JP7575658B2 - Alkaline earth aluminate phosphor, light emitting device, and method for manufacturing alkaline earth aluminate phosphor - Google Patents

Description

The present disclosure relates to an alkaline earth aluminate phosphor, a light emitting device, and a method for producing an alkaline earth aluminate phosphor.

A variety of light-emitting devices have been developed that combine excitation light sources such as light-emitting diodes (LEDs) and laser diodes (LDs) with phosphors to emit white light, incandescent light, and other colors based on the principle of light mixing. These light-emitting devices are used in a wide range of fields, including lighting, automotive applications, medical applications, and backlighting for liquid crystal display devices.

In such light emitting devices, various kinds of phosphors are used depending on the purpose. For example, Non-Patent Document 1 (Ruixia Zhong et al. "Red phosphorescence in Sr ₄ Al ₁₄ O ₂₅ : Cr ³⁺ , Eu ³⁺ , Dy ³⁺ through persistent energy transfer" APPLIED PHYSICS LETTERS 88.201916 (2006)) describes an alkaline earth aluminate phosphor represented by Sr ₄ Al ₁₄ O ₂₅ : Cr ³⁺ , Eu ³⁺ , Dy ³⁺ having an emission peak wavelength of 693 nm.

Ruixia Zhong et al. “Red phosphorescence in Sr4Al14O25: Cr3+, Eu3+, Dy3+ through persistent energy transfer” APPLIED PHYSICS LETTERS 88.201916 (2006 )

The present disclosure aims to provide an alkaline earth aluminate phosphor with improved luminescence intensity, a light emitting device, and a method for producing an alkaline earth aluminate phosphor.

The first aspect includes at least one element A selected from the group consisting of alkaline earth metal elements, Al, and Cr, and may include at least one element ^M1 selected from the group consisting of Group 13 elements excluding Al as necessary, and at least one element M2 selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm as necessary, and the molar ratio of the element A is in the range of 1.0 to 4.0, the molar ratio of the sum of the Al and ^the element ^M1 is in the range of 4.0 to 14.0, the molar ratio of the Cr is in the range of 0.004 to 0.8, the molar ratio of the element ^M2 is in the range of 0 to 0.4, the molar ratio of the sum of the Cr and the element ^M2 is in the range of 0.004 to 0.8, and the molar ratio of the element M2 when the molar ratio of the sum of the Al and the element ^M1 is 1 is 1. The alkaline earth aluminate phosphor has a composition in which the molar ratio of 1 to ¹ is 0.7 or less, and has a peak emission wavelength in the range of 720 nm to 900 nm.

The second aspect is a light-emitting device comprising the alkaline earth aluminate phosphor and a light source that irradiates the alkaline earth aluminate phosphor.

The third aspect includes a first compound including at least one element A selected from the group consisting of alkaline earth metal elements, a second compound including Al, and a third compound including Cr, and may include a fourth compound including at least one element M 1 selected from the group consisting of Group 13 elements excluding Al as necessary, and a fifth compound including at least one element ^{M 2} selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er and Tm as necessary, and at least one compound selected from the group consisting of the first compound, the second compound, and the third compound is an oxide, and in 1 mole of composition, the molar ratio of the element A is in the range of 1.0 to 4.0, the molar ratio of the sum of the Al and the element M ¹ is in the range of 4.0 to 14.0, the molar ratio of the Cr is in the range of 0.004 to 0.8, and the molar ratio of the element M ² is in the range of 0 to 0.4, and the Al and the element M preparing a raw material mixture containing the first compound, the second compound, and the third compound, and optionally containing a fourth compound and, optionally, the fifth compound, such that a molar ratio of ^the element ^M1 is 0.7 or less when a molar ratio of the total of the first compound, the second compound, and the third compound is taken as 1; and heat-treating the raw material mixture in a reducing atmosphere at a temperature within a range of 1000° C. or more and 1500° C. or less to obtain an alkaline earth aluminate phosphor.

The present disclosure can provide an alkaline earth aluminate phosphor with improved luminescence intensity, a light-emitting device using the same, and a method for manufacturing the alkaline earth aluminate phosphor.

FIG. 1 is a diagram showing the emission spectrum of the alkaline earth aluminate phosphor of Example 1 and the emission spectrum of a compound having the alkaline earth aluminate composition of Comparative Example 1. FIG. 2 is a diagram showing the excitation spectrum of the alkaline earth aluminate phosphor according to Example 1. FIG. 3 is a diagram showing the emission spectra of the alkaline earth aluminate phosphors according to Examples 4, 5 and 6, and the emission spectrum of a compound having the alkaline earth aluminate composition according to Comparative Example 2.

The alkaline earth aluminate phosphor, light emitting device, and method for manufacturing an alkaline earth aluminate phosphor according to the present invention will be described below. However, the following embodiments are merely examples for embodying the technical concept of the present invention, and the present invention is not limited to the following alkaline earth aluminate phosphor, light emitting device, and method for manufacturing an alkaline earth aluminate phosphor. The relationship between color names and chromaticity coordinates, the relationship between the wavelength range of light and the color name of monochromatic light, etc., conform to JIS Z8110. In this specification, in the formula representing the composition of the phosphor, a plurality of elements separated by a comma (,) indicate that at least one of these elements is contained in the composition, and two or more elements may be contained in combination. In this specification, in the formula representing the composition of the phosphor, the elements before the colon (:) represent the elements constituting the host crystal and their molar ratio, and the elements after the colon (:) represent the activating element. In this specification, the "molar ratio" represents the ratio of each element in 1 mole of the chemical composition of the compound or phosphor, unless otherwise specified.

Light-emitting devices using phosphors are required to emit optimal light depending on the visual target. For example, in medical settings, it may be required to easily obtain information inside a living body. The living body contains light absorbers such as water, hemoglobin, and melanin. For example, hemoglobin has a high absorption rate of light in the visible light range with a wavelength of less than 650 nm, and it is difficult for light-emitting devices that emit light in the visible light range to penetrate the living body, making it difficult to obtain information inside the living body. Therefore, there may be a need for a light-emitting device that emits light in the near-infrared wavelength range of 650 nm to 1000 nm, which is called the "biological window" through which light can easily penetrate inside the living body. For example, if it is possible to measure the increase or decrease in the oxygen concentration in blood inside a living body by the increase or decrease in the absorption of light by hemoglobin that binds to oxygen, it will be possible to easily obtain information inside the living body by irradiating light from a light-emitting device.

In addition, in the midst of environmental changes such as climate change, it is desirable to stably supply plants such as vegetables and to increase plant production efficiency. Plant factories that allow artificial management can stably supply safe vegetables to the market and are expected to be the next generation industry. In such plant factories, a light emitting device that irradiates light that can promote plant growth is required. The reaction of plants to light can be divided into photosynthesis and photomorphogenesis. Photosynthesis is a reaction that uses light energy to decompose water, generate oxygen, and fix carbon dioxide to organic matter, and is a reaction necessary for plant growth. Photomorphogenesis is a morphological reaction that uses light as a signal to perform seed germination, differentiation (germination formation, leaf formation, etc.), movement (stoma opening and closing, chloroplast movement), light refraction, etc. It has been found that light in the wavelength range of 690 nm to 800 nm affects the photoreceptors of plants in photomorphogenesis reactions. For this reason, light-emitting devices used in plant factories and the like may be required to be capable of emitting light in a wavelength range that affects plant photoreceptors (chlorophyll a, chlorophyll b, carotenoids, phytochromes, cryptochromes, phototropins) and promotes plant growth.
Regarding the alkaline earth aluminate phosphors described above, when they are combined with an excitation light source such as a light emitting diode (LED) or a laser diode (LD) to form a light emitting device, there is room for improving the light emitting characteristics of the phosphor so that the device becomes a light source suitable for these applications.

Alkaline earth aluminate phosphor The alkaline earth aluminate phosphor according to the first embodiment includes at least one element A selected from the group consisting of alkaline earth metal elements, Al, and Cr, and may include at least one element M1 selected from the group consisting of Group 13 elements excluding Al as necessary, and at least one element ^M2 selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm as necessary, in which a molar ratio of the element ^A is within a range of 1.0 to 4.0, a molar ratio of the sum of the Al and the element ^M1 is within a range of 4.0 to 14.0, a molar ratio of the Cr is within a range of 0.004 to 0.8, a molar ratio of the element ^M2 is within a range of 0 to 0.4, a molar ratio of the sum of the Cr and the element ^M2 is within a range of 0.004 to 0.8, and the element M2 is within a range of 0 to 0.4 when the molar ratio of the sum of the Al and the element ^M1 is taken as 1. The alkaline earth aluminate phosphor has a composition in which the molar ratio of 1 to ¹ is 0.70 or less, and has an emission peak wavelength in the range of 720 nm to 900 nm. The alkaline earth aluminate phosphor can absorb excitation light and emit light having an emission peak wavelength in the range of 720 nm to 900 nm, emit light having an emission peak wavelength in the near-infrared wavelength range called the "biological window," and emit light that affects the photoreceptors of plants. In this specification, the near-infrared wavelength range refers to the wavelength range of 700 nm to 2500 nm.

The alkaline earth aluminate phosphor preferably has a composition represented by the following formula (I) containing elements A, Al, Cr, and optionally contained element ^M1 and optionally contained element ^M2 .
A _x (Al _1-y M ¹ _y ) _z O _{x + 3/2z} : Cr _v , M ² _w (I)
(In formula (I), A is at least one element selected from the group consisting of alkaline earth metal elements, ^M1 is at least one element selected from the group consisting of Group 13 elements excluding Al, ^M2 is at least one element selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm, and v, w, x, y, and z satisfy 0.004≦v≦0.8, 0≦w≦0.4, 0.004≦v+w≦0.8, 1.0≦4.0, 0≦y≦0.7, and 4.0≦z≦14.0.)

By firing the alkaline earth aluminate phosphor having the above-mentioned composition in a reducing atmosphere, the activator Cr has a trivalent valence and easily enters the host crystal of the alkaline earth aluminate phosphor, so that it can absorb the excitation light and emit light with an emission peak wavelength in the range of 720 nm to 900 nm.

The element A is at least one element selected from the group consisting of alkaline earth metal elements, and may contain two or more elements. The element A may be at least one element selected from the group consisting of Ca, Sr, and Ba. The element A may contain two or more elements selected from the group consisting of alkaline earth metal elements. The element A may be Sr, or may be Sr and Ca. When the element A contains two or more elements A ^a and A ^b selected from the group consisting of alkaline earth metal elements, the molar ratio of the element A ^a to the element A ^b (A ^{a /} A ^{b )} may be 1/9 or more or 9/1 or less when the molar ratio of the sum of the element A ^a and the element A ^b is 10. The molar ratio x of element A in the composition of the alkaline earth aluminate phosphor is in the range of 1.0 to 4.0, and is preferably 4 when the molar ratio of Al plus element ^M1 in 1 mole of the alkaline earth aluminate composition is 14.

When element A includes two or more elements selected from the group consisting of alkaline earth metal elements, the alkaline earth aluminate phosphor may have a composition represented by the following formula (I-1).
(A ^a _1-u A ^b _u ) _x (Al _1-y M ¹ _y ) _z O _x+3/2z :Cr _v , M ² _w (I-1)
(In formula (I-1), A ^a is one element selected from the group consisting of alkaline earth metal elements, A ^b is one element selected from the group consisting of alkaline earth metal elements excluding A ^a , M ¹ is at least one element selected from the group consisting of Group 13 elements excluding Al, M ² is at least one element selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er and Tm, and u, v, w, x, y and z satisfy 0.1≦u≦0.9, 0.004≦v≦0.8, 0≦w≦0.4, 0.004≦v+w≦0.8, 1.0 ≦x ≦4.0, 0≦y≦0.7, 4.0≦z≦14.0.)

The Al contained in the composition of the alkaline earth aluminate phosphor, together with the element A and oxygen (O), constitutes a crystal skeleton that becomes the host crystal of the alkaline earth aluminate phosphor. Even when the composition of the alkaline earth aluminate phosphor contains at least one element ^M1 selected from the group consisting of elements of group 13 except Al in addition to Al, if the molar ratio z of the sum of Al and element ^M1 is within the range of 4.0 to 14.0 (4.0≦z≦14.0), the crystal skeleton of the host crystal of the alkaline earth aluminate phosphor is formed. When the composition of the alkaline earth aluminate phosphor contains element ^M1 , it is preferable that the Al is contained at least 0.3 moles when the molar ratio of Al and element ^M1 is 1. If the Al is contained at least 0.3 moles when the molar ratio of Al and element ^M1 is 1, a stable crystal structure can be maintained.

When the element ^M1 is included in the composition of the alkaline earth aluminate phosphor, it is preferably at least one element selected from the group consisting of group 13 elements except Al. The element ^M1 is preferably at least one element selected from the group consisting of B, Ga, In, and Tl, more preferably at least one element selected from the group consisting of B, Ga, and In, and may be at least one element selected from the group consisting of B and Ga, or may be Ga. The element ^M1 included in the composition of the alkaline earth aluminate phosphor is preferably such that the molar ratio y of the element ^M1 when the sum of Al and the element ^M1 in the composition is 1 is in the range of 0 to 0.7 (0≦y≦0.7), and may be in the range of 0.1 to 0.7 (0.1≦y≦0.7), or may be in the range of 0.2 to 0.6 (0.2≦y≦0.6).

When the composition of the alkaline earth aluminate phosphor contains the element ^M1 and the molar ratio y of the element ^M1 is within the range of 0.1 to 0.7 (0.1≦y≦0.7) when the sum of Al and the element ^M1 in the composition is taken as 1, the emission wavelength and shape can be changed without significantly decreasing the luminous efficiency.

In the composition of the alkaline earth aluminate phosphor, the element A may be at least one element selected from the group consisting of Ca, Sr, and Ba, and the element ^M1 may be at least one element selected from the group consisting of Ba, Ga, and In. In addition, in the composition of the alkaline earth aluminate phosphor, the element A may be Sr, and the element ^M1 may be Ga.

The alkaline earth aluminate phosphor contains Cr, which is an activating element, and the molar ratio v of Cr in 1 mole of the composition of the alkaline earth aluminate phosphor is preferably in the range of 0.004 to 0.8 (0.004≦v≦0.8), may be in the range of 0.005 to 0.7 (0.005≦v≦0.7), may be in the range of 0.008 to 0.6 (0.008≦v≦0.6), or may be in the range of 0.010 to 0.5 (0.010≦v≦0.5). When the alkaline earth aluminate phosphor contains Cr, which is an activating element, and the molar ratio of Cr in 1 mole of the composition of the alkaline earth aluminate phosphor is in the range of 0.004 to 0.8, a phosphor that emits light having an emission peak wavelength in the range of 720 nm to 900 nm is obtained.

The alkaline earth aluminate phosphor may contain at least one element M2 selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er and Tm as a coactivator element in addition to Cr. When the alkaline earth aluminate phosphor contains the element ^M2 , a characteristic emission due to the inclusion of the element ^M2 is obtained. For example, when the element ^M2 is contained, the emission peak wavelength may be in a wavelength range different from that of an alkaline earth metal aluminate phosphor containing only Cr. The alkaline earth aluminate phosphor may contain ^the element ^M2 as a coactivator element in its composition, and the molar ratio of the element ^M2 may be in the range of 0 to 0.4 (0≦w≦0.4) or in the range of 0.1 to 0.3 (0.1≦w≦0.3). In the composition of the alkaline earth aluminate phosphor, the molar ratio of Cr and the element ^M2 in total is in the range of 0.004 to 0.8.

In the emission spectrum of the alkaline earth aluminate phosphor, the half-width of the emission peak wavelength in the range of 720 nm to 900 nm is preferably 80 nm or more, and may be 90 nm or more, 150 nm or less, or 120 nm or less. When light having an emission peak wavelength in the range of 720 nm to 900 nm is emitted from the alkaline earth aluminate phosphor, for example, information on the increase or decrease in the oxygen concentration in blood in a living body can be obtained by the increase or decrease in the absorption of light by hemoglobin that binds to oxygen. In a living body, light is absorbed and scattered, and in order to measure subtle changes in the propagation behavior of light in blood in a living body, it is preferable that the half-width of the emission peak in the range of 720 nm to 900 nm emitted from the light-emitting device is wide. In addition, it is desirable for the color of an object to appear when irradiated with light (hereinafter also referred to as "color rendering") to have an emission spectrum in a wide range, and a wide half-width can emit light with excellent color rendering. For example, in a plant factory, even when emitting light in a wavelength range that affects plant growth, it may be required to emit light that does not disrupt the spectral balance of light so that workers can work easily. In the emission spectrum of an alkaline earth aluminate phosphor, if the half-width of the emission peak in the range of 720 nm to 900 nm is 80 nm or more and 150 nm or less, the color rendering can be improved. The half-width refers to the full width at half maximum of the emission peak in the emission spectrum, and refers to the wavelength width of the emission peak that shows 50% of the maximum value of the emission peak in the emission spectrum.

The light emitting device includes an alkaline earth aluminate phosphor and a light source that irradiates the alkaline earth aluminate phosphor. The aluminate phosphor according to one embodiment of the present invention can be used as a member that constitutes a wavelength conversion member together with a light-transmitting material.

The light emitting device preferably includes a light emitting element, such as an LED or LD, as a light source, and a wavelength conversion member containing an alkaline earth aluminate phosphor that emits light when irradiated with light from the light emitting element.

The light emitting element may be, for example, an LED chip or an LD chip, which is a semiconductor light emitting element using a nitride semiconductor.
The light-emitting element preferably has an emission peak wavelength in the range of 380 nm or more and 500 nm or less, more preferably has an emission peak wavelength in the range of 390 nm or more and 495 nm or less, even more preferably has an emission peak wavelength in the range of 400 nm or more and 490 nm or less, and particularly preferably has an emission peak wavelength in the range of 420 nm or more and 490 nm or less.

The wavelength conversion member includes an alkaline earth aluminate phosphor and a translucent material.

In addition to the alkaline earth aluminate phosphor and the translucent material, other phosphors other than the alkaline earth aluminate phosphor may be included.

The first phosphor may be an alkaline earth aluminate phosphor, and the second phosphor may have an emission peak wavelength different from that of the first phosphor. The second phosphor may be one type of phosphor used alone, or two or more types of phosphors may be used in combination. Examples of the second phosphor include a phosphor having a composition represented by the following formula:
M ¹ ₁₀ (PO ₄ ) ₆ Cl ₂ :Eu (i)
(In formula (i), ^M1 is at least one element selected from the group consisting of Ca, Sr, and Ba.)
^M2MgAl10O17 : _{Mn ,} Eu (ii)
(In formula (ii), ^M2 is at least one element selected from the group consisting of Ba and Sr.)
M ³ ₈ MgSi ₄ O ₁₆ Cl ₂ :Eu (iii)
(In formula (iii), ^M3 is at least one element selected from the group consisting of Ca, Sr, and Ba.)
Sr ₄ Al ₁₄ O ₂₅ :Eu (iv)
M ⁴ ₃ M ⁵ ₅ O ₁₂ :Ce (v)
(In formula (v), ^M4 is at least one element selected from the group consisting of Y and Gd, and ^M5 is at least one element selected from the group consisting of Al and Ga.)
Lu ₃ M ⁶ ₅ O ₁₂ :Ce (vi)
(In formula (vi), ^M6 is at least one element selected from the group consisting of Al and Ga.)
Si _6-z Al _z O _z N _8-z :Eu (vii)
(In formula (vii), z satisfies 0<z≦4.2.)
M ⁷ AlSiN ₃ :Eu (viii)
(In formula (viii), ^M7 is at least one element selected from the group consisting of Sr and Ca.)

The translucent material may be at least one selected from the group consisting of resin, glass, and inorganic material. The resin is preferably at least one selected from the group consisting of epoxy resin, silicone resin, phenolic resin, and polyimide resin. The inorganic material may be at least one selected from the group consisting of aluminum oxide and aluminum nitride. In addition to the phosphor and the translucent material, the wavelength conversion member may contain a filler, a colorant, and a light diffusing material as necessary. Examples of the filler include silicon oxide, barium titanate, titanium oxide, and aluminum oxide.

3. Method for manufacturing alkaline earth aluminate The method for manufacturing an alkaline earth aluminate phosphor according to the third embodiment includes a first compound including at least one element A selected from the group consisting of alkaline earth metals, a second compound including Al, and a third compound including Cr, and may include a fourth compound including at least one element ^M1 selected from the group consisting of Group 13 elements excluding Al as required, and a fifth compound including at least one element ^M2 selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm as required, wherein at least one compound selected from the group consisting of the first compound, the second compound, and the third compound is an oxide, and in 1 mole of composition, the molar ratio of the element A is within a range of 1.0 to 4.0, the molar ratio of the sum of the Al and the element ^M1 is within a range of 4.0 to 14.0, the molar ratio of the Cr is within a range of 0.004 to 0.8, and the element M the molar ratio of the ^Cr and the element M2 being within a range of 0 or more and 0.4 or less, the molar ratio of the sum of the Cr and ^the element ^M2 being within a range of 0.004 or more and 0.8 or less, and the molar ratio of the element ^M1 being 0.7 or less when the molar ratio of the sum of the Al and the element M1 is 1; and the step of heat-treating the raw material mixture in a reducing atmosphere at a temperature within a range of 1000° C. or more and 1500° C. or less to obtain an alkaline earth aluminate phosphor.

Preparation of raw material mixture Raw materials The raw materials for producing an alkaline earth aluminate phosphor include a first compound containing element A, a second compound containing Al, and a third compound containing Cr. The first compound, the second compound, and the third compound each include nitrides, hydrides, fluorides, oxides, carbonates, chlorides, and hydrates thereof. At least one compound selected from the group consisting of the first compound, the second compound, and the third compound is an oxide, and two or more of them may be oxides. The second compound and the third compound may be oxides. Specific examples of the first compound include _Ca3N2 , _CaH2 , _CaF2 , _CaO , _CaCO3 , _CaCl2 , _SrH2 , _Sr3N2 , _Sr2N , _SrN , _SrF2 , _SrO , _SrCO3 , _SrCl2 , _Ba3N2 , _BaF2 , BaO, _BaCO3 , _BaCl2 , etc. Specific examples of the second compound include AlN, _AlF3 , _Al2O3 , _{AlCl3 ,} etc. Specific examples _of the third compound include CrN _{, CrF3} , _Cr2O3 , _Cr2 ( _CO3 ) ₃ , _CrCl3.6H2O . When the element A is at least one element selected from the group consisting of Ca, Sr, and Ba, the first compound is preferably at least one compound selected from the group consisting of a compound containing Ca, a compound containing Sr, and a compound containing Ba. When the element A is Sr, the first compound is preferably a compound containing Sr.

The fourth compound containing the element ^M1 may be a nitride, a hydride, a fluoride, a bromide, an oxide, a carbonate, a chloride, or a hydrate thereof, containing the element ^M1 . The fourth compound may be an oxide. The fourth compound is preferably a solid, and specifically includes BN, _{B2O3 , BCl3} , _GaN , GaBr3 _{, Ga2O3} , _InBr3 , _In2O3 , _{InCl3, Tl2O3 ,} and _TlF3 . When the element ^M1 is at least one selected from the group consisting of B, _Ga , _and In, the fourth compound is preferably at least one compound selected from the group consisting of a compound containing B, a compound containing Ga, and a compound containing In. When the element ^M1 is Ga, the fourth compound is preferably a compound containing Ga.

The fifth compound containing the element ^M2 may be a nitride, a hydride, a fluoride, a bromide, an oxide, a carbonate, a chloride, or a hydrate thereof, which contains the element ^M2 . The fifth compound may be an oxide. _The fifth compound is preferably _{a solid} , and specifically, _MnO2 , _Eu2O3 , _EuCl3.6H2O , _CeCl3.7H2O , _{CeO2 , TbCl3.6H2O , Tb4O7 , PrCl3.7H2O} , _PrF3 , _Pr6O11 , _NdCl3.6H2O , Nd2O3 _{, SmCl3.6H2O} , _{SmF3 , Sm2O3 , YbF3 , Yb2O3 , Ho2O3 , ErCl3.6H2O , Er2O3 , ErF3 , TmCl3.6H2O , TmF3 .} , _{Tm2O3 .}

Raw material mixture Each compound to be a raw material is weighed out so that the molar ratio of each element in 1 mole of the composition is a specific value, and then the weighed raw material compounds are mixed in a mixer in a wet or dry manner to obtain a raw material mixture. As the mixer, in addition to a ball mill that is commonly used industrially, a vibration mill, a roll mill, a jet mill, etc. can be used.

It is preferable to prepare a raw material mixture containing each compound, which is measured so that the elements A, Al, and Cr contained in each compound, and the elements ^M1 and ^M2 which may be contained as necessary, have the composition represented by the formula (I). When the element A contains two or more elements ^Aa and ^Ab , it is preferable to prepare a raw material mixture containing a compound containing the element ^Aa , a compound containing the element ^Ab , and other compounds, which are measured so as to have the composition represented by the formula (I-1).

Flux The raw material mixture may contain a flux. By including a flux in the raw material mixture, the reaction between the raw materials is promoted, and furthermore, the solid-phase reaction proceeds more uniformly, so that a phosphor having a large particle size and excellent luminescence characteristics can be obtained. When the temperature of the heat treatment for obtaining the phosphor is about the same as the temperature at which the liquid phase of the compound used as the flux is generated, the flux promotes the reaction between the raw materials. As the flux, a halide containing at least one element selected from the group consisting of rare earth metal elements, alkaline earth metal elements, and alkali metal elements can be used. As the flux, among the halides, a fluoride can be used. When the element contained in the flux is the same element as at least a part of the elements constituting the alkaline earth aluminate phosphor, the flux can be added as a part of the raw materials of the alkaline earth aluminate phosphor having the desired composition so that the composition of the alkaline earth aluminate phosphor becomes the desired composition, or the flux can be added by further adding after mixing the raw materials so as to obtain the desired composition.

Step of obtaining alkaline earth aluminate phosphor by heat treatment The raw material mixture can be placed in a crucible or boat made of a material such as carbon such as graphite, boron _nitride (BN), alumina ( _Al2O3 ), tungsten (W), molybdenum (Mo), or the like, and heat-treated in a furnace.

Heat Treatment Atmosphere The heat treatment is performed in a reducing atmosphere. The reducing atmosphere may be a hydrogen-nitrogen atmosphere containing hydrogen gas having reducing properties and nitrogen gas. The hydrogen-nitrogen atmosphere may contain nitrogen gas preferably at 70 vol% or more, 80 vol% or more, or 90 vol% or more. The hydrogen-nitrogen atmosphere may contain hydrogen gas at 1 vol% or more, 2 vol% or more, 3 vol% or more, or 10 vol% or less.

Heat Treatment Temperature The heat treatment temperature is within the range of 1000° C. to 1500° C., preferably 1100° C. to 1450° C., and more preferably 1200° C. to 1400° C. If the heat treatment temperature is 1000° C. to 1500° C., decomposition due to heat is suppressed, and a phosphor having a desired composition and a stable crystal structure can be obtained.

The heat treatment may be performed in two or more stages. For example, when performing a two-stage heat treatment, the first heat treatment may be performed at a temperature between 1000°C and 1500°C, and the second heat treatment may be performed at a temperature between 1200°C and 1400°C. If the first heat treatment temperature is between 1000°C and 1500°C, it is easier to obtain a heat-treated product having the desired composition. If the second heat treatment temperature is between 1200°C and 1400°C, it is possible to obtain a phosphor having a stable crystal structure.

In the heat treatment, a holding time may be set at a predetermined temperature. For example, between the first and second heat treatments, a holding time may be set at a temperature of about room temperature, between 20°C and 28°C. The holding time may be, for example, between 0.5 hours and 48 hours, between 1 hour and 40 hours, or between 2 hours and 30 hours. By setting the holding time to between 0.5 hours and 48 hours, crystal growth can be promoted.

The pressure of the heat treatment atmosphere may be standard atmospheric pressure (0.101 MPa) or may be 0.101 MPa or more, and is preferably performed in a pressurized atmosphere of 0.11 MPa to 200 MPa. The higher the heat treatment temperature, the more easily the crystal structure of the heat-treated product obtained by heat treatment is decomposed. However, by using a pressurized atmosphere, the decomposition of the crystal structure is suppressed and the decrease in luminescence intensity can be suppressed. The pressure of the heat treatment atmosphere is, in terms of gauge pressure, more preferably 0.11 MPa to 100 MPa, even more preferably 0.5 MPa to 10 MPa, and from the viewpoint of ease of production, even more preferably 1.0 MPa or less.

The heat treatment time can be appropriately selected depending on the heat treatment temperature and the pressure of the atmosphere during the heat treatment, and is preferably 0.5 to 20 hours. Even when two or more stages of heat treatment are performed, it is preferable that the heat treatment time for each stage is 0.5 to 20 hours. If the heat treatment time is 0.5 to 20 hours, decomposition of the heat-treated product is suppressed, and a phosphor having a stable crystal structure and the desired emission intensity can be obtained. In addition, production costs can be reduced and the manufacturing time can be relatively short. The heat treatment time is more preferably 1 to 10 hours, and even more preferably 1.5 to 9 hours.

The heat-treated product obtained by the heat treatment may be subjected to post-treatment such as pulverization, dispersion, solid-liquid separation, drying, etc. Solid-liquid separation can be carried out by a method commonly used in industry, such as filtration, suction filtration, pressure filtration, centrifugation, decantation, etc. Drying can be carried out by a device commonly used in industry, such as a vacuum dryer, a hot air heating dryer, a conical dryer, a rotary evaporator, etc.

The present invention will be described in detail below with reference to examples. The present invention is not limited to these examples.

Example 1
As raw materials, _SrCO3 was weighed out to 8.86g, _{Al2O3 was} weighed out to 10.71g, _{and Cr2O3} was weighed out to _0.14g . Each raw material was weighed out to have a composition of _Sr4Al14O25 : _Cr0.12 . Each raw material was mixed for 10 minutes using an _agate mortar and an agate pestle to obtain a raw material mixture. The obtained raw material mixture was heat-treated for 8 hours at 1300°C, standard pressure (0.101MPa), in a hydrogen-nitrogen atmosphere containing hydrogen gas and nitrogen gas (hydrogen: 3% by volume, nitrogen: 97% by volume). After the heat treatment, the obtained heat-treated product was pulverized to obtain the alkaline earth aluminate phosphor of Example 1.

Example 2
The raw materials were weighed out so that the amounts were 6.01 _g of CaCO3, 10.71 _g of _{Al2O3 ,} and 0.15 _g of _Cr2O3 . An _alkaline earth aluminate phosphor of Example 2 was obtained in the same manner as in Example 1, except that the raw materials were used so that the charged composition was _Ca4Al14O25 : _Cr0.12 .

Example 3
The raw materials were weighed out so that the amounts were 4.43 _g of SrCO3, 3.01 _g of CaCO3, 10.71 _g of _Al2O3 , and 0.14 _g of _Cr2O3 . The alkaline earth aluminate phosphor of Example ₃ was obtained in the same manner as in Example ₁ , except that the raw materials were weighed out so that the composition was ( _Sr0.5Ca0.5 ) _4Al14O25 : _Cr0.12 , and the heat treatment temperature was ₁₂₅₀ °C.

Example 4
As raw materials, 8.86g of _SrCO3 , 7.66g _{of Al2O3} , 5.64g _{of Ga2O3} , and 0.14g _{of Cr2O3} were weighed. The alkaline earth aluminate phosphor of Example ₄ was obtained in the same manner as in Example ₁ , except that the raw materials were weighed and used so that the composition of the raw materials was _{Sr4Al10Ga4O25} : _Cr0.12 , and the heat treatment temperature was 1250°C. The molar ratio of element _M1 (Ga) in the raw material composition when the molar ratio of the sum of Al and element ^M1 (Ga) was ¹ is shown in Table 1. Table 1 also shows the molar ratios of element M ^{1 (Ga) in the alkaline earth aluminate phosphors and compounds having the alkaline earth aluminate compositions of Examples 1 to 3, Examples 5 and 6 described below, and Comparative Examples 1 and 2, when the molar ratio of the sum of Al and element M 1 (} Ga) is taken as 1.

Example 5
The raw materials were weighed out to be 8.86 _g of SrCO3, 5.36 _g of _Al2O3 , 9.86 g _{of Ga2O3} , and 0.14 g of _Cr2O3 . The alkaline earth aluminate _phosphor of Example ₅ was obtained in the same manner as in Example 1, except that the raw materials were weighed out to be used so that _the composition was _Sr4Al7Ga7O25 : _{Cr0.12 ,} and the heat treatment temperature was 1200°C.

Example 6
The raw materials were weighed out to be 8.86 _g of SrCO3, 4.60 _g of _Al2O3 , 11.27 g _{of Ga2O3} , and 0.14 g _{of Cr2O3} . The alkaline earth aluminate _phosphor of Example ₆ was obtained in the same manner as in Example 1, except that the raw materials were weighed out to be used so that _the composition was _Sr4Al6Ga8O25 : _Cr0.12 , and the heat treatment temperature was 1200°C.

Comparative Example 1
A compound having the composition of the alkaline earth aluminate of Comparative Example 1 was obtained in the same manner as in Example 1, except that the heat treatment was performed in an air atmosphere (oxygen: about 20 vol %, nitrogen: about 78 vol %).

Comparative Example 2
The raw materials were weighed out to be 8.86 _g of SrCO3, 3.07 _g of _Al2O3 , 14.09 g _{of Ga2O3} , and 0.14 g of _Cr2O3 . Each raw material was weighed out to be _{Sr4Al4Ga10O25 : Cr0.12} , and the heat treatment temperature was 1200°C _. Except for _this , a compound having the composition of the alkaline earth aluminate of Comparative Example 2 was obtained in the same manner as _in Example 1.

Measurement of Emission Spectrum The emission spectrum of each alkaline earth aluminate phosphor of the Examples and the compound having the composition of each alkaline earth aluminate of the Comparative Examples was measured using a quantum efficiency measurement system (QE-2000, manufactured by Otsuka Electronics Co., Ltd.). The emission peak wavelength of the excitation light used in the quantum efficiency measurement system was 450 nm. From each obtained emission spectrum, the emission peak wavelength (nm) and the half width (nm) at the emission peak in the range of 720 nm to 900 nm were obtained. The results are shown in Table 1. In addition, the emission intensity at the emission peak wavelength of Example 2 was set to 100%, and the relative emission intensity (%) at the emission peak wavelength of the alkaline earth aluminate phosphor of the Examples and the compound having the composition of each alkaline earth aluminate of the Comparative Examples was measured. The results are shown in Table 1. FIG. 1 shows the emission spectrum of the alkaline earth aluminate phosphor of Example 1 and the emission spectrum of the compound having the composition of alkaline earth aluminate of Comparative Example 1. FIG. 3 shows the emission spectra of the alkaline earth aluminate phosphors according to Examples 4, 5 and 6, and the emission spectrum of a compound having the alkaline earth aluminate composition according to Comparative Example 2.

Measurement of Excitation Spectrum The excitation spectrum of the alkaline earth aluminate phosphor according to Example 1 was measured using a spectrofluorophotometer (F-4500, manufactured by Hitachi High-Technologies Corporation) at an emission wavelength of 791 nm, at 25° C.±5° C. (room temperature), in the range of 350 nm to 700 nm. FIG. 2 shows the excitation spectrum of the alkaline earth aluminate phosphor according to Example 1.

The alkaline earth aluminate phosphors according to Examples 1 to 6 have a peak emission wavelength in the range of 720 nm to 900 nm in the emission spectrum, and show a wide emission peak with a half-width of 80 nm or more. From these results, it can be seen that the alkaline earth aluminate phosphors according to Examples 1 to 6 can emit light having a peak emission wavelength in the near-infrared wavelength range known as the "biological window," and can emit light that has an effect on the photoreceptors of plants.

As shown in Figures 1 and 3, each of the alkaline earth aluminate phosphors according to Examples 1 and 4 to 6 had an emission peak wavelength in the range of 720 nm to 900 nm, and a wide half-width of 80 nm or more.

As shown in Figure 2, the alkaline earth aluminate phosphor of Example 1 has an excitation spectrum in the wavelength range of 350 nm to 700 nm, in which the relative intensity is high in the wavelength range of 400 nm to 450 nm and in the wavelength range of 550 nm to 580 nm. This result shows that by selecting the emission peak wavelength of the excitation light source, the alkaline earth aluminate phosphor can efficiently emit light having an emission peak wavelength in the range of 720 nm to 900 nm.

The compounds having the alkaline earth aluminate composition according to Comparative Examples 1 and 2 emitted almost no light even when irradiated with light having an emission peak wavelength of 450 nm.

The alkaline earth aluminate phosphor of the present disclosure can be used in light-emitting devices used in lighting devices, backlights for liquid crystal display devices, and the like. The alkaline earth aluminate phosphor of one embodiment of the present invention can also be used in light-emitting devices for medical lighting to obtain information from within living organisms, and light-emitting devices for plant cultivation that affect the photoreceptors of plants.

Claims (15)

An alkaline earth aluminate phosphor comprising at least one element A selected from the group consisting of alkaline earth metal elements, Al, and Cr, and optionally comprising at least one element ^M1 selected from the group consisting of Group 13 elements excluding Al, and optionally comprising at least one element ^M2 selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm, wherein the element A, Al, Cr, and the elements M1 and ^{M2 which} are included as necessary have a composition represented by the following formula (I) , and has an emission peak wavelength in the range of 720 nm to 900 nm.
A _x (Al _1-y M ¹ _y ) _z O _{x + 3/2z} : Cr _v ,M ² _w (I)
(In the formula (I), v, w, x, y, and z satisfy 0.004≦v≦0.8, 0≦w≦0.4, 0.004≦v+w≦0.8, x=4.0, 0≦y≦0.7, and 4.0≦z≦14.0.) 2. The alkaline earth aluminate phosphor according to claim 1, wherein when the element A contains two or more elements selected from the group consisting of alkaline earth metal elements, the phosphor has a composition represented by the following formula (I-1):
(A ^a _1-u A ^b _u ) _x (Al _1-y M ¹ _y ) _Z O _{x + 3/2z} : Cr _v , M ² _W (I-1)
(In formula (I-1), A ^a is an element selected from the group consisting of alkaline earth metal elements, A ^b A ^a An element selected from the group consisting of alkaline earth metal elements excluding M ¹ is at least one element selected from the group consisting of Group 13 elements excluding Al, M ² is at least one element selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm, and u, v, w, x, y, and z satisfy 0.1≦u≦0.9, 0.004≦v≦0.8, 0≦w≦0.4, 0.004≦v+w≦0.8, x=4.0, 0≦y≦0.7, 4.0≦z≦14.0. 3. The alkaline earth aluminate phosphor according to claim 1, wherein the element A is at least one element selected from the group consisting of Ca, Sr and Ba, and the element ^M1 is at least one element selected from the group consisting of B, Ga and In. 3. The alkaline earth aluminate phosphor according to claim 1, wherein the element A is Sr and the element ^M1 is Ga. The alkaline earth aluminate phosphor according to any one of claims 1 to 4, having an emission peak wavelength in the range of 720 nm to 900 nm and an emission spectrum with a half-width of 80 nm or more. 6. The alkaline earth aluminate phosphor according to claim 1, wherein z=14.0 in formula (I) or formula (I-1). A light emitting device comprising: the alkaline earth aluminate phosphor according to claim 1 ; and a light source for irradiating the alkaline earth aluminate phosphor. The composition may include a first compound including at least one element A selected from the group consisting of alkaline earth metals, a second compound including Al, and a third compound including Cr, and may optionally include a fourth compound including at least one element ^M1 selected from the group consisting of Group 13 elements excluding Al, and optionally a fifth compound including at least one element ^M2 selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm, and at least one selected from the group consisting of the first compound, the second compound, and the third compound is an oxide;
preparing a raw material mixture so that the element A, Al, Cr, and the element ^M1 and element M2 ^contained as necessary have a composition represented by the following formula (I);
and heat-treating the raw material mixture in a reducing atmosphere at a temperature in the range of 1000° C. to 1500° C. to obtain an alkaline earth aluminate phosphor.
A _x (Al _1-y M ¹ _y ) _z O _{x + 3/2z} : Cr _v ,M ² _w (I)
(In the formula (I), v, w, x, y, and z satisfy 0.004≦v≦0.8, 0≦w≦0.4, 0.004≦v+w≦0.8, x=4.0, 0≦y≦0.7, and 4.0≦z≦14.0.) 9. The method for producing an alkaline earth aluminate phosphor according to claim 8, wherein, in the step of preparing the raw material mixture, when the element A contains two or more elements selected from the group consisting of alkaline earth metal elements, the raw material mixture is prepared so as to have a composition represented by the following formula (I-1):
(A ^a _1-u A ^b _u ) _x (Al _1-y M ¹ _y ) _Z O _{x + 3/2z} : Cr _v , M ² _W (I-1)
(In formula (I-1), A ^a is an element selected from the group consisting of alkaline earth metal elements, A ^b A ^a An element selected from the group consisting of alkaline earth metal elements excluding M ¹ is at least one element selected from the group consisting of Group 13 elements excluding Al, M ² is at least one element selected from the group consisting of Mn, Eu, Ce, Tb, Pr, Nd, Sm, Yb, Ho, Er, and Tm, and u, v, w, x, y, and z satisfy 0.1≦u≦0.9, 0.004≦v≦0.8, 0≦w≦0.4, 0.004≦v+w≦0.8, x=4.0, 0≦y≦0.7, 4.0≦z≦14.0. 10. The method for producing an alkaline earth aluminate phosphor according to claim 8, wherein the element A is at least one element selected from the group consisting of Ca, Sr and Ba, and the element ^M1 , which is included as necessary, is at least one element selected from the group consisting of B, Ga and In . 10. The method for producing an alkaline earth aluminate phosphor according to claim 8, wherein the element A is Sr, and the element ^M1 which is included as necessary is Ga. 12. The method for producing an alkaline earth aluminate phosphor according to claim 8 , wherein at least one selected from the group consisting of the fourth compound and the fifth compound is an oxide. The method for producing an alkaline earth aluminate phosphor according to claim 8 , wherein the temperature of the heat treatment is within a range of 1100° C. or more and 1450° C. or less. 14. The method for producing an alkaline earth aluminate phosphor according to claim 8, wherein the reducing atmosphere contains nitrogen gas and hydrogen gas, and the hydrogen gas content is 1 volume % or more. The method for producing an alkaline earth aluminate phosphor according to any one of claims 8 to 14, wherein in formula (I) or formula (I-1), z = 14.0.

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