Claims
- 1. A cathode ray tube having a face plate glass which contains neodymium oxide (Nd.sub.2 O.sub.3) and exhibits a sharp main absorption band having a peak at about 580 nm and a sub-absorption at about 530 nm and on the inner surface of which a phosphor screen having blue, green and red phosphors is formed, wherein said blue phosphor is a phosphor of zinc sulfide activated with Ag(ZnS:Ag), said red phosphor is a phosphor of yttrium oxysulfide activated with Eu(Y.sub.2 O.sub.2 S:Eu), and said green phosphor is a phosphor of zinc sulfide activated with copper and aluminum (ZnS:Cu, Al) to reduce the spectral reflectance of said phosphor screen at the wavelength band of 470-480 nm so that the chromaticity point of a reflected exterior light reflected from said phosphor screen is prevented from displacement with respect to the chromaticity point of an exterior light due to the influence of said main and sub-absorption bands.
- 2. The cathode ray tube according to claim 1, wherein a content of copper (Cu) as an activator is 3.times.10.sup.-4 g, or more to 1 g. of zinc-sulfide (ZnS) as the main component.
- 3. The cathode ray tube according to claim 1, wherein each of said blue and red phosphors is a phosphor with a colorant.
- 4. A cathode ray tube having a face plate glass which contains neodymium oxide (Nd.sub.2 O.sub.3) and exhibits a sharp main absorption band having a peak at about 580 nm and a sub-absorption band at about 530 nm and on the inner surface of which a phosphor screen having blue, green and red phosphors is formed, wherein said blue phosphor is a phosphor of zinc sulfide activated with Ag(ZnS:Ag), said red phosphor is a phosphor of yttrium oxysulfide activated with Eu(Y.sub.2 O.sub.2 S:Eu) and said green phosphor is a phosphor of zinc sulfide activated with copper, gold and aluminum (ZnS:Cu, Au, Al) to reduce the spectral reflectance of said phosphor screen at the wavelength band of 470-480 nm so that the chromaticity point of a reflected exterior light reflected from said phosphor screen is prevented from displacement with respect to the chromaticity point of an exterior light due to the influence of said main and sub-absorption bands.
- 5. The cathode ray tube according to claim 4, wherein a content of gold (Au) as an activator is 4.times.10.sup..times.4 g. or more to 1 g. of zinc-sulfide (ZnS) as the main component.
- 6. The cathode ray tube according to claim 4, wherein each of said blue and red phosphors is a phosphor with a colorant.
Priority Claims (2)
| Number |
Date |
Country |
Kind |
| 56-21151 |
Feb 1981 |
JPX |
|
| 56-21170 |
Feb 1981 |
JPX |
|
SUMMARY OF THE INVENTION
This application is a continuation of application Ser. No. 338,993, filed Jan. 12, 1982 now abandoned.
1. Field of the Invention
The present invention relates to a color cathode ray tube having a phosphor screen.
2. Description of the Prior Art
It has been proposed to reduce a transmittance of a face plate glass on a phosphor screen as an effective manner for improving image contrast of a phosphor screen of a cathode ray tube.
Referring to FIG. 1, the principle will be illustrated in detail.
FIG. 1 is a sectional model of the phosphor screen of the color cathode ray tube wherein the reference numeral (1) designates a face plate glass on an inner surface of which three color phosphors (2) of red (R), green (G) and blue (B) are formed.
The following equations are give:
A contrast C is defined by the equation: ##EQU1## Thus, the following equation is given by substituting (I) and (II) in (III): ##EQU2##
In precise calculation, it is necessary to apply factors caused by effects of reflection of exterior light on the surface of the face plate glass, multiple reflections in the face plate glass (1) and halation caused by scattered electrons. Thus, the effects are neglected because the effects are negligible.
In order to improve the contrast of images of the cathode ray tube, the light transmittance (T.sub.f) of the face plate glass (1) must be reduced as clearly considered by the equation (IV).
The glass used as the face plate glass (1) of the cathode ray tube has been classified into a clear glass having a transmittance of 75% or more; a grey glass having a transmittance of 60-75% and a tint glass having a transmittance of 60% or less.
FIG. 2 show typical spectral transmittance curves of (a) a clear glass, (b) a grey glass and (c) a tint glass and also emission spectra of the three color phosphors of red (R), green (G), blue (B).
On the other hand, as it is clearly found from FIG. 2 and the equation (II), the output of light emitted from the phosphor screen as brightness of the phosphor screen decreases depending upon a decrease of the transmittance (T.sub.f) of the face plate glass (1). This is opposite to the contrast. In view of the transmittance (T.sub.f) of the face plate glass (1), both of the contrast characteristic of images and the brightness characteristic are not easily improved. The kind of the face plate glass (1) has been selected depending upon the weight of the contrast or the brightness characterstic.
It has been defined to give selective photo-absorption for the face plate glass (1) in the region of small light emission energy as the wavelength region in roots of the emission spectra of the three color phosphors on the phosphor screen instead of the face plate glass having flat transmittance in visible wavelength region as shown in FIG. 2 in order to overcome the difficulty for improving both the brightness and the contrast and to improve both the brightness characteristic and the contrast characteristic.
FIG. 3 shows a spectral transmittance curve of the face plate glass (1) proposed for the aforementioned purposes.
The face plate glass is formed by incorporating neodymium oxide (Nd.sub.2 O.sub.3) (at 1.0 wt. %) in a glass formulation similar to those of the conventional clear glass (hereinafter referring to as Nd-containing glass). The Nd-containing glass has main sharp absorption peak in 560-615 nm and sub-absorption peaks in 490-540 nm, which is resulted by the specific characteristics of Nd.sub.2 O.sub.3. The absorption peaks are quite sharp and accordingly, even though light transmittances in the other wavelength except the absorption peaks are remarkably high as those of the conventional clear glass an average light transmittance in the all visible wavelength region is similar to those of the grey glass thereby contributing to the improvement of the contrast.
FIG. 4 shows spectral transmittance curve (d) of the Nd-containing glass and emission spectra of the three color phosphors of red (R), green (G), blue (B) of the color cathode ray tube.
When the Nd-containing glass is used for the face plate glass, the brightness characteristic of the phosphor screen and the contrast characteristic are remarkably improved. However, the body color of the phosphor screen is quite different from those of the conventional color cathode ray tubes to cause uneasy feeling for a spectator in appearance.
Referring to FIG. 5, the body color of the phosphor screen will be illustrated in detail. In FIG. 5, the points A, B, C are typical chromaticity points of white exterior light plotted on a CIE chromaticity diagram in the case of watching a TV set at home. The A point is the chromaticity point of the A standard light source which is similar to the chromaticity point of light of an incandescent lamp used at home. The B point is one example of chromaticity points of light of white flurescent lamp used at home. The C point is a chromaticity point of the C standard light source as an average daylight.
When the spectral reflectance of the phosphors (2) of the phosphor screen is substantially flat in the visible wavelength region and the spectral transmittance of the face plate glass (1) is substnatially flat in the visible wavelength region as that of the clear glass, the chromaticity point of the reflected exterior light reflected from the phosphor screen, that is the body color of the phosphor screen is similar to the chromaticity point of the exterior lighter.
On the other hand, when the Nd-containing glass is used for the face plate glass on the phosphor screen, the spectral transmittance of the face plate glass is not flat in the visible wavelength region but has complicated cuves. Thus, the chromaticity point of the reflected exterior light reflected from the phosphor screen, that is, the body color of the phosphor screen is different from the chromaticity point of the white exterior light.
The case of the illuminant A (A point shown in FIG. 5) will be illustrated. In the case of the exterior light from the illuminant A, the exterior light incident to the phosphor screen is reflected by the phosphors (2) in substantially flat form in the visible wavelength, however, the component of wavelength of the reflected exterior light is different from that of the incident exterior light because of the sharp absorption at 580 nm and sub-absorption in the sub-absorption band at 530 nm of the Nd-containing glass. The effect is shown in the CIE chromaticity diagram to find the following fact. The main absorption band at 580 nm results in a reduction of the component of the wavelength at the band of the exterior light whereby the chromaticity point is affected to depart from the single color chromaticity point (Q) at 580 nm on the line (.beta.) connecting the single color chromaticity point (Q) at 580 nm and the chromaticity point (A) of the A light source. (This is shown by the vector a.sub.2.)
The sub-absorption band at 530 nm results in a reduction of the component of the wavelength at the band of the exterior light whereby the chromaticity point of the reflected exterior light is affected to depart from the single color chromaticity point (R) at 530 nm on the line (.alpha.) connecting the single color chromaticity point (R) at 530 nm and the chromaticity point (A) of the illuminant A. (This is shown by the vector a.sub.1.) Therefore, the chromaticity point of the reflected exterior light, that is, the body color of the phosphor screen is shifted to the vector a.sub.3 as a combination of the vectors a.sub.1 and a.sub.2. The absorption in the main absorption band is remarkably greater than that of the subabsorption band. Thus, the absolute value of the vector a.sub.2 is remarkably greater than the absolute value of the vector a.sub.1.
In the cases of the white fluorescent lamp (B point) and the illuminant C (C point), the chromaticity point of the reflected exterior light, that is, the body color of the phosphor screen is respectively shifted in the direction of the vector b.sub.3 or the vector c.sub.3. In these cases, the absolute value of the vector b.sub.2 or the vector c.sub.2 is respectively greater than that of the vector b.sub.1 or the vector c.sub.1 because of the great difference of the absorptions in the main absorption band and the sub-absorption band. As described, when the Nd-containing glass is used as a face plate glass, the body color of the phosphor screen is different from the chromaticity of the white exterior light to be unstable. This is not preferable in view of the apperance of the phosphor screen.
It is an object of the present invention to overcome a disadvantage of unstable body color of a phosphor screen which causes by using a Nd-containing glass as a face plate glass of a color cathode ray tube.
It is another object of the present invention to provide a color cathode ray tube having stable body color of a phosphor screen in the use of a face plate glass made of a Nd-containing glass.
The foregoing and other objects of the present invention have been attained by providing a cathode ray tube which comprises a face plate glass containing neodymium oxide (Nd.sub.2 O.sub.3); and a phosphor screen of plural color phosphors formed on an inner surface of said face plate glass wherein a phosphor of zinc sulfide activated with copper and aluminum (ZnS:Cu, Al) is used as a green phosphor of said phospor screen.
US Referenced Citations (3)
| Number |
Name |
Date |
Kind |
| 3143683 |
Duncan et al. |
Aug 1964 |
|
| 4038205 |
Minnier et al. |
Jul 1977 |
|
| 4309481 |
Wakatsuki et al. |
Jan 1982 |
|
Foreign Referenced Citations (3)
| Number |
Date |
Country |
| 2804155 |
Mar 1978 |
DEX |
| 3010386 |
Sep 1980 |
DEX |
| 2807085 |
Mar 1986 |
DEX |
Continuations (1)
|
Number |
Date |
Country |
| Parent |
338993 |
Jan 1982 |
|
Patent Grant
4728856
