than 8 weight %. For example, the weight ratio is not higher than 200 weight %, preferably not higher than 100 weight %, and more preferably not higher than 80 weight %. When using alkaline substances in a weight ratio of more than 0.5 weight %, the reaction of the components such as the pyrolyzer tends to be fully carried out. By controlling the ratio to be not higher than 200 weight %, it tends to prevent the adverse effects on the fluorescent material particles.

[0067] For example, the alkali treatment step can be carried out in an oxidizing atmosphere (such as air) or in an inert atmosphere (such as nitrogen or argon). The inert gas concentration in the inert atmosphere is, for example, not less than 90% by volume, and preferably not less than 95% by volume. The pressure in the atmosphere during the alkali treatment step is, for example, not less than 10 Pa and not more than 1 MPa, and preferably not less than 100 Pa and not more than 0.2 MPa.

[0068] The temperature of the alkali treatment step is, for example, not less than 50°C and not more than 650°C, preferably not less than 50°C and not more than 500°C, and more preferably not less than 70°C and not more than 400°C. Controlling the contact temperature to 50°C or higher increases the reactivity between components such as pyrolyzates present in the product subjected to the first heat treatment and the alkaline substance, and thus tends to further increase productivity. Limiting the contact temperature to not more than 650°C tends to prevent adverse effects on the produced fluorescent material.

[0069] The alkali treatment step can take multiple temperature conditions. For example, the alkali treatment step may include contacting the product of the first heat treatment with an alkaline substance at a first temperature (also referred to as a "first hot alkali treatment") and contacting at a second temperature higher than the first temperature (also referred to as a "second hot alkali treatment"). Carrying out the first hot alkali treatment and the second hot alkali treatment tends to allow the reaction between the alkaline substance and components such as pyrolyzates to proceed more efficiently, and tends to prevent adverse effects on the fluorescent material particles. For example, the first temperature is not less than 50°C and not higher than 150°C, preferably not less than 60°C and not higher than 140°C, and more preferably not less than 60°C and not higher than 120°C. The second temperature is higher than the first temperature, and for example not less than 90°C and not higher than 650°C, preferably not less than 120°C and not higher than 500°C, and more preferably not less than 150°C and not higher than 400°C.

[0070] The contact time in the alkali treatment step can suitably be selected according to factors such as alkaline material type, weight ratio and contact temperature.For example, the contact time is no less than 0.1 hour and no more than 48 hours, and preferably is no less than 0.5 hour and no more than 20 hours.Comprise that the first hot alkali is handled and the second hot alkali is handled under the situation that the alkali treatment step, the processing time of the first hot alkali is handled for example is no less than 0.1 hour and no more than 48 hours, and preferably is no less than 0.5 hour and no more than 20 hours, and the processing time of the second hot alkali is handled for example is no less than 0.1 hour and no more than 24 hours, and preferably is no less than 0.5 hour and no more than 12 hours.

[0071] The method in which the product of the first heat treatment is contacted with the alkaline substance preferably includes mixing the product of the first heat treatment with a solution of the alkaline substance. By using the alkaline substance in the form of a solution, the reaction between the product of the first heat treatment and the alkaline substance can be carried out more uniformly. The solvent for forming the solution of the alkaline substance can be appropriately selected from commonly used solvents. Examples of solvents include: water; alcohols such as methanol, ethanol and isopropanol; and amines such as ethanolamine, triethanolamine and ethylenediamine. The solvent can be used alone or in combination of two or more. In particular, the solvent preferably includes water.

[0072] The concentration of the solution of the alkaline substance can be appropriately selected according to factors such as the type of alkaline substance and the solvent. The concentration of the solution of the alkaline substance can be, for example, not less than 0.1 wt % and not more than 80 wt %, and preferably not less than 1 wt % and not more than 50 wt %.

[0073] The alkali treatment step preferably comprises mixing the product through the first thermal treatment with the solution of alkaline substances, and removing at least a portion of the solvent present in the solution. The removal of at least a portion of the solvent tends to further improve the efficiency of the reaction between alkaline substances and the pyrolyzate. When the solvent is removed from the mixture of the solution of the first thermal treatment product and alkaline substances, the removal rate of the solvent can be no less than 1 % by weight, preferably no less than 10 % by weight, and more preferably no less than 20 % by weight.

[0074] The example of the method for removing solvent comprises heat treatment and evaporation treatment.These methods can be used in combination.The solvent removal method is suitably the method that the alkaline substance in solution is not removed together with the solvent, and preferably comprises at least heat treatment.When removing solvent by heat treatment, temperature is preferably similar to the first temperature described above.

[0075] Alkali treatment step preferably comprises that product through the first heat treated is mixed with the solution of alkaline matter, make product through the first heat treated be contacted with alkaline matter at first temperature (the first hot alkali treatment), and make product through the first heat treated be contacted with alkaline matter at the second temperature higher than first temperature (the second hot alkali treatment) from the first hot alkali treatment.More preferably, the first hot alkali treatment comprises at least a portion of the solvent existing in the solution of removing alkaline matter, and the second hot alkali treatment is included in the mixture of the first heat treated product and alkaline matter at the second temperature thermal treatment, wherein at least a portion of solvent is removed.By so that at the first temperature, remove at least a portion of solvent and at the second temperature, heat-treat this mode of mixture afterwards, heat-treat, the reaction between the component such as pyrolyzer and the alkaline matter existing in the first heat treated product tends to be more evenly and efficiently carried out.

[0076] The time that carries out solvent removal at first temperature can suitably be selected according to the factor such as required solvent removal rate.The solvent removal time at first temperature is similar to the processing time of the first hot alkali treatment, and the thermal treatment time at second temperature is similar to the processing time of the second hot alkali treatment.Herein, carrying out solvent removal at first temperature can be for example air or inert gas atmosphere.On the other hand, the thermally treated atmosphere at second temperature is preferably inert gas atmosphere.

[0077] The alkali treatment step may include a step in which the alkali-treated product resulting from the alkali treatment is treated by crushing, pulverizing, etc. Treatments such as crushing and pulverizing can be performed by the methods described above.

[0078] (Washing Step)

[0079] If desired, the method for preparing a β-sialon fluorescent material may include washing the alkali-treated product from the alkali treatment step with a liquid medium (also referred to as a "washing step"). Washing the alkali-treated product with a liquid medium removes at least a portion of unwanted components (such as alkali metal silicates) present in the alkali-treated product.

[0080] The method for preparing β-sialon fluorescent material according to the present embodiment is basically completed at the alkali treatment step. The washing step does not play a big role in enhancing the emission characteristics of the fluorescent material particles themselves after the alkali treatment step, and its purpose is to remove unnecessary components (such as trace amounts of alkali metal silicates) produced during the alkali treatment step. The pyrolysis products (such as elemental silicon) formed in the first heat treatment step are converted into components such as alkali metal silicates during the alkali treatment step. Such compounds themselves do not participate in the emission characteristics to a large extent. However, the washing step of removing such compounds formed in the alkali treatment step makes it possible to prevent adverse effects on materials (such as silicone resins) used in the manufacture of light-emitting devices including fluorescent material particles.

[0081] The washing step involves a liquid medium. The liquid medium can be appropriately selected from commonly used liquid media according to the purpose, as long as the unwanted components can be removed. Liquid media with any properties can be used without limitation. Examples include: water; neutral liquid media, such as alcohols, for example ethanol and isopropanol; and acidic liquid media, such as hydrochloric acid and nitric acid, and it is preferred to use at least one selected from the group consisting of these media. More preferably, the liquid medium includes at least water. The use of acidic media (such as hydrochloric acid and nitric acid) sometimes enables more efficient removal of unwanted components.

[0082] Regarding the washing method, washing can be performed, for example, by immersing the alkali-treated product in a liquid medium, optionally stirring it, and separating the solid and the liquid. The solid-liquid separation may be followed by a drying treatment as needed.

[0083] The temperature of the liquid medium used for washing is, for example, not lower than 5° C. and not higher than 95° C., and preferably not lower than 25° C. and not higher than 80° C. The washing time may be, for example, not less than 0.01 hour and not more than 48 hours, and preferably not less than 0.1 hour and not more than 20 hours.

[0084] The liquid medium used in the washing step can be a neutral solution, an acidic solution or an alkaline solution. Because the alkali-treated product has been treated with alkali, it exhibits alkalinity when added to water. Therefore, the washing step preferably includes washing with a neutral to acidic solution.

[0085] The washing step can be performed two or more times using the same or different liquid media. For example, the first wash can be performed using water, a neutral solution, an acidic solution, or an alkaline solution, and then the second wash can be performed using water. In this way, for example, basic or acidic compounds adhering to the surface of the β-sialon fluorescent material can be efficiently removed by the first wash.

[0086] (Second Heat Treatment Step)

[0087] The method for preparing a β-sialon fluorescent material may include heat-treating the composition provided in the providing step in a nitrogen atmosphere prior to the first heat-treating step. (This treatment will also be referred to as the "second heat-treating step.") The addition of the second heat-treating step ensures that the resulting β-sialon fluorescent material will achieve a higher emission intensity. For example, some of the reasons why the second heat-treating step provides an increase in emission intensity are due to increased crystallinity and because poorly grown crystal particles present in the composition obtained in the providing step are incorporated into larger particles, resulting in the particles becoming larger in size.

[0088] The heat treatment temperature in the second heat treatment step is, for example, not lower than 1800°C and not higher than 2100°C, preferably not lower than 1850°C and not higher than 2040°C, and more preferably not lower than 1900°C and not higher than 2040°C.

[0089] The atmosphere in the second heat treatment step is a nitrogen atmosphere containing at least nitrogen, and preferably a nitrogen atmosphere consisting essentially of nitrogen. The nitrogen atmosphere in the second heat treatment step may contain other gases in addition to nitrogen, such as hydrogen, oxygen, and ammonia. The nitrogen content in the nitrogen atmosphere in the second heat treatment step is, for example, not less than 90% by volume, and preferably not less than 95% by volume.

[0090] The pressure in the second heat treatment step is, for example, normal pressure to 200 MPa. To prevent decomposition of the formed β-sialon fluorescent material, a higher pressure is preferred, and a pressure of not less than 0.1 MPa and not more than 200 MPa is preferred, and a pressure of not less than 0.6 MPa and not more than 1.2 MPa is more preferred because it imposes fewer restrictions on industrial facilities.

[0091] In the second heat treatment step, the composition is heat-treated by raising the temperature from, for example, room temperature to a predetermined temperature. The time for raising the temperature is, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 24 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0092] In the second heat treatment step, the composition may be maintained at a predetermined temperature for a predetermined time, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 30 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0093] In the second heat treatment step, the cooling time for the composition that has been heated to the specified temperature to cool to room temperature is, for example, not less than 0.1 hours and not more than 20 hours, preferably not less than 1 hour and not more than 15 hours, and more preferably not less than 3 hours and not more than 12 hours. During the cooling period from the specified temperature to room temperature, the mixture can be kept at an appropriate temperature for an appropriate holding time. The holding time is controlled so that, for example, the emission intensity of the β-sialon fluorescent material will become higher. The holding time at the specified temperature during the cooling period is, for example, not less than 0.1 hours and not more than 20 hours, and preferably not less than 1 hour and not more than 10 hours. The temperature at which the composition is maintained is, for example, not less than 1000°C and less than 1800°C, and preferably not less than 1200°C and not higher than 1700°C.

[0094] When the method for preparing a β-sialon fluorescent material includes a second heat treatment step, the composition resulting from the second heat treatment step is subjected to the first heat treatment step. Furthermore, in the method for preparing a β-sialon fluorescent material, the second heat treatment step may be performed two or more times. In this case, the first heat treatment step is performed on the composition resulting from the final second heat treatment step.

[0095] (Third Heat Treatment Step)

[0096] When the method for preparing a β-sialon fluorescent material includes a washing step, the method may include heat-treating the alkali-treated product after the washing step. (This treatment will also be referred to as a "third heat treatment step.") The addition of a third heat treatment step is likely to increase the crystallinity of the fluorescent material particles, thereby ensuring that the resulting β-sialon fluorescent material will achieve higher emission intensity. The heat treatment temperature in the third heat treatment step is, for example, not less than 1000°C and not more than 1800°C, preferably not less than 1100°C and not more than 1700°C, and more preferably not less than 1150°C and not more than 1650°C.

[0097] The atmosphere in the third heat treatment step is not particularly limited. The atmosphere in the third heat treatment step is preferably a nitrogen-containing atmosphere. More preferably, the atmosphere is essentially a nitrogen atmosphere. When the atmosphere in the third heat treatment step contains nitrogen, other gases such as hydrogen, oxygen, and ammonia may be present in addition to nitrogen. The nitrogen content in the atmosphere in the third heat treatment step is, for example, not less than 90% by volume, and preferably not less than 95% by volume.

[0098] The pressure in the third heat treatment step is, for example, normal pressure to 200 MPa. To prevent decomposition of the formed β-sialon fluorescent material, a higher pressure is preferred, and a pressure of not less than 0.1 MPa and not more than 200 MPa is preferred, and a pressure of not less than 0.6 MPa and not more than 1.2 MPa is more preferred because it imposes fewer restrictions on industrial facilities.

[0099] In the third heat treatment step, the alkali-treated product is heat-treated by raising the temperature from, for example, room temperature to a predetermined temperature. The time for raising the temperature is, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 24 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0100] In the third heat treatment step, the alkali-treated product may be maintained at a predetermined temperature for a predetermined time, for example, not less than 1 hour and not more than 48 hours, preferably not less than 2 hours and not more than 30 hours, and more preferably not less than 3 hours and not more than 20 hours.

[0101] In the third heat treatment step, the cooling time for cooling the alkali-treated product, which has been heated to a prescribed temperature, to room temperature is, for example, not less than 0.1 hours and not more than 20 hours, preferably not less than 1 hour and not more than 15 hours, and more preferably not less than 3 hours and not more than 12 hours. During the cooling period from the prescribed temperature to room temperature, the alkali-treated product can be maintained at an appropriate temperature for an appropriate holding time. The holding time is controlled so that, for example, the emission intensity of the β-sialon fluorescent material becomes higher.

[0102] (β-sialon fluorescent material)

[0103] The β-sialon fluorescent material of this embodiment is obtained by a specific preparation method and therefore exhibits high emission intensity. For example, the emission intensity can be increased by 5% or more, sometimes by 10% or more, and further by 50% or more compared to preparation without alkali treatment.

[0104] The β-sialon fluorescent material of this embodiment has a composition represented by the formula described above and may further contain a trace amount of an alkali metal element. When the β-sialon fluorescent material contains an alkali metal element, its content is, for example, not less than 0.1 ppm and not more than 1000 ppm, and preferably not less than 0.1 ppm and not more than 100 ppm.

[0105] The β-sialon fluorescent material of the present embodiment absorbs light in the region of short-wave light from ultraviolet light to visible light, and emits light with a peak wavelength longer than the emission peak wavelength of the excitation light. The short-wavelength light in the visible light is mainly in the blue light region. Specifically, the fluorescent material is excited by light with an emission peak wavelength in the range of 250nm to 480nm (including end values) from an excitation light source, and emits fluorescence with an emission peak wavelength in the range of 520nm to 560nm (including end values). By using an excitation light source with a peak wavelength in the range of 250nm to 480nm, the higher emission efficiency of the β-sialon fluorescent material can be achieved due to the higher intensity of the excitation spectrum of the β-sialon fluorescent material in this wavelength range. In particular, it is preferred to use an excitation light source with an emission peak wavelength of 350nm to 480nm (including end values), and it is more preferred to use an excitation light source with an emission peak wavelength of 420nm to 470nm (including end values).

[0106] In addition, the β-sialon fluorescent material of this embodiment has a high degree of crystallinity. For example, glass (amorphous) has an irregular structure and low degree of crystallinity. Therefore, unless the reaction conditions in the preparation step can be strictly controlled to be constant, the ratio of the components in the fluorescent material is variable and tends to cause problems such as uneven chromaticity. In contrast, the β-sialon fluorescent material according to this embodiment is a powder or particle with high crystallinity in at least a portion of its structure, and this characteristic tends to allow the fluorescent material to be easily prepared and processed. In addition, the β-sialon fluorescent material can be easily and evenly dispersed in an organic medium, which makes it easy to prepare products such as luminescent plastics and polymer film materials. Specifically, for example, at least 50% by weight, and more preferably at least 80% by weight, of the structure of the β-sialon fluorescent material has crystallinity. This ratio represents the proportion of the luminescent crystalline phase, and when such a crystalline phase accounts for at least 50% by weight of the structure, it is advantageous to achieve light emission that can withstand practical use. Therefore, the higher the proportion of the crystalline phase, the higher the emission efficiency, and therefore, the emission intensity can be increased and the processing of the fluorescent material can be made simpler.

[0107] For the average particle size of the β-sialon fluorescent material of the present embodiment, the volume median diameter (Dm) measured based on the Coulter principle is, for example, not less than 4 μm and not more than 40 μm, and preferably not less than 8 μm and not more than 30 μm. It is preferred that the β-sialon fluorescent material contains particles having this average particle size at a high frequency. That is, it is preferred that the particle size distribution is within a narrow range. The use of a β-sialon fluorescent material having a small particle size distribution half width enables the manufacture of a light-emitting device with improved color uniformity and good hue. In addition, the larger the average particle size, the higher the light absorption rate and the higher the emission efficiency. Therefore, the use of a fluorescent material having the above-mentioned excellent optical properties and a large average particle size in a light-emitting device improves the emission efficiency of the light-emitting device.

[0108] [Example]

[0109] (Example 1)

[0110] Provide steps

[0111] Silicon nitride (Si3N4), aluminum nitride (AlN), and europium oxide (Eu2O3) were weighed as starting compounds at a molar ratio of Si:Al:Eu = 5.88:0.12:0.01 and mixed to form a first raw material mixture. This raw material mixture was enclosed in a boron nitride crucible and heat-treated in a nitrogen atmosphere at approximately 0.92 MPa (gauge pressure) and 2030°C for 10 hours. This yielded a β-sialon fluorescent material.

[0112] Next, the β-sialon fluorescent material obtained by the above heat treatment is mixed with silicon nitride, aluminum nitride, and europium oxide to obtain a second raw material mixture. Here, Si:Al:Eu is the same as above, and the content of the β-sialon fluorescent material is 20% by weight of the total weight of the second raw material mixture. The second raw material mixture is heat-treated in such a way that the mixture is calcined at about 0.92 MPa (gauge pressure) and 1970°C for 10 hours in a nitrogen atmosphere, and cooled to room temperature while maintaining a temperature of 1500°C for 5 hours during the cooling process. Thus, a composition represented by formula (I) described above is obtained.

[0113] Second heat treatment step

[0114] The obtained composition was pulverized, packaged in a boron nitride crucible, and heat-treated in a nitrogen atmosphere at about 0.92 MPa (gauge pressure) in such a manner that the temperature was raised to 2030° C. over 10 hours and maintained at 2030° C. for 10 hours, and the composition was cooled to room temperature while being maintained at 1500° C. for 5 hours during the cooling process. Through this second heat treatment step, a heat-treated product was obtained.

[0115] First heat treatment step

[0116] The heat-treated product obtained by the second heat treatment step was mixed with 0.5% by weight of europium oxide relative to the heat-treated product. The resulting mixture was heat-treated in an argon atmosphere at normal pressure, heating the mixture at 1400°C for 5 hours in a nitrogen atmosphere, and then cooled to room temperature while maintaining a temperature of 1100°C for 5 hours during the cooling process. The heat treatment was followed by pulverization and dispersion. This resulted in a product that had undergone the first heat treatment.

[0117] Alkali treatment step

[0118] The product after the first heat treatment was mixed with a solution containing 10% by weight of sodium hydroxide and 90% by weight of pure water relative to the product after the first heat treatment. Thereafter, heat treatment was performed in air at 70°C for 3 hours to remove water. Thus, an alkali-treated product was obtained.

[0119] Washing steps

[0120] The alkali-treated product was stirred in pure water (up to 10 times the weight of the alkali-treated product). The pure water was then replaced several times. The washed product was subjected to solid-liquid separation and drying. Fluorescent material 1 was thus obtained.

[0121] (Example 2)

[0122] Fluorescent material 2 was obtained by performing synthesis under the same conditions as in Example 1, except that the amounts of sodium hydroxide and pure water in the alkali treatment step were changed to 1 wt % and 99 wt %, respectively.

[0123] (Example 3)

[0124] Fluorescent material 3 was obtained by performing synthesis under the same conditions as in Example 1, except that the amounts of sodium hydroxide and pure water in the alkali treatment step were changed to 5 wt % and 95 wt %, respectively.

[0125] (Example 4)

[0126] Fluorescent material 4 was obtained by performing synthesis under the same conditions as in Example 1, except that the amounts of sodium hydroxide and pure water in the alkali treatment step were changed to 20 wt % and 80 wt %, respectively.

[0127] (Example 5)

[0128] Fluorescent material 5 was obtained by performing synthesis under the same conditions as in Example 1, except that the amounts of sodium hydroxide and pure water in the alkali treatment step were changed to 50 wt % and 50 wt %, respectively.

[0129] (Example 6)

[0130] Fluorescent material 6 was obtained by synthesis under the same conditions as in Example 2, except that the alkali treatment step was performed by performing a first hot alkali treatment at 70° C. for 3 hours and further performing a second hot alkali treatment at 200° C. in a nitrogen atmosphere for 2 hours similarly to Example 2.

[0131] (Example 7)

[0132] Fluorescent material 7 was obtained by synthesis under the same conditions as in Example 3, except that the alkali treatment step was performed by performing a first hot alkali treatment at 70° C. for 3 hours and further performing a second hot alkali treatment at 200° C. in a nitrogen atmosphere for 2 hours similarly to Example 3.

[0133] (Example 8)

[0134] Fluorescent material 8 was obtained by synthesis under the same conditions as in Example 1, except that the alkali treatment step was performed by first hot alkali treatment at 70° C. for 3 hours and further second hot alkali treatment at 200° C. in a nitrogen atmosphere for 2 hours similarly to Example 1.

[0135] (Example 9)

[0136] Fluorescent material 9 was obtained by synthesis under the same conditions as in Example 4, except that the alkali treatment step was performed by performing a first hot alkali treatment at 70° C. for 3 hours and further performing a second hot alkali treatment at 200° C. in a nitrogen atmosphere for 2 hours similarly to Example 4.

[0137] (Example 10)

[0138] The fluorescent material 10 was obtained by synthesis under the same conditions as in Example 5, except that the alkali treatment step was performed by performing a first hot alkali treatment at 70° C. for 3 hours and further performing a second hot alkali treatment at 200° C. in a nitrogen atmosphere for 2 hours similarly to Example 5.

[0139] (Example 11)

[0140] The fluorescent material 11 was prepared by performing synthesis under the same conditions as in Example 6, except that the amounts of sodium hydroxide and pure water in the alkali treatment step were changed to 10 wt % and 70 wt %, respectively.

[0141] (Example 12)

[0142] The fluorescent material 12 was obtained by performing synthesis under the same conditions as in Example 6, except that the alkaline substance in the alkali treatment step was changed to 0.5 wt % of potassium hydroxide.

[0143] (Example 13)

[0144] The fluorescent material 13 was obtained by performing synthesis under the same conditions as in Example 6, except that the alkaline substance in the alkali treatment step was changed to 1 wt % of potassium hydroxide.

[0145] (Example 14)

[0146] The fluorescent material 14 was obtained by performing synthesis under the same conditions as in Example 7, except that the alkaline substance in the alkali treatment step was changed to 5 wt % of potassium hydroxide.

[0147] (Example 15)

[0148] The fluorescent material 15 was obtained by performing synthesis under the same conditions as in Example 8, except that the alkaline substance in the alkali treatment step was changed to 10 wt % of potassium hydroxide.

[0149] (Example 16)

[0150] The fluorescent material 16 was obtained by performing synthesis under the same conditions as in Example 9, except that the alkaline substance in the alkali treatment step was changed to 20 wt % of potassium hydroxide.

[0151] (Example 17)

[0152] Fluorescent material 17 was obtained by performing synthesis under the same conditions as in Example 8, except that the temperature in the second hot alkali treatment step was changed to 100°C.

[0153] (Example 18)

[0154] The fluorescent material 18 was obtained by performing synthesis under the same conditions as in Example 8, except that the temperature in the second hot alkali treatment step was changed to 150°C.

[0155] (Example 19)

[0156] Fluorescent material 19 was obtained by performing synthesis under the same conditions as in Example 8, except that the temperature in the second hot alkali treatment step was changed to 300°C.

[0157] (Example 20)

[0158] The fluorescent material 20 was obtained by performing synthesis under the same conditions as in Example 8, except that the temperature in the second hot alkali treatment step was changed to 400°C.

[0159] (Example 21)

[0160] The fluorescent material 21 was obtained by performing synthesis under the same conditions as in Example 8, except that the temperature in the second hot alkali treatment step was changed to 600°C.

[0161] (Example 22)

[0162] The fluorescent material 22 was obtained by performing synthesis under the same conditions as in Example 8, except that the time for which the second hot alkali treatment step was performed was changed to 0.5 hours.

[0163] (Example 23)

[0164] The fluorescent material 23 was obtained by performing synthesis under the same conditions as in Example 8, except that the time for which the second hot alkali treatment step was performed was changed to 1 hour.

[0165] (Example 24)

[0166] The fluorescent material 24 was obtained by performing synthesis under the same conditions as in Example 8, except that the time for which the second hot alkali treatment step was performed was changed to 4 hours.

[0167] (Example 25)

[0168] The fluorescent material 25 was obtained by performing synthesis under the same conditions as in Example 8, except that the time for which the second hot alkali treatment step was performed was changed to 8 hours.

[0169] (Example 26)

[0170] The fluorescent material 26 was obtained by performing synthesis under the same conditions as in Example 8, except that the alkaline substance in the alkali treatment step was changed to 10 wt % of lithium hydroxide.

[0171] (Example 27)

[0172] The fluorescent material 27 was obtained by performing synthesis under the same conditions as in Example 8, except that the alkaline substance in the alkali treatment step was changed to 10% by weight of rubidium hydroxide.

[0173] (Example 28)

[0174] The fluorescent material 28 was obtained by performing synthesis under the same conditions as in Example 8, except that the alkaline substance in the alkali treatment step was changed to 10% by weight of cesium hydroxide.

[0175] (Example 29)

[0176] Fluorescent material 29 was obtained by synthesis under the same conditions as in Example 12, except that the alkali treatment step involved 8.5 wt % potassium hydroxide, 1.5 wt % pure water and 90 wt % ethanol, and the temperature and time in the first hot alkali treatment were changed to 100° C. and 1 hour.

[0177] (Comparative Example 1)

[0178] The fluorescent material C1 was obtained by performing synthesis under the same conditions as in Example 1, except that the alkali treatment step was not performed.

[0179] (Comparative Example 2)

[0180] Fluorescent material C2 was obtained by performing synthesis under the same conditions as in Example 11, except that sodium hydroxide in the alkali treatment step was replaced by sodium nitrate.

[0181] (Example 30)

[0182] The fluorescent material 30 is obtained by synthesizing under the same conditions as in Example 1, except that: in the providing step, the content of the β-sialon fluorescent material is changed to 10 weight % of the total weight of the second raw material mixture, and in the alkali treatment step, the obtained first heat-treated product is contacted with a solution containing 18 weight % of sodium hydroxide and 82 weight % of pure water relative to the first heat-treated product, and heat-treated in air at 105°C for 16 hours to remove water, thereby obtaining an alkali-treated product.

[0183] (Example 31)

[0184] The fluorescent material 31 is obtained by synthesizing under the same conditions as in Example 30, except that: in the alkali treatment step, the obtained product after the first heat treatment is mixed with a solution containing 20 weight % of sodium carbonate and 100 weight % of pure water relative to the product after the first heat treatment.

[0185] (Example 32)

[0186] The fluorescent material 32 is obtained by synthesizing under the same conditions as in Example 30, except that: in the alkali treatment step, the obtained product after the first heat treatment is mixed with a solution containing 20 weight% of potassium carbonate and 100 weight% of pure water relative to the product after the first heat treatment.

[0187] (Example 33)

[0188] The fluorescent material 33 was obtained by performing synthesis under the same conditions as in Example 30, except that after the first alkali treatment step was performed at 70° C. for 3 hours, the second alkali treatment step was performed at 300° C. under a nitrogen atmosphere for 2 hours.

[0189] (Example 34)

[0190] The fluorescent material 34 was obtained by performing synthesis under the same conditions as in Example 31, except that after the first alkali treatment step was performed at 70° C. for 3 hours, the second alkali treatment step was performed at 300° C. under a nitrogen atmosphere for 2 hours.

[0191] (Example 35)

[0192] The fluorescent material 35 was obtained by performing synthesis under the same conditions as in Example 32, except that after the first alkali treatment step was performed at 70° C. for 3 hours, the second alkali treatment step was performed at 300° C. under a nitrogen atmosphere for 2 hours.

[0193] (Comparative Example 3)

[0194] Fluorescent material C3 was obtained by performing synthesis under the same conditions as in Example 30, except that the alkali treatment step was not performed.

[0195] <Evaluation>

[0196] The obtained β-sialon fluorescent material was analyzed by a pore resistance method (electrical sensing area method) based on the Coulter principle using a particle size distribution analyzer (Multisizer manufactured by BECKMAN COULTER) to determine an average particle size (Dm, median diameter).

[0197] The emission characteristics of the fluorescent materials were measured using a fluorescence spectrophotometer QE-2000 (manufactured by OTSUKA ELECTRONICS Co., LTD.). Specifically, the emission spectrum was recorded using 450nm wavelength excitation light, and the relative emission intensity (%) and emission peak wavelength (nm) at the peak of the emission spectrum were measured. Here, for Examples 1 to 29 and Comparative Example 2, the relative emission intensity was calculated relative to the intensity of fluorescent material C1 of Comparative Example 1, while for Examples 30 to 35, the relative emission intensity was calculated relative to the intensity of fluorescent material C3 of Comparative Example 3. All emission peak wavelengths were around 538nm.

[0198] The evaluation results are described in Table 1 below.

[0199] [Table 1]

[0200]

[0201]

[0202]

[0203] Figure 1 Shown are emission spectra of the β-sialon fluorescent materials obtained in Examples 1 to 5 and Comparative Example 1, which are normalized based on the maximum emission intensity of Comparative Example 1. As also shown in Table 1, it has been demonstrated that the β-sialon fluorescent materials 1 to 29 have high relative emission intensities.

[0204] Figure 2 and Figure 3are electron micrographs (SEM images) showing the shapes of particles of the β-sialon fluorescent material obtained in Comparative Example 1 and Example 1, respectively. Figure 2 and Figure 3 As can be seen, the β-sialon fluorescent material has substantially the same particle shape, and no changes are found. This likely indicates that the alkali treatment step does not cause changes in particle size or shape. In other words, the treatment with an alkaline substance can remove unwanted components (such as decomposition products) formed during the first heat treatment step without causing changes in the shape of the β-sialon fluorescent material itself, thereby allowing the β-sialon fluorescent material to achieve higher emission intensity.

[0205] Examples 6 to 11 involve a second thermal alkali treatment at a higher temperature in addition to the first thermal alkali treatment, and thus achieve further improvement in relative emission intensity compared to Examples 1 to 5, in which the alkali treatment step includes only the first thermal alkali treatment. This result is likely due to the accelerated reaction between the alkaline substance of the thermal alkali treatment at a higher temperature and the heat-treated β-sialon.

[0206] Examples 12 to 16 have shown that the relative emission intensity is improved even when potassium hydroxide is used as the alkaline substance, similarly to when sodium hydroxide is used.

[0207] In Examples 17 to 21 in which the second thermal alkali treatment was performed at various temperatures, it has been shown that when the temperature of the second thermal alkali treatment was 300° C. in Example 19, the relative emission intensity was particularly improved.

[0208] Examples 22 to 25, in which the second hot alkaline treatment was carried out for various lengths of time, have shown that the relative emission intensity is particularly improved when the treatment time is 1 hour or longer.

[0209] In Examples 26 to 28 involving various basic substances, it has been shown that basic substances believed to have higher reactivity provide higher relative emission intensity improvements.

[0210] Example 29 has shown that the solvent is not limited to water and using alcohol also improves the relative emission intensity.

[0211] In each of Examples 30 to 35, the amount of β-sialon fluorescent material in the second raw material mixture is 1 / 2 of the amount in Example 1, and the average particle size is larger than the average particle size in Example 1. In some of Examples 30 to 35, the relative emission intensity is approximately twice the relative emission intensity in Example 1. Generally, it is believed that the emission intensity becomes higher as the particles become larger. However, during the growth process of the particles into larger particles, it is believed that the possibility of amorphous occurrence becomes higher. These facts indicate that the effect of alkali treatment that brings higher emission intensity is particularly significant in β-sialon fluorescent materials that have a higher possibility of amorphous occurrence due to a larger average particle size.

[0212] The β-sialon fluorescent material obtained by the preparation method according to the above embodiment can be suitably used in applications such as: lighting light sources with excellent emission characteristics, particularly using blue light-emitting diodes or ultraviolet light-emitting diodes as excitation light sources, LED displays, backlight sources, traffic lights, lighting switches, various sensors and various indicators.

[0213] From the above, it should be apparent that many other embodiments are possible without departing from the spirit and scope of the invention. Therefore, the scope and spirit of the present invention should be limited only by the following claims.

[0214] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0215] While the present disclosure has been described with reference to several exemplary embodiments, it is to be understood that the words which have been used are words of description and illustration, rather than words of limitation. Changes may be made, within the scope of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present disclosure. While the present disclosure has been described with reference to specific examples, means, and embodiments, the present disclosure is not intended to be limited to the details disclosed; rather, the present disclosure extends to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims.

[0216] For convenience only and without intending to actively limit the present application to any specific disclosure or inventive concept, one or more embodiments or implementations of the present disclosure may be referred to herein individually or collectively as the term "disclosure". In addition, although specific embodiments and implementations have been illustrated and described herein, it should be understood that any subsequent arrangements designed to achieve the same or similar purposes may replace the specific embodiments or implementations shown. The present disclosure may be intended to cover any and all subsequent adaptations or variations of the various embodiments and implementations. Combinations of the above-described embodiments and implementations, as well as other embodiments and implementations not specifically described herein, will be apparent to those skilled in the art upon reading this specification.

[0217] Additionally, in the foregoing detailed description, various features may be grouped together or described in a single embodiment to simplify the disclosure. This disclosure should not be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to fewer than all features of any disclosed embodiment. The following claims are therefore incorporated into the detailed description, with each claim independently and separately defining the claimed subject matter.

[0218] The subject matter disclosed above is to be considered illustrative and not restrictive, and the appended claims are intended to cover all such changes, modifications, and other embodiments that fall within the true spirit and scope of the disclosure. Therefore, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

1. A method for preparing a β-sialon fluorescent material, the method comprising: Providing a silicon nitride-containing composition in which aluminum, oxygen atoms and europium are solid-dissolved, heat-treating the composition in the presence of a europium compound, contacting the heat-treated composition with an alkaline substance, wherein contacting the heat-treated composition with the alkaline substance comprises contacting at a first temperature and contacting at a second temperature higher than the first temperature; wherein the first temperature is not lower than 50°C and not higher than 150°C, and the second temperature is not lower than 90°C and not higher than 650°C; and The weight ratio of the alkaline substance in contact with the heat-treated composition relative to the heat-treated composition is not less than 5% by weight and not more than 80% by weight.

2. The method according to claim 1, wherein the alkaline substance comprises at least one selected from the group consisting of LiOH, NaOH, KOH, RbOH, CsOH, and NH3.

3. The method according to any one of claims 1 to 2, wherein contacting the heat-treated composition with the alkaline substance comprises mixing the heat-treated composition with a solution of the alkaline substance and removing at least a portion of the solvent present in the solution.

4. The method according to any one of claims 1 to 2, wherein the method further comprises washing the composition that has been contacted with the alkaline substance with a liquid medium. 5 . The method according to claim 1 , wherein the heat-treating the composition is performed under the condition that the weight ratio of the europium compound to the composition is not less than 0.01 wt % and not more than 50 wt %.

6. The method according to any one of claims 1 to 2, wherein the heat treatment of the composition is performed at a temperature of not less than 1300°C and not more than 1600°C.

7. The method according to any one of claims 1 to 2, wherein the heat treatment of the composition is performed in a rare gas atmosphere.

8. The method according to any one of claims 1 to 2, wherein providing the composition comprises heat treating a mixture comprising an aluminum compound, a europium compound, and silicon nitride. 9 . The method according to claim 1 , wherein the method further comprises heat-treating the provided composition in a nitrogen atmosphere before heat-treating the composition.

10. The method according to any one of claims 1 to 2, wherein the composition has a composition represented by the following formula: Si 6-z Al z O z N 8-z :Eu, where z satisfies 0 < z ≦ 4.2.

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