JP3189626B2 - Display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having two kinds of phosphors in a light emitting portion.

[0002]

2. Description of the Related Art In a fluorescent display tube or a fluorescent display device using a field emission element as an electron source, for example, a phosphor of ZnS type, CaS type or the like is used for displaying a plurality of kinds of emission colors. It may be used for the light emitting part of the anode.

For example, as a red-emitting phosphor, (Z
_nx , Cd1 _-x ) S: Ag, Cl (x = 0.22), Z
nS: Cu, Al, Y ₂ O ₂ S: Eu and the like are known, and ZnS: Zn is known as a blue light emitting phosphor, and ZnS: Zn is used as a green light emitting phosphor.
Cu, Al, (Zn _x , Cd _1-x ) S: Ag, Cl (x
= 0.6) is known.

The sulfide phosphor is gradually decomposed from the surface by receiving electron bombardment in the fluorescent display tube. The decomposed phosphor scatters around and adheres to the surface of a filament-shaped cathode or a field emission element, which is an electron emission portion, and reduces the electron emission ability.

In order to avoid such a problem, a means has been proposed in which an ultraviolet light emitting phosphor such as BaSi ₂ O ₅ : Pb is laminated on the phosphor layer to protect the lower phosphor. . In such a fluorescent display tube having a phosphor of a two-layer structure, electrons impinge on the upper BaSi ₂ O ₅ : Pb phosphor, and the lower sulfide phosphor on which the electrons do not directly strike decompose and scatter. I will not do it. BaSi struck by electrons
_{The 2} O ₅ : Pb phosphor emits ultraviolet rays, and the ultraviolet rays excite the lower sulfide phosphor to emit light.

[0006]

In a conventional fluorescent display tube or the like, the electron acceleration voltage is generally 1 kV or less. In order to make the phosphor emit light with practical luminance under this driving condition, the resistance of the phosphor layer is reduced. It needs to be low to some extent. According to the above-described conventional phosphor having a two-layer structure, BaSi ₂ O ₅ : Pb
The resistance of the phosphor was high and sufficient luminance could not be obtained with an acceleration voltage of 1 kV or less.

[0007] The sulfide phosphor is BaSi ₂ O ₅ :
BaS, protected by Pb phosphor, but directly hit by electrons
There was a problem that the life of the i ₂ O ₅ : Pb phosphor was short.

The present invention relates to a phosphor comprising a sulfide phosphor, such as the above-mentioned conventional phosphor having a two-layer structure, and another phosphor, which is irradiated with electrons accelerated at a low voltage of, for example, 1 kV or less. It also aims to emit light with sufficient luminance and prolong the life.

[0009]

According to a first aspect of the present invention, there is provided a display device comprising: a sulfide phosphor layer attached to a light-transmitting electrode on an anode substrate; and a surface of the sulfide phosphor layer. A display device having a layer of an electron beam-excited ultraviolet light-emitting phosphor that is applied so as to cover and emits ultraviolet light by excitation with an electron beam of 1 kV or less,
ZnO having an emission peak only at 385 nm;
Zn having emission peaks at two points of 5 nm and 505 nm
O, and the intensity ratio between the ultraviolet component having a peak at 385 nm and the visible component having a peak at 505 nm is selected in the range of 100/0 to 10/90.

According to a second aspect of the present invention, in the display device of the first aspect, the ZnO having an emission peak only at 385 nm is Zn produced by a reduction treatment.
It is characterized by being obtained by firing an O phosphor in an O ₂ atmosphere.

[0011]

[0012]

[0013]

[0028]

The electrons emitted from the electron source strike the phosphor excited by the electron beam. The electron beam excited ultraviolet light emitting phosphor generates ultraviolet light having a wavelength shorter than 400 nm. The sulfide phosphor beneath the electron beam excited ultraviolet light emitting phosphor emits light when excited by the ultraviolet light generated by the electron beam excited ultraviolet light emitting phosphor. Sulfide phosphors are not easily decomposed and scattered because electrons do not strike directly.

[0029]

EXAMPLES The present inventors conducted experiments using various phosphors to achieve the above object. As a result, it has been recognized that if the sulfide phosphor is covered with the ZnO phosphor having low resistance, the sulfide phosphor can emit light with sufficient luminance even by the electron bombardment accelerated at a low voltage of 1 kV or less.

The inventors of the present invention have proposed a low-resistance phosphor Z
As a result of further research on the phosphor coated with the sulfide phosphor with the nO phosphor, the following facts have been found. That is, the emission spectrum of the normal ZnO phosphor is 40
Since it is in the range of 0 nm to 700 nm, a sulfide phosphor having an excitation peak in this wavelength region, for example, ZnCd
When the phosphor that emits yellow to red light, such as the S: Ag phosphor, is combined with the ZnO phosphor, good results can be obtained as described above.

However, ZnS: Ag and ZnS: C
With respect to a blue light emitting sulfide phosphor having an excitation peak in a wavelength region shorter than 400 nm, such as u or Al, the sulfide phosphor emits light even when the ZnO phosphor is laminated thereon. I can't let that happen. This is because almost no light having a wavelength shorter than 400 nm is emitted from the ZnO phosphor onto which electrons have hit, so that the lower-layer sulfide phosphor cannot be excited to emit light.

Therefore, the present inventors set the sulfide phosphor to Z
In the study of phosphors coated with nO phosphors, various attempts were made on the production method of ZnO phosphors, focusing on the emission spectrum of the phosphors, with the aim of obtaining not only yellow and red emission but also blue emission. Found the following facts. That is, a normal ZnO phosphor has an emission peak near 505 nm, but some ZnO phosphors include:
Depending on the specific production method, a compound having an emission peak at around 385 nm can be obtained.

FIG. 1 shows the Z obtained by the method of the embodiment.
an emission spectrum of the nO phosphor, a ZnS: Ag phosphor,
It shows each excitation (absorption) spectrum of ZnS: Cu, Al phosphor and Zn, CdS: Ag phosphor. Thus, the ZnO phosphor is 400 nm together with the visible wavelength light.
If ultraviolet light having a shorter wavelength is generated, ZnCdS: A
g red phosphor and ZnS: Ag phosphor.
Blue and green light emission by ZnS: Cu, Al phosphor and the like is also possible.

According to the findings of the present inventors, the peak at 385 nm in the emission spectrum of the ZnO phosphor is caused by interband emission. The ZnO phosphor having such a light emission peak is obtained by firing a normal ZnO phosphor produced by a reduction treatment in an O ₂ atmosphere. The ZnO phosphor having a peak of 385 nm obtained in this way has a slightly higher matrix resistance than the conventional ZnO phosphor, but has almost no practical problem as a phosphor used for the display section of a fluorescent display tube.

Next, Zn applied to the display device of the present embodiment will be described.
A phosphor layer having a two-layer structure in which a sulfide phosphor is coated with an O phosphor and a manufacturing method thereof will be described. The Zn powder is fired in an atmosphere containing oxygen (for example, in the air) to obtain ZnO. This phosphor was annealed to prepare a sample having an emission peak only at 385 nm and a sample having emission peaks at two points of 385 nm and 505 nm. In addition,
This annealing reduces the resistance value of the phosphor itself.

The annealing of ZnO may be performed using a normal furnace or lamp annealing. In the case of lamp annealing, current flows along the surface of the ZnO particles, so that only the surface layer of the phosphor particles is processed. Since light emission is emitted not only from the surface of the phosphor particles but also from the inside, lamp annealing can improve the conductivity of the phosphor without attenuating ultraviolet components.

As shown in FIG. 2, an ITO electrode 2 which is a translucent electrode is formed as an anode conductor on an anode substrate 1 which is an insulating glass substrate. Sulfide phosphor 3
To adhere. The sulfide phosphor 3 may be mixed with a conductive substance such as In ₂ O ₃ to reduce the resistance. A ZnO phosphor 4 as a visible light emitting phosphor is applied so as to cover the surface of the sulfide phosphor 3. The anode substrate 1 is fired at 400 to 500 ° C. to complete the anode substrate 1 such as a fluorescent display tube.

Although only a single layer of the sulfide phosphor 3 is shown in FIG. 2, specific phosphors of the sulfide include a ZnS: Ag phosphor emitting blue light and a Zn phosphor emitting green light.
S: Cu, Al phosphor, Zn _0.2 Cd for red emission
_0.8 S: Ag phosphors were separately used, and anodes as independent light emitting display portions were formed on the anode substrate.

The ZnO phosphor, which is an ultraviolet ray emitting phosphor excited by an electron beam, has an intensity ratio of an ultraviolet component having a peak at a wavelength of 385 nm to a visible light component having a peak at a wavelength of 505 nm, ie, ultraviolet component / visible light component = 100 / 0-0
/ 100 kinds of samples were prepared. In addition,
The intensity ratio between the ultraviolet component and the visible light component is simply referred to as a wavelength component intensity ratio in this description.

A fluorescent display tube is formed using the anode substrate. The ITO electrode on the anode substrate of the fluorescent display tube has a thickness of 100 to
Applying a voltage of 1000 V and applying 10 to 100 mA / cm ²
Of current. At that time, the emission luminance and life characteristics of the phosphor layer of each anode were measured, and evaluation was performed using the results.
The evaluation of each luminescent color for each of the sulfide phosphors will be described below with reference to FIGS.

For comparison, a sample having only a sulfide phosphor emitting in each of the red, blue and green colors as a phosphor and a Zn having an emission peak only at a wavelength of 505 nm were used.
A sample having only the O phosphor as the phosphor was also prepared.

(1) In the case of ZnS: Ag phosphor emitting blue light The relationship between the wavelength component intensity ratio of the ZnO phosphor provided on the ZnS: Ag phosphor and the relative luminance of the entire phosphor layer is shown in FIG. . The evaluation was performed at an anode voltage of 200V. When the component of 505 nm is large in the ZnO phosphor, ZnO
Since the ratio of components other than the blue component in the phosphor increased and the color purity of blue deteriorated, evaluation was performed through a blue filter.
As a comparative example, the luminance in the case where a filter is used in combination with a ZnO phosphor whose emission spectrum peak is only 505 nm is shown in FIG.

In this example, the wavelength component intensity ratio is 385 nm
In the range of / 505nn = 100/0 to 10/90, the relative luminance exceeded 50, and a better result for practical use than the comparative example was obtained. Within this range, a more preferable result can be obtained if the wavelength component intensity ratio is 97/3 to 40/60. Within this range, the wavelength component intensity ratio is 9
If it is 0/10 to 75/25, still more preferable results can be obtained.

In the range where the wavelength component intensity ratio is smaller than 5/95, the blue component of the 505 nm component of the ZnO phosphor is irregularly reflected by the lower ZnS: Ag phosphor layer and attenuated. The characteristics are inferior to those of the sample. Further, the wavelength component intensity ratio is 99/1.
If it is larger, the matrix resistance of the ZnO phosphor becomes high, and the luminance is reduced.

(2) In the case of ZnS: Cu, Al phosphor emitting green light FIG. 4 shows the results of an experiment performed in the same manner as in the case of the ZnS: Ag phosphor. In this example, among the light generated by the ZnO phosphor, in addition to the blue component or ultraviolet light having a wavelength of 385 nm, a part of the component having a wavelength of 505 nm is also used for exciting the sulfide phosphor. The preferred wavelength component intensity ratio was expanded from 100/0 to 7/93. Within this range, the wavelength component intensity ratio is 90/10 to 40/60.
If so, more preferable results can be obtained. Within this range, even more favorable results can be obtained if the wavelength component intensity ratio is 75/25 to 55/45. CaS: Ce
Similar results were obtained for the phosphor.

(3) Red-emitting Zn _0.2 Cd _0.8 S: Ag
In the case of a phosphor FIG. 5 shows the results of an experiment performed in the same manner as in the case of the ZnS: Ag phosphor. In this example, the preferred wavelength component intensity ratio was 100/0 to 0/100. This is shown in FIG.
This is because the excitation band of the red light emitting phosphor extends to the visible region, which is the 505 nm component of the emission spectrum of the ZnO phosphor, as shown in FIG. In the sulfide phosphor of the present example, Cd was set to 80%. However, if the Cd content is 80% or less, the band gap structure approaches the structure of the ZnS phosphor, and the effect of the ultraviolet light emitted by the ZnO phosphor is obtained. Will be larger. Conversely, when Cd is larger than 80%, the light is mainly excited by light in the visible region.

When electrons impinge on the phosphor to excite it and emit light, most of the energy of the electrons is converted to heat, causing the phosphor to generate heat and reduce the emission luminance of the phosphor. Such a relationship between the temperature of the phosphor and the emission luminance is called a temperature quenching characteristic.
In each of the examples described above, the 385 nm
The light emission having a peak of has good temperature quenching characteristics. Compared to the case where a conventional ZnO phosphor uses light emission having inferior temperature quenching characteristics such as light emission centered at a wavelength of 505 nm and uses filters in combination with each other to obtain red, green and blue colors, as shown in FIG. The phosphor of this embodiment has excellent temperature quenching characteristics.

From the experimental results described above, ZnO in the phosphor of the display device of this embodiment has a wavelength component intensity ratio of 385 nm / 505nn = 100/0 to 10/0.
It is considered that selection within the range of 90 is practically effective.

A life test was conducted to confirm that the decomposition and degradation of the lower sulfide phosphor were suppressed by the ZnO phosphor described above. FIG. 7A shows the case of ZnS: Ag alone, and FIG. 7B shows the case of the above example (1) in which the surface of ZnS: Ag is coated with ZnO. In the graphs shown in these figures, the horizontal axis represents time, and the vertical axis represents the residual ratio of the anode current. When the upper layer of the sulfide phosphor layer was covered with ZnO, no reduction in the anode current was observed, and it was confirmed that this was effective as an emission measure for preventing contamination of the cathode and the emitter.

According to the embodiment described above, since the sulfide phosphor is covered with the phosphor that emits ultraviolet light having a wavelength shorter than 400 nm together with the visible light, the electrons accelerated at a relatively low voltage of 1 kV or less. By the collision, sulfide phosphors of any of red, blue and green emission colors can be efficiently emitted with high luminance. In addition, the sulfide phosphor is coated on another phosphor, and decomposition and scattering of the sulfide phosphor due to direct impact of electrons can be prevented, so that there is no risk of contaminating the electron source of the display device, and the sulfide phosphor is used as a display device. Reliability and life are improved.

In the embodiment described above, ZnS: Ag phosphor, ZnS: Cu, Al phosphor, and sulfide phosphor are used.
The (Zn _0.2 , Cd _0.8 ) S: Ag phosphor has been described, but this is merely an example. Examples of the sulfide phosphor that achieves the above-described effects in combination with the ZnO phosphor include:
(Zn _1-x Cd _x ) S: M, N (where x = 0 to 0.8,
M = Ag, Cu or Au, N = Cl, I, P, Al or In), CaS: Eu, CaS: Ce, CaS: Cu,
Na, Ln ₂ O ₂ S: Re (where Ln is Y, Gd, L
a selected from a, and a phosphor such as Re = Eu or Tb).

[0062]

According to the present invention, since the sulfide phosphor is covered with the electron-beam-excited ultraviolet-emitting phosphor that emits ultraviolet light having a wavelength shorter than 400 nm, the phosphor is accelerated at a relatively low voltage of, for example, 1 kV or less. By the electron bombardment, sulfide phosphors of any of red, blue, and green emission colors can be efficiently emitted with high luminance. In addition, since the sulfide phosphor is coated with the electron-beam-excited ultraviolet light-emitting phosphor and the decomposition and scattering of the sulfide phosphor due to the direct impact of electrons can be prevented, there is no risk of contaminating the electron source of the display device, and the display is not performed. The reliability and life of the device are improved. For this reason, a sulfide phosphor can be used for a high-voltage driven color graphic display tube, a field emission device, and the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing an emission spectrum of each phosphor used in one embodiment of the present invention.

FIG. 2 is a cross-sectional view of an anode substrate according to one embodiment of the present invention.

FIG. 3 shows an intensity ratio between an ultraviolet component having a peak at a wavelength of 385 nm and a visible light component having a peak at a wavelength of 505 nm in one embodiment of the present invention in which a ZnS: Ag phosphor is coated with a ZnO phosphor; 5 is a graph showing a relationship with the relative brightness of the whole.

FIG. 4 shows an embodiment of the present invention in which a ZnS: Cu, Al phosphor is coated with a ZnO phosphor, and an intensity ratio between an ultraviolet component having a peak at a wavelength of 385 nm and a visible light component having a peak at a wavelength of 505 nm; 5 is a graph showing the relationship between the relative brightness of the entire body layer.

FIG. 5 shows an example of the present invention in which a Zn _0.2 Cd _0.8 S: Ag phosphor is coated with a ZnO phosphor;
5 is a graph showing the relationship between the intensity ratio of an ultraviolet component having a peak at m and a visible light component having a peak at a wavelength of 505 nm, and the relative luminance of the entire phosphor layer.

FIG. 6 is a graph showing a comparison between temperature quenching characteristics of one example of the present invention and a comparative example.

FIG. 7A is a graph showing a relationship between a remaining rate of an anode current and a continuous lighting time in a life test of a comparative example;
(B) is a graph showing the relationship between the residual ratio of the anode current and the continuous lighting time in the life test of one embodiment of the present invention.

FIG. 8 is a diagram illustrating spectra of a conventional ZnO phosphor and a ZnO phosphor that emits ultraviolet light according to another embodiment.

[Explanation of References] 2 ITO electrode as an anode conductor which is a translucent electrode 3 Sulfide phosphor 4 ZnO phosphor as electron beam excited ultraviolet light emitting phosphor 13 Phosphor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01J 1/30 H01J 29/20 29/20 29/89 29/89 31/15 E 31/15 1/30 Z (56) Reference Document JP-A-63-19737 (JP, A) JP-A-63-8457 (JP, A) JP-A-52-19964 (JP, A) JP-A-50-146580 (JP, A) JP-A-58-1996 204087 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) C09K 11/00-11/89 H01J 29/10-29/34 H01J 31/00-31/24

Claims (2)

(57) [Claims] 1. A sulfide phosphor layer applied to a light-transmitting electrode on an anode substrate, and excitation by an electron beam of 1 kV or less applied so as to cover a surface of the sulfide phosphor layer. A display device having a layer of an electron beam-excited ultraviolet light-emitting phosphor that emits ultraviolet rays according to the invention, wherein the electron beam-excited ultraviolet light-emitting phosphor has ZnO having an emission peak only at 385 nm;
m, an ultraviolet component having a peak at 385 nm, and a mixture of ZnO having emission peaks at two points of m.
The intensity ratio of the visible light component having a peak at nm is 100/0.
The display device according to claim 1, wherein the display device is selected in a range of 10 to 90. 2. The ZnO having an emission peak only at 385 nm is a ZnO phosphor produced by a reduction treatment.
_2. The display device according to claim 1, wherein the display device is obtained by firing in _two atmospheres.