JP2005048107A - Phosphor and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phosphor emitting red light on receiving ultraviolet excitation, suitable for uses such as a fluorescent lamp, an LED display and others, and to provide an inexpensive method for producing the same. <P>SOLUTION: The phosphor is obtained by immersing zeolite, especially faujasite-type zeolite, in an aqueous solution of a trivalent europium soluble salt to ion-exchange and firing the ion-exchanged zeolite at 700-1,100°C in an oxidizing atmosphere. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a phosphor that emits light upon being excited by ultraviolet rays, and a method for producing the same.

A phosphor that emits visible light in response to ultraviolet light to near ultraviolet light has been put to practical use in a wide field. Such a phosphor is activated by adding a rare earth element such as europium Eu, terbium Tb, or cerium Ce to a basic material such as a metal oxide, sulfide, or halide. For example, the yttria-based phosphor is manufactured by mixing the trivalent europium oxide Eu ₂ O ₃ with yttria Y ₂ O ₃ and baking it.

  As an example of the technology proposed so far, first, a rare earth metal ion mixed in a zeolite cavity is formed into a complex in which a rare earth metal ion (for example, Rb) has an aromatic carboxylate as a ligand. There is a phosphor with improved quantum efficiency (Japanese Patent Laid-Open No. 5-194951). However, since it is difficult to make the complex exist stably, the lifetime is shortened when the use condition of the phosphor is severe.

  A phosphor that can enjoy a stable lifetime has a structure in which an oxide base is activated by a rare earth metal oxide. For example, an aluminosilicate compound having a meteorite-type crystal structure activated with divalent Eu (Japanese Patent Laid-Open No. 2003-105334) can be mentioned. This phosphor is manufactured by mixing powders such as sodium hydrogen carbonate, silica, alumina, and europium oxide as raw materials and firing in a reducing atmosphere, and has a peak at around 538 nm due to ultraviolet rays in the wavelength range of 220 to 400 nm. It emits yellow light.

    Another example is an alkali metal aluminosilicate having an orthorhombic crystal structure activated with divalent Eu (Japanese Patent Laid-Open No. 2003-105335). This phosphor is also produced by mixing powders such as potassium carbonate, sodium hydrogen carbonate, silica, alumina, and europium oxide as raw materials and firing in a reducing atmosphere, and by using ultraviolet rays in a wavelength range of 220 to 400 nm, 440 And emits blue light having a peak at 446 nm.

  Since the luminance of this type of phosphor increases in proportion to the amount of activator, efforts are made to increase the activator content in the production of the phosphor. However, in the manufacturing method as described above, since both the base material and the activator are powders, and it is difficult to mix the powders uniformly, the activators are likely to be unevenly distributed locally. When unevenly distributed, resonance transfer of energy occurs between the activators, and only a part of the energy given by the excitation light can be used for light emission. This means a decrease in emission intensity.

  As a laser glass for performing laser light emission, there have been proposed ones in which a zeolite and silica, on which a rare earth element is fixed, are mixed and sintered at a temperature of about 1750 ° C. (JP-A-9-86951, JP-A-9-86952). ). This configuration is advantageous in that the emission intensity is not reduced due to the association of rare earth elements.

The inventors noticed that if the ion exchange ability of zeolite is used, it is possible to carry a state in which the rare earth element is uniformly dispersed even at a high concentration. It has been found that a phosphor having high emission intensity and emission efficiency can be obtained by destroying the original crystal structure.
JP-A-5-194941 JP 2003-105334 A JP 2003-105335 A JP-A-9-86951 JP-A-9-86952

  An object of the present invention is to provide a phosphor suitable for applications such as the above-described fluorescent lamp and LED display, particularly a phosphor emitting red light, by utilizing the knowledge of the inventors. It is also included in the object of the present invention to provide a production method capable of producing the above phosphor at a low cost.

  The phosphor of the present invention that achieves the above object is a phosphor obtained by firing zeolite ion-exchanged with a rare earth element.

  The method of the present invention for producing the above phosphor is a production method comprising subjecting zeolite to ion exchange by treating with an aqueous solution of a soluble salt of a rare earth element, followed by firing at a temperature of 700 to 1100 ° C.

  Since the phosphor of the present invention is produced by using zeolite as a base material and carrying a rare earth element as an activator by its ion exchange, even though a relatively high concentration of rare earth is uniformly dispersed, A high emission intensity can be realized by avoiding a decrease in emission intensity due to local uneven distribution of the activator. As a result of the destruction of the original crystal structure of the zeolite by firing, there is no possibility that the light emission is absorbed and the emission intensity is lowered even when left in the atmosphere.

  Since the firing temperature is low, the equipment for firing is simple and the energy required for firing is small, the production cost of the phosphor of the present invention is low. By selecting the firing temperature, the shape and size of the phosphor particles can be adjusted within a certain range, so that a final product suitable for the application, for example, a paint or a molded product can be obtained.

  The zeolite used as a raw material in the present invention may be any of natural and synthetic zeolites, but synthetic zeolites of faujasite type, typically zeolites X and Y are preferred. Needless to say, zeolite having a high ion exchange capacity (CEC) is preferred from the principle of the invention.

  As the rare earth element, trivalent europium is used in order to obtain a phosphor that emits red light by ultraviolet excitation. The so-called impregnation method, in which the zeolite is immersed in an aqueous solution of soluble salts of rare earth elements, such as chlorides, sulfates, nitrates and certain oxides, is suitable for ion exchange with sodium and potassium originally present in the zeolite. .

  Simply exchanging zeolite cations and rare earth elements is not practical as a phosphor because the emission intensity is weak. This is because a quenching phenomenon occurs due to water molecules present in the crystal structure of the zeolite. Water molecules in the crystal are dehydrated by heating to 100 ° C. or higher and 250 ° C., and light emission becomes stronger. However, if left in the atmosphere, it absorbs moisture and the emission intensity decreases again.

  In the present invention, zeolite ion-exchanged with a rare earth element is calcined to a temperature higher than a mere dehydration temperature, and the crystal structure of the zeolite is destroyed. It is a phosphor. When the rare earth element is trivalent Eu by firing, a phosphor that emits red light having a wavelength of 560 to 660 nm is obtained by excitation with ultraviolet light of 350 to 470 nm.

  It is appropriate to perform the baking at a temperature in the range of 700 to 1100 ° C. In the case of zeolite X or Y, which are suitable zeolites, 800 ° C. or higher is preferred. Zeolite X becomes amorphous at 900-1000 ° C. When heated to 1000 to 1100 ° C., a carnegilite-type or nepheline-type crystal structure is obtained. Depending on whether it is amorphous or crystalline (a crystal different from the original crystal structure of the zeolite) and what type of crystal it is, the shape of the phosphor particles will differ, but the emission intensity will vary greatly. Not confirmed. Therefore, a firing temperature that gives a particle shape suitable for the phosphor application should be selected.

  The firing conditions are appropriately selected according to the type and valence of the rare earth element. In the case of the above-described trivalent Eu, if it is made a reducing atmosphere, it is reduced to divalent, so it is necessary to fire in an oxidizing atmosphere. The fired product is subjected to particle size adjustment by pulverization and classification in accordance with the use to obtain a phosphor product. By combining this with an appropriate binder or material to make a product such as a paste, paint or molded article, a final product suitable for the desired application can be obtained.

Prepare 200 mL of EuCl ₃ (Kanto Chemical Co., Inc., purity 99.95%) 0.1 mol / L aqueous solution, and add 5 g of zeolite “F-9” (Zeolite X manufactured by Tosoh Corporation) at room temperature. Stirred and ion exchanged. After 24 hours, solid-liquid separation was performed by suction filtration, and the cake was washed with distilled water. The washing was performed by dropping a silver nitrate solution into the filtrate until no cloudiness occurred. After washing, it was dried at 60 ° C. for 24 hours to obtain Eu-exchanged zeolite. This was put into a platinum crucible and baked at 900 ° C. for 2 hours in an air atmosphere to obtain the phosphor of the present invention.

  FIG. 1 shows an X-ray diffraction chart of the Eu exchanged zeolite obtained in the above production process and the fired product. It turns out that it became amorphous by baking.

  The fluorescence characteristics of this phosphor were measured using a spectrofluorometer. As a result, red fluorescence having an excitation wavelength of 395 nm and an emission wavelength of 610 nm was observed. An emission spectrum at an excitation wavelength of 395 nm is shown in FIG. The emission intensity was 200 times or more that of calcium halophosphate used in ordinary fluorescent lamps.

  The phosphor of the present invention can be used in a wide range of fields such as fluorescent lamps, LED displays, radiation intensifying screens, indoor and outdoor decorations, and the like.

The X-ray-diffraction chart of the Eu exchange zeolite in the fluorescent substance manufacturing process of an Example, and the fluorescent substance obtained by baking it. The chart of the emission spectrum in the excitation wavelength of 395 nm of the fluorescent substance manufactured in the Example.

Claims (6)

A phosphor made by firing zeolite ion-exchanged with rare earth elements. The phosphor according to claim 1, wherein the zeolite is a faujasite type zeolite. The phosphor according to claim 2, wherein the rare earth element is trivalent europium and emits red light when excited by ultraviolet rays. The phosphor according to claim 3, wherein the excitation wavelength is 350 to 470 nm and the emission wavelength is 560 to 660 nm. 4. The phosphor according to claim 3, wherein the zeolite is amorphous or has a nepheline type or carnegilite type structure. The method for producing a phosphor according to claim 1, wherein the zeolite is ion-exchanged by treating with an aqueous solution of a soluble salt of a rare earth element, and then calcined at a temperature of 700 to 1100 ° C.

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