JPH0114960B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field of the Invention) The present invention relates to a method for producing a rare earth oxysulfide phosphor, and particularly to an improvement in the method for producing a rare earth oxysulfide phosphor suitable for a fluorescent surface with a high current density. (Technical Background of the Invention and Problems Thereof) In recent years, in addition to conventional direct-view color televisions, projection-type color televisions capable of producing large-sized images have become increasingly popular. This video device is blue,
The images of three high-intensity cathode capillary tubes that emit green, red, and three primary colors are enlarged and combined using an optical lens and projected onto a large screen to reproduce a color image. In this projection video device, in order to maximize the brightness on the screen, the fluorescent surface of the cathode ray tube is stimulated by an electron beam with a current density more than 10 times higher than that of a normal direct-view color cathode ray tube. be done. As a result, the temperature of the fluorescent surface rises to over 60°C during normal operation. In general, the brightness of a fluorescent surface often decreases as the temperature rises, so different considerations are required for the fluorescent surface of a projection type cathode ray tube than for a direct view type cathode ray tube. A known method for lowering the temperature of the fluorescent surface is, for example, to create a structure in which a layer of water can be retained on the outside of the fluorescent surface of the tube to reduce the temperature rise. Another known method is to use a fan to blow air onto the outside of the fluorescent surface. However, these methods have drawbacks such as complicating the structure of the cathode ray tube and increasing manufacturing costs, so it is desirable to use a phosphor that is as efficient as possible in the operating state. That is, the phosphor used in projection cathode ray tubes must have good temperature characteristics and low volatility saturation at high current and excitation densities. As for the red phosphor in projection cathode ray tubes, the europium-activated yttrium oxysulfide (Y ₂ O ₂ S: Eu) phosphor, which is often used in direct-view cathode ray tubes, suffers from a significant drop in luminous efficiency due to temperature rise, so the temperature characteristics An excellent europium-activated yttrium oxide (Y ₂ O ₃ :Eu) phosphor is used. Silver-activated zinc sulfide (ZnS:
Ag) Fluorescent material is used. In green phosphor,
Zinc sulfide _- based phosphors _, which are often used in direct-view cathode ray tubes, have significant brightness current saturation characteristics. ₂ O ₂ S:Tb) phosphor, Y ₂ O ₂ S:Tb phosphor, etc. are used. However, the Zn ₂ SiO ₄ :Mn phosphor has a low energy efficiency of about 7% when stimulated with an electron beam, and high electron energy stimulation tends to cause deterioration of the phosphor surface, so-called discoloration. In addition, the method for producing the above-mentioned Gd ₂ O ₂ S:Tb, Y ₂ O ₂ S: Tb phosphor is described in Japanese Patent Publication No. 47-9562, for example, in which a red phosphor similar to the above-mentioned phosphor (Y, La, Gd , Ln) _{2O2S :}
A method for producing Eu is described. The terbium-activated rare earth oxysulfide phosphor obtained by this method has an energy efficiency of 10% or more, but has the drawback of poor temperature characteristics. (Object of the Invention) An object of the present invention is to provide a method for producing a rare earth oxysulfide phosphor that improves the brightness characteristics with respect to temperature of the phosphor. (Summary of the Invention) In order to achieve the above object, the inventors have conducted various studies regarding the manufacturing method of a rare earth oxysulfide phosphor. First, as a general method, a mixture of starting materials and flux is calcined, cooled, calcined,
I tried cooling and firing repeatedly. As a result, the temperature characteristics of brightness were only slightly improved. Next, when repeating firing, cooling, firing, and cooling, I tried adding sulfur and a flux before firing, but even with this method, the properties were only slightly improved, and the crystal grain size was rather abnormal. This resulted in the drawback that the grain size became difficult to control. This phenomenon was considered to be due to the increased amount of flux in the fired product in the case of oxysulfide phosphors. Therefore, under the above experimental conditions, the inventors added a step of adding and mixing a flux before firing, as well as a step of rinsing with water after firing to wash away the unnecessary flux, and found that the temperature characteristics of brightness were significantly improved. They discovered this and completed the present invention. That is, the present invention provides a method for producing a rare earth oxysulfide phosphor represented by the general formula Re ₂ O ₂ S:Re',
A step of adding and mixing a fluxing agent to a raw material mixture of starting materials Re ₂ O ₃ and Re′ ₂ O ₃ and firing the mixture at a predetermined temperature, a step of washing the fired product with water to wash away the fluxing agent residue, and the washing with water This method of manufacturing a phosphor is characterized by comprising the steps of drying the fired product, adding and mixing a flux again, and firing at a predetermined temperature. If Re is at least one of Y and Gd, Re′ is
Tb or Tb, Dy or Eu. The method for manufacturing the phosphor of the present invention is as follows. First, the phosphor raw materials are at least one of yttrium oxide (Y ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), lanthanum oxide (La ₂ O ₃ ), terbium oxide (Tb ₄ O ₇ ), or terbium oxide and oxidized Disprosium (Dy ₂ O ₃ ) Sulfur (S) Sodium carbonate (Na ₂ CO ₃ ) Potassium phosphate (K ₃ PO ₄ ), Sodium phosphate (Na ₃ PO ₄ ), Lithium phosphate (Li ₃ PO ₄ ) Mix at least one of the ingredients thoroughly, fill an alumina crucible, and perform primary firing in a high-temperature electric furnace in a neutral or weakly reducible atmosphere. The firing temperature is preferably in the range of 1000°C to 1300°C. The firing time varies depending on the filling amount of raw materials, firing temperature, etc., but 3 to 6 hours is appropriate. After primary firing under the above firing conditions,
The fired product is washed to remove denatured fluxing agent residue. Furthermore, the above-mentioned substances are mixed and secondary firing is performed under substantially the same conditions as the above-mentioned primary firing. The fired product is subjected to various operations generally employed in the production of phosphors, such as washing, drying, and sieving, to obtain the phosphor of the present invention. The phosphor produced in this way has superior crystallinity and granularity compared to the phosphor produced by the conventional method (primary firing only), and has excellent temperature characteristics, i.e., fluorescein resistance due to temperature rise. Decrease in brightness of the light body is significantly improved. Curve a in FIG. 1 is Y ₂ O ₂ S of the production method of the present invention:
This figure shows the relationship between the brightness and temperature of a projection cathode ray tube manufactured using a Tb phosphor. The temperature was controlled by heating from the outside of the tube using an infrared lamp. As Comparative Example 1, curve b shows the characteristics of a conventionally produced phosphor that has undergone only the first firing. From Figure 1, the brightness of the conventional phosphor at 60° is 20.
℃, it is about 85% in the manufacturing method of the present invention, and the temperature characteristics are extremely improved. Although it is possible to further advance the production method of the present invention and increase the number of firings, the two-time firing of the present invention is sufficient in terms of crystallinity, granularity, and temperature characteristics. (Examples of the Invention) Next, the present invention will be explained with reference to Examples. Example 1 Yttrium oxide (Y ₂ O ₃ ) 95g Terbium oxide (Tb ₄ O ₇ ) 5g Sulfur (S) 30g Sodium carbonate (Na ₂ CO ₃ ) 30g Potassium phosphate (K ₃ PO ₄ ) 8g
Mix thoroughly. The obtained mixture was filled into an alumina crucible, placed in a high-temperature electric furnace, and primarily fired at a temperature of 1100° C. for 4 hours in an N ₂ atmosphere. After firing,
Wash the fired product 5 times with deionized water and
Wash with _HNO3 , then with deionized water and dry. After drying, add 30 g of S, 30 g of Na ₂ CO ₃ to the powder obtained,
Add 8g of K ₃ PO ₄ and mix well. The obtained mixture was filled into an alumina crucible, placed in a high-temperature electric furnace, and subjected to secondary firing at a temperature of 1100° C. for 3 hours in an N ₂ atmosphere. After firing, the fired product is washed 5 times with deionized water and 3 times with 1N HNO ₃ . A Y ₂ O ₂ S:Tb _0.03 phosphor can then be obtained by washing with deionized water, drying and sieving. The phosphors thus obtained had superior properties as shown in the table compared to the phosphors obtained by the conventional methods (Comparative Example 1) (Comparative Example 2) described below. Ta. Comparative Example 1 Yttrium oxide (Y ₂ O ₃ ) 95 g Terbium oxide (Tb ₄ O ₇ ) 5 g Sulfur (S) 30 g Sodium carbonate (Na ₂ CO ₃ ) 30 g Potassium phosphate (K ₃ PO ₄ ) 8 g
Mix thoroughly. The resulting mixture is filled into an alumina crucible, placed in a high-temperature electric furnace, and fired at a temperature of 1100° C. for 8 hours in an N ₂ atmosphere. After firing, the fired product is washed five times with deionized water and then with 1N HNO ₃ . Then, after washing with deionized water, drying and sieving, a Y ₂ O ₂ S:Tb _0.03 phosphor is obtained. The properties of this phosphor are shown in the table. Comparative Example 2 Yttrium oxide (Y ₂ O ₃ ) 95 g Terbium oxide (Tb ₄ O ₇ ) 5 g Sulfur (S) 30 g Sodium carbonate (Na ₂ CO ₃ ) 30 g Potassium phosphate (K ₃ PO ₄ ) 8 g
Mix thoroughly. The resulting mixture was filled into an alumina crucible and heated in a high-temperature electric furnace in an _N2 atmosphere.
Bake at a temperature of 1100℃ for 3 hours. After firing, grind thoroughly in a mortar and add 30 g of sulfur (S), 30 g of sodium carbonate (Na ₂ CO ₃ ), 8 g of potassium phosphate (K ₃ PO ₄ ).
g was mixed, filled into an alumina crucible, and secondarily fired at a temperature of 1100° C. for 3 hours in an N ₂ atmosphere. Thereafter, the same treatment as in Example 1 is carried out to obtain a Y ₂ O ₂ S:Tb _0.03 phosphor. The characteristics of this phosphor are listed below. The table shows the characteristic results of the phosphors of Example 1, Comparative Example 1, and Comparative Example 2.

[Table] As is clear from this table, the phosphor produced by the method of the present invention in Example 1 has a sharper particle size distribution and better dispersibility than the phosphor produced by the conventional method in Comparative Example 1. (The smaller the median value/average particle size, the greater the dispersibility), and it can be seen that the brightness temperature characteristics are also improved. In addition, a new flux was added without removing the modified flux remaining in the first firing, and the second firing was performed. There is no significant improvement in distribution dispersion, and there is no significant difference in brightness or temperature characteristics. Example 2 Gadolinium oxide (Gd ₂ C ₃ ) 97.13g Terbium oxide (Tb ₄ O ₇ ) 2.87g Soda carbonate (Na ₂ CO ₃ )
Mix 15g S15g potassium phosphate 5g thoroughly. Fill the resulting mixture into an aluminium crucible,
The product is placed in a high-temperature electric furnace and fired for 4 hours at a temperature of 1100°C in an _N2 atmosphere. After firing, the fired product is washed five times with deionized water, washed with 1N HNO ₃ , and then washed with deionized water and dried. After drying, 15 g of S, 15 g of Na ₂ CO ₃ and 5 g of K ₃ PO ₄ were added to the powder obtained and mixed thoroughly. The resulting mixture was filled into an alumina crucible and placed in a high-temperature electric furnace for 1100 min in an _N2 atmosphere.
Secondary firing is carried out at a temperature of ℃ for 3 hours. After firing, the fired product is washed five times with deionized water and three times with 1N hydrochloric acid. The Gd ₂ O ₂ S:Tb phosphor can then be obtained by washing with deionized water, drying and sieving. Compared to the phosphor obtained by the conventional method, the phosphor obtained in this way has a luminance of 106 by cathode ray excitation at 20°C, and a luminance maintenance rate of 80% at 60°C, compared to the phosphor obtained by the conventional method. This was higher than the 63% (60°C) method. Example 3 Yttrium oxide (Y ₂ O ₃ ) 100g Terbium oxide (Tb ₄ O ₇ ) 4.21g Disprosium oxide (Dy ₂ O ₃ ) 1.05g Soda carbonate 30g Sulfur (S) 30g
9 g of potassium phosphate (K ₃ PO ₄ ) are thoroughly mixed. The obtained mixture was filled into an alumina crucible, placed in a high-temperature electric furnace, and primarily fired at a temperature of 1100° C. for 4 hours in an N ₂ atmosphere. After firing, the fired product is washed five times with deionized water, washed with 1N HNO ₃ , and then washed with deionized water and dried. After drying, 30 g of S, 30 g of Na ₂ CO ₃ and 9 g of K ₃ PO ₄ were added to the powder obtained and thoroughly mixed. The resulting mixture was filled into an alumina crucible and placed in a high-temperature electric furnace for 1100 min in an _N2 atmosphere.
Secondary firing is carried out at a temperature of ℃ for 3 hours. After firing, the fired product is washed 5 times with deionized water and 3 times with 1N HNO ₃ . The Y ₂ O ₂ S:Tb, Dy ₃ phosphor can then be obtained by washing with deionized water, drying and sieving. The luminance of the phosphor obtained in this way due to cathode ray excitation at 20°C is lower than that of the phosphor obtained by the conventional method (Comparative Example 1).
107, and the brightness maintenance rate at 60°C was 87%, which was higher than the conventional method, which was 67%. Example 4 100 g of yttrium oxide (Y ₂ O ₃ ), 59 g of europium oxide, 30 g of soda carbonate, 30 g of sulfur (S), and 9 g of potassium phosphate (K ₃ PO ₄ ) are thoroughly mixed. The resulting mixture was filled into an alumina crucible and fired in a high-temperature electric furnace at a temperature of 1100°C for 4 hours. After firing, the fired product is washed five times with deionized water, washed with 1N nitric acid, and then washed with deionized water and dried.
After drying, add 30 g of S, 30 g of Na ₂ CO ₃ to the powder obtained,
Add 9g of K ₃ PO ₄ and mix well. The resulting mixture was filled into an alumina crucible and heated in a high-temperature electric furnace.
Secondary firing is performed at a temperature of 1100°C for 3 hours. After firing, the fired product was washed 5 times with deionized water, and then washed with 1N nitric acid for 3 times.
Wash twice. Then, after washing with deionized water, a dry sieving process is performed to obtain the Y ₂ O ₂ S:Eu phosphor of the present invention. The phosphor obtained in this way is superior to the conventional phosphor made using almost the same method as Comparative Example 1.
The brightness due to cathode ray excitation at 20°C is 105 and 60
The brightness maintenance rate at ℃ was 83%, which was higher than that of the conventional method, which was 65%. (Effects of the Invention) As explained above, according to the method for producing a phosphor of the present invention, a rare earth oxysulfide phosphor with improved brightness characteristics against high temperatures and further improved dispersibility can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the brightness temperature characteristics of a cathode ray tube using a Y ₂ O ₂ S:Tb phosphor. The curve a shows the characteristics of the phosphor produced by the manufacturing method of the present invention, and the broken line b shows the characteristics of the phosphor produced by the conventional method.

Claims (1)

[Claims] 1. In a method for producing a rare earth oxysulfide phosphor represented by the general formula Re ₂ O ₂ S: Re', a fluxing agent is added to a raw material mixture of starting materials Re ₂ O ₃ and Re' ₂ O ₃ . a step of adding and mixing and firing at a predetermined temperature; a step of washing the fired product with water to wash away flux residue;
A method for producing a phosphor, comprising the steps of drying the water-washed fired product, adding and mixing a flux again, and firing at a predetermined temperature. If Re is at least one of Y and Gd, Re′ is
Tb or Tb, Dy or Eu.