JP2011021125A - Hollow phosphor and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow phosphor with a small impurity content and good PL characteristics, and a method for producing the hollow phosphor simply by few production processes without requiring a surplus raw material. <P>SOLUTION: The method for producing the hollow phosphor comprises an atomization process 2, 3 for atomizing a raw material solution prepared by dissolving a salt containing a constituent metal of chloroapatite, a metal chloride containing at least one of Ca, Ba, Sr and Mg, and a salt containing at least one of samarium, europium, terbium and dysprosium, a heating synthesis process for heating atomized droplets in a reaction furnace 4, a collection process 10 for collecting produced hollow phosphor particles, and a control process for controlling the concentration of the raw material solution so as to convert particles into the hollow phosphor particles. The method produces the hollow phosphor particles by using a spray thermal-decomposition method without using a template. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hollow phosphor that can be used as a material for solid-state lighting (SSL) and a method for producing the hollow phosphor.

  As prior art document information related to this type of hollow phosphor, there is Patent Document 1 shown below. This patent document 1 relates to a method of manufacturing a plasma display panel (PDP) capable of displaying TV images and the like. By using a hollow phosphor as a PDP partition, the relative permittivity of the partition is reduced, and the PDP is driven. The idea of reducing power consumption is noted.

Japanese Patent Laying-Open No. 2007-324098 (paragraphs 0013 and 0065, FIGS. 4 and 8)

  However, the hollow phosphor described in Patent Document 1 first forms composite particles in which the periphery of the mother particles is coated with a large number of child particles having a softening point higher than that of the mother particles, and then only the mother particles are dissolved. It is made by a method of hollowing out the interior (template method). Therefore, since impurities such as carbon as a constituent component of the mother particles remain in the hollow phosphor, the PL (photoluminescence) characteristics of the hollow phosphor are impaired, and subsequent processes for removing the mother particles, etc. Therefore, there are problems such that the manufacturing process is complicated and many kinds of complicated apparatuses are required for manufacturing, and extra raw materials constituting the mother particles are required.

  Therefore, in view of the situation known from the prior art exemplified above, the object of the present invention is to provide a hollow phosphor having less PL problems and having excellent PL characteristics, and having a manufacturing process. An object of the present invention is to provide a method for producing a hollow phosphor which is relatively small and simple and requires as little extra raw material as possible.

  The characteristic structure of the empty phosphor according to the present invention is that it is a hollow phosphor that contains chloroapatite as a main component and is produced without using a template by a spray pyrolysis method.

  The hollow phosphor according to the first characteristic configuration of the present invention is produced (directly synthesized) without using a template (mother particle) for creating a hollow portion by finally removing most of the phosphor ( (Template-free, template-less), impurities derived from the components of the template do not remain in the hollow phosphor, so that a hollow phosphor excellent in PL characteristics can be obtained. In addition, since a raw material for base particles necessary as a template is not required, a lower-cost hollow phosphor can be obtained. Furthermore, since it is hollow and has a low density, an ideal phosphor that is lightweight and has a high light transmittance can be obtained. In addition, since the phosphor synthesis is completed in a single step of spray pyrolysis, which is completed in a remarkably short time within several seconds, it is a very efficient manufacturing method. Furthermore, spray pyrolysis is advantageous in that the phosphor particles can be produced in a remarkably short time within a few seconds, and the characteristics of the phosphor can be easily controlled by the raw material solution and the synthesis conditions.

  Furthermore, as a result of preparing the composition of the raw material liquid used in the spray pyrolysis method so that the hollow phosphor mainly comprises chloroapatite, the outer shape has an ideal spherical shape, and the quantum yield is very high. High-cost hollow phosphors can be manufactured stably at low cost. Moreover, since chloroapatite is also a well-known non-toxic phosphor for lamps, handling at the time of production is easy. For the same reason, the existing technology can be easily used when installing in the light emitting part of the LED for solid state lighting (SSL) or when installing it on the partition of the plasma display panel (PDP).

  Another characteristic configuration of the present invention is that it contains at least one of Ca, Ba, Sr, and Mg as a metal element constituting chloroapatite.

  If at least one of Ca, Ba, and Sr is applied as the main metal element constituting chloroapatite as in this configuration, a stable crystal form as chloroapatite can be obtained, and a hollow shape with a high quantum yield can be obtained. The phosphor can also be manufactured stably. Furthermore, when a part of these main metal elements is substituted with Mg, the crystallinity is further improved, so that it is possible to achieve a very quantum yield of 1.00.

  Another characteristic configuration of the present invention is a hollow phosphor having a quantum efficiency of 0.90 or more.

  With this configuration, a very practical level of solid state lighting (SSL) can be realized by providing the hollow phosphor according to the present invention in, for example, a light emitting portion of an LED. Also, it is predicted that less power is consumed when installed on the PDP partition.

  Another feature of the present invention is that it is a hollow phosphor that emits blue light when excited by ultraviolet rays.

With this configuration, the hollow phosphor according to the invention is a cerium-doped YAG (yttrium aluminum garnet) phosphor that is relatively easily available on the market (emits yellow light that is excited by ultraviolet rays and is a blue opposite color). ) And an appropriate ratio to form a coating that covers the light emitting part of the UV-LED, the coating with these two phosphors receives ultraviolet light and emits white light with very high quantum efficiency. Therefore, it is possible to obtain a general and practical white illumination device.
In addition, in this configuration, since the light emitting action based on the ultraviolet light having a very stable peak wavelength from the UV-LED is used, the chromaticity variation is smaller than that of the white illumination using the visible light LED in which the peak wavelength is likely to vary. Fewer white lighting devices can be obtained.

  Another characteristic configuration of the present invention is a hollow phosphor having a particle diameter of 1 to 2 μm.

  With this configuration, a hollow fluorescent material with a particle diameter of 1 to 2 μm that is well aligned in a relatively narrow range can be obtained. Therefore, it can be easily used for various purposes without being classified after the production.

The characteristic configuration of the method for producing a hollow phosphor according to the present invention is as follows:
A raw material in which a salt containing at least one metal constituting chloroapatite, a metal chloride containing at least one of Ca, Ba, Sr, and Mg and a salt containing at least one of samarium, europium, terbium, and dysprosium are dissolved. An atomization step of atomizing the solution;
A heating and synthesizing step of heating droplets of the raw material solution atomized by the ultrasonic atomizer in a reaction furnace in a reducing atmosphere;
A collection step of collecting the hollow phosphor particles generated by the heating synthesis step;
And a control step for controlling at least the concentration of the raw material solution so that the particles become hollow phosphor particles.

  According to various research results by the applicant of the present invention, a raw material solution in which a salt containing a metal constituting chloroapatite is dissolved is prepared, and this is atomized. It has been found that one of the most dominant factors for hollowing out is the concentration of the raw material solution. Therefore, if it is this configuration, firstly having a component of a fluorescent element such as chloroapatite and europium and preparing a raw material solution controlled to a concentration such that the particles are hollow, the rest is an atomization step, A hollow phosphor can be obtained simply by repeating the three relatively simple processes of the heat synthesis process and the collection process.

  In another characteristic configuration of the present invention, the control step further includes at least one control of a heating temperature in the heating synthesis step, a time length during which the droplets and the particles are exposed to the heating synthesis step. It is in.

  Also, according to various research results by the applicant of the present invention, the next dominant factor for hollowing out the particles is the evaporation rate to which the droplets are subjected, and it is the heating that determines the evaporation rate. It was found that the temperature and the residence time of the particles in the furnace. Therefore, if the control process further includes at least one control of the heating temperature in the heat synthesis process, the time period during which the droplets and the particles are exposed to the heat synthesis process, as in this configuration, it is even higher. A hollow phosphor can be obtained with a yield. It has also been found that it is the gas flow rate in the furnace and the internal shape of the reactor that influence the residence time of the particles in the furnace.

  Another feature of the present invention is that the heating temperature in the heating and synthesizing step is between 1050 ° C. and 1150 ° C.

  If the heating temperature according to this configuration is used, the maximum PL intensity can be stably obtained, and a phosphor that emits blue light can be obtained stably, so that it can be combined with a commercially available Ce-doped YAG phosphor that emits yellow light. With this, white illumination with high brightness can be obtained.

  Another feature of the present invention is that in the heating and synthesizing step, a carrier gas for conveying particles is flowed, and the control step includes a step of controlling the total gas flow rate in the reaction furnace.

  If the total gas flow rate in the reactor is controlled by the process of this configuration, the PL intensity (quantum yield) can be controlled more accurately, and the Ca chloroapatite phosphor with blue chromaticity can be stabilized stably by excitation with ultraviolet rays. Can be made.

It is a schematic block diagram which shows the manufacturing apparatus of the hollow fluorescent substance by an ultrasonic spray pyrolysis method. It is a FESEM photograph and XRD pattern of Ca chloroapatite fluorescent substance prepared at various synthesis temperatures. FIG. 4 is a PL spectrum (a) of Ca chloroapatite phosphors prepared at various synthesis temperatures and a graph (b) showing relative PL intensity as a function of temperature. PL spectrum (a) of Ca chloroapatite phosphors prepared at various raw material solution concentrations, graph (b) showing the correlation between raw material solution concentration and particle (dp) and droplet diameter (dd), and calcium It is the schematic (c) which shows the formation mechanism of a chloroapatite fluorescent substance. It is the FESEM photograph of Ca chloroapatite prepared by various raw material solution concentration, and the corresponding volume average diameter (inset) measured based on the FESEM photograph. The relative PL intensity as a function of total flow, residence time, and is a graph showing the flow rate of H ^2. They are the normalized PL spectrum, SEM photograph, digital photograph (a), and XRD pattern (b) of each chloroapatite phosphor of Ca, Sr, and Ba. It is the TEM photograph regarding Sr chloroapatite fluorescent substance particle (a) and Ba chloroapatite fluorescent substance particle (b), and a SAED pattern. It is a photograph which shows the CIE chromaticity diagram of each chloroapatite fluorescent substance of Ca, Sr, and Ba, and the external chromaticity of the upper surface and side surface of white LED produced using these fluorescent substance. It is a STEM (upper left), element mapping image, and EDS pattern of Ca chloroapatite phosphor particles. It is STEM (upper left) of Sr chloroapatite fluorescent substance particle, an element mapping image, and an EDS pattern. It is a STEM (upper left), element mapping image, and EDS pattern of Ba chloroapatite phosphor particles. It is a table | surface which shows the various characteristics of the chloroapatite fluorescent substance by this invention with a comparative example.

EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated, referring drawings.
FIG. 1 is a schematic view showing an example of an apparatus for producing a hollow phosphor by an ultrasonic spray pyrolysis method according to the present invention.

(Configuration of manufacturing equipment)
The manufacturing apparatus 1 includes an ultrasonic sprayer 2 that atomizes a raw material solution into micrometer-sized droplets, a long tubular reactor 4 for heating the obtained droplets, and a tubular reactor 4 The electrostatic collector 8 which collects the particle | grains produced | generated by this, and the gas supply source 18 for supplying the carrier gas required for manufacture are provided.

For example, NE-U17 manufactured by OMRON Healthcare Co., Ltd. can be used as the ultrasonic sprayer 2. When the raw material liquid A for synthesis is introduced into the precursor container 3 provided in the ultrasonic sprayer 2 and driven at about 1.7 MHz or the like, the raw material liquid A is atomized by ultrasonic waves, and is micrometer-sized. Droplets are obtained.
The droplets sprayed in the interior space of the precursor container 3 are carried into the tubular reaction furnace 4 arranged substantially vertically by the carrier gas sent from the gas supply source 18, and further conveyed in the tubular reaction furnace 4. While being maintained, it is maintained at a predetermined temperature and heated for several seconds. The carrier gas is composed of a mixture of N ₂ gas whose main purpose is conveyance and H ₂ gas for making the inside of the tubular reactor 4 a reducing atmosphere. The mixing ratio of N ₂ gas and H ₂ gas may be 95: 5 (vol%), for example.

  The tubular reaction furnace 4 includes, for example, an alumina furnace body 5 having a length of 1 m and an inner diameter of 13 mm, and a heating means 6 arranged in an annular shape on the outer periphery of the furnace body 5. As the heating means 6, a resistance heating element or the like can be used. However, the heating means 6 is not limited to this as long as the inside of the furnace can be maintained at a constant temperature in the range of 1050 ° C to 1150 ° C. In the figure, the heating means 6 is divided into five sections along the length direction of the furnace, and the heating amount and temperature can be controlled for each section. For this purpose, thermocouples (not shown) for measuring the temperature of the central portion in the radial direction in the furnace are arranged corresponding to each section. Further, the tubular reactor 4 has a control device (not shown) capable of feedback control so that the temperature in the furnace body 5 becomes substantially equal based on the temperature measurement value of each section obtained by these thermocouples. Is provided.

The electrostatic collector 8 includes a collection container main body 10, a collection filter 11 disposed inside the collection container main body 10, a corona discharge body 12 inserted and installed on the upper surface of the collection container main body 10, and And a high-voltage power supply 13 for discharging. The particles synthesized in the tubular reactor 4 are introduced into the collection container main body 10 by the carrier gas, charged with the corona discharge body 12, and electrostatically deposited on the collection filter 11. The electrostatic collector 8 can collect micrometer-sized particles with a collection efficiency of about 95%.
After passing through the collection filter 11, the carrier gas that has entered the collection container body 11 is forcibly exhausted from the collection container body 10, passes through a NaOH trap 15 for absorbing acidic gas, and then outside the system. Go out.

(Raw material liquid)
The particle to be produced in the present invention using the above production apparatus is a chloroapatite phosphor, and its scientific formula is M ₅ (PO ₄ ) ₃ Cl _x : Eu ²⁺ . Here, the metal element constituting M is any one of Ca, Sr, and Ba.
Therefore, the following aqueous solutions are prepared, and these are mixed so that each element of M, P, Cl, and Eu has a stoichiometric ratio based on the above chemical formula, and this chloroapatite phosphor is produced. A precursor, that is, a raw material liquid A was set in the precursor container 3. Here, the case where Ca is used as M is described.

1. M _{nitrate: Ca (NO 3) 2 ·} 4H 2 O,
2. M chloride: CaCl ₂
3. Europium nitrate: Eu (NO ₃ ) ₃ · 6H ₂ O
4). Phosphoric acid: H ₃ PO ₄
5. Nitric acid: HNO ₃

However, when M of M ₅ (PO ₄ ) ₃ Cl _x : Eu ²⁺ is Sr, M nitrate is Sr (NO ₃ ) ₂ .4H ₂ O, and M chloride is SrCl ₂ . When M of M ₅ (PO ₄ ) ₃ Cl _x : Eu ²⁺ is Ba, M nitrate is Ba (NO ₃ ) ₂ .4H ₂ O, and M chloride is BaCl ₂ .
Eu atoms were added at a doping concentration of 3 mol% with respect to M atoms.

As a result of examination by the applicant, the characteristics of the particles obtained by using the above-described production apparatus using the above-mentioned raw material liquid A as a precursor are several operational parameters, in particular, the heating temperature in the tubular reactor 4, the precursor It has been found that it varies greatly depending on the concentration of the raw material liquid A installed in the body container 3 and the total gas flow rate in the tubular reactor 4.
In the following, first, when Ca is used as the metal element M constituting chloroapatite, that is, to determine the optimum conditions for synthesizing calcium chloroapatite phosphor particles (hereinafter abbreviated as Ca apatite phosphor particles). Next, the relationship between each of these important parameters and the characteristics of the particles will be examined.

(Heating temperature)
FIG. 2 (a) is a picture of a field emission scanning electron microscope (FESEM) image of Ca apatite phosphor particles prepared at various synthesis temperatures between 800-1400 ° C. Also, in the upper right corner of each FESEM image photograph, the corresponding digital image (the emission color obtained by applying an apatite phosphor to a UV-LED chip having a peak wavelength of 365 nm and excitation by this wavelength light is shown. Image taken with a digital camera) is attached. The concentration of the raw material solution A was 0.10 M, and the total gas flow rate was fixed at 5 L / min.
From these FESEM images, it can be seen that spherical particles having substantially the same particle size in the range of about 1 to 1.5 μm can be obtained regardless of the temperature difference within the above temperature range.

However, a comparative study of digital images showed that the chromaticity varies depending on the synthesis temperature. That is, in the present invention, blue light emission that is convenient for obtaining white illumination in combination with a commercially available Ce-doped YAG phosphor that exhibits yellow light emission appears only at 1100 ° C., and dark red purple and intermediate at 800 ° C. and 900 ° C. A pale purple color was observed. Such a shift from blue is considered to be due to an incomplete reduction reaction, that is, reduction of Eu ³⁺ by H ² at a low speed at 800 ° C. and 900 ° C. On the other hand, when it exceeds 1100 ° C., it becomes light purple at 1200 ° C. and finally becomes red at 1400 ° C. Although this phenomenon appears to be unreasonable, it can be logically considered that at a high temperature of 1200 ° C. or higher, the time during which particles can stay in the furnace body 5 is shortened, and the reduction reaction is difficult to proceed.

That is, the internal gas flow rate of the tubular reactor 4 (5 L / min at room temperature) = Q _gi , the synthesis temperature = T, the total gas flow rate at high temperature = Q _gt , the length of the furnace body 5 = L (here 1.0 m) ), Assuming that the inner diameter of the furnace body = D (here, 30 mm) and the temperature in the tubular reactor 4 is constant, the particle residence time τr is expressed by the following equation.
τr = Vr / Q _gt = 298πLD ² / (4Q _gi T) (Equation 1)
However, Vr is expressed by πLD ^2/4 is the volume of the reactor.
According to the formula (1), when elements other than the synthesis temperature are made constant, the residence time at a synthesis temperature of 800 ° C. is calculated to be 2.36 seconds, and the residence time at 1400 ° C. is calculated to be 1.51 seconds. It can be seen that the higher the value, the shorter the residence time. That is, when the synthesis temperature is 1400 ° C., the residence time is extremely short, so that the reduction of Eu ³⁺ to Eu ²⁺ by H ² is incomplete, and this is also the reason why red luminescent particles were obtained at the same temperature It is considered one of the above.

FIG. 2 (b) shows XRD (X-ray diffraction) patterns of Ca apatite phosphor particles prepared at various synthesis temperatures within the same temperature range.
From this figure, it is confirmed that the surfaces (211), (112), and (300) tend to shift to the right as the synthesis temperature increases. This tendency means that the crystal structure is changed from chloroapatite to hydroxide apatite (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ). This change in crystal structure is presumed to be due to the lack of chloride, because chloride forms hydrogen chloride gas at high temperatures.

FIG. 3 (a) shows PL spectra when Ca apatite phosphor particles prepared at various synthesis temperatures are excited by a UV-LED having a peak wavelength of 365 nm. FIG. 3B shows the relative PL intensity that represents the PL intensity peak value at each temperature read from FIG. 3A as a function of temperature. From these figures it is understood that the maximum PL intensity is also obtained at a synthesis temperature of 1100 ° C. This phenomenon may be explained by the change in crystal structure discussed above for FIG.
In any case, it was found that the optimum synthesis temperature for obtaining blue light emission and the optimum synthesis temperature for obtaining the maximum PL intensity were also 1100 ° C., so when examining other parameters below As a standard synthesis temperature, 1100 ° C. was used.
The PL spectrum of the phosphor was recorded with a spectrofluorometer (RF-5300PC manufactured by Shimadzu Corporation) equipped with a xenon laser source.

(Concentration of raw material liquid)
FIG. 4A shows the PL fluorescence of the Ca apatite phosphor particles obtained when the concentration of the raw material liquid A installed in the precursor container 3 of the ultrasonic sprayer 2 is changed in the range of 0.05 to 0.33M. It is a graph which shows a spectrum (the unit M of a density | concentration shows mol / liter). Again, the phosphor particles were excited by a UV-LED having a peak wavelength of 365 nm. From this graph, in this concentration range, it is clearly recognized that the PL intensity tends to increase as the concentration of the raw material solution increases. Further, when the raw material liquid A having a concentration of 0.33 M where the maximum PL intensity was observed was used, the quantum efficiency (QE) was a very high value of 92%.
The quantum yield (QE or critical quantum yield) is analyzed using an absolute PL quantum yield measurement system (C9920-02, manufactured by Hamamatsu Photonics) equipped with an integrating sphere coated with BaSO ₄ and a 150 W xenon lamp. It was.

  FIG. 4B shows the droplet diameter (dd) with respect to the concentration of the raw material solution used in the experiment whose result is shown in FIG. 4A and the diameter (dp) of the particles synthesized by the tubular reactor 4. It is a graph which shows correlation. The image inserted in the graph is a representative TEM photograph of the phosphor obtained at a low density (0.05M, lower left) and a high density (0.33M, upper right). The droplet diameter of the raw material solution was measured using a laser diffraction particle size system. It can be seen from this graph that the droplet size (o-shaped plot) is approximately constant at all concentrations. On the other hand, the diameter of the synthesized particles tends to increase with the concentration of the raw material solution in both the calculated particle size (□ -shaped plot) and the measured particle size (▽ -shaped plot). Recognized. In addition, this tendency is shown in FESEM photographs (Fig. 5) of Ca chloroapatite prepared at various raw material solution concentrations, and a bar graph of corresponding volume average diameters measured based on the FESEM photographs (inset of Fig. 5). Can also be confirmed.

  According to the theory of the drop-per-particle (ODOP) mechanism typically seen in the SP process, if the droplet size is constant, the diameter of the resulting particle is the calculated value entered in FIG. As shown by the curve (□-□), it simply increases with increasing concentration. However, the measured value curve (▽-▽) does not necessarily coincide with the calculated value curve, and it is clearly recognized that the upward deviation from the calculated value curve increases as the concentration increases. This phenomenon seems to show a tendency that hollow particles are formed as the concentration of the raw material solution A is increased. Moreover, formation of a hollow structure is also confirmed from a TEM photograph of particles with a concentration of 0.33 M shown in the upper right of FIG.

Here, the formation mechanism of the hollow structure as described above will be described. First, FIG. 4 (c) shows a conceptual diagram of a transition mechanism for the particles from the droplets, indicating a low concentration and a high concentration of C _l and C _h are the raw material solution A. In a typical SP process, as shown in FIG. 4 (c), the droplets introduced into the furnace first undergo a “nucleation-crystallization” step (t _nc ) and then “dry-sinter”. Through the step (t _ds ), final particles are formed. However, in order to obtain chloroapatite phosphor particles having high PL intensity, “reduction” of Eu ³⁺ → Eu ²⁺ with H ² or the like following the above-mentioned “dry-sintering” step (t _ds ). The process (t _r ) is indispensable. Only when the raw material solution A has a high concentration (C _h ), the phenomenon that the hollowing of the particles occurs in the “drying-sintering” step (t _ds ) is that the dry solidification at the outer periphery of the droplet precedes the release of moisture. May be caused by

  In any case, it is a remarkable fact that a hollow chloroapatite phosphor can be produced by a method that does not use a template. And, since the particles are hollow, the “reduction” step important in the production of the chloroapatite phosphor proceeds more efficiently. It is expected to be highly reduced.

Moreover, further see detail Figure 4c, in the figure, t _nc, t _ds, the length of each arrow labeled t _r is "nucleation - Crystallization", "dry - sintering", " The average characteristic time in each step of “reduction” is shown symbolically. The total residence time of each droplet (particle) is in a tubular reactor 4 coincides with the sum of _{t nc, t ds, t r} .
Here, if the synthesis temperature and the gas flow rate are the same, it can be assumed that the residence times are the same even for the raw material solutions having different concentrations. First, when the raw material solution has a low concentration, since it takes a long time to reach supersaturation, the characteristic time t _nc of “nucleation and crystallization” becomes very long and occupies much of the total residence time. . On the other hand, the time until the supersaturation is shortened at a high concentration, and the time provided for the “reduction” step (t _r ) becomes longer corresponding to the shortening of the “nucleation-crystallization” characteristic time t _nc. Sufficient reduction action can be easily obtained, and fluorescence characteristics due to reduced Eu ²⁺ can be obtained. Thus, it is understood that the enhancement of the PL characteristics obtained when the raw material solution is made high in concentration involves the promotion of the reduction reaction at a high concentration.

(Total gas flow rate)
Further, it has been found that the total gas flow rate in the tubular reactor 4 plays an important role in controlling the PL intensity of the Ca apatite phosphor particles in addition to the concentration of the raw material solution A and the temperature effect. FIG. 6 is a graph showing relative PL intensity (a), residence time (b), and H ₂ flow rate (c) as a function of total gas flow rate. From FIG. 6A, when the total gas flow rate is in the range of 2-7 (L / min), the relative PL intensity gradually increases as the total gas flow rate increases and exceeds 7 (L / min). It can be seen that it decreases as the total gas flow rate increases.

This phenomenon is considered to be caused by a trade-off effect between “residence time” and “H ₂ flow rate” caused by a change in the total gas flow rate. That is, as shown in Equation 1, the residence time of the droplet (particle): τr is a function of the total gas flow rate Q _gt , temperature: T, and reactor volume: Vr. Keeping the other parameters constant, similar results are achieved with the temperature. That is, as the total gas flow rate increases, the residence time inevitably decreases, so the reduction reaction by H ₂ should be hindered as the total gas flow rate increases. On the other hand, since the H ₂ flow rate itself increases while the total gas flow rate increases, the reduction reaction is promoted. As a result of the trade-off between these two conflicting phenomena, the relative PL intensity gradually decreases with the total gas flow rate of 7 (L / min) as a boundary, whether the total gas flow rate exceeds or falls below the same boundary value. It seems to show the tendency to do.

Further, in addition to the above discussion, when the total gas flow rate exceeded a value near 7 (L / min), there was a tendency for the fluid flow (flow pattern) in the reactor to be disturbed. Therefore, in the subsequent experiments for examining other parameters, 5 (L / min) was adopted as the total gas flow rate for the purpose of maintaining good experimental conditions for obtaining stable results.
As described above, only by controlling the three parameters of the heating temperature, the concentration of the raw material liquid A, and the total gas flow rate, a hollow and high quantum yield (0.92) is exhibited, and blue chromaticity is obtained by excitation with ultraviolet rays. It was found that a Ca chloroapatite phosphor provided with can be stably produced (see FIG. 13).

(Substitution with Mg ²⁺ )
However, the PL characteristics and quantum yield of these Ca chloroapatite phosphors are not always sufficient as practical levels.
Therefore, with the aim of further improving the light emitting performance, an attempt was made to change the europium dope concentration by replacing calcium in the Ca chloroapatite phosphor with magnesium. This is the method previously reported by the applicant (Adv. Mater. 2008, 20, 3422-3426: “Rapid Synthesis of Non-Aggregated Fine Chloroapatite Blue Phosphor with High Quantum Efficiency”). In the experimental results for the present invention, this method was actually effective, and when the concentration of the raw material liquid A was 0.33 M, a very quantum yield of 1.00 was achieved (see FIG. 13). Specifically, as described in the above-mentioned Adv. Mater., The effect that the crystallinity of Ca chloroapatite is improved by replacing a part of Ca ²⁺ with Mg ²⁺ having a smaller ionic radius. The technical contents using

(Sr apatite and Ba apatite)
The following is the effect of the composition constituting apatite as other parameters, specifically, Sr apatite phosphor in which Sr is applied instead of Ca as M of M ₅ (PO ₄ ) ₃ Cl _x : Eu ²⁺ And the result of having compared Ba apatite fluorescent substance to which Ba was applied instead of Ca as M is shown. Each phosphor particle was produced under the conditions of a heating synthesis temperature: 1100 ° C., a total gas flow rate: 5 L / min, and a raw material solution concentration: 0.33 M.

  The three curves shown in FIG. 7A are normalized PL spectra of the Ca apatite phosphor, the Sr apatite phosphor, and the Ba apatite phosphor. In the coordinates, SEM photographs of these three types of apatite phosphors and corresponding digital images at the time of excitation with 365 nm UV light are inserted. FIG. 7B shows XRD patterns of the obtained Sr apatite phosphor and Ba apatite phosphor.

From the normalized PL spectrum of FIG. 7 (a), the Sr apatite phosphor tends to shift to blue than the Ca apatite phosphor, and the Ba apatite phosphor shifts further to the blue than the Sr apatite phosphor. The tendency to do is shown. This phenomenon is explained by the theory of the bound ionicity (P) of the compound and is closely related to the g factor of Eu ²⁺ ions.

FIG. 8A shows a TEM photograph of the Sr apatite phosphor. An enlarged TEM photograph is inserted in the upper right corner, and a corresponding SAED pattern is inserted in the lower right corner. FIG. 8B shows a TEM photograph of the Br apatite phosphor, and a corresponding SAED pattern is inserted in the lower right corner.
From each TEM photograph, it can be seen that in addition to Ca apatite phosphor particles, Sr apatite phosphor and Ba apatite phosphor also show a hollow shape. These Sr apatite phosphor and Ba apatite phosphor were also prepared from the raw material solution A having a concentration of 0.33M.

  When these TEM photographs are observed in detail, these hollow particles have a large number of primary nanocrystals produced by fast nucleation and crystallization, as supported by the dot-like electron diffraction (ED) pattern found in the SAED pattern. It is understood that it is configured by gathering. These Sr apatite phosphor and Ba apatite phosphor exhibited excellent PL performance with a QE value close to 100% (see FIG. 13).

FIG. 9 is an XY chromaticity coordinate graph (CIE1931 chromaticity diagram) of the three types of phosphors thus produced (Ca, Sr, and Ba apatite phosphors). Among these phosphors, the Sr apatite phosphor shows the lowest y coordinate (0.154, 0.030), while Ba apatite exactly matches the commercially available BAM: Eu written together as a reference example. The chromaticity coordinate values (0.156, 0.044) are shown. BAM: Eu (chemical formula: Ba _1-x MgAl ₁₀ O ₁₇ : Eu _x ) has already been widely used as a blue light emitting material for plasma display panels and rare gas lamps.
As for the Ca apatite phosphor, as the concentration of the raw material solution A is increased from 0.05M, the chromaticity coordinate values are indicated by black circles (0.203, 0.178) and clear blue coordinates. It is shown that an ideal (0.144, 0.054) coordinate value can be obtained at a density of 0.33 M indicated by a white circle, and the state of markedly changing to a value.

  In order to confirm the practicality of the three types of phosphors according to the present invention (Ca, Sr, and Ba apatite phosphors) obtained as a result of various studies as described above, as described in detail below, A white LED was prepared by coating an epoxy resin suspension prepared by mixing the three types of phosphors together with a commercially available cerium-doped yttrium aluminum garnet (YAG: Ce) phosphor on a UVLED chip. A photograph of white light obtained by each of these white LEDs is shown on the right side of FIG. As can be seen from these photographs, very strong white light was generated from any of the white LEDs.

(Procedure of white LED)
0.5 g of each phosphor particle (apatite, YAG, etc.) was added to 50 g of ethanol, and PVP resin was added to the solution at a weight ratio of 3: 1. The clear phosphor-polymer suspension was ball milled for 3 hours. Finally, the phosphor / polymer composite droplets described above were dropped onto the UV-LED and dried at room temperature for 6 hours for solidification. As the UV-LED chip, NSHU550B (manufactured by Nichia Corporation) that emits a peak wavelength of 365 nm was used.

  10, 11, and 12 are respectively a STEM (upper left) and element mapping images of Ca chloroapatite phosphor, Sr chloroapatite phosphor particles, and Ba chloroapatite phosphor particles, and an EDS (energy dispersive X-ray spectrometer). ). The result of the EDS pattern agrees with the atomic ratio of almost all the elements in the particle, that is, that of the raw material solution, that is, (P: Cl: Ca: Eu = 1.00: 3.00: 1.72: 0.017) Indicates to do. The extreme difference in the Cl ratio is caused by the lack of Cl element. The fact that impurities were not detected from the elemental analysis results of the Sr apatite and Ba apatite phosphors is that the SP method is effective and promising again. It shows that it can be controlled more easily. Elemental mapping and chemical composition of the particles were performed using a scanning transmission electron microscope (STEM) equipped with an energy dispersive X-ray spectrometer.

  Provided is a hollow phosphor having less PL problems and excellent PL characteristics by a process without a template by spray pyrolysis, and a simple method and apparatus for producing a hollow phosphor having a relatively small number of manufacturing steps. In addition, the present invention can be used to provide a method and an apparatus for manufacturing a hollow phosphor that does not require extra raw materials.

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Ultrasonic atomizer 3 Precursor container 4 Tubular reaction furnace 5 Furnace body 6 Heating means 8 Electrostatic collector 10 Collection container main body 11 Collection filter 12 Corona discharge body 13 High voltage power supply 15 NaOH trap 18 Gas supply source

Claims (9)

A hollow phosphor that contains chloroapatite as a main component and is produced by spray pyrolysis without using a template. The hollow fluorescent substance according to claim 1, comprising at least one of Ca, Ba, Sr, and Mg as a metal element constituting the chloroapatite. The hollow phosphor according to claim 1 or 2, having a quantum efficiency of 0.90 or more. The hollow phosphor according to any one of claims 1 to 3, which emits blue light when excited by ultraviolet rays. The hollow phosphor according to any one of claims 1 to 4, which has a particle diameter of 1 to 2 µm. A method for producing a hollow phosphor, comprising:
A raw material in which a salt containing at least one metal constituting chloroapatite, a metal chloride containing at least one of Ca, Ba, Sr, and Mg and a salt containing at least one of samarium, europium, terbium, and dysprosium are dissolved. An atomization step of atomizing the solution;
A heating and synthesizing step of heating droplets of the raw material solution atomized by the ultrasonic atomizer in a reaction furnace in a reducing atmosphere;
A collection step of collecting the hollow phosphor particles generated by the heating synthesis step;
And a control step of controlling at least the concentration of the raw material solution so that the particles become hollow phosphor particles. The manufacturing method according to claim 6, wherein the control step further includes at least one control of a heating temperature in the heat synthesis step, a time length during which the droplets and the particles are exposed to the heat synthesis step. The manufacturing method according to claim 7, wherein a heating temperature in the heating synthesis step is between 1050 ° C. and 1150 ° C. The manufacturing method according to claim 7 or 8, wherein in the heating and synthesizing step, a carrier gas for conveying particles is flowed, and the control step includes a step of controlling a total gas flow rate in the reaction furnace.