Phosphors having longer lifespan

Details Phosphors having longer lifespan Phosphors having longer lifespan

2001-12-27

2004-06-22

Koslow, C. Melissa (Department: 1755)

Compositions

Inorganic luminescent compositions

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

C252S30140S, C313S486000

Reexamination Certificate

active

06752933

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application No. 01-3887, filed Jan. 27, 2001, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to phosphors for use in display devices such as vacuum fluorescent displays (VFDs) or field emission displays (FEDs).
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 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 on a low-resistance host matrix, and the second type 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.
Japanese Patent Publication Gazette No. Heisei 8-85788 and U.S. Pat. No. 5,619,098 disclose an SrTiO
2
based phosphor prepared by adding a rare earth element and a Group 13 element to a host matrix composed of alkaline earth metal oxide and titanium oxide, the disclosures of which are incorporated by reference. The disclosed phosphor does not contain cadmium (Cd), which is known to be environmentally toxic and can be excited by low-velocity electron beams to emit light. However, this phosphor has not yet been put into practice due to its short lifespan.
SUMMARY OF THE INVENTION
To solve the above and other problems, it is an object of the present invention to provide a phosphor having a host matrix that does not contain cadmium (Cd) which is harmful to the environment, and which has good luminance and lifespan characteristics as compared to a conventional SrTiO
3
based phosphor.
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 other objects of the present invention, there is provided a phosphor according to an embodiment of the invention comprising a perovskite structure which includes sulfur (S) and satisfies the following formula:
MTiO
3
:A
where M is an alkaline earth metal and A is a rare earth element.
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.
According to another aspect of the invention, 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 a further aspect of the invention, the phosphor having the formula MTiO
3
:A further comprises a Group 13 element of the periodic table.
According to a still further aspect of the invention, the Group 13 element is Al, Ga, In, or Tl.
According to yet another aspect of the invention, 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 an additional aspect of the invention, the sulfur contained in the phosphor is added in a form of a sulfur element or an alkaline metal sulfur-containing compound, and the alkaline metal sulfur-containing compound is one of Na
2
S
2
O
3
·5H
2
O and Na
2
SO
4.
According to a yet additional aspect of the invention, the phosphor having the formula MTiO
3
:A above contains 0.1-10 wt % sulfur based on a total weight of the phosphor.
According to a still additional aspect of the invention, the phosphor having the formula MTiO
3
:A above further comprising the Group 13 element of the periodic table is SrTiO
3
:Pr,Al which includes S or SrTiO
3
:Pr,Ga which includes S.
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 Abstracts of Japan, Publication No.: 08-0855788, dated Feb. 4, 1996.

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