Red fluorescent body powder, light-emitting element, and light-emitting device

Abstract

Provided are: a red fluorescent body powder having a short afterglow time; and a light-emitting element and a light-emitting device which comprise the red fluorescent body powder. This red fluorescent body powder has a main component containing calcium (Ca) and / or strontium (Sr), sulfur (S), and europium (Eu), and contains at least one alkali metal element selected from the group consisting of sodium (Na) and potassium (K).

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 composition of the phosphor. 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' investigations revealed that there was room for improvement in conventional phosphor powders. Specifically, phosphor powders used in applications such as displays are desired to have a short decay time, i.e., short decay characteristics. In displays, adjacent cells (packages) are filled with phosphors that emit different luminescent colors. Furthermore, the luminescent color of each pixel changes rapidly during operation. If the decay time is long, color mixing with the luminescence from adjacent cells may occur, which may result in deterioration of color rendering. In this regard, conventional phosphor powders have limitations in achieving displays with long decay times and excellent color rendering.

[0011] The present inventors have conducted extensive research in light of these problems, and as a result have discovered that the afterglow time of a red phosphor powder can be shortened by adding a specific element to the red phosphor powder having a predetermined composition.

[0012] The present invention was completed based on these findings, and an object of the present invention is to provide a red phosphor powder having a short decay time, and a light emitting element and a light emitting device including the red phosphor powder.

[0013] 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.

[0014] (1) A red phosphor powder having a main component including either or both of calcium (Ca) and strontium (Sr), sulfur (S), and europium (Eu), and containing at least one alkali metal element selected from the group consisting of sodium (Na) and potassium (K).

[0015] (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).

[0016] (3) The red phosphor powder of (1) or (2) above, wherein the molar amount of the alkali metal element relative to the total molar amount of Ca, Sr, Eu and the alkali metal element is 0.10% or more and 10.0% or less.

[0017] (4) The red phosphor powder according to any one of (1) to (3) above, having an internal quantum efficiency (IQE) of 35% or more and a decay time of 13 ms or less.

[0018] (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.

[0019] (6) A light-emitting device comprising the light-emitting element of (5) above.

[0020] According to the present invention, there are provided a red phosphor powder having a short decay time, and a light emitting element and a light emitting device including the red phosphor powder.

[0021] 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.

[0022] <<1. Red Phosphor Powder>> The red phosphor powder of this embodiment (sometimes simply referred to as "phosphor powder") has a main component containing either or both of calcium (Ca) and 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). In other words, the red phosphor powder preferably contains, but is not limited to, a compound (main component compound) represented by the above general formula as its main component. This main component compound has a rock salt type crystal structure. In this specification, the term "main component" refers to a component (compound) that is contained in the phosphor powder at a content ratio of 50% by mass or more. The content ratio of the main component may be 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more.

[0023] The main component compound of the phosphor powder contains a (Ca, Sr)S-based compound as a host crystal and europium (Eu) as a luminescent center. This compound is excited by irradiation light having a wavelength of 420 nm or more and 500 nm or less, and emits red light.

[0024] The ratio of calcium (Ca) to strontium (Sr) contained in the host crystal is not limited. That is, the Sr content x is 0 or more and 1-y or less (0≦x≦1-y). When x is 0, the host crystal becomes a calcium sulfide (CaS)-based compound, and when x is 1-y, the host crystal becomes a strontium sulfide (SrS)-based compound. 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 a SrS-based compound (x=1-y), the maximum emission wavelength is 620 nm. Therefore, by adjusting x within the range of 0 or more and 1-y or less, the maximum emission wavelength can be controlled within the range of 620 nm or more and 655 nm or less.

[0025] 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).

[0026] The red phosphor powder of this embodiment contains at least one alkali metal element selected from the group consisting of sodium (Na) and potassium (K). This shortens the afterglow time. The reason for this is believed to be that the inclusion of an alkali metal element causes defects in the phosphor powder, and these defects suppress the long-life luminescent components (deactivation of the long-afterglow components) in the light emitted from the excited luminescence center (Eu). Although this should not be interpreted in a limiting manner, the following mechanism is thought to be the cause.

[0027] General formula: MS:Eu ２＋(where M is a divalent alkaline earth metal ion, and S is sulfur) may actually have various crystallographic defects. These defects can cause long-life emission. For example, when M is calcium (Ca), Ca is a divalent ion (Ca ２＋ ) in the phosphor. Also, europium (Eu), a rare earth element, is usually present as a divalent ion (Eu ２＋ ) and Ca ２＋ However, Eu is a trivalent ion (Eu ３＋ ) state, so Eu ３＋ Becoming Ca ２＋ In this case, to keep the charge balance between the cations and anions neutral, that is, for charge compensation, Ca ２＋ Ca from the crystal position where ２＋ This type of defect acts as a trapping center that traps holes generated by photoexcitation. The trapped holes are held in the trapping center until they are thermally excited, resulting in light emission with a long time constant. In other words, the decay time is long.

[0028] In contrast, Eu ３＋ Ions and Schottky defects (Ca ２＋ The phosphor further contains monovalent alkali metal ions (AM ＋ ) is added, AM ＋ is Ca ２＋ is substituted to compensate for the Schottky defect. ２＋ Only the emission with a short time constant due to the inherent fd allowed transition is observed, which means that the afterglow time is suppressed from becoming long.

[0029] By the way, the ionic radius of alkali metal ions varies depending on the type. ＋ ) ionic radius (0.102 nm) is Ca ２＋ Therefore, when the phosphor composition is CaS:Eu, the ionic radius of Ca is close to that of CaS:Eu. ２＋ Easily replaces Na ＋It is preferable to use potassium ions (K ＋ ) ionic radius (0.138 nm) is Sr ２＋ Therefore, when the phosphor composition is (Ca, Sr)S:Eu, Sr ２＋ Easily replaces K ＋ can also be used.

[0030] On the other hand, lithium ion (Li ＋ ) has a relatively small ionic radius (0.076 nm). Therefore, it can enter interstitial sites where ions do not exist. ＋ If a trapping center is introduced, it is not possible to cancel out the trapping center. Since light emitted from the phosphor exhibits afterglow, the afterglow time does not shorten. For this reason, in this embodiment, Na or K is used instead of Li as the alkali metal element. The phosphor powder may contain only one or both of Na and K as alkali metal elements. Furthermore, from the viewpoint of increasing the absorption rate, it is preferable to contain both Na and K. In this case, the ratio of Na to K is not particularly limited. For example, Na:K may be 30 mol%:70 mol% to 70 mol%:30 mol%.

[0031] From the viewpoint of shortening the afterglow time, it is desirable that the content of the alkali metal elements (Na, K) is relatively high. The molar amount of the alkali metal elements (Na, K) relative to the total molar amount of Ca, Sr, Eu and the alkali metal elements (molar ratio of the alkali metal elements) is preferably 0.10% or more, more preferably 0.15% or more, and even more preferably 0.17% or more.

[0032] On the other hand, from the viewpoint of improving luminous efficiency, the molar amount of alkali metal elements (Na, K) relative to the total molar amount of Ca, Sr, Eu and alkali metal elements (molar ratio of alkali metal elements) is preferably 10.0% or less, more preferably 7.0% or less, and even more preferably 4.0% or less. Furthermore, from the viewpoint of improving luminous efficiency and shortening the afterglow time, the molar ratio of alkali metal elements is preferably 0.10% or more and 10.0% or less, more preferably 0.15% or more and 7.0% or less, and even more preferably 0.17% or more and 4.0% or less.

[0033] Preferably, the phosphor powder has an internal quantum efficiency (IQE) of 35% or more and a decay time of 13 ms (milliseconds) or less. 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 and a short decay time, a display with high luminous intensity and excellent color rendering can be obtained. The IQE is more preferably 40% or more, and even more preferably 45% or more. There is no upper limit for the IQE.

[0034] The decay time is more preferably 10 ms or less, even more preferably 5.0 ms or less, and particularly preferably 2.5 ms or less. There is no lower limit to the decay time. However, it is typically 0.03 ms or more. In this specification, the term "decay time" refers to the time it takes for the emission intensity to decrease to 3 / 100 of the reference intensity, where the emission intensity at the time when the excitation light is blocked (reference time) is 100%.

[0035] Although not limited thereto, the primary particle diameter (average primary particle diameter, SEM diameter) of the phosphor powder is preferably 3 μm or less, more preferably 1 μm or less. By appropriately reducing the particle diameter of the phosphor powder, it becomes possible to miniaturize the package and thereby increase the resolution of the display. Furthermore, when filling the phosphor powder into the package, it becomes possible to employ an inkjet process, which is effective in reducing manufacturing costs. Meanwhile, the primary particle diameter (SEM diameter) of the phosphor powder is preferably 0.05 μm or more, more preferably 0.1 μm or more. By appropriately increasing the particle diameter of the phosphor powder, the crystallinity of the phosphor particles is improved, the specific surface area of ​​the phosphor particles is reduced, and surface defects of the phosphor particles can be reduced. As a result, a phosphor powder with high luminous efficiency can be obtained. The primary particle diameter is preferably 0.05 μm or more and 3 μm or less, more preferably 0.1 μm or more and 1 μm or less.

[0036] <<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 the above-mentioned requirements are satisfied. 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 also has the advantage of excellent fluidity. Therefore, phosphor powder synthesized by the liquid-phase method is particularly suitable for use in μLED displays.

[0037] 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 one or both of a strontium (Sr) source and a calcium (Ca) 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.

[0038] <Raw Material Mixing Step> In the raw material mixing step, starting materials including one or both of a strontium (Sr) source and a calcium (Ca) 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. Here, the alkali metal is at least one selected from the group consisting of sodium (Na) and potassium (K). The alkali metal has the function of shortening the afterglow time of the phosphor powder.

[0039] 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 ３７The 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.

[0040] <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, ...

[0041] <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. This allows for the addition of sulfur even when the amount of sulfur in the phosphor precursor powder is insufficient.

[0042] <<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.

[0043] 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.

[0044] <<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.

[0045] 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.

[0046] (1) Synthesis of Phosphor Powder [Example 1] In Example 1, phosphor powder was synthesized by a liquid phase method. Specifically, strontium chloride (SrCl 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.

[0047] The resulting starting material solution was then heated to 1000°C with nitrogen (N２ ) 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.

[0048] 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. ２ The 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.

[0049] [Examples 2 to 12] 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 Example 1. In Examples 2 to 11, sodium (Na) was used as the alkali metal element, as in Example 1. On the other hand, in Example 12, sodium (Na) and potassium (K) were used in combination. In this case, potassium chloride (KCl) was used as the starting material for potassium (K). In Example 9, the Sr source (SrCl ２ ), but a Ca source (CaCl ２ ) was not used.

[0050]

[0051] (2) Evaluation of Phosphor Powder Using the phosphor powders obtained in Examples 1 to 12 as samples, various properties were evaluated as follows.

[0052] <ICP analysis method> The sample was completely dissolved by acid decomposition, and the content of each element was confirmed by a calibration curve method using an ICP atomic emission spectrometer (Hitachi High-Tech Science Corporation, PS3520UVDDII). From the content of each element obtained, the molar amount of alkali metal elements relative to the total molar amount of Ca, Sr, Eu, and alkali metal elements (molar ratio of alkali metal elements) was calculated.

[0053] <Primary Particle Diameter> The 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 diameters) 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 primary particle diameter (D50).

[0054] <Emission characteristics (absorbance, quantum efficiency)> Using a fluorescence spectrophotometer (JASCO, FP-8700DS), the absorptance (Abs) and internal quantum efficiency (IQE) of the phosphor powder were determined according to a quantum efficiency calculation program. The calculation formulas for absorptance and internal quantum efficiency are shown below.

[0055] 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.

[0056]

[0057] 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):

[0058]

[0059] <Afterglow Time> The sample was packed into a powder holder and attached to a fixing holder of a fluorescence lifetime photometer (Horiba, Ltd., DeltaFlex). Pulsed LED light (459 nm) was irradiated onto the powder holder, and an emission decay curve at 645 nm was obtained. The emission intensity at the time when the excitation light was blocked (baseline) was defined as 100%, and the time until the emission intensity became 3 / 100 of the baseline was calculated as the afterglow time. The measurements were performed under the following conditions.

[0060] - Method: Multi-channel scaling method - Excitation wavelength: 459 nm (LED pulse) - Excitation filter: 475 SPF - Target emission wavelength: 645 nm - Slit width (band pass): 1 nm, 2 nm - Emission filter: 550 LPF - TAC range setting: 700 ms

[0061] (3) Evaluation Results The evaluation results obtained for the phosphor powders of Examples 1 to 12 are summarized in Table 2 below.

[0062] The phosphor powders of Examples 1 to 12 emitted red light with peak emission wavelengths of 624 to 653.0 nm. They also contained alkali metal elements and had short decay times of 12.9 ms (milliseconds) or less. In particular, Examples 3 to 12, in which the molar ratio of alkali metal elements was between 0.15% and 7.0%, maintained relatively high internal quantum efficiency (IQE) while exhibiting short decay times of 11.5 ms or less. Furthermore, Example 12, in which sodium (Na) and potassium (K) were used in combination as alkali metal elements, exhibited a high absorptivity (Abs) of 79%.

[0063]

[0064] From the above results, it can be seen that this embodiment provides a red phosphor powder with a short decay time, and a light emitting element and a light emitting device including the red phosphor powder.

Claims

1. A red phosphor powder having a main component containing either one or both of calcium (Ca) and strontium (Sr), sulfur (S), and europium (Eu), and containing at least one alkali metal element selected from the group consisting of sodium (Na) and potassium (K).

2. The main component has 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 red phosphor powder according to claim 1 or 2, wherein the molar amount of the alkali metal element with respect to the total molar amount of Ca, Sr, Eu, and the alkali metal element is 0.10% or more and 10.0% or less.

4. The red phosphor powder according to claim 1 or 2, wherein the internal quantum efficiency (IQE) is 35% or more and the afterglow time is 13 ms or less.

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.

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