Red phosphor powder, light-emitting element, and light-emitting device

Abstract

Provided are: a red phosphor powder that has high luminous efficacy despite having a small particle size; and a light-emitting element and a light-emitting device comprising the red phosphor powder. The red phosphor powder includes a main component containing strontium (Sr), sulfur (S), and europium (Eu), has an average primary particle size of 2.7 μm or less according to SEM observation, and has a crystallite diameter of 155 nm or less.

Description

Red phosphor powder, light-emitting element, and light-emitting device

[0001] The present invention relates to a red phosphor powder, a light-emitting element, and a light-emitting device.

[0002] Light-emitting devices that use a light-emitting diode (LED) that emits near-ultraviolet light or blue light as a light source (excitation source) in combination with a phosphor are widely used in various light-emitting devices such as lighting, backlights for mobile terminals, and display devices (displays).

[0003] In this light-emitting device, the phosphor absorbs the light emitted by the LED (radiated light) and emits light of a different wavelength from the absorbed light. Therefore, it is possible to obtain light emission of a different color tone from the LED-radiated light. For example, green light and / or red light can be obtained by combining a blue LED with a green phosphor and / or a red phosphor, and light-emitting devices having such a configuration are used in applications such as displays. A phosphor is a substance that emits light (mainly visible light) during the process of returning from an excited state to a ground state (relaxation process) after being irradiated with excitation light, an electron beam, or various other methods.

[0004] In recent years, advances in display technology have garnered attention toward mini (mini) LED displays and micro (μ) LED displays. μLED displays are composed of independent μLEDs for each of the R (red), G (green), and B (blue) subpixels. Each package (cell) corresponding to a subpixel is separated by a partition (package rib), preventing color mixing due to light from adjacent packages. Reflecting the size of the subpixel, the package is extremely small, measuring, for example, less than 1000 μm on a side. An excitation source, such as an LED, is provided on the bottom of the package, and a phosphor layer is provided on top of it. The phosphor layer is fabricated by filling the package with phosphor powder.

[0005] The emitted light of a phosphor varies depending on the phosphor composition. A (Ca, Sr)S:Eu-based compound has been proposed as a red phosphor. Phosphors are often used in powder form, and powdered phosphors (phosphor powders) are often synthesized by a solid-phase method.

[0006] As a document disclosing such a technique, Patent Document 1 discloses a compound having the general formula: (Ca １－ｘ Sr ｘ )S:Eu (where 0<x≦1) ３ and SrCO ３ and BaCO ３ After wet mixing and drying, the mixture was fired at 850°C in a hydrogen sulfide gas atmosphere. ２ O was added and fired at 1000°C in an argon gas atmosphere to obtain a compound represented by the general formula (Ca １－ｘ Sr ｘ It is disclosed that a red phosphor powder represented by the formula: S:Eu,Ba is obtained (Patent Document 1, claim 2,

[0011] and

[0060] , etc.).

[0007] On the other hand, it has also been proposed to synthesize phosphor powders by a liquid phase method. Patent Document 2, which discloses such a technique, discloses a method for producing a phosphor, including a precursor formation step of forming a phosphor precursor by a liquid phase method and a firing step of firing the precursor to form a phosphor (claim 1 of Patent Document 2). It is also described that the liquid phase method makes it easy to obtain phosphors with high stoichiometric purity and that particles with a small particle size can be obtained without a pulverization step (paragraph

[0028] of Patent Document 2).

[0008] International Publication No. 2013 / 021990 Japanese Patent Application Laid-Open No. 2007-106831

[0009] As described above, it has been conventionally known to synthesize phosphor powders such as red phosphor powders by solid-phase or liquid-phase methods, and to apply the synthesized phosphor powders to applications such as μLED displays.

[0010] However, the inventors' investigation revealed that there was room for improvement in conventional phosphor powders. Specifically, in displays such as μLED displays, different phosphors, i.e., red phosphors and green phosphors, are used for each subpixel. Therefore, a phosphor layer is created by filling each package corresponding to each subpixel with a different phosphor powder.

[0011] On the other hand, there is a demand for higher resolution displays, and as a result, package sizes are becoming smaller. Accordingly, there is a need to make phosphor powder finer. This is because it is difficult to uniformly fill coarse phosphor powder into a tiny package. By using fine phosphor powder, it becomes possible to uniformly fill a tiny package and manufacture high-resolution displays. Another advantage of using fine phosphor powder is that it allows the use of inkjet processes, which can reduce costs, for phosphor powder filling.

[0012] However, conventional phosphor powders have a problem in that the luminous efficiency decreases as the particle size decreases. Therefore, it has been difficult to obtain phosphor powders with small particle size and high luminous efficiency. If the luminous efficiency of a phosphor powder is low, it is impossible to obtain high-brightness light emission in a light-emitting device such as a display.

[0013] The present inventors have conducted extensive research in light of these problems. As a result, they have found that for red phosphor powders of a given composition, in the small particle size range, there is a specific relationship between the crystallite size and the luminous efficiency. They have also found that even if the particle size is small, the luminous efficiency can be increased by reducing the crystallite size.

[0014] The present invention was completed based on these findings, and its objective is to provide a red phosphor powder that has high luminous efficiency despite its small particle size, as well as a light-emitting element and a light-emitting device that include the red phosphor powder.

[0015] The present invention encompasses the following aspects (1) to (6). In this specification, the expression "to" includes both the numerical values ​​at both ends. In other words, "X to Y" is synonymous with "X or more and Y or less." In addition, in this specification, any combination of suitable aspects can be adopted as long as technical consistency can be achieved. For example, one of the suitable numerical ranges can be combined with the other.

[0016] (1) A red phosphor powder having a main component including strontium (Sr), sulfur (S), and europium (Eu), and having an average primary particle size of 2.7 μm or less and a crystallite size of 155 nm or less as measured by SEM observation.

[0017] (2) The main component is represented by the general formula: (Ca １－ｘ－ｙ Sr ｘ ) S: Eu ｙ (1) Red phosphor powder having a composition expressed by the formula (where 0<x≦1−y, 0<y≦0.01).

[0018] (3) The main component is represented by the general formula: (Ca １－ｘ－ｙ Sr ｘ ) S: Eu ｙ (1) or (2) above, having a composition expressed by (where 0<x<1-y, 0<y≦0.01).

[0019] (4) The red phosphor powder according to any one of (1) to (3) above, having an internal quantum efficiency (IQE) of 40% or more.

[0020] (5) A light-emitting device comprising a light source that generates excitation light and the red phosphor powder of any one of (1) to (4) above.

[0021] (6) A light-emitting device comprising the light-emitting element of (5) above.

[0022] According to the present invention, there are provided a red phosphor powder having high luminous efficiency despite its small particle size, and a light emitting element and a light emitting device including the red phosphor powder.

[0023] 1 shows SEM images of phosphor powder (Comparative Example 1) and phosphor powder (Example 5).

[0024] A specific embodiment of the present invention (hereinafter referred to as the "present embodiment") will be described below. However, the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0025] <<1. Red Phosphor Powder>> The red phosphor powder of this embodiment (sometimes simply referred to as "phosphor powder") has a main component containing strontium (Sr), sulfur (S), and europium (Eu). The main component is preferably represented by the general formula: (Ca １－ｘ－ｙ Sr ｘ ) S: Eu ｙ (where 0<x≦1−y, 0<y≦0.01), and particularly preferably has a composition represented by the general formula: (Ca １－ｘ－ｙ Sr ｘ ) S: Eu ｙ (where 0<x<1-y, 0<y≦0.01). In other words, the red phosphor powder preferably contains, but is not limited to, a compound (main component compound) represented by the above-mentioned general formula as a main component. This main component compound has a rock salt crystal structure. In this specification, the term "main component" refers to a component (compound) whose content in the phosphor powder is 50% by mass or more. The content of the main component may be 60% by mass or more, 70% by mass or more, 80% by mass or more, or even 90% by mass or more. The phosphor powder may also contain components other than Ca, Sr, S, and Eu. Examples of such components include, but are not limited to, at least one alkali metal selected from the group consisting of sodium (Na) and potassium (K).

[0026] The phosphor powder contains a main component compound of a SrS-based compound or a (Ca, Sr)S-based compound as a host crystal and europium (Eu) as a luminescent center, which is excited by irradiation light having a wavelength of 420 nm or more and 500 nm or less to emit red light.

[0027] The host crystal contains strontium (Sr) as an essential component. The host crystal may contain both calcium (Ca) and strontium (Sr) as essential components. However, the ratio of Ca to Sr is not limited. By adjusting the ratio of Ca to Sr in the host crystal, the maximum emission wavelength (peak emission wavelength) of the emitted light can be controlled. Specifically, when the host crystal is a CaS-based compound (x = 0), the maximum emission wavelength is 655 nm. When the host crystal is an SrS-based compound (x = 1 - y), the maximum emission wavelength is 620 nm. Therefore, by adjusting x within the range of more than 0 and not more than 1 - y, the maximum emission wavelength can be controlled within the range of 620 nm or more and less than 655 nm.

[0028] Europium (Eu) acts as a luminescence center. By including an appropriate amount of Eu, it is possible to prevent a decrease in luminescence intensity due to concentration quenching, while obtaining high luminous efficiency. From this viewpoint, it is desirable that the Eu content y is greater than 0 and equal to or less than 0.01 (0<y≦0.01).

[0029] The red phosphor powder of this embodiment has an average primary particle diameter of 2.7 μm or less as determined by SEM observation. Reducing the particle diameter enables miniaturization of the package and therefore higher resolution of the display. Furthermore, when filling the package with the phosphor powder, it becomes possible to employ an inkjet process, which is effective in reducing manufacturing costs. On the other hand, if the particle diameter of the phosphor powder is large, it becomes difficult to fill the display's small package and employ the inkjet process. The average primary particle diameter is more preferably 2.2 μm or less, and even more preferably 1.8 μm or less. Meanwhile, by appropriately increasing the particle diameter of the phosphor powder, particle aggregation is suppressed, thereby improving the handleability of the phosphor powder. The average primary particle diameter is preferably 0.05 μm or more, and more preferably 0.1 μm or more. The average primary particle diameter is preferably 0.05 μm or more and more preferably 0.1 μm or more. The average primary particle diameter is preferably 0.05 μm or more and 2.2 μm or less, and more preferably 0.1 μm or more and 1.8 μm or less.

[0030] The red phosphor powder of this embodiment has a crystallite diameter of 155 nm or less. According to the inventors' findings, red phosphor powders with a small average primary particle diameter of 2.7 μm or less have high luminous efficiency when the crystallite diameter is small. While this reason should not be interpreted in a limiting sense, it is speculated that phosphor powders with a small crystallite diameter contain fewer impurities. It is also believed that phosphor powders with a small crystallite diameter and large lattice distortion are less susceptible to temperature quenching. The crystallite diameter is preferably 150 nm or less, more preferably 130 nm or less. On the other hand, powders with excessively small crystallite diameters have the problem of low luminous efficiency. The crystallite diameter is preferably 90 nm or more, more preferably 100 nm or more. From the perspective of improving luminous efficiency, the crystallite diameter is preferably 90 nm or more and 150 nm or less, more preferably 100 nm or more and 130 nm or less. The crystallite diameter is determined by analyzing the phosphor powder using X-ray diffraction.

[0031] Preferably, the internal quantum efficiency (IQE) of the phosphor powder is 40% or more. The internal quantum efficiency is the efficiency with which a phosphor converts absorbed light into another light, and is a measure of luminous efficiency. By applying a phosphor powder with a high IQE, the luminous intensity of a light-emitting device such as a display can be increased. The IQE is more preferably 45% or more, and even more preferably 50% or more. There is no upper limit for the IQE.

[0032] Although not limited thereto, the circularity of the phosphor powder is preferably 0.60 or more and 0.75 or less, and more preferably 0.63 or more and 0.72 or less. Circularity is an index of the circularity (sphericity) of the particles (phosphor particles) constituting the phosphor powder. If the particles constituting the phosphor powder have a shape close to a perfect sphere, the circularity will be close to 1, and if they have a shape that is far from a perfect sphere, the circularity will be close to 0. By appropriately increasing the circularity, the fluidity of the powder is improved. Therefore, it is possible to achieve a higher level of package miniaturization and high-resolution displays. On the other hand, phosphor powder with an excessively high circularity may result in increased manufacturing costs. By appropriately reducing the circularity, manufacturing costs can be reduced.

[0033] The circularity is determined by observing the phosphor powder with an SEM and analyzing the resulting SEM image. Specifically, the area S and perimeter L of each particle in a two-dimensional projected image are measured for multiple particles constituting the powder. The circularity of each particle is then calculated according to the following formula (1), and the arithmetic mean value is defined as the circularity of the phosphor powder.

[0034]

[0035] <<2. Manufacturing Method of Red Phosphor Powder>> The manufacturing method of the red phosphor powder of this embodiment is not particularly limited as long as it satisfies the above-mentioned requirements. It may be synthesized by a solid-phase method or a liquid-phase method. However, phosphor powder synthesized by the liquid-phase method is characterized by high crystallinity despite being fine. It is also characterized by high circularity (sphericity) and excellent fluidity. Therefore, phosphor powder synthesized by the liquid-phase method is particularly suitable for use in μLED displays.

[0036] An example of a liquid-phase method for producing a red phosphor powder is shown below. This production method includes the following steps: a step of dissolving starting materials including a strontium (Sr) source, a europium (Eu) source, a sulfur (S) source, and an alkali metal source in a solvent to prepare a starting material solution (a raw material mixing step), a step of subjecting the resulting starting material solution to a heat treatment and a solid-liquid separation treatment to obtain a phosphor precursor powder (a reaction step), and a step of firing the resulting phosphor precursor powder (a firing step). Each step is described in detail below.

[0037] <Raw Material Mixing Step> In the raw material mixing step, starting materials including a strontium (Sr) source, a europium (Eu) source, a sulfur (S) source, and an alkali metal source are dissolved in a solvent to prepare a starting material solution. The starting materials may also include a calcium (Ca) source. Here, the alkali metal is at least one selected from the group consisting of sodium (Na) and potassium (K). Among the alkali metal elements, Na and K have ionic radii close to those of Ca and Sr. Therefore, when Eu is used in the phosphor powder, ３＋ Ions are generated and Ca ２＋ Even if the phenomenon of ion disappearance (Schottky defect) occurs, Na＋ Aeon and K ＋ Ions are Ca ２＋ The alkali metal occupies the sites and compensates for Schottky defects, which shortens the decay time of the phosphor powder.Alkali metals also act as fluxes in the firing process, which will be described later.

[0038] Chlorides, sulfates, nitrates, etc. can be used as the Sr source, Ca source, Eu source, and alkali metal source. Sulfur, sodium sulfide, potassium sulfide, and / or sulfamic acid can be used as the sulfur (S) source. Sodium sulfide and potassium sulfide also function as alkali metal sources. Heptane (C ７ H １６ A hydrocarbon solvent such as oleylamine (C) can be used. An additive may also be added to the solvent. １８ H ３７ The starting materials can be dissolved in a known manner. For example, the starting materials can be added to a solvent and stirred using a stirrer.

[0039] <Reaction Step> In the reaction step, the obtained starting material solution is subjected to a heat treatment and a solid-liquid separation treatment to obtain a phosphor precursor powder. The reaction of the starting materials in the solution progresses by the heat treatment, and a precipitate is generated. The heat treatment is carried out in the presence of nitrogen (N ２ The process is preferably carried out at a temperature of 200°C to 300°C in an inert gas atmosphere such as toluene, ...

[0040] <Firing Step> In the firing step, the phosphor precursor powder is fired. Firing can produce phosphor powder with improved crystallinity. The firing conditions are not particularly limited. However, firing is preferably performed at a temperature of 500°C or higher and 1200°C or lower. This allows for the production of highly crystalline and fine phosphor powder. It is also preferable to perform firing in a sulfur atmosphere. Even if the amount of sulfur in the phosphor precursor powder is insufficient, sulfur can be replenished.

[0041] <<3. Light-Emitting Element>> The light-emitting element of this embodiment includes a light source (excitation source) that generates excitation light and the above-described red phosphor powder. The light source functions to emit light toward the phosphor powder to excite the phosphor. A blue-emitting LED with a wavelength of 420 nm or more and 500 nm or less is suitable as the light source. The arrangement of the phosphor powder and the light source is not limited as long as light from the light source is incident on the phosphor powder. For example, when the light-emitting element is applied to a μLED display, it is preferable that an LED serving as a light source is arranged at the bottom within each package, and phosphor powder is filled and arranged above it.

[0042] The light-emitting element may contain the red phosphor powder in a powder state alone. Alternatively, the light-emitting element may contain the red phosphor powder and another known phosphor powder. For example, the light-emitting element may contain a red phosphor powder and a green phosphor powder. Alternatively, the light-emitting element may contain a mixture of a phosphor powder such as the red phosphor powder and a resin. The resin may be, for example, one or more selected from a thermoplastic resin, a thermosetting resin, an ionizing radiation curable resin, and a two-part mixed curable resin.

[0043] <<4. Light-Emitting Device>> The light-emitting device of this embodiment includes the light-emitting element described above. Examples of light-emitting elements include, but are not limited to, well-known applications such as lighting, backlights for mobile devices, and displays (display devices). Among these, μLED displays and mini LED displays, particularly μLED displays, are preferred.

[0044] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples.

[0045] (1) Synthesis of Phosphor Powder [Comparative Example 1] In Comparative Example 1, phosphor powder was synthesized by a solid phase method. Specifically, calcium carbonate (CaCO ３ ) to hydrogen sulfide (H ２ The mixture was fired at 850°C for 4 hours in a sintered state in an atmosphere of europium oxide (EuS) to obtain calcium sulfide (CaS). ２ O ３ ) and europium fluoride (EuF ３) was dry mixed, and the resulting mixture was fired in an argon (Ar) atmosphere at 1000°C for 4 hours to obtain a fired product. The argon (Ar) flow rate during firing was 1.0 L / min. The fired product was pulverized and classified using a jet mill (manufactured by Dec Corporation) under a fluid pressure of 12 MPa to obtain a phosphor powder with a CaS:Eu composition.

[0046] Comparative Example 2 A phosphor powder of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that the fluid pressure of the jet mill was changed to 0.3 MPa.

[0047] Comparative Example 3 In Comparative Example 3, a phosphor powder was synthesized by a liquid phase method. ２ ), calcium chloride (CaCl ２ ), sulfur (S), europium chloride (EuCl ３ ), sodium chloride (NaCl) were prepared as starting materials. ７ H １６ ) and oleylamine (C １８ H ３７ N) was prepared as a solvent, and the starting materials were dissolved in the solvent to prepare a starting material solution. The blending amounts of the starting materials were adjusted so as to obtain phosphor powders having the compositions shown in Table 2 below. ２ The ratio of the starting materials (NaCl to NaCl) to the solvent (heptane, oleylamine) was adjusted so that the solvent was 1,000 parts by mass per 100 parts by mass of the total starting materials. Furthermore, the mixing ratio of heptane to oleylamine was adjusted so that the oleylamine was 150 parts by mass per 100 parts by mass of heptane.

[0048] The resulting starting material solution was then heated to 1000°C with nitrogen (N ２ ) under a flow rate of 250°C for 0.5 hours. A reaction occurred due to the heating, and a precipitate was formed in the solution. After heating, the starting material solution was subjected to solid-liquid separation using a centrifuge, and the resulting precipitate was washed with ethanol to obtain a phosphor precursor powder.

[0049] The obtained phosphor precursor powder was placed in a firing furnace together with sulfur (S) and fired at 900°C for 2 hours in a nitrogen atmosphere. ２The flow rate was 0.2 L / min. In this way, phosphor powder was synthesized. The manufacturing conditions for the phosphor powder are shown in Table 1 below, and the properties of the phosphor powder are shown in Table 2 below.

[0050] [Examples 1 to 8 and Comparative Example 4] The manufacturing conditions for the phosphor powder were changed as shown in Tables 1 and 2 below. Otherwise, the phosphor powder was synthesized in the same manner as in Comparative Example 3. In Example 7, the Sr source (SrCl ２ ), but a Ca source (CaCl ２ ) was not used.

[0051]

[0052] (2) Evaluation of Phosphor Powders Using the phosphor powders obtained in Examples 1 to 8 and Comparative Examples 1 to 4 as samples, various properties were evaluated as follows.

[0053] <ICP Emission Analysis> A sample was completely dissolved by acid decomposition, and the content of each element was measured by a calibration curve method using an ICP emission spectrometer (Hitachi High-Tech Science Corporation, PS3520UVDDII).

[0054] <SEM Observation (Average Primary Particle Diameter)> The average primary particle diameter (SEM diameter) of the phosphor powder was measured. First, the phosphor powder was observed using a scanning electron microscope (SEM) to obtain an SEM image. The observation was performed at a magnification of 1000 to 3000 times. Next, the SEM image was analyzed using image analysis particle size distribution measurement software (Mountec, Mac-View, Version 4, File Version: v1.0.0.14) to measure the particle diameters (Heywood diameter) of the particles constituting the powder. At this time, 300 or more particles were selected and analyzed in areas where the particles did not overlap. Next, a particle size distribution based on a volume standard was obtained from the particle diameters obtained. The median particle diameter of the particle size distribution was defined as the average primary particle diameter (D50).

[0055] <SEM Observation (Circularity)> The circularity of the phosphor powder was determined from the SEM image obtained during the primary particle size measurement. Specifically, the SEM image was analyzed using image analysis particle size distribution measurement software, and the area S and perimeter L of the two-dimensional projection image of the particles constituting the powder were measured. In this case, 300 or more particles were selected and measured in areas where the particles did not overlap. The circularity of each particle was then calculated according to the above formula (1), and the arithmetic average value was defined as the circularity of the phosphor powder.

[0056] <XRD Analysis (Crystallite Diameter, Lattice Distortion)> The phosphor powder was analyzed by X-ray diffraction (XRD) to obtain an XRD pattern. The XRD analysis was carried out under the following conditions.

[0057] - X-ray diffractometer: Multipurpose horizontal sample type high-power X-ray diffractometer (Rigaku Corporation, RINT-TTRIII) - Radiation source: CuKα (X-ray wavelength: 0.154056 nm) - Detector: D / teX Ultra 2 - Scan axis: 2θ / θ - Scan range: 5 to 120 deg - Step width: 0.01 deg - Scan speed: 1 deg / min - Entrance slit: 2 / 3° - Tube voltage: 50 kV - Tube current: 300 mA

[0058] Additionally, measurements were performed under the same conditions on SRM660a (compound name: LaB6) manufactured by NIST (National Institute of Standards and Technology). The obtained XRD pattern was analyzed using integrated powder X-ray analysis software (PDXL, Rigaku Corporation) according to the following procedure. First, the pattern was identified using LaB6 using the software's automatic search function, and the "split-type Pearso VII function" was used as the peak shape model function. Next, "Intensity decomposition" was selected under "Precision parameter settings" - "Method" from the "Basic" tab. Next, refinement was performed. During refinement, various parameters were set until convergence was achieved. This was saved as a width standard data file.

[0059] Next, the XRD patterns obtained from each phosphor powder were analyzed to calculate the crystallite size and lattice distortion. The analysis was performed using integrated powder X-ray analysis software (PDXL, Rigaku Corporation) according to the following procedure. First, the crystalline phase was identified using the software's automatic search function. Next, intensity decomposition was performed using WPPF. For line correction, a width standard data file was selected, and the peak angle and width were corrected. The "split-type Pearso VII function" was used as the peak shape model function. Next, from the "Basic" tab, "Precision Parameter Settings" - "Method" was selected to select "Intensity Decomposition." Next, refinement was performed. During refinement, various parameters were set until convergence was achieved.

[0060] <Emission characteristics (absorbance, quantum efficiency)> The absorbance (Abs) and internal quantum efficiency (IQE) of the phosphor powder were determined using a fluorescence spectrophotometer (JASCO, FP-8700DS) according to a quantum efficiency calculation program. The calculation formulas for the absorbance and internal quantum efficiency are shown below.

[0061] P1(λ) was the LED light spectrum at 450 nm, and P2(λ) was the sample spectrum. The area L1 enclosed by the spectrum P1(λ) in the excitation wavelength range of 430 nm to 500 nm was calculated according to the following formula (i), and the obtained value was used as the excitation intensity. The area L2 enclosed by the spectrum P2(λ) in the excitation wavelength range of 430 nm to 500 nm was calculated according to the following formula (ii), and the obtained value was used as the sample scattering intensity. The area E2 enclosed by the spectrum P2(λ) in the excitation wavelength range of 500 nm to 850 nm was calculated according to the following formula (iii), and the obtained value was used as the sample fluorescence intensity.

[0062]

[0063] The absorptance (Abs) is the ratio of the excitation light attenuated by the sample to the incident light, and was calculated according to the following formula (iv): Furthermore, the internal quantum efficiency (IQE) is the lattice number Nem of the fluorescence emitted from the sample divided by the number of photons Nabs of the excitation light absorbed by the sample, and was calculated according to the following formula (v):

[0064]

[0065] (3) Evaluation Results The evaluation results obtained for the phosphor powders of Examples 1 to 8 and Comparative Examples 1 to 4 are summarized in Table 2 below.

[0066] The phosphor powders of Examples 1 to 8 satisfied the composition (0<x≦1-y, 0<y≦0.01), average primary particle size (2.7 μm or less), and crystallite size (155 nm or less) specified in this embodiment. These phosphor powders emitted red light with an emission peak wavelength of 627.0 to 650.6 nm. In addition, the internal quantum efficiency (IQE) was high, at 40% or more. In particular, Examples 1, 2, 4, 5, 7, and 8, which had crystallite sizes of 150 nm or less, had IQEs of 48% or more, and Examples 2, 4, 5, and 8, which had crystallite sizes of 130 nm or less, had IQEs of 50% or more.

[0067] In contrast, Comparative Example 1 does not contain Sr and does not satisfy the composition specified in this embodiment. Comparative Examples 2 and 3 have a large average primary particle size or a large crystallite size, which does not satisfy the range specified in this embodiment. Therefore, Comparative Examples 2 and 3 have a low IQE of 36 to 37%.

[0068] On the other hand, Comparative Example 4, which had both a large average primary particle size and a large crystallite size, had a relatively high IQE of 47%. However, the large average primary particle size may make it difficult to uniformly fill a small package. Therefore, this is not desirable for achieving high-resolution displays.

[0069]

[0070] SEM images of the phosphor powders of Comparative Example 1 and Example 5 are shown in Figures 1 and 2, respectively. The phosphor powders of Comparative Example 1, synthesized by the solid-phase method, and Example 5, synthesized by the liquid-phase method, both had primary particle diameters of about 1 µm. However, the phosphor powder of Comparative Example 1 had a relatively irregular particle shape, whereas the phosphor powder of Example 5 had a particle shape that was relatively close to a perfect sphere.

[0071] From the above results, it can be seen that this embodiment provides a red phosphor powder that has high luminous efficiency despite its small particle size, as well as a light-emitting element and a light-emitting device that include the red phosphor powder.

Claims

1. A red phosphor powder having a main component containing strontium (Sr), sulfur (S), and europium (Eu), an average primary particle diameter by SEM observation of 2.7 μm or less, and a crystallite diameter of 155 nm or less.

2. The main component has a composition represented by the general formula: (Ca １－ｘ－ｙ Sr ｘ )S:Eu ｙ (where 0 < x ≦ 1 - y, 0 < y ≦ 0.01), the red phosphor powder according to claim 1.

3. The main component has a composition represented by the general formula: (Ca １－ｘ－ｙ Sr ｘ )S:Eu ｙ (where 0 < x < 1 - y, 0 < y ≤ 0.01), the red phosphor powder according to claim 1 or 2.

4. The red phosphor powder according to claim 1 or 2, having an internal quantum efficiency (IQE) of 40% or more.

5. A light-emitting element including a light source that generates excitation light and the red phosphor powder according to claim 1 or 2.

6. A light-emitting device including the light-emitting element according to claim 5.

Images