Phosphor and imaging device using the same

Details Phosphor and imaging device using the same Phosphor and imaging device using the same

2002-06-27

2004-06-22

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S446000, C428S697000, C428S702000, C428S704000, C313S467000, C313S468000, C313S309000, C313S336000, C313S495000, C313S582000, C252S30140R, C252S30140F, C423S263000, C423S618000, C423S624000

Reexamination Certificate

active

06753099

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to phosphors and imaging devices such as projection-type cathode ray tubes and display panels using the phosphors. More particularly, the invention relates to green emitting phosphors that emit high-luminance light with less luminance degradation and are suitable for image display and imaging devices such as projection-type cathode ray tubes and image display panels using such phosphors.
In recent years, imaging devices using cathode ray tubes for displaying color images have made advances toward higher solution and luminance to meet the need of higher performance. The imaging devices discussed herein are those for imaging from image data through light emission in such a way that phosphors are excited by irradiation of electron beams or ultraviolet rays; namely, cathode ray tubes (especially, projection-type cathode ray tubes), display panels using low energy electron beams, such as a field-emitter display (FED), and plasma display panels (PDP). The imaging devices include a system for imaging from image data which incorporates a drive for driving any tube or panel mentioned above, image data processing circuitry, and the like.
Higher solution and luminance of these imaging devices have been achieved by reducing the diameter of an excitation spot of electron beams or the like, increasing the scan speed, and increasing the excitation intensity. However, this is accompanied by the following drawbacks: luminance saturation of phosphors used in the imaging device, luminance degradation, and significant afterimages due to afterglow, resulting in a decline in image quality as a problem. At the same time, better color reproduction quality is required. Therefore, phosphors must satisfy requirements of luminance saturation, degradation, and afterglow properties and color enhancement.
Using a projection-type cathode ray tubes (hereinafter referred to as a projection tube) typical of the imaging devices as an example, its problems will be explained below. For the cathode ray tube, its luminance intensity is controlled by regulating the current of excited electron beams. Thus, it is required that the luminance of phosphors linearly increases in proportion to the current. However, generally, as the excitation intensity becomes high, luminance saturation takes place, that is, the luminance runs off the linear. When an image is displayed with highly intense excitation, phosphor materials are damaged. Consequently, luminance decreases and color emission degrades during continued use of the projection tube.
The projection tube is a cathode ray tube for use in a projection-type display and projects an image generated by the cathode ray tube on a screen through the optics that enlarge the image area by several tens of times. Thus, excitation is performed by current of 10 to 100 times as much as a generally used direct-viewing cathode ray tube producing non-enlarged images.
Accordingly, requirements for phosphors for the projection tube are less luminance saturation especially when the tube carries a large quantity of current and less degradation when the tube carries a large quantity of current. Among the phosphors used for emission of three primary colors R (read), B (green), and B (blue), especially for green emitting phosphors which generate 70% of luminance in a white light, the above improvements of phosphor properties are important.
Varieties of materials have so far been used for green emitting phosphors for the cathode ray tube. For example, a phosphor composition expressed by chemical formula Y
2
SiO
5
:Tb is known. The feature of this phosphor composition is less luminance saturation when excited with high-density current and it has been generally used as a practical phosphor. However, such a problem with this phosphor composition has been posed that a decline in coloring and color emission efficiency occurs by irradiation of electron beams and luminance degrades as irradiation continues. Another problem thereof is insufficient luminance of light it generates.
To solve these problems, luminance improvement was attempted by replacing a part of the composition with Sc as disclosed in, for example, Japanese Examined Patent Publication No. Sho 61-21505 and Japanese Examined Patent Publication No. Hei 6-62939.
Furthermore, as disclosed in, for example, Japanese Laid-Open No. Hei 2-289679, improvement to luminance and suppressing luminance degradation were attempted by replacing a part of the composition with any one of the substances Gd, Tm, Sm, and Eu.
Furthermore, as disclosed in, for example, the above-mentioned Japanese Examined Patent Publication No. Sho 61-21505, luminance improvement was attempted by replacing a part of the composition with Mu.
Furthermore, as disclosed in, for example, Japanese Examined Patent Publication No. Hei 6-60354, luminance improvement was attempted by replacing a part of the composition with Dy or Pr.
Even these improved phosphors, however, are not enough to satisfy the requirements of recent cathode ray tubes carrying a large quantity of current to provide higher solution and luminance degradation is still a problem. Improvement to luminance is constantly required.
Luminance degradation to a great degree was regarded as a drawback of the above-mentioned conventional phosphor composition Y
2
SiO
5
:Tb.
SUMMARY OF THE INVENTION
The object of the present invention is to provide phosphors to emit high-luminance light with less luminance degradation and provide an imaging device producing good-quality images using such phosphors.
The above object can be achieved by synthesizing a phosphor that is specified below in chemical composition.
In one aspect, the invention provides a green emitting phosphor whose composition is expressed by chemical formula:
{(Y
1−y−z
M
y
Gd
z
)
1−x
Tb
x
}
2
(Si
1−b
Ge
b
O
2
)
1+a
O
3
where values of x, y, z, a, and b are assigned, subject to 0<x≦0.5, 0≦y≦1, 0≦z≦1 (where 0<y+z≦1), 0<a≦1, and 0≦b≦1, and M is at least one element (rare earth) to be selected from a group of Sc, In, La, Lu, Yb, Ce, Eu, Sm, Tm, Ho, Er, and Nd.
Green emitting phosphors synthesized by prior art are those obtained by replacing a part of component Y of parent material Y
2−2x
SiO
5
activated by Tb
x
with Gd, Sc, Yb, Eu, Sm, Tm, Mn, Dy, Pr, or the like.
In contrast, the first phosphor of the present invention is a green emitting phosphor that has composition including an excess of SiO
2
in terms of stoichiometric ratio (0<a≦1), wherein Y is replaced with Gd, its fundamental composition being expressed by chemical formula:
{(Y
1−z
Gd
z
)
1−x
Tb
x
}
2
(SiO
2
)
1+a
O
3
.
The second phosphor of the present invention is a green emitting phosphor that has composition including an excess of SiO
2
in terms of stoichiometric ratio (0<a≦1), wherein Y is replaced with at least one element (rare earth) of the following: Sc, In, La, Lu, Yb, Ce, Eu, Sm Tm, Ho, Er, and Nd, its fundamental composition being expressed by chemical formula:
{(Y
1−y
M
y
)
1−x
Tb
x
}
2
(SiO
2
)
1+a
O
3
.
The third phosphor of the present invention is a green emitting phosphor that has composition including an excess of SiO
2
in terms of stoichiometric ratio (0<a≦1), wherein Y is replaced with Gd and at least one element of the following: Sc, In, La, Lu, Yb, Ce, Eu, Sm Tm, Ho, Er, and Nd, its fundamental composition being expressed by chemical formula:
{(Y
1−y−z
M
y
Gd
z
)
1−x
Tb
x
}
2
(SiO
2
)
1+a
O
3
.
The fourth phosphor of the present invention is a green emitting phosphor derived from the foregoing three phosphor compositions wherein a part or all of Si is replaced with Ge, its fundamental composition being expressed by chemical formula:
{(Y
1−y−z
M
y
Gd
z
)
1−x
Tb
x
}
2
(Si
1−b
Ge
b
O
2
)
1+a
O
3
.
In accordance with the present invention described above, phosphors can be obtained that emit higher luminance

Affiliated with

Also associated with

Rating

Phosphor and imaging device using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Phosphor and imaging device using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Phosphor and imaging device using the same will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3335698