KR100424866B1 - Preparation method of strontium titanate phosphor particles by flame spray pyrolysis - Google Patents

Abstract

The present invention relates to a method for producing a strontium titanate phosphor by flame spray pyrolysis, and more particularly, to prepare a precursor solution by dissolving an active agent doping the mother and the parent of the phosphor in distilled water, and then using a spray apparatus. By spraying the solution into droplets and enclosing the sprayed droplets into a diffusing flame and converting them into phosphors, the strontium titanate phosphor produced by the conventional general spray pyrolysis method has a hollow form, so that it can Contrary to spherical shape, irregular shape and very porous, which has poor luminescence properties, it is closer to spherical shape, uniform distribution, filled inside of sphere, no aggregation between phosphors, and perfect crystal without post heat treatment process. Outstandingly superior to conventional ones The present invention relates to a method for producing a revolutionary strontium titanate phosphor capable of producing a phosphor having a light emission luminance in a short time.

Description

Preparation method of strontium titanate phosphor particles by flame spray pyrolysis

The present invention relates to a method for producing a strontium titanate phosphor by flame spray pyrolysis, and more particularly, to prepare a precursor solution by dissolving an active agent doping the mother and the parent of the phosphor in distilled water, and then using a spray apparatus. By spraying the solution into droplets and enclosing the sprayed droplets into a diffusing flame and converting them into phosphors, the strontium titanate phosphor produced by the conventional general spray pyrolysis method has a hollow form, so that it can Contrary to spherical shape, irregular shape and very porous, which has poor luminescence properties, it is closer to spherical shape, uniform distribution, filled inside of sphere, no aggregation between phosphors, and perfect crystal without post heat treatment process. Outstandingly superior to conventional ones The present invention relates to a method for producing a revolutionary strontium titanate phosphor capable of producing a phosphor having a light emission luminance in a short time.

Phosphors are materials that are excited by the collision of electrons and emit light, and are used as means for reproducing images in various display devices. Such display devices include cathode ray tubes (CRTs), which are high-voltage display devices, field emission displays (FED), and vacuum fluorescence displays, which are low-voltage display devices, depending on the voltage used. VFD), plasma display panels (PDPs), etc., which are excited by discharge ultraviolet rays of a penning gas. The phosphor emits light when an electron emitted from an electron emitting means of the display device, an electron beam, a heating wire, an emitter, or the like strikes the surface, or is excited by a discharge ultraviolet light of a gas. Therefore, different colors can be reproduced.

As such phosphors for displays and lamps, sulfide phosphors doped with a noble metal in a matrix such as ZnS, CdS, ZnCdS and the like have been mainly used. These sulfide phosphors have been studied for decades and have evolved to the point where efficiency is now improved to the point where no further increase in efficiency is possible. Thus, a few years ago, research on these phosphors had been done by very few research groups.

However, as the interest in high definition television (HDTV) has recently increased, the development of display apparatuses has been invigorating accordingly. Representative of these are plasma displays (PDPs) and field emission displays (FEDs), which are recently popular flat panel displays. Unlike the related art, these display devices are of interest due to their lightness and thinness, and have potential applications in various fields such as wall-mounted TVs, computers, camcorders, and auto navigation devices.

On the other hand, in a conventional cathode ray tube (CRT) display, there is no problem because sulfide phosphors have excellent luminescence properties, but it is difficult to use conventional sulfide phosphors in flat panel displays and field emission displays. That is, in the flat panel display and the field emission display, since the phosphors emit light under high vacuum, when the conventional sulfide phosphor is used, problems such as deterioration of vacuum degree and deterioration due to decomposition of the sulfide occur.

Accordingly, in order to solve the problem of the sulfide phosphor, research on an oxide phosphor has recently been conducted.

Unlike the sulfide phosphors, the oxide phosphors are very stable to ultraviolet rays or electron beams, which are energy sources for emitting light in displays, and thus are used as flat panel phosphors. Representative examples are aluminates, silicates, titanates and borates.

At present, multi-component oxide phosphors using these materials are mostly produced by the solid phase method. In the solid phase method, the oxides of the respective components are mixed, and the desired multicomponent oxide phosphor is finally manufactured through repeated high temperature heat treatment and pulverization. Therefore, in order to obtain a pure composition by the solid phase method, a high temperature and a long process must be performed. In addition, impurities may be contained in the phosphor through repeated heat treatment and grinding processes, and phosphors prepared by this method generally correspond to several microns in size, and the surface is rough and irregular in shape.

In order to solve these problems of the solid phase method, a manufacturing method using the liquid phase method has been studied. Unlike the solid phase method, a liquid phase method such as a coprecipitation method or a sol-gel method can produce a desired multicomponent phosphor at a very low temperature. In addition, since the doping material can be mixed at the molecular level, good fluorescence characteristics can be expected at a lower heat treatment temperature. However, since the multicomponent oxide phosphors produced by the liquid phase method are very heterogeneous in shape, they are difficult to be used for flat panel displays.

Therefore, there is a need to develop a method of manufacturing an oxide phosphor having a uniform size and shape and excellent luminescence properties so that it can be widely used for plasma displays, field emission displays, and conventional cathode ray tubes (CRTs) and lamps in a simpler process. This has been emerging.

Accordingly, the present inventors have studied to develop a method for easily manufacturing a phosphor having a uniform size and shape and excellent luminescence properties. As a result, the precursor mixed solution of strontium titanate is fine droplets using a droplet spraying device such as ultrasonic waves. By spraying, drying and pyrolysis and melting inside the flame, it is confirmed that it is possible to produce a phosphor filled with the inside of the sphere, which is a uniform spherical form without aggregation and requires no post-heat treatment step. The present invention was completed.

After all, the main object of the present invention is to provide a spherical and internally filled strontium titanate phosphor by flame spray pyrolysis using a nozzle for generating a diffusion flame.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows the structure of a flame spray pyrolysis apparatus.

FIG. 2 is a schematic diagram showing the configuration of a nozzle in the apparatus of FIG. 1.

3 is a schematic diagram showing a process of generating a phosphor in a diffusion flame reactor.

4 is a scanning electron micrograph of the SrTiO ₃ : Pr, Al phosphor prepared by the flame spray pyrolysis method of the present invention.

5 is a scanning electron micrograph of a SrTiO ₃ : Pr, Al phosphor prepared by a conventional conventional spray pyrolysis method.

Figure 6 is a graph showing the X-ray diffraction pattern of the phosphor prepared by the flame spray pyrolysis method of the present invention and the conventional conventional spray pyrolysis method.

Figure 7 is a graph showing the light emission characteristics of the phosphor prepared by the flame spray pyrolysis method of the present invention and the conventional conventional spray pyrolysis method.

[Description of Symbols for Main Parts of Drawing]

10: spraying apparatus 20: nozzle

30 reactor 40 bag filter

50: pump

The present invention in the production of a phosphor by spray pyrolysis,

Iv) precursor materials of strontium (Sr) and titanium (Ti) as the phosphor matrix and praseodymium (Pr), aluminum (Al) and gallium (Ga) as activators for doping the matrix in distilled water Preparing a solution;

Ii) injecting the precursor solution into a spray apparatus to generate droplets having a diameter of 1 to 100 µm; And

Iii) drying, decomposing, reacting and crystallizing the droplets in a diffusion flame to obtain a phosphor powder represented by the following formula (1);

It characterized by a method for producing a strontium titanate phosphor by the flame spray pyrolysis method comprising a.

Formula 1

SrTiO ₃ : Pr _x Al _y Ga _z

In Formula 1: 0.0001 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, and 0 ≦ z ≦ 0.5.

The present invention will be described in more detail as follows.

In the flame spray pyrolysis process of the present invention, even if the droplets generated from the precursor solution stay in the flame for a very short time, the flame temperature is about 1500 to 4000 ° C., so the crystallinity is perfectly crystallized even without the post-heat treatment process. It has a luminescence brightness about 4.5 times better than a phosphor produced by phosphorus spray pyrolysis process.

The method for producing strontium titanate phosphor by the flame spray pyrolysis method of the present invention will be described in more detail by dividing according to processes.

First Process: Preparation of Precursor Solution

The precursor solution of the phosphor is prepared by dissolving the phosphor mother and the activator doping the mother in distilled water.

In the present invention, the phosphor matrix is composed of strontium (Sr) and titanium (Ti). As a precursor material of strontium, water-soluble salts such as nitrate, acetate and chloride may be used, and the precursor material of titanium (Ti) is alkoxide. Titanium tetraisopropoxide (titanium (IV) isopropoxide (TTIP)) or nanometer-sized titania (TiO ₂ ) powder may be used. The nanometer-sized titania powder may be a product manufactured by a liquid phase method using a titania powder (Fumed titania) or an alkoxide supplied as a commercial product by the aerosol method. If the titanium isopropoxide is used as a titanium precursor material, it is added to distilled water according to a stoichiometric ratio, and then a small amount of nitric acid is added to obtain a clean solution, and the strontium and doping materials praseodymium, aluminum and gallium are added thereto. Precursor solutions are prepared by adding precursor materials. As the activator for doping the matrix, as the precursor material of praseodymium (Pr), aluminum (Al) and gallium (Ga), water-soluble salts such as nitrates, acetates, sulfides, and chlorides may be used. Here, aluminum and gallium may be used individually or in a mixed form, and serve to increase the emission intensity of the strontium titanate phosphor by several tens to several hundred times.

In addition, since the size of the phosphor powder to be prepared is determined according to the concentration of the precursor solution, the concentration of the precursor solution should be appropriate in order to prepare particles of a desired size, and the total concentration of the precursor solution is preferably in the range of 0.02 to 3 M. . In this case, when the total concentration of the precursor solution does not reach 0.02 M, there is a problem that the productivity of the powder falls, and it is difficult to dissolve in distilled water to obtain a precursor solution having a concentration exceeding 3 M because of the solubility of the precursor material. If the concentration is too high, there is a problem that spraying droplets is difficult.

Second Process: Spraying Droplets

The spray device may be an ultrasonic spray device, an air nozzle spray device, an electrostatic spray device, an ultrasonic nozzle spray device, and a filter expansion aerosol generator (FEAG). Ultrasonic nebulizers and filter expansion droplet generators can produce submicron-sized fine phosphors at high concentrations, while air and ultrasonic nozzle nebulizers can produce large quantities of micron-sized phosphors from microns. Particularly, in the present invention, in the case of the ultrasonic atomizer, a large amount of droplets are generated by connecting at least six vibrators, which are parts of generating droplets, side by side, and by connecting the atomizers in parallel to generate several hundred liters of droplets per hour. Pyrolysis allowed commercial production of the phosphor.

Third Step: Generation of Phosphors

The droplets are dried, decomposed, reacted, melted and crystallized inside the diffusion flame. That is, droplets are introduced into a nozzle that generates a diffusion flame to generate a phosphor inside the diffusion flame. At this time, the diffusion flame is generated as the fuel and oxygen is diffused out of the nozzle, a fuel source may be used as propane gas or hydrogen gas, oxygen or air may be used as the oxygen source. Here, the temperature of the flame can be adjusted by adjusting the type and flow rate of the fuel gas, the flow rate of oxygen or air, the ratio with the fuel gas, and the like, and the temperature of the diffusion flame is preferably in the range of 1500 to 4000 ° C. If the temperature of the flame does not reach 1500 ° C., the phosphor may not melt after the reaction.

1 is a schematic diagram showing the configuration of a diffusion flame spray pyrolysis apparatus, and FIG. 2 is a schematic diagram showing the configuration of a nozzle in the apparatus. 1, it can be seen that the droplets generated by the spray device 10 are supplied to the nozzle 20, and the droplets passing through the nozzle are processed in the reactor 30 surrounded by the diffusion flame. In addition, the bag filter 40 and the pump 50 are connected in order. As shown in FIG. 2, the nozzle 20 is composed of a central tube to which droplets are supplied and four concentric tubes to which fuel gas, oxygen, fuel gas, and oxygen are separately supplied, respectively. Therefore, the diffusion flame is generated when fuel gas and oxygen supplied to the concentric tubes exit the nozzle and ignite.

Figure 3 is a schematic diagram showing the process of generating the phosphor in the diffusion flame reactor, where the drying is a process in which the moisture contained in the droplets is evaporated and converted into a solid phosphor, decomposition is nitrogen present in the phosphor phase-transformed into a solid B is a process in which carbon components are released into gases such as nitrogen dioxide (NO ₂ ) and carbon dioxide (CO ₂ ). The reaction is a process in which metals such as strontium, titanium, praseodymium, aluminum, and gallium are combined with oxygen and converted into oxides, and melting is a process in which phosphors produced by the reaction melt inside a high-temperature flame to form a spherical filled sphere. to be. In addition, the oxides having completed the reaction and melting are converted into phosphors through crystallization which is rearranged regularly. In the case of flame spray pyrolysis, all these processes are completed in the flame, and the processing time is less than milliseconds. In addition, since the phosphor is manufactured at a high temperature near the melting point, an activation process in which an active agent such as praseodymium, aluminum, and gallium enters into the phosphor lattice also proceeds in the flame, thereby producing a phosphor capable of emitting light without post-treatment.

The phosphor thus prepared is completely crystallized and does not require a post-treatment process, but additionally includes a post-treatment process at a temperature of 800 to 1500 ° C. for 1 to 5 hours to increase luminance and make the surface of the powder smoother. It may be.

Hereinafter, the present invention will be described in more detail with reference to the following examples, which are only intended to explain the present invention more specifically, and the scope of the present invention according to the gist of the present invention to these examples. It will be apparent to one of ordinary skill in the art that the present invention is not limited thereto.

Example 1 SrTiO by Flame Spray Pyrolysis ₃ : Preparation of Pr, Al phosphor (using strontium nitrate)

The precursor solution was prepared using the following components. Among the starting materials, titanium tetraisopropoxide was used as a precursor material and dissolved in distilled water using a small amount of nitric acid. A precursor solution was prepared by dissolving nitrates of strontium, praseodymium, and aluminum in this titanium solution. At this time, the total concentration of the precursor solution was 0.4 M, and the doping concentrations of praseodymium and aluminum were 0.002 M and 0.1 M, respectively, based on 1 M of strontium metal.

The precursor solutions thus prepared were generated into droplets of several microns size using an ultrasonic atomizer, and the droplets were sprayed using an oxygen gas having a flow rate of 5.0 l / min as a carrier gas. The phosphor was prepared by entering the diffusion flame. At this time, propane gas was used as the fuel gas, and the temperature of the adiabatic diffusion flame obtained by calculation was adjusted to 3500 ° C.

Example 2: SrTiO by Flame Spray Pyrolysis ₃ : Preparation of Pr, Al phosphor (using strontium acetate)

A phosphor was prepared in the same composition and method as Example 1, except that acetate was used as the strontium precursor material.

Example 3: SrTiO by Flame Spray Pyrolysis ₃ : Preparation of Pr, Al Phosphor (using Strontium Chloride)

A phosphor was prepared in the same composition and method as Example 1, except that chloride was used as the strontium precursor material.

Comparative Example: SrTiO by Conventional Spray Pyrolysis ₃ : Preparation of Pr, Al Phosphor

The composition and the concentration of the spray solution were the same as in Example 1, and the phosphor was prepared by a spray pyrolysis process in which the temperature of the tubular electric furnace was 900 ° C. The phosphor prepared by spray pyrolysis was subjected to a post-heat treatment process at 1200 ° C. for 3 hours because crystals were not crystallized because the temperature of the reactor was lowered to 900 ° C.

Test Example: Determination of Crystallinity, Phosphor Size and Luminescent Properties

The shape and crystallinity of the prepared phosphors were observed using a scanning electron microscopy (SEM) and an X-ray diffractometer (XRD), and the results are shown in FIGS. 4 to 6, respectively. . Photoluminescence (PL) characteristics were measured using a spectrophotometer as an optical property of the phosphor, and UV was generated using a xenon lamp to excite the phosphor. And the light emission characteristic measurement result is shown in FIG.

FIG. 4 is a scanning electron micrograph of SrTiO ₃ : Pr, Al phosphor (Example 2) prepared by flame spray pyrolysis when acetate was used as a raw material of strontium, and FIG. 5 is prepared by conventional spray pyrolysis. Scanning electron micrograph of the obtained SrTiO ₃ : Pr, Al phosphor (Comparative Example). It can be seen that the phosphor of FIG. 4 prepared by flame spray pyrolysis is closer to a more complete spherical shape in comparison with the phosphor of FIG. 5 prepared by conventional spray pyrolysis. In addition, even in the state of charge inside the sphere, the phosphor by the conventional spray pyrolysis method has found a large number of phosphors incompletely filled state and the spherical shape is broken during the heat treatment process, whereas the phosphor by the flame spray pyrolysis method of the present invention In the case of the empty phosphor was not found. This is because when the phosphor is manufactured by flame spray pyrolysis, all reactions occur inside the diffusion flame, which is a high temperature near the melting point, so that the formed phosphor is melted to generate spherical phosphors which are completely filled. Further, even in the state of aggregation between the phosphors, in the case of the conventional phosphor pyrolysis, the phosphors are highly aggregated, whereas in the case of the phosphors by the flame spray pyrolysis of the present invention, the phosphors are not subjected to a heat treatment process. No aggregation occurred.

Figure 6 is a graph showing the X-ray diffraction pattern of the phosphor prepared by the flame spray pyrolysis method of the present invention and the conventional conventional spray pyrolysis method. The phosphor prepared by the general spray pyrolysis process of Comparative Example 1 is a phosphor that has undergone a post heat treatment process, and the phosphor obtained in the flame spray pyrolysis process of Example 1 does not undergo a post heat treatment process. As shown in FIG. 6, the phosphor prepared by the flame spray pyrolysis process has a perfect crystal even without undergoing a post-heat treatment process. Moreover, it has crystallinity which may be compared with the fluorescent substance obtained by the general spray pyrolysis process which heat-processed at high temperature for a long time. The reason why the phosphor prepared by the flame spray pyrolysis process has good crystallinity even without the post-heat treatment process is because the flame temperature is very high, more than 2000 ° C.

Figure 7 is a graph showing the light emission characteristics of the phosphor prepared by the change in the precursor type of strontium by the flame spray pyrolysis method of the present invention and the phosphor prepared by the conventional spray pyrolysis method. The phosphor prepared by the flame spray pyrolysis according to the present invention exhibited better luminescence properties than the phosphor produced by the conventional spray pyrolysis and had a high luminescence intensity of up to 4.7 times. Under the influence of the strontium precursor material in the flame spray pyrolysis process, the phosphor prepared using strontium acetate and nitrate had good luminescence intensity, and the luminescence intensity was poor when strontium chloride was used. The reason is that the composition of the prepared phosphor is not constant because of the high volatility of strontium chloride.

In addition, the use of titania powder (Degussa, P25) as a titanium precursor material in the preparation of the SrTiO ₃ : Pr, Al phosphors may yield similar results to those obtained using titanium isopropoxide in terms of form and luminescence properties. there was. In addition, when a part or all of aluminum was replaced with gallium as an active agent, the prepared phosphor had similar morphology and luminescence properties as when only aluminum was used.

As described and demonstrated in detail above, in the method for producing a strontium titanate phosphor by flame spray pyrolysis according to the present invention, a precursor solution is prepared by dissolving an active agent for doping the parent and the parent in distilled water to prepare a precursor solution. By spraying the precursor solution into droplets, and converting the droplets into phosphors in the diffusion flame, which is closer to the spherical form than the phosphors produced by conventional spray pyrolysis, and the distribution of the spheres is uniform. The spherical phosphor, which is in a charged state and does not have aggregation between the phosphors, can be produced in a short time.

Claims (8)

In preparing the phosphor by spray pyrolysis, Iv) precursor materials of strontium (Sr) and titanium (Ti) as the phosphor matrix and praseodymium (Pr), aluminum (Al) and gallium (Ga) as activators for doping the matrix in distilled water Preparing a solution; Ii) injecting the precursor solution into a spray apparatus to generate droplets having a diameter of 1 to 100 µm; And Iii) drying, decomposing, reacting and crystallizing the droplets in a diffusion flame to obtain a phosphor powder represented by the following formula (1); Method for producing a strontium titanate phosphor by the flame spray pyrolysis method comprising a. Formula 1 SrTiO ₃ : Pr _x Al _y Ga _z In Formula 1: 0.0001 ≦ x ≦ 0.5, 0 <y ≦ 0.5, and 0 <z ≦ 0.5. The method of claim 1, wherein the temperature of the diffusion flame is in the range of 1500 to 4000 ° C. The method of claim 1, wherein the fuel source for generating the diffusion flame is propane and hydrogen gas, and the oxygen source is oxygen or air. The method of claim 1, wherein the precursor material of titanium (Ti) is titanium tetraisophoroxide (TTIP) or nanometer-sized titania (TiO ₂ ) powder, the strontium (Sr) precursor material of strontium nitrate Method for producing a strontium titanate phosphor, characterized in that the water-soluble salts selected from acetate, chloride. The precursor material of praseodymium (Pr) is a water-soluble salt selected from nitrates, chlorides and acetates of praseodymium, and the precursor materials of aluminum (Al) and gallium (Ga) are nitrates, chlorides, A method for producing a strontium titanate phosphor, characterized in that it is a water-soluble salt selected from acetates and sulfates. The method of claim 1, wherein the atomizer is an ultrasonic atomizer, an air nozzle atomizer, an electrostatic atomizer, or an ultrasonic nozzle atomizer. The method of claim 1, further comprising post-treating the prepared phosphor at 800 to 1500 ° C. for 1 to 5 hours. Strontium titanate phosphor represented by the following formula (1), characterized in that prepared by the method of claim 1. Formula 1 SrTiO ₃ : Pr _x Al _y Ga _z In Formula 1: 0.0001 ≦ x ≦ 0.5, 0 <y ≦ 0.5, and 0 <z ≦ 0.5.