KR20060131524A - Preparation method of red phosphors based on sulfide - Google Patents

Abstract

Provided is a method for preparing red phosphor based on sulfide of alkali earth metal having improved luminous property at the condition excluding solvent and noxious ingredient for decreasing a temperature, in which heating is achieved at lower temperature than conventional method. The method comprises the steps of (1) dispersing an acid solution containing 0.5-0.9999 mole of alkali earth metal precursor and 0.0001-0.5 mole of europium precursor dissolved therein, into distilled water to prepare an aqueous solution of metal mixture, (2) adding an aqueous solution of sulfate and sulfide of metal of period 3 in elements periodic table to the aqueous solution of metal mixture, adjusting a pH of the solution to 5-10, and filtrating and drying the solution to prepare a precursor of phosphor based on sulfide alkali earth metal sulfide, and (3) heating the precursor at 600-1000 deg.C at the atmosphere of mixture of nitrogen and hydrogen gases.

Description

Preparation method of alkaline earth metal sulfide-based red phosphors {Preparation method of red phosphors based on sulfide}

1 shows X-ray diffraction diagrams of alkaline earth metal sulfide-based red phosphors in Examples 1 and 2 according to the present invention.

Figure 2 shows the emission spectrum of the alkaline earth metal sulfide-based red phosphor in Examples 1 and 2 in accordance with the present invention.

3 shows excitation spectra of alkaline earth metal sulfide-based red phosphors in Examples 1 and 2 according to the present invention.

Figure 4 shows the emission spectrum of the alkaline earth metal sulfide-based red phosphor prepared in Examples 1, 3 and 4 and Comparative Example 1 according to the present invention.

The present invention relates to a method for producing an alkaline earth metal sulfide-based red phosphor, and more particularly, an alkali metal complex solution in which an alkaline earth metal and an activator are dissolved, and a precipitant of a 3-week metal sulfide and an aqueous sulfate solution are co-precipitated at a specific pH to give an alkali. The introduction of a novel process for preparing an earth metal sulfide-based phosphor precursor and heat-treating the prepared precursor under a mixed gas atmosphere of nitrogen and hydrogen enables heat treatment at a lower temperature than in the prior art, thereby using flux and toxicity for lowering the temperature. A method for producing an alkaline earth metal sulfide-based red phosphor having excellent luminescence under conditions in which the use of the component is excluded.

In general, sulfide-based phosphors are well known for display industry materials such as cathode ray tube (CRT) and low voltage display (LED or VFD) because of their excellent luminous efficiency.

Among them, ZnS: Cu, Al, and Y ₂ O ₂ S: Eu are well known green and red phosphors, and in particular, alkaline earth metal sulfide-based phosphors are phosphorescent phosphors in the 1980s and 1990s. It has a long afterglow property by making a trap by using an activator other than the active agent, and many studies have been conducted on it as a phosphor.

Recently, there is a growing interest in luminaires and displays using light emitting diodes (LEDs), and there is a demand for phosphors excited in the long wavelength region, and alkaline earth metal sulfide-based phosphors are very suitable as phosphors satisfying such conditions.

To date, alkaline earth metal sulfide-based phosphors are prepared by using oxides or carbonates, H ₂ S or CS ₂ gases, which are toxic gases, and alkaline earth metal sulfides using sulfates, and then impregnating an activator with precursors. After the preparation, a method of heat treatment using a toxic gas H ₂ S or CS ₂ gas and hydrocarbon gas and a large amount of sulfur together is widely used. In addition, the active agent was mixed well with the alkaline earth metal sulfide, and then prepared by heat treatment in an atmosphere where nitrogen and hydrogen gas were mixed.

This method is prepared using toxic H ₂ S or CS ₂ gas, and has been using a separate flux to lower the firing temperature because the firing temperature is higher than 1,000 ℃ when the heat treatment.

In addition, it has been proposed to introduce a method using a metal complex designed to use no toxic gas. However, it excludes toxic gases but uses a lot of activated carbon and sulfur as well as using a flux such as a solid phase reaction method to lower the firing temperature.

Accordingly, the present inventors have tried to solve the problem of the reaction conditions such as the toxic gas in the conventional sulfide-based phosphor manufacturing process, economic and environmental problems due to the use of sulfur, firing temperature. As a result, a precipitating agent of 3-cycle metal sulfide and sulfate solution was added to a metal complex solution in which the alkaline earth metal dissolved in the acid and the activator were dispersed in distilled water to maintain a pH in a specific range, and then filtered and dried to prepare a phosphor precursor. By heat-treating the prepared precursor under a reaction gas in which nitrogen and hydrogen are mixed in a certain component ratio, it is possible to manufacture sulfide-based phosphors in a low temperature range without using a separate flux for reducing the conventional firing temperature, and H ₂ S or The present invention has been completed by knowing that the use of toxic components such as CS ₂ gas, sulfur and the like can be eliminated.

Accordingly, an object of the present invention is to provide a method for producing a sulfide-based phosphor by coprecipitation of the reactants at a low temperature reaction temperature without the use of toxic components and reaction flux.

The present invention comprises the steps of preparing an aqueous metal mixed solution by dispersing an acid solution in which 0.5 to 0.9999 mol of alkaline earth metal precursor and 0.0001 to 0.5 mol of europium precursor are dissolved in distilled water;

In step 2 to prepare an alkaline earth metal sulfide-based phosphor precursor by adding a three-cycle metal sulfide and sulfate solution to the metal mixed aqueous solution, adjusted to a pH range of 5 to 10, and filtered and dried; And

Three steps of heat-treating the alkaline earth metal sulfide-based phosphor precursor in a temperature range of 600 ~ 1000 ℃ under a nitrogen and hydrogen mixed gas atmosphere

There is a feature in the method for producing an alkaline earth metal sulfide-based phosphor comprising.

Hereinafter, the present invention will be described in detail.

The present invention prepares a phosphor precursor by dissolving a predetermined ratio of alkaline earth metal and activator in an acid and then dispersing it in a metal complex aqueous solution dispersed in distilled water to maintain a specific pH range by adding a metal sulfide and a sulfate solution. The present invention relates to a novel method for producing alkaline earth metal sulfide-based phosphors by performing heat treatment on the precursor of the prepared phosphors under a reaction gas in which nitrogen and hydrogen are mixed at a constant component ratio.

In general, sulfide-based phosphors are mostly synthesized by a solid phase reaction method, but the use of toxic gases such as H ₂ S or CS ₂ and a high firing temperature have required a flux to lower them. The method using the metal complex introduced as an alternative to the solid phase reaction method uses a large amount of activated carbon and sulfur instead of the harmful gas, but the flux for lowering the firing temperature has the disadvantage that it is invariably required.

In contrast, the present invention introduces a wet compounding method, that is, a coprecipitation method of simultaneously precipitating dissolved cations in a solution, so that each component of the precursor is uniformly distributed and forms fine particles. Compared with heat treatment at a temperature of 1200 ° C. or higher, the reaction can be performed at a relatively low temperature range, and a separate flux for lowering the reaction temperature is not required. In general, during the phosphor manufacturing process, the type of phosphors and their physical properties vary greatly depending on the slight difference in firing temperature. Thus, the firing temperature not only acts as an important factor, but it is an innovative method to lower the firing temperature range. Can be. In addition, the present invention does not require a separate flux for lowering the reaction temperature, and reacts with hydrogen gas during precursor heat treatment to decompose a precursor of sulfate to form sulfide and water vapor, and the formed water vapor is vaporized during heat treatment to sulfide. Since only the formation of the toxic components such as H ₂ S or CS ₂ gas and sulfur, which is required in the prior art is possible.

Looking at the method for producing an alkaline earth metal sulfide-based phosphor according to the present invention in more detail.

First, an alkaline earth metal precursor and a europium precursor are dissolved in an acid, and then dispersed in distilled water to prepare a metal mixed aqueous solution. In this case, it is preferable to dissolve each metal in an acid completely, and then to disperse it in distilled water. If the dissolution is not completely performed, an additional reaction in which the metal precipitates and reacts with a precipitant is not performed to form sulfate. Is generated, so a complete dissolution in acid is required.

The acid may be in the range of pH 2 to 4, specifically, for example nitric acid, hydrochloric acid, and the like. In the case of sulfuric acid, in the case of sulfuric acid, a precipitated phase is formed before alkaline earth metals are dissolved to obtain metal ions that are completely dissolved. It is not preferable to use it because it shows a phenomenon in which phase separation with the activator solution and uniform precipitation does not occur. Such acid is used in an appropriate amount to sufficiently dissolve the alkaline earth metal and europium.

In addition, the alkaline earth metal is generally used in the art and specifically, for example, calcium (Ca), strontium (Sr) and barium (Ba) may be used, and such alkaline earth metal may be carbonate, nitrate, hydroxide and chloride. Form compounds can be used. The alkaline earth metal is used in an amount of 0.5 to 0.9999 moles, and when the amount is less than 0.5 moles, the activator forms a main crystal, and thus the luminescence does not occur well, and the manufacturing cost also increases rapidly. This is very small and there is a problem that light emission does not occur easily.

Europium, an active agent, is generally used in the art, and specifically, for example, carbonate, nitrate, acetate, hydroxide, and chloride compounds may be used, and 0.0001 to 0.5 mole are used. If the amount of use is less than 0.0001 mole, light emission hardly occurs, and if the amount exceeds 0.5 mole, the manufacturing cost increases, and the light emission decreases significantly due to the concentration quenching phenomenon.

 After dissolving in acid as described above, it is dispersed in distilled water, which is a process for completely dissolving by controlling the number of moles of the metal solution by distilled water and reducing the particle size and gelation of the precipitate during precipitation. In this case, all alkaline earth metals used in the art may be used, but in the present invention, it is preferable to use strontium (Sr) and barium (Ba) having better solubility in distilled water. The distilled water is used in an amount of 500 to 3000% by weight, and when the amount of the distilled water is less than 500% by weight, fine precipitates remain upon dissolution and the precipitated particles become coarse and coarse. It is preferable to maintain the above range because the solution is too thin to cause a problem of low productivity.

Apart from the above, a 3-cycle metal sulfide and sulfate aqueous solution is prepared and used as a precipitant.

The metal sulfide and sulfate may be used as the three cycle elements of the periodic table of the elements, in the present invention ammonium sulfide ((NH ₄ ) ₂ S), sodium sulfide (Na ₂ S), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) And sodium sulfate (Na ₂ SO ₄ ). The precipitant may be used in a 1 to 2 molar ratio with respect to 1 mole of the mixed metal of the alkaline earth metal precursor and the europium precursor. When the amount is less than 1 molar ratio, complete precipitation does not occur and when the molar ratio exceeds 2 molar ratio, a large amount of precipitant may be used. It is preferable to maintain the above range because the manufacturing cost rises sharply and the problem of precipitation of the precipitant itself together with the precipitate occurs.

Next, the precipitating process is performed by adding the precipitant aqueous solution to the metal mixed solution and stirring for 1 to 3 hours while maintaining the pH 5 to 10 range. If the pH is less than 5, the perfect precipitation is not obtained. If the pH is more than 10, it is preferable to maintain the above range because the aggregation phenomenon of the precipitate is strong and the luminous efficiency of the phosphor is relatively decreased. In order to recover the precipitate precipitated by the co-precipitation, it is filtered using a filter or centrifugation commonly used in the art, preferably centrifugation rather than a filter.

The filtered precipitate is dried using a conventional dryer, and drying in a vacuum atmosphere is more preferable than drying in an air atmosphere, since the content of oxygen may be further reduced.

Next, the alkaline earth metal sulfide-based phosphor precursor is heat-treated under a nitrogen and hydrogen mixed gas atmosphere to prepare an alkaline earth metal sulfide-based phosphor.

The mixed gas is introduced to react with the precursor and hydrogen gas to reduce the activator and form a sulfide-based phase, and nitrogen and hydrogen are preferably maintained at a volume ratio of 60 to 95: 5 to 40, If the volume of the nitrogen exceeds the range, the activator is not reduced well, the light of the desired color is not good and if the volume of the hydrogen exceeds the range, the hydrogen gas reacts with the outside oxygen, causing a problem of explosion It is preferable to maintain the above range.

The temperature during the heat treatment is preferably 600 to 1000 ° C, preferably 700 to 1000 ° C, more preferably 850 to 950 ° C. If the temperature is less than 600 ℃ it is not possible to obtain a sulfide crystal phase, the light emission does not occur and if it exceeds 1000 ℃ it is preferable to maintain the above range because the problem of coarse particles and decrease the luminous efficiency occurs.

In addition, in order to replace some hydroxyl groups and oxygen with sulfur during the heat treatment, sulfur (S) is 0 to 200% by weight, preferably 25 to 150% by weight, more preferably 50 to 100%, based on the alkaline earth metal sulfide-based phosphor precursor. Use by weight mix.

Since the alkaline earth metal sulfide-based phosphor prepared as described above can be heat treated at a low temperature, it is possible to prepare a phosphor having excellent luminescence properties even under conditions in which the use of flux and toxic components used for temperature reduction is excluded.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Example 1

2.8050 g of SrCO _{3 and} 0.1760 g of Eu ₂ O ₃ were dissolved in 3 mL of nitric acid, and then dispersed in 100 mL of distilled water to prepare a metal mixed solution. Thereafter, 16 mL of an aqueous ammonium sulfide ((NH ₄ ) ₂ S) solution having a sulfur content of 1% was added to the metal mixed solution. At this time, it was adjusted with sulfuric acid so that the hydrogen ion concentration is between 7.5 and 8.0. After the two solutions were thoroughly mixed, slow stirring at about 400 rpm was performed for 2 hours, resulting in complete precipitation. The precipitate prepared above was filtered and dried at a temperature of 70 ° C. for 2 hours to prepare a precursor. 2.45 g of sulfur was mixed with the precursor prepared above, placed in an alumina crucible and heat-treated at 900 ° C. for 2 hours. At this time, the strontium sulfide red phosphor was manufactured by firing in a mixed gas atmosphere supplied with 95 cc / min of nitrogen gas and 5 cc / min of hydrogen gas.

Crystallinity (X-ray diffraction pattern), emission (465 nm), and excitation spectrum of the strontium sulfide prepared above were measured and shown in FIGS. 1, 2, and 3.

Example 2

Calcium sulfide red phosphor was prepared in the same manner as in Example 1, using 1.9017 g of CaCO ₃ and 0.1760 g of Eu ₂ O ₃ .

Crystallinity (X-ray diffraction pattern), emission (465 nm), and excitation spectrum of the calcium sulfide red phosphor prepared above were measured and shown in FIGS. 1, 2, and 3.

Example 3

The same procedure as in Example 1, except that instead of an aqueous solution of ammonium sulfide ((NH ₄ ) ₂ S) using 16 mL of 1.2009 g of sodium sulfide (Na ₂ S.H ₂ O) aqueous solution to strontium sulfide red phosphor Prepared. At this time, the heat treatment for 2 hours at a temperature of 850 ℃.

The emission (465 nm) spectrum of the strontium sulfide prepared above was measured and shown in FIG. 4.

Example 4

In the same manner as in Example 1, in place of the ammonium sulfide ((NH ₄ ) ₂ S) aqueous solution of 16% ammonium sulfide ((NH ₄ ) ₂ S) of sulfur content, ammonium sulfate ((NH ₄ ) ₂ SO ₄₎ 3.96 g was prepared was dissolved, with this, strontium sulfide red phosphor.

The emission (465 nm) spectrum of the strontium sulfide red phosphor prepared above was measured and shown in FIG. 4.

Comparative Example 1

       SrS: Eu phosphor, which is an alkaline earth metal sulfide-based phosphor, was prepared by a conventional solid-phase reaction method, and the emission spectrum thereof was measured. The results are shown in FIG. 4.

As described above, the alkaline earth metal sulfide-based phosphor prepared by the coprecipitation method according to the present invention can be heat treated at a lower temperature than the conventional one, thereby eliminating the use of a separate flux for reducing the temperature, and H ₂ S or CS. Instead of toxic gases such as ₂ , hydrogen and nitrogen are used in combination, which is expected to be excellent in terms of environment and economy.

Claims (7)

1 step of dispersing an acid solution in which 0.5 to 0.9999 mol of alkaline earth metal precursor and 0.0001 to 0.5 mol of europium precursor are dissolved in distilled water to prepare a metal mixed aqueous solution; In step 2 to prepare an alkaline earth metal sulfide-based phosphor precursor by adding a three-cycle metal sulfide and sulfate solution to the metal mixed aqueous solution, adjusted to a pH range of 5 to 10, and filtered and dried; And Three steps of heat-treating the alkaline earth metal sulfide-based phosphor precursor in a temperature range of 600 ~ 1000 ℃ under a nitrogen and hydrogen mixed gas atmosphere Method for producing an alkaline earth metal sulfide-based phosphor comprising a. The method of claim 1, wherein the alkaline earth metal precursor is a compound of a metal selected from calcium (Ca), strontium (Sr), and barium (Ba). The method of claim 1, wherein the alkaline earth metal precursor is a compound of the form of carbonate, nitrate, hydroxide and chloride. The method of claim 1, wherein the europium precursor is a compound of the form of carbonate, nitrate, acetate, hydroxide and chloride. The method of claim 1, wherein the sulfides and sulfates of the tricycle metal are ammonium sulfide ((NH ₄ ) ₂ S), sodium sulfide (Na ₂ S), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) and sodium sulfate (Na ₂ SO ₄ ) A process for producing an alkaline earth metal sulfide-based phosphor, characterized in that selected from. According to claim 1, wherein the sulfide and sulfate of the three-cycle metal A method for producing an alkaline earth metal sulfide-based phosphor, characterized by coprecipitation at a molar ratio of 1 to 2 per mole of a mixture of an alkaline earth metal precursor and a europium precursor. The method for producing an alkaline earth metal sulfide-based phosphor according to claim 1, wherein the nitrogen and hydrogen are mixed and used in a volume ratio of 60 to 95: 5 to 40.

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