JP2013144728A - Method for producing europium-activated alkaline earth metal sulfide phosphor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high luminance (Ca, Sr)S:Eu-based phosphor having a desired light emission wavelength inexpensively in a short time and efficiently.SOLUTION: A mixed powder is obtained by mixing strontium carbonate, calcium carbonate and europium oxide; the obtained mixed powder and a flux being at least one alkaline metal compound selected from potassium bromide and potassium chloride are mixed; and the flux and the mixed powder are placed under a mixed gas atmosphere in which argon gas is mixed with carbon disulfide in an amount ≤4 times of the theoretical amount necessary for sulfurizing the mixed powder, and are heat treated under the temperature condition of 700°C to 1,000°C.

Description

The present invention relates to a method for producing a europium-activated alkaline earth metal sulfide phosphor, and more specifically, a three-wavelength type together with a blue LED and a green phosphor (for example, (Ba, Sr) ₂ SiO ₄ : Eu phosphor). The present invention relates to a method for producing a europium-activated alkaline earth metal sulfide phosphor that can be used as a red phosphor used in a white LED.

  In general, red phosphors have lower visibility and lower luminance than green and orange phosphors. Therefore, a high-luminance red phosphor is demanded. In lighting applications such as LEDs, an orange red color is required, and a material that can adjust the color by changing the emission wavelength according to the application is desirable. In that respect, the (Ca, Sr) S: Eu-based red phosphor disclosed in Patent Document 1 is excellent in that the emission wavelength can be adjusted according to the application by adjusting the blending ratio of Ca and Sr. .

  As a method for producing a (Ca, Sr) S: Eu-based red phosphor, there is described a method of obtaining a sulfide by firing a raw material such as sulfate in hydrogen sulfide as disclosed in Patent Document 1. However, the method described in Patent Document 1 requires three firing steps, and the atmosphere gas in each firing step is different from a mixed gas of nitrogen and hydrogen, hydrogen sulfide gas, and nitrogen gas, respectively. Each atmospheric gas needs to be controlled, and the process is very complicated. In addition, since the firing time is as long as 3 to 6 hours and the temperature is as high as 1100 ° C., sulfur in the sulfide phosphor evaporates, and the phase purity of the resulting crystal is lowered to lower the luminance. It is not preferable.

  On the other hand, Patent Document 2 describes a method of obtaining a sulfide phosphor by adding a fluoride to a sulfide raw material and baking it in an argon gas atmosphere. However, when a sulfide raw material is used as the starting material, the raw material cost is expensive, and thus the obtained sulfide phosphor must be expensive.

JP 2005-509081 A JP 2005-146190 A

  Therefore, the present invention has been proposed in view of such circumstances, and a high-luminance (Ca, Sr) S: Eu-based phosphor having a desired emission wavelength can be obtained at low cost and in a short time. It aims at providing the method which can be manufactured efficiently.

  The inventors of the present invention have made extensive studies to solve the above-described problems. As a result, in a method for producing a europium-activated alkaline earth metal sulfide phosphor having (Ca, Sr) S as a base and Eu as a light emission center, an inexpensive carbonate and europium oxide are used as raw materials, and a specific halogen-based flux is obtained. In addition, by using a mixed gas of carbon disulfide and argon gas as the atmosphere for the reduction and sulfidation heat treatment, a high-brightness europium-activated alkaline earth sulfide phosphor can be obtained by low-temperature conditions and short-time heat treatment. I found it.

That is, the method for producing the europium-activated alkaline earth metal sulfide phosphor according to the present invention includes (Ca _1-x , Sr _x ) S: _y Eu (0 ≦ x ≦ 1, 0.001 ≦ y ≦ 0.010). ) Represented by the first mixing step of mixing europium oxide together with strontium carbonate and / or calcium carbonate to obtain a mixed powder, and the above mixing A second mixing step of mixing powder and at least one alkali metal compound selected from the group consisting of potassium bromide and potassium chloride as a flux, and the mixed powder obtained through the second mixing step, 700 ° C. in an atmosphere of a mixed gas in which argon gas is mixed with carbon disulfide in an amount ranging from the theoretical amount necessary for sulfiding the powder to a value not more than four times the theoretical amount. And having a firing step of firing and heat-treated at a temperature of 1000 ° C..

  Here, in the said baking process, heat processing can be performed by hold | maintaining on the temperature conditions of 700 to 1000 degreeC for 1 to 5 hours.

  According to the present invention, a high-luminance phosphor having an arbitrary wavelength of 615 to 655 nm, for example, can be manufactured at low cost and in a short time under low temperature conditions. And the high-luminance phosphor manufactured in this way can be suitably used for white LED application by blue diode excitation, particularly white LED application for illumination.

It is process drawing of the manufacturing method of a europium activated alkaline-earth metal sulfide. FIG. 4 is an excitation / emission spectrum diagram of the phosphor prepared in Example 1 and YAG: Ce. FIG. 6 is an excitation / emission spectrum diagram of the phosphor prepared in Example 3 and YAG: Ce. FIG. 5 is an excitation / emission spectrum diagram of the phosphor prepared in Comparative Example 2 and YAG: Ce.

  Hereinafter, a specific embodiment to which the present invention is applied (hereinafter referred to as “the present embodiment”) will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention.

The europium-activated alkaline earth metal sulfide phosphor produced by the production method according to the present embodiment has a composition formula (Ca _1-x , Sr _x ) S: _y Eu (0 ≦ x ≦ 1, 0.001). ≦ y ≦ 0.010), with calcium sulfide and / or strontium sulfide as the base crystal and europium as the emission center.

In this europium-activated alkaline earth metal sulfide phosphor, x (0 ≦ x ≦ 1), which is the content ratio of calcium sulfide and / or strontium sulfide represented by (Ca _1-x , Sr _x ) S which is a matrix structure It is possible to arbitrarily control the emission wavelength by adjusting. That is, the emission wavelength of CaS: Eu is 655 nm, the emission wavelength of SrS: Eu is 615 nm, and the emission wavelength can be arbitrarily controlled between the wavelengths by adjusting the content ratio of calcium and strontium. .

  Specifically, the method for producing the europium activated alkaline earth metal sulfide phosphor (hereinafter simply referred to as “phosphor”) according to the present embodiment includes strontium carbonate and / or Alternatively, a first mixing step S1 in which europium oxide is mixed with calcium carbonate to obtain a mixed powder, the obtained mixed powder, and at least one alkali metal compound selected from the group of potassium bromide and potassium chloride as a flux. The mixed powder obtained through the second mixing step S2 to be mixed and the second mixing step S2 is 700 ° C. to 1000 ° C. in an atmosphere of a mixed gas in which argon gas is mixed with a predetermined amount of carbon disulfide. And a baking step S3 for baking by heat treatment under the temperature conditions. Hereinafter, it demonstrates for every process.

[First mixing step]
In the first mixing step S1, the raw materials weighed so as to have a predetermined composition ratio are mixed using a ball mill or the like to obtain raw material mixed powder.

As raw materials, strontium carbonate, calcium carbonate, and europium oxide are used. In the first mixing step S1, in order to obtain a phosphor represented by the composition formula (Ca _1−x , Sr _x ) S: _y Eu (0 ≦ x ≦ 1, 0.001 ≦ y ≦ 0.010) These raw materials are weighed and mixed so as to have a predetermined composition ratio.

  Here, strontium carbonate and calcium carbonate which are carbonates used as raw materials are inexpensive raw materials. Therefore, a phosphor having the desired composition can be produced at a lower cost than in the prior art by producing a phosphor having the above composition formula using these as starting materials.

  Although it does not specifically limit as a mixing process of a raw material, For example, it can carry out using a ball mill etc. as mentioned above. Moreover, as the mixing time, it can be set as about 10 to 60 minutes, for example.

[Second mixing step]
In the second mixing step S2, the raw material mixed powder obtained in the first mixing step S1 is mixed with at least one alkali metal compound selected from the group consisting of potassium bromide and potassium chloride.

  At least one alkali metal compound selected from the group consisting of potassium bromide and potassium chloride is used as a flux. Thus, by adding these fluxes to the mixed powder obtained by mixing the raw materials in the first mixing step S1, and further mixing them, the growth of particles is promoted and europium is uniformly diffused. Can be made.

  In particular, in this embodiment, at least one alkali metal compound selected from the group of potassium bromide and potassium chloride is used as the flux. Thereby, it is possible to manufacture a phosphor having higher brightness than conventional phosphors. This is thought to be because potassium (K), which is an alkali metal, is taken into the defect site of the raw material strontium or calcium and acts to compensate for the defect, thereby causing fluorescence that emits light with high brightness. It is presumed that the body can be manufactured. On the other hand, for example, when strontium chloride, barium chloride, strontium fluoride, or the like is used as a flux, the obtained phosphor has an accumulation property in which fluorescence continues even when irradiation of excitation light is stopped. It is not preferable.

  Of course, at least one alkali metal compound selected from the group consisting of potassium bromide and potassium chloride is not itself sulfided with carbon disulfide during the reduction sulfurization firing in the subsequent step, but reacts with strontium or calcium as a raw material. Does not form product.

  The mixing ratio of the above-described flux and mixed powder is preferably such that the flux is mixed at a rate of 5 to 80 parts by weight, more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the mixed powder. preferable. When the mixing ratio of the flux with respect to 100 parts by weight of the mixed powder is less than 5 parts by weight, when the flux is melted, it is not mixed with the entire mixed powder and the effect is not sufficiently exhibited. On the other hand, when the mixing ratio of the flux with respect to 100 parts by weight of the mixed powder exceeds 80 parts by weight, the amount remaining after the subsequent baking step increases, and as a result, the luminance of the phosphor is lowered, which is not preferable. .

  Moreover, the mixing process of a flux and mixed powder can be performed using a ball mill etc. similarly to 1st mixing process S1, for example. The mixing time can be about 5 to 30 minutes.

[Baking process]
In the firing step S3, the mixed powder with the flux obtained through the second mixing step S2 is fired by heat-treating under a predetermined condition to produce a fired phosphor.

  In the present embodiment, in the firing step S3, reduced sulfidation firing is performed in an atmosphere of a mixed gas in which a predetermined amount of carbon disulfide and argon gas are mixed. By this reduction sulfidation firing, the mixed powder is reduced and sulfided to form a base crystal of (Ca, Sr) S, and europium oxide is doped to the Ca site and Sr site of the base crystal to reduce the fluorescence. A fired body is obtained.

  Here, in the reduction firing by heat treatment, when carried out under a high temperature condition for a long time, there is a tendency for sulfur to escape from the reduced and sulfided base crystal, and the phosphor has a high luminance and a desired emission wavelength. It becomes difficult to manufacture. Therefore, in the present embodiment, reduction sulfidation firing is performed in an atmosphere of a mixed gas of carbon disulfide and argon gas. Carbon disulfide can sulfide an oxide at a lower temperature than hydrogen sulfide. Therefore, according to the manufacturing method according to the present embodiment, firing by heat treatment can be performed under a temperature condition lower than that in the past, and it is possible to effectively prevent a phosphor having a desired composition by preventing sulfur from escaping. Can be manufactured. Further, it is possible to reduce labor and cost at the time of raising the temperature, which is preferable from an economical viewpoint.

  Furthermore, as described above, in the present embodiment, at least one alkali metal compound selected from the group consisting of potassium bromide and potassium chloride as a flux is added to and mixed with the mixed powder made of the starting material. I am doing so. As a result, the growth of particles after sulfidation and the uniform diffusion of europium can be performed more effectively, so that reduction firing can be completed in a short time under a lower temperature condition. Thus, a high-intensity red phosphor can be produced efficiently without firing multiple times.

  More specifically, in the firing step S3, first, the mixed powder with the flux obtained through the second mixing step S2 is put in a container. The container to be used is not particularly limited, but for example, a graphite container is preferably used. Thereby, it is possible to cause a reduction reaction more effectively and efficiently.

  Next, the mixed powder with the flux placed in a graphite container or the like is charged into a firing furnace, the furnace core tube is evacuated once, and argon gas is bubbled into a predetermined amount of liquid carbon disulfide to obtain disulfide. A mixed gas of carbon and argon gas is introduced. Then, the mixed powder is reduced and sulfided by raising the temperature to a predetermined heat treatment temperature and then holding it for a predetermined time.

  The amount of carbon disulfide is in the range of the theoretical amount necessary for sulfiding the mixed powder to an amount not more than 4 times the theoretical amount. When the amount of carbon disulfide exceeds 4 times the theoretical amount required to sulfidize the mixed powder, excessive carbon will adhere to the surface of the resulting phosphor particles, resulting in a black surface and brightness. Is not preferable because of the possibility of lowering. The amount of carbon disulfide can be controlled by the temperature of liquid carbon disulfide and the flow rate of bubbling argon gas.

  The firing furnace is not particularly limited, and for example, a tubular furnace in which the furnace core tube is quartz can be used. Further, as the temperature raising condition, for example, the temperature raising rate is 10 to 30 ° C./min, and the temperature can be set at a relatively low temperature condition of 700 ° C. to 1000 ° C. as described above. In this embodiment, mixed powder is formed using potassium bromide or potassium chloride as the flux. However, during firing, the flux and sulfide become eutectic and lower the melting point. The firing temperature need not be higher than the melting point of these fluxes.

  And in baking process S3, it heat-processes by hold | maintaining, for example for 1 to 5 hours on the temperature conditions of 700 to 1000 degreeC, and reduces and bakes mixed powder.

  After the completion of the holding under the temperature condition of 700 ° C. to 1000 ° C., the bubbling of the argon gas with respect to the carbon disulfide is stopped, and only the argon gas is flowed from the bypass line to be cooled. And the high-intensity fluorescent substance which has a desired composition is obtained by lightly crushing the sintered body taken out from the baking furnace at room temperature.

  In the firing step S3, sulfur powder may be placed in an alumina container and placed in the furnace core tube of the firing furnace to generate sulfur vapor in the furnace core tube. This can more effectively prevent sulfur from escaping from the sulfurized base crystal. In the firing step S3, after the reduction firing is completed, excess flux remaining in the phosphor may be removed by washing with water or heat treatment in an inert gas atmosphere. Further, excess oxygen disulfide that has not contributed to the reaction in the firing furnace can be recovered by being adsorbed on activated carbon or the like.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
In Example 1, a red phosphor represented by the composition formula CaS: 0.002Eu was produced as follows.

  First, 13.8 g of calcium carbonate (4N, manufactured by Kanto Chemical Co., Ltd.) and 0.049 g of europium oxide (3N5, manufactured by Kanto Chemical Co., Ltd.) were mixed in a mortar for 10 minutes. Next, 20 parts by weight of KBr (manufactured by Kanto Chemical Co., Inc.) as a flux was added to 100 parts by weight of the obtained raw material mixed powder, and further mixed for 5 minutes in a mortar.

Next, the mixed powder obtained by mixing with the flux is put into a graphite container, and heated to 900 ° C. at a temperature rising rate of 20 ° C./min in a mixed gas atmosphere of carbon disulfide and argon gas in a tubular furnace, After that, heat treatment was performed by holding for 1 hour, and the mixed powder was reduced and sulfided and fired. After completion of the holding, only argon gas was allowed to flow to room temperature. The mixed gas used for the firing was obtained by bubbling with a carbon disulfide container temperature of 20 ° C. and flowing argon gas into the carbon disulfide in the container at 92 cc / min. The carbon disulfide consumed in this firing was 19 g (0.25 mol), which was 3.6 times the theoretical amount (number of moles) required for sulfiding the raw material calcium carbonate. The reaction formula is CaCO ₃ + 0.5CS ₂ = CaS + 1.5CO ₂ .

  After the heat treatment, the obtained fired product was lightly crushed in a mortar to produce a red phosphor.

  About the produced red fluorescent substance, the excitation and the emission spectrum were measured using the fluorescence spectrophotometer (FP6500, JASCO Corporation make). The emission spectrum was measured at an excitation wavelength of 455 nm, and the excitation spectrum was measured at the peak wavelength of the emission spectrum. In addition, the luminance (light emission intensity) is obtained by using YAG: Ce (P46-KG, No. QMK58 / F-C1) manufactured by Phosphor Technology as a reference example, and determining the light emission intensity ratio with the maximum luminance of the YAG: Ce as 1. It was.

(Example 2)
In Example 2, a red phosphor represented by the composition formula (Sr _0.85 , Ca _0.15 ) S: 0.002Eu was produced. In Example 2, 1.33 g of strontium carbonate (3N, manufactured by Kanto Chemical Co., Ltd.) and 11.1 g of strontium carbonate (3N, manufactured by Kanto Chemical Co., Ltd.) were added as raw materials, and europium oxide (3N5, Kanto Chemical Co., Ltd.) was added. Ex.) A red phosphor was prepared in the same manner as in Example 1 except that KCl (manufactured by Kanto Chemical Co., Inc.) was used as the flux, and the excitation / emission spectrum was measured.

(Example 3)
In Example 3, a red phosphor represented by the composition formula CaS: 0.002Eu was produced. In Example 3, a red phosphor represented by the composition formula CaS: 0.002Eu was prepared in the same manner as in Example 1 except that KCl (manufactured by Kanto Chemical Co., Inc.) was used as the flux. The emission spectrum was measured.

Example 4
In Example 4, a red phosphor represented by the composition formula SrS: 0.002Eu was produced. In this Example 4, in place of calcium carbonate, 12.3 g of strontium carbonate was used, 0.029 g of europium oxide was used, and KCl (manufactured by Kanto Chemical Co., Inc.) was used as the flux. A red phosphor was prepared, and excitation and emission spectra were measured.

(Comparative Example 1)
In Comparative Example 1, a red phosphor represented by the composition formula CaS: 0.002Eu was produced. In Comparative Example 1, a red phosphor was prepared in the same manner as in Example 1 except that hydrogen sulfide gas was used as the atmosphere gas during the heat treatment, and excitation and emission spectra were measured.

(Comparative Example 2)
In Comparative Example 2, a red phosphor represented by the composition formula CaS: 0.002Eu was produced. In Comparative Example 2, a red phosphor was used in the same manner as in Example 1 except that BaCl ₂ (manufactured by Kanto Chemical Co., Inc.) was added as a flux at a ratio of 10 parts by weight with respect to 100 parts by weight of the raw material mixed powder. An excitation / emission spectrum was measured.

(Comparative Example 3)
In Comparative Example 3, the temperature of the carbon disulfide container was set to 20 ° C., and firing was performed in an atmosphere of a mixed gas obtained by bubbling by flowing argon gas into the carbon disulfide in the container at 130 cc / min. A red phosphor was produced in the same manner as in Example 1 except that. The carbon disulfide consumed in this calcination was 27 g (0.35 mol), which was 5.1 times the theoretical amount (number of moles) required to sulfidize the raw material calcium carbonate.

<Evaluation>
Table 1 below summarizes the excitation / emission spectrum measurement results of the red phosphors produced in the examples and comparative examples. 2, 3, and 4, the excitation and emission spectra of the red phosphors produced in Example 1, Example 3, and Comparative Example 2, respectively, and YAG: Ce measured as a reference example, respectively. Excitation / emission spectrum is shown.

  As can be seen from the results shown in Table 1 and FIGS. 2 and 3, the red phosphors produced in Examples 1 to 4 have a maximum luminance that is twice or more that of YAG: Ce at wavelengths of 615 nm to 655 nm. As a result, a high-intensity red phosphor could be obtained. Thus, by using at least one alkali metal compound selected from the group consisting of potassium bromide and potassium chloride as the flux, heat treatment is performed in a mixed gas atmosphere of carbon disulfide and argon gas. It was found that a high-intensity red phosphor having a desired emission wavelength can be obtained by heat treatment.

  On the other hand, in Comparative Example 1 in which the heat treatment was performed in a hydrogen sulfide gas atmosphere, the brightness was higher than that of YAG: Ce, which was 1.2 times as high as that of YAG: Ce. Further, in Comparative Example 2 in which barium chloride (BaCl) was used as the flux, as can be seen from the spectrum diagram shown in FIG. 4, the luminance was extremely low, 0.4 times that of YAG: Ce.

  Moreover, in the comparative example 3 which used 5.1 times the number of moles required for sulfiding carbon disulfide as a raw material for carbon disulfide during firing, the obtained phosphor was black, and its luminance was Compared with YAG: Ce, it was 0.1 times as low. This is thought to be due to the carbon disulfide in the mixed gas adhering to the surface of the phosphor, resulting in a black surface and a decrease in luminance.

  According to the method for producing a red phosphor according to the present invention, a phosphor having a desired emission wavelength and a higher luminance than conventional ones can be produced efficiently at a low cost in a short time. It can be suitably used as a phosphor used for white LED illumination by blue diode excitation, and its industrial value is extremely high.

Claims (2)

(Ca _1-x , Sr _x ) S: _y Eu (0 ≦ x ≦ 1, 0.001 ≦ y ≦ 0.010) is a method for producing a europium-activated alkaline earth metal sulfide phosphor represented by And
A first mixing step of mixing europium oxide with strontium carbonate and / or calcium carbonate to obtain a mixed powder;
A second mixing step of mixing the mixed powder with at least one alkali metal compound selected from the group consisting of potassium bromide and potassium chloride as a flux;
Argon gas is mixed with carbon disulfide in the range from the theoretical amount necessary to sulfidize the mixed powder to the amount not more than four times the theoretical amount of the mixed powder obtained through the second mixing step. And a firing step of firing and firing under a temperature condition of 700 ° C. to 1000 ° C. in a mixed gas atmosphere. A method for producing a europium activated alkaline earth metal sulfide phosphor.   The method for producing a europium-activated alkaline earth sulfide phosphor according to claim 1, wherein in the firing step, the heat treatment is performed by maintaining the temperature at 700 ° C to 1000 ° C for 1 to 5 hours.

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