JPS6219794B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode ray tube for color television, and more particularly to a cathode ray tube for color television that is characterized by being equipped with a green-emitting fluorescent film that emits light with high brightness and exhibits no current saturation characteristics. It is something.

The green-emitting phosphor films used in cathode ray tubes for color television are ZnS/Cu, Al ZnCdS/Cu, Al
Alternatively, ZnS-based phosphors such as ZnS/Au, Cu, and Al are generally used. Green-emitting phosphors based on these ZnS-based compounds have high efficiency among electron beam-excited green-emitting phosphors and have the advantage of providing a bright screen, but they also have the disadvantage of exhibiting current saturation characteristics. It is combined. When a phosphor is excited by an electron beam at a high current density, it is prevented from increasing the brightness corresponding to the increase in current density from a low current density. Therefore, when using a ZnS-based phosphor, if the current density of the electron beam reaches a certain value, even if it is excited with an electron beam exceeding this value, a green screen with higher brightness cannot be obtained. Other two-color fluorescent films of cathode ray tubes for color television, such as Y ₂ O ₂ S/
Neither the red-emitting fluorescent film made of Eu nor the blue-emitting fluorescent film made of ZnS/Ag exhibits the current saturation phenomenon exhibited by the green-emitting fluorescent film.
Therefore, in a cathode ray tube equipped with a phosphor film using each of these color-emitting phosphors, when the electron beam has a high current density, the balance of the emission intensity of each color for color reproduction is disturbed. For example, in the case of a white screen that requires excitation by a high current density electron beam, the green light-emitting phosphor film does not increase the brightness, so the white screen brightness is reduced by lowering the balance with the brightness exhibited by each of the other two color light-emitting phosphor films. Don't make it what you want. Furthermore, when trying to obtain a white screen with a desired color temperature, the red component has a stronger emission intensity ratio than the green component, so the red component wins and a white screen with a lower color temperature is obtained.

Among these green-emitting phosphors, ZnCdS/Cu, Al has the highest luminous efficiency, but from a pollution standpoint, the use of ZnS/Cu, Al or ZnS/Au, Cu,
There is a tendency to switch to Al. In this case, the low luminance of both phosphors is also a problem, as is the current saturation characteristic.

The present invention eliminates these drawbacks and provides a cathode ray tube for color television equipped with an improved green-emitting phosphor film. In this cathode ray tube, the red-emitting phosphor layer and the blue-emitting phosphor layer may be formed from conventionally used phosphors, such as Y ₂ O ₂ S/Eu and ZnS/Ag phosphors. First, the green-emitting phosphor film is made of at least one of ZnS-based phosphors such as ZnS/Cu, Al, ZnCdS/Cu, Al, or ZnS/Au, Cu, and Al, and is attached to the face plate side. The first layer phosphor film placed on the Gd ₂ OSXTb
Gd ₂ O ₂ S/Tb in which the ratio of Tb to the phosphor is 0.004 mol% or more and less than 0.8 mol%, or the ratio of Tb to the Y ₂ O ₂ S/Tb phosphor is 0.005 mol% or more and less than 1 mol% Y ₂ O ₂ S/Tb is defined as a composite layer consisting essentially of at least one type of each Tb-activated phosphor and a second layer phosphor layer laminated on the first layer phosphor layer. Incidentally, if the Tb content in Y ₂ O ₂ S/Tb is less than 0.005 mol % or less than 0.004 mol % in Gd ₂ O ₂ S/Tb, the emission intensity will be weak, which is not preferable. Furthermore, in the above paragraph, it is specified that the second layer phosphor film is formed of a phosphor whose weight is equal to or less than the same weight as the phosphor forming the first layer phosphor film.

In the cathode ray tube of the present invention, the green-emitting fluorescent film forming the composite layer does not exhibit current saturation phenomenon, and the brightness increases to match the increased current density by electron beam irradiation with high current density. I can do it. Also, which phosphor is used for the second layer phosphor film?
The amount of Tb activation is set to a small amount, making the product price low.

Now, in Figure 1, ZnS/Cu, Al, ZnCdS/Cu, Al
Or, for ZnS/Au, Cu, and Al green-emitting phosphors, the excitation spectra are 11, 12, or 13 in order, and the emission spectra are 14, 15, or 16 in order.
Shown by each curve. However, the vertical axis represents relative energy as an arbitrary value, and the horizontal axis represents wavelength in nm. When the ZnS phosphor matrix is 100% by weight, each phosphor is activated in the following order: 0.015% by weight Cu, 0.02% by weight Al activated example, 0.004% by weight.
Weight % Cu, 0.01 weight % Al activation example or 0.01 weight %
This is an example of activation of Cu, 0.05% by weight Au, and 0.02% by weight Al. What is known from Figure 1 is that each green-emitting phosphor is not only capable of emitting electron beams, but also emitting light from approximately 300nm to approximately 450nm.
It absorbs ultraviolet light and blue light of m and emits green light of about 530 nm to about 540 nm at its emission peak. On the other hand, Gd ₂ O ₂ S/Tb and Y ₂ OS/Tb phosphors emit not only green light but also ultraviolet light and
It has the property of emitting blue light. In the composite layer defined in the green-emitting phosphor film in this invention, the layer made of the green-emitting phosphor having the ZnS-based compound as a matrix is the first layer on the face plate side, and the layer made of the Tb-activated phosphor is the second layer. It is laminated on top of the first layer. Therefore, ultraviolet light from the electron beam of the second layer phosphor,
The first layer phosphor is excited by blue light emission, which is combined with electron beam excitation, so that the brightness characteristics, particularly the current saturation characteristics, of the first layer phosphor film are eliminated by the second layer phosphor characteristics.

Improvement of the green-emitting phosphor film characteristics of a phosphor based on a ZnS-based compound using Gd ₂ O ₂ S/Tb or Y ₂ O ₂ S/Tb has been described, for example, in Utility Model Application Publication No. 49-80657 and JP-A No. It has already been stated in the publications of No. 130966/1983. However, in both cases, the phosphor film is formed by a simple mixture of a Tb-activated phosphor with a high activation amount and a ZnS-based compound host phosphor, which is completely different from the present invention.

The amount of Tb activator in the phosphor related to the second layer changes the emission color of each. As the amount of activator decreases, the direction shifts from green light emission to blue light emission. Therefore, the phosphor used in the second layer is Gd ₂ O ₂ S/
When Tb, the Tb ratio should be 0.8 mol% or less, or
Y ₂ O ₂ S/Tb is defined as 1 mol% or less,
This second layer fluorescent film is a blue-green light emitting film. When the amount of Tb activation is reduced to this extent, there is an added advantage of increasing the luminous efficiency during electron beam excitation. Blue emission, which has a lower Tb activation amount, is more dependent on the amount of Tb activator than green emission, which has a higher Tb activation amount. For example, when the amount of Tb activator is increased and used as a green-emitting phosphor, blue light becomes very weak compared to green light, whereas when the amount of Tb activator is decreased and used as a blue-green-emitting phosphor, the blue light becomes green. Blue light becomes noticeably stronger. As a result, when the amount of activator is reduced, the overall light emission due to electron beam excitation is strengthened. Since Tb activator is expensive, reducing the amount to 1/2 to 1/3 of the amount used to emit green light is an advantage in terms of lowering the price of the composite layer. be. The amount of Tb used is expressed as Gd ₂ O ₂ S or Y ₂ O ₂ S as a weight% of each parent body.
Both amounts to only a few percent by weight when converted to
This is because the former costs about 10 times as much, and the latter costs about 20 times as much.

_{The Y 2 O 2 S /} Tb phosphor used in the second layer phosphor film with a Tb activation amount of 0.04 mol % relative to Y ₂ O 2 S emits whitish blue-green light, and does not react well with electron beams. The emission spectrum upon excitation is shown in Figure 2. However, the vertical axis represents relative energy, and the horizontal axis represents wavelength. The luminescence of the Y ₂ O ₂ S/Tb phosphor in this example is approximately
Around 380nm, around 420nm and 440nm in the blue region
The spectrum consists of several lines with emission peaks near 540 nm and near 540 nm in the green region. FIG. 3 is a cross-sectional view of a green-emitting fluorescent film, that is, a composite layer, used in an embodiment of a color television cathode ray tube, in which the first layer phosphor film 18 on the face plate 17 consists of substantially 0.05% by weight of Au and 0.01% by weight. of
ZnS/Au activated with Cu, 0.015 wt% Al,
A ZnS-based phosphor of Cu and Al is deposited, and this Y ₂ O ₂ S/Tb activated phosphor is further laminated to form a second layer phosphor film 19 . An aluminum film 20 is deposited on the surface of the composite layer. The first layer phosphor film has a thickness of 2 to 3 particles of phosphor having an average particle size of 7 μm, and the second layer phosphor film has a thickness of 1 to 2 particles of phosphor having an average particle size of 5 μm. If this is converted into weight per unit area, ZnS/Au of the first layer fluorescent film,
Cu and Al are 3 mg/cm ² Y ₂ O ₂ S/Tb of the second light film is 0.9
mg/ ^cm2 . When an electron beam is irradiated from the back side of the composite layer, it first hits the second layer phosphor film, and most of the energy is consumed in excitation emission of Y ₂ O ₂ S/Tb, and the remaining energy is emitted from the first layer phosphor film. ZnS/Au, Cu,
This will cause Al to emit light. The green light emitted from the second layer phosphor film is directly extracted to the front of the screen through the first layer phosphor film, and the blue light and ultraviolet light are
As expected from the excitation spectrum curve 13 in Figure 1 and the emission spectrum in Figure 2, once ZnS/Au
After being absorbed by Cu and Al, it is converted into green light emitted by this phosphor and emitted from the front of the screen.

The current saturation characteristics of this composite layer green-emitting fluorescent film are:
25KV electron beam, current density per unit 0.1μ
When excited by varying A/cm ² to 3 μA/cm ² , the current saturation curve 21 shown in FIG. 4 is obtained. In the figure, the vertical axis represents the relative value of brightness per unit area measured by a photocell receiver, the horizontal axis represents the current density, and the curve 22 represents ZnS/Au, Cu, Al
This is a comparative example curve measured on a single-layer phosphor film made only of ZnS-based phosphors. The composite layer green-emitting phosphor film exhibits about 85% brightness at a low current density of 0.2 μA/cm ² and is darker than the single-layer phosphor film of the comparative example. but
It is bright, showing 115% brightness at a high current density of 3 μA/cm ² or higher, reversing from 0.8 μA/cm ² o'clock. It is certain that blue light and ultraviolet light are not recognized in the spectral distribution of the output light that appears in front of the screen due to this composite layer fluorescent film, and that most of the light is converted into green light.

The amount of Y ₂ O ₂ S/Tb used in the composite layer is
When the amount of Cu and Al is 50% by weight, the green emission relative brightness is the highest, and when the amount is equal to or less than the same weight%, a combined effect is exhibited. FIG. 5 shows the relationship between relative brightness and Y ₂ O ₂ S/Tb composite ratio. In Figure 5, the vertical axis is 25KV, 2μ
The relative brightness of the composite layer phosphor film measured by the photocell receiver when excited by a high current density electron beam of A/ ^cm2 , the horizontal axis is
When ZnS/Au, Cu, Al is 100 parts by weight
Represents parts by weight of Y ₂ O ₂ S/Tb composite.

As described above, according to the present invention, the current saturation phenomenon of the entire fluorescent film is improved, and the luminance of the fluorescent film is improved at high current densities, and the image quality of the fluorescent film is further improved at low current densities. Since the linearity of the luminance of the phosphor film with respect to current density is improved, a black screen becomes vivid black at low current densities, improving the overall contrast. This effect is due to the fact that the ZnS-based green-emitting phosphor is ZnS/Cu, and the Al is
Even if ZnCdS/Cu or Al is substituted, or the Tb-activated phosphor is substituted with Gd ₂ O ₂ S/Tb at a specified activation amount, the same behavior will occur. However, it is necessary to form a ZnS-based green light-emitting phosphor in the first layer on the face plate side, and a Tb-activated phosphor such as Y ₂ O ₂ S/Tb or Gd ₂ O ₂ S/Tb in the second layer. . When this arrangement is reversed, most of the blue light emitted from the Tb-activated phosphor is emitted in front of the screen, destroying the purity of the green light emission. With two layers, the ZnS-based phosphor is placed in a state where current saturation is likely to occur, negating the improvement effect.

The green-emitting fluorescent film used in other examples will be described below.

Example 1 A phosphor slurry containing PVA, surfactant, water, etc. is applied in a conventional manner to form a phosphor screen of a color cathode ray tube equipped with a phosphor film that emits light in three colors of red, blue, and green. . At that time, when obtaining a green-emitting fluorescent film, a ZnS/Cu, Al fluorescent film with an average particle size of 7μ activated with 0.05% by weight Cu and 0.015% by weight Al was converted into a weight per unit area of 2.5mg/ First apply it to a size of cm ² . Then the ZnS/Cu,
Y ₂ O ₂ S/Tb phosphor with an average particle size of 0.5μ activated with 0.5 mol% Tb was placed on the Al phosphor film so that the weight per unit area was 1.3 mg/cm ² to form a composite layer. Curve 23 in FIG. 6 shows the current saturation characteristics when only the green-emitting phosphor film of the phosphor screen thus obtained is excited and emitted by a 25 KV electron beam. In the figure, the vertical axis represents the relative luminance of the green-emitting fluorescent film, and the horizontal axis represents the current density. Further, curve 24 represents the characteristics of the conventional ZnS/Cu, Al single film. As can be seen from the figure, the composite layer used in this invention has improved current saturation characteristics compared to conventionally used fluorescent films, and the luminance of the fluorescent film is particularly low when excited with an electron beam of 3 μA/cm ² at high current density. It was 111% of the previous level. Furthermore, when the entire screen was illuminated, a high-quality screen with vivid white and black colors could be obtained.

Example 2 A phosphor slurry containing PVA, a surfactant, water, etc. is applied in a conventional manner to form a color cathode ray tube phosphor screen having a phosphor film that emits light in three colors: red, blue, and green. At this time, when obtaining a green-emitting fluorescent film, 0.04% by weight, 0.01% by weight of Cu, 0.03% by weight of Al
First, a ZnS/Au, Cu, Al fluorescent film with an average particle size of 7 μm activated with ZnS/Au, Cu, and Al fluorescent film is coated so that the weight per unit area is 2.5 mg/cm ² . Then the ZnS/Au,
On top of the Cu, Al fluorescent film, Gd ₂ O ₂ S/Tb activated with 0.3 mol % Tb and having an average particle size of 4.5 μ is coated at a concentration of 2.1 mg/cm ² to form a composite layer. Curve 25 in FIG. 7 shows the current saturation characteristics when only the green-emitting phosphor film of the phosphor screen thus obtained is excited and emitted by a 25 KV electron beam. In the figure, the vertical axis represents the relative luminance of the green-emitting fluorescent film, and the horizontal axis represents the current density. Further, curve 26 shows the characteristics of the conventional ZnS/Au, Cu, Al-only fluorescent film. As can be seen from the figure, the composite layer used in this invention has improved current saturation characteristics compared to conventionally used fluorescent films, especially at high current densities.
The luminance of the fluorescent film is 114% when excited with an electron beam of A/cm ²
It was hot. Furthermore, when the entire screen was illuminated, a high-quality screen with vivid white and black colors could be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the excitation spectrum and emission spectrum of various ZnS-based green-emitting phosphors, Figure 2 is a diagram showing the electron beam excitation emission spectrum of the Y ₂ O ₂ S/Tb phosphor used in this invention, Figure 3 is a schematic diagram showing the composite layer used in this invention, Figure 4 is a diagram showing current saturation curves of green-emitting fluorescent films used in the past and in this invention, and Figure 5 is a diagram showing the laminated composite layer used in this invention. 6 _and 7 are diagrams showing the current saturation curves of _the conventional green-emitting phosphor film and the present invention, respectively. 11...Excitation spectrum of ZnS/Cu, Al phosphor, 12...Excitation spectrum of ZnCdS/Cu, Al phosphor, 13...Excitation spectrum of ZnS/Au, Cu, Al phosphor, 14...ZnS/Cu , emission spectrum of Al phosphor, 15...ZnCdS/Cu, emission spectrum of Al phosphor, 16...ZnS/Au, Cu,
Emission spectrum of Al phosphor, 17...Face plate, 18...ZnS/Au, Cu, Al phosphor film, 19...Y ₂ O ₂ S/Tb phosphor film, 20... Aluminum film, 22, 24 , 26...ZnS/Au, Cu,
Current saturation curve of Al phosphor single film, 21, 23,
25...Current saturation curves of ZnS/Au, Cu, Al and Y ₂ O ₂ S/Tb phosphor composite layers used in this invention.

Claims (1)

[Scope of Claims] 1. A cathode ray tube for color television comprising a red-emitting phosphor film, a green-emitting phosphor film, and a blue-emitting phosphor film deposited on the inner surface of the face plate in a regular distribution, wherein the green-emitting phosphor film However, ZnS/Cu,
Al, ZnCdS/Cu, Al or ZnS/Au, Cu, Al
A _first layer phosphor film substantially made of at least one type of ZnS- _based phosphor and disposed on the face plate side;
The ratio of Tb is 0.004 mol% or more and less than 0.8 mol%
For Gd ₂ O ₂ S/Tb or Y ₂ O ₂ S/Tb phosphors
The Tb ratio is 0.005 mol% or more and less than 1 mol%
Y ₂ O ₂ S/Tb A composite layer consisting essentially of at least one type of Tb-activated phosphor and a second phosphor layer laminated on the first phosphor layer. A cathode ray tube for color television characterized by: 2. Claim 1, characterized in that the second layer phosphor film is formed of a phosphor that is equal to or more than 0.1% by weight of the phosphor forming the first layer phosphor and equal to or less than the same weight of the phosphor. The cathode ray tube for color television according to item 1.