Phosphor material, phosphor material powder, plasma display...

Details Phosphor material, phosphor material powder, plasma display... Phosphor material, phosphor material powder, plasma display...

2002-11-14

2003-12-23

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

With gas or vapor

Three or more electrode discharge device

C313S485000, C313S486000, C313S487000, C313S586000, C313S587000, C252S30140R

Reexamination Certificate

active

06667574

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a phosphor material and a phosphor material powder that emit light with a high efficiency, a plasma display panel used in display devices and a method of producing the same.
BACKGROUND ART
The CRT has been commonly used as the display device for television sets. The CRT, although better in resolution and is picture quality than the plasma display panel and the liquid crystal display, is not suited to large screens having diagonal size of 40 inches or more for the reason of depth size and weight. The liquid crystal display is limited in the screen size and the viewing angle, in spite of such advantages as the low power consumption and low drive voltage.
The plasma display panel, on the other hand, can be used in a large-screen display because there is no problem of depth size and weight, and 40-inch class products using the plasma display panel have already been developed (for example, see Functional Materials, February issue, 1996, Vol. 16, pp. 2, 7).
Constitution of a plasma display panel of the prior art will be described below with reference to the accompanying drawing.
FIG. 23
is a sectional view showing schematic constitution of the AC type plasma display panel.
In
FIG. 23
, numeral
41
denotes a front cover plate (front glass substrate) with a display electrode
42
formed on the front glass substrate
41
. The front cover plate
41
with the display electrode
42
formed thereon is also covered by a dielectric glass layer
43
and a protective layer
44
made of magnesium oxide (MgO) (see, for example, Unexamined Patent Publication (Kokai) No. 5-342991).
Numeral
45
denotes a back plate (back glass substrate), with an address electrode
46
, barrier rib
47
and spherical phosphor layer
48
being provided on the back glass substrate
45
, and numeral
49
denotes an electric discharge space filled with a discharge gas. The phosphor layer comprises phosphor layers of three colors, red, green and blue, disposed in this order for color display. The phosphor layers of different colors are excited to emit light by ultraviolet rays of short wavelength (147 nm) emitted by electric discharge.
As the phosphor layer
48
of the plasma display panel, (YGd)BO
3
:Eu is used for red, BaMgAl
10
O
17
:Eu is used for blue and Zn
2
SiO
4
:Mn is used for green today (for example, Electronics Packaging Technology; July, 1997; Vol. 113, No. 7, pp. 23-26).
The plasma display panels of 40- to 42-inch class described above that are produced at present have luminance of 150 to 250 cd/m
2
at the pixel level of NTSC (640×480 pixels, cell pitch 0.43 mm×1.29 mm, area of one cell 0.55 mm
2
) (for example, refer to Functional Materials, February issue, 1996, Vol. 16, pp. 2, 7) Recently, plasma display panels of 40- to 42-inch class having luminance of 250 to 450 cd/m
2
at the pixel level of NTSC have also been reported (for example, see Flat Panel Display, 1997, Part 5-1, pp. 198-199). The conventional CRT technology is said, by contrast, to be capable of achieving a luminance of about 500 cd/m
2
.
The high-definition television of full specification that is at the focus of attention recently requires 1920×1125 pixels, resulting in a resolution as fine as cell pitch of 0.15 mm×0.48 mm and cell area of 0.072 mm
2
in the case of 42-inch class. When a high-definition television set is produced with 42-inch plasma display panel, screen area per one pixel become as small as {fraction (1/7)} to ⅛ that of the NTSC display. As a result, when the high-definition television set is produced with the 42-inch plasma display panel of the conventional cell configuration, emission intensity of the display panel becomes {fraction (1/7)} to ⅛ that of the NTSC display, namely 0.15 to 0.171 m/W.
Thus luminance of a high-definition television produced with the 42-inch plasma display panel is predicted to be as low as 30 to 40 cd/m
2
, given the same phosphor, gas composition and gas pressure, making it desirable to improve the luminance.
As described above, when a television set of such a small pixel size as in the high-definition television is produced using the plasma display panel with similar brightness, luminance must be greatly increased.
There are also such problems as described below with regard to phosphor material.
The first problem is that phosphor materials of different colors have different levels of luminance.
While several types of phosphor have been investigated for each of red, green and blue light in the plasma display panel, green phosphor has the highest luminance and blue phosphor has the lowest luminance in any of these types.
For example, when YBO
3
:Eu is used as the red phosphor, Zn
2
SiO
4
:Mn is used as the green phosphor and BaMgAl
10
O
17
:Eu is used as the blue phosphor (Eu content 0.15), luminance ratio of the colors of red, green and blue is about 2:3:1, with a low color temperature of about 5000 degrees.
Accordingly in the plasma display panel of the prior art, color temperature is increased by electronically suppressing the light emission by the green phosphor that has high luminance, thereby to improve the white balance. However, this configuration leads to lower brightness of the plasma display panel as a whole due to the reduction in the emission of light from the phosphor having high luminance.
This indicates that increasing the luminance of blue light is very effective in solving the problem, since color temperature can be increased without reducing the luminance of green and red light by increasing the luminance of blue light that is the lowest of the phosphors.
Second, phosphor layers of the plasma display panels of the prior art are formed by applying an ink that contains phosphor particles by a printing process or coating a photosensitive sheet that contains phosphor particles. In either of these processes, it is necessary to fire the panel at a temperature of around 500° C. after forming the phosphor layer, in order to remove an organic binder component included in the ink or the sheet. It is also necessary to fire the panel at a temperature of 400° C. or higher to have the front cover plate and the back plate bonded with each other.
In these firing processes, the phosphors used in the panel are subject to a certain extent of thermal change that results in degradation of luminance and/or chromaticity.
As described above, the plasma display panel has the problem of the thermal deterioration of the phosphor material in the firing process that are required for the production (for example, Transaction of the 263rd Conference of Phosphor Engineering Association, pp. 9-13, 1996; Optonics, 1997, No.6, pp. 149-155).
In the firing processes, the phosphors are subject to a certain extent of thermal change that results in degradation of luminance and/or chromaticity. Ba
(1-x)
MgAl
10
O
17
:Eu
x
used as the blue phosphor at present experiences particularly significant thermal deterioration.
The Ba
(1-x)
MgAl
10
O
17
:Eu
x
used as the blue phosphor can easily be damaged by vacuum ultraviolet rays (wavelength 147 nm, 172 nm) that excite the plasma display panel, and the emission intensity decreases as the panel is operated longer, thus giving rise to a problem of service life.
As described above, the blue phosphor material of the plasma display panel has the problems of thermal deterioration of the phosphor material in the firing processes required for the producing and short service life.
There have been efforts being made to mitigate the thermal deterioration of the phosphor.
For example, the Optical Technology Contact, Vol. 34, No. 1 (1996) pp. 23-24 reports that the BaMgAl
10
O
17
:Eu
2+
that had been known as an excellent blue phosphor showed such problems as deterioration during operation of the panel and change in chromaticity, and that BaMgAl
10
O
17
:Eu
2+
was developed to solve such problems with an improvement achieved in mitigating the decrease in luminance caused by firing in the panel producing process.
As demands for high quality display increase, however, such techno

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