Patent Application
20060033418
1. Technical Field
The present invention relates to a green emitting yttrium silicate phosphor and a cathode-ray tube using it, more particularly to a green emitting yttrium silicate phosphor, which has an improved temperature characteristic and life, and a cathode-ray tube using it.
2. Description of Related Art
In these years, cathode-ray tubes, such as a color cathode-ray tube (CRT), a projection cathode-ray tube (PRT), a field emission display (FED), and a vacuum fluorescent display (VFD), are getting to display a higher resolution image in higher brightness for responding needs. Phosphors used in these cathode-ray tubes are required to be further improved. Particularly, since a projection cathode-ray tube projects and displays an enlarged image, a higher brightness is required compared with a direct-view tube, and a high voltage and a high current are applied thereto. Accordingly, phosphors, which have good characteristics, such as a high resistance against high load, a brightness saturation characteristic, a temperature characteristic and its life, are necessary. Among phosphors, since a green emitting phosphor highly contributes to white, requirements on it is also high, and various phosphors have been studied.
Hereafter, a projection cathode-ray tube is described as an example of a typical cathode-ray tube. A projection type television displays an enlarged image composed of red, green and blue light emitted from three small monochromatic cathode-ray tubes (projection cathode-ray tubes). Since the projection cathode-ray tube is used as the light source, a fluorescence surface is subjected to double digits the load as compared with a direct-view-type cathode-ray tube. For this reason, the following requirements exist on such a projection cathode-ray tube.
An yttrium silicate phosphor with the above characteristics is in actual use as a green emitting phosphor for projection cathode-ray tubes. However, as recently digital broadcasting becomes widespread, it is required to display a higher resolution image in higher brightness, and such a phosphor is subjected, to a higher load. Accordingly, further improvement of characteristics is necessary. Particularly, an yttrium silicate phosphor has a problem, of its temperature characteristic and life. High requirements for improvement of these characteristics exist.
Although Patent Document 1 and or the like discloses improvement of the temperature characteristic and life of the yttrium silicate phosphor for the projection cathode-ray tubes, since a phosphor is subjected to a higher load in recent years, further improvement is still necessary. Although Patent Documents 2 and 3 disclose that substituting Sc for a part of phosphor composition improves luminance, the disclosed compositions do not sufficiently improve their temperature and life characteristics. Accordingly, improvement is still necessary.
The present invention is aimed at solving the problems. It is an object of the present invention to provide a green emitting yttrium silicate phosphor, which has an improved temperature characteristic and its life, and a cathode-ray tube using it.
The inventors of the present invention have diligently studied to solve the above problems. As a result, they found that an yttrium silicate phosphor, which had particular composition, could solve the above problems, and finally developed the present invention.
A green emitting yttrium silicate phosphor according to the present invention comprises a composition having the general composition (Y, Sc, Tb)2SiO5, wherein the mole ratio of Sc to the entire rare-earth element in the phosphor is 0.045<Sc/(Y+Sc+Tb)<0.17. Adding the above concentration range of Sc improves a temperature characteristic and life. It is more preferable that the concentration range is 0.07<Sc/(Y+Sc+Tb)<0.13.
According to the green emitting yttrium silicate phosphor of another aspect of the present invention, the general formula is represented as follows.
(Y1-x-y, Scx, Tby)2SiO5
0.045<x<0.17
0.05≦y≦0.17
In this general formula, Tb as an activation agent relates to the color of luminescent radiation, and emits green luminescent radiation. The, value y is preferably in the range 0.05≦y≦0.17, and more preferably in the range 0.06≦y≦0.15. If the value y is less than 0.05, the luminance of the phosphor is low. On the other hand, if the value y is greater than 0.17, the luminance is low due to concentration quenching.
In addition, adding Sc improves a temperature characteristic and life as mentioned above. The value x as the amount of Sc is preferably in the range 0.045<x<0.17, and more preferably in the range 0.07<x<0.13. If the value x is less than 0.045, or is greater than 0.17, the effects both on the temperature characteristic and life are reduced.
According the green emitting yttrium silicate phosphor of another aspect of the present invention, the phosphor may contain 1000 ppm or less of Ge in the phosphor. In this case, a similar effect on the temperature characteristic and life is obtained.
A cathode-ray tube according to another aspect of the present invention comprises a phosphor film, and an exciting device which irradiates the phosphor film with an electron beam, wherein the phosphor film includes the above phosphor. For example, a projection type television displays an enlarged image composed of red, green and blue light emitted from three monochromatic cathode-ray tubes. When the phosphor according to the present invention is used alone, or when a green emitting phosphor mixture containing the phosphor according to the present invention is used, as a phosphor film applied on a face plate of a green cathode-ray tube in the cathode-ray tubes, it is possible to produce a green projection cathode-ray tube with an improved temperature characteristic and life.
The green emitting yttrium silicate phosphor, according to the present invention, comprising a composition having the general composition (Y, Sc, Tb)2SiO5 whose mole ratio of Sc to the entire rare-earth element in the phosphor is 0.045<Sc/(Y+Sc+Tb)<0.17 has an improved temperature characteristic and life. Particularly, it exhibits excellent characteristics as, a phosphor for a projection cathode-ray tube which is used under a high load condition. A projection cathode-ray tube employing the phosphor of the present invention can display an image in high quality.
The following description will describe the embodiments according to the present invention with reference to the drawings. It should be appreciated, however, that the embodiments described below are illustrations of a green emitting yttrium silicate phosphor and a cathode-ray tube using it, a green emitting yttrium silicate phosphor and a cathode-ray tube using it to give a concrete form to technical ideas of the invention, and a green emitting yttrium silicate phosphor and a cathode-ray tube using it of the invention are not specifically limited to description below.
Furthermore, it should be appreciated that the members shown in claims attached hereto are not specifically limited to members in the embodiments. Unless otherwise specified, any dimensions, materials, shapes and relative arrangements of the parts described in the embodiments are given as an example and not as a limitation. Additionally, the sizes and the arrangement relationships of the members in each of drawings are occasionally shown larger exaggeratingly for ease of explanation. Members same as or similar to those of this invention are attached with the same designation and the same reference numerals and their description is omitted. In addition, a plurality of structural elements of the present invention may be configured as a single part which serves the purpose of a plurality of elements, on the other hand, a single structural element may be configured as a plurality of parts which serve the purpose of a single element.
A method for producing of an yttrium silicate phosphor according to the embodiments of the present invention is now described. First, an yttrium compound, a scandium compound, a terbium compound, and a silicon compound are measured, respectively, so that the amount of Y, the amount of Sc, the amount of Tb, and the amount of Si in a material mixture satisfy the general formula (Y1-x-y, Scx, Tby)2SiO5 (0.045<x<0.17, and 0.05≦y≦0.17). Subsequently, they are mixed, or mixed additionally with a flux such as ammonium fluoride. After this material mixture is filled in a crucible, it is placed in a furnace and burned at the temperature 1100 to 1650° C. in a reducing atmosphere. After the burned material is cooled, and dispersed by a wet process, it is separated and dried. Finally, the yttrium silicate phosphor according to, the embodiments of the present invention is obtained.
An oxide or a compound, which becomes into an oxide by thermal decomposition, is preferably used as a phosphor material. For example, an oxide, a carbonate, a hydroxide, and so on, are preferably used as the yttrium compound, the scandium compound, and a terbium compound. A coprecipitated material, which contains all of, or some of Y, Sc, and Tb, or an oxide, which is obtained by calcination of such a material, can be used. Compounds, such as a silicon dioxide are preferably used as a silicon compound. In addition, in order to substitute a part of silicon in the phosphor with germanium that is congener to silicon, optionally, a germanium compound is used together with a silicon compound for mixture. In this case, a similar effect on the temperature characteristic and life is obtained. A typical process such as mixture atmosphere nitrogen and hydrogen is used as the reducing atmosphere, for example.
Luminance is measured by irradiating a phosphor with an electron beam at an acceleration voltage of 10 kV and a current density of 0.5 μA/cm2. It is generally said that, when a projection cathode-ray tube is turned on continuously, the phosphor temperature of a lighting portion thereof reaches 150° C. When a projection cathode-ray tube is actually used, parts corresponding to high temperature rise and parts corresponding to low temperature rise coexist in the phosphor of the lighting portion, due to switching images. In this case, when the difference of the luminance values due to the difference of temperatures is large, a user notices it as luminance unevenness. This greatly reduces image quality. It is generally said that humans can notice the difference of the luminance values between two parts adjacent to each other with their naked eyes when the difference is 2% or more. Accordingly, it is preferable that the temperature characteristic is 98% or more.
In the yttrium silicate phosphor according to the embodiments of the present invention, the phosphor exhibits a very excellent temperature characteristic in the range where the amount of Sc (value x) is 0.045<x<0.7, especially 0.07<x<0.13. In addition, the phosphor also exhibits an excellent life characteristic in this range. According to the present invention, a long-life phosphor with less aging in luminance and less luminance reduction even in high temperature can be obtained, thus, it is very useful as a phosphor for projection cathode-ray tubes.
As mentioned above, a phosphor with high luminance, and excellent temperature and life characteristics can be obtained in the range where the amount of Sc (value x) is 0.045<x<0.17, and the amount of Tb (value y) is 0.05≦y≦0.17.
First, a coprecipitated rare earth oxide and a silicon dioxide were measured as raw materials so that their moles are equal as follows.
(Y0.887,S0.048,Tb0.085)2O3 . . . 100 g
SiO2 . . . 26.1 g
These were mixed by a ball mill in a ceramic pot. The mixed materials were filled in an alumina crucible, and were burned at 1580° C. for 4 hours in nitrogen atmosphere containing 3% by volume of hydrogen gas. After the burned materials were dispersed by a wet process, they were separated and dried. Finally, the yttrium silicate phosphor having the general formula (Y0.887, Scx0.048, Tb0.065)2SiO5 according to the embodiment of the present invention was obtained.
Yttrium silicate phosphors having the general formulas shown in Table 1 according to the embodiments of the present invention were obtained by a process similar to the example 1 except using coprecipitated rare earth oxides shown in the Table 1 as raw materials.
First, a coprecipitated rare earth oxide and a silicon dioxide are measured as raw materials so that their moles are equal as follows.
(Y0.934,Tb0.066)2O3 . . . 100 g
SiO2 . . . 25.6 g
These are mixed by a ball mill in a magnetic pot. The mixed materials are filled in an alumina crucible, and are burned at 1580° C. for 4 hours in nitrogen atmosphere containing 3% by volume of hydrogen gas. After the burned materials are dispersed by a wet process, they are separated and dried. Finally, the yttrium silicate phosphor having the general formula (Y0.934, Tb0.085)2SiO5 is obtained.
Yttrium silicate phosphors having the general formulas shown in Table 1 are obtained by a process similar to the comparative example 1 except using coprecipitated rare earth oxides shown in the Table 1 as raw materials.
Table 2 shows the results of the temperature and life characteristics of the yttrium silicate phosphors obtained by the examples 1 to 6 and the comparative examples 1 to 6 that are measured by the aforementioned method. This table shows that the phosphors according to the examples 1 to e of the present invention had good temperature and life characteristics as compared with the phosphors of the comparative examples 1 to 6. Accordingly, it is found that the phosphors according to the examples of the present invention had excellent characteristics as a phosphor for the projection cathode-ray tubes especially under high load conditions.
A phosphor film composed of the phosphor of the example 1 was formed on the interior surface of a face plate of a glass bulb of 18 cm (7 inches) so as to have 3.5 mg/cm2 by sedimentation method. An aluminum deposited film was formed thereon. The bulb was provided with an electromagnetic focusing electron gun, and was vacuum-sealed. Thus, a projection cathode-ray tube was produced.
As mentioned above, a green emitting yttrium silicate phosphor according to the embodiments of the present invention comprises a composition having the general composition (Y, Sc, Tb)2SiO5 whose mole ratio of Sc to the entire rare-earth element in the phosphor is 0.045<S(Y+Sc+Tb)<0.17, and thus has good temperature and life characteristics. A cathode-ray tube using the phosphor according to the embodiment of the present invention can display an image in high quality.
This application is based on application No. 2003-382765 filed in Japan on Nov. 12, 2003, the content of which is incorporated hereinto by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 382765/2003 | Nov 2003 | JP | national |
