JP2007177010A - Core/shell type particulate phosphor and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a core/shell type particulate phosphor having high crystallinity and excellent particle size distribution and is particularly excellent in light emission luminance, and to provide a method for producing the same. <P>SOLUTION: The method for producing a particulate phosphor comprises forming core/shell type particles through three specific steps including a step using spray pyrolysis. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a core / shell type fine particle phosphor and a method for producing the same. In particular, the present invention relates to a so-called nanoparticle phosphor having an average particle diameter of 1 to 10 nm.

  Phosphors are materials that convert the energy of excitation rays into light (ultraviolet rays, visible light, infrared rays, etc.) by irradiating excitation rays (ultraviolet rays, visible light, infrared rays, heat rays, electron rays, X-rays, etc.). As commonly used. Examples of the device using the phosphor include a fluorescent lamp, an electron tube, a cold cathode display, a fluorescent display tube, a plasma display panel (hereinafter also referred to as “PDP”), an electroluminescence panel, a scintillation detector, An X-ray image intensifier, a thermofluorescence dosimeter, an imaging plate, etc. are mentioned (for example, refer nonpatent literature 1). Each of these devices is a device that converts electrical energy into excitation ray energy and further converts excitation ray energy into light. An electronic device in which such a device is combined with an electronic circuit or a device component (such as a lighting device, a computer, a keyboard, and an electronic device that does not use a phosphor) is widely used as a lighting device or a display device.

  In addition, as a phosphor-using article using a phosphor, a phosphor in which a powdery phosphor is combined with a substance other than the phosphor, such as a liquid such as water or an organic solvent, a resin, a plastic, a metal, or a ceramic material. These include, for example, liquids and pastes such as phosphor paints, solids such as ashtrays, display materials such as guide plates and guidance articles, seals, stationery, outdoor products, safety signs, etc. Widely used.

  Furthermore, not only the above-mentioned uses but also progress in utilization in the medical field and bio field such as use as a tracer is expected.

  On the other hand, in recent years, attention has been paid to the fact that nanostructure crystals exhibit specific optical characteristics in II-VI group semiconductors such as ultrafine particles such as Si and Ge, and porous silicon. Here, the nanostructure crystal means a crystal grain having a particle diameter of about 1 nm to 100 nm, and is generally called a nanocrystal.

  In the II-VI group semiconductor, when the nanostructure crystal as described above is compared with the case of having a bulk crystal, when the nanostructure crystal is included, good light absorption characteristics and light emission characteristics are exhibited. It will be. This is presumably because a II-VI group semiconductor having a nanostructure crystal has a larger band gap than a bulk crystal structure because a quantum size effect is exhibited. That is, in the II-VI group semiconductors having nanostructure crystals, it is considered that the band gap may be widened by the quantum size effect.

  By the way, various phosphors are used in displays such as televisions. At present, the particle size of a phosphor used in a display such as a television is about several microns (3 to 10 μm). In recent years, various displays have been developed. In particular, from the viewpoint of thinning, a plasma display (PDP), a field emission display (FED), an electroluminescence display (ELD), and a SED (Surface-conduction Electron-emitter Display). ) Is attracting attention.

  Among them, in the FED, when the thickness is reduced, it is necessary to lower the voltage of the electron beam. However, in a thin display, when a phosphor having a particle size of about several μm as described above is used, the voltage of the electron beam is low, so that it does not emit light sufficiently. That is, such a thin display cannot sufficiently excite a conventional phosphor. This is because the conventional phosphor crystal is large and the irradiated electron beam cannot reach the light emitting portion of the light emitter. That is, a conventional phosphor having a particle size of about several μm does not emit light sufficiently when used in a thin display. Therefore, it can be said that phosphors that can be excited at a low voltage are suitable for thin displays, particularly FEDs. Examples of the phosphor satisfying such conditions include II-VI group semiconductors having the nanostructure crystals as described above. However, the nanostructure crystals that have been studied so far have problems such as insufficient luminance due to size distribution failure due to aggregation and light emission killer due to a large number of crystal surface defects, and uneven brightness (for example, Patent Document 1). ~ 4).

  Also, in the field of biotechnology, fluorescent substances made of organic molecules have been used as labels for research and clinical examinations of viruses and enzymes, and the fluorescence emitted when irradiated with ultraviolet light has been used in optical microscopes or photodetectors. The method of measuring with is taken. As such a method, for example, an antigen-antibody fluorescence method is widely known.

  In this method, an antibody (referred to as a specific binding substance) bound with an organic fluorescent substance that emits fluorescence is used. Since the antigen-antibody reaction is very selective, the position of the antigen can be known from the fluorescence intensity distribution.

  By the way, in this field, in recent years, there is a strong demand for observing a size smaller than about 1 μm and studying a more precise antibody distribution. In order to achieve this, it is necessary to rely on an electron microscope.

  In observation with an electron microscope, an image is observed using the difference in electron beam reflectance or transmittance of the specimen. For this reason, when an antibody is observed with an electron microscope, a molecule containing iron or osmium having a large atomic weight or a gold colloid having a size of about 1 to 100 nm is currently used as a label for the antibody. For example, when gold colloid is used as a label, a complex of protein A and gold colloid is bound to the antibody. Since this antibody binds to the corresponding antigen by an antigen-antibody reaction, the location of the antigen can be clarified by measuring the position of the gold colloid on the specimen. Furthermore, if two or more types of gold colloids having different sizes are bound to a plurality of types of antibodies, a plurality of antigens can be observed simultaneously. However, this method has a drawback that colloids may overlap at the time of measurement, and quantitative determination is difficult only by measuring the number of colloids.

  It is also difficult to observe the cathodoluminescence image using the above-described organic phosphor as a label. In other words, in addition to the low luminous efficiency inherently, organic phosphors are easily broken due to electron beam irradiation, and the light emission ability is reduced by a single scan. It does not endure. These organic phosphors also lack stability during storage and cause deterioration. In addition to molecular organic fluorescent dyes, polystyrene spheres having a particle size of several tens of nm and emitting red, green, or blue light are known as phosphors composed of organic molecules. There are exactly the same problems.

On the other hand, inorganic phosphors are stable to ultraviolet irradiation and electron beam irradiation and have little deterioration. However, phosphors industrialized for TVs or lamps are usually 1 μm or more in size and cannot be used as they are as antigen-antibody reaction phosphors. In order to reduce the particle size, it is conceivable to pulverize the phosphor or etch it with an acid. However, in these methods, the ratio of the non-light emitting layer covering the surface of each particle increases, so that the luminous efficiency is improved. It will drop significantly.
JP 2002-322468 A JP 2005-239775 A Japanese Patent Laid-Open No. 10-310770 JP 2000-104058 A “Phosphor Handbook” edited by Phosphors Society, Ohmsha, 1987

  The present invention has been made in view of the above problems, and its object is to provide a core / shell type fine particle phosphor having high crystallinity, excellent particle size distribution, and particularly excellent emission luminance, and a method for producing the same. There is to do.

  The above-described problems of the present invention are solved by the following means.

1. In the method for producing a fine particle phosphor, a core / shell type particle is formed through at least the following three steps.
First step: An aqueous solution (A) containing a constituent metal element forming a core of a phosphor and an aqueous solution (B) containing a constituent element forming a shell are prepared in advance, and a precursor is prepared from the aqueous solution (A) by a reaction crystallization method. A body particle-containing liquid is prepared, the precursor particle-containing liquid is finely dropletized, introduced into a tubular heating furnace while flowing together with a carrier gas, and dried and heated to form core particles.
Second step: A liquid containing the constituent elements forming the shell is finely formed into droplets and mixed with the core particles formed in the first step while flowing together with the carrier gas.
Third step: The mixed droplets / core particles are introduced into a tubular heating furnace, heated and dried to form a shell.

  2. 2. The method for producing a fine particle phosphor according to 1 above, wherein the particle size dispersion coefficient of the precursor particles formed by the reaction crystallization method is 5% to 20%.

  3. A fine particle phosphor produced by the method for producing a fine particle phosphor according to 1 or 2 above, wherein the fine particle phosphor has an average particle diameter of 1 to 10 nm.

  According to the present invention, it is possible to provide a core / shell type fine particle phosphor having high crystallinity, excellent particle size distribution, and particularly excellent emission luminance, and a method for producing the same.

The method for producing a fine particle phosphor of the present invention is characterized in that in the method for producing a fine particle phosphor, core / shell type particles are formed through at least the following three steps.
First step: An aqueous solution (A) containing a constituent metal element forming a core of a phosphor and an aqueous solution (B) containing a constituent element forming a shell are prepared in advance, and a precursor is prepared from the aqueous solution (A) by a reaction crystallization method. A liquid containing body particles is prepared, the precursor particle-containing liquid is made into fine droplets, introduced into a tubular heating furnace while flowing together with a carrier gas, and dried and heated to form core particles. .
Second step: A liquid containing the constituent elements forming the shell is finely formed into droplets and mixed with the core particles formed in the first step while flowing together with the carrier gas.
Third step: The mixed droplets / core particles are introduced into a tubular heating furnace, heated and dried to form a shell.

  As a result of intensive studies aimed at solving the above-mentioned problems of phosphors having nanostructure crystals (also referred to as “nanoparticle phosphors”), the present inventors have prepared precursors in a process in which the particle size should be controlled in the direction of fine particles. In addition to obtaining core particles of high crystallinity and uniform composition by sometimes taking a reactive crystallization method and heating it while controlling the temperature in the gas flow path in the state of being atomized by spraying, Similarly, it has been found that fine particles having a highly core / shell structure can be obtained by coating the surface of the core particles with a shell component by spray pyrolysis. This is thought to be due to the shell affecting the stabilization of surface defects.

  This is because, in addition to the core, the shell is coated with a uniform composition and a uniform thickness on the surface of the core with a uniform composition, so that the effect of dramatically increasing the quantum confinement effect can be achieved with a nano-sized crystal. In addition, the present invention has been found that the same effect can be exhibited not only in the nano size but also in a fine particle phosphor of 0.1 μm or less.

  Hereinafter, the present invention and its components will be described in detail.

  The reaction crystallization method is a method of producing fine particles by controlling the degree of supersaturation while stirring the two liquids that react. This reactive crystallization method is useful in terms of energy saving and the like as compared with a method for producing fine particles by other physical and chemical methods. In addition, it is an effective technique for easily obtaining a monodispersed particle distribution and obtaining high composition uniformity among liquid phase methods. As a specific application example of the reaction crystallization method, a method of producing silver halide fine particles which are hardly soluble salts by reacting silver ions and halide ions in an apparatus is known and manufactured. Silver halide fine particles are preferably used as photosensitive fine particles in the photographic industry and the like. Even in the phosphor forming the nanostructured crystal of the present invention, the particle size distribution is monodispersed and high by controlling the size to be atomized (less than 3 μm) by using the reaction crystallization method to make the composition within the particles and the composition between the particles uniform. A uniform precursor can be obtained, followed by atomization and spraying, followed by heating and drying to achieve nano-sizing, high crystallization, and improved particle size distribution.

  Conventionally, in the case of producing a hardly soluble salt such as silver halide by the reaction crystallization method, the fine particles are generated under a high supersaturation level, so that the fine particles grow excessively or cause aggregation between the fine particles. There was a thing. For this reason, normally, a monodisperse fine particle has been made uniform by using gelatin which is an aggregation inhibitor. Similarly, in the present invention, depending on the composition of the target crystal, a dispersing agent (for example, a certain surfactant, protective colloid agent, low molecular glycol etc) may be added.

  The 50% volume particle size (Dv50) of the precursor particles obtained by the reaction crystallization method is 0.5 μm (= 500 nm) or less, preferably 0.1 μm (= 100 nm) or less, particularly preferably 0.03 μm. (= 30 nm) or less. For the particle size, the cumulative 50% volume particle size measured by the laser scattering method was taken as 50% volume particle size (Dv50).

  Although it is preferable to be in the state of a dispersion in the state of primary particles (fine particles in which the precursor is initially formed), the aggregated secondary particles may be in the particle size range of the present invention. The particle size dispersion coefficient (Σ [(particle size−average particle size) / average particle size] / percentage of the number of particles) of the precursor particles is preferably 5% to 20%.

  In the method for producing a fine particle phosphor according to the present invention, a precursor having a monodispersed and highly uniform particle size distribution as described above is obtained, and it is nanosized in a particle forming process in which fine droplets are sprayed, heated and dried.・ High crystallization and improved particle size distribution can be achieved. For example, the average particle diameter of the fine particle phosphor according to the present invention can be set in the range of 1 to 10 nm by the method of Examples described later.

  For the production of the droplets, any means usually used in the thermal decomposition method can be used. For example, there are superheated sprayers, ultrasonic sprayers, vibration sprayers, rotary desk sprayers, electrostatic sprayers, reduced pressure sprayers, and the like. The size and distribution of droplets produced by the spraying means have an influence on the size and particle size distribution of the produced primary particles, so they are properly used according to the target particles.

  In the present invention, it is preferable to use droplets of the precursor particle-containing liquid that are formed into droplets in proportion to the size of the precursor particles.

  The droplet heat treatment step uses a carrier gas such as air, nitrogen, helium, argon or hydrogen, and is heated at an optimum flow rate in the flow path of the heating furnace. By setting the temperature of the heating furnace so that the temperature can be controlled, the size / distribution and crystallinity of the fine particles targeted by the present invention can be controlled.

  As described above, the method for producing a fine particle phosphor of the present invention is also applicable as a method for producing a fine particle phosphor having a 50% volume particle size (Dv50) of 1 to 10 nm, that is, a so-called nanoparticle phosphor. is there.

  The nanoparticle phosphor according to the present invention can be used for various purposes and applications as described in the “Background Art” section.

  For example, when a fine particle or nanoparticle phosphor of 500 nm or less is used in the form of a coating film, a coating method using an inkjet nozzle can be used. Conventional phosphors with a size of several μm are likely to be clogged with nozzles, and the nozzle diameter needs to be adjusted to the size of the phosphor, which is unsuitable for applying fine patterns. By applying the nanoparticles using an inkjet nozzle having a small nozzle diameter, a fine pattern can be applied.

  Examples of such application applications include the production of fluorescent panels such as PDP / FPD, and the production of fluorescent ink prints (posters, signboards, T-shirts, etc.) using nanoparticles.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this.

<Production of phosphor>
<Preparation of precursor (reaction crystallization method)>
1000 ml of water was used as solution A. Liquid B was prepared by dissolving sodium metasilicate so that the ion concentration of silicon was 0.25 mol / l in 500 ml of water. Zinc nitrate and manganese nitrate were dissolved in 500 ml of water so that the ion concentration of zinc was 0.47 mol / l and the ion concentration of the activator (manganese) was 0.03 mol / l.

  The solution A was put into a double jet reaction crystallizer (reaction vessel) which is a phosphor production apparatus shown in FIG. 1, and the mixture was kept at 40 ° C. and stirred using a stirring blade 3R. In this state, solutions B and C kept at 50 ° C. were added from the bottom of the reaction vessel containing the solution A at a constant rate of 50 ml / min from the nozzles 4R and 5R while controlling the pH of the reaction solution. At that time, the precursor having the dispersion coefficient of the particle size shown in Table 1 was obtained by changing the stirring speed, the number of nozzles, and the flow rate. All precursors are stirred for 10 minutes while reducing the temperature after addition (→ 30 ° C.) in order to stabilize the reaction system. The particle diameter of the obtained precursor particles was determined by a laser scattering method (Seishin) and the results are shown in Table 1.

<Preparation of core / shell particles>
[First step]
After adjusting the viscosity of the precursor produced by the above method to be a spray droplet, this liquid is put into an ultrasonic sprayer having a 1.7 MHz vibrator to form a droplet, and 1% by volume of hydrogen gas The droplets are introduced into a tubular reactor formed by connecting a plurality of tubular thermal reactors capable of controlling the temperature in the range of 1300 ° C. to 700 ° C. using nitrogen gas containing nitrogen as a carrier gas, and then passed through a flow path for 4 seconds. Got.

[Second step]
Formed in the first step is a droplet of shell solution consisting of 5% colloidal silica formed with an ultrasonic sprayer, introduced into a tubular furnace maintained at 500 ° C. with 1% by volume of nitrogen gas as carrier gas. Mix with the prepared core particles.

[Third step]
The mixed gas substance of core particles and shell droplets discharged from the second step is introduced into a tubular reactor formed by connecting a plurality of tubular reactors capable of controlling the temperature in the range of 1300 ° C. to 700 ° C. Core / shell fine particles were obtained.

The core having the particle size distribution and the average particle size shown in Table 1 is Zn ₂ SiO ₄ : Mn by controlling the temperatures of the intermediate point and the end point of the flow path at the start of the first and third steps. A core / shell phosphor having a shell of SiO ₂ was obtained.

<Production of comparative phosphor (solid phase method)>
Zinc oxide (ZnO) and silicon oxide (SiO ₂ ) are blended in a molar ratio of 2: 1 as raw materials for the base material. Next, manganese oxide (Mn ₂ O ₃ ) in an amount of 1: 0.15 ratio relative to silicon oxide and magnesium oxide (MgO ₂ ) in an amount of 1: 0.05 are added to the mixture, After mixing, calcination was performed at 1250 ° C. in a weak reducing atmosphere (in N ₂ ) for 2 hours. In order to obtain a desired atomized phosphor, it was pulverized by a wet ball mill to obtain Zn ₂ SiO ₄ : Mn having a particle size shown in Table 1.

Further, the SiO ₂ powder having an average particle size of 0.1 μm was pulverized and mixed with the above Zn ₂ SiO ₄ ; Mn, mixed for 1 hour and then fired at 1350 ° C. for 1 hour to obtain a comparative phosphor having the characteristics shown in Table 1. .

<Evaluation of phosphor>
<Uniformity of shell thickness in core / shell phosphor>
The composition component of the shell was traced from the surface using an X-ray photoelectron spectrometer (XPS) manufactured by Nitto Denko Corporation, and the thickness from each particle was determined.

<Luminance measurement>
Luminance measurement uses a 146m vacuum ultraviolet lamp (USHIO) as a light source, sets a sample in the vacuum chamber, irradiates from a certain distance at a vacuum degree of 1.33 × 10Pa, and measures the excitation luminescence with a luminance meter. Is shown in Table 1.

  The luminance is shown as a relative value when the comparative sample 1 is 100%.

<Afterglow evaluation>
The afterglow time of the initial powder state of the phosphor was measured using a fluorescence lifetime measuring device. The afterglow time is the time until the emission intensity after blocking becomes 1/10 of the emission intensity just before blocking, and the relative afterglow time when Comparative Example 1 is 100 is shown in Table 1.

  As shown in Table 1, it can be seen that the phosphors having the atomized size are greatly excellent in luminance by taking the embodiment of the present invention. In addition, it can be seen that it has superiority for displays due to its excellent afterglow characteristics. In addition, by controlling the dispersion coefficient to 5 to 20% as in claim 2 of the present invention, the effect of the present invention is excellent, and by controlling the average particle size as in claim 3, the quantum effect is exerted. It turns out that the effect of invention is exhibited.

Example 2
Semiconductor nanoparticles obtained by surface modification with 11-mercaptoundecanoic acid were obtained by mixing the semiconductor nanoparticles obtained in Example 1 and an 11-mercaptoundecanoic acid solution for several hours. 1 mg of this and 10 mg of bovine serum albumin (BSA) are dissolved in 0.1 ml of distilled water in advance, and 3.4 ml of 0.1 M 2- [N-morpholino] ethanesulfonic acid (MES) buffer (pH 4.8) is added. And mixed thoroughly. Next, 0.5 ml of 10 mg / ml 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride solution dissolved in distilled water was added, and the reaction was allowed to stir at room temperature for 2 hours. Unreacted BSA was removed by centrifuging the reaction solution with Microcon YM-100 (Millipore) at 15000 × g for 5 minutes. After centrifugation, the plate was washed twice with PDS buffer (pH 7.2), and then dissolved in 0.5 ml of PBS to obtain luminescent semiconductor nanoparticles in which bovine serum albumin was bonded to the semiconductor surface.

  The obtained BSA-bonded semiconductor nanoparticles were dissolved in 10 mM phosphate buffer (pH 7.2) containing sodium chloride having a concentration of 0, 0.25, 0.5, 1, 2, 4M, and allowed to stand at room temperature for 3 days. After sufficiently stirring, electrophoresis was performed at 135 V for 50 minutes on a 0.5% agarose gel prepared with 10 mM phosphate buffer (pH 7.4).

  As shown in FIG. 2, when the phosphor of the present invention is used, a sufficiently dispersed and broad electrophoretic image is observed, whereas when the comparative phosphor is used, it does not migrate at all and aggregates. I found out.

  Thus, it can be seen that the phosphor of the present invention has high affinity for a living body and is excellent in dispersibility even in a living body when adapted to a living body.

Schematic configuration diagram of double jet reaction crystallizer The NO. 1 and NO. Electrophoresis image after treatment with 10 at different pH

Explanation of symbols

  1R double jet reactor

Claims (3)

In the method for producing a fine particle phosphor, a core / shell type particle is formed through at least the following three steps.
First step: An aqueous solution (A) containing a constituent metal element forming a core of a phosphor and an aqueous solution (B) containing a constituent element forming a shell are prepared in advance, and a precursor is prepared from the aqueous solution (A) by a reaction crystallization method. A body particle-containing liquid is prepared, the precursor particle-containing liquid is finely dropletized, introduced into a tubular heating furnace while flowing together with a carrier gas, and dried and heated to form core particles.
Second step: A liquid containing the constituent elements forming the shell is finely formed into droplets and mixed with the core particles formed in the first step while flowing together with the carrier gas.
Third step: The mixed droplets / core particles are introduced into a tubular heating furnace, heated and dried to form a shell. The method for producing a fine particle phosphor according to claim 1, wherein the particle size dispersion coefficient of the precursor particles formed by the reaction crystallization method is 5% to 20%. A fine particle phosphor produced by the method for producing a fine particle phosphor according to claim 1 or 2, wherein the fine particle phosphor has an average particle diameter of 1 to 10 nm.

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