JP7766176B2 - Phosphor powder, method for manufacturing phosphor powder, and light-emitting device - Google Patents

Description

The present disclosure relates to phosphor powder, a method for manufacturing phosphor powder, and a light-emitting device.

Light-emitting devices containing light-emitting elements such as light-emitting diodes are used in general lighting, backlights for liquid crystal displays, LED displays, and other applications. LED displays use light-emitting elements that contain, for example, a light-emitting element that emits blue light and a wavelength converter that absorbs the primary light from the light-emitting element and emits light of a different wavelength. Various types of phosphors, such as red and green phosphors, are used as wavelength converters.

CASN-based phosphors such as CASN phosphors and SCASN phosphors are known as red phosphors (see, for example, Patent Document 1). These CASN-based phosphors are generally synthesized by heating raw material powders containing europium oxide or europium nitride, calcium nitride, silicon nitride, and aluminum nitride.

International Publication No. 2005/052087

To achieve high color reproducibility in LED displays, it is important to use green and red phosphors that have emission peak wavelengths in their respective wavelength ranges and that exhibit sufficient emission intensity. In cases such as micro-LED displays, where a cured resin layer filled with green or red phosphor is placed on a blue LED and multicoloring is achieved through wavelength conversion using blue primary light as excitation light, it is necessary to achieve a wide color gamut for the cured resin layer.

With red phosphors, as the phosphor's emission spectrum shifts to the longer wavelength range and the reddish color deepens, the overlap with the human luminosity curve decreases, resulting in a tendency for brightness to be insufficient. In other words, with red phosphors, it is difficult to achieve both a reddish color to improve the color rendering properties of light-emitting devices that use them and brightness.

The present disclosure aims to provide a phosphor powder capable of emitting fluorescence with a sufficient reddish hue while exhibiting excellent brightness, and a method for manufacturing the same. The present disclosure also aims to provide a light-emitting device that uses the above-mentioned phosphor powder and exhibits excellent color rendering properties.

One aspect of the present disclosure provides a phosphor powder including phosphor particles whose main crystalline phase has the same crystal structure as CaAlSiN ₃ and is represented by the general formula: (Sr _1-xy , Ca _x , Eu _y )AlSi(N,O) ₃ [in the general formula, x and y satisfy 0.0100≦x≦0.0300 and 0.0500≦y≦0.0900].

The phosphor powder contains phosphor particles whose main crystal structure is the same as _CaAlSiN3 , and therefore can function as a red phosphor. Furthermore, the phosphor powder has an elemental ratio of strontium (Sr), calcium (Ca), and europium (Eu) within the above-mentioned predetermined range, enabling it to emit fluorescence with a sufficient reddish tinge while exhibiting excellent brightness. While the reason for this effect is unclear, the inventors speculate as follows: First, in a SCASN phosphor, as the calcium content in the composition formula decreases (i.e., as the proportion of calcium sites in the crystal lattice replaced by other elements increases), the half-width of the emission spectrum narrows and brightness improves, but the emission peak wavelength tends to shift to shorter wavelengths and the reddish tinge of the fluorescence tends to decrease. On the other hand, as the europium content in the composition formula of a SCASN phosphor increases, concentration quenching occurs due to the increase in europium, and although the luminous efficiency decreases, the emission peak wavelength tends to shift to longer wavelengths. Strontium, calcium, and europium are elements that share the same site in the crystal lattice, and in the above phosphor powder, the proportions of strontium, calcium, and europium in the composition formula are specific and satisfy the above-mentioned ranges of x and y. This is presumably to improve the luminance and adjust the wavelength position, thereby increasing the overlap with the human visual sensitivity curve, while keeping the emission peak position in a sufficiently reddish wavelength range and improving the luminous intensity.

The above phosphor powder may have an emission peak wavelength of 635 nm or longer when irradiated with light having a wavelength of 455 nm. Having an emission peak wavelength of 635 nm or longer makes the above phosphor powder more suitable for use as a red phosphor that emits fluorescence with a more reddish hue.

One aspect of the present disclosure provides a light-emitting device comprising a light-emitting element that emits primary light and a wavelength converter that absorbs a portion of the primary light and emits secondary light having a wavelength longer than the wavelength of the primary light, wherein the wavelength converter contains the above-mentioned phosphor powder.

The light-emitting device contains the above-mentioned phosphor powder, and therefore can exhibit excellent color rendering properties. The light-emitting device also contains the above-mentioned phosphor powder, and therefore can be expected to exhibit sufficient brightness.

One aspect of the present disclosure provides a method for producing phosphor powder, comprising: a firing step of heat-treating a mixed powder containing a raw material powder including a strontium source, a calcium source, an aluminum source, a silicon source, a nitrogen source, and a europium source, and a nucleating agent composed of a CASN-based compound, to obtain a fired product; and an annealing step of heat-treating the fired product at a temperature lower than the heat treatment temperature in the firing step to obtain an annealed product, wherein the ratio of the total amount of substance of strontium, calcium, and europium to the amount of substance of aluminum in the raw material powder exceeds 1.0000, and the amount of substance of calcium is 0.0050 or more and the amount of substance of europium is 0.0880 or less, based on the amount of substance of aluminum.

In the above-described phosphor powder manufacturing method, the raw material powder is adjusted so that the ratio of the total amount of strontium, calcium, and europium to the amount of aluminum exceeds 1 and the amounts of calcium and europium are within a predetermined range. Furthermore, firing is performed in the presence of a nucleating agent to form the desired particles, thereby enabling the preparation of phosphor powder represented by the above-described general formula. Conventionally, in the manufacture of CASN-based phosphors, raw materials are typically mixed according to the target composition, and the blending is adjusted so that the ratio of the total amount of strontium, calcium, and europium to the amount of aluminum is 1. For example, increasing the amount of calcium so that the ratio deviates from 1 can result in the formation of heterophases and a decrease in luminous efficiency. In response, it has been discovered that by adjusting the amounts of calcium and europium to fall within a predetermined range, the formation of the heterophases can be suppressed, and the above-described phosphor can be manufactured using the manufacturing method disclosed herein.

The present disclosure provides a phosphor powder capable of emitting fluorescence with a sufficient reddish hue while exhibiting excellent brightness, as well as a method for manufacturing the same. The present disclosure also provides a light-emitting device that uses the above-described phosphor powder and exhibits excellent color rendering properties.

FIG. 1 is a schematic diagram showing the relationship between the luminosity curve and the emission spectrum of a SCASN phosphor.

Embodiments of the present disclosure are described below. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content.

Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of those multiple substances present in the composition, unless otherwise specified.

One embodiment of the phosphor powder includes phosphor particles whose main crystal phase has the same crystal structure as _CaAlSiN3 and is represented by the general formula: (Sr1 _-x-y , _Cax , _Euy )AlSi(N,O) ₃ , where x and y satisfy 0.0100≦x≦0.0300 and 0.0500≦y≦0.0900. In the general formula: (Sr1 _-x-y , _Cax , _Euy )AlSi(N,O) ₃ , the value of x may be, for example, 0.0105 or more, 0.0108 or more, 0.0110 or more, or 0.117 or more, and may be 0.0280 or less, 0.0250 or less, or 0.0240 or less. The value of y may be, for example, 0.0600 or more, 0.0700 or more, or 0.0750 or more, and may be 0.0880 or less, or 0.0850 or less. The phosphor powder is an aggregate of phosphor particles. The phosphor particles may be a CASN phosphor or a SCASN phosphor.

The crystalline structure of phosphor particles can be confirmed by powder X-ray diffraction. Furthermore, the content of strontium (Sr), calcium (Ca), europium (Eu), aluminum (Al), and silicon (Si) in the composition of phosphor particles can be determined by subjecting the object to pressure acid decomposition to prepare a sample solution, and then quantitatively analyzing this using an ICP optical emission spectrometer.

The lower limit of the emission peak wavelength of the phosphor powder may be, for example, 635 nm or more, 636 nm or more, 637 nm or more, more than 637 nm, or 638 nm or more. By having the lower limit of the emission peak wavelength within the above range, the phosphor powder can be more suitably used as a red phosphor that tends to emit a more reddish color. The upper limit of the emission peak wavelength of the phosphor powder may be, for example, 645 nm or less, 642 nm or less, 640 nm or less, less than 640 nm, or 639 nm or less. By having the upper limit of the emission peak wavelength within the above range, the overlap between the emission spectrum of the phosphor powder and the human luminosity curve can be further increased, making it more suitable for use as a red phosphor with excellent brightness. The emission peak wavelength of the phosphor powder may be adjusted within the above range, for example, between 635 and 645 nm.

The half-width at the emission peak wavelength of the phosphor powder is relatively small. The upper limit of the half-width at the emission peak wavelength of the phosphor powder may be, for example, 75.0 nm or less, 74.8 nm or less, 74.6 nm or less, 74.5 nm or less, 74.4 nm or less, less than 74.4 nm, or 74.3 nm or less. Having the upper limit of the half-width within the above range further improves the luminous brightness of the phosphor powder. The lower limit of the half-width at the emission peak wavelength of the phosphor powder may be, for example, 70.0 nm or more, 71.0 nm or more, 72.0 nm or more, 73.0 nm or more, or 73.5 nm or more. Having the lower limit of the half-width within the above range can achieve emission with a more excellent reddish hue. The half-width at the emission peak wavelength of the phosphor powder may be within the above range, for example, 70.0 to 75.0 nm, or 73.5 to 74.3 nm.

In this specification, the emission peak wavelength of a phosphor refers to the value determined by measuring the fluorescence spectrum when irradiated with light having a wavelength of 455 nm. In this specification, the half-width refers to the full width at half maximum (FWHM) and can be determined from the fluorescence spectrum obtained by measuring the fluorescence spectrum when irradiated with light having a wavelength of 455 nm.

The upper limit of the average particle size of the phosphor powder may be, for example, 40.0 μm or less, 30.0 μm or less, or 25.0 μm or less. By setting the upper limit of the average particle size within the above range, it is possible to suppress variations in the chromaticity of the emitted color when the phosphor powder is used on the LED light-emitting surface. The lower limit of the average particle size of the phosphor powder may be, for example, 0.1 μm or more, 0.5 μm or more, or 1.0 μm or more. By setting the lower limit of the average particle size within the above range, it is possible to further suppress decreases in brightness. The average particle size of the phosphor powder may be adjusted within the above range, for example, 0.1 to 40.0 μm, 0.5 to 30.0 μm, or 1.0 to 25.0 μm.

In this specification, the term "average particle size" refers to the particle size (D50, median diameter) at which the cumulative value from the smallest particle size reaches 50% of the total in the volume-based particle size distribution curve measured by laser diffraction/scattering. The particle size distribution curve for phosphor powder is measured in accordance with the particle size distribution measurement method using laser diffraction/scattering described in JIS R 1629:1997, "Method for Measuring Particle Size Distribution of Fine Ceramics Raw Materials by Laser Diffraction/Scattering." A particle size distribution analyzer can be used for measurement. Specifically, 0.1 g of the phosphor powder to be measured is first placed in 100 mL of ion-exchange water, a small amount of sodium hexametaphosphate is added, and the mixture is dispersed using an ultrasonic homogenizer for 3 minutes to obtain a measurement sample. The particle size is measured using a particle size distribution analyzer, and the D50 is determined from the resulting particle size distribution. D50 is also known as the median diameter. The particle size distribution measuring device may be, for example, "Microtrac MT3300EX II" (product name) manufactured by Microtrac Bell Co., Ltd. The ultrasonic homogenizer may be, for example, "Ultrasonic Homogenizer US-150E" (product name, tip size: φ20, Amplitude: 100%, oscillation frequency: 19.5 kHz, amplitude: approximately 31 μm) manufactured by Nippon Seiki Seisakusho Co., Ltd.

The above-mentioned phosphor powder is capable of emitting fluorescence with a sufficient reddish hue while exhibiting excellent brightness, making it suitable for use as a phosphor in light-emitting devices such as LEDs and display devices. The light-emitting devices obtained in this way can exhibit excellent color rendering properties and sufficient brightness.

The above-mentioned phosphor powder can be manufactured, for example, by the following method. One embodiment of a method for manufacturing a phosphor powder includes a firing step in which a mixed powder containing a raw material powder including a strontium source, a calcium source, an aluminum source, a silicon source, a nitrogen source, and a europium source and a nucleating agent composed of a CASN-based compound is heat-treated to obtain a fired product, and an annealing step in which the fired product is heat-treated at a temperature lower than the heat treatment temperature in the firing step to obtain an annealed product.

The terms strontium source, calcium source, aluminum source, silicon source, nitrogen source, and europium source refer to compounds or elements that serve as sources of strontium (Sr), calcium (Ca), aluminum (Al), silicon (Si), nitrogen (N), and europium (Eu), respectively. Note that when strontium nitride, for example, is used as the strontium source, the strontium nitride is both a strontium source and a nitrogen source.

Examples of strontium compounds include strontium nitride (Sr ₃ N ₂ ), strontium oxide (SrO), and strontium hydroxide (Sr(OH) ₂ ).

Examples of calcium compounds include calcium nitride (Ca ₃ N ₂ ), calcium oxide (CaO), and calcium hydroxide (Ca(OH) ₂ ).

Examples of aluminum compounds include aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), and aluminum hydroxide (Al(OH) ₃ ).

Examples of silicon compounds include silicon nitride (Si ₃ N ₄ ) and silicon oxide (SiO ₂ ). It is preferable to use silicon nitride with a high α fraction. The α fraction of silicon nitride may be, for example, 80 mass % or more, 90 mass % or more, or 95 mass % or more. When the α fraction of silicon nitride is within the above range, the growth of primary particles of the inorganic compound can be promoted.

The term "europium source" refers to a compound or element that serves as a source of europium. Compounds containing europium as a constituent element (europium compounds) may be, for example, nitrides, oxides, oxynitrides, or hydroxides, with oxides being preferred.

Examples of europium compounds include europium oxide (europium oxide), europium nitride (europium nitride), and europium halides. Examples of europium halides include europium fluoride, europium chloride, europium bromide, and europium iodide. Europium compounds preferably include europium oxide. The valence of europium in europium compounds may be divalent or trivalent, and is preferably divalent.

In the above raw material powder, the ratio of the total amount of strontium, calcium, and europium to the amount of aluminum exceeds 1.0000, and the amount of calcium is 0.0050 or more and the amount of europium is 0.0880 or less, based on the amount of aluminum.

In the raw material powder, the lower limit of the ratio of the total amount of strontium, calcium, and europium to the amount of aluminum may be, for example, 1.0200 or more, 1.0300 or more, 1.0400 or more, 1.0450 or more, or 1.0500 or more. By setting the lower limit of this ratio within the above range, the reddishness and brightness of the fluorescence spectrum emitted by the resulting phosphor powder can be both achieved at a higher level. In the raw material powder, the upper limit of the ratio of the total amount of strontium, calcium, and europium to the amount of aluminum may be, for example, 1.5000 or less, 1.4000 or less, 1.3000 or less, 1.2000 or less, or 1.1000 or less. By setting the upper limit of this ratio within the above range, the formation of heterogeneous phases can be more sufficiently suppressed. In the raw material powder, the ratio of the total amount of strontium, calcium, and europium to the amount of aluminum may be adjusted within the above-mentioned range, and may be, for example, more than 1.0000 and not more than 1.5000, more than 1.0000 and not more than 1.3000, or 1.0200 to 1.2000.

The lower limit of the amount of calcium in the raw material powder may be, for example, 0.0050 or more, 0.0100 or more, 0.0105 or more, 0.0108 or more, 0.0110 or more, 0.0130 or more, or 0.0150 or more, based on the amount of aluminum. Having the lower limit of the amount of calcium within the above range can achieve a more excellent reddish light emission. The upper limit of the amount of calcium in the raw material powder may be, for example, 0.0280 or less, 0.0250 or less, 0.0240 or less, or 0.0220 or less, based on the amount of aluminum. Having the upper limit of the amount of calcium within the above range can further improve the luminance of light emission. The amount of calcium in the raw material powder may be adjusted within the above range, and may be, for example, 0.0050 to 0.0280, based on the amount of aluminum.

The lower limit of the amount of europium in the raw material powder may be, for example, 0.0550 or more, 0.0600 or more, 0.0650 or more, or 0.0700 or more, based on the amount of aluminum. Having the lower limit of the amount of europium within the above range can achieve a more excellent reddish emission. The upper limit of the amount of europium in the raw material powder may be, for example, 0.0880 or less, 0.0860 or less, 0.0850 or less, or 0.0830 or less, based on the amount of aluminum. Having the upper limit of the amount of europium within the above range can further improve the luminance of emitted light. The amount of europium in the raw material powder may be adjusted within the above range, and may be, for example, 0.0550 to 0.0880, based on the amount of aluminum.

The nucleating agent composed of a CASN-based compound blended in the mixed powder may be any compound as long as it has the same crystal structure as CaAlSiN ₃ and may contain a luminescent center element.

The firing in the firing step may be carried out, for example, by filling a heat-resistant container with a lid with the mixed powder to be fired and heating the container. Materials that can be used to make the heat-resistant container include boron nitride, tungsten, molybdenum, and tantalum. An electric furnace or the like can be used for heating.

The firing process is carried out by adjusting conditions such as firing temperature, firing time, firing pressure, and firing atmosphere in order to form the same crystal structure as _CaAlSiN3 and reduce variations in composition when forming the crystal structure.

It is desirable that the firing temperature in the firing process be constant throughout the process. The firing temperature in the firing process may be, for example, 1500°C or higher, or 1550°C or higher. By setting the lower limit of the firing temperature within the above range, variation in the composition of the resulting fired product can be further reduced. The firing temperature in the firing process may be, for example, 2000°C or lower, 1980°C or lower, or 1950°C or lower. By setting the upper limit of the firing temperature within the above range, volatilization of the various compounds that serve as raw materials for the inorganic compound can be suppressed, and decomposition of the inorganic compound formed can be suppressed, preventing the destruction of the crystalline structure. The firing temperature in the firing process can be adjusted within the above range, for example, 1500 to 2000°C, or 1550 to 1950°C.

The lower limit of the firing time in the firing step may be, for example, 0.5 hours or more, 1.0 hours or more, 1.5 hours or more, 3.0 hours or more, or 4.0 hours or more. By setting the lower limit of the firing time within the above range, the conversion of the various raw material compounds into a fired product having the same crystal structure as the _CaAlSiN3 crystal phase can be further promoted, thereby improving the yield in the production of phosphor powder. The upper limit of the firing time in the firing step may be, for example, 30.0 hours or less, 20.0 hours or less, 10.0 hours or less, or 8.0 hours or less. By setting the upper limit of the firing time within the above range, excessive crystal growth of primary particles in the fired product can be further suppressed. The firing time in the firing step can be adjusted within the above range, for example, 0.5 to 30.0 hours, 1.5 to 10.0 hours, or 4.0 to 8.0 hours.

In this specification, firing time means the time (holding time) during which the temperature of the ambient environment of the object to be heated is maintained at a predetermined temperature after it reaches that temperature.

The firing process may be carried out under atmospheric pressure or under pressure. When the firing process is carried out in a pressurized environment, the lower limit of the firing pressure in the firing process may be, for example, 0.1 MPaG or more, or 0.2 MPaG or more. When the lower limit of the firing pressure is within the above range, decomposition of the main crystals constituting the fired product can be further suppressed. The upper limit of the firing pressure in the firing process may be, for example, 1.0 MPaG or less, or 0.9 MPaG or less. When the upper limit of the firing pressure is within the above range, decomposition of the inorganic compound can be further suppressed. The pressure in the firing process can be adjusted within the above range, and may be, for example, 0.1 to 1.0 MPaG, or 0.1 to 0.9 MPaG.

Pressure in this specification refers to gauge pressure.

The firing process is preferably carried out in an atmosphere containing at least one gas selected from the group consisting of rare gases and inert gases. The rare gas may contain, for example, argon, helium, etc., or may contain or consist of argon. The inert gas may contain, for example, nitrogen, etc., or may consist of nitrogen.

In the annealing process, the fired product is heat-treated at a temperature lower than the heat treatment temperature in the firing process to obtain an annealed product.

The heat treatment temperature in the annealing step may be, for example, 1200°C or higher, 1250°C or higher, or 1300°C or higher. By keeping the lower limit of the heat treatment temperature within the above range, crystal defects that occur during the firing and pulverization steps can be reduced, resulting in a phosphor powder with higher luminous efficiency. The heat treatment temperature in the annealing step may be, for example, 1450°C or lower, 1400°C or lower, or 1350°C or lower. By keeping the upper limit of the heat treatment temperature within the above range, crystal defects can be sufficiently reduced while further suppressing decomposition of the main phase. The heat treatment temperature in the annealing step can be adjusted within the above range, and may be, for example, 1200 to 1450°C or 1250 to 1350°C.

The lower limit of the heat treatment time in the annealing step may be, for example, 0.5 hours or more, 1.0 hours or more, 1.5 hours or more, 3.0 hours or more, or 4.0 hours or more. The upper limit of the heat treatment time in the annealing step may be, for example, 30.0 hours or less, 20.0 hours or less, 10.0 hours or less, 8.0 hours or less, or 5.0 hours or less. The heat treatment time in the annealing step can be adjusted within the above range and may be, for example, 0.5 to 30.0 hours, 1.5 to 10.0 hours, or 4.0 to 8.0 hours.

The annealing process may be performed under atmospheric pressure or under pressure. When the annealing process is performed in a pressurized environment, the lower limit of the pressure in the annealing process may be, for example, 0.1 MPaG or more, or 0.2 MPaG or more. When the lower limit of the pressure is within the above range, decomposition of the phosphor particles can be further suppressed. The upper limit of the pressure in the annealing process may be, for example, 1.0 MPaG or less, or 0.9 MPaG or less. When the upper limit of the pressure is within the above range, decomposition of the formed phosphor particles can be further suppressed. The pressure in the annealing process can be adjusted within the above range, and may be, for example, 0.1 to 1.0 MPaG, or 0.1 to 0.9 MPaG.

The annealing step is preferably carried out in an atmosphere containing at least one gas selected from the group consisting of a rare gas and an inert gas. The rare gas may contain, for example, argon, helium, etc., or may contain argon or consist of argon. The inert gas may contain, for example, nitrogen, etc., or may consist of nitrogen.

The above-mentioned method for producing phosphor powder may include other processes in addition to the firing and annealing processes. Examples of other processes include a crushing process, a classification process, and an acid treatment process.

The crushing process is a process for crushing the fired product obtained in the firing process or the annealed product obtained in the annealing process, which may be in a lump form, to adjust the particle size. A mortar or mortar may be used in the crushing process, or a general crusher or crusher may also be used. Examples of crushers and crushers include ball mills, jet mills, and Henschel mixers. While agglomerates of fired product may be crushed using relatively high-intensity methods, when crushing annealed product agglomerates, it is desirable to crush them under gentle conditions to prevent scratches, cracks, etc. on the surface of the phosphor particles. To achieve gentle crushing, for example, the crushing process is desirably performed using a wet ball mill in the presence of a medium such as ion-exchanged water. Zirconia balls can also be used in the ball mill.

The classification process may be a process for removing fine particles that reduce the luminance and other properties of the phosphor powder. When the required optical properties of the phosphor powder are high, it is desirable for the above-mentioned phosphor powder manufacturing method to include a classification process. The classification process may be performed, for example, by decantation. The classification process is performed by adding the material to be processed (e.g., phosphor powder that has been subjected to a crushing process) to a dispersion medium, preparing and stirring a dispersion, allowing the phosphor powder in the dispersion to settle, and removing the supernatant. After removing the supernatant, the precipitate is filtered and collected, and dried to obtain phosphor powder from which the fine particles have been removed. In the classification process, the preparation of the above-mentioned dispersion and the removal of the supernatant may be repeated. Examples of dispersion media include an aqueous solution of sodium hexametaphosphate.

The acid treatment process may be a process of treating the phosphor powder with acid to reduce the content of impurities that do not contribute to light emission. Examples of acids include hydrofluoric acid, sulfuric acid, phosphoric acid, hydrochloric acid, and nitric acid. The acid may contain at least one acid selected from the group consisting of hydrofluoric acid, sulfuric acid, phosphoric acid, hydrochloric acid, and nitric acid, and may be a mixed acid, but is preferably hydrochloric acid. The acid treatment process is carried out by bringing the phosphor powder into contact with the acid. Specifically, the phosphor powder is placed in an aqueous solution containing the acid to prepare a dispersion, and the dispersion is treated for a predetermined period of time while being stirred.

The lower limit of the stirring time in the acid treatment step may be, for example, 0.1 hour or more, 0.5 hour or more, or 1.0 hour or more. The upper limit of the stirring time may be, for example, 6.0 hours or less, 3.0 hours or less, or 1.5 hours or less. Furthermore, in the acid treatment step, the acid treatment may be performed while the aqueous solution is cooled, heated, or boiled. The temperature of the aqueous solution in this case may be, for example, 20 to 90°C, or 30 to 80°C. After the acid treatment, the phosphor powder may be washed with water to remove the acid, and then dried. The drying temperature may be, for example, 100 to 120°C. The drying time may be, for example, approximately 12 hours.

The above-mentioned phosphor powder is suitable as a phosphor for use in light-emitting devices such as display devices. One embodiment of the light-emitting device is a light-emitting device comprising a light-emitting element that emits primary light and a wavelength converter that absorbs a portion of the primary light and emits secondary light having a wavelength longer than that of the primary light.

The light-emitting element that emits the primary light may be, for example, an InGaN blue LED.

The wavelength converter includes the above-mentioned phosphor powder. The wavelength converter may also include other phosphors in addition to the above-mentioned phosphor powder. Examples of other phosphors include red phosphors, yellow phosphors, yellow-green phosphors, and green phosphors other than the above-mentioned phosphor powders. The other phosphors can be selected depending on the application for which the phosphor composition is used, and can be selected and combined depending on, for example, the brightness, color, and color rendering properties required for the light-emitting device. Examples of red phosphors include conventional CASN-based phosphors. Examples of green to yellow phosphors (phosphors having fluorescent wavelengths in the green to yellow wavelength band) include YAG phosphors and LuAG phosphors. Examples of yellow phosphors include Ca-α-SiAlON phosphors, and examples of green phosphors include β-SiAlON phosphors.

The light-emitting element and wavelength converter may be dispersed in a sealing resin or the like. The sealing resin is preferably colorless and has excellent transparency to visible light wavelengths. The sealing resin is generally recognized as transparent. Examples of such resins include silicone resin and acrylic resin.

Display devices such as monitors are required to provide sufficient brightness for the transmission of information. To achieve this, it is desirable that the light components emitted from the display fall within the range of high human luminous efficiency. Relative luminous efficiency is generally determined based on the standard luminous efficiency curve established by the International Commission on Illumination (CIE). The more overlap there is between light's emission spectrum and this standard luminous efficiency curve, the brighter it will appear to humans. The standard luminous efficiency curve approximates a normal distribution, spreading from 400 to 700 nm with a peak around 550 nm. For example, in bright places, humans are said to perceive light around 555 nm as most sensitive.

As shown in Figure 1, the emission spectrum of SCASN phosphors generally overlaps with the standard luminous efficacy curve, making them useful as red phosphors. The emission spectrum of SCASN phosphors generally spans the 600-800 nm range. The phosphor powder described above has a specific composition in which the proportions of strontium, calcium, and europium in the composition formula satisfy the above-mentioned ranges of x and y. This shifts the peak position of the emission spectrum toward shorter wavelengths, resulting in greater overlap with the standard luminous efficacy curve and sufficient brightness. Furthermore, because it exhibits a sufficient reddish tint, the phosphor powder described above can be a useful red phosphor for manufacturing display elements with excellent brightness.

Although several embodiments have been described above, the present disclosure is in no way limited to the above-described embodiments. Furthermore, the descriptions of the above-described embodiments can be applied to each other.

The present disclosure will be explained in more detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the following examples.

Example 1
[Preparation of nucleating agent]
First, 60.61 g of α-type silicon nitride (Si ₃ N ₄ , manufactured by Ube Industries, Ltd., SN-E10 grade), 53.13 g of aluminum nitride (AlN, manufactured by Tokuyama Corporation, E grade), and 13.68 g of europium oxide (Eu ₂ O ₃ , manufactured by Shin-Etsu Chemical Co., Ltd.) were placed in a container and premixed.

Next, in a glove box maintained in a nitrogen atmosphere with a moisture content of 1 mass ppm or less and an oxygen concentration of 50 ppm or less, 5.76 g of calcium nitride (Ca ₃ N ₂ , manufactured by Materion) and 106.82 g of strontium nitride (Sr ₃ N ₂ , manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 2N) were further added to the container and dry-mixed to obtain a mixture.

In a glove box, 240 g of the above mixture was placed in a tungsten container with a lid. After closing the lid, the container was removed from the glove box and placed in an electric furnace equipped with a carbon heater. The electric furnace was then thoroughly evacuated until the pressure inside was 0.1 PaG or less.

While continuing to evacuate, the temperature inside the electric furnace was raised to 600°C. After reaching 600°C, nitrogen gas was introduced into the electric furnace and the pressure inside the electric furnace was adjusted to 0.9 MPaG. The temperature inside the electric furnace was then raised to 1950°C under a nitrogen gas atmosphere, and after reaching 1950°C, heat treatment was carried out for 8 hours. Heating was then terminated and the material was cooled to room temperature. After cooling to room temperature, red lumps were recovered from the container. The recovered lumps were crushed and sieved in a mortar to prepare core particles (nucleating agent) with an average particle size of 16 μm.

[Production of phosphor powder]
51.50 g of α-type silicon nitride (Si ₃ N ₄ , manufactured by Ube Industries, Ltd., SN-E10 grade), 45.14 g of aluminum nitride (AlN, manufactured by Tokuyama Corporation, E grade), 15.50 g of europium oxide (Eu ₂ O ₃ , manufactured by Shin-Etsu Chemical Co., Ltd.), and 24.00 g of the nucleating agent prepared as described above were weighed and premixed in a container.

Next, in a glove box maintained in a nitrogen atmosphere with a moisture content of 1 mass ppm or less and an oxygen concentration of 50 ppm or less, 0.27 g of calcium nitride ( _{Ca3N2 ,} manufactured by Materion) and 103.58 _g of strontium nitride ( _Sr3N2 , manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 2N) were further weighed and dry-mixed into the container. A mixed powder was thus obtained. The relationship (mass %) between the charged amounts of the nucleating agent and the raw material powder, and the breakdown (molar ratio) of the charged amounts of each element in the raw material powder are shown in Table 1.

In a glove box, 240 g of the above mixed powder was placed in a tungsten container with a lid. After closing the lid, the container was removed from the glove box and placed in an electric furnace equipped with a carbon heater. The electric furnace was then evacuated to a vacuum until the pressure inside was 0.1 PaG or less.

While continuing to evacuate, the temperature inside the electric furnace was raised to 600°C. After reaching 600°C, nitrogen gas was introduced into the electric furnace and the pressure inside the electric furnace was adjusted to 0.9 MPaG. The temperature inside the electric furnace was then raised to 1950°C in a nitrogen gas atmosphere, and once 1950°C was reached, heat treatment was carried out for 8 hours. Heating was then terminated and the material was allowed to cool to room temperature. After cooling to room temperature, red lumps were recovered from the container. The recovered lumps were crushed and sieved to adjust the particle size and obtain sintered powder.

The resulting sintered powder was loaded into a tungsten container and quickly transferred to an electric furnace equipped with a carbon heater. The furnace was thoroughly evacuated until the pressure inside was 0.1 PaG or less. Heating began while continuing the evacuation, and when the temperature reached 600°C, argon gas was introduced into the furnace and the pressure inside the furnace was adjusted to atmospheric pressure. The temperature continued to rise to 1350°C even after the introduction of argon gas began. Once the temperature reached 1350°C, the heat treatment took 8 hours. Heating was then terminated and the mixture was cooled to room temperature. After cooling to room temperature, the annealed powder was recovered from the container. The recovered powder was passed through a sieve to adjust the particle size. In this way, the annealed powder was obtained.

The annealed powder was placed in 2.0 M hydrochloric acid at room temperature to a slurry concentration of 25% by mass and immersed for 1 hour. This resulted in acid treatment. After acid treatment, the hydrochloric acid slurry was boiled for 1 hour while stirring. After boiling, the slurry was cooled to room temperature and filtered to separate the acid treatment liquid from the solids, yielding an acid-treated product. The acid-treated product was then dried in a dryer set at a temperature between 100 and 120°C for 12 hours, yielding an acid-treated powder.

The acid-treated powder was placed in an alumina crucible and heated in air at a rate of 10°C/min until it reached 400°C for 3 hours. After the heat treatment, the mixture was allowed to cool to room temperature, yielding a heat-treated powder.

The obtained heat-treated powder was subjected to powder X-ray diffraction using CuKα radiation using an X-ray diffractometer (Rigaku Corporation, product name: Ultima IV). The obtained X-ray diffraction pattern was identical to that of _CaAlSiN3 crystals, confirming that the main crystalline phase had the same crystal structure as _CaAlSiN3 crystals. This heat-treated powder was used as the phosphor powder of Example 1.

(Example 2, Comparative Examples 1 to 4)
A phosphor powder was prepared in the same manner as in Example 1, except that the mixing ratio was adjusted so that the breakdown (molar ratio) of the amount of each element in the raw material powder was as shown in Table 1.

<Evaluation of phosphor powder>
The composition ratio, fluorescence emission peak wavelength and half-width, color rendering index, and total luminous flux of each of the phosphor powders obtained in Examples 1 and 2 and Comparative Examples 1 to 4 were measured according to the methods described below. The results are shown in Table 2.

[Composition ratio]
The phosphor powder was subjected to acid decomposition under pressure to prepare a sample solution, which was then quantitatively analyzed using an ICP emission spectrometer to determine the composition ratio of the elements that make up the phosphor powder.

[Fluorescence Emission Peak Wavelength and Half Width]
The fluorescence spectrum of the phosphor powder was measured using a spectrofluorometer (Hitachi High-Technologies Corporation, product name: F-7000) corrected using rhodamine B and a secondary standard light source. A solid sample holder attached to the spectrometer was used for the measurement, and the fluorescence spectrum was measured at an excitation wavelength of 455 nm. From the obtained fluorescence spectrum, the peak wavelength and half-width of the emission spectrum were determined.

[Color rendering index and total luminous flux]
The color rendering properties and total luminous flux of the phosphor powder were evaluated by blending it with the LuAG phosphor in a silicone resin to prepare a white LED, which was used as an evaluation sample.

First, phosphor powder and LuAG yellow phosphor (with a peak emission wavelength of 535 nm when exposed to excitation light with a wavelength of 455 nm) were blended with silicone resin, followed by degassing and kneading to obtain a kneaded mixture. The resulting kneaded mixture was potted into a surface-mount package to which a blue LED element with a peak wavelength of 450 nm was bonded, and then thermally cured to prepare a white LED. The blending ratio of phosphor powder to YAG phosphor was adjusted so that the chromaticity coordinates (x, y) of the white LED were (0.460, 0.411) when powered on.

The special color rendering index R9 and total luminous flux of the obtained white LED when it was energized and emitting light were measured using a total luminous flux measuring device (manufactured by Otsuka Electronics Co., Ltd., a device combining a 500 mm diameter integrating hemisphere and a spectrophotometer (MCPD-9800)).

According to the present disclosure, it is possible to provide a phosphor powder capable of emitting fluorescence with a sufficient reddish tinge while exhibiting excellent brightness, and a method for manufacturing the same. Furthermore, according to the present disclosure, it is possible to provide a light-emitting device that uses the above-mentioned phosphor powder and exhibits excellent color rendering properties.

Claims (4)

The main crystalline phase has the same crystalline structure as _CaAlSiN3 ,
A phosphor powder comprising phosphor particles represented by the general formula: (Sr _1-xy , Ca _x , Eu _y )AlSi(N,O) ₃ (wherein x and y satisfy 0.0100≦x≦0.0300 and 0.0500≦y≦0.0900). The phosphor powder according to claim 1, which has an emission peak wavelength of 635 nm or longer when irradiated with light having a wavelength of 455 nm. A light emitting device comprising: a light emitting element that emits primary light; and a wavelength converter that absorbs a part of the primary light and emits secondary light having a wavelength longer than the wavelength of the primary light,
A light emitting device, wherein the wavelength converter comprises the phosphor powder according to claim 1 . A method for producing the phosphor powder according to claim 1 or 2, comprising:
a firing step of heat-treating a mixed powder containing a raw material powder including a strontium source, a calcium source, an aluminum source, a silicon source, a nitrogen source, and a europium source, and a nucleating agent composed of a CASN-based compound, to obtain a fired product;
an annealing step of heat-treating the fired product at a temperature lower than the heat treatment temperature in the firing step to obtain an annealed product;
In the raw material powder,
The ratio of the total amount of substance of strontium, calcium, and europium to the amount of substance of aluminum is greater than 1.0000,
The amount of calcium is 0.0050 or more and the amount of europium is 0.0880 or less, based on the amount of aluminum.
Method for manufacturing phosphor powder.