Process for preparing rare earth activated alkaline earth...

Details Process for preparing rare earth activated alkaline earth... Process for preparing rare earth activated alkaline earth...

2002-01-14

2003-08-05

Gutierrez, Diego (Department: 2859)

Radiant energy

Invisible radiation responsive nonelectric signalling

Luminescent device

C252S30140H

Reexamination Certificate

active

06603129

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for preparing rare earth activated alkaline earth metal fluorohalide stimulable phosphor particles and rare earth activated alkaline earth metal fluorohalide stimulable phosphor particles, and in particular to a process for preparing rare earth activated alkaline earth metal fluorohalide stimulable phosphor particles without causing deterioration of performance due to moisture absorption and rare earth activated alkaline earth metal fluorohalide stimulable phosphor particles.
BACKGROUND OF THE INVENTION
Radiographic images such as X-ray images are frequently employed for use in medical diagnosis. To obtain such X-ray images, radiography is employed, in which X-rays transmitted through an object are irradiated onto a phosphor layer (so-called fluorescent screen), thereby producing visible light, which exposes silver salt photographic film and the thus exposed film is developed in such a manner similar to that conducted in conventional photography. Recently, there has been introduced a technique of reading images directly from the phosphor layer, without using the silver salt photographic film. However, this phosphor layer exhibits relatively high hygroscopicity, thereby easily leading to lowering in sensitivity and therefore, a technique for enhancing moisture resistance has been strongly sought.
As such a technique, there is known a method, in which radiation transmitted through an object is allowed to be absorbed by a phosphor, followed by exciting the phosphor with light or thermal energy to release radiation energy stored therein as fluorescent light emission, and the emitted fluorescent light is detected to form images. Exemplarily, a radiation image conversion method using stimulable phosphors is known, as described in U.S. Pat. No. 3,859,527 and JP-A No. 55-12144 (hereinafter, the term, JP-A refers to an unexamined and published Japanese Patent Application).
In this method, a radiation image conversion panel containing a stimulable phosphor is employed. Thus, a stimulable phosphor layer of the radiation image conversion panel is exposed to radiation transmitted through an object to store radiation energies corresponding to respective portions of the object, followed by sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as “stimulating rays”) to release the radiation energy stored in the phosphor as light emission (stimulated emission), photo-electrically detecting the emitted light to obtain electric signals, and reproducing the radiation image of the object as a visible image from the electrical signals on a recording material such as photographic film or a CRT.
The foregoing radiation image recording and reproducing method has an advantage in that radiation images having abundant information content can be at a low exposure dose relative to conventional radiography using the combination of a conventional radiographic film and intensifying screen.
Stimulable phosphors are phosphor material that, after having been exposed to radiation rays, causes stimulated emission by exposing to stimulating rays. Phosphors capable of causing stimulated emission at a wavelength of 400 to 900 nm with a stimulating ray of 400 to 900 nm are generally applied to practical use.
Examples of the stimulable phosphor used in the radiation image conversion panel include,
(1) a rare earth activated alkaline earth metal fluorohalide phosphor represented by the formula of (Ba
1-x
, M
2+
x
)FX:yA, as described in JP-A No. 55-12145, in which M
2+
is at least one of Mg, Ca, Sr, Zn and Cd; X is at least one of Cl, Br and I; A is at least one of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb, and Er; x and y are numbers meeting the conditions of 0≦x≦0.6 and 0≦y≦0.2; and the phosphor may contain the following additives:
X′, BeX″ and M
3
X
3
′″, as described in JP-A No. 56-74175 (in which X′, X″ and X′″ are respectively at least a halogen atom selected from the group of Cl, Br and I; and M
3
is a trivalent metal);
a metal oxide described in JP-A No. 55-160078, such as BeO, BgO, CaO, SrO, BaO, ZnO, Al
2
O
3
, Y
2
O
3
, La
2
O
3
, In
2
O
3
, SiO
2
, TiO
2
, ZrO
2
, GeO
2
, SnO
2
, Nb
2
O
5
or ThO
2
;
Zr and Sc described in JP-A No. 56-116777;
B described in JP-A No. 57-23673;
As and Si described in JP-A No. 57-23675;
M·L (in which M is an alkali metal selected from the group of Li, Na, K, Rb and Cs; L is a trivalent metal Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Ga, In, and Tl) described in JP-A 58-206678;
calcined tetrafluoroboric acid compound described in JP-A No. 59-27980;
calcined, univalent or divalent metal salt of hexafluorosilic acid, hexafluorotitanic acid or hexafluorozirconic acid described in JP-A No. 59-27289;
NaX′ described in JP-A No. 59-56479 (in which X′ is at least one of Cl, Br and I);
a transition metal such as V, Cr, Mn, Fe, Co or Ni, as described in JP-A No. 59-56479;
M
1
X′, M′
2
X″, M
3
X′″ and A, as described in JP-A No. 59-75200 (in which M
1
is an alkali metal selected from the group of Li, Na, K, Rb and Cs; M′
2
is a divalent metal selected from the group of Be and Mg; M
3
is a trivalent metal selected from the group Al, Ga, In and Tl; A is a metal oxide; X′, X″ and X′″ are respectively a halogen atom selected from the group of F, Cl, Br and I);M
1
X′ described in JP-A No. 60-101173 (in which M
1
is an alkali metal selected from the group of Rb and Cs; and X′ is a halogen atom selected from the group of F, Cl, Br and I);
M
2
′X′
2
.M
2
′X″
2
(in which M
2
′ is at least an alkaline earth metal selected from the group Ba, Sr and Ca; X′ and X″ are respectively a halogen atom selected from the group of Cl, Br and I, and X′≠X″); and
LnX″
3
described in JP-A No. 61-264084 (in which Ln is a rare earth selected from the group of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; X″ is a halogen atom selected from the group of F, Cl, Br and I);
(2) a divalent europium activated alkaline earth metal halide phosphor described in JP-A No. 60-84381, represented by the formula of M
2
X
2
.aM
2
′
2
:xEu
2+
(in which M
2
is an alkaline earth metal selected from the group of Ba, Sr and Ca; X and X′ is a halogen atom selected from the group of Cl, Br and I and X≠X′; a and x are respectively numbers meeting the requirements of 0≦a≦0.1 and 0<x≦0.2);
the phosphor may contain the following additives;
M
1
X″ described in JP-A No. 60-166379 (in which M
1
is an alkali metal selected from the group of Rb, and Cs; X″ is a halogen atom selected from the group of F, Cl, Br and I;
KX″, MgX
2
′″ and M
3
X
3
″″ described in JP-A No. 221483 (in which M
3
is a trivalent metal selected from the group of Sc, Y, La, Gd and Lu; X″, X′″ and X″″ are respectively a halogen atom selected from the group of F, Cl Br and I;
B described in JP-A No. 60-228592;
an oxide such as SiO
2
or P
2
O
5
described in JP-A No. 60-228593;
LiX″ and NaX″ (in which X″ is a halogen atom selected from the group of F, Cl, Br and I;
SiO
2
described in JP-A No. 61-120883;
SnX
2
′ described in JP-A 61-120885 (in which X″ is a halogen atom selected from the group of F, Cl, Br and I;
CsX″ and SnX
2
′″ described in JP-A No. 61-235486 (in which X″ and X′″ are respectively a halogen atom selected from the group of F, Cl, Br and I;
CsX″ and Ln
3+
described in JP-A 61-235487 (in which X″ is a halogen atom selected from the group of F, Cl, Br and I; Ln is a rare earth element selected from the group of Sc, Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu;
(3) a rare earth element activated rare earth oxyhalide phosphor represented by the formula

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