JP2014019803A - Alumina crystal powder having oxygen defect by sulfur atom doping, method for manufacturing the same and emitter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an emitter capable of using an inexpensive aluminium compound and emitting light even when excited by ordinary ultraviolet rays.SOLUTION: A method for manufacturing an alumina crystal powder having oxygen defects by sulfur atom doping comprises the steps of: (I) preparing an aqueous solution (A) of a polyamine; (II) preparing an aqueous solution (B) of an aluminium sulfate; (III) mixing the aqueous solutions (A) and (B) obtained by the step (I) and (II) to deposit an insoluble composite (C) including the polyamine and the aluminium sulfate from the mixed solution; (IV) collecting and drying the composite (C) deposited in the step (III); and (V) heating and sintering the dried composite obtained in the step (IV). The alumina crystal powder obtained by the method and the emitter made of the powder are provided.

Description

  The present invention relates to an oxygen-deficient alumina crystal powder doped with sulfur atoms and a method for producing the same. More specifically, a sulfur atom-doped oxygen-deficient alumina crystal powder, which is obtained by heating and firing a composite of polyamine and aluminum sulfate, is excited by light in the ultraviolet region wavelength, and emits fluorescence and phosphorescence, and a method for producing the same , And a light emitter.

  Luminescent materials and fluorescent materials in the visible light region are widely used in industries ranging from various electronic and optical devices to various medical and sensor reagents and markers. For example, in the medical field, a fluorescent material is often used as a labeling substance, and silica beads adsorbing fluorescent dye molecules are known (see, for example, Patent Document 1). This has the advantage that the dye molecules can be trapped in the pores of the porous silica beads that can be easily synthesized. On the other hand, when this material is used in a solvent, there is a problem that the physically adsorbed fluorescent dye molecules are easily detached.

  In addition, a rare earth metal ion is doped into an oxide crystal matrix, and a metal oxide-based light-emitting material having the metal ion as a light emission center is required for industrial devices and precision machinery as photoluminescence and electroluminescence materials. It is a luminescent material that must not be. Compared with light emitting materials of organic light emitting materials or rare earth metal complexes, rare earth metal ion doped metal oxide light emitting materials are less likely to deteriorate due to the operating environment, and their light emitting functions remain stable even under severe conditions of high temperature and high humidity. it can. However, since rare earth metals are used, the development of oxide light emitters using base metal elements widely embedded in the earth has become an important issue because it is difficult to guarantee industrial supply with the depletion of resources. .

  Base metal oxide-based light-emitting materials include oxides composed of alkaline earth metals (Ba, Mg), transition metals (Zn), semimetals (Si), and the like, which are visible light by vacuum ultraviolet irradiation or electron beam irradiation. It is known that light can be emitted in a region (see, for example, Patent Document 2). However, these luminescent materials emit light by high excitation energy such as vacuum ultraviolet rays and electron beams, and cannot emit light with ordinary ultraviolet rays.

  In addition, as base metal oxide-based light emitting materials, zinc oxides and sulfides have long been known as semiconductors that can emit light in the visible light region by ultraviolet excitation, and phosphor materials that use them have been actively designed. (For example, see Non-Patent Documents 1 and 2 and Patent Document 3). However, there is a problem that the zinc compound generally has low alkali resistance and acid resistance, so that the light emitting function is affected by ambient conditions, and there is a limit to practical applications that require long-term stability. .

  In addition, when α-alumina is heat-treated in a high-temperature and high-vacuum atmosphere, oxygen defects (F +, F) are generated in the alumina crystal, and this acts as a luminescent center, thereby providing photoluminescence. It is known (for example, see Non-Patent Document 3). There is also a report that a phosphor composite material can be obtained by combining silica, alumina or the like with nitrogen atoms or carbon atoms (see, for example, Patent Document 4). In Patent Document 4, an organic compound such as melamine, urea or cyanuric acid is mixed with silica and an alumina porous body and heat-treated in a vessel with a lid in the range of 250 ° C. to 600 ° C. to bond carbon and nitrogen. A method for producing a fluorescent material from an intermolecular condensate of a compound having a repeating structure is provided. However, in this production method, at the time of firing, sublimation of the carbon nitride raw material is used to adsorb it to porous pores, and a phosphor is synthesized by intermolecular condensation of the carbon nitride raw material inside the pores. However, since the penetration of the carbon nitride raw material into the pores hardly occurs from the beginning, variation in the composition of the luminescent material after firing cannot be avoided, and ensuring uniformity as the luminescent material is not easy.

C. Klingshirn, ChemPhysChem, 8, 782, 2007 J. et al. Mater. Sci. Technol. , Vol. 24, no. 4,2008 Akselrod, M.M. S. et al. , Radiation Protection Dosimetry, Vol. 47 (1-4), 1993, P159-164

JP 2003-270154 A JP 2006-274274 A JP 2010-215787 A JP 2008-144012 A

  The problem to be solved by the present invention is to provide a luminous body that exists universally on the earth and that uses inexpensive aluminum as a metal component and emits light even under normal ultraviolet excitation. It is an object of the present invention to provide a defective alumina crystal powder, a simple manufacturing method thereof with good reproducibility, and a light emitter using the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have established a crosslinked gel-insoluble complex formed from a polyamine and aluminum sulfate that can be coordinated to a metal ion and can be protonated. However, focusing on the fact that it exhibits plasticity and foamability under heating, forming a foam film in the process of increasing the heating temperature, thermal decomposition of polyamine and oxidation of aluminum proceed in the foam film, and sulfur in alumina The inventors have found that atoms are converted into oxygen-deficient crystals that are doped, and that they emit light by ultraviolet absorption, and the present invention has been completed.

That is, the present invention is a method for producing sulfur atom doping oxygen defect alumina crystal powder,
(I) a step of preparing an aqueous solution (A) of a polyamine,
(II) preparing an aqueous solution (B) of aluminum sulfate;
(III) A step of mixing the aqueous solutions (A) and (B) obtained in step (I) and step (II) and precipitating an insoluble complex (C) containing polyamine and aluminum sulfate from the mixed solution,
(IV) recovering and drying the composite (C) precipitated in step (III),
(V) a step of heating and firing the dried composite obtained in step (IV),
The present invention provides a method for producing a sulfur atom-doped oxygen-deficient alumina crystal powder, an alumina crystal powder obtained therefrom, and a luminescent material comprising the powder.

  Since the phosphor of the present invention can be manufactured by a simple process using aluminum sulfate, which is industrially inexpensive and easily available, as a starting material, it can be manufactured in any region without any resource limitation. It can be manufactured and has excellent reproducibility.

  In addition, since the phosphor of the present invention is an alumina γ crystal, it is strong in heat resistance, chemical resistance, solvent resistance, alkali resistance, acid resistance, and is widely applied as a light emitting material without being restricted by the environment. it can.

It is the X-ray diffraction pattern before and behind baking at 800 degreeC of composite_body | complex Al-0.5 and Al-0.7. It is a transmission electron microscope image of the sample which baked composite Al-0.5 at 790 degreeC. It is a fluorescence and phosphorescence emission spectrum of the sample which baked composite Al-0.5 at 790 degreeC. In the figure, EX is an excitation spectrum, and EM is an emission spectrum.

  The production of the sulfur atom-doped oxygen-deficient alumina crystal powder of the present invention is a method using a crosslinked structure of a cationic polyamine / sulfuric acid radical ion (hereinafter sometimes abbreviated as a complex) containing a large amount of metal aluminum ions. is there. The feature of this production method is that aluminum ions are uniformly distributed at the molecular level in the above-described complex due to coordinate bond with polyamine. When the composite after drying is heated and calcined, aluminum ions combine with oxygen, and at the same time, the oxygen concentration decreases due to thermal decomposition of organic components present around them, and sulfur generated by thermal decomposition of sulfate radical ions. Atoms are doped into the crystal lattice of aluminum oxide instead of some oxygen atoms. Therefore, after firing, the composite becomes an oxygen defect type alumina crystal doped with sulfur atoms, and becomes a light emitter by the action of the doping of different atoms and crystal structure defects.

  In general, polyamines can complex with metal aluminum ions. Due to the high polarity and strong hydrophilicity derived from the molecular structure of the polyamine itself, when a sulfate radical anion, which is a counter ion of the metal cation (aluminum ion) of the metal compound, is added to the polyamine in an aqueous medium, it causes protonation of the polyamine. This causes an electrostatic interaction between the cationic polyamine and the sulfate radical anion to induce a physically crosslinked gel. At the same time, a hydroxyl group is bonded to the aluminum cation, and the aluminum ion is also involved in the physical crosslinking and is taken into the gel. Thus, a complex formed from the polyamine, the aluminum cation and the sulfate radical anion is obtained. When such a gel-like composite is dried, it becomes powdery, but the glass transition temperature of the powder appears in the range of room temperature or higher. As the foaming proceeds, the initial powder is formed into a film. When the film is further baked on the higher temperature side, the organic component of the polyamine is completely pyrolyzed, and at the same time, the aluminum oxide contained in the film remains as a sheet-like alumina having a two-dimensional structure.

  In the present invention, based on such an idea, the formation of a complex containing a polyamine and a metal aluminum ion is examined in detail, and a complex having a basic composition of a polyamine, a sulfate radical anion, and an aluminum cation is insoluble in water. It has been found that it precipitates as a complex. Furthermore, when this gel-like composite is dried, it becomes powder, and this powder is fired at a high temperature, so that it is contained in the composite in a reducing atmosphere formed by thermal decomposition of polyamine organic components and sulfate radical ions. The present inventors have found that aluminum ions are changed to alumina crystals having oxygen defects. Further, finally, a sulfur atom-doped oxygen defect alumina crystal having a small amount of sulfur atoms as impurities is obtained. Hereinafter, the present invention will be described in detail.

[Polyamine]
The polyamine used in the present invention may be a polymer having an amine functional group, and the amine functional group may be any of primary, secondary and tertiary amines, or a mixed state containing a plurality of these functional groups.

  Polyamines are generally polyethyleneimine, polyallylamine, polyvinylamine, polylysine, chitosan, polydiallylamine, poly (N-dimethylaminoethyl (meth) acrylate), poly (N-diethylaminoethyl (meta) ) Acrylate), poly (4-vinylpyridine), poly (2-vinylpyridine), poly [4- (N, N-dimethylaminomethylstyrene)] and the like can be suitably used. Among these, polyethyleneimine is industrially easily available, excellent in chemical stability, and strong in coordination with metal ions, so that it can be particularly preferably used. These polyamines are preferably water-soluble, and the number average molecular weight is preferably appropriately selected from the range of 1000 to 1,000,000 depending on the type. The polyamine is used as an aqueous solution, and the concentration of the aqueous solution may be in the range of 2 to 30 wt%. That is, the concentration is preferably a uniform aqueous solution in this range, and most preferably a uniform aqueous solution at room temperature (range of 20 to 30 ° C.). From the viewpoint of easy handling (viscosity is not excessively high, etc.), it is actually preferable to prepare in the range of 2 to 18 wt%. Further, a solvent miscible with water may be used in combination as long as the effects of the present invention are not impaired.

[Composite (C)]
By mixing the aqueous solution of polyamine (A) and the aqueous solution of aluminum sulfate (B) at room temperature (about 20 ° C.) to 80 ° C. with stirring, it is a gum-like insoluble gel from the mixed aqueous solution. The composite (C) can be precipitated. This precipitate cannot be dissolved even when heated in water, and cannot be dissolved in other organic solvents.

  The complex (C) is composed of a polyamine, an aluminum cation, and a sulfate radical anion. Among them, the aluminum cation and the sulfate radical anion interact with an amino group in the polyamine to form an insoluble structure. It is a gel. Specifically, in the case of a sulfate radical anion, due to the acidity of the pH value in the solution, the amino group in the polyamine is protonated in an aqueous solution, the polyamine behaves as a polycation, and the sulfate radical anion is in contact with the polycation. A crosslinked structure is formed by electrostatic interaction. Also, the aluminum cation is coordinated to an amino group in the polyamine, but if the coordination bond occurs between polyamine molecules, it can also cause a gel structure. As a result of such interaction, the complex (C) contains the aluminum cation and sulfate anion electrolytes used in the mixing uniformly.

  In the step of obtaining the composite (C), the molar ratio of the amino group and the aluminum cation in the polyamine is set in the range of 4: 1 to 1: 4 from the viewpoint that the composite can be easily obtained. Is preferred. In order to obtain a more stable composite (C) with good yield, it is desirable to set the molar ratio in the range of 0.3 to 1.5.

  The complex (C), which is a precipitated insoluble gel, tends to become one lump in water, and the supernatant can be removed by decantation and washed with distilled water or a solvent such as ethanol or acetone. The complex (C) after washing can be dried to a powder state by drying at room temperature or under reduced pressure heating at 60 to 90 ° C.

[Step of obtaining sulfur atom-doped oxygen-deficient alumina crystal powder by heating and firing composite (C)]
By heating and firing the composite (C) in the dry state obtained above, the behavior described above occurs, and as a result, sulfur atom-doped oxygen-deficient alumina crystal powder is obtained. The method for heating and baking is not particularly limited. For example, in accordance with a normal method, for example, a program in which the composite after drying is put in a crucible and set in an electric furnace, and the furnace temperature is set. You can raise it.

  Although the maximum temperature for heating and firing can be set up to 1500 ° C., the maximum firing temperature is appropriately adjusted to 1000 ° C., 800 ° C., 700 ° C., 600 ° C. or 500 ° C. in order to develop the desired light emission characteristics. It is desirable. Although baking time is related also to temperature, it is preferable to set in the range of 1 hour-about 5 hours in general. The heating and baking may be performed in an atmosphere in which polyamine and sulfate anion are thermally decomposed, and are not particularly limited.

[Luminescent body made of sulfur atom-doped oxygen-deficient alumina crystal powder]
Alumina in the sulfur atom-doped oxygen-deficient alumina crystal powder of the present invention obtained through the above-described steps indicates that it is a γ crystal. When the alumina crystal is a γ crystal, the powder has properties such as heat resistance, chemical resistance, solvent resistance, alkali resistance, and acid resistance.

  The powder has a sheet-like structure as a basic structure, and a thickness of about 50 nm to 500 nm can be obtained. Although the degree of spread in the two-dimensional direction depends on the firing conditions, a range of 80 nm to 300 nm can be obtained.

  In the sulfur atom-doped oxygen-deficient alumina crystal powder, the content of doped sulfur atoms can be adjusted in the range of 1.0 to 10.0% by mass by adjusting the firing conditions and the like. is there.

  By being doped with such heterogeneous atoms to form an oxygen-deficient alumina crystal, the powder absorbs ultraviolet rays in a range of 250 to 380 nm and generates phosphorescence in a range of 390 to 650 nm. Will have. The wavelength center of the generated phosphorescence can be adjusted by the content of doped sulfur atoms and the like, and in the case of phosphorescence, a long afterglow life of about 1 second is a major feature.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, “%” represents “mass%”.

[Analysis by X-ray diffraction method]
Place the isolated and dried sample on the holder for the measurement sample, set it on the wide-angle X-ray diffractometer “Rint-Ultma” manufactured by Rigaku Corporation, Cu / Kα ray, 40 kV / 30 mA, scan speed 1.0 ° / min. The measurement was performed under conditions of a scanning range of 10 to 70 °.

[Differential scanning calorimetry]
The isolated and dried sample is weighed with a measurement patch, set in a SII nano-technological differential scanning calorimetry measuring device (TG-TDA6300), and the temperature rise rate is 10 ° C./min. Measurements were made at

[Microstructural analysis by transmission electron microscope]
A sample dispersed with ethanol was placed on a sample support film and observed with a transmission electron microscope apparatus (JEM-2000FS) manufactured by JEOL Ltd.

[Evaluation of photoluminescence characteristics by fluorescence phosphorescence spectrometer]
An ultraviolet-excited photoluminescence characteristic was evaluated with a fluorescent phosphorescence spectrometer (F-4500) manufactured by Hitachi, with a powdery sample sandwiched between two quartz glass plates.

Example <Preparation of complex containing hyperbranched polyethyleneimine and aluminum ion>
An aqueous solution of 5% multi-branched polyethyleneimine (Epomin, sp-200, manufactured by Nippon Shokubai Co., Ltd.) was prepared, and 10 mL of an aqueous aluminum sulfate solution having different molar concentrations as shown in Table 1 was added to 10 g of the aqueous solution. The mixture was added dropwise and the mixture was stirred at room temperature (25 ° C.) for 1 hour. The precipitate from the solution was isolated with a centrifuge (10000 rpm, 10 minutes), and the supernatant was removed, followed by washing with distilled water three times. The obtained solid was dried under reduced pressure at 90 ° C. for 10 hours to obtain a solid powder.

  As shown in Table 1, when the aqueous solution was mixed, the yield increased as the molar ratio of aluminum cation to nitrogen in polyethyleneimine was increased. As a result of thermal analysis (TG-DTA) of the powder after drying of the composite Al-0.5, an endothermic peak at 326 ° C. and a heat release peak at 553 ° C. appeared. By calcination up to 800 ° C., the total weight loss was 82.7%. Further, as a result of DSC measurement, the complex showed glass transition behavior in a temperature range higher than room temperature.

<Baking of composite>
It was confirmed that the powder after drying of the composite Al-0.5 synthesized above was fired in the air at each temperature to obtain a γ-alumina crystal structure at 800 ° C. from the amorphous state (FIG. 1). ). According to the result of X-ray fluorescence analysis, the content of the main component Al ₂ O ₃ was 96.2 wt% and the residual amount of SO ₃ was 3.8 wt% in the obtained powder fired at 800 ° C. (Table 2). The powder after firing swelled several times as much as the composite before firing and was a porous body. When this powder was crushed and observed with a transmission electron microscope, many sheet-like structures could be confirmed (FIG. 2).

When the composite Al-0.7 obtained above is fired in the air at each temperature, the composite in an amorphous state is converted into a crystal of γ-Al ₂ O ₃ partially crystallized by firing at 800 ° C. It was confirmed that it became (Fig. 1). Furthermore, when it baked to 1000 degreeC, the X-ray-diffraction peak became strong and it was suggested that the crystal | crystallization of (gamma) -alumina progressed notably. According to the result of X-ray fluorescence elemental analysis, the content of the main component Al ₂ O ₃ was 98.0 wt% and the residual amount of SO ₃ was 2.0 wt% in the powder obtained at 800 ° C. (Table 2).

  Table 3 shows the influence of the firing temperature on the light emission characteristics. In the case of the composite Al-0.5, the strongest luminescence intensity (white) was confirmed in the powder obtained at the firing temperature of 790 ° C. (FIG. 3). A fluorescence emission spectrum centered on a wavelength of 460 nm is detected for excitation light having a wavelength of 350 nm, and a wide range of 380 to 650 nm is centered on wavelengths of 390 and 500 nm by absorbing light of wavelengths 280 and 340 nm, respectively. Phosphorescence emission was observed in.

Comparative Examples 1 and 2
5 g of alumina powder (Wako Pure Chemical Industries) was thoroughly mixed with 5 g of multi-branched polyethyleneimine (PEI, Nippon Shokubai, molecular weight 10,000) and dried under reduced pressure conditions for 24 hours. A white powder was obtained after baking at 800 ° C. No fluorescent phosphorescence was detected in all the obtained powders.

Claims (11)

A method for producing sulfur atom doping oxygen defect alumina crystal powder,
(I) a step of preparing an aqueous solution (A) of a polyamine,
(II) preparing an aqueous solution (B) of aluminum sulfate;
(III) A step of mixing the aqueous solutions (A) and (B) obtained in step (I) and step (II) and precipitating an insoluble complex (C) containing polyamine and aluminum sulfate from the mixed solution,
(IV) recovering and drying the composite (C) precipitated in step (III),
(V) a step of heating and firing the dried composite obtained in step (IV),
A method for producing a sulfur atom-doped oxygen-deficient alumina crystal powder, comprising: The method for producing a sulfur atom-doped oxygen-deficient alumina crystal powder according to claim 1, wherein the polyamine used in the step (I) is water-soluble and has a number average molecular weight of 1,000 to 1,000,000. The use ratio of the aqueous solution (A) and the aqueous solution (B) in the step (III) is in the range of 0.3 to 1.5 as the molar ratio of the amino group to the aluminum cation in the polyamine. The manufacturing method of the sulfur atom doping oxygen defect alumina crystal powder of description. The method for producing a sulfur atom-doped oxygen-deficient alumina crystal powder according to any one of claims 1 to 3, wherein the heating and firing in the step (V) is performed in an air atmosphere. A sulfur atom-doped oxygen-deficient alumina crystal powder obtained by the production method according to any one of claims 1 to 4. The sulfur atom-doped oxygen-deficient alumina crystal powder according to claim 5, wherein the alumina in the sulfur atom-doped oxygen-deficient alumina crystal powder is a γ crystal. The sulfur atom doping oxygen defect alumina crystal powder according to claim 5 or 6, wherein the sulfur atom doping oxygen defect alumina crystal powder has a sheet-like structure as a basic structure. The sulfur atom doping according to any one of claims 5 to 7, wherein the sulfur atom doping oxygen-deficient alumina crystal powder has a doped sulfur atom content of 1.0 to 10.0% by mass. Oxygen-deficient alumina crystal powder. An illuminant using an oxygen-deficient alumina crystal doped with sulfur atoms. The phosphor according to claim 9, wherein the oxygen-deficient alumina crystal doped with sulfur atoms is obtained by the production method according to claim 1. The light-emitting body according to claim 9 or 10, which emits light in the near-ultraviolet region or visible light region by absorbing ultraviolet rays.