Phosphor powder, light emitting device, image display device, and lighting device

Abstract

The phosphor powder of the present invention comprises phosphor particles, which are represented by the general formula Mx(Si,Al)2(N,O)3±y, wherein M is Li and one or more alkaline earth metal elements, with a molecular weight of 0.52≦x≦0.9 and 0.06≦y≦0.36, and a portion of M is replaced by Ce. The phosphor particles have a Si / Al atomic ratio of 1.5 to 6 and an O / N atomic ratio of 0 to 0.1. 5 to 50 mol% of M is Li and 0.5 to 10 mol% of M is Ce. The total content of Cr, Fe and Ni elements in the phosphor powder is less than 20 ppm.

Description

Technical Field

[0001] This invention relates to a phosphor powder, a light-emitting device, an image display device, and a lighting device. Prior Technology

[0002] To manufacture white LEDs (Light Emitting Diodes), phosphors are typically used. That is, phosphors are used as wavelength conversion materials to convert the blue light emitted by a blue LED into white light. With the increasing prevalence of white LEDs in lighting applications and the exploration of their suitability for image display devices, the development of phosphors that can convert blue light into longer wavelengths continues.

[0003] As an improvement to phosphors, one approach is to modify the chemical composition of the phosphor. For example, Patent Document 1 describes a phosphor represented by the general formula Mx(Si,Al)2(N,O)3±y (where M is Li and one or more alkaline earth metal elements, and 0.52≦x≦0.9, 0.06≦y≦0.23), in which a portion of M is replaced by Ce, and the Si / Al atomic ratio is 1.5 to 6 or less, the O / N atomic ratio is 0 to 0.1 or less, 5 to 50 mol% of M is Li, and 0.5 to 10 mol% of M is Ce. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent No. 5969391 Summary of the Invention

[0005] In view of this specification, the phosphor described in Patent Document 1 has room for improvement in the point of peak fluorescence intensity when the phosphor is irradiated with blue light.

[0006] The inventor's objective is to provide a phosphor powder with a high peak fluorescence intensity when irradiated with blue light, and this exploration is conducted accordingly. [Solution to the Problem]

[0007] The inventors conducted a review and completed the invention described below.

[0008] According to the present invention, a phosphor powder is provided, comprising phosphor particles, wherein the phosphor particles are phosphors represented by the general formula Mx(Si,Al)2(N,O)3±y (wherein M is Li and one or more alkaline earth metal elements, and 0.52≦x≦0.9, 0.06≦y≦0.36), and a portion of M is replaced by Ce element, wherein the Si / Al atomic ratio of the phosphor particles is 1.5 or more to 6 or less, and the O / N atomic ratio is 0 or more to 0.1 or less, wherein 5 to 50 mol% of M is Li, and 0.5 to 10 mol% of M is Ce; the total content of Cr, Fe and Ni elements in the phosphor powder is 20 ppm or less.

[0009] Furthermore, according to the present invention, a light-emitting device is provided, comprising: the above-mentioned phosphor powder; and a light-emitting light source.

[0010] Furthermore, according to the present invention, an image display device is provided, comprising: the above-described light-emitting device.

[0011] Furthermore, according to the present invention, a lighting device is provided, comprising the aforementioned light-emitting device. [Effects of the Invention]

[0012] The phosphor powder of the present invention can provide a phosphor powder with a high fluorescence peak intensity when the phosphor is irradiated with blue light. Simple Explanation of the Diagram

[0013] [Figure 1] A schematic cross-sectional view showing an example of the structure of the light-emitting device. [Figure 2] An XRD pattern of the phosphor of Example 1 obtained by measuring it with powder X-ray diffraction (XRD). Implementation

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the diagram, the same symbols are added to the same constituent elements, while the explanations are omitted appropriately. The illustrations are for illustrative purposes only. The shapes or dimensions of the components in the illustrations do not necessarily correspond to actual objects.

[0015] In this specification, unless otherwise specified, the notation "X~Y" in the description of numerical ranges means from X to Y. For example, "1~5% by mass" means "more than 1% by mass and less than 5% by mass".

[0016] <Fluorescent Powder> The phosphor powder of this embodiment contains phosphor particles represented by the general formula Mx(Si,Al)₂(N,O)₃±y. In this formula, M is Li and one or more alkaline earth metal elements, and 0.52≦x≦0.9 and 0.06≦y≦0.36. Furthermore, a portion of M is replaced by Ce, and the Si / Al atomic ratio is 1.5 to 6 or more, the O / N atomic ratio is 0 to 0.1 or more, 5 to 50 mol% of M is Li, and 0.5 to 10 mol% of M is Ce. The total content of Cr, Fe and Ni elements in the phosphor powder is less than 20 ppm.

[0017] According to the inventors' understanding, it is known that the fluorescence properties of a fluorite can be evaluated by using the content of a plurality of elements contained in trace amounts in the fluorite powder as an indicator. Based on this understanding, it has been found that the fluorescence properties can be stably evaluated by using the total content of Cr, Fe, and Ni elements as an indicator, and by setting the total content of the indicator to below the aforementioned upper limit, a fluorite powder with a high fluorescence peak intensity when irradiated with blue light can be obtained.

[0018] The total content of Cr, Fe, and Ni elements is limited to 20 ppm or less, preferably 15 ppm or less, and even more preferably 10 ppm or less. This enables the production of phosphor powders with high fluorescence peak intensity when irradiated with blue light. The lower limit of the above total is not specifically limited and can be above 0 ppm or above 0.01 ppm.

[0019] The maximum content of Cr is below 10 ppm, preferably below 5 ppm, and even more preferably below 3 ppm. This enables the production of phosphor powders with high internal quantum efficiency and improved blue light conversion efficiency. There is no specific limit to the lower limit of the Cr element content mentioned above; it can be above 0 ppm or above 0.01 ppm.

[0020] The upper limit of the Fe element content is below 20 ppm, preferably below 15 ppm, and even more preferably below 10 ppm. This enables the production of phosphor powders with high internal quantum efficiency and improved blue light conversion efficiency. There is no specific limit to the lower limit of the Fe element content mentioned above; it can be above 0 ppm or above 0.01 ppm.

[0021] The upper limit of the Ni element content is below 10 ppm, preferably below 5 ppm, and even more preferably below 3 ppm. This enables the production of phosphor powders with high internal quantum efficiency and improved blue light conversion efficiency. There is no particular limit to the lower limit of the Ni content mentioned above; it can be above 0 ppm or above 0.01 ppm.

[0022] The upper limit of the Ti element content is below 10 ppm, preferably below 5 ppm, and even more preferably below 3 ppm. This enables the production of phosphor powders with high internal quantum efficiency and improved blue light conversion efficiency. There is no specific limit to the lower limit of the Ti element content mentioned above; it can be above 0 ppm or above 0.01 ppm.

[0023] Regarding the elements Cr, Fe, Ni, and Ti, the phosphor powder is dissolved by a mixture of hydrofluoric acid and nitric acid using a pressurized acid decomposition method, and then determined by an ICP-based luminescence spectrophotometer. The term "0 ppm" refers to the detection limit of the measuring device.

[0024] In this embodiment, the phosphor powder with the desired content of Cr, Fe, Ni, and Ti can be manufactured not only by using suitable materials but also by selecting appropriate manufacturing methods and conditions. "Appropriate manufacturing methods and conditions" include, for example, one or more of the following: (i) applying appropriate classification treatment (preferably sedimentation classification) to the phosphor powder, and (ii) acid treatment. Details regarding the manufacturing methods and conditions will be described later.

[0025] The description of the phosphor powder in this embodiment will continue.

[0026] (Crystal structure, chemical composition, etc.) The crystalline framework of fluorescein is constructed through (Si,Al)-(N,O)₄ tetrahedral bonds, with nitrogen (M) elements located in the interstices. The above general formula maintains a wide range of electroneutrality by considering the overall parameters of the valence and amount of M, the Si / Al ratio, and the N / O ratio. A representative fluorescein represented by this formula is CaAlSiN₃, where M is Ca, x=1, and thus Si / Al=1 and O / N=0. When a portion of the Ca in CaAlSiN₃ is replaced by Eu, it becomes a red fluorescein; when replaced by Ce, it becomes a yellow to orange fluorescein.

[0027] The crystalline structure of the phosphor particles contained in the phosphor powder of this embodiment is typically based on CaAlSiN3 crystals. A characteristic of these phosphor particles is that they can be significantly altered in terms of constituent elements and composition to achieve very high luminescence efficiency even when Ce is activated. In the above general formula, element M is a combination of Li and alkaline earth metals, with a portion of it replaced by Ce, which serves as the luminescence center. By using Li and combining divalent alkaline earth elements with trivalent Ce, the average valence of element M can be broadly controlled. Furthermore, the ionic radius of Li+ is very small, and its quantity can be used to create large variations in crystal size, thus obtaining diverse forms of fluorescence. In the above general formula, the coefficient x of element M is 0.52 or higher to 0.9 or lower, preferably 0.6 or higher to 0.9 or lower, and even more preferably 0.7 or higher to 0.9 or lower. If the coefficient x exceeds 0.9, that is, if it is close to CaAlSiN3 crystallization, there is a tendency to decrease the fluorescence intensity. If the coefficient x is less than 0.52, there is a tendency to significantly decrease the fluorescence intensity because different phases other than the target crystalline phase will be generated in large quantities.

[0028] In this embodiment, when charge neutrality is maintained by the average valence or amount of element M, the Si / Al ratio, and the O / N ratio, and there are no defects in the single crystal, y = 0. However, considering the overall composition of the phosphor, a second crystalline phase or an amorphous phase may exist, or, considering the crystal itself, charge balance may be disrupted due to crystal defects. In this embodiment, in terms of improving fluorescence intensity, y is preferably 0.06 or more to 0.36 or less, more preferably 0.1 or more to 0.35 or less, and particularly preferably 0.06 or more to 0.23 or less.

[0029] In this embodiment, the O / N atomic ratio (molar ratio) is 0 or more to 0.1 or less, more preferably 0.01 or more to 0.08 or less, and particularly preferably 0.02 or more to 0.07 or less. If the O / N atomic ratio is too large, the amount of different phases formed will increase, which will reduce the luminous efficiency and decrease the covalentity of the crystals, and tend to cause a deterioration in temperature characteristics (a decrease in luminance at high temperatures).

[0030] The Si / Al atomic ratio (molar ratio) is usually determined by setting the average valence or amount of element M and the O / N atomic ratio within a specific range. The Si / Al atomic ratio is 1.5 to 6, preferably 2 to 4, and even more preferably 2.5 to 4.

[0031] The Li content in the phosphor particles is 5~50 mol% of the M element, preferably 15~45 mol%, and even more preferably 25~45 mol%. Although the effect of Li is easily exerted above 5 mol%, if it exceeds 50 mol%, the crystalline structure of the target phosphor cannot be maintained and different phases are generated, which easily leads to a decrease in luminescence efficiency. To be on the safe side, it should be clarified beforehand that the term "Li content" refers to the Li content in the final phosphor powder, not the amount of raw material used in the formulation. The Li compounds used in the raw materials have high vapor pressure and are easily volatile; a considerable amount will volatilize when synthesizing nitrides and oxides at high temperatures. In other words, the amount of Li in the raw material formulation will differ significantly from the content in the final product, and therefore does not refer to the Li content in the phosphor itself.

[0032] If the Ce content, which serves as the luminescence center of fluorescein particles, is too low, it tends to reduce the luminescence contribution; if it is too high, it tends to cause concentration extinction of the fluorescein due to energy transfer between Ce³⁺ ions. Therefore, the Ce content is 0.5~10 mol% of M, preferably 0.5~5 mol%.

[0033] The alkaline earth metal element used as element M in the above formula can be any element, but when Ca is used, high fluorescence intensity and stable crystal structure are obtained over a wide compositional range. Therefore, element M is preferably Ca. It can be a combination of multiple alkaline earth metal elements, or, for example, a portion of element Ca can be replaced with element Sr.

[0034] The fluorescent particles have an orthorhombic crystal structure, which can be the same as that of the aforementioned CaAlSiN3 crystal. The lattice constants of CaAlSiN3 crystal, as an example, are a = 0.9800 nm, b = 0.5649 nm, and c = 0.5062 nm. In this embodiment, the lattice constants are typically a = 0.9350~0.9650 nm, b = 0.5500~0.5700 nm, and c = 0.4800~0.5000 nm, all of which are smaller than those of CaAlSiN3 crystal. This range of lattice constants reflects the aforementioned constituent elements and composition.

[0035] The crystalline phase present in the phosphor particles is preferably the aforementioned single-crystal phase. However, the phosphor particles may also contain different phases as long as they do not significantly affect the fluorescence properties. Examples of different phases that have a low impact on fluorescence properties when excited by blue light include: α-type silane (SiAlON, aluminum silicon nitride), AlN, LiSi₂N₃, and LiAlSi₂N₄. The amount of different phases is preferably such that, as evaluated by powder X-ray diffraction, the diffraction intensity of other crystalline phases is less than 40% of the strongest diffraction intensity of the aforementioned crystalline phases.

[0036] The phosphor powder of this embodiment is excited by light with a broad wavelength range from ultraviolet to visible light. For example, when irradiated with blue light at a wavelength of 455 nm, it exhibits a wide range of fluorescence emission, represented by orange light with a peak wavelength of 570-610 nm, indicating a fluorescence spectrum with a full width at half maximum (FWHM) of 125 nm or more. Such phosphor powder is suitable as a phosphor for a wide-range light-emitting device. Furthermore, the phosphor powder of this embodiment, like conventional nitride and oxide nitride phosphors such as CaAlSiN3, exhibits excellent heat resistance and chemical stability, and has the characteristic of minimal decrease in luminance due to temperature increases. Such characteristics make it particularly suitable for applications requiring durability.

[0037] (Particle size distribution) By properly designing the particle size distribution of the phosphor powder in this embodiment, it is possible to further improve quantum efficiency or improve the balance of various properties. Specifically, the volumetric cumulative distribution diameter D50 (i.e., median particle size) of the phosphor powder of this embodiment, as determined by laser diffraction, is preferably 8 μm or more to 25 μm or less, more preferably 10 μm or more to 20 μm or less, and particularly preferably 12 μm or more to 20 μm or less.

[0038] As another perspective, the volumetric cumulative distribution diameter (D10) of the phosphor powder in this embodiment, as measured by laser diffraction, is preferably 2 μm to 15 μm or more, and more preferably 5 μm to 12 μm or less. A larger D10 value indicates a lower amount of microparticles (excessively fine phosphor particles that tend to decrease the conversion efficiency of blue light) in the phosphor powder. Therefore, by making D10 a relatively large value, there is a tendency to further improve the conversion efficiency of blue light.

[0039] As another point of view, the volumetric cumulative distribution diameter (D 90) of the phosphor powder in this embodiment, as measured by laser diffraction, is preferably 15 μm to 50 μm, and more preferably 18 μm to 40 μm. "A small D 90" refers to a low amount of coarse particles in the phosphor powder. Phosphor powder with a small D 90 is effective in reducing chromaticity inhomogeneity in light-emitting devices.

[0040] In other words, generally speaking, the larger the particle size of the powder, the smaller the effect of light scattering, and the lower the diffusion reflectance tends to be. In other words, the particle size and the value of diffusion reflectance are mutually compensating. However, although the preferred particle size (D50, etc.) of the fluorescent powder of this embodiment is relatively large, the diffusion reflectance of the fluorescent powder of this embodiment tends to be relatively large.

[0041] (Manufacturing method) The phosphor powder of this embodiment is preferably manufactured by a series of steps including (1) to (4), a series of steps including (1) to (3) and (5), or a series of steps including (1) to (5). In terms of appropriately adjusting (D 90-D 10) / D 50, the manufacturing steps of the phosphor powder are preferably including the classification step (5) (preferably sedimentation classification). (1) Preparation steps of raw material mixed powder (2) Calcination steps (3) Pulverization steps of calcined materials (4) Acid treatment steps (5) Grading steps (sedimentation grading is preferred)

[0042] The following will explain in detail (1) to (5).

[0043] (1) Preparation steps of raw material mixed powder In the preparation step of raw material mixed powder, appropriate raw material powders are usually mixed to obtain raw material mixed powder. As raw material powders, nitrides of constituent elements are suitable, namely silicon nitride, aluminum nitride, lithium nitride, cerium nitride, and nitrides of alkaline earth elements (such as calcium nitride). Generally, nitride powders are unstable in air, resulting in the particle surface being covered with an oxide layer. Even when using nitride raw materials, a certain degree of oxide content will still be present in the raw material. When controlling the O / N ratio of the phosphor, this situation should be considered, and in cases of oxygen deficiency, a portion of the nitride can be used as an oxide (including compounds that become oxides through heat treatment). Examples of oxides include cerium oxide.

[0044] In the raw material powder, lithium compounds exhibit significant volatilization due to heating, and in some cases, they almost completely volatilize under calcination conditions. Therefore, the optimal amount of lithium compound to be incorporated should be determined by considering the amount of volatilization during the calcination process, corresponding to the calcination conditions.

[0045] Nitride raw material powders, particularly those containing lithium nitride, cerium nitride, and alkaline earth elements, react violently with moisture in the air. Therefore, the processing of these compounds is preferably carried out in a glove box after being purged with an inactive atmosphere. In terms of operational efficiency, it is preferable to (i) first weigh out a specific amount of silicon nitride, aluminum nitride and various oxide raw material powders that can be processed in air, and mix them thoroughly in air beforehand to prepare a premixed powder; (ii) then mix the premixed powder and substances such as lithium nitride that are easily reacted with moisture in the glove work box to prepare a raw material mixed powder.

[0046] (2) Calcination steps In the calcination step, the raw material mixture powder prepared in the preparation step of (1) raw material mixture powder is filled into a suitable container and heated using a calcination furnace or the like.

[0047] In terms of ensuring the reaction proceeds fully and suppressing lithium volatilization, the calcination temperature is preferably 1600~2000℃, more preferably 1700~1900℃. In terms of ensuring the reaction proceeds fully and suppressing lithium volatilization, the calcination time is preferably 2 to 24 hours, and more preferably 4 to 16 hours.

[0048] The calcination process is preferably carried out under a nitrogen atmosphere. Furthermore, it is preferable to appropriately adjust the pressure of the calcination atmosphere. Specifically, the pressure of the calcination atmosphere is preferably 0.5 MPa·G or higher. At calcination temperatures, especially above 1800°C, fluorescein tends to decompose easily, but by using a high pressure calcination atmosphere, the decomposition of the fluorescein can be suppressed. In addition, considering industrial productivity, the pressure of the calcination atmosphere is better not to reach 1 MPa·G.

[0049] The container for filling the raw material mixture is preferably made of a material that is stable under a high-temperature nitrogen atmosphere and does not react with the raw material mixture or its reaction products. The container material is preferably boron nitride.

[0050] (3) Pulverization steps of calcined materials (2) The calcined product obtained is usually in block form, so it is better to crush it into a small size so that mechanical force can be applied. Various devices such as crushers, mortars, ball mills, vibratory mills, jet mills, and pulverizers can be used for pulverization. Two or more of these devices can also be combined for pulverization. In the embodiments described later, a pulverizer is first used to obtain coarsely pulverized material from the calcined material, and then the coarsely pulverized material is further pulverized using a jet mill. By appropriately controlling the pulverization conditions, one or more of D10, D50, D90, and (D90-D10) / D50 can be adjusted.

[0051] (4) Acid treatment steps In the acid treatment step, for example, the pulverized material obtained in (3) above is soaked in an acidic aqueous solution. Although the details are not yet clear, it can be considered that the acid treatment is used to remove or reduce the "different phases" of the phosphor that do not contribute to luminescence or reduce luminescence efficiency.

[0052] Examples of acidic aqueous solutions include an acidic aqueous solution containing one acid selected from hydrofluoric acid, nitric acid, hydrochloric acid, etc., or a mixed acid aqueous solution obtained by mixing two or more of the above-mentioned acids. Nitric acid or hydrochloric acid is preferred as the acid, and hydrochloric acid is more preferred. The concentration of the acidic aqueous solution can be appropriately set according to the strength of the acid used, for example, 0.5~50% by mass, preferably 1~30% by mass, and even more preferably 1~10% by mass. The preferred temperature for acid treatment is between 25°C and 90°C, and more preferably between 60°C and 90°C. Treatment at higher temperatures facilitates the removal of different phases. The acid treatment time (soaking time) is preferably between 15 minutes and 80 minutes, and more preferably between 15 minutes and 60 minutes. After acid treatment, it is preferable to thoroughly wash the phosphor powder with water and then dry it.

[0053] (5) Grading steps To reduce the amount of microparticles (excessively fine phosphor particles that tend to reduce the conversion efficiency of blue light) in the powder, appropriate classification is preferable. For effective removal of microparticles, sedimentation classification as described below is preferred.

[0054] First, the powder obtained in the pulverization step of (3) calcination or the powder after the acid treatment step of (4) is dispersed in a suitable liquid (e.g., an aqueous solution of sodium hexametaphosphate) in a container to form a dispersion. Next, the dispersion was allowed to stand for a fixed time, allowing the larger particles in the powder within the dispersion to precipitate. Then, the clear liquid is drained. Then, fresh sodium hexametaphosphate aqueous solution is added to the container containing the remaining precipitate to disperse the powder. The mixture is then allowed to stand, and the clear liquid is drained. This process is repeated several times. "Several times" preferably refers to five or more times. There is no specific upper limit to the number of times, but in terms of cost, it is, for example, less than 15 times, specifically less than 10 times.

[0055] While the specific conditions for classification are only estimates, it is preferable to set the classification conditions to remove microparticles with a diameter of 10 μm or less, and even more preferably to remove microparticles with a diameter of 7.5 μm or less. For information on sedimentation classification and condition settings, refer to the Stokes equations related to particle settling velocity. For an example of the specific conditions for settlement classification, please refer to the following implementation example.

[0056] <Light-emitting devices, image display devices and lighting devices> By combining the phosphor powder of this embodiment with a light source, a light-emitting device can be obtained. Typically, the light source emits ultraviolet or visible light. For example, in the case of a blue LED as the light source, the blue light emitted by the light source shines on the phosphor powder, and then the blue light is converted into longer wavelength light. That is, the phosphor powder of this embodiment can be used as a wavelength conversion material to convert blue light into longer wavelength light.

[0057] Referring to Figure 1, one example of the specific structure of the light-emitting device will be described. Figure 1 is a schematic cross-sectional view showing an example of the structure of a light-emitting device. As shown in Figure 1, the light-emitting device 100 includes a light-emitting element 120, a heat sink 130, a housing 140, a first lead frame 150, a second lead frame 160, a connecting wire 170, a connecting wire 172, and a composite 40.

[0058] The light-emitting element 120 is mounted on a specific area of ​​the heat sink 130. By mounting the light-emitting element 120 on the heat sink 130, the heat dissipation performance of the light-emitting element 120 can be improved. Alternatively, a packaging substrate can be used instead of the heat sink 130.

[0059] The light-emitting element 120 is a semiconductor element that emits excitation light. For example, an LED chip that produces light with wavelengths between 300 nm and 500 nm, corresponding to near-ultraviolet to blue light, can be used as the light-emitting element 120. An electrode (not shown) disposed on one side of the upper surface of the light-emitting element 120 is connected to the surface of the first lead frame 150 via bonding wires 170 such as gold wires. Furthermore, an electrode (not shown) formed on the other side of the upper surface of the light-emitting element 120 is connected to the surface of the second lead frame 160 via bonding wires 172 such as gold wires.

[0060] The housing 140 has a slightly funnel-shaped recess with an aperture that gradually widens from the bottom surface upwards. The light-emitting element 120 is disposed on the bottom surface of the recess. The wall surface of the recess surrounding the light-emitting element 120 serves as a reflector.

[0061] The composite 40 is filled in the aforementioned recess with walls formed by the housing 140. The composite 40 is a wavelength conversion component that converts the excitation light emitted by the self-emitting element 120 into light with a longer wavelength. The composite 40 disperses at least the phosphor powder of this embodiment in the sealant 30, such as a resin. To obtain a higher quality white light, the sealant 30 may contain not only the phosphor powder of this embodiment but also other phosphor powders. The light-emitting device 100 emits a mixture of light from the light-emitting element 120 and light emitted by the phosphor particles 1 excited by absorbing the light emitted by the light-emitting element 120. Preferably, the light-emitting device 100 emits white light by mixing the light from the light-emitting element 120 and the light generated by the phosphor particles 1.

[0062] In addition, Figure 1 shows an example of a surface-mount type light-emitting device, but the light-emitting device is not limited to the surface-mount type, and can also be a bullet type, COB (Chip-to-Block) type, or CSP (Chip-Scale Package) type.

[0063] As a light-emitting device, it can be used in image display devices such as displays, or in lighting devices. For example, the light-emitting device 100 can be used as a backlight to manufacture a liquid crystal display. Furthermore, by using one or more light-emitting devices 100 and applying appropriate wiring, a lighting device can also be manufactured.

[0064] While the embodiments of the present invention have been described above, these are merely examples, and various other configurations may be employed. Furthermore, the present invention is not limited to the above embodiments; modifications and improvements within the scope of achieving the objectives of the present invention are also covered by the present invention. [Example]

[0065] The embodiments of the present invention will be described in detail based on examples and comparative examples. It should be noted beforehand that the present invention is not limited to the embodiments.

[0066] <Manufacturing of Fluorescent Powder> (Example 1) (1) Preparation of raw material mixed powder First, a preliminary mixing process is performed. Specifically, Si3N4, AlN, and CeO2 are mixed for 30 minutes using a small V-type mixer (dry mixing) from the raw materials listed in Table 1, and then sieved through a nylon sieve with a mesh size of 150 μm. This yields a pre-mixed powder. Next, in a nitrogen-atmospheric working chamber, the remaining raw materials (Ca3N2 and Li3N) listed in Table 1 were added to the pre-mixed powder for thorough dry mixing. Afterward, the mixture was sieved through a 500μm mesh sieve to obtain the raw material mixed powder.

[0067] (2) Calcination The raw material mixture was filled into a container made of boron nitride. The container was placed in a furnace, and the raw material mixture was calcined at 1800°C for 8 hours under a N2 atmosphere of 0.72 MPa·G.

[0068] (3) Crushing of calcined materials The calcined material obtained in (2) was pulverized using a crusher. The pulverization was repeated until the passing rate of a vibrating screen with a mesh size of 250 μm exceeded 90%. The calcined material, which had been pulverized using a pulverizer, was further pulverized using a jet mill (Nippon Pneumatic Kogyo PJM-80SP). The pulverization conditions were set as follows: sample feed rate: 50 g / min, pulverization air pressure: 0.3 MPa.

[0069] (4) Acid treatment The pulverized calcined material is then placed in hydrochloric acid for acid treatment. Specifically, first, prepare a hydrochloric acid aqueous solution by mixing 35-37% hydrochloric acid and distilled water in a volume ratio of 50 mL: 300 mL and heating it to 80°C. Add the calcined material crushed in (3) to the hydrochloric acid aqueous solution and stir for 0.5 hours for acid treatment. The acid-treated calcined material was thoroughly washed with distilled water and then dried at 110°C for 3 hours. It was then passed through a 45μm sieve to remove large / agglomerated particles.

[0070] (5) Removal of fine powder using sedimentation classification First, prepare a 0.05% (w / w) sodium hexametaphosphate aqueous solution. Then, pour the aqueous solution into a container with an inner diameter of 70 mm and a height of 120 mm until the height reaches 110 mm. Next, the acid-treated calcined material was added to the container containing the above aqueous solution and stirred thoroughly to disperse it. It was then allowed to stand for 22 minutes. After standing, 90 mm of the clear liquid was drained from the top. Then, sodium hexametaphosphate aqueous solution was poured in until a height of 110 mm, and the powder was dispersed again by stirring. This process was repeated 7 times to remove the fine powder contained in the acid-treated powder (the fractionation point is 7.5 μm based on Stokes' equation). Next, the slurry at the bottom of the container is washed with water and filtered to recover the solid components. It is then dried at 110°C for 3 hours and passed through a 45μm sieve to break up the aggregated particles. Fluorescent powder is obtained through the above methods.

[0071] (Example 2) Except for the absence of sedimentation classification, phosphor powder was obtained in the same manner as in Example 1.

[0072] (Comparative Example 1) Except that (a) the substances listed in Table 1 were used as raw materials, (b) no acid treatment was performed, and (c) no sedimentation classification was performed, the phosphor powder was obtained in the same manner as in Example 1.

[0073] <Confirmation of Chemical Composition / Crystal Structure> The composition of a portion of the fluorescent powder is analyzed as follows. The amounts of Ca, Li, Ce, Si, and Al were determined by dissolving the phosphor powder using an alkaline fusion method and then measuring it using an ICP-based luminescence spectrophotometer (CIROS-120 manufactured by Rigaku Corporation). The amounts of O and N were measured using a nitrogen and oxygen analyzer (EMGA-920 manufactured by HORIBA). Based on the measurement results, the x, y, Si / Al atomic ratio, O / N atomic ratio, Li ratio of M, and Ce ratio of M in the general formula Mx(Si,Al)2(N,O)3±y were determined. Furthermore, regarding Cr, Fe, Ni, and Ti elements, the phosphor powder was dissolved by a pressure acid decomposition method using a mixture of hydrofluoric acid and nitric acid, and then measured using an ICP-based luminescence spectrophotometer.

[0074] For the phosphor of Example 1, powder X-ray diffraction (XRD) measurements were also performed using an X-ray diffraction apparatus (Ultima IV-N manufactured by Rigaku Co., Ltd.) with a Cu-Kα line source. The obtained XRD pattern is shown in Figure 2. From the analysis of the obtained XRD pattern, it was confirmed that the crystal with lattice constants a=0.9486nm, b=0.5586nm, and c=0.4933nm in the orthorhombic system is the main phase, and a small amount of LiAlSi₂N₄ exists as a different phase.

[0075] <Determination of Particle Size Distribution> Particle size distribution was determined using an LS13 320 (manufactured by Beckman Coulter, Inc.) by laser diffraction scattering according to JIS R 1629:1997. Water was used as the solvent. In the specific sequence, firstly, a small amount of fluorescent powder was added to an aqueous solution containing 0.05% by mass of sodium hexametaphosphate as a dispersant. Next, a dispersion was prepared by dispersing the powder using a probe-type ultrasonic homogenizer (300W output, 26mm probe diameter). The particle size distribution was then measured using this dispersion. From the obtained cumulative volumetric frequency distribution curve, the 10% volumetric diameter (D10), 50% volumetric diameter (D50), and 90% volumetric diameter (D90) were determined.

[0076] <Evaluation> (Peak fluorescence intensity) The fluorescence spectrum of the phosphor powder was measured using a fluorescence spectrophotometer (Hitachi High-Tech Science F-7000) calibrated with rose red B and a secondary standard light source. Specifically, the phosphor powder was excited with monochromatic light at a wavelength of 455 nm, and the spectrum of the emitted fluorescence was measured to determine the peak fluorescence intensity and peak fluorescence wavelength. The peak fluorescence intensity varies depending on the measuring device or conditions. The peak fluorescence intensity listed in the table below is the value when the peak fluorescence intensity of the standard sample (YAG, more specifically P46Y3 manufactured by Mitsubishi Chemical Co., Ltd.) is set to 100.

[0077] (Internal quantum efficiency and external quantum efficiency) Using a spectrophotometer (MCPD-7000 manufactured by Otsuka Electronics Co., Ltd.), the internal and external quantum efficiencies of each phosphor powder were determined in the following order. (1) Fluorescent powder is filled into the recessed portion of a concave groove with a smooth surface. This concave groove is installed at a specific position (sample section) inside an integrating sphere. Monochromatic light with a wavelength of 455 nm is dispersed from a self-emissive light source (Xe lamp) and guided to the integrating sphere using an optical fiber. This monochromatic light (excitation light) is irradiated onto the fluorescent powder filled into the recessed portion of the concave groove, and the fluorescence spectrum is measured. The peak wavelength is determined from the obtained spectral data, and the excitation-reflected photon number (Qref) and the fluorescence photon number (Qem) are calculated. The excitation-reflected photon number is calculated in the wavelength range of 450 nm to 465 nm, while the fluorescence photon number is calculated in the range of 465 nm to 800 nm. (2) In addition, instead of the concave groove, a standard reflector plate (Spectralon manufactured by Labsphere) with a reflectivity of 99% was installed on the sample section, and the spectrum of the excitation light with a wavelength of 455 nm was measured. Then, the number of excitation photons (Qex) was calculated from the spectrum in the wavelength range from 450 nm to 465 nm. (3) The internal quantum efficiency and external quantum efficiency are calculated based on the following formulas from Qref, Qem and Qex obtained from (1) and (2) above. Internal quantum efficiency = (Qem / (Qex-Qref)) × 100 External quantum efficiency = (Qem / Qex) × 100

[0078] The various intelligence reports are compiled and presented in Table 1. In Table 1, "ND" is short for Not Detected.

[0079] Furthermore, the raw materials listed in the "Raw Materials Used" column of Table 1 are as follows.

[0080] Ca 3N 2-1: Ca 3N 2 manufactured by Taiheiyo Cement. Ca3N2-2: Ca3N2 manufactured by CERAC (now Materion).

[0081] Li 3N-1: Li 3N manufactured by Materion Li 3N-2: Li 3N manufactured by CERAC (now Materion).

[0082] CeO 2-1: CeO 2, C category manufactured by Shin-Etsu Chemical Co., Ltd.

[0083] Si 3N 4-1: Si3N4, E10 category manufactured by Ube Industries, Ltd.

[0084] AlN-1: AlN, E class manufactured by Tokuyama Corporation.

[0085] [Table 1] Examples / Comparative Examples Example 1 Example 2 Comparative Example 1 raw material (quality%) Ca 3N 2 19.528 19.528 19.528 Li 3N 3.900 3.900 3.900 CeO 2 3.345 3.345 3.345 Si 3N 4 55.437 55.437 55.437 AlN 17.791 17.791 17.791 Raw materials used Ca 3N 2 Ca 3N 2-1 Ca 3N 2-1 Ca 3N 2-2 Li 3N Li 3N-1 Li 3N-1 Li 3N-2 CeO 2 CeO 2-1 CeO 2-1 CeO 2-1 Si 3N 4 Si 3N 4-1 Si 3N 4-1 Si 3N 4-1 AlN AlN-1 AlN-1 AlN-1 Chemical composition x 0.78 0.76 0.84 y 0.33 0.34 0.34 Si / Al 2.49 2.46 2.72 O / N 0.04 0.05 0.05 Li / M (mol%) 32.39 30.43 40.45 Ce / M (mol%) 2.87 3.02 2.73 impurities (ppm) Cr ND ND 3.1 Fe 6.6 7.3 17.4 Ni ND ND Undetermined Cr+Fe+Ni 6.6 7.3 >20.5 Ti ND ND Undetermined Particle size distribution D 10(μm) 9.9 6.0 6.4 D 50(μm) 16.2 14.7 13.9 D 90(μm) 25.0 24.5 23.0 Fluorescence peak wavelength (nm) 595.8 600.3 595.3 Regarding the method of preparation Hydrochloric acid treatment Settlement classification Hydrochloric acid treatment No Settlement Classification Hydrochloric acid-free treatment No Settlement Classification Relative peak fluorescence intensity (455nm, P46Y3 ratio) 126.3 118.6 100.9 Internal quantum efficiency 80.9% 80.0% 71.9% External quantum efficiency 70.9% 65.8% 62.6%

[0086] The phosphor powder systems of Examples 1 and 2 showed that the total content of Cr+Fe+Ni was lower than that of Comparative Example 1, and that they had good fluorescence peak intensity, internal quantum efficiency and external quantum efficiency.

[0087] This application asserts priority based on Japanese Patent Application No. 2020-202770, filed on December 7, 2020, and all its disclosures are incorporated herein by reference.

[0088] 1: Fluorescent particles 30: Sealing material 40: Complex 100: Light-emitting device 120: Light-emitting element 130: Heat dissipation section 140: Casing 150: First conductor frame 160: Second conductor frame 170: Connecting wires 172: Connecting wires

Claims

1. A phosphor powder comprising phosphor particles, wherein the phosphor particles are represented by the general formula Mx(Si,Al)2(N,O)3±y, wherein, M is Li and one or more alkaline earth metal elements, with a chromaticity of 0.52≦x≦0.9 and 0.06≦y≦0.

36. The phosphor is a phosphor in which a portion of M is replaced by Ce, and the Si / Al atomic ratio of the phosphor particles is 1.5 to 6 and the O / N atomic ratio is 0 to 0.

1. 5 to 50 mol% of M is Li and 0.5 to 10 mol% of M is Ce. The total content of Cr, Fe and Ni elements in the phosphor powder is 0.01 ppm to 10 ppm. The Cr content in the phosphor powder is 3 ppm or less. D10 is 2 μm to 15 μm and D90 is 15 μm to 50 μm.

2. The fluorescent powder as described in claim 1, wherein, The Ti element content in this phosphor powder is less than 5 ppm.

3. A light-emitting device comprising: a phosphor powder as described in claim 1 or 2; and a light-emitting source.

4. The light-emitting device as described in claim 3, wherein, The light source emits ultraviolet or visible light.

5. An image display device comprising: a light-emitting device as described in claim 3 or 4.

6. A lighting device comprising: a light-emitting device as described in claim 3 or 4.

Images