JP5051079B2 - Rare earth phosphate - Google Patents

Description

  The present invention relates to rare earth phosphates.

  Rare earth phosphate phosphors are known to have excellent luminescence properties, and many types of rare earth phosphate phosphors have been developed and used for fluorescent lamps and cathode ray tubes since the early 1970s. .

  In the field of fluorescent lamps for general lighting, a three-wavelength light emitting fluorescent lamp that satisfies both high color rendering and high efficiency has been developed and put into practical use. As the phosphor used in the three-wavelength region emission type fluorescent lamp, a mixture of three kinds of phosphors of red, green, and blue having a relatively narrow emission spectrum distribution in an appropriate ratio is used. Among these phosphors, cerium (Ce) and terbium (Tb) activated lanthanum phosphate, which is one of the rare-earth phosphate phosphors, is a typical green phosphor in this three-wavelength region emission fluorescent lamp. It has been put into practical use. Moreover, cerium (Ce) activated yttrium phosphate phosphors are used for ultraviolet light emitting fluorescent lamps along with lead (Pb) activated barium silicate phosphors and europium (Eu) activated strontium borate phosphors. Has been.

  In order to remove the solvent and binder in the phosphor coating solution, the fluorescent lamp heat-treats the applied phosphor film at a temperature of 500 to 650 ° C. and further processes the glass bulb to a desired shape. By heating at a temperature of ˜850 ° C., there is a problem in that the initial luminance of the fluorescent lamp is lowered and the light emission output maintenance ratio is lowered.

  In recent years, in the case of high-load type fluorescent lamps such as compact fluorescent lamps that are used in place of incandescent bulbs, light-emitting tubes with a small tube diameter are used, which is more than conventional straight tube or round tube fluorescent lamps. Since the tube wall load is large and the tube wall temperature becomes 100 ° C or higher during lamp lighting, when the conventional phosphor for a three-wavelength light emitting fluorescent lamp is used as it is, the tube wall temperature rises as the lighting time elapses. As a result, there were problems such as the lamp becoming dark or changing color.

  In particular, phosphors applied to high-load type fluorescent lamps are required to have as low a decrease in emission intensity as the temperature of the phosphor layer (phosphor) rises (hereinafter referred to as “temperature quenching”) as much as possible. Similarly, rare earth phosphate phosphors used as green phosphors for light-emitting fluorescent lamps are also stable with respect to the heat treatment temperature in the manufacturing process of the fluorescent lamp, and the reduction in initial luminance and the maintenance rate of light emission output There is a demand for a material that has a small decrease in temperature quenching as much as possible.

  By the way, as a method for producing a rare earth phosphate phosphor, a predetermined amount of each oxide of rare earth elements constituting a phosphor matrix and a phosphate compound such as diammonium hydrogen phosphate are mixed together with a compound containing an activator element, A dry production method in which a reaction between solids is performed by firing, a solution containing a rare earth element constituting the phosphor matrix, and a solution containing phosphate ions such as phosphoric acid are mixed with a solution containing an activator element. There is a wet manufacturing method in which a precipitate of a rare earth phosphate that is a phosphor precursor is generated in a solution, and the precursor is solid-liquid separated and fired.

  In order to increase the yield and luminous efficiency of rare earth phosphate phosphors, it is necessary to make the phosphor composition as close as possible to the stoichiometric composition, but in the dry manufacturing method, a purely stoichiometric composition is required. It is difficult to produce only rare earth phosphate phosphors, and as a result of reaction between solids, excess phosphorous that does not react with rare earth elements remains as impurities such as oxides, and a phosphor with a stoichiometrically high purity composition Difficult to get. In order to obtain a compositionally uniform rare earth phosphate phosphor, the wet manufacturing method is more suitable than the dry manufacturing method.

  When producing a rare earth phosphate phosphor by a wet method, first, a precipitate of a rare earth phosphate that is a precursor of the phosphor is generated and baked to form a rare earth phosphate phosphor. The characteristics of the phosphor, such as the emission characteristics, greatly depend on the properties of the rare earth phosphate that is the precursor. Therefore, it is necessary to consider the control of the particle size distribution of the rare earth phosphate initially produced and the exclusion of impurities. However, the particle size of the phosphor obtained by the wet method is extremely small, and washing and solid-liquid separation are difficult, the particle size and particle size distribution are difficult to control, and many impurities present in the precipitation medium of rare earth phosphate are present. There was a problem of mixing.

  Therefore, many improvements have been proposed for the production of rare-earth phosphate phosphors by the dry method and wet method. However, the reduction of the initial luminance and the luminance maintenance rate, which are particularly suitable for fluorescent lamps, and the improvement of temperature quenching are pointed out. However, it is not always sufficient, and there has been a demand for further improvements regarding rare earth phosphate phosphors and methods for producing the same, focusing on these points.

The present invention, when used as a fluorescent film of a fluorescent lamp, is less likely to cause a decrease in initial luminance in the lamp manufacturing process, a decrease in luminance maintenance ratio when continuously lit, and temperature quenching, and easy control of the particle size. it is intended to provide a rare earth phosphate.

  In order to achieve the above object, the present inventors have intensively studied a method for producing a rare earth phosphate phosphor by a wet method, and as a result, controlled the production conditions such as the precipitation conditions of the rare earth phosphate that is a precursor of the phosphor. As a result, a rare earth phosphate phosphor having a desired particle size can be produced in a high yield. When this is used as a fluorescent film of a fluorescent lamp, the initial luminance of the fluorescent lamp and the luminance maintenance during continuous lighting are maintained. The inventors have found that a rare earth phosphate phosphor with little reduction in temperature and low temperature quenching can be obtained, and the present invention has been completed. The configuration of the present invention is as follows.

(1) The composition formula is Ln _x Ce _y Tb _z PO ₄ (where Ln represents one or more elements selected from the group of La, Gd and Y, and x, y and z are each 0 ≦ x <1 , 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4 and x + y + z = 1), and the powder reflectance at a wavelength of 490 nm after calcining in air at a temperature of 120 to 900 ° C. Is a rare earth phosphate characterized in that is 99% or more with respect to the reflectance of the MgO powder.

(2) The rare earth phosphate according to (1) above, wherein 10 to 50,000 ppm of an aluminum compound in terms of aluminum is mixed or adhered.

  The present invention can obtain a rare-earth phosphate having no body color by adopting the above-described configuration, and when the rare-earth phosphate phosphor using this is used as a fluorescent film of a fluorescent lamp, the luminance is reduced in the heat treatment process. Less, the initial luminance of the fluorescent lamp is high, and even when the fluorescent lamp is continuously lit, the luminance maintenance rate is higher than that of the conventional rare earth phosphate phosphor. Further, the rare earth phosphate phosphor of the present invention containing a specific amount of Al has a markedly improved temperature quenching of the phosphor emission compared to the conventional rare earth phosphate phosphor not containing Al. Furthermore, the particle diameter can be easily controlled, and a rare earth phosphate precursor and a rare earth phosphate phosphor having a desired particle diameter can be obtained in a high yield.

In order to produce the rare earth phosphate of the present invention, first, the composition formula Ln _x Ce _y Tb _z PO ₄ (where Ln represents one or more elements selected from the group consisting of La, Gd and Y, and x, y And z are numbers satisfying the following conditions: 0 ≦ x <1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 0.4 and x + y + z = 1, and so on. And the compound of Tb are dissolved in water. These rare earth compounds may be water-soluble salts such as nitrates, sulfates and chlorides of Ln, Ce and Tb, but those obtained by previously dissolving the rare earth oxides in mineral acids such as nitric acid may also be used. good. A first solution is prepared by adding phosphoric acid to a solution in which the compounds of Ln, Ce and Tb are dissolved.

The amount of phosphoric acid contained in the first solution is stoichiometrically excessive from the above composition formula, but preferably the molar ratio of the total amount of rare earth element ions and the total amount of phosphate ions {( When the amount of phosphoric acid in the first solution is kept slightly higher than the stoichiometric amount so that PO ₄ ) ⁻³ / (Ln + Ce + Tb) ⁺³ } is 1.05 to 1.10. It is preferable because excessive phosphate ions that become impurities can be prevented from adhering to the surface of the rare earth phosphate. At this time, conditions such as liquid temperature and pH are set so that rare earth element ions and phosphate ions coexist in an ion state in the first solution and precipitation of the rare earth phosphate does not occur in the first solution. It is necessary to control.

Next, a predetermined amount of nitric acid and aqueous ammonia are mixed separately from the first solution, and the pH value of the mixed solution is in the range of 1.0 to 2.0, preferably in the range of 1.0 to 1.3. A second solution composed of ammonium ions and nitrate ions adjusted to become is prepared.
Then, when stirring while gradually dropping the first solution into the second solution, a precipitate of rare earth phosphate is gradually generated in the second solution. In a conventional method for producing a rare earth phosphate by a wet method, a solution containing a rare earth element ion and a solution containing a phosphate ion are mixed, and at the same time, a phosphate precipitate is immediately formed in the mixed solution. For this reason, fine-grained or glue-like rare earth phosphates are formed, and it is difficult to filter and wash them, and it is difficult to control the particle diameter of the produced phosphate particles.

  However, according to the method for producing a rare earth phosphate of the present invention, the first solution in which the ions of the rare earth element and the phosphate ions coexist in an ionic state and the rare earth phosphate has not yet been formed has a specific pH value. Since the rare earth phosphate is added in the second solution in which the adjusted ammonium ions and nitrate ions coexist, and depending on the addition amount and the addition speed of the first solution, The rate of formation of the rare earth phosphate precipitate and the growth rate of the particles can be freely adjusted, and the precipitation of the rare earth phosphate controlled to a desired particle size can be obtained.

  As will be described later, when the rare earth phosphate phosphor contains a specific amount of aluminum (Al), the temperature quenching of the phosphor is improved, and when the phosphor film is formed using the phosphor, the coatability is good. Become. When producing a rare earth phosphor using the rare earth phosphate of the present invention, Al may be physically mixed in advance with the rare earth phosphate. For example, by adding further alumina to the solution containing the precipitate of the rare earth phosphate obtained as described above, mixing thoroughly, dehydrating and solid-liquid separation, the alumina adheres to the surface of the precipitated particles or An alumina-containing rare earth phosphate may be obtained by mixing the particles. The alumina added at this time is suitably 10 to 50000 ppm in terms of aluminum (Al). As the aluminum (Al) source to be added, it is preferable to use alumina. However, an aluminum compound that does not dissolve in the second solution, such as aluminum hydroxide in addition to alumina, and generates alumina during firing may be used. . When the addition amount of the alumina of the present invention is less than 10 ppm in terms of aluminum (Al), the above effect cannot be obtained sufficiently. On the contrary, when it exceeds 50000 ppm, the emission luminance of the rare earth phosphate phosphor is reduced. It is not preferable. In addition, the preferable range of the addition amount of said aluminum is 1000-10000 ppm.

  One of the characteristics of the rare earth phosphate obtained in this way is that the body color does not appear even after the heat treatment as compared with the conventional rare earth phosphate, and it is close to white. When the obtained rare earth phosphate is heated in the range of 120 to 900 ° C. in air, the powder reflectivity is high even when heated at any temperature, and the powder reflectivity at a wavelength of 490 nm is measured. A reflectance of 99% or more with respect to a rate of 100 is shown. In this way, the rare earth phosphate phosphor made of a rare earth phosphate that exhibits high reflectivity even after the heat treatment has a high initial luminance after the heat treatment, and a phosphor with a low decrease in luminance maintenance rate is obtained. It was.

  The rare earth phosphate phosphor of the present invention can be produced in the same manner as in the conventional method except that the rare earth phosphate described above is used as the phosphor raw material. That is, after adding and mixing the above-mentioned rare earth phosphate and a flux such as a lithium compound or a boron compound as necessary, the mixture is filled in a heat-resistant container and fired at a temperature of 900 to 1300 ° C. for 1 to 10 hours in a reducing atmosphere. And pulverizing, washing, drying and sieving.

  In addition, what is necessary is just to calcinate as it is as mentioned above, when the surface is previously coated with alumina as a phosphor raw material or mixed rare earth phosphate is used. Further, when a rare earth phosphate not coated or mixed with alumina is used as a phosphor raw material, a predetermined amount of alumina is further added and mixed thoroughly before firing. The rare earth phosphate phosphor of the present invention thus obtained contains 1 to 500 ppm of aluminum (Al) in the phosphor in which alumina is added to the raw material. The rare earth phosphate phosphor containing Al has an extremely low degree of temperature quenching compared to the phosphate phosphor not containing Al. If the aluminum (Al) content in the phosphor is less than 1 ppm, the effect of suppressing temperature quenching is hardly observed. Conversely, if it exceeds 500 ppm, the emission luminance is lowered even at room temperature, which is not preferable. In addition, the preferable range of aluminum content in fluorescent substance is 100-400 ppm. When the rare earth phosphate phosphor is produced using the rare earth phosphate of the present invention, in order to make the Al content in the phosphor 1 to 500 ppm, an aluminum compound such as alumina of 10 to 50000 ppm in terms of Al is used. A mixed or adhered rare earth phosphate may be used.

FIG. 1 is a graph showing the relationship between the pH value of the second solution and the powder reflectance of the rare earth phosphate. Specifically, the first solution containing rare earth ions and phosphate ions when producing an Al-free rare earth phosphate represented by the composition formula La _0.55 Ce _0.30 Tb _0.15 PO _4. Is added to a second solution containing ammonium ions and nitrate ions to cause a precipitate to form. In this step, the powder reflectance of the rare earth phosphate produced when the pH value of the second solution is changed from 0 to 7.0 is shown in FIG. In this figure, the horizontal axis represents the pH value of the second solution, and the vertical axis represents the powder reflectance at a wavelength of 490 nm of the rare earth phosphate obtained from the second solution having the respective pH values, and the reflection of the MgO powder. It was expressed as a relative value to the rate.

As can be seen from FIG. 1, when the pH value of the second solution to which the first solution is added is adjusted to 2 or less, the reflectance of the rare earth phosphate obtained is 99% or more. When the pH value exceeds 2, the reflectivity rapidly decreases. This indicates that Ce ³⁺ and Tb ³⁺ are inherently stable in a trivalent state at pH 2 or lower. When pH becomes high, Ce ³⁺ and Tb ³⁺ are easily oxidized to a higher-order oxidation state, and Ce and Tb in the higher-order oxidation state are subjected to heat treatment, and are changed to oxides having body color, thereby rare earth phosphates. It seems to reduce the reflectance.

2 is similar to each sample of FIG. 1 in that the first solution is added to the second solution and reacted, and a rare earth phosphate not containing Al (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ) Shows the yield of the rare earth phosphate obtained when the pH value of the second solution was changed from 0 to 7.0. In this figure, the horizontal axis indicates the pH value of the second solution, and the vertical axis indicates each rare-earth phosphate (La _0.55 Ce _0.30 Tb _0.15 PO ₄ when the second solution has the pH value). ) Yield. In addition, the yield of the rare earth phosphate of FIG. 2 is obtained by calcining the precipitate of the rare earth phosphate (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ) obtained from the second solution at 900 ° C. The weight of the rare earth phosphate is expressed as a percentage with respect to the theoretical amount of the rare earth phosphate calculated from the rare earth element (Ln) ions and phosphate ions introduced into the first solution in order to form the precipitate.

As can be seen from FIG. 2, the yield of rare earth phosphate (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ) is the same as that of the first solution (mixed solution of rare earth element ions and phosphate ions). When the pH value of the second solution (a solution containing ammonium ions and nitrate ions) is about 1.2 or more, a high yield of 97% or more is obtained, and when the pH value is below 1.0, the yield is obtained. Is significantly reduced.

  Although not shown, the residual amounts of La, Ce, and Tb in the supernatant of the second solution after precipitation of the phosphate are pH 1.2 to 10 ppm, whereas pH 1.0 It is confirmed that the residual amount increases, particularly, the increase amount of La is large. From this, most of lanthanum, cerium and terbium react at pH 1.2 or more to produce a uniform phosphate precipitate, but it is estimated that an uneven precipitate with a small lanthanum composition is formed at a lower pH. Is done.

A rare earth phosphate containing no Al (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ) obtained in the same manner as each sample of FIGS. 1 and 2 was used as a raw material, and boric acid and tetraboric acid were added thereto. Lithium was added as a flux and fired at 1200 ° C. for 2 hours to obtain a rare earth phosphate phosphor (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ). Further, FIG. 3 shows the correlation between the emission luminance under ultraviolet excitation after baking this phosphor in air at 800 ° C. and the pH value of the second solution. In this figure, the horizontal axis indicates the pH value of the second solution, and the vertical axis indicates the brightness of 253.times. After baking of the obtained rare earth phosphate (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ). The emission luminance under ultraviolet excitation of 7 nm is shown as a relative value to the emission luminance of the conventional rare earth phosphate phosphor (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ) used as the standard phosphor.

As can be seen from FIG. 3, the luminance of the rare earth phosphate phosphor (La _0.55 Ce _0.30 Tb _0.15 PO ₄ ) after production and after baking at 800 ° C. in the air, In the process of preparing the rare earth phosphate that is a precursor of the second solution, when the pH value of the second solution is 2.0 or less, it becomes 90% or more, and particularly when the pH value is 1.1 to 1.2 (98% In the phosphor using the precursor obtained by adding the first solution to the second solution having a pH value of greater than 2.0, the initial brightness after the heat treatment is small. The initial brightness after processing is significantly reduced.

  Thus, the initial luminance after baking of the rare earth phosphate phosphor manufactured by the wet method is significantly reduced when the pH value of the second solution when the precipitate of the rare earth phosphate as the precursor is generated is larger than 2. To do. This coincides with the critical pH value of the second solution under the precipitation conditions that rapidly decreases the reflectance of the rare earth phosphate precursor of the rare earth phosphate phosphor (see FIG. 1). As described above, Ce ions and Tb ions are stable in a trivalent state at a pH of 2.0 or lower, whereas Ce ions and Tb ions are increased when the pH value of the second solution is greater than 2. This is considered to be due to being easily oxidized to a higher-order oxidation state. Thus, the manufacturing conditions of the rare earth phosphate greatly affect the luminance (thermal degradation) after baking of the rare earth phosphate phosphor.

The first solution containing a predetermined amount of rare earth element ions and phosphate ions is added to the second solution containing ammonium ions and nitrate ions and the pH value is adjusted to 1.2, and four kinds of rare earths having the same composition are added. Phosphate precipitates were generated, and four types of alumina suspensions containing different amounts of different aluminas prepared separately were added and mixed in each precipitate, followed by dehydration, and alumina was attached to each of the four suspensions. Kinds of rare earth phosphates were obtained. This was fired as a raw material to obtain four types of rare earth phosphate phosphors having a composition formula of La _0.55 Ce _0.30 Tb _0.15 PO ₄ and containing 10 ppm, 200 ppm, 350 ppm and 500 pm of aluminum, respectively. FIG. 4 is a graph showing the temperature dependence of the emission luminance of this phosphor. The diagram of each phosphor in the figure shows that ■ is no alumina addition (A), ◆ is alumina content 10 ppm (B), ▲ is alumina content 200 ppm (C), □ is alumina content 350 ppm (D), ◇ indicates an alumina content of 500 ppm (E).

  The temperature dependence of the phosphor luminance is measured by placing the phosphor on a metal sample plate, heating the sample plate with a heater, and irradiating the phosphor sample with 253.7 nm ultraviolet rays while heating. Light was emitted, and the emission luminance of the phosphor and the temperature of the sample plate at that time were measured. In FIG. 4, the horizontal axis represents the temperature of the sample plate on which the phosphor is placed, and the vertical axis represents the light emission luminance of the phosphor. The emission luminance on the vertical axis is the emission luminance when excited with 253.7 nm ultraviolet light at room temperature (25 ° C.) using the same rare earth phosphate phosphor as the standard phosphor used in FIG. The relative value when 100 is assumed. In FIG. 4, curve A is the case of the phosphor of the present invention containing no Al, and curves B, C, D, and E are the present inventions having Al contents of 10 ppm, 200 ppm, 350 ppm, and 500 ppm, respectively. This phosphor is shown.

  As can be seen from FIG. 4, in the case of the rare earth phosphate phosphor of the present invention that does not contain Al, when the temperature is raised to around 100 ° C., the emission luminance decreases sharply as in the case of the conventional rare earth phosphate phosphor. Although the temperature quenching is not improved, the rare earth phosphate phosphor of the present invention containing Al in the present invention has a very low decrease in emission luminance even when the temperature is increased to 200 ° C. or higher, and almost no temperature quenching is observed. I can't. As described above, the rare earth phosphate and the rare earth phosphate phosphor in which Ln is La have been described in detail, but it has been confirmed that similar results can be obtained when Ln is Y or Gd.

Hereinafter, the present invention will be described by way of examples.
Example 1
Add 61.0 g of cerium oxide (CeO ₂ ), 33.1 g of terbium oxide (Tb ₄ O ₇ ), and 105.9 g of lanthanum oxide (La ₂ O ₃ ) in pure water, and stir well to suspend each rare earth oxide. Nitric acid having a specific gravity of 1.42 was gradually added thereto to dissolve each rare earth oxide. At this time, in order to facilitate the dissolution of each rare earth oxide, the liquid temperature was heated to 60 ° C. while adding 35% hydrogen peroxide, and stirring was continued to obtain a total amount of 1000 ml of a transparent rare earth nitrate aqueous solution.
Next, the obtained aqueous solution of rare earth nitrate is cooled to 25 ° C., and while stirring, 144 g of 85% phosphoric acid is added dropwise with pure water and mixed, so that the total ion concentration of each rare earth ion of Ce, Tb and La is 0. A first solution having a total amount of rare earth ions: phosphate ions of 1: 1.06 was prepared.

On the other hand, 100 ml of 28% ammonia water is added to 500 ml of pure water, and nitric acid having a specific gravity of 1.42 is gradually added to this while stirring to adjust the pH to 1.2. did.
Next, the rare earth hydrochloride precipitate was generated by slowly dropping the first solution into the second solution while stirring at a dropping rate of 400 ml / hour. At this time, since the pH value of the second solution changed every time as the first solution was added, the pH of the second solution was constantly adjusted to about 1.2 by simultaneously adding ammonia water each time.
Thereafter, the obtained precipitate of rare earth phosphate was washed by decantation, filtered, dried at 120 ° C., and then sieved with an opening 60 micron sieve to obtain 274 g of the rare earth phosphate of Example 1. The theoretical yield was 280.4 g in terms of the amount of raw material, so the yield was 98%.

The composition of the rare earth phosphate of Example 1 is La _0.55 Ce _0.30 Tb _0.15 (PO ₄ ) _1.02 , the powder reflectance at a wavelength of 490 nm is 99% of the magnesium oxide powder, Body color was not recognized in appearance.
Next, 240 g of rare earth phosphate of Example 1, 1.2 g of alumina (Al ₂ O ₃ ), 2.4 g of lithium tetraborate (Li ₂ B ₄ O ₇ ) as a flux, and boric acid (H ₃ BO ₃ ) as a flux 24g and weighed and mixed well, put in a quartz crucible, baked at 1200 ° C for 2 hours in a nitrogen gas atmosphere containing 2% hydrogen, pulverized, washed and dried And each process of sieving was performed sequentially, the composition formula was La _0.55 Ce _0.30 Tb _0.15 PO ₄ , and the rare earth phosphate phosphor of Example 1 containing 220 ppm of Al was obtained.

The emission luminance when the rare earth phosphate phosphor of Example 1 is excited by irradiation with ultraviolet rays of 253.7 nm is equivalent to the emission luminance of the conventional rare earth phosphate phosphor used as the standard phosphor, In addition, after the phosphor of Example 1 was baked in air at 800 ° C., the emission luminance measured in the same manner as described above was 98% of the standard phosphor, and thermal degradation due to heat treatment of the phosphor was slight. Met.
Further, the phosphor of Example 1 had a relative light emission luminance of 101% at 200 ° C. with respect to 25 ° C., and no temperature quenching was observed.

(Example 2)
The first solution and the second solution prepared in Example 1 were used, the first solution was dropped into the second solution to form a rare earth phosphate precipitate, and then the raw materials were mixed before filtering. 276 g of the rare earth phosphate of Example 2 was added in the same manner as in Example 1 except that an alumina-containing slurry containing Al corresponding to 5000 ppm of the theoretical yield of the rare earth phosphate converted from the amount was added and sufficiently stirred. Got. The theoretical yield was 280.4 g in terms of the amount of raw material, so the yield was 98%.

The composition of the rare earth phosphate of Example 2 was La _0.55 Ce _0.30 Tb _0.15 (PO ₄ ) _1.02 , and 4370 ppm of Al was deposited. This rare earth phosphate had a powder reflectance at a wavelength of 490 nm of 99% of the magnesium oxide powder, and no body color was recognized in appearance.
Next, the composition formula was La _0.55 Ce _0.30 Tb in the same manner as in Example 1 except that the rare earth phosphate of Example 2 was used instead of the rare earth phosphate of Example 1 and alumina was omitted. The rare earth phosphate phosphor of Example 2 having _0.15 (PO ₄ ) _1.02 and an Al content of 350 ppm was obtained.

The light emission luminance when the rare earth phosphate phosphor of Example 2 is excited by being irradiated with ultraviolet rays of 253.7 nm is equivalent to the light emission luminance of the standard phosphor used in Example 1. After the phosphor of No. 2 was baked at 800 ° C. in the air, the emission luminance measured in the same manner as described above was 98% of that of the standard phosphor, and thermal degradation due to heat treatment of the phosphor was slight.
Moreover, the relative light emission luminance of the phosphor of Example 2 at 200 ° C. with respect to 25 ° C. was 101%, and no temperature quenching was observed.

(Comparative Example 1)
Add 76.1 g of cerium oxide (CeO ₂ ), 38 g of terbium oxide (Tb ₄ O ₇ ) and 139.4 g of lanthanum oxide (La ₂ O ₃ ) in pure water, and stir well to suspend each rare earth oxide suspension. In this, nitric acid having a specific gravity of 1.42 was gradually added to dissolve each rare earth oxide. At this time, in order to facilitate dissolution of each rare earth oxide, while adding 35% hydrogen peroxide, the liquid temperature was heated to 60 ° C. and stirring was continued, and the total ions of each rare earth ion of Ce, Tb, and La 1500 ml of a transparent rare earth nitrate aqueous solution having a concentration of 1.5 mol / liter was prepared as a first solution.

On the other hand, 66 g of 85% phosphoric acid is added to pure water, heated and kept at 60 ° C., and further 28% ammonia water is gradually added until the pH of the liquid becomes 1.4. A 500 ml solution of 4 phosphoric acid was prepared and used as the second solution.
Next, the second solution is heated to 60 ° C., and the first solution kept at 60 ° C. is dropped at a dropping rate of 500 ml / hour, and at the same time, 5.6% ammonia water is dropped. By adjusting the pH value of the second solution so as to be always about 1.4, a precipitate of rare earth phosphate was formed, heated to 60 ° C., and held for 1 hour. The molar ratio of the total rare earth ions in the dropped rare earth nitrate solution to the nitrate ions in the phosphoric acid solution was 1: 1.15.

The precipitate of the rare earth phosphate thus obtained was washed with decantation with pure water, filtered, dried at 120 ° C., sieved with an opening 60 micron sieve, and 176 g of the rare earth phosphate of Comparative Example 1 Salt was obtained. Since the theoretical yield was 177.9 g in terms of the amount of raw material, the yield was 99%.
The composition of the rare earth phosphate of Comparative Example 1 was La _0.55 Ce _0.30 Tb _0.15 (PO ₄ ) _1.06 , and the powder reflectance at a wavelength of 490 nm was 98% of the magnesium oxide powder, Had a brown body color.

Next, 120 g of the rare earth phosphate of Comparative Example 1 was used in place of 240 g of the rare earth phosphate of Example 1, the amount of lithium tetraborate (Li ₂ B ₄ O ₇ ) added was 2.4 to 1.2 g, and boric acid (H ₃ BO ₃ ) The rare earth phosphate of Comparative Example 1 having the composition formula of La _0.55 Ce _0.30 Tb _0.15 PO _{4 in} the same manner as in Example 1 except that the amount added was changed from 24 g to 12 g. A phosphor was obtained.

The emission luminance when the rare earth phosphate phosphor of Comparative Example 1 is excited by irradiation with ultraviolet rays of 253.7 nm is equivalent to the emission luminance of the standard phosphor used in Example 1, and Comparative Example After the phosphor No. 1 was baked at 800 ° C. in the air, the emission luminance measured in the same manner as described above was 93% of the standard phosphor, and a decrease in emission luminance due to thermal deterioration of the phosphor was observed. It was.
Moreover, the relative light emission luminance of the phosphor of Comparative Example 1 at 200 ° C. with respect to 25 ° C. was 88%, and remarkable temperature quenching was recognized.

(Comparative Example 2)
49.2 g of cerium oxide (CeO ₂ ), 28.0 g of terbium oxide (Tb ₄ O ₇ ) and 89.6 g of lanthanum oxide (La ₂ O ₃ ) were dissolved in nitric acid in the same manner as in Comparative Example 1 to obtain a rare earth nitrate solution. Then, oxalic acid was added thereto to coprecipitate Ce, Tb and La rare earth element oxalates, which were filtered off, dried and then calcined at 600 ° C. for 1 hour to obtain La, Ce and 169.3 g of Tb coprecipitated oxide and 132.1 g of diammonium hydrogen phosphate [(NH ₄ ) ₂ HPO ₄ ] were weighed and mixed well, and then put in an alumina crucible at 700 ° C. in air. For 2 hours.

The fired product was cooled to room temperature, and 2.4 g of lithium tetraborate (Li ₂ B ₄ O ₇ ) and 24 g of boric acid (H ₃ BO ₃ ) as a flux were added thereto and mixed well. Comparative Example 2 in which the composition formula is La _0.55 Ce _0.30 Tb _0.15 PO _{4 after} being packed in an alumina crucible and sequentially subjected to firing, pulverization, washing, drying, and sieving in the same manner as in Example 1. A rare earth phosphate phosphor was obtained.

The emission brightness when the rare earth phosphate phosphor of Comparative Example 2 was excited by irradiation with ultraviolet rays of 253.7 nm was 98% of the emission brightness of the standard phosphor used in Example 1. Further, after the phosphor of Comparative Example 2 was baked at 800 ° C. in the air, the emission luminance measured in the same manner as described above was 90% of the standard phosphor, and the emission luminance associated with thermal deterioration of the phosphor. The decrease was significant.
Moreover, the relative light emission luminance of the phosphor of Comparative Example 2 at 200 ° C. with respect to 25 ° C. was 80%, and remarkable temperature quenching was observed.

It is the graph which showed the relationship between the pH value of the reaction solution at the time of precipitation production | generation of rare earth phosphate, and the reflectance of the obtained rare earth phosphate. It is the graph which showed the relationship between the pH value of the reaction solution at the time of precipitation formation of rare earth phosphate, and the yield of rare earth phosphate precipitation. It is the graph which showed the relationship between the pH value of the reaction solution at the time of the precipitation production | generation of rare earth phosphate, and the luminescent brightness after baking of the rare earth phosphate fluorescent substance manufactured with the obtained rare earth phosphate. It is the graph which showed the temperature dependence of the luminescent brightness of rare earth phosphate fluorescent substance.

Claims (2)

The composition formula is Ln _x Ce _y Tb _z PO ₄ (where Ln represents one or more elements selected from the group of La, Gd and Y, and x, y and z are 0 ≦ x <1, 0 ≦ respectively. y ≦ 1, 0 ≦ z ≦ 0.4 and x + y + z = 1), and the powder reflectance at a wavelength of 490 nm after calcining in air at a temperature of 120 to 900 ° C. is MgO powder. A rare earth phosphate characterized by having a reflectivity of 99% or more. The rare earth phosphate according to claim 1, wherein 10 to 50,000 ppm of an aluminum compound in terms of aluminum is mixed or adhered.

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