JP2013151617A - Method of manufacturing alkaline earth metal silicate phosphor and alkaline earth metal silicate phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a method of manufacturing an alkaline earth metal silicate phosphor having a high luminance and having composition formula (A, Eu)SiO(wherein, A is an alkaline earth metal element) system by an aqueous solution method not using an organic acid; and the alkaline earth metal silicate phosphor obtained by the manufacturing method.SOLUTION: An Euactivating alkaline earth metal silicate phosphor having a composition formula (A, Eu)SiO(wherein, A is an alkaline earth metal element) system is formed by a manufacturing method that includes: a process 1 in which at least one alkaline earth metal carbonate chosen from Ba or Sr that is a raw material constituent metal component, a water dispersion of europium that is an activator raw material of a europium source, and an aqueous solution of a water soluble silicon compound are mixed to be a gel body in which the total amount of constituents is uniformly dispersed; a process 2 in which a precursor that is a dried product of the gel body is made; a process 3 in which the precursor is heat-treated to obtain a calcination powder; a process 4 in which the obtained calcination powder is mixed with a flux and is heat-treated under a reducing atmosphere to obtain a fired product; and a process 5 in which the residual flux is removed from the made fired product.

Description

In the present invention, Eu ²⁺ activation of a composition formula (A, Eu) ₂ SiO ₄ (where A is an alkaline earth metal element selected from Ba and Sr) that emits light with high luminance by photoexcitation in the ultraviolet to visible range. The present invention relates to a method for producing an alkaline earth metal silicate phosphor and an alkaline earth metal silicate phosphor.

White LEDs are a mixture of LEDs that emit light from near ultraviolet to blue and phosphors to generate white light. Conventionally, white LEDs have been actively developed as LCD backlight sources for small portable devices. As an application, the development of lighting applications is progressing.
Conventionally, YAG: Ce ³⁺ that exhibits yellow fluorescence by blue excitation has been widely used as a phosphor for white LED used in this white LED. In addition, (Ba, Sr, Ca) ₂ SiO ₄ : Eu ²⁺ , which is an alkaline earth metal silicate, can be excited widely from the ultraviolet to the visible range, and its emission wavelength is changed from green to orange by changing its composition. It has long been known that this is possible (Non-Patent Document 1). Furthermore, these phosphors are required to have higher luminance.

By the way, a general phosphor synthesis method is that a precursor obtained by mixing raw material powders in a wet or dry manner is calcined in the atmosphere to obtain a calcined powder, which is synthesized by a solid-state reaction between the raw materials by high-temperature reduction firing. (See Patent Document 1).
In addition, as a method for producing an alkaline earth metal silicate phosphor, a precursor is prepared by a sol-gel reaction using an aqueous solution of an alkaline earth metal and an organosilicon compound such as tetraethoxysilane (TEOS), followed by reduction firing. (See Patent Document 2) is also known.

Furthermore, in order to increase the brightness of the alkaline earth metal silicate phosphor, it is necessary to increase the crystal phase purity and uniformly disperse Eu ²⁺ as the activator in the base crystal. However, in the solid-phase firing method shown in Patent Document 1, it is essentially difficult to obtain a microscopically uniform precursor, and the crystal phase purity is increased or the activator Eu ²⁺ is homogeneously dispersed. Therefore, it is difficult to obtain a high brightness phosphor. Therefore, in order to further improve the phase purity and to uniformly diffuse Eu ²⁺ in the host crystal, it is necessary to perform reduction baking at a high temperature for a long time, but this is not industrially preferable. In this case, the obtained phosphor is strongly sintered and needs to be pulverized and crushed, but there is also a problem in that it tends to cause a decrease in luminance due to surface damage.
On the other hand, in the phosphor synthesis from the phosphor precursor by the liquid phase method such as the sol-gel method or the coprecipitation method, the raw material metal elements are uniformly mixed, and the element is essentially compared with the solid phase firing method. It is advantageous for diffusion.

As a silicon raw material used for the production of the alkaline earth silicate phosphor by the liquid phase method, an organic silicon compound such as TEOS disclosed in Patent Document 2 is often used. This TEOS is used because it is mixed with other raw materials and then becomes SiO ₂ by hydrolysis and polymerization. However, organosilicon compounds such as TEOS and tetramethoxysilane (TMOS) are generally water-insoluble and cannot be uniformly mixed with an aqueous solution, and when an alkaline earth metal that is a raw material other than silicon is used as an aqueous solution. Is difficult to mix uniformly.
Therefore, when an organic solvent such as alcohol is used as the solvent, the silicon raw material is uniformly dispersed in the solution, but when the water for hydrolysis is added, it is separated into two phases. Further, when the solvent is an organic solvent such as alcohol, there is a problem that it is difficult to dissolve the alkaline earth metal. Furthermore, organosilicon compounds such as TEOS are liable to evaporate, the composition fluctuates during synthesis, and it is difficult to obtain a precursor having a uniform composition.

By the way, in order to solve these problems, a water-soluble silicon compound (Water Soluble Silicon compounds: hereinafter referred to as WSS), which is a new silicon raw material, has recently been developed (Patent Document 3), and silicate fluorescence using this WSS. Body synthesis has been studied and reported (for example, Patent Document 4, Non-Patent Document 2).
Patent Document 4 shows an example in which a silicate phosphor is synthesized by mixing a metal salt aqueous solution and a WSS aqueous solution, and firing the gel obtained by hydrothermal synthesis of the mixture over several stages. Yes. However, when the gel body is synthesized by the hydrothermal synthesis method, the water is separated from the gel body, and the raw material metal salt is dissolved in the water. There was a problem that it was difficult to get a body.

  On the other hand, in Non-Patent Document 2, a metal ion is complexed and fixed with an organic acid such as citric acid, and then WSS is gelled to obtain a gel in which constituent elements are uniformly distributed. An example is shown in which a silicate phosphor is synthesized by thermally decomposing an organic substance to obtain a precursor and subjecting the body to reduction firing. In the case of such a method, the constituent elements are easily dispersed uniformly in a state close to the atomic level, and a high-luminance phosphor is easily obtained. However, since a large amount of citric acid or the like is used, it is necessary to remove organic matter, soot, and off-flavor by thermal decomposition of a large amount of organic matter when a large amount of precursor is prepared. Therefore, it is good for a small amount of experiment, but it is not industrial. When the amount is large, uniform pyrolysis is difficult, and there is a problem that carbon tends to remain and adversely affects the luminance of the phosphor. In addition, when the water-soluble metal salt used as a raw material is not sufficiently decomposed, chlorides, nitrates, etc. have a low melting point, so that they precipitate as the original salt during heat treatment, locally generate a liquid phase, and the brightness decreases. There is also a problem that it ends up.

JP 2009-173905 A JP 2007-186664 A JP 2010-007032 A JP 2010-188953 A

Journal The Electrochemical Society, Vol. 115, (1968), p. 1181. Proceedings of 2011 Annual Meeting of the Ceramic Society of Japan, Lecture Number: 3C03, p. 266.

In view of problems in the synthesis of silicate phosphors using water-soluble silicon compounds as the silicon source of such alkaline earth metal silicate phosphors, the present invention provides organic acids and nitrates and chlorides that are prone to problems such as melting. Without using as a raw material, by mixing and heating a water-soluble silicon compound aqueous solution, alkaline earth metal carbonate and europium oxide dispersion, a gel body in which constituent elements are uniformly distributed is obtained, and then the gel The body is dried by heating to prepare a precursor, and then subjected to calcination and reduction firing to emit light with high brightness (A, Eu) ₂ SiO ₄ (where A is at least one selected from Ba and Sr) A method of producing an alkaline earth metal silicate phosphor represented by at least two kinds of alkaline earth metal elements) and an alkaline earth metal silicate obtained from the production method It is intended to provide a fluorescent material.

As a result of intensive studies to solve the above problems, the present inventors have found that the composition formula (A, Eu) ₂ SiO ₄ (where A is at least one alkaline earth metal element selected from Ba and Sr). When producing the silicate phosphor represented, if the alkaline earth metal salt is dispersed in water, the particle surface becomes basic, and the water-soluble silicon compound (WSS) immediately gels in the basic aqueous solution. Paying attention to this, by mixing and heating an aqueous dispersion of BaCO ₃ , SrCO ₃ and Eu ₂ O ₃ and a WSS aqueous solution, a gel body in which the constituent components are uniformly distributed can be obtained, and calcined. Thus, the knowledge that a calcined powder having a fine and high phase purity can be obtained was obtained.

Further, this calcined powder is mixed with a flux for growing an alkaline earth metal silicate phosphor selected from BaCl ₂ and SrCl ₂ and reduced and fired at a temperature of 1300 ° C. from the melting point of the flux to obtain a sieve after firing. The inventors have found that the above problems can be solved by obtaining the knowledge that a high-brightness alkaline earth metal silicate phosphor can be easily obtained with a high yield with little loss due to the above, and have completed the present invention.

The alkaline earth metal silicate phosphor according to the first aspect of the present invention has a composition of (A, Eu) ₂ SiO ₄ (where A is at least one alkaline earth metal element selected from Ba and Sr). It is obtained by the manufacturing method which has a formula and has the process of the following process 1-process 5.

[Step 1]
At least one alkaline earth metal carbonate selected from Ba and Sr as constituent metal components of the raw material, an aqueous dispersion of the activator raw material of the europium source, and an aqueous solution of a water-soluble silicon compound are mixed, and 20-100 The process which makes it the gel body of the state by which the whole quantity of the structural component was disperse | distributed uniformly by heating and stirring at the liquid temperature of ° C.
[Step 2]
The process which makes the gel body produced by the process 1 the precursor which is the dried material which removed the solvent contained by drying.
[Step 3]
The process of heat-treating the precursor produced by the process 2 at 800-1300 degreeC in air | atmosphere atmosphere, and obtaining calcining powder.
[Step 4]
The calcined powder produced in step 3 is mixed with at least one flux selected from BaCl ₂ and SrCl ₂ and heat treated at a temperature between the melting temperature of the flux and 1300 ° C. in a reducing atmosphere to obtain a fired product. Process.
[Step 5]
A step of removing the residual flux from the fired product produced in step 4 to obtain phosphor powder.

  According to a second aspect of the present invention, the water dispersion in the first aspect of the present invention is the same amount or more and five times or less the amount of water added as the total amount of the raw material combined with the alkaline earth metal carbonate and the activation raw material. And a method for producing an alkaline earth metal silicate phosphor.

  3rd invention which concerns on this invention mixes the flux in 1st and 2nd invention in the range of 0.1 mass% or more and 20 mass% or less with respect to calcined powder, The alkaline earth characterized by the above-mentioned. This is a method for producing a metal silicate phosphor.

  A fourth invention according to the present invention has an emission peak at a wavelength of 500 nm or more and 580 nm or less when excited with light having a peak wavelength of 455 nm, obtained by the production method according to any of the first to third inventions, and externally An alkaline earth metal silicate phosphor having a quantum efficiency of 56% or more and an absorption efficiency of 75% or more.

The phosphor according to the present invention is prepared by mixing a water-soluble silicon compound (WSS) aqueous solution and an alkaline earth metal element aqueous dispersion and maintaining stirring at a predetermined temperature to produce a gel body in which constituent components are uniformly distributed, A composition formula (A, Eu) ₂ SiO ₄ (where A is at least one selected from Ba and Sr), which is obtained by subjecting the gel body to thermal decomposition, calcination, and reduction firing, and emits light with high brightness. Eu ²⁺ activated alkaline earth metal silicate phosphor represented by (alkaline earth metal element).

According to the production method of the present invention, Eu, which is a constituent component and an activator, can be uniformly dispersed, so that a high-luminance phosphor can be obtained. Moreover, since the constituent components are uniformly distributed, fine adjustment of the composition is easy, and a phosphor having the targeted composition can be obtained with high accuracy. In addition, since Eu as an activator is uniformly dispersed, high luminance can be obtained with a smaller amount of added Eu.
In addition, since no organic acid such as citric acid is used, the generation of cracked gases, soot, and offensive odors during pyrolysis, which is a problem with conventional aqueous solutions using organic acids, is prevented, and carbon residues after pyrolysis are also prevented. In addition, it is possible to provide a manufacturing method that is easy to put to practical use in the industry.
Since alkaline earth metal carbonates and europium oxide are used as raw materials instead of aqueous solutions such as nitrates and chlorides, they are precipitated as the original salts during heat treatment, and a liquid phase is locally generated, resulting in a decrease in luminance. The problem that is difficult to occur.

  Since the phosphor according to the present invention has high luminance, it is an optimum phosphor for use in a light-emitting diode with higher efficiency and higher characteristics.

It is PL spectrum figure which shows the emission spectrum in 455 nm excitation of the alkaline-earth silicate fluorescent substance obtained in Example 1, and the excitation spectrum in an emission peak wavelength. It is PL spectrum figure which shows the emission spectrum in 455 nm excitation of the alkaline-earth silicate fluorescent substance obtained in Example 6, and the excitation spectrum in an emission peak wavelength.

The alkaline earth silicate phosphor according to the present invention has a composition formula of (A, Eu) ₂ SiO ₄ (where A is at least one alkaline earth metal element selected from Ba and Sr), and the following steps: It is obtained by a manufacturing method including steps 1 to 5.
[Step 1]
At least one alkaline earth metal carbonate as a constituent metal component, an aqueous dispersion of europium as an activator, and an aqueous solution of a water-soluble silicon compound are mixed and heated and stirred at a liquid temperature of 20 to 100 ° C. The process of setting it as the gel body of the state by which the whole quantity of the structural component was disperse | distributed uniformly.
[Step 2]
The process of forming the precursor which is the dried material which removed the solvent contained by drying the gel body produced by the process 1.
[Step 3]
The process of heat-treating the precursor produced by the process 2 at 800-1300 degreeC in air | atmosphere atmosphere, and obtaining calcining powder.
[Step 4]
The calcined powder produced in step 3 is mixed with at least one flux selected from BaCl ₂ and SrCl ₂ and heat treated at a temperature between the melting temperature of the flux and 1300 ° C. in a reducing atmosphere to obtain a fired product. Process.
[Step 5]
A step of removing the residual flux from the fired product produced in step 4 to obtain phosphor powder.

Below, each process which is the manufacturing method of the alkaline-earth metal silicate fluorescent substance which concerns on this invention is demonstrated in detail.
The alkaline earth metal silicate phosphor according to the present invention is a phosphor having a composition formula of (A, Eu) ₂ SiO ₄ (where A is at least one alkaline earth metal element selected from Ba and Sr). Which is obtained by the method for producing a phosphor through the steps 1 to 5.

[Step 1]
1. Preparation of dispersion of alkaline earth metal carbonate and europium The alkaline earth metal element includes at least one selected from Ba and Sr.
By changing the ratio of Ba and Sr, the emission peak can be changed in the wavelength range of 500 nm (green) to 580 nm (yellow). Moreover, Ca and Mg can also be included as an alkaline-earth metal element component.

First, an aqueous dispersion of europium oxide of at least one alkaline earth metal element selected from Ba and Sr and an activator element is prepared.
Carbonates are used as alkaline earth metal salts.
In addition, alkaline earth metal chlorides, nitrates, acetates, etc., which are water-soluble and can be converted into oxides by thermal decomposition, can be considered as raw materials. Become more. If the amount of water is too large, water may ooze out from the water-soluble silicon compound gel described below. In this case, since the component is contained in the exuded water, a uniform gel body cannot be obtained, and the luminance is lowered, which is not preferable. In addition, there is a problem that salt decomposition due to heat does not occur uniformly, resulting in non-uniform composition of the resulting phosphor. In order to avoid this, for example, it is necessary to add a treatment such as a heat treatment in a medium temperature range of about 300 to 800 ° C. after step 2, which is not preferable because the step becomes complicated.
In addition, since chlorides and nitrates have a low melting point, they are once dissolved in an aqueous solution, and then precipitated as an original salt during heat treatment to locally generate a liquid phase and lower the luminance.

As the europium source, it is preferable to use europium oxide dispersed in water. Water-soluble raw materials can also be used.
Alkaline earth metal carbonate and europium oxide as an activator raw material are weighed so that a predetermined phosphor composition is obtained, water is added, and the mixture is stirred and dispersed at room temperature to obtain a dispersion slurry. The amount of water added is preferably equal to or more than 5 times the weight of the raw material, which is the total amount of the raw alkaline earth metal carbonate and the activation raw material. If it is less than the weight of the raw material, the viscosity of the dispersion slurry is high, and the raw material settles or lumps, which is not preferable. Even if it is more than 5 times, there is no difference in the degree of dispersion, and the amount of water is too much to prevent uniform gelation as described above, or the drying step in step 2 becomes very long. However, when there is a special purpose such as performing dry granulation after mixing with WSS, a water amount of 5 times or more can be added.

2. Preparation of aqueous solution of water-soluble silicon compound (WSS) The water-soluble silicon compound (WSS) can be prepared by a known production method disclosed in Patent Document 3.
Specifically, it is produced by the method shown below.
The organosilicon compound tetraethoxysilane (TEOS) is used as the Si source material, and TEOS and propylene glycol as the diol compound are weighed to a molar ratio of 1: 4 and mixed at 80 ° C. for 1 hour. Add a small amount of hydrochloric acid or lactic acid as an acid (about 0.2% of the mixed solution) and stir for 1 hour, and dilute with water so that the concentration of WSS obtained is 2 mol / L or less. A WSS aqueous solution is obtained. In addition, when the WSS concentration is higher than 2 mol / L, the liquid viscosity becomes high, so that it becomes uneven when added to the aqueous dispersion of alkaline earth metal salt and europium oxide, and it is difficult to obtain a uniform slurry. This is not preferable because it may cause a typical gelation reaction.

  Here, tetraethoxysilane or tetramethoxysilane can be suitably used as the organic silicon compound of the Si source material used for the production of the water-soluble silicon compound, and the glycol compound forming the mixed solution can be ethylene glycol or propylene. Glycol can be preferably used, and hydrochloric acid or lactic acid can be preferably used as the acid added to the mixed solution.

3. Preparation of gel body with uniformly distributed components Utilizing the gelation ability of water-soluble silicon compound (WSS) and the ability to retain moisture inside the gel body, the gel contains the raw material slurry uniformly contained inside the gel. Get the body. Hereinafter, the reaction mechanism when gelling will be described.
First, by adding an alkaline earth metal aqueous solution to water-soluble silicon (WSS: Si (OROH) ₄ , R is a divalent alkyl group), the liquid becomes basic and hydrolyzes to form Si (OH) _n. (OROH) _4-n . And it is thought that a Si-O-Si network is formed by the progress of OH group dehydration condensation reaction or dealcoholization condensation reaction to form a gel body.
At this time, the alkaline earth metal salt or the Eu slurry of the activator is confined in the Si—O—Si network, thereby obtaining a gel body in which the constituent components are uniformly distributed.

The time required for this gelation varies depending on the type of alkaline earth metal element and the amount of water in the aqueous solution, but can be carried out within a range that does not deviate from the gelation conditions shown below.
An aqueous WSS solution is added to an aqueous dispersion of alkaline earth metal salt and europium while stirring at room temperature. After stirring for 10 minutes or more and confirming that the entire liquid is in a uniform slurry state, gelation can be achieved by starting heating.

The gelation temperature is preferably 20 to 100 ° C, more preferably 40 to 60 ° C.
Specifically, for example, it is preferable to set the temperature to 50 ° C. At a liquid temperature of 50 ° C., the entire solution gels in about 15 minutes with a mixed liquid amount of 150 ml and becomes a uniform lump. The lower the liquid temperature, the longer the time required for gelation. If the liquid temperature is higher than 100 ° C., the time required for gelation is shortened to about 5 minutes, but it is difficult to uniformly warm the whole liquid, and this causes local gelation. Absent.
Depending on the volume of the mixture, the heating and stirring method can be selected as appropriate. is there.

[Step 2]
Next, the gel body produced in step 1 is dried to form a precursor, and the solvent contained in the gel body is removed.
The point to note in this process is that when moisture moves inside the gel body during drying to form a high-concentration part and precipitates are generated, the phosphor obtained through the subsequent process has a non-uniform composition. In order to prevent the emission of high-luminance light, it is important to dry the gel so that no moisture transfer occurs in the gel body.
A drying temperature shall be 100-200 degreeC.
The drying method is not particularly limited except for the above precautions, and a general dryer can be used. A hot-air circulating dryer, a vacuum dryer, or a freeze dryer can also be used. In addition, when the obtained dried material is agglomerated, it is preferable to proceed to the next step after crushing.

[Step 3]
In this step, the precursor obtained in step 2 is heat-treated in an air atmosphere to obtain calcined powder.
This heat treatment is performed for the purpose of decomposing propylene glycol and the like contained in WSS, decomposing the raw material carbonate, and forming a target phase of (Ba, Sr) SiO ₄ .
Since the raw material is dispersed in water and a uniform gel body with a water-soluble silicon compound is used as a starting material, it is easy to obtain a calcined powder with a high phase purity having a fine structure of submicron to micron order by firing.
By obtaining such a calcined powder, uniform grain growth and reduction doping of Eu during subsequent reduction firing in the flux are promoted, and as a result, a high-luminance phosphor is obtained.

The heat treatment in this step is not particularly required to control the atmosphere, and can be performed by a known method such as heating in a box-type electric furnace in an air atmosphere.
Specifically, it heats at 800-1300 degreeC in an atmospheric condition in the container made from an alumina.
Since the residual carbonate in the calcined powder is increased at a temperature lower than 800 ° C., the target phase purity is low, and in order to inhibit the uniform grain growth during the subsequent reduction firing in the flux, the high brightness fluorescence is finally obtained. I can't get a body.
At temperatures exceeding 1300 ° C., the target phase purity is high, but the grain growth of the calcined powder proceeds too much, hindering uniform grain growth during flux reduction firing and reducing reduction of Eu, resulting in a final phosphor. The brightness decreases.
That is, it is important to select firing conditions that have a high target phase purity and that do not cause excessive grain growth. For this purpose, heat treatment can be performed by dividing the temperature into two stages, or heat treatment can be repeated at the same temperature.

[Step 4]
In this step, the calcined powder produced in step 3 and the flux are mixed and heat-treated in a reducing atmosphere to obtain a fired product.
The calcined powder has a target crystal phase, and the alkaline earth metal element site is doped with europium as an activator.
Europium in the calcined powder after step 3 is trivalent as in the case of the raw material, but becomes bivalent by heat treatment in a reducing atmosphere in step 4 and enters the site of the divalent alkaline earth metal element. The light emission with high luminance can be obtained by substitution.

Furthermore, by reducing and firing in the presence of flux, crystal growth is promoted, and a higher-brightness alkaline earth metal silicate phosphor can be obtained. Since the calcined powder of this method has a uniform fine structure as described above, it is easier to obtain the flux effect than the solid phase method, and a high-luminance phosphor can be obtained even by relatively low temperature reduction firing.
As the flux, BaCl ₂ and SrCl ₂ can be preferably used. You may use these individually or in mixture.

  The amount of the flux added varies depending on the type and particle size of the raw material, the flux material, the firing temperature, the atmosphere, the type of furnace, the structure of the firing container, etc., but 0.1% by mass or more and 20% by mass with respect to the calcined powder. % Or less is preferable. If the addition amount of the flux is less than 0.1% by mass with respect to the calcined powder, the effect of the flux cannot be obtained, which is not preferable. If the addition amount of the flux is more than 20% by mass with respect to the calcined powder, the flux This is not preferable because the effect may be saturated, the particle size becomes too large, or it may be incorporated into the host crystal to deteriorate the characteristics or cause a decrease in luminance.

  The mixing method of the flux and calcined powder is not particularly limited and can be mixed by a known method. For example, dry pulverization mixing using a ball mill or a mortar, water or alcohol solvent is added, and mixing is performed using a ball mill or mortar. It is also possible to use wet mixing such as drying.

The reducing atmosphere uses an inert gas such as N ₂ or Ar mixed with ₁ to 10 vol% H ₂ . Depending on the type of flux, the melted flux itself acts as a reducing agent, so that heat treatment can also be performed in an inert gas atmosphere.

  As a baking container to be used, a material having high heat resistance and low reactivity with each phosphor raw material is used. As the material, ceramics such as alumina, quartz, boron nitride, silicon carbide, silicon nitride, magnesium oxide, metals such as platinum, molybdenum, tungsten, tantalum, niobium, iridium, rhodium, or alloys based on them, Carbon etc. are mentioned. Of these materials, alumina, metal, and carbon are preferable. A strong reducing atmosphere can be obtained by mixing carbon.

  The heat treatment temperature varies slightly depending on the type and amount of added flux and the composition of the phosphor, but is set to the flux melting temperature to 1300 ° C. In the present invention, since the calcined powder is uniform and fine, there is an advantage that a high-luminance phosphor can be easily obtained at a lower temperature and in a shorter time than the solid phase method. However, when the heat treatment temperature is lower than the melting temperature of the flux, grain growth, Eu reduction and substitution are insufficient, and a high-luminance phosphor cannot be obtained. When the heat treatment temperature is higher than 1300 ° C., the crystal growth of the phosphor particles proceeds and the coarse particles increase, or the secondary particles are formed by sintering to obtain primary particles suitable as the phosphor. Separately, strong pulverization is required, and this pulverization causes a decrease in the luminance of the phosphor. Moreover, since it becomes necessary to perform sieving to remove coarse particles, the yield is deteriorated, which is not preferable.

[Step 5]
In this step, residual phosphor is removed from the fired product produced in step 4 to obtain final phosphor particles.
In step 5, if necessary, the fired product obtained in step 4 is crushed and the flux is washed, followed by drying, pulverization, classification, and the like.

An automatic mortar or a stamp mill can be used for the crushing treatment.
The cleaning process can be performed with deionized water, an organic solvent such as methanol or ethanol, or an alkaline aqueous solution such as ammonia water, depending on the type of flux. In the case of using a water-soluble flux, cleaning is performed by stirring in water. be able to. You may wash | clean using warm water.
In the drying treatment, since alkaline earth silicate is weak to water, it is preferable to dry after removing water by alcohol substitution or the like.
A phosphor having a desired particle size and good dispersibility and fluidity can be obtained by pulverizing and classifying the phosphor powder obtained through the drying treatment.

  In order to improve the moisture resistance of the phosphor of the present invention, a surface treatment such as coating the surface of the phosphor with a different substance may be performed as necessary. Examples of the material for the surface treatment include organic compounds, inorganic compounds, glass materials, etc. Among them, oxides, particularly silicon oxide is preferable.

The phosphor particles of the present invention obtained through the above steps have a uniform and fine structure by heat treatment starting from a precursor obtained by drying a gel body in which constituent components are uniformly distributed by an aqueous solution method. Since the calcined powder is obtained, and crystal growth and reduction doping of Eu are performed by reduction firing in a flux, high luminous efficiency from green to yellow is exhibited.
Specifically, it has a green to yellow emission peak at a wavelength of 500 nm or more and 580 nm or less when excited with light having a peak wavelength of 455 nm, an external quantum efficiency of 56% or more, and an absorption efficiency of 75% or more. Thus, it is possible to obtain a high-luminance phosphor that cannot be obtained by the solid phase method. In addition, it is easy to put to practical use industrially by preventing the generation of cracked gas, soot, and offensive odor that were generated during the thermal decomposition of organic acids such as citric acid in conventional aqueous solutions, and also preventing carbon residue after thermal decomposition. An alkaline earth metal silicate phosphor can be produced by the production method.

  Furthermore, the high-efficiency phosphor according to the present invention has a relatively flat excitation spectrum over a range of near ultraviolet to visible light. Therefore, a light emitting diode that absorbs light with a wavelength of 320 to 420 nm and emits light with a wavelength of 420 nm or more and 800 nm or less, absorbs light with a wavelength of 420 to 480 nm, and has a wavelength of 480 nm or more and 800 nm or less. It can be suitably used as a phosphor of a light emitting diode that emits light, and a light emitting diode with higher efficiency and higher characteristics can be provided.

Hereinafter, the present invention will be described more specifically with reference to examples.
The WSS used was prepared by weighing TEOS and propylene glycol so as to have a molar ratio of 1: 4, adding a small amount of lactic acid to a mixed solution obtained by mixing at 80 ° C. for 1 hour, and further stirring for 1 hour. Pure water was added thereto to obtain a 2 mol / L WSS aqueous solution.

X-ray diffraction of the obtained phosphor particles was measured by a fully automatic multipurpose X-ray diffractometer X'pert Pro / MPD manufactured by Spectris Co., Ltd.
Using a fluorescence spectrophotometer FP-6500 (manufactured by JASCO Corporation), the emission spectrum was measured with excitation at 455 nm, and the absorptance, internal quantum efficiency, and external quantum efficiency were determined.
The excitation spectrum was measured at each emission peak wavelength.

As a Eu ²⁺ activated alkaline earth metal silicate phosphor, a green phosphor of (Ba _1.41 Sr _0.47 Eu _0.12 ) SiO ₄ is used and the production method thereof will be described.
[Step 1]
BaCO ₃ , SrCO ₃ (all manufactured by Kanto Chemical Co., Ltd.) and Eu ₂ O ₃ (3N, manufactured by High-Purity Chemical Laboratory) are weighed to a predetermined composition as raw materials, and 3.5 times the total weight Was added to water and stirred at room temperature for 30 minutes to obtain an aqueous dispersion. Subsequently, a predetermined amount of the 2 mol / L water-soluble silicon (WSS) aqueous solution was weighed.
Next, an aqueous WSS solution was added to an aqueous dispersion of BaCO ₃ , SrCO ₃ and Eu ₂ O ₃ and stirred for 10 minutes at room temperature. After confirming that the entire liquid became a uniform slurry, Heating with a tic stirrer was started. The heating temperature was set so that the temperature of the mixed solution was 50 ° C. The whole gelled in about 20 minutes from the start of heating, and a uniform gel was obtained.

[Step 2]
The gel body obtained in step 1 was put into a hot air dryer set at 120 ° C. and dried for 6 hours, and then taken out and lightly crushed in a mortar to obtain a precursor which was a dried product.

[Step 3]
The precursor, which is a dried product obtained in step 2, was put in an alumina container and subjected to heat treatment at 1000 ° C. for 3 hours in the atmosphere.
Smoke, burnt odor and soot were hardly generated during the process due to thermal decomposition of organic matter.

[Step 4]
10% by weight of BaCl ₂ .2H ₂ O (manufactured by Kanto Chemical Co., Inc.) was added to the calcined powder obtained in step 3 as a flux, and pulverized and mixed for 10 minutes in an agate mortar.
This mixture was put into a carbon boat, and reduction firing was performed at 1200 ° C. for 4 hours in an Ar-4% H ₂ atmosphere using an electric tubular furnace (HTF-410, manufactured by Ito Seisakusho) to obtain a fired product.

[Step 5]
The obtained fired product was crushed in an agate mortar, the remaining flux component was washed with pure water, then replaced with ethanol and dried in warm air.

The obtained phosphor had a single-phase (Ba, Sr) ₂ SiO ₄ XRD pattern, and the formation of heterogeneous phases was not confirmed.
FIG. 1 shows an emission spectrum at 455 nm excitation and an excitation spectrum at the emission peak wavelength. In FIG. 1, the solid line is the emission spectrum at 455 nm excitation, and the broken line is the excitation spectrum at the emission peak wavelength. The horizontal axis is Wavelength (wavelength) [nm], and the vertical axis is intensity (relative emission intensity) [a. u. ].
Table 1 shows the emission peak wavelength, absorption rate, internal quantum efficiency, and external quantum efficiency at 455 nm excitation.

A phosphor was obtained by performing the same operation as in Example 1 except that the flux added in Step 4 was SrCl ₂ .6H ₂ O (Kanto Chemical).
Table 1 shows the emission peak wavelength, absorption rate, internal quantum efficiency, and external quantum efficiency at 455 nm excitation.

A phosphor was obtained by performing the same operation as in Example 2 except that the firing temperature in Step 4 was 1100 ° C. × 4 hr.
Table 1 shows the emission peak wavelength, absorption rate, internal quantum efficiency, and external quantum efficiency at 455 nm excitation.

A phosphor was obtained in the same manner as in Example 1 except that the firing temperature in Step 4 was 1000 ° C. × 4 hr.
Table 1 shows the emission peak wavelength, absorption rate, internal quantum efficiency, and external quantum efficiency at 455 nm excitation.

The same operation as in Example 1 was performed except that the composition was (Ba _1.43 Sr _0.49 Eu _0.08 ) SiO ₄ and the heat treatment conditions in Step 3 were 1100 ° C. × 3 hr.
Table 1 shows the emission peak wavelength, absorption rate, internal quantum efficiency, and external quantum efficiency at 455 nm excitation.

A yellow phosphor is obtained by performing the same operation as in Example 1 except that the composition is (Sr _1.46 Ba _0.5 Eu _0.04 ) SiO ₄ and the heat treatment condition in Step 3 is 1100 ° C. × 3 hr. It was.
The obtained phosphor had a single-phase (Sr, Ba) ₂ SiO ₄ XRD pattern, and the generation of a different phase was not confirmed.
FIG. 2 shows an emission spectrum at 455 nm excitation and an excitation spectrum at the emission peak wavelength. In FIG. 2, the solid line is the emission spectrum at 455 nm excitation, and the broken line is the excitation spectrum at the emission peak wavelength. The horizontal axis is Wavelength (wavelength) [nm], and the vertical axis is intensity (relative emission intensity) [a. u. ].
Table 1 shows the emission peak wavelength, absorption rate, internal quantum efficiency, and external quantum efficiency at 455 nm excitation.

(Comparative Example 1)
The following aqueous solutions were prepared using Sr acetate aqueous solution, Ba acetate aqueous solution, and Eu acetate aqueous solution as starting materials.
An aqueous Sr acetate solution was prepared by dissolving Sr acetate (99.9%, manufactured by Kanto Chemical Co., Ltd.) in water to form a 0.5 M / L aqueous solution.
The acetic acid Ba aqueous solution was prepared by dissolving Ba acetate (99.9%, manufactured by Kanto Chemical Co., Ltd.) in water to give a 1 M / L aqueous solution.
As the aqueous solution of Eu acetate, 0.1 M / L aqueous solution was prepared by dissolving Eu acetate (manufactured by Furuuchi Chemical Co., Ltd.) in water.

  To the WSS prepared separately, the aqueous solution of Sr acetate, Ba acetate, and Eu acetate were added so that the composition ratio of Si: Sr: Ba: Eu would be the composition ratio of Example 1, and further 4 times the total metal element amount. Of citric acid was added, stirred for 10 minutes, and completely dissolved to obtain a mixed aqueous solution. Then, when stirring was continued for 30 minutes at 50 ° C., gelation occurred. Subsequent steps were the same as in Example 1, but smoke, burnt odor, and soot were generated due to the thermal decomposition of citric acid in the middle of Step 3.

As shown in the examples, all of the phosphors of Examples 1 to 6 according to the present invention have a high luminance with an external quantum efficiency of 56% or more and an absorptance of 75% or more.
In Example 4, a phosphor with high brightness was obtained even by low-temperature reduction firing at 1000 ° C., because the production method of the present invention starts with a uniform precursor by a liquid phase method, It is considered that high-purity calcined powder can be produced, and since it is fired in a flux, crystal growth is promoted and high-luminance phosphor particles are obtained.
On the other hand, in Comparative Example 1 using citric acid, smoke, burnt odor, and soot are generated due to the thermal decomposition of citric acid in the middle of Step 3, but in Examples 1 to 6, all such decomposition occurs. There is no generation of materials, which can be said to be an industrially practical process.

Claims (4)

A method for producing an alkaline earth metal silicate phosphor represented by a composition formula of (A, Eu) ₂ SiO ₄ (wherein A is at least one alkaline earth metal element selected from Ba and Sr),
A method for producing an alkaline earth metal silicate phosphor comprising the following steps 1 to 5.
[Step 1]
At least one alkaline earth metal carbonate selected from Ba and Sr as constituent metal components of the raw material, an aqueous dispersion of the activator raw material of the europium source, and an aqueous solution of a water-soluble silicon compound are mixed, and 20-100 The process which makes it the gel body of the state by which the whole quantity of the structural component was disperse | distributed uniformly by heating and stirring at the liquid temperature of ° C.
[Step 2]
The process of obtaining the precursor which is the dried material which dried the gel body obtained by the process 1, and removed the solvent contained.
[Step 3]
A step of obtaining a calcined powder by heat-treating the precursor obtained in step 2 at 800 to 1300 ° C. in an air atmosphere.
[Step 4]
The calcined powder obtained in step 3 is mixed with at least one flux selected from BaCl ₂ and SrCl ₂ , and heat treated at a temperature between the melting temperature of the flux and 1300 ° C. in a reducing atmosphere to obtain the fired product. Obtaining step.
[Step 5]
A step of removing the residual flux from the fired product obtained in step 4 to obtain phosphor powder.   2. The water dispersion is mixed at a moisture addition amount equal to or more than 5 times the total weight of the raw material combined with the alkaline earth metal carbonate and the activation raw material. Method for producing alkaline earth metal silicate phosphors.   The method for producing an alkaline earth metal silicate phosphor according to claim 1 or 2, wherein the flux is mixed in a range of 0.1 mass% or more and 20 mass% or less with respect to the calcined powder. An alkaline earth metal silicate phosphor obtained by the production method according to claim 1,
An alkaline earth metal silicate having an emission peak at a wavelength of 500 nm or more and 580 nm or less, an external quantum efficiency of 56% or more, and an absorption efficiency of 75% or more when excited with light having a peak wavelength of 455 nm Phosphor.

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