JPH1088127A - Production of rare earth element aluminate fluorescent substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rare earth element aluminate fluorescent substance improved in a brightness-electric current characteristic (γ characteristic), a temperature characteristic and a life characteristic. SOLUTION: This method for producing a rare earth element aluminate fluorescent substance comprises sintering a raw material mixture containing at least a rare earth element oxide and alumina or an aluminum compound capable of being easily converted into the alumina at a high temperature. Therein, the rare earth element oxide satisfies the following conditions, and has a spherical particle shape and a uniform particle distribution. The raw material mixture is sintered in a temperature range of 1350-1650 deg.C. D1 /Ds <=1.5; 1.0<=Da <=6.0; 1.0<=Dm <=12.0; 1.0<=Dm /Da <=2.0, and 0<=σlog <=0.30. Therein, D1 is the major axis (μm) of the particle; Ds is the minor axis (μm); Da is an average particle diameter (μm); Dm is a middle particle diameter (μm); σlog is an index representing the width of a particle size distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare-earth aluminate phosphor, and more particularly to a rare-earth aluminum phosphor having a good .gamma. The present invention relates to a method for producing a nate phosphor.

[0002]

2. Description of the Related Art Color televisions for large screens are blue, green,
2. Description of the Related Art A projection display that uses three red monochrome CRTs to project an enlarged image on a screen to project a color image is used. In order to realize a large-screen and high-luminance video, a high voltage and a high current are applied to a fluorescent screen of a monochrome CRT (projection tube). Therefore, the following characteristics are required for the phosphor constituting the phosphor screen.

(1) As a phosphor applied to the inner surface of a projection tube, a phosphor having good luminance-current characteristics (γ characteristics) that does not saturate the luminance even when a high current flows is desired. This is a condition because it is necessary to perform enlarged projection on a large screen with high luminance.

(2) A phosphor that emits light with high luminance stably even at high temperatures. (Temperature Characteristics) An extremely large electric power is supplied to the phosphor for the projection tube as described above. This is about 100 times that of a normal CRT. Therefore, any energy not used for light emission generates heat. As a result, the phosphor inside the projection tube is heated to 100 ° C. or higher, and it is required that the phosphor be hardly reduced in luminance even at a high temperature.

(3) It has a long life even when excited and emitted under high load conditions. Further, since such a large current is applied to the phosphor, the phosphor is required to be a phosphor having a stable crystal structure which is unlikely to be broken.

[0006] Rare earth phosphors whose phosphor matrix or activator is composed of a rare earth element are generally (1) to (4)
It is suitable for projection tubes because it has excellent characteristics of (3).
Was activated by Tb (terbium) as a green-emitting phosphor for a projection tube _{(Y 1-x Tb x)} 3 (Al 1-y Ga y) 5 O 12 phosphor (where, R represents a group consisting of Tb and Ce At least one kind selected, 1 × 10 ⁻³ ≦ x ≦ 2 × 10 ⁻¹ , 0 ≦
y ≦ 1) is used. This phosphor is a rare earth aluminate phosphor whose host crystal has a garnet structure and is relatively strong for use at high temperatures.

[0007]

The rare earth aluminate phosphor having a garnet structure described above is described in (1) to (4) above.
The present invention is one of the most practical phosphors as a green light emitting phosphor for a projection tube, which satisfies the characteristic of (3), but an object of the present invention is to provide a rare earth aluminate phosphor which can further improve these characteristics. It is in. That is, an object of the present invention is to provide a rare-earth aluminate phosphor having better luminance-current characteristics (γ characteristics), temperature characteristics, and life characteristics.

[0008]

Means for Solving the Problems The present inventor considered that the key to solving the above problems was to improve the crystal stability of the phosphor itself. In particular, paying attention to the particle properties of the rare earth oxide raw material, it is thought that this greatly affects the above-described luminescence performance of the final phosphor, and as a result of earnestly examining many rare earth oxide particles, as a phosphor raw material The present inventors have found that there are optimal particle shapes, particle diameters, and particle size distributions, and that the above-mentioned problems can be solved by combining the particles with an optimal firing temperature, and have completed the present invention.

That is, the method for producing a rare earth aluminate phosphor of the present invention is characterized by the following items (1) to (3).

(1) In a method for producing a rare-earth aluminate phosphor, a rare-earth oxide and alumina or a mixed material containing at least an aluminum compound which easily becomes alumina when heated at a high temperature is fired. And the particle shape is spherical and has a uniform particle size distribution, and the mixed raw material is 1350-1650 °
A method for producing a rare earth aluminate phosphor characterized by firing in the range of C.

D _l / D _s ≦ 1.5 1.0 ≦ D _a ≦ 6.0 1.0 ≦ D _m ≦ 12.0 1.0 ≦ D _m / D _a ≦ 2.0 0 ≦ σ _log ≦ 0.30 here, Dl is the major axis of the particle (μm), D _s is the short diameter (mu
m), D _a is the average particle diameter (μm), D _m is the median particle size (mu
m) and σ _log are indices indicating the spread of the particle size distribution.

(2) The rare earth oxide is composed of yttrium (Y), terbium (Tb), or cerium (C
e) At least one coprecipitated oxide selected from the group consisting of: e) a method for producing a rare earth aluminate phosphor according to item 1);

(3) The composition formula of the rare earth aluminate phosphor is represented by (Y _1-x R _x ) ₃ (Al _1-y G _ay ) ₅ O _12. 3. The method for producing a rare earth aluminate phosphor according to item 1. (Where R is at least one selected from the group consisting of Tb and Ce, and 1 × 10 ⁻³ ≦
x ≦ 2 × 10 ⁻¹ and 0 ≦ y ≦ 1)

BEST MODE FOR CARRYING OUT THE INVENTION The characteristics of the rare earth oxide particles used in the present invention are that the particle shape is spherical, the particle size is about 1.0 to 6.0 μm, and the particle size distribution is uniform. The feature is to have. Rare earth oxides having such particle characteristics can be obtained by the methods disclosed in JP-A-3-271117, JP-A-3-271118, and JP-A-8-59233.

For example, JP-A-8-59233 discloses that in the reaction of rare earth ions with oxalate ions, from the start of the reaction to filtration and washing with water, the temperature is kept at -5 ° C or more and 20 ° C or less and an organic base is used. Precipitate the rare earth oxalate in the co-presence of, and wash by filtration and place in a steam-saturated air stream at -5 ° C to 20 ° C, or vacuum at -20 ° C to 20 ° C A method is disclosed in which attached water is removed by drying or freeze-vacuum drying, followed by baking. In the present invention, the spherical rare earth oxide obtained by these methods can be used as it is, but is not limited to this method. Further, by classifying this oxide, rare earth oxide particles having a sharper particle size distribution can be obtained.

The rare earth oxide obtained by such a method is mixed in stoichiometric ratio with alumina or an aluminum compound which easily becomes alumina when heated at a high temperature. As such an aluminum compound, aluminum hydroxide,
Aluminum nitrate and the like. At the time of mixing the raw materials, if necessary, a halide of an alkali metal and / or an alkaline earth metal is blended as a flux and mixed well in a wet or dry manner, and at a high temperature of 1350 to 1650 ° C., an electric furnace,
The phosphor of the present invention can be obtained by baking for 2 to 10 hours, depending on the conditions such as the crucible or the amount of baking.

<Shape of Rare-Earth Oxide Particle> Since the shape of the oxide particle is spherical, the reaction with Al 2 O 3 (alumina) at the time of firing becomes uniform, so that the rare-earth aluminate phosphor is unlikely to grow abnormally. A homogeneous product can be fired regardless of the temperature. In addition, because of its spherical shape, the mixing with alumina or the aluminum compound Al2O3 which easily becomes alumina when heated at a high temperature is uniformly performed, and as a result, the composition variation of the fired product is reduced. It can be seen that the particles are spherical by observing the particles with a microscope. To evaluate the shape with an objective index, the major diameters of a plurality of typical particles in a micrograph of a rare earth oxide particle are shown.
and _l, by measuring the short diameter D _s, and calculate the value of D _l / D _s, D _l
The range that satisfies the relationship of / D _s ≦ 1.5 is the range of the spherical shape, and works well for the firing reaction.

FIG. 1 plots the relationship between D _l / D _s and the luminance-current characteristic (relative γ characteristic). Here, the relative γ characteristic is defined as follows. The measurement sample fluorescent screen mounted on Demantaburu device, a phosphor screen to determine the relative emission luminance L0.05 respect to the reference phosphor when scanned by an electron beam current density of 0.05 A / cm ^2, of 50 .mu.A / cm ² when measuring the relative emission brightness L ₅₀ with respect to the reference phosphor when scanning the phosphor screen with the electron beam current density, γ = L ₅₀ / L _0.05
× 100% is defined as a relative γ characteristic. From FIG. 1, D
It can be seen that the γ characteristic is improved as the value of _l / D _s approaches 1, that is, as it approaches a true sphere. When the value of D _l / D _s is 1.5 or less, the relative γ characteristic exceeds 1%, and the effect can be confirmed.

<Size of Rare Earth Oxide Particles> The particle size of the rare earth oxide depends on the target particle size of the phosphor. The size of the phosphor can be increased by increasing the particle size of the rare earth oxide. The particle size of the rare earth oxide is suitably in the range of the following formula.

1.0 ≦ D _a ≦ 6.0 1.0 ≦ D _m ≦ 12.0 where Da is Fisher Sub-S which is an air permeation method.
It is an average diameter measured using an item sizer, and Da is measured from the specific surface area of the oxide, corresponds to a particle diameter close to a size relationship seen in a micrograph, and can be said to be a basic particle diameter. On the other hand, Dm is a median particle size measured using ELZONE80xy which is a particle size distribution measuring device of an electric resistance method. This can be said to be a particle size that includes a knowledge of whether it is in a dispersed state or an aggregated state from the measurement principle.

[0020] <dispersibility of the rare earth oxide particles> Usually, D _m
Is larger than D _a, this indicates that the aggregation tendency. Therefore, the closer the value of D _m / D _a is to 1, the higher the dispersion state is. It is desirable that the rare earth oxide has high dispersibility in order to be ideally mixed with alumina or an aluminum compound which easily becomes alumina when heated at a high temperature. If agglomerated, the raw materials will not be uniformly mixed. Although the value of D _m / D _a affects the γ characteristics, it is particularly effective in improving the temperature characteristics.

FIG. 2 plots the relationship between D _m / D _a and temperature characteristics. Here, the temperature characteristic is a relative light emission luminance at a temperature of 110 ° C. with respect to the light emission luminance at room temperature, and the luminance is measured while heating the measurement cell. FIG. 2 shows this for each D _m
/ Were measured for the value of D _a. From FIG. 2, it can be seen that as the value of D _m / D _a approaches 1, that is, the better the dispersibility, the better the temperature characteristics. The value of D _m / D _a is in a range where the temperature characteristic is 88% or more, that is, 1.0 ≦ D _m / D _a
It is preferable that the range is ≦ 2.0.

<Particle Size Distribution of Rare Earth Oxide> One of the important requirements of rare earth oxide particles is that the particle size distribution is sharp. That is, it is important that the particles of the rare earth oxides are uniform. As a result, the raw materials are uniformly mixed, and the luminous performance of the fired rare earth aluminate can be improved. It can be expressed using σ _log as an index indicating that the particle size distribution is sharp. Here, σ _log is a value defined by the following equation.

[0023] _{σ log = [Σ {P i} (logD i -logD G) 2}] 1/2 _{where, logD G = ΣP i logD i} , where, D _i is class value, P _i is the relative frequency, log Is the natural logarithm with e as the base.

The actual value of σ _log is obtained by using an electric resistance type particle size distribution measuring device EL as a water suspension of a rare earth oxide.
The weight-based distribution of the rare earth oxide is measured using ZONE80xy, and the above formula is calculated and obtained by a computer.

The physical meaning of this value is the standard deviation of the logarithmic value of the measured particle size, and the smaller this value is, the sharper the particle size distribution is. In the present invention, the value of sigma _{lo g} of the rare earth oxide particles can be improved in all the light-emitting performance as described above, it is effective in particularly improved temperature characteristics.

FIG. 3 plots the relationship between σ _log and temperature characteristics. Gets closer to the value of D _m / D _a is 1, i.e. the particle size distribution is improved temperature characteristics as good dispersibility as sharp. The value of σ _log is preferably in a range where the temperature characteristic shows a value of 90% or more, that is, in a range of 0 ≦ σ _{l og} ≦ 0.3.

In the present invention, the rare earth aluminate phosphor is fired at a high temperature of 1350 to 1650 ° C. Therefore, an abnormal reaction is likely to occur unless the phosphor raw material mixture is highly uniformly mixed. In order to prevent this abnormal reaction, it is preferable that the rare-earth oxide is easily mixed more uniformly. As a result, a rare earth aluminate phosphor excellent in light emission performance can be obtained.

The life characteristics are defined as a luminance maintenance ratio (%) when a measurement sample is mounted on a demountable device and scanned with an electron beam having a voltage of 30 kV and a current density of 8.6 μA / cm ² for 250 hours.

The present invention relates to (Y _1-x R _x ) ₃ (Al _1-y G
a _y ) ₅ O ₁₂ , wherein R is at least one selected from the group consisting of Tb and Ce, and 1 × 10 ⁻³ ≦ x ≦ 2 ×
Among the aluminate phosphors having a garnet structure in which 10 ^-1 and 0 ≦ y ≦ 1, only those activated with Tb have been described. However, the same applies to the case where the phosphor having Ce as an activator improves the light emission performance. Can be.

[0030]

【Example】

 [Example 1] (Y_0.93Tb_0.07)_TwoO_ThreeThe composition of the next grain
D for 100 g of rare earth oxide having_l/ D_s= 1.1 D_a= 3.4 D_m= 5.7 D_m/ D_a= 1.68 σ_log= 0.244 Al2O3 86 g Ga2O3 106 g BaF2 18 g was thoroughly dry mixed. And put it in a crucible and put it in an oxidizing atmosphere for 15
It was baked at 00 ° C for 2 hours. Perform the resulting phosphor normally
Dispersion, washing, drying, sieving, (Y_0.93Tb _0.07)
_Three(Al_0.6Ga_0.4)_FiveO₁₂A phosphor was obtained. Current characteristics, temperature
Degree characteristics and life characteristics were measured, and the results are summarized in Table 1.

Example 2 A rare earth oxide having the following particle characteristics and having the composition of (Y _0.93 Tb _0.07 ) ₂ O ₃ was obtained as follows: D ₁ / D _s = 1.1 _Da = 2.3 D _m = A rare earth aluminate phosphor was obtained in the same manner as in Example 1, except that 4.2 D _m / D _a = 1.83 σ _log = 0.271. The current characteristics, temperature characteristics, and life characteristics were measured, and the results are summarized in Table 1.

Example 3 A rare earth oxide having the following particle characteristics and having the composition of (Y _0.93 Tb _0.07 ) ₂ O ₃ was obtained as follows: D ₁ / D _s = 1.1 _Da = 5.4 D _m = 8.4 D _m / D _a = 1.75 σ _log = 0.250 except that it was the same as in Example 1 (Y _0.93 Tb
_0.07 ) ₃ (Al _0.6 Ga _0.4 ) ₅ O ₁₂ phosphor was obtained. A phosphor was obtained. The current characteristics, temperature characteristics, and life characteristics were measured, and the results are summarized in Table 1.

[0033] [Example 4] (Y _0.93 Tb _0.07) in the composition of the ₂ O _3, relative to 100g of rare earth oxides with the following particle _{characteristics, D l / D s = 1.1} D a = 3.4 D _m = 5.7 D _m / D _a = 1.68 σ _log = 0.244 Al 2 O 3 ··· 86 g Ga 2 O 3 ··· 106 g YF 2 · 0.3 g AlF2 0.3 g was thoroughly dry-mixed and packed in a crucible.
It was baked at 00 ° C for 2 hours. The obtained phosphor is dispersed, washed with water, dried, and sieved in a usual manner to give (Y _0.93 T
b _{0.07) 3} (to obtain a Al _0.6 Ga _{0.4) 5} O ₁₂ phosphor. The current characteristics, temperature characteristics, and life characteristics were measured, and the results are summarized in Table 1.

[Comparative Example 1] A rare earth oxide having a composition of (Y _0.93 Tb _0.07 ) ₂ O ₃ and having the following particle characteristics was obtained as follows: D ₁ / D _s = 1.8 _Da = 3.4 D _m = 11.1 In the same manner as in Example 1 except that D _m / D _a = 3.26 σ _log = 0.386 (Y _0.93 Tb)
_0.07 ) ₃ (Al _0.6 Ga _0.4 ) ₅ O ₁₂ phosphor was obtained. A phosphor was obtained. The current characteristics, temperature characteristics, and life characteristics were measured, and the results are summarized in Table 1.

[0035]

[Table 1]

[0036]

According to the method for producing a phosphor of the present invention, the crystallinity of the phosphor is improved so that the γ characteristics are small even when a high current is applied and the luminance is reduced even at a high temperature. It is possible to obtain a rare-earth aluminate phosphor which has a good temperature characteristic and a long life even when excited and emitted under high addition conditions.

When this phosphor is used for a phosphor film on the inner surface of a projection tube or other phosphor films used at a high current density, a high-performance cathode ray tube can be provided.

In particular, when the rare earth oxide is a coprecipitated oxide of Y and Tb, a rare earth aluminate phosphor suitable for a projection tube can be obtained.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between a value of D _l / D _s and a relative γ characteristic.

FIG. 2 is a characteristic diagram showing a relationship between _a value of D _m / D _a and a temperature characteristic.

FIG. 3 is a characteristic diagram showing a relationship between a value of σ _log and a temperature characteristic.

Claims (3)

[Claims] 1. A method for producing a rare earth aluminate phosphor, comprising sintering a rare earth oxide and a mixed raw material containing at least alumina or an aluminum compound which easily becomes alumina when heated at a high temperature, wherein the rare earth oxide comprises:
A method for producing a rare earth aluminate phosphor, characterized in that the following conditions are satisfied, the particle shape is spherical, the particle size distribution is uniform, and the mixed raw material is fired at 1350 to 1650 ° C. D ₁ / D _s ≦ 1.5 1.0 ≦ D _a ≦ 6.0 1.0 ≦ D _m ≦ 12.0 1.0 ≦ D _m / D _a ≦ 2.0 0 ≦ σ _log ≦ 0.30 here, Dl the major axis of the particle (μm), D _s is the short diameter (mu
m), D _a is the average particle diameter (μm), D _m is the median particle size (mu
m) and σ _log are indices indicating the spread of the particle size distribution. 2. The rare earth oxide includes yttrium (Y), terbium (Tb), or cerium (C).
The method for producing a rare earth aluminate phosphor according to claim 1, wherein the oxide is at least one coprecipitated oxide selected from e). 3. The composition of the rare earth aluminate phosphor is represented by (Y _{1 -x} R _x ) ₃ (Al _{1 -y} G _ay ) ₅ O _12. Production method of rare earth aluminate phosphors. (Where R is at least one selected from the group consisting of Tb and Ce, and 1 × 10 ⁻³ ≦ x ≦
2 × 10 ⁻¹ , 0 ≦ y ≦ 1)