Method for recording and reproducing a radiation image, apparatus using said method, photostimulable phosphor panel for storing said radiation image

A method for recording and reproducing a radiation image comprising the steps of (i) causing a phosphor, which can be stimulated with visible or infrared radiations, to absorb a high energy radiation passing through an object, (ii) stimulating phosphor with visible or infrared radiations to release the energy stored as fluorescent light, and (iii) detecting fluorescent light with light detecting means, wherein the photostimulable phosphor is selected from the group consisting of green-emitting trivalent erbium activated barium ytterbium halides, trivalent erbium activated barium fluorohalides and solid solutions thereof, optionally comprising an alkali metal halide. Apparatus for recording and reproducing a radiation image using the above described method. Radiation image storage panel containing the above described photostimulable phosphors. Light-stimulable phosphors selected within the group consisting of green-emitting trivalent erbium activated barium ytterbium halides, trivalent erbium activated barium fluorohalides and solid solutions thereof, optionally comprising an alkali metal halide.

FIELD OF THE INVENTION 
This invention relates to a method for recording and reproducing a 
radiation image by causing a visible or infrared radiation-stimulable 
phosphor to absorb a high energy radiation after it has passed through an 
object, stimulating said phosphor to release the energy stored as 
fluorescent light, and detecting said fluorescent light, the 
photostimulable phosphor being selected in the group consisting of 
green-emitting trivalent erbium activated barium ytterbium halides, 
trivalent erbium activated barium fluorohalides and solid solutions 
thereof. An alkali metal halide may optionally be present. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 3,859,527 discloses a method for recording and reproducing a 
high energy radiation image using a radiation image storage panel 
comprising a stimulable phosphor which emits light when stimulated with 
visible or infrared light after exposure to that radiation (high energy 
radiation meaning an electromagnetic wave or a corpuscular radiation such 
as x-ray, .alpha.-rays, .beta.-rays, .gamma.-rays, neutron rays, 
ultraviolet rays, or the like). 
U.S. Pat. No. 4,258,264 discloses a method and an apparatus for reproducing 
a radiation image by stimulating a storage phosphor with stimulating rays, 
whose wavelengths are in the range of 600 to 700 nm, and detecting the 
stimulated light by means of a photodetector, the detected light being in 
the range of 300 to 500 nm. 
U.S. Pat. No. 4,239,968 discloses a method and an apparatus for recording 
and reproducing a radiation image by utilizing the photostimulability of a 
blue-emitting alkaline earth metal fluorohalide phosphor activated with 
rare earth elements. The claimed phosphors are stimulated with a radiation 
having a wavelength of from 500 to 700 nm and emit light in the blue 
portion of the spectrum (at wavelength lower than 450 nm). The alkaline 
earth metal mainly consists of barium, optionally mixed with other 
alkaline earth metals or divalent metals selected in the group consisting 
of Ba, Mg, Ca, Sr, Zn, and Cd. The rare earth activators are selected in 
the group consisting of Eu, Tb, Ce, Tm, Dy, Pr, Ho, Nd, Yb and Er 
(erbium). The only phosphors exemplified relate to barium fluorohalides 
activated with europium, cerium and terbium. There are no suggestions that 
barium fluorohalides activated with erbium can emit in the green portion 
of the spectrum. On the contrary FIGS. 3 and 4 disclose that the claimed 
phosphors emit a light in the blue portion of the spectrum, and, when 
stimulated with a radiation having a wavelength higher than 700 nm they do 
not show substantial emission. 
Other patents disclose a method for reproducing a radiation image by using 
particular classes of barium fluorohalide phosphors. For example U.S. Pat. 
No. 3,951,848 discloses BaFCl:Eu phosphors containing a 
brightness-improving additive selected among thallium, lead and aluminum; 
U.S. Pat. No. 4,336,154 discloses a photostimulable boron-containing 
phosphor having the formula 
EQU (Ba.sub.1-x M.sub.x)F.sub.2.aBaX.sub.2 :yEu,zB 
wherein M and X are the same as in the aforesaid U.S. Pat. No. 4,239,968, 
except that M can also be Be, and a, x, y, and z respectively satisfy the 
conditions 0.5.ltoreq.a.ltoreq.1.25, 0.ltoreq.x.ltoreq.1, 10.sup.-6 
.ltoreq.y.ltoreq.0.2, and 0.ltoreq.z.ltoreq.0.2. 
U.S. Pat. No. 4,608,190 discloses a photostimulable potassium-containing 
anion deficient BaFCl:Eu/BaFBr:Eu phosphor. 
EP patent application 83,085 discloses the preparation of radiation image 
storage panels containing a divalent europium activated complex halide 
represented by formula BaFX.xNaX': aEu.sup.2+, wherein X and X' each 
designate at least one of Cl, Br and I, 0.ltoreq.x.ltoreq.0.1 and 
0.ltoreq.a.ltoreq.0.2. Other patents or patent applications disclosure 
improvements of this patent such as, for example, EP patent application 
146,974 which discloses a similar photostimulable phosphor further 
comprising an alkali metal selected from K, Rb and Cs, EP patent 
application 146,973 which disclosed a similar photostimulable phosphor 
further comprising scandium, EP patent application 148,507 disclosed a 
similar photostimulable phosphor in which part of Ba can be substituted 
which Ca and/or Sr, JP Patent Publication 60-90286 (1985), in which part 
of bromide is substituted by iodide, and the like. 
All these phosphors exhibit a stimulable emission in the wavelength region 
of the visible spectrum shorter than 500 nm and they are preferably 
stimulated with light having a wavelength higher than 500 nm (such as an 
Ar.sup.+ ion laser beam of 514.5 nm or a He-Ne laser beam of 633 nm), 
where they exhibit the maximum stimulability. 
On the other hand, the same phosphors do not exhibit a sufficient 
stimulable emission when they are stimulated with light of a wavelength 
longer than 700 nm. 
SUMMARY OF THE INVENTION 
The present invention relates to new phosphors for use in panels, apparatus 
and methods for recording and reproducing a high energy radiation image, 
including the steps of stimulating a phosphor imagewise exposed to 
radiation and detecting the fluorescent light emitted by said phosphor 
upon stimulation, said phosphor being selected in the group consisting of 
green-emitting trivalent erbium activated barium ytterbium halides, 
trivalent erbium activated barium fluorohalides and solid solutions 
thereof, optionally comprising an alkali metal halide. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention relates to a method for recording and reproducing a 
radiation image comprising the steps of (i) causing a visible or infrared 
radiation-stimulable phosphor to absorb high energy radiation passing 
through an object, (ii) stimulating said phosphor with visible or infrared 
radiation to release the energy stored as fluorescent light and (iii) 
detecting said fluorescent light with light detecting means, said method 
being characterized in that said phosphor is selected in the group 
consisting of green-emitting trivalent erbium activated barium ytterbium 
halides, trivalent erbium activated barium fluorohalides and solid 
solutions thereof, and optionally an alkali metal halide may be added. 
Preferably, the present invention relates to a method as described above 
wherein said phosphor is represented by the following general formula: 
EQU (1-y)BaFX.yBaYb.sub.n X.sup.I.sub.m X.sup.II.sub.o.aMX.sup.III :zEr(I) 
wherein X is Cl, Br, or I, X.sup.I and X.sup.II, the same or different, are 
F, Cl, Br or I, X.sup.III is Cl or F, M is an element selected from the 
group of Li,Na,K,Rb and Cs; n is 1 or 2 and m+o is 5 or 8, 
0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.0.2, 0.ltoreq.a.ltoreq.0.5. 
More preferably, the present invention relates to a method as described 
above wherein said phosphor is represented by the following general 
formula: 
EQU (1-y)BaFX.yBaYbX.sup.I.sub.m X.sup.II.sub.o.aMX.sup.III :zEr(II) 
wherein X is Cl, Br, or I, X.sup.I and X.sup.II, the same or different, are 
F, Cl, Br or I, X.sup.III is Cl or F, M is an element selected from the 
group of Li,Na,K,Rb and Cs; m+o is 5, 0.ltoreq.y.ltoreq.1, 
0.ltoreq.z.ltoreq.0.2, 0.ltoreq.a.ltoreq.0.5. 
In particular, the present invention relates to the method described above 
wherein the wavelength of said stimulating radiation is in the range of 
500 to 1100 nm. 
More in particular, the present invention relates to the method described 
above wherein the wavelength of said stimulating radiation is in the range 
of 700 to 1000 nm. 
The method described above is further characterized in that said 
fluorescent light emitted by the above mentioned phosphor has a wavelength 
higher than 500 nm, preferably in the range of from 500 to 600 nm. 
In another aspect, the present invention relates to an apparatus for 
recording and reproducing a radiation image comprising (i) means for 
causing a visible or infrared radiation-stimulable phosphor to absorb high 
energy radiation after passing through an object, (ii) means for 
stimulating said phosphor with visible or infrared stimulating radiation 
to release the energy stored as fluorescent light and (iii) means for 
detecting said fluorescent light, said apparatus being characterized in 
that said phosphor is selected in the group consisting of green-emitting 
trivalent erbium activated barium ytterbium halides, trivalent erbium 
activated barium fluorohalides and solid solutions thereof, optionally 
comprising an alkali metal halide. 
In a further aspect, the present invention relates to a high energy 
radiation image storage panel having a fluorescent layer comprising a 
binder and a stimulable phosphor dispersed in said binder, wherein said 
stimulable phosphor selected in the group consisting of green-emitting 
trivalent erbium activated barium ytterbium halides, trivalent erbium 
activated barium fluorohalides and solid solutions thereof, optionally 
comprising of an alkali metal halide. 
In a still further aspect, the present invention relates to a 
photostimulable phosphor selected in the group consisting of 
green-emitting trivalent erbium activated barium ytterbium halides, 
trivalent erbium activated barium fluorohalides and solid solutions 
thereof, optionally comprising of an alkali metal halide. 
The method and the apparatus for recording and reproducing a high energy 
radiation image using the radiation image storage panel of the present 
invention schematically comprise: a high energy radiation source, an 
object, a radiation image storage panel, a light source emitting 
stimulating radiations which stimulate the fluorescent layer of the panel 
to release the radiation energy stored therein as fluorescent light, a 
filter for cutting off the radiation emitted by the light source and 
reflected by the panel at a selected wavelength and for transmitting only 
the fluorescent light emitted by the panel, and a focusing optic for 
collecting the light emitted by the panel and passed through the filter. 
The combination of a photosensor with a photomultiplier is used to detect 
and convert the light emitted by the panel into electrical signals, the 
electrical signal being amplified by means of an amplifier and said 
amplified electrical signal being analyzed by a data analyzer. 
Means for causing a visible or infrared radiation-stimulable phosphor to 
absorb high energy radiation passing through an object are known in the 
art, as described in U.S. Pat. No. 4,239,968. They include a high energy 
radiation source (such as e.g. an X-ray tube) and a radiation image 
storage panel similar to that of the present invention including a 
phosphor different from those of the present invention. When the phosphor 
is exposed to X-rays, the radiation passes through the object. The 
intensity of the radiation which has passed through the object represents 
the transmittance factor of the object. Furthermore, an image which 
represents the transmittance pattern of the object is obtained by means of 
the radiation impinging upon the panel. The radiation is absorbed by the 
fluorescent layer of the panel and electrons or holes are generated in the 
fluorescent layer in proportion to the amount of the absorbed radiation. 
The electrons or holes are stored in the traps of the phosphors of the 
present invention. The radiation image stored in the panel is converted to 
visible radiation upon stimulation with a stimulating radiation beam. 
Means for stimulating said panel with visible or infrared radiations are 
known in the art to include stimulating radiation sources emitting in the 
infrared or visible field, such as for example, respectively, a 0.06 mW QJ 
Lamp emitting at 800 nm or a He-Ne laser emitting a laser beam at 633 nm, 
as described in U.S. Pat. No. 4,239,968. A scanner apparatus allows the 
fluorescent layer of the panel to be scanned with stimulating radiations 
emitted by a light source, as described in U.S. Pat. No. 4,258,264. 
Focusing means allow said stimulating light to be focused on the panel in 
a small spot (such as 0.7 mm.sup.2), as described in U.S. Pat. No. 
4,258,264. The electrons or holes stored in the traps of the 
photostimulable phosphors are expelled therefrom, and the radiation image 
stored in the panel is released as fluorescent light. 
The luminescence of the fluorescent light emitted by the panel is 
proportional to the number of the electrons or holes stored in the 
fluorescent layer of the panel, that is to the amount of the radiation 
absorbed therein. 
Means for detecting said fluorescent light emitted by the panel are known 
in the art to include: (a) interference filter means, whose transmission 
peak is tuned to the wavelength of the signal emitted by the sample to 
filter-out the unwanted stimulating light (such as e.g. a BG1 or BG3 
Schott filter); (b) optical means to collect the light emitted by the 
panel such as for example light guide members having a linear or arcuate 
end portion to be located adjacent to a scan line of the photostimulable 
phosphor to receive and guide the light emitted by the phosphor and an 
anular end portion to be located adjacent to the light receiving face of 
the photodetector, such as described in U.S. Pat. No. 4,346,295. Useful 
optical means to collect the light emitted by the panel are also 
represented by elliptical mirrors having the concave side turned towards 
the panel and on opening for the passage of said stimulating radiation, as 
described in European Patent Application S.N. 210,505; (c) the combination 
of a photosensor with a photomultiplier to detect and convert the 
fluorescent light into electrical signals (such as e.g. a Thorn Emi 9635 
QB photomultiplier); (d) a picoammeter for the amplification of the signal 
(such as e.g. and EG & G Parc Model 181 amplifier) and (e) evaluation 
means to evaluate the obtained electrical signal (corresponding to the 
original high energy radiation image), such as e.g. a data analyzer. 
The radiation image storage panel of the above described apparatus has a 
fluorescent layer comprising, as a stimulable phosphor, at least one 
phosphor selected in the group consisting of green-emitting trivalent 
erbium activated barium ytterbium halides, trivalent erbium activated 
barium fluorohalides and solid solutions thereof, optionally comprising an 
alkali metal halide. 
BaFX (X=Cl or Br) is a typical host for Eu.sup.2+, which gives a 
bell-shaped blue-UV emission band with a maximum depending upon the nature 
of X. On the contrary the barium fluorohalide, the barium ytterbiumhalide 
and the solid solutions thereof activated with erbium, optionally 
containing an alkali metal halide show a green emission with a maximum 
between 500 and 600 nm. 
The storage capability of the BaFX phosphors is believed to be due to the 
hole trapping at Eu.sup.2+ sites and to electron trapping at F.sup.+ 
centers with respective formation of Eu.sup.3+ and F centers. 
Photostimulation with visible or infrared light is believed to release 
electrons from F-centers (F.fwdarw.F.sup.+ +e.sup.-) promoting their 
recombination with holes at Eu.sup.3+ with consequent emission of light 
(Eu.sup.3+ +e.sup.- .fwdarw.Eu.sup.2+ +hv). 
In agreement with this model, the efficiency of storage capability is 
enhanced by increasing the concentration of F.sup.+ centers (and of course 
of Eu.sup.2+ ions, in a certain range). 
The storage capability of the phosphors of the present invention, as a 
preliminary hypothesis, is believed to be due to the hole trapping at 
Yb.sup.2+ (as Yb at least at low concentration can be reasonable supposed 
in the divalent state, due to its low reduction potential) and to the 
electron trapping at anion vacancy centers. However increasing Yb 
concentration, the probability that it takes the 3+ valence state 
increases as well. In this condition, Yb.sup.3+ could compete with anion 
vacancies for electron trapping. The optical stimulability reaches a 
maximum versus Yb concentration, in agreement with this preliminary 
theory. 
In particular, the radiation image storage panel of the apparatus above has 
a fluorescent layer comprising, as a stimulable phosphor, at least one 
phosphor represented by the formula: 
EQU (1-y)BaFX.yBaYb.sub.n X.sup.I.sub.m X.sup.II.sub.o.aMX.sup.III :zEr(I) 
wherein X is Cl, Br, or I, X.sup.I and X.sup.II, the same or different, are 
F, Cl, Br or I, X.sup.III is Cl of F, M is an element selected from the 
group of Li, Na, K, Rb and Cs; n is 1 or 2 and m+o is 5 or 8, 
0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.0.2, 0.ltoreq.a.ltoreq.0.5. 
More preferably, said panel comprises at least one phosphor represented by 
the following general formula: 
EQU (1-y)BaFX.yBaYbX.sup.I.sub.m X.sup.II.sub.O.aMX.sup.III :zEr(II) 
wherein X is Cl, Br, or I, X.sup.I and X.sup.II, the same or different, are 
F, Cl, Br, or I, X.sup.III is Cl or F, M is an element selected from the 
group of Li, Na, K, Rb and Cs; m+o is 5, 0.ltoreq.y.ltoreq.1, 
0.ltoreq.z.ltoreq.0.2, 0.ltoreq.a.ltoreq.0.5. 
The phosphor of the present invention, as defined in the general formulas 
(I) and (II) described above, is characterized in that the fluorescent 
light emitted upon stimulation by electromagnetic radiation has a 
wavelength higher than 500 nm, preferably in the range of from 500 to 600 
nm. 
Furthermore, it has been found that the luminescence of the fluorescent 
light emitted by the stimulable phosphors of the present invention tends 
to be higher than that of any other known storage europium activated 
barium fluorohalide phosphor, when stimulated by electromagnetic radiation 
having wavelength in the range from 500 to 1100 nm, preferably of from 700 
to 1100. 
In fact, while the photostimulable europium activated barium fluorohalide 
phosphors known in the art do not exhibit a significant emission when 
stimulated by an infrared stimulating radiation, the light emitted by the 
phosphors of the present invention exhibits a significant fluorescence 
even when the phosphor is stimulated with radiations in the infrared 
region of the electromagnetic spectrum. 
The above mentioned phosphors of the present invention are thermally 
processed. 
Such thermal processing includes heating which can be performed in the 
presence of a salt acting as a "flux" (such as ammonium chloride, sodium 
carbonate, and the like), at a temperature in the range of 600.degree. to 
1000.degree. C., preferably 700.degree. to 900.degree. C., and cooling at 
room temperature before the obtained phosphors are repeatedly washed with 
water to be purified. Heating can be performed with a mechanical mixture 
of the reagents in a crucible in the air or inert gas atmosphere, e.g. 
argon, for a time ranging from 1 to 10, preferably from 1 to 5 hours. 
The radiation image storage panels of the present invention normally 
comprise a fluorescent layer including a binder and, dispersed therein, at 
least one phosphor of the present invention. The fluorescent layer is 
formed by dispersing the phosphor in the binder to prepare a coating 
dispersion, and then applying the coating dispersion according to 
conventional coating methods to form a uniform layer. Although the 
fluorescent layer itself can be a radiation image storage panel when the 
fluorescent layer is self-supporting, the fluorescent layer is generally 
provided on a substrate to form a radiation image storage panel. Further, 
a protective layer is usually provided on the surface of the fluorescent 
layer for physically and chemically protecting the fluorescent layer. 
Furthermore, a primer layer is sometimes provided between the fluorescent 
layer and the substrate for closely binding the fluorescent layer to the 
substrate. 
As the binder employed in the fluorescent layer of the radiation image 
storage panel of the present invention, there can be used for example 
those binders commonly used for forming layers, such as gum arabic, 
proteins such as gelatin, polysaccharides such as dextrane, organic 
polymer binders such as polyvinylbutyral, polyvinylacetate, 
nitrocellulose, ethylcellulose, ethylcellulose, 
vinylidene-chloride-vinylchloride copolymers, polymethyl-methacrylate, 
polybutylmethacrylate, vinylchloride-vinylacetate copolymers, 
polyurethane, cellulose acetate-butyr-ate, polyvinyl alcohol, and the 
like. 
Generally, the binder is used in an amount of 0.01 to 1 part by weight per 
one part by weight of the phosphor. However, from the viewpoint of 
sensitivity and sharpness of the panel obtained, the amount of the binder 
should preferably be small. Accordingly, in consideration of both the 
sensitivity and sharpness of the panel and the easiness of application of 
the coating dispersion, the binder is preferably used in an amount of 0.03 
to 0.2 parts by weight per one part by weight of the stimulable phosphor. 
The thickness of the fluorescent layer is generally within the range of 10 
.mu.m to 1 mm. 
In the radiation image storage panel of the present invention, the 
fluorescent layer is generally coated on a substrate. As the substrate, 
various materials such as polymer material, glass, wool, cotton, paper, 
metal, or the like can be used. From the viewpoint of handling the panel 
as an information recording medium, the substrate should preferably be 
processed into a sheet or flexible roll. In this connection, as the 
substrate is preferable an organic polymeric film such as a cellulose 
acetate film, polyester film, polyethylene-terephthalate film, polyamide 
film, triacetate film, polycarbonate film, or the like, or ordinary paper, 
or processed paper such as a photographic paper, baryta paper, resincoated 
paper, paper which contains a pigment such as titanium dioxide, or the 
like. The substrate may have a primer layer on one surface thereof (the 
surface on which the fluorescent layer is provided) for the purpose of 
holding the fluorescent layer tightly. As the material of the primer 
layer, an ordinary adhesive can be used. In providing a fluorescent layer 
on the substrate or on the primer layer, a coating dispersion comprising 
the phosphor dispersed in a binder may be directly applied to the 
substrate or to the primer layer to form the fluorescent layer. 
Alternatively, a fluorescent layer formed be-forehand may be bound to the 
substrate or to the primer. Where the substrate used is permeable to the 
stimulating radiations of the phosphor, the radiation image storage panel 
can be exposed to the stimulating radiation from the substrate side. 
Further, in the radiation image storage panel of the present invention, a 
protective layer for physically and chemically protecting the fluorescent 
layer is generally provided on the surface of the fluorescent layer 
intended for exposure (on the side opposite the substrate). When, as 
mentioned above, the fluorescent layer is self-supporting, the protective 
layer may be provided on both surfaces of the fluorescent layer. The 
protective layer may be provided on the fluorescent layer by directly 
applying thereto a coating dispersion to form the protective layer 
thereon, or may be provided thereon by bonding thereto the protective 
layer formed beforehand. As the material of the protective layer, a 
conventional material for a protective layer such as nitrocellulose, 
ethylcellulose, cellulose acetate, polyester, polyethyleneterephthalate, 
and the like can be used. The radiation image storage panel of the present 
invention may be colored with a colorant. Further, the fluorescent layer 
on the radiation image storage panel of the present invention may contain 
a white powder dispersed therein. By using a colorant or a white powder, a 
radiation image storage panel which provides a very sharp image can be 
obtained.

The present invention will be described with more details referring to the 
following examples. 
Approximations in expressions of the numerical values which indicate the 
molar fractions are the cause of approximation in the numerical value 
expressing the sum thereof (in some cases 0.9999,- in other cases 0.9998-, 
rather than 1.0000). 
EXAMPLE 1 
Preparation of the phosphor shown as compound 11 in the following table 1 
0.997BaFCl.0.003Er.sup.3+ 
A mixture consisting of 4.571 g of BaF.sub.2, 5.429 g of BaCl.sub.2, and 
0.04036 g of ErCl.sub.3 was put in a silica reaction vessel and then 
heated at a temperature of 800.degree. C. for 2 hours in inert atmosphere. 
The obtained phosphor was then left to cool in the air to room 
temperature, pulverized, sieved in cold water and dried at 150.degree. C. 
Compound 1 of Table 1 was prepared in the same way by using the appropriate 
amount of ingredients. 
EXAMPLE 2 
Preparation of the phosphor shown as compound 12 in the following table 1 
0.9854BaFCl.0.0115BaYbFCl.sub.4 :0.003Er.sup.3+ 
A mixture consisting of 4.478 g of BaF.sub.2, 5.318 of BaCl.sub.2, 0.1645 g 
of YbCl.sub.3 and 0.0397 g of ErCl.sub.3 was put in a silica reaction 
vessel and then heated at a temperature of 800.degree. C. for 2 hours in 
inert atmosphere. The obtained phosphor was then left to cool in the air 
to room temperature, pulverized, sieved in cold water and dried at 
150.degree. C. 
Compounds 2 to 9, 13, 14, and 16 of Table 1 were prepared in the same way 
by using the appropriate amount of ingredients. 
EXAMPLE 3 
Preparation of the phosphor shown as compound 10 in the following table 1 
0.9997BaYbFCl.sub.4 :0.0003Er.sup.3+ 
A mixture consisting of 1.8607 g of BaF.sub.2, 5.9273 g of YbCl.sub.3 and 
0.0016 g of ErCl.sub.3 was put in a silica reaction vessel and then heated 
at a temperature of 800.degree. C. for 2 hours in inert atmosphere. The 
obtained phosphor was then left to cool in the air to room temperature, 
pulverized, sieved in cold water and dried at 150.degree. C. 
Compounds 15 and 17 of Table 1 were prepared in the same way by using the 
appropriate amount of ingredients. 
EXAMPLE 4 
Preparation of the phosphor shown as compound 25 in the following table 1 
0.9639BaFCl.0.0331NaCl:0.003Er.sup.3+ 
A mixture consisting of 4.505 g of BaF.sub.2, 5.351 g of BaCl.sub.2, 0.1027 
g of NaCl and 0.0413 g of ErCl.sub.3 was put in a silica reaction vessel 
and then heated at a temperature of 800.degree. C. for 2 hours in inert 
atmosphere. The obtained phosphor was then left to cool in the air to room 
temperature, pulverized, sieved in cold water and dried at 150.degree. C. 
Compound 18 of Table 1 was prepared in the same way by using the 
appropriate amount of ingredients. 
EXAMPLE 5 
Preparation of the phosphor shown as compound 26 in the following table 1 
0.9522BaFCl.0.01114BaYbFCl.sub.4.0.0337NaCl:0.003Er.sup.3+ 
A mixture consisting of 7.4310 g of BaF.sub.2, 5.2626 g of BaCl.sub.2, 
0.1033 g of NaCl, 0.1626 g of YbCl.sub.3 and 0.0406 g of ErCl.sub.3 was 
put in a silica reaction vessel and then heated at a temperature of 
800.degree. C. for 2 hours in inert atmosphere. The obtained phosphor was 
then left to cool in the air to room temperature, pulverized, sieved in 
cold water and dried at 150.degree. C. 
Compounds 19 to 24, 27, and 29 of Table 1 were prepared in the same way by 
using the appropriate amount of ingredients. 
EXAMPLE 6 
Preparation of the phosphor shown as compound 28 in the following table 1 
0.9159BaYbFCl.sub.4.0.0812NaCl:0.003Er.sup.3+ 
A mixture consisting of 1.837 g of BaF.sub.2, 2.181 g of BaCl.sub.2, 0.1085 
g of NaCl, 5.855 g of YbCl.sub.3 and 0.0177 g of ErCl.sub.3 was put in a 
silica reaction vessel and then heated at a temperature of 800.degree. C. 
for 2 hours in inert atmosphere. The obtained phosphor was then left to 
cool in the air to room temperature, pulverized, sieved in cold water and 
dried at 150.degree. C. 
TABLE 1 
______________________________________ 
Phos- 
phor 
Sample 
Formula 
______________________________________ 
1 0.99997 BaFCl.0.00003 Er.sup.3+ 
2 0.9988 BaFCl.0.0012 BaYbFCl.sub.4 :0.00003 Er.sup.3+ 
3 0.9884 BaFCl.0.0116 BaYbFCl.sub.4 :0.00003 Er.sup.3+ 
4 0.942 BaFCl.0.0058 BaYbFCl.sub.4 :0.00003 Er.sup.3+ 
5 0.884 BaFCl.0.116 BaYbFCl.sub.4 :0.00003 Er.sup.3+ 
6 0.9985 BaFCl.0.0012 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
7 0.9881 BaFCl.0.011 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
8 0.9417 BaFCl.0.0579 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
9 0.8837 BaFCl.0.1159 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
10 0.9997 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
11 0.997 BaFCl.sub.4 :0.0003 Er.sup.3+ 
12 0.9854 BaFCl.0.011 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
13 0.9392 BaFCl.0.0578 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
14 0.8810 BaFCl.0.1156 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
15 0.997 BaYbFCl.sub.4 :0.003 Er.sup.3+ 
16 0.8575 BaFCl.0.1185 BaYbFCl.sub.4 :0.0003 Er.sup.3+ 
17 0.97 BaYbFCl:0.03 Er.sup.3+ 
18 0.9679 BaFCl.0.0321 NaCl:0.00003 Er.sup.3+ 
19 0.9551 BaFCl.0.0112 BaYbFCl.sub.4.0.0337 NaCl:0.00003 Er.sup.3+ 
20 0.8497 BaFCl.0.111 BaYbFCl.sub.4.0.0387 NaCl:0.00003 Er.sup.3+ 
21 0.9653 BaFCl.0.0012 BaYbFCl.sub.4.0.0332 NaCl:0.0003 Er.sup.3+ 
22 0.9548 BaFCl.0.0112 BaYbFCl.sub.4.0.0337 NaCl:0.0003 Er.sup.3+ 
23 0.9078 BaFCl.0.0558 BaYbFCl.sub.4.0.0359 NaCl:0.0003 Er.sup.3+ 
24 0.8494 BaFCl.0.1114 BaYbFCl.sub.4.0.0387 NaCl:0.0003 Er.sup.3+ 
25 0.9639 BaFCl.0.0331 NaCl:0.003 Er.sup.3+ 
26 0.9622 BaFCl.0.01114 BaYbFCl.sub.4.0.0337 NaCl:0.003 Er.sup.3+ 
27 0.8469 BaFCl.0.11114 BaYbFCl.sub.4.0.0387 NaCl:0.003 Er.sup.3+ 
28 0.9159 BaYbFCl.0.0838 NaCl.sub.4 :0.003 Er.sup.3+ 
29 0.825 BaFCl.0.1082 BaYbFCl.sub.4.0.0385 NaCl:0.03 
______________________________________ 
Er.sup.3+ 
EXAMPLE 7 
Samples of phosphors of Table 1 were exposed to 40 KVp and 30 mA X-ray 
radiation for 5 seconds. After 2 minutes they were then stimulated with a 
633 nm light beam, which was obtained by causing the light to be emitted 
by a 0.7 mV He-Ne laser and passed through a Melles-Griot type FIL026 
filter. The light power was 0.017 .mu.W/cm.sup.2 as measured by a EG&G 
Parc Model 450 radiometer. Stimulation was performed for 60 seconds, with 
shot of 1 second, by using a Programmable Shutter Supply (Ealong). 
Photostimulated light emitted by the phosphor was collected by a 
green-sensitive photomultiplier (Emi Thorn 9635 QB type) and converted 
into electrical signals. Light collection was performed by using an 
interference optical filter (Schott TVM1.5 type) collecting light in the 
blue-green range of wavelength, provided with two gray filters, i.e., 
Melles-Griot FIL007 (D=0.3) and FIL015 (D=0.5). 
The electrical signal was amplified by the combination of an EG&G Parc 
Model 181 pre-amplifier and an EG&G Parc Model 113 amplifier. The signal 
was then evaluated by a Data Precision 6000, Division Analogic Corp., data 
analyser. 
EXAMPLE 8 
Samples of phosphors of table 1 were exposed to X-ray radiations as 
described in Example 7, with the only difference that the phosphors were 
stimulated with a 800 nm light beam obtained by causing such light to be 
emitted by a QJ Lamp (Osram, HLX-64625-FCR) and passed through 
Melles-Griot type FIL007 plus FIL015 and Schott RG850 filters. The light 
power was 0.2 .mu.W/cm.sup.2 measured as above. 
EXAMPLE 9 
The following Table 2 reports the photostimulated emitted light emission 
values of the phosphors of table 1, processed as described in Examples 7 
and 8. In comparison a sample of BaFCl:0.0001Eu.sup.2+ phosphor (Sample 
30) described in the art was evaluated under the same conditions with the 
exception that an interference optical filter (Schott BG3) collecting 
light in the UV-blue range of wavelength was used and that the data read 
by the photomultiplier were corrected for different sensitivity. 
In Table 2, the emission efficiency value of the reference phosphor 
(compound 5) has been normalized to 100 in both the cases of 633 and 800 
nm stimulation. This does not mean that the emission efficiency value of 
such phosphor when stimulated at 633 nm is equal to the emission 
efficiency value of the same phosphor when stimulated at 800 nm. 
The emission efficiency values of comparison sample 30 do not mean that 
this sample has a superior result, because the emission light is measured 
at different wavelength. These values means that the phosphors of the 
present invention show a blue-green emission comparable to the UV-blue 
emission of the comparison sample 30, which does not show a significant 
emission at wavelength higher than 400 nm. 
TABLE 2 
______________________________________ 
Emission efficiency 
Sample 633 800 
______________________________________ 
1 125 135 
2 127 138 
3 140 150 
4 155 175 
5 100 100 
6 77 84 
7 100 100 
8 125 125 
9 80 60 
10 4 0.6 
11 15 25 
12 48 44 
13 80 75 
14 21 16 
15 6 0.8 
16 41 25 
17 0.1 0.4 
18 220 450 
19 230 530 
20 200 500 
21 136 390 
22 197 460 
23 225 540 
24 190 450 
25 76 263 
26 140 310 
27 103 172 
28 30 5 
29 130 200 
30 52 156 
______________________________________ 
EXAMPLE 10 
Preparation of the phosphor shown as compound 33 in the following table 3 
0.97BaYbF.sub.5 :0.03Er.sup.3+ 
A mixture consisting of 4.2526 g of BaF.sub.2, 5.5793 g of YbF.sub.3 and 
0.1682 g of ErF.sub.3 was put in a silica reaction vessel and then heated 
at a temperature of 800.degree. C. for 2 hours in inert atmosphere. The 
obtained phosphor was then left to cool in the air to room temperature, 
pulverized, sieved in cold water and dried at 150.degree. C. 
Compounds 31 and 32 of Table 3 were prepared in the same way by using the 
appropriate amount of ingredients. 
EXAMPLE 11 
Preparation of the phosphor shown as compound 36 in the following table 3 
0.8771BaYbF.sub.5.0.0958NaF:0.027Er.sup.3+ 
A mixture consisting of 4.2482 g of BaF.sub.2, 0.0111 g of NaF, 5.5734 g of 
YbF.sub.3 and 0.1673 g of ErF.sub.3 was put in a silica reaction vessel 
and then heated at a temperature of 800.degree. C. for 2 hours in inert 
atmosphere. The obtained phosphor was then left to cool in the air to room 
temperature, pulverized, sieved in cold water and dried at 150.degree. C. 
Compounds 34 and 35 of Table 3 were prepared in the same way by using the 
appropriate amount of ingredients. 
TABLE 3 
______________________________________ 
Phosphor 
Sample Formula 
______________________________________ 
31 0.9997 BaYbF.sub.5 :0.0003 Er.sup.3+ 
32 0.997 BaYbF.sub.5 :0.0003 Er.sup.3+ 
33 0.97 BaYbF.sub.5 :0.0003 Er.sup.3+ 
34 0.8995 BaYbF.sub.5.0.0975 NaF:0.0003 Er.sup.3+ 
35 0.8999 BaYbF.sub.5.0.0973 NaF:0.0003 Er.sup.3+ 
36 0.8771 BaYbF.sub.5.0.0958 NaF:0.0003 Er.sup.3+ 
______________________________________ 
EXAMPLE 12 
Samples of phosphors of table 3 were exposed to X-ray radiations as 
described in Examples 7 and 8. 
EXAMPLE 13 
The following Table 4 reports the photostimulated emitted light emission 
values of the phosphors of table 3, processed as described in Example 12. 
TABLE 4 
______________________________________ 
Emission Efficiency 
Sample 633 800 
______________________________________ 
31 0.3 0.1 
32 0.6 0.14 
33 0.7 0.16 
34 0.5 4 
35 1 5 
36 1.2 7 
______________________________________ 
The results of emission efficiency of table 4 are comparable with the data 
of table 2. In particular compounds 31, 32, and 33 can be compared with 
compounds 10, 15, and 17 having a similar composition, and compound 35 can 
be compared with compound 28.