Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
1999-11-12
2001-11-13
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
C250S483100, C250S484200, C250S484400
Reexamination Certificate
active
06315923
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to phosphors. The phosphors of this invention show particularly useful properties for the field of storage phosphors and radiographic imaging, including penetrating radiation storage phosphors and penetrating radiation imaging, such as X-ray storage phosphors and X-ray imaging.
BACKGROUND OF THE INVENTION
Phosphor materials are well known for various uses. One such use is as X-ray storage phosphors. An X-ray storage phosphor exhibits photostimulated luminescence after exposure to an X-ray dose of radiation and subsequent exposure to an excitation source, such as a light source (e.g., visible light, infrared). Thus, the phosphor has the ability to store some of the X-rays it is initially dosed with so that it can emit that energy later. The secondary excitation needed to cause the emission of radiation in storage phosphors is commonly referred to as stimulation radiation. Storage phosphors are used in imaging plates to acquire images in a digital format and to produce images that may be electronically displayed on a screen or printed. The storage phosphor is typically incorporated into a binder in the imaging plates, with the binder applied to a suitable support. There are several known methods for recording and reproducing an X-ray pattern using X-ray storage phosphors. See, e.g., U.S. Pat. Nos. 5,514,298 and 4,258,264, each of which is incorporated in their entirety herein by reference.
It would be desirable to identify useful storage phosphors having relatively high densities. Theoretically, phosphors having high densities are capable of producing a useful phosphor layer that is thinner than is currently in use. Higher density phosphors provide relatively high absorption of penetrating radiation, which potentially results in higher image resolution. One prototypical X-ray storage phosphor, BaFBr:Eu, has the relatively low density of about 4.96 g/cc.
Phosphors commonly comprise a host compound that may be doped with an activator element. For example, U.S. Pat. No. 5,391,884 discloses a gadolinate host activated with either terbium or terbium and samarium. Other gadolinium-hosted phosphors are known, see, e.g., U.S. Pat. Nos. 4,959,174, 4,829,188 and 4,857,741. Certain compositions are known as direct conversion x-ray phosphors, but not as storage phosphors. See U.S. Pat. No. 4,822,696.
There continues to be a need for materials that are suitable storage phosphors, particularly those having higher densities.
SUMMARY OF THE INVENTION
In accord with the present invention, a storage phosphor has been discovered, comprising a composition characterized by the general formula:
(Ln
1−x−y
)
3+&dgr;
M
5−&dgr;
O
12
:Tb
x
,Z
y
where
Ln is selected from the group consisting of Gd, La, Lu, Y and combinations thereof;
M is selected from the group consisting of Al, Ga, Sc, Fe and combinations thereof;
O is oxygen;
Tb is terbium;
Z is selected from the group consisting of Tl, Sm, Yb, In, Eu and combinations thereof;
x is greater than or equal to zero, but less than or equal to 0.05 (i.e., 0≦x≦0.05);
y is greater than or equal to zero, but less than or equal to 0.05 (i.e., 0≦y≦0.05);
&dgr; is greater than or equal to minus 0.5, but less than or equal to 0.5 (i.e., −0.5≦&dgr;≦0.5)
and wherein the sum of x and y is not zero.
This phosphor is useful for storing and thereafter reading out penetrating radiation from a variety of sources, including X-rays, ultraviolet rays, electrons, alpha particles, beta particles or neutrons.
This invention also discloses a phosphor comprising an activated garnet host comprising oxygen and combined elements satisfying the relationship
Ln
3+&dgr;
M
5−&dgr;
:cQ
wherein Ln, &dgr; and M are as defined above; and Q is selected from the group consisting of terbium, samarium, thallium, indium, europium, ytterbium and combinations thereof; and c is an amount sufficient to produce a phosphor that exhibits a higher luminescence emission intensity than said phosphor absent Q when, after first being exposed to penetrating radiation, the phosphor is stimulated by light of a wavelength ranging from 600 to 1200 nm or thermally. In this aspect, c is a mole percent with respect to Ln and is in the range of greater than zero, but less than or equal to 3 (i.e., 0<c≦3). In a preferred embodiment, Q is a combination of terbium and thallium, which are present in a ratio of about one to one, and c is about 0.1 mole percent with respect to Ln.
Another aspect of this invention is a method for storing an image produced by exposure to penetrating radiation and releasing the stored image, comprising imagewise exposing a storage screen to radiation of a first wavelength, said storage screen comprised of a storage phosphor comprising oxygen and combined elements satisfying the relationship
Ln
3+&dgr;
M
5−&dgr;
:cQ
wherein Ln, M and Q are as defined above. In this aspect, c is a mole percent with respect to the other side of the formula (e.g., any of the host ions) and is in the range of greater than zero, but less than or equal to 3 (i.e., 0<c≦3). After the storage screen has been exposed to the penetrating radiation, the storage screen is exposed to radiation of a second wavelength, thereby causing emission of a third wavelength. The emitted radiation of the third wavelength is then collected and used to produce an image representative of the image pattern initially stored on the image screen.
The storage phosphors of this invention are made using methods known to those skilled in the art. One method of making the phosphors of this invention is a sol-gel technique where the starting materials are mixed in a solvent in the desired stoichiometric ratios, placed in or on a substrate and then heat-treated.
REFERENCES:
patent: 4258264 (1981-03-01), Kotera et al.
patent: 4757232 (1988-07-01), Berkstresser et al.
patent: 4822696 (1989-04-01), Lammers et al.
patent: 4829188 (1989-05-01), Shinomiya et al.
patent: 4857741 (1989-08-01), Yokota et al.
patent: 4959174 (1990-09-01), Nakajima et al.
patent: 5037577 (1991-08-01), Yamanoi et al.
patent: 5104573 (1992-04-01), Ono et al.
patent: 5343316 (1994-08-01), Morimoto et al.
patent: 5391884 (1995-02-01), Sieber et al.
patent: 5514298 (1996-05-01), Terrell et al.
patent: 292616 (1992-05-01), None
patent: 0 292 616 B1 (1992-05-01), None
patent: WO 00/17413 (2000-03-01), None
Pelletier-Allard, N., et al., Journal of Luminescence, vol. 62, No. 2, pp. 61-67 (1994) no month.
Brenier, A., et al., Journal of Luminscence, vol. 54, No. 5, pp. 271-277 (1993) no month.
Ohno, K. et al., Journal of Electrochemical Society, vol. 134, No. 8, pp. 2072-2076 (1987) no month.
Danielson Earl
Devenney Martin
Leblans Paul
Koslow C. Melissa
Symyx Technologies, Inc
LandOfFree
Storage phosphors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Storage phosphors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Storage phosphors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2591774