Phosphors having improved luminance and longer lifespan

Details Phosphors having improved luminance and longer lifespan Phosphors having improved luminance and longer lifespan

2001-12-27

2003-12-30

Koslow, C. Melissa (Department: 1755)

Compositions

Inorganic luminescent compositions

Compositions containing halogen; e.g., halides and oxyhalides

C313S486000, C313S483000

Reexamination Certificate

active

06669868

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to phosphors for use in a display device such as a vacuum fluorescent display (VFD), or field emission display (FED).
2. Description of the Related Art
Like cathode ray tubes (CRTs), VFDs are self-radiating displays using phosphors, and are widely used in applications such as digital displays of household electric appliances and gauge panels of automobiles. While VFDs have mainly been used for low-capacity, small-sized products that simply display numbers, characters, and signs, they are currently in use for high-density graphic image displays. In the near future, a full color VFD having a large display capacity will be commercially viable.
FEDs have received considerable attention as a next generation display device having advantages of flat panel displays, such as liquid crystal displays (LCDs) and CRTs. Thus, research on FEDs continues to be actively conducted. FEDs, which operate on the principle of field emission of electrons from microscopic tips, are known to be capable of overcoming the drawbacks of CRTs, such as excessive bulk and weight, and the drawbacks of LCDs, such as high manufacturing cost and limited size and viewing angle.
Furthermore, since FEDs have various advantages, such as a thin film form, low power consumption, low manufacturing cost, excellent temperature characteristics, and high-speed operation, they can be used in a wide variety of applications ranging from home televisions to industrial equipment and computers. In particular, FEDs are likely to be widely used in commercial applications such as notebook PCs, monitors, and televisions, like thin film transistor (TFT) LCDs.
A phosphor able to be excited by a low-velocity electron beam is required for use in VFDs or FEDs in order to emit light at an anode operating voltage of no greater than 1 kV. Conventional phosphors able to be excited by low-velocity electron beams are divided into two types. The first type is a phosphor based upon a low-resistance host matrix and the second is a phosphor based on a high-resistance host matrix and having a phosphor layer formed by adding a conductive material to reduce the resistance of the host matrix.
The host matrix of the high-resistance phosphors mostly contains sulfur (S) and thus the sulfur-containing phosphor is referred to as a “sulfide phosphor”. It is known that the sulfide phosphor is readily decomposed when bombarded by electrons and the decomposed sulfide phosphor is scattered within a VFD. The sulfide based material impinges on a cathode in the VFD, thereby contaminating the cathode and thus degrading the emission power of the VFD. Another problem of the sulfide phosphor is that sulfide impinges on other oxide phosphors to contaminate an anode. Additionally, a ZnCdS-based host matrix contains a pollutant such as cadmium (Cd) that is harmful to the environment.
To overcome the drawbacks of conventional phosphors, a phosphor prepared by adding a rare earth element and a Group 13 element to a host matrix composed of an alkaline earth metal oxide and a titanium (Ti) oxide is disclosed in Japanese Patent Publication Gazette No. Heisei 8-85788 and U.S. Pat. No. 5,619,098, the disclosures of which are incorporated by reference. The phosphor host lattice does not contain sulfur and cadmium and can be excited by low-velocity electron beams to emit light. However, this phosphor has not been yet put into practice due to its short lifespan.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a phosphor whose host matrix does not contain sulfur and which has a longer lifespan and an improved luminance in spite of the fact that it does not contain cadmium.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and/or other aspects of the present invention, there is provided a phosphor with a perovskite structure according to an embodiment of the present invention which includes a halide flux of the Group 1 element of the periodic table and satisfies the following formula:
MTiO
3
: (A,B)
where M is an alkaline earth metal, A is a rare earth element, and B is a Group 13 element of the periodic table.
According to an aspect of the invention, the alkaline earth metal is Mg, Sr, Ca, or Ba, and the rare earth element is Ce, Pr, Eu, Tb, or Tm, where an amount of the rare earth element added is in the range of 0.05-5 mol % based on 1 mol of Ti.
According to another aspect of the invention, the Group 13 element is Al, Ga, In, or TI, and an amount of the Group 13 element added is in the range of 0.05-80 mol % based on 1 mol of Ti.
According to a further aspect of the invention, a halide flux of a Group 1 element is at least one selected from the group consisting of Lil, Nal, Kl, LiCl, NaCl, KCl, LiBr, NaBr, and KBr, and an amount of the halide flux of a Group 1 element is in the range of 0.01-10 mol % based on 1 mol of Ti.
According to another embodiment of the present invention, there is provided a fluorescent display device such as one of a field emission display and a vacuum fluorescent display comprising a phosphor of the present invention.


REFERENCES:
patent: 5619098 (1997-04-01), Toki et al.
patent: 6139774 (2000-10-01), Yamada et al.
Patent Abstracts of Japan, Publication No.: 08-085788, dated Feb. 4, 1996.

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