JPH09316444A - Production of yttrium silicate fluorescent substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process for a fluorescent substance of yttrium silicate which has good γ-characteristics, temperature characteristics and a long life. SOLUTION: This yttrium silicate fluorescent substance is produced by firing a mixed raw material comprising a rare earth element oxide and silicon dioxide. The rare earth element oxide is a powder of spherical particles with a uniform particle size distribution, satisfies the following conditions, and prepared by firing a raw material mixture without flux at 1,450-1,650 deg.C: D1 /Ds <=1.5, 2.0<=Da <=6.0, 2.7<=Dm <=11.0, 1.0<=Dm /Da <=2.0, 0<=σlog <=0.30; where D1 is the longer axis (μm), Ds is the shorter axis (μm), Da is an average particle size (μm), Dm is a median particle size (μm) and σlog is an index showing an expansion of 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 yttrium silicate phosphor, and in particular, it is used as a green light emitting phosphor for a projection tube and has good γ characteristics and temperature characteristics,
The present invention also relates to a method for producing a yttrium silicate phosphor having a long life.

[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 1000 times higher than 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).
A yttrium silicate phosphor whose composition formula is Y ₂ SiO ₅ : Tb, which is a silicate-based phosphor that is activated by terbium as a green light-emitting phosphor for a projection tube and is relatively strong when used at high temperatures, is used. .

[0007]

The Y ₂ SiO ₅ : Tb phosphor satisfies the above-mentioned characteristics (1) to (3) and is one of the most practical phosphors currently available as a green phosphor for projection tubes. However, an object of the present invention is to provide an yttrium silicate phosphor that can further improve these characteristics. That is, it is an object of the present invention to provide an yttrium silicate phosphor having even 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 yttrium silicate phosphor of the present invention is the method for producing an yttrium silicate phosphor in which a mixed raw material comprising a rare earth oxide and silicon dioxide is fired, wherein the rare earth oxide satisfies the following conditions. The particle shape is spherical and has a uniform particle size distribution, and the mixed raw material is fired in the range of 1400 ° C. to 1650 ° C. without adding a flux. D _l / D _s ≦ 1.5 2.0 ≦ D _a ≦ 6.0 2.0 ≦ D _m ≦ 12.0 1.0 ≦ D _m / D _a ≦ 2.0 0 ≦ σ _log ≦ 0.30 Here, D ₁ is the major axis (μm) of the particle, and Ds is the minor axis (μm).
m), Da is the average particle size (μm), and Dm is the median particle size (μm).
m) and σ _log are indices indicating the spread of the particle size distribution.

Particularly, when the rare earth oxide is yttrium (Y) and at least one coprecipitated oxide selected from terbium (Tb) or Ce (cerium), yttrium silicate (Y) activated by Tb is used. ₂ SiO ₅ :
Tb phosphor) and Ce-activated yttrium silicate phosphor (Y ₂ SiO ₅ : Ce phosphor).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The characteristics of the rare earth oxide particles used in the present invention are that the particles are spherical, the size of the particles is about 2.0 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, in Japanese Unexamined Patent Publication (Kokai) No. 8-59233, in the reaction of a rare earth ion and an oxalate ion, the temperature is kept at -5 ° C. or higher and 20 ° C. or lower and the coexistence of an organic base is maintained from the start of the reaction to the filtration and washing with water. By precipitating the rare earth oxalate below, washing by filtration and washing, and placing it in an air flow of -5 ° C or higher and 20 ° C or lower that is not saturated with water vapor, or by vacuum drying at -20 ° C or higher and 20 ° C or lower, or freeze-vacuum drying. A method of firing after removing the attached water is disclosed. 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 with silica in a stoichiometric ratio, and without using a flux (fluxing agent), at a high temperature of 1400 ° C. to 1650 ° C., an electric furnace, a crucible, or firing. The phosphor of the present invention can be obtained by firing for 2 to 10 hours, depending on conditions such as the amount.

<Shape of particles> Since the shape of the particles is spherical, the reaction with SiO ₂ (silica) at the time of firing becomes uniform, and abnormal growth of the yttrium silicate phosphor hardly occurs. Homogeneous products can be fired without the use of flux. Further, since it is spherical, the dry mixing with SiO ₂ is uniformly performed, and as a result, the variation in the composition of the fired product is reduced. It can be seen from a microscope that the particles are spherical, but in order to evaluate the shape by an objective index, the major axis D ₁ and the minor axis of a plurality of typical rare earth oxide particle micrographs are used. D _s is measured, the value of D ₁ / D _s is calculated, and the range satisfying the relationship of D ₁ / D _s ≦ 1.5 is the spherical range, which favorably affects the firing reaction.

FIG. 1 plots the relationship between D ₁ / 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 ₁ / D _s is 1.5 or less, the relative γ characteristic exceeds 101%, and the effect can be confirmed.

<Particle Size> 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. 2.0 ≦ D _a ≦ 6.0 2.0 ≦ D _m ≦ 12.0 where Da is an air permeation method Fisher Sub-S
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.

<Dispersibility of Particles> Normally, D _m is larger than D _a, which means that the particles tend to aggregate.
Therefore, the closer the value of D _m / D _a is to 1, the higher the dispersion state is. Since the rare earth oxide is ideally mixed with SiO ₂ , it is desirable that it has high dispersibility. If agglomerated, uniform mixing with SiO ₂ is not performed. 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. Figure 2 shows this as D _m /
It was measured with respect to the value of D _a . From FIG. 2, the value of D _m / D _a is 1
It can be seen that the temperature characteristics are improved as the value approaches, that is, the better the dispersibility is. The value of D _m / D _a is in the range where the temperature characteristic is 95% or more, that is, 1.0 ≦ D _m / D _a ≦
It is preferably in the range of 2.0.

<Particle size distribution> One of the important requirements for 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, uniform mixing with SiO ₂ is achieved, and the light emission performance of the yttrium silicate to be baked 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.

Σ _log = [Σ {P _i (logD _i −logD _G ) ² }] ^1/2 where logD _G = ΣP _i logD _i , where D _i is a class value, P _i is a relative frequency, log Is the natural logarithm with base e.

The actual value of σ _log is EL, which is an electric resistance type particle size distribution measuring device, in which a rare earth oxide is used as a water suspension.
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 values of the measured particle size, and the smaller this is, the sharper the particle size distribution is. In the present invention, σ of rare earth oxide particles
_Although the value of _log can be improved in all of the above-mentioned light emission performance, it is particularly effective in improving 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 yttrium silicate phosphor is fired at a high temperature of 1400 ° C to 1650 ° C. Moreover, no flux is used during firing. If the phosphor uses a large amount of flux,
Although the reaction takes place relatively homogeneously and can be fired at a lower temperature, the flux is not used in this phosphor because the residual flux component deteriorates the luminous performance of the phosphor. 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 important that the rare earth oxide is easily mixed more uniformly. As a result, an yttrium silicate phosphor having excellent light emitting performance can be obtained.

The life characteristics are defined as the luminance retention rate (%) when a measurement sample is mounted on a demantable apparatus and an electron beam having a voltage of 30 kv and a current density of 8.6 μA / cm ² is scanned for 250 hours.

The present invention is effective when the phosphor has a matrix composition of yttrium silicate. For example, not only the Y ₂ SiO ₅ : Tb phosphor whose activator is Tb but also the activator is Ce. It is possible to improve the light emission performance of a certain Y ₂ SiO ₅ : Ce phosphor. The same applies to activators other than Tb and Ce.

[0027]

【Example】

[Example 1] With _respect to 100 g of a rare earth oxide having the composition of (Y _1.84 Tb _0.14 ) ₂ O ₃ and having the following particle characteristics, D ₁ / D _s = 1.1 _Da = 3.4 D _m = 5.7 D _m / D _a = 1.68 σ _log = 0.244 SiO2 (silica) (D _a = 0.5, D _m = 0.8)
7 g was mixed by a ball mill, packed in a crucible, and baked in a reducing atmosphere at 1580 ° C. for 4 hours. The obtained phosphor is usually dispersed, washed with water, dried, and passed through a sieve to obtain Y _1.84 T.
b _0.14 SiO ₅ phosphor was obtained. The current characteristics, temperature characteristics, and life characteristics were measured, and the results are summarized in Table 1.

Example 2 A rare earth oxide having a composition of (Y _1.84 Tb _0.14 ) ₂ O ₃ and having the following particle characteristics was used: D ₁ / D _s = 1.1 _Da = 2.3 D _m = An yttrium silicate 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 composition of (Y _1.84 Tb _0.14 ) ₂ O ₃ and having the following particle characteristics was used: D _l / D _s = 1.1 _Da = 5.4 D _m = An yttrium silicate phosphor was obtained in the same manner as in Example 1 except that 8.4 D _m / D _a = 1.75 σ _log = 0.250. 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 _1.84 Tb _0.14 ) ₂ O ₃ and having the following particle characteristics was used: D ₁ / D _s = 1.8 _Da = 3.4 D _m = An yttrium silicate phosphor was obtained in the same manner as in Example 1 except that 11.1 D _m / D _a = 3.26 σ _log = 0.386. The current characteristics, temperature characteristics, and life characteristics were measured, and the results are summarized in Table 1.

[0031]

[Table 1]

[0032]

According to the method for producing a phosphor of the present invention, by improving the crystallinity of the crystal of the phosphor, the brightness is low even when a high current is applied, the γ characteristic is good, and the brightness is reduced even at high temperatures. The yttrium silicate phosphor has good temperature characteristics, has a good temperature characteristic, and has a long life even when excited and emitted under high load conditions.

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

Particularly, when the rare earth oxide is a coprecipitated oxide of Y and Tb, Y ₂ SiO ₅ : Tb suitable for a projection tube is used.
A phosphor can be obtained.

[Brief description of 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 (2)

[Claims] 1. A method for producing a yttrium silicate phosphor, which comprises firing a mixed raw material comprising a rare earth oxide and silicon dioxide, wherein the rare earth oxide satisfies the following conditions and has a spherical particle shape and a uniform particle size distribution. And a method for producing an yttrium silicate phosphor, which comprises firing the mixed raw material in the range of 1400 ° C. to 1650 ° C. without adding a flux. D _l / D _s ≦ 1.5 2.0 ≦ D _a ≦ 6.0 2.0 ≦ D _m ≦ 12.0 1.0 ≦ D _m / D _a ≦ 2.0 0 ≦ σ _log ≦ 0.30 Here, Dl is the major axis (μm) of the particle, and D _s is the minor axis (μm).
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 yttrium (Y) and at least one coprecipitated oxide selected from terbium (Tb) and Ce (cerium). 1. A method for producing a yttrium silicate phosphor.