JP2008101094A - Method for producing fluorescent material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method for synthesizing a carbon nitride-based fluorophor emitting white fluorescence, while being capable of easily obtaining in high reproducibility and in high efficiency a carbon nitride of high nitrogen content with the N/C ratio of 1 or greater without using any catalyst and solvent. <P>SOLUTION: The method comprises the following process. Using such a compound as to be composed of carbon atom(s), nitrogen atom(s) and hydrogen atom(s), or composed of carbon atom(s), nitrogen atom(s) and hydrogen atom(s) and oxygen atom(s), and represent a carbon-nitrogen bond-recurring structure, the compound is heat-treated under such a condition that the sublimation vapor pressure of the compound is saturated at its decomposition or sublimation temperature or higher. In the above method, the compound representing the carbon-nitrogen bond-recurring structure: (C-N)n is melamine, urea or cyanuric acid, and the heat-treatment condition is such that the temperature is 250-550°C and there is substantially no gas inflow in a lidded vessel or in a low-spacing volume state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a fluorescent material, particularly a fluorescent material mainly composed of amorphous carbon nitride.

Carbon nitride is a compound consisting only of nitrogen and carbon, and carbon nitride (α-C ₃ N ₄ crystal, β-C ₃ N ₄ crystal, graphite-like C ₃ N ₄ ) having a particularly high nitrogen content is an ultra-hard material. It is attracting attention and may be expected to be used in various fields such as industrial, physics and chemistry, and medical applications, such as semiconductors, machine parts, or wear-resistant materials such as teeth and bone joints. Active consideration is ongoing from both sides. Furthermore, in the process of synthesizing an ultra-hard carbon nitride material, it has been confirmed that a carbon nitride material having a nitrogen / carbon molar ratio exceeding 1 emits fluorescence.

  Regarding the synthesis of a compound of carbon, nitrogen and hydrogen using a compound containing carbon and nitrogen triazine ring and chlorine, such as cyanuric chloride and trichloromelamine, similar to the starting material employed in the present invention, as described in Patent Document 1 and It can be seen in Non-Patent Document 1.

  Patent Document 1 discloses that carbon nitride having a layered structure is produced by reacting cyanuric chloride and ammonia or cyanuric chloride and melamine at 500 ° C. to 600 ° C., and that the obtained carbon nitride becomes a fluorescent material. is there. The feature of this method is that a triazine ring is bridged with nitrogen to form a carbon nitride intermediate by reacting a chlorine moiety with ammonia or melamine using cyanuric chloride as a starting material. Furthermore, this carbon nitride intermediate is thermally decomposed at 500 ° C. to 600 ° C. to remove excess hydrogen, thereby producing carbon nitride having a yellow layered structure.

  Non-Patent Document 1 describes a method for synthesizing orange carbon nitride in a short time by bringing trichloromelamine into contact with a nichrome wire heated to 500 ° C. in an autoclave. The feature of this method is that trichloromelamine is used as a starting material, and thermal decomposition is rapidly performed in a few tens of seconds by heating with a nichrome wire to obtain fine nitrogen-containing carbon nitride.

Japanese Patent Publication No. 5-16364 (Claims, third column) J. Mater. Chem. 12, P.2463-2469, 2000 (P.2467. Conclusions et al.)

  In Patent Document 1 and Non-Patent Document 1 described above, chloride is used as a starting material for carbon nitride. Chlorine is easily desorbed by heat treatment to generate radicals or ions, which serve as reaction points for cross-linking between molecules. When this reaction is utilized, molecules easily polymerize by a crosslinking reaction, and therefore, in Patent Document 1 and Non-Patent Document 1, it is presumed that a chlorine compound is used as a starting material for carbon nitride.

  However, when the starting material chloride is thermally decomposed, hydrochloric acid or chlorine is generated, which causes a problem that the apparatus is corroded. In addition, chlorides such as cyanuric chloride and trichloromelamine are expensive and are not suitable for producing inexpensive fluorescent materials. Furthermore, in Patent Document 1 and Non-Patent Document 1, the reaction is performed in an inert gas atmosphere such as nitrogen or argon. The inert gas atmosphere prevents the oxidative decomposition of the starting material of carbon nitride and is optimal for the production of carbon nitride, but requires complicated operation for replacement of the inert gas and ensures the airtightness of the apparatus. There is a need.

  Since carbon nitride is being researched as an ultra-hard material, it is a pure compound of nitrogen and carbon and has to be highly crystalline. Therefore, in the research so far, emphasis has been placed on how to produce high-quality carbon nitride, in a highly airtight sealed container filled with a chlorine-containing carbon nitride raw material with an inert gas, or It was mainstream to manufacture by heat treatment at 550 ° C. or higher under active gas flow. Therefore, the present situation is that amorphous carbon nitride obtained at a low temperature of less than 550 ° C. and containing hydrogen as an impurity has not been required.

  The present invention overcomes such problems of the prior art, solves the problem of corrosion of the apparatus by hydrochloric acid without using chloride as a starting material, and does not contain chlorine as an impurity. An object of the present invention is to provide a novel method for synthesizing a carbon nitride-based phosphor, which is an inexpensive compound that emits white fluorescence.

  The present invention, as a result of intensive studies on a method for synthesizing a carbon nitride-based phosphor, revealed that a compound comprising carbon, nitrogen and hydrogen or a compound comprising carbon, nitrogen, hydrogen and oxygen is subjected to sublimation vapor pressure at a temperature equal to or higher than the decomposition temperature or sublimation temperature. It has been found that a carbon nitride phosphor that emits white light efficiently can be obtained by heat-treating under the condition that becomes saturated.

  That is, the present invention uses a compound composed of carbon, nitrogen and hydrogen, or composed of carbon, nitrogen, hydrogen and oxygen and having a repeating structure of a bond of carbon and nitrogen, and the compound is decomposed at its decomposition temperature or sublimation. A method for producing a fluorescent material, characterized in that heat treatment is performed at a temperature equal to or higher than a temperature so that a sublimation vapor pressure is saturated.

  Here, the compound having a carbon-nitrogen bond repeating structure (CN) n is melamine, urea or cyanuric acid, and these compounds can easily form a bluish white phosphor by the following method. Is obtained. When a compound containing a C—C bond such as adenine is used as a starting material, it is difficult to produce a phosphor.

  The heat treatment of the compound is carried out at a temperature in the range of 250 ° C. to 550 ° C., preferably in a range of 300 ° C. to 500 ° C.

  The heat treatment of the compound of the fluorescent material is a production method in which the compound is carried out in a container with a lid or in a low gap volume state with almost no gas inflow, so that it is not necessary to use a special autoclave or the like.

  According to the method for producing a fluorescent material of the present invention, inactive in a range of 250 ° C. to 550 ° C., which is lower than the temperature range in which research has been mainstream using nitrogen and carbon compounds such as melamine, urea or cyanuric acid. Inorganic phosphor can be easily manufactured by performing in a simple container with a lid or in a state of low gap volume and almost no gas inflow without gas replacement.

  The carbon nitride phosphor produced in the present invention can be used in various fields. For example, there is a usage method in which a fluorescent pigment is mixed with a resin-based paint. Since it is an inorganic phosphor, it can be expected to have high durability with little deterioration caused by solar ultraviolet rays. In addition, an alternative to white phosphors used in fluorescent lamps can be expected. Currently used white phosphors contain Sb. Although it is incorporated in the crystal and does not elute easily, it is likely to become a future problem. Since carbon nitride phosphors do not contain harmful substances, they can be expected as environmentally friendly products.

  Furthermore, since the carbon nitride phosphor of the present invention also has characteristics as a semiconductor, it may be used as an inorganic EL light emitter. White light-emitting panels are expected to be used for small screens such as mobile phones and mobile games. Inorganic EL light-emitting panels are expected to have high durability as thin screens, and inexpensive products are required. A carbon nitride phosphor that can be manufactured at low cost is optimal as a raw material for an inorganic EL light-emitting panel.

  Hereinafter, the phosphor production method of the present invention will be described in more detail. As shown in FIG. 1, the method for synthesizing a carbon nitride-based phosphor of the present invention uses a compound consisting of carbon, nitrogen and hydrogen as a raw material or a compound consisting of carbon, nitrogen, hydrogen and oxygen as a starting material, and a decomposition temperature or This is a method of synthesizing a fluorescent material by intermolecular condensation by heat treatment at a sublimation temperature or higher. The starting material preferably has a structure in which carbon and nitrogen atoms are alternately bonded. Examples of the compound having such a structure include urea, cyanuric acid, melamine, melam and the like.

  These compounds have a structure in which carbon and nitrogen are alternately bonded. For example, urea has a N—C—N structure, and cyanuric acid and melamine have a C—N—C—N—C—N— six-membered ring structure. Moreover, the raw material by which the similarity compound of a melamine and melam is synthesize | combined by heat processing, a mill process, a pressurization process, etc. can also be used.

  However, even with similar nitrogen and carbon compounds, if a compound containing a C—C bond such as adenine is used as a starting material, it is difficult to produce a phosphor.

  These starting materials have the property of sublimation when heated. Therefore, it is necessary to prevent the compound from evaporating due to sublimation.

  In the present invention, a lidded container is used to prevent sublimation. The lid may be a lid with a screw with high airtightness or a lid with high adhesion with a fixing jig, but it can also be used with a lid with low airtightness that is lightly placed. In addition, such a lid with low airtightness may allow oxygen to enter from the outside air, but this is not a problem in the production of the carbon nitride phosphor of the present invention. Actually, a carbon nitride-based phosphor can be produced even by using a lid that is lightly placed on a crucible and filling the starting material with about 80% to 90% of the crucible volume and performing heat treatment. This is considered to be due to generation of ammonia gas due to partial decomposition of the starting material and generation of sublimation gas of the starting material, making it difficult for gas from the outside to enter the container. However, even if the decomposition gas or sublimation gas is filled in the container, it is difficult to completely prevent the invasion of gas from the outside. Therefore, it is considered that a small amount of oxygen does not particularly affect.

  Further, it is preferable that the container occupies a large volume in the heating furnace of the apparatus for heating as much as possible and has few gaps. This is because if the voids are small, the decomposition gas or sublimation gas of the raw material is easily filled in the heating furnace, sublimation of the raw material is suppressed, and the production amount increases. Next, the low gap volume state will be described. The low gap volume means a state in which the container containing the carbon nitride raw material occupies most of the heating furnace inner volume and there are few gaps other than the container. In such a state in which the container occupies most of the volume in the heating furnace, the conditions are the same as those in the pseudo-sealed container, and it is not necessary to cover the container containing the carbon nitride raw material. . The heating apparatus can be used in either an electric furnace or a gas furnace, but in the case of a gas furnace, an external heating type in which heating is performed from the outside of the heating furnace is preferable instead of an internal heating type in which a burner is provided in the heating furnace. When the flame is injected into the heating furnace, the combustion gas and the combustion air are injected together, so that the gas in and out of the heating furnace is increased and decreased, the sublimation of the raw material is promoted, and the production amount is reduced. Moreover, a heating container can be moved in a heating furnace with a conveying apparatus, or a carbon nitride phosphor can be continuously produced in a kiln type heating furnace. In this case, it is important to suppress the sublimation of the raw material by reducing the gas entry and exit.

  The heat treatment temperature when producing the carbon nitride-based phosphor by heat-treating the starting material with the container and the heating device as described above is 250 ° C. to 550 ° C., preferably 300 ° C. to 500 ° C. . If it is less than 250 ° C., the intermolecular condensation of the starting material is difficult to proceed, and a long-time treatment is required, and the production amount is small and not economical. When the temperature exceeds 550 ° C., the product is colored or the intensity of the fluorescence spectrum is extremely lowered, and therefore, it is not suitable as a fluorescent material.

  The heat treatment temperature of the present invention is considerably lower than the temperature for producing ordinary carbon nitride materials. Since carbon nitride is expected as an ultra-hard material, high crystallinity and few impurities have been demanded. Therefore, in order to remove hydrogen which is an impurity and to obtain high crystallinity, it is required to process at a high temperature of 550 ° C. or higher. It was not done.

  It is known that urea as a starting material used in the present invention undergoes intermolecular condensation by heat treatment to become cyanuric acid and melamine. Furthermore, melamine is said to become melam as intermolecular condensation proceeds. Therefore, it can be said that these compounds are intermediate products of intermolecular condensation starting from urea. As this intermolecular condensation proceeds, the final compound becomes only carbon and nitrogen. When melamine is used as a starting material, melam is first produced, but further intermolecular condensation proceeds and the N / C ratio approaches 1.6. A compound of carbon and nitrogen obtained by further intermolecular condensation of melamine from melam is considered to be a phosphor. This compound is produced when a heat treatment at a temperature equal to or higher than the decomposition temperature is performed and becomes a phosphor.

  Since this phosphor is amorphous when heat-treated at less than 500 ° C., it cannot be confirmed by X-ray diffraction. Actually, only the structure of cyanuric acid or melam can be confirmed by measuring the heat-treated compound emitting fluorescence by X-ray diffraction. Therefore, it is not easy to specify a carbon nitride-based phosphor that is partially generated by heat treatment at 450 ° C. or lower. Above 500 ° C., the carbon nitride phosphor has a peak showing a layered structure similar to that of graphite around 2θ = 27 ° as measured by X-ray diffraction. The appearance of the carbon nitride phosphor is white or slightly yellowish white and light gray powder at a processing temperature of 450 ° C. or lower, but is white with a maximum wavelength of 430 nm to 480 nm when excited by 360 nm ultraviolet light. Emits light. At a processing temperature of 500 ° C. or higher, the appearance of the carbon nitride-based phosphor is a yellow powder, which is excited by ultraviolet rays of 360 nm and emits white light having a maximum wavelength around 500 nm.

  In the above, the manufacturing method and utilization method of the phosphor containing no rare earth and noxious substances have been described in detail. Next, the present invention will be described in more detail based on examples.

Example 1
50 g of a commercial reagent, melamine, was placed in a 100 ml crucible. The crucible was covered and heat-treated at 450 ° C. for 2 hours in an electric furnace. The atmosphere in the electric furnace was in the air without nitrogen replacement. After cooling, when taken out from the crucible, it was white powder and its weight was 31 g. Further, when a black light having a central wavelength of 360 nm was irradiated, the light emitted bluish white. The results are shown in Table 1.

Examples 2-5
In the same manner as in Example 1, 50 g of a commercially available melamine was placed in a 100 ml crucible. The crucible was covered, and the temperature of the electric furnace was changed to 300 ° C., 350 ° C., 400 ° C., and 500 ° C., and heat treatment was performed for 2 hours. The atmosphere in the electric furnace was in the air without nitrogen replacement. After cooling, the powder was taken out from the crucible and was white powder. Moreover, when black light having a central wavelength of 360 nm was irradiated, all emitted light with bluish white. The results are shown in Table 1.

Examples 6-10
Cyanuric acid was used as a raw material, and the heat treatment was performed in the same manner as in Example 1 while changing the heat treatment temperature in the range of 300 ° C to 500 ° C. The heat treatment time was 2 hours. The obtained powders were all white powders up to a heating temperature of 450 ° C., but became light yellow when the temperature reached 500 ° C. However, when irradiated with black light having a central wavelength of 360 nm, all emitted light in bluish white. The results are shown in Table 1.

Examples 11-15
Urea was used as a raw material, and the heat treatment was performed in the same manner as in Example 1 while changing the heat treatment temperature in the range of 300 ° C to 500 ° C. The heat treatment time was 2 hours. All of the obtained powders were white powders, and when irradiated with black light having a central wavelength of 360 nm, all emitted light with a bluish white color. The results are shown in Table 1.

Comparative Examples 1-5
As a raw material, melamine, cyanuric acid and urea were used as in the example, and the heat treatment was performed in the same manner as in Example 1 at a low temperature or high temperature outside the range of 300 ° C. to 500 ° C. of the heat treatment temperature of the example. . The heat treatment time was 2 hours. Naturally, the obtained powder was a white powder at a low temperature of 200 ° C., but changed to yellow at a high temperature of 600 ° C. and to an orange color at 700 ° C. When black light having a central wavelength of 360 nm was irradiated, it did not emit light at a low temperature, but emitted light to a yellowish white at a high temperature. The results are shown in Table 1.

Comparative Example 6
About 10 g of a commercially available reagent, adenine, was placed in a 30 ml crucible. The crucible was covered and subjected to heat treatment at 450 ° C. for 2 hours in an electric furnace. The atmosphere in the electric furnace was in the air without nitrogen replacement. After cooling, it was taken out from the crucible and was a bluish black powder. Moreover, although the black light which makes 360nm a center wavelength was irradiated, the fluorescence was not recognized.

  Table 1 summarizes the processing temperature of the nuclear material, the color of the product, and the fluorescent color. Table 2 shows the change in the element molar ratio (N / C and H / C) of each product at the processing temperature. Indicated.

  The molar ratio of the nitrogen carbide product in Table 2 is a value measured with a CHN analyzer. Melamine is N / C = 2 as a raw material, but the heat treatment temperature does not change up to 300 ° C., and when it becomes as high as 500 ° C., N / C = 1.5, and hydrogen is also heated in the molecule. As the condensation proceeds, it decreases. When the heating temperature is increased to 600 ° C. or more, N / C = 1.49 becomes stable.

  The raw material of cyanuric acid is N / C = 1. In this case, the N / C ratio does not change much even when the heat treatment temperature is increased, but the fluorescence intensity is increased. At 500 ° C., the nitrogen content ratio increases. For cyanuric acid only, no correlation between N / C ratio and emission intensity was observed.

  The raw material of urea is N / C = 2. When urea is heat-treated, as shown in the X-ray diffraction spectrum, it polymerizes at 300 ° C. and changes to cyanuric acid. Here, N / C = 1, and then, as the temperature increased, intramolecular condensation progressed, and the N / C ratio approached 1.55.

  Next, each embodiment will be described with reference to the drawing data of FIG. FIG. 2 shows an emission spectrum of a carbon nitride fluorescent material using melamine as a raw material. At a heat treatment temperature of 350 ° C. (Example 3), the center wavelength is 400 nm, which shows a high relative value. The emission intensity increased from the low temperature side, and the emission intensity decreased sharply above 450 ° C. (Example 1) and above 500 ° C. (Example 5).

  FIG. 3 is an X-ray diffraction pattern of the product at each temperature when melamine is used as a raw material. In the case of melamine, it can be seen that the structure of melamine remains up to a heat treatment temperature of 300 ° C., and a melam formed by polymerization of melamine is formed at 400 ° C. to 450 ° C. Furthermore, it can be seen that the product has a layered structure similar to that of graphite after heat treatment at 500 ° C. or higher (Example 5).

  FIG. 4 is an X-ray diffraction pattern of the product at each temperature when cyanuric acid is used as a raw material. Cyanuric acid does not show structural changes up to 450 ° C. This is presumably because the X-ray diffraction intensity of cyanuric acid is large and it is difficult to confirm other peaks. At 500 ° C., a layered structure similar to that of graphite was observed.

  FIG. 5 is an X-ray diffraction diagram of the product at each temperature when urea is used as a raw material. Urea changes to the structure of cyanuric acid at a heat treatment temperature of 200 ° C. or higher. Above 450 ° C., a layered structure similar to that of graphite could be confirmed.

  FIG. 6 is an infrared absorption spectrum of melamine as a raw material. FIGS. 7, 8 and 9 are infrared absorption spectra of the product from the melamine after heat treatment. When the heat treatment temperatures are 400 ° C. and 450 ° C., the melam structure formed by polymerization of melamine is observed. As a result, the spectrum becomes smaller, and a large broad peak can be confirmed as a whole. Rather, thermal decomposition occurs.

  FIG. 10 is an electron microscopic image (10,000 magnifications) of the product of Example 1, in which a state in which the surface is melted is observed, and it is considered that the structure is formed by partial sublimation of melamine as a raw material. It is done.

  FIG. 11 is an electron microscopic image (1000 ×) of the product of Example 14. Here, when urea was heat-treated at 450 ° C., a layered structure similar to that of graphite was already confirmed.

  FIG. 12 is an electron microscope image (13,000 times) of the product of Comparative Example 1. A layered structure similar to that of graphite was confirmed as a whole.

  FIG. 13 is a TG-DTA curve of melamine in nitrogen. When melamine is heated in nitrogen, it completely sublimates at 350 ° C. FIG. 14 is a TG-DTA curve of the product of Example 1 in nitrogen, and it became clear that the carbon nitride fluorescent material started sublimation from 440 ° C. and all sublimated at about 700 ° C.

It is a flowchart which shows the synthesis | combining method of the carbon nitride fluorescent substance of this invention. It is a fluorescence spectrum. It is an X-ray diffraction of the product of each temperature when melamine is used as a raw material. It is an X-ray diffraction of the product of each temperature when using cyanuric acid as a raw material. It is X-ray diffraction of the product of each temperature when urea is used as a raw material. It is an infrared absorption spectrum of melamine. It is an infrared absorption spectrum of the product in Example 1. It is an infrared absorption spectrum of the product of Example 4. 2 is an infrared absorption spectrum of the product of Example 5. It is an electron microscope image (10,000 times) of the product of Example 1. It is an electron microscope image (1000 times) of the product of Example 14. It is an electron microscope image (13000 times) of the product of Comparative Example 1. It is a TG-DTA curve in nitrogen of melamine. 2 is a TG-DTA curve of the product of Example 1 in nitrogen.

Claims (4)

  Using a compound consisting of carbon, nitrogen and hydrogen, or consisting of carbon, nitrogen, hydrogen and oxygen and having a repeating structure of carbon and nitrogen bonds, the compound is at a temperature equal to or higher than its decomposition temperature or sublimation temperature. A method for producing a fluorescent material, characterized in that a heat treatment is performed under a condition in which a sublimation vapor pressure is saturated.   The method for producing a fluorescent material according to claim 1, wherein the compound having a repeating structure of a bond of carbon and nitrogen is melamine, urea or cyanuric acid.   The method for producing a fluorescent material according to claim 1 or 2, wherein the heat treatment of the compound is performed in a temperature range of 250 ° C to 550 ° C.   The method for producing a fluorescent material according to any one of claims 1 to 3, wherein the heat treatment of the compound is performed in a state where there is almost no gas inflow in a lidded container or in a low gap volume state.