CA1059747A - Method of producing a luminescent alkaline earth metal fluorohalide activated by bivalent europium - Google Patents
Method of producing a luminescent alkaline earth metal fluorohalide activated by bivalent europiumInfo
- Publication number
- CA1059747A CA1059747A CA236,769A CA236769A CA1059747A CA 1059747 A CA1059747 A CA 1059747A CA 236769 A CA236769 A CA 236769A CA 1059747 A CA1059747 A CA 1059747A
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- Canada
- Prior art keywords
- europium
- alkaline earth
- temperature
- suspension
- fluorohalide
- Prior art date
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
- C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
- C09K11/7732—Halogenides
- C09K11/7733—Halogenides with alkali or alkaline earth metals
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Luminescent Compositions (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
ABSTRACT:
Method of preparing a luminescent alkaline earth metal fluoroilalide activated by Eu2+ defined by the formula Me1-pEupFX (Me = Ba, Sr; X = Cl, Br, I;
0.001 ? p ? 0.20). MeF2 is suspended in water after which 1 mole of MeX2 per mole of MeF2 is dissolved in the suspension. The suspension, which may already contain europium, is evaporated to dryness at 50°C to 250°C.
The obtained product is mixed with the additional re-quired amount of europium in the form of a europium halide and then is subjected to at least one temperature treatment at 600°C to 1000°C in a weakly reducing atmos-phere. The obtained reaction product is subjected, pos-sibly after being ground, to a final heating at 600°C
to 850°C in an inert or weakly reducing atmosphere.
Method of preparing a luminescent alkaline earth metal fluoroilalide activated by Eu2+ defined by the formula Me1-pEupFX (Me = Ba, Sr; X = Cl, Br, I;
0.001 ? p ? 0.20). MeF2 is suspended in water after which 1 mole of MeX2 per mole of MeF2 is dissolved in the suspension. The suspension, which may already contain europium, is evaporated to dryness at 50°C to 250°C.
The obtained product is mixed with the additional re-quired amount of europium in the form of a europium halide and then is subjected to at least one temperature treatment at 600°C to 1000°C in a weakly reducing atmos-phere. The obtained reaction product is subjected, pos-sibly after being ground, to a final heating at 600°C
to 850°C in an inert or weakly reducing atmosphere.
Description
PHN 77~0 597~
The invention relates to a method of preparing a luminescent alkaline earth metal fluorohalide activated by bivalent europium. The invention further relates to the resulting alkaline earth metal fluorohalide and to an X-ray image intensifier screen provided with a lu-minescent alkaline earth metal fluorohalid made in such manner.
The said alkaline earth metal fluorohalides may be defined by the general formula MeFX, where Me represents one or more of the alkaline earth metals Ba and Sr, and X represents one or more of the halogens Cl, Br and I. The crystal structure of these materials is known as the PbFCl structure and has a tetragonal symmetry. It is known from our Canadian Patent 1,003,206 wh;ch ;ssued on January 11, 1977, that these fluorohalldes are highly efficient luminescent materials when act;vated by bivalent europium. The europium then replaces part of the alkaline earth metal in the fluorohalide base lattice. These known luminescent fluorohalides can be verY satisfactorily excited both by ultraviolet radiation and by electrons and X-rays. The spectral distribution of the emitted radiation consists of a narrow band (half-Yalue width approximately 30 nm) with a maximum
The invention relates to a method of preparing a luminescent alkaline earth metal fluorohalide activated by bivalent europium. The invention further relates to the resulting alkaline earth metal fluorohalide and to an X-ray image intensifier screen provided with a lu-minescent alkaline earth metal fluorohalid made in such manner.
The said alkaline earth metal fluorohalides may be defined by the general formula MeFX, where Me represents one or more of the alkaline earth metals Ba and Sr, and X represents one or more of the halogens Cl, Br and I. The crystal structure of these materials is known as the PbFCl structure and has a tetragonal symmetry. It is known from our Canadian Patent 1,003,206 wh;ch ;ssued on January 11, 1977, that these fluorohalldes are highly efficient luminescent materials when act;vated by bivalent europium. The europium then replaces part of the alkaline earth metal in the fluorohalide base lattice. These known luminescent fluorohalides can be verY satisfactorily excited both by ultraviolet radiation and by electrons and X-rays. The spectral distribution of the emitted radiation consists of a narrow band (half-Yalue width approximately 30 nm) with a maximum
- 2 - ~
", ),.
~ P~IN 7740 1~59747 at approximately 380 nm. For the materials which contain a considerable quantity of iodine the emission maximum is shifted to longer wavelengths. Notably for the fluoro-iodide this maximum is found at approximately 410 nm. It was found that in these materials up to 20 mole % of the Ba and Sr represented by Me can be replaced by Ca whilst retaining the crystal structure.
An important use of the known fluorohalides activated by b;valent europium is found in the so-called X-ray image intensifier screens. Such intensifier screens comprise a material which luminesces under X-ray radiation and serve to shorten the exposure time when taking X-ray images on photographic material. In general they take the form of film cassettes which contain a support coated with the luminescent material which is in con-tact with the photographic film when taking the X-ray image. The known luminescent fluorohalides when excit-ed by X-rays have a very high luminous flux which may be up to five times that of the known calcium tungstate which is frequently used in X-ray image intensifier ; screens.
The above-mentioned Canadian Patent 1,003,206 describes a method of manufacturing the fluorohalides activated by bivalent europium, starting from a dry mixture of halides (for example alkaline earth metal chloride, alkaline earth metal fluoride and europium fluoride) which by a reaction ~597~'7 at a high temperature is conver~ed into the desired fluorohalide. It has also been found possible to start from a mixture of oxides or carbonates of the alkaline earth metals and of europium together with ammonium halides.
A serious disadvantage of the luminescent fluorohalides obtained in the aforedescribed manner is that they have a high persistence level. This means that these substances have a comparatively high-in-tensity afterglow for a comparatively long time on ces-sation of the excitation. For these materials the said persistence level may, for example, be 20 to 100 times that of the known calcium tungstate. Persistence of the luminescent material in an intensifier screen is particularly objectionable because for some time after exposure each movement of the screen relative to the photographic film (when opening film cassettes) results in blurred images. An even more serious draw-back is that owing to the persistence considerable waiting periods must be observed before a new film can be placed in the cassette.
~nited Kingdom Patent Specification 1,254,271 describes a method of preparing alkaline earth metal fluorohalides in which these materials are obtained by precipitation from solutions. During the precipi-tation a solution containing alkaline earth metal cations, for example an alkaline earth metal chloride, 3L~5974~7 and a solution containing the fluorine anions, for example hydrogen fluoride, potassium fluoride or ammo-nium fluoride, are added to the reaction vessel. It has now been found that if alkaline earth metal fluorohalides activated by bivalent europium are prepared by this ; method, materials are obtained which have a very high afterglow level.
It is an object of the present invention t~
provide a method of preparing fluorohalides activated by bivalent europium by which materials having a very low afterglow level are obtained.
A method according to the invention of pre-paring a luminescent alkaline earth metal fluorohalide activated by bivalent europium and defined by the for-mula Mel pFupFX, where Me represents at least one of the alkaline earth metals Ba and ~r whilst up to 20 mole% of these metals can be replaced by Ca, X re-presents at least one of the halogens Cl, Br and I
and 0.001 _ p C 0.20, is characteri~ed in tha~ an aqueous suspension of MeF2 is made which contains 1 mole of MeX2 in dissolved form per mole MeF2 and may further contain europium in the form-of europium halide in an amount at most equal to the amount desired in the fluorohalide, in that the suspension is evaporat-ed to dryness at a temperature from 50C to 250C, the resulting product is mixed with the amount of europium halide which still may be required, the mixture is sub-~C~597~
jected to at least one temperature treatment at 600C to 1000C in a weakly reducing atmosphere and the obtained reaction product, after cooling, is subjected to a final heating at a temperature of 600C to 850C in an inert or weakly reducing atmosphere.
A method according to the invention starts from an aqueous suspension of MeF2, i.e. a mixture of fine-grained MeF2, which is substantially insoluble in water, and an aqueous dissolving medium. Prior or subsequent to the preparation of this suspension MeX2 is dissolved in the dissolving medium in the stoichio-metric amount of 1 mole per mole of the MeF2 used.
Small deviations from the stoichiometry are found to be permissible and in general have little effect on the properties of the fluorohalide obtained. When preparing this suspension the required amount of europium can entirely or partly be added either as insoluble EuF3 or as soluble EuX3. The suspension then ;s evaporated to dryness at a temperature of 50C to 250C. X-ray diffraction analyses show that the obtained product already has the characteristic PbFCl structure, and this product is mixed with the amount of europium which still may be required in the form of europium halide. The mixture is subjected to one or more temperature treatments at 600C to 1000C
in a weakly reducing atmosphere. During this treatment the already incorporated europium is reduced to the ~6:)5~7~7 bivalent state and/or the admixed europium is incorporated as bivalent europium in the crystal lattice. The result-ing reaction product is subiected to a final heating at 600C to 850C in an inert or weakly reducing at-mosphere to improve the crystal structure and to ob-tain optimum grain size of the powder.
Formation of the fluorohalide compound, in-corporation of europium in the desired bivalent state and recrystallization of the obtained pulverulent product take place separately and successively in a method according to the invention. This is highly ad-vantageous, because thus these three steps in the pre-paration can separately be optimized and a luminescent material having optimum luminescence properties can be obtained. In particular, with respect to the afterglow level it proves to be an essential requirement that the fluorohalide compound is formed at a comparatively low temperature (during evaporation to dryness at 50C
to 250C). It is assumed that under these cond;tions the incorporation of traces of oxygen which may be the cause of a h;gh afterglow level is avoided as far as possible.
It was -found that by means of a method ac-cording to the invention a luminescent fluorohalide is obtainable the afterglow level of which has been reduced to an amount about equal to that of the known calcium tungstate. It was further found that, in com-~L135~7~7 .
par;son to the fluorohalide prepared in the known man-ner, the luminous flux obtained by the said materials when excited by X-rays has the same high value or even a higher value.
Although it is possible to add the desired amount of the europium activator in its entirety to the suspension in the form of EuX3 or EuF3, a method according to the invention is preferred ;n which the suspension contains no europium at all, p moles of EuX3 being added per mole of the MeFX obtained by evaporation to dryness, for it has been found that the best results are obtained, in particular in respect of the afterglow level, if a europium halide (except the fluoride) is used as the activator compound and if this activator compound is added after the synthesis of the fluoro-halide compound.
It was found to be of advantage for the reaction product obtained after the temperature treatment at 600C to 1000C in a weakly reducing at-mosphere to be ground before it is subjected to the final heat;ng, for if the conditions during the tem-~ perature treatment are optimized for the incorporation ; of bivalent europium in many cases a reaction product may be formed which is too coarse-grained for practical uses. Any deleterious effect of the grinding operation on the afterglow level is entirely eliminated by the final heating.
5~747 The most important use of the fluorohalides activated by bivalent europium is found, as mentioned hereinbefore, in X-ray image intensifier screens. Ad-vantageously the element Me then is barium because this gives the highest luminous fluxes on excitation by X-rays. For obtaining high luminous fluxes upon X-ray ex-citation it is also advantageous to use bromine for the element X. It was found, however, that the afterglow level of BaFBr is high compared with that of BaFCl.
1~ For example, the BaFBr prepared in known manner has an afterglow level which is up to 100 times that of calcium tungstate. A method according to the invention enables this level to be reduced to a few times that of calcium tungsta~e. The best combination of a low afterglow level and a high luminous flux is obtained with materials of the formula Bal pEupFCl. Hence a method according to the invention for preparing such materials is preferred.
In a preferred embodiment of a method ac-cording to the invention in which Bal pEupFCl is pre-pared, evaporation to dryness is performed at a tem-perature of 160C to 180C, for under these conditions the formation of the BaFCl is optimal.
When preparing Bal pEupFCl the best results are further obtained if the temperature treatment is effected at a temperature of 800C to 950C in nitro-gen containing from 0.1 to 1 volume percent of hydrogen ~13597~7 and if the final treatment is performed at a temperature of 700C to 800C in nitrogen. Hence these conditions are preferred.
The invention will now be described more fully ; 5 with reference to a few Examples of preparation.
Example 1.
An amount of 8.765 9 of BaF2 is added to water and suspended by st;rring. 12.240 9 of BaC12.2H20 are dissolved in this suspension. The suspension then is evaporated to dryness at a temperature of 170C. The' resulting substance consists of BaFCl and, as is shown by X-ray diffraction analyses, has the PbFCl structure.
The BaFCl is mixed with 1.374 9 oAF EuC13 and then heat-ed in a quartz crucible'at 900C in a furnace in a weakly reducing atmosphere for 1 hour. The said at-mosphere is obtained by passing a stream of nitrogen ~about 137 1 per h~ur) containing 0.7 volume percent of hydrogen into the furnace. After cooling the result-ing product is ground in a ball mill.' Then the product is subjected to final heating at 750C in a nitrogen stream (about 18 1 per hour) for 1 hour. After cooling, the product, which has a composition defined by the formula BaO 95Euo 05FCl, is ready for use-In order to compare the luminescence pro-perties on excitation by X-rays of the material ob~
tained according to the above Example of preparation which those of the known CaW04, screens are manufactured ~0597~7 using the said material and identical screens which, however, contain calcium tungstate in the same amounts by weight. A photographic film is brought into contact with these screens. Then the film density rate is measured under standard conditions (primary voltage of the X-ray tube; distance of the X-ray tubè from the screen and the filmi filters). The fluorohalide prepar-ed by the method according to the invention proves to have a rate which is 7 times that of the known CaWO~.
The afterglow level of the fluorohalide also is measured and compared with that of CaW04. For this purpose the screens are exposed to X-rays for some time (under standard conditions). One minute after cessation of the excitation a photographic film is placed on the screen and held in contact with it for 5 minutes.
The film density measured, which is a measure of the afterglow level, proves to be equal for the fluoro-halide and for the CaW04.
Example 2 Example 1 is repeated with the difference that the amount of 1.374g of EuC13 is added to the suspension and dissolved in it. The product obtained is equal to that of Example 1 and has substantially the same luminescence properties.
Example 3 Example 1 is repeated with the difference that the temperature treatment in the weakly reducing 1~59747 atmosphere is performed at 850C for 1 hour. The density rate of the obtained material is found to be 6.3 times that of CaW04 whilst the afterglow level is found to be about twice that of CaW04.
Example 4.
Example 1 is repeated with the difference that the temperature treatment in the weakly reducing atmos-phere is performed at 950C for 1 hour. The density rate of the resulting material is 5.2 times that of CaW04 and the afterglow level is about equal to that of CaW04.
", ),.
~ P~IN 7740 1~59747 at approximately 380 nm. For the materials which contain a considerable quantity of iodine the emission maximum is shifted to longer wavelengths. Notably for the fluoro-iodide this maximum is found at approximately 410 nm. It was found that in these materials up to 20 mole % of the Ba and Sr represented by Me can be replaced by Ca whilst retaining the crystal structure.
An important use of the known fluorohalides activated by b;valent europium is found in the so-called X-ray image intensifier screens. Such intensifier screens comprise a material which luminesces under X-ray radiation and serve to shorten the exposure time when taking X-ray images on photographic material. In general they take the form of film cassettes which contain a support coated with the luminescent material which is in con-tact with the photographic film when taking the X-ray image. The known luminescent fluorohalides when excit-ed by X-rays have a very high luminous flux which may be up to five times that of the known calcium tungstate which is frequently used in X-ray image intensifier ; screens.
The above-mentioned Canadian Patent 1,003,206 describes a method of manufacturing the fluorohalides activated by bivalent europium, starting from a dry mixture of halides (for example alkaline earth metal chloride, alkaline earth metal fluoride and europium fluoride) which by a reaction ~597~'7 at a high temperature is conver~ed into the desired fluorohalide. It has also been found possible to start from a mixture of oxides or carbonates of the alkaline earth metals and of europium together with ammonium halides.
A serious disadvantage of the luminescent fluorohalides obtained in the aforedescribed manner is that they have a high persistence level. This means that these substances have a comparatively high-in-tensity afterglow for a comparatively long time on ces-sation of the excitation. For these materials the said persistence level may, for example, be 20 to 100 times that of the known calcium tungstate. Persistence of the luminescent material in an intensifier screen is particularly objectionable because for some time after exposure each movement of the screen relative to the photographic film (when opening film cassettes) results in blurred images. An even more serious draw-back is that owing to the persistence considerable waiting periods must be observed before a new film can be placed in the cassette.
~nited Kingdom Patent Specification 1,254,271 describes a method of preparing alkaline earth metal fluorohalides in which these materials are obtained by precipitation from solutions. During the precipi-tation a solution containing alkaline earth metal cations, for example an alkaline earth metal chloride, 3L~5974~7 and a solution containing the fluorine anions, for example hydrogen fluoride, potassium fluoride or ammo-nium fluoride, are added to the reaction vessel. It has now been found that if alkaline earth metal fluorohalides activated by bivalent europium are prepared by this ; method, materials are obtained which have a very high afterglow level.
It is an object of the present invention t~
provide a method of preparing fluorohalides activated by bivalent europium by which materials having a very low afterglow level are obtained.
A method according to the invention of pre-paring a luminescent alkaline earth metal fluorohalide activated by bivalent europium and defined by the for-mula Mel pFupFX, where Me represents at least one of the alkaline earth metals Ba and ~r whilst up to 20 mole% of these metals can be replaced by Ca, X re-presents at least one of the halogens Cl, Br and I
and 0.001 _ p C 0.20, is characteri~ed in tha~ an aqueous suspension of MeF2 is made which contains 1 mole of MeX2 in dissolved form per mole MeF2 and may further contain europium in the form-of europium halide in an amount at most equal to the amount desired in the fluorohalide, in that the suspension is evaporat-ed to dryness at a temperature from 50C to 250C, the resulting product is mixed with the amount of europium halide which still may be required, the mixture is sub-~C~597~
jected to at least one temperature treatment at 600C to 1000C in a weakly reducing atmosphere and the obtained reaction product, after cooling, is subjected to a final heating at a temperature of 600C to 850C in an inert or weakly reducing atmosphere.
A method according to the invention starts from an aqueous suspension of MeF2, i.e. a mixture of fine-grained MeF2, which is substantially insoluble in water, and an aqueous dissolving medium. Prior or subsequent to the preparation of this suspension MeX2 is dissolved in the dissolving medium in the stoichio-metric amount of 1 mole per mole of the MeF2 used.
Small deviations from the stoichiometry are found to be permissible and in general have little effect on the properties of the fluorohalide obtained. When preparing this suspension the required amount of europium can entirely or partly be added either as insoluble EuF3 or as soluble EuX3. The suspension then ;s evaporated to dryness at a temperature of 50C to 250C. X-ray diffraction analyses show that the obtained product already has the characteristic PbFCl structure, and this product is mixed with the amount of europium which still may be required in the form of europium halide. The mixture is subjected to one or more temperature treatments at 600C to 1000C
in a weakly reducing atmosphere. During this treatment the already incorporated europium is reduced to the ~6:)5~7~7 bivalent state and/or the admixed europium is incorporated as bivalent europium in the crystal lattice. The result-ing reaction product is subiected to a final heating at 600C to 850C in an inert or weakly reducing at-mosphere to improve the crystal structure and to ob-tain optimum grain size of the powder.
Formation of the fluorohalide compound, in-corporation of europium in the desired bivalent state and recrystallization of the obtained pulverulent product take place separately and successively in a method according to the invention. This is highly ad-vantageous, because thus these three steps in the pre-paration can separately be optimized and a luminescent material having optimum luminescence properties can be obtained. In particular, with respect to the afterglow level it proves to be an essential requirement that the fluorohalide compound is formed at a comparatively low temperature (during evaporation to dryness at 50C
to 250C). It is assumed that under these cond;tions the incorporation of traces of oxygen which may be the cause of a h;gh afterglow level is avoided as far as possible.
It was -found that by means of a method ac-cording to the invention a luminescent fluorohalide is obtainable the afterglow level of which has been reduced to an amount about equal to that of the known calcium tungstate. It was further found that, in com-~L135~7~7 .
par;son to the fluorohalide prepared in the known man-ner, the luminous flux obtained by the said materials when excited by X-rays has the same high value or even a higher value.
Although it is possible to add the desired amount of the europium activator in its entirety to the suspension in the form of EuX3 or EuF3, a method according to the invention is preferred ;n which the suspension contains no europium at all, p moles of EuX3 being added per mole of the MeFX obtained by evaporation to dryness, for it has been found that the best results are obtained, in particular in respect of the afterglow level, if a europium halide (except the fluoride) is used as the activator compound and if this activator compound is added after the synthesis of the fluoro-halide compound.
It was found to be of advantage for the reaction product obtained after the temperature treatment at 600C to 1000C in a weakly reducing at-mosphere to be ground before it is subjected to the final heat;ng, for if the conditions during the tem-~ perature treatment are optimized for the incorporation ; of bivalent europium in many cases a reaction product may be formed which is too coarse-grained for practical uses. Any deleterious effect of the grinding operation on the afterglow level is entirely eliminated by the final heating.
5~747 The most important use of the fluorohalides activated by bivalent europium is found, as mentioned hereinbefore, in X-ray image intensifier screens. Ad-vantageously the element Me then is barium because this gives the highest luminous fluxes on excitation by X-rays. For obtaining high luminous fluxes upon X-ray ex-citation it is also advantageous to use bromine for the element X. It was found, however, that the afterglow level of BaFBr is high compared with that of BaFCl.
1~ For example, the BaFBr prepared in known manner has an afterglow level which is up to 100 times that of calcium tungstate. A method according to the invention enables this level to be reduced to a few times that of calcium tungsta~e. The best combination of a low afterglow level and a high luminous flux is obtained with materials of the formula Bal pEupFCl. Hence a method according to the invention for preparing such materials is preferred.
In a preferred embodiment of a method ac-cording to the invention in which Bal pEupFCl is pre-pared, evaporation to dryness is performed at a tem-perature of 160C to 180C, for under these conditions the formation of the BaFCl is optimal.
When preparing Bal pEupFCl the best results are further obtained if the temperature treatment is effected at a temperature of 800C to 950C in nitro-gen containing from 0.1 to 1 volume percent of hydrogen ~13597~7 and if the final treatment is performed at a temperature of 700C to 800C in nitrogen. Hence these conditions are preferred.
The invention will now be described more fully ; 5 with reference to a few Examples of preparation.
Example 1.
An amount of 8.765 9 of BaF2 is added to water and suspended by st;rring. 12.240 9 of BaC12.2H20 are dissolved in this suspension. The suspension then is evaporated to dryness at a temperature of 170C. The' resulting substance consists of BaFCl and, as is shown by X-ray diffraction analyses, has the PbFCl structure.
The BaFCl is mixed with 1.374 9 oAF EuC13 and then heat-ed in a quartz crucible'at 900C in a furnace in a weakly reducing atmosphere for 1 hour. The said at-mosphere is obtained by passing a stream of nitrogen ~about 137 1 per h~ur) containing 0.7 volume percent of hydrogen into the furnace. After cooling the result-ing product is ground in a ball mill.' Then the product is subjected to final heating at 750C in a nitrogen stream (about 18 1 per hour) for 1 hour. After cooling, the product, which has a composition defined by the formula BaO 95Euo 05FCl, is ready for use-In order to compare the luminescence pro-perties on excitation by X-rays of the material ob~
tained according to the above Example of preparation which those of the known CaW04, screens are manufactured ~0597~7 using the said material and identical screens which, however, contain calcium tungstate in the same amounts by weight. A photographic film is brought into contact with these screens. Then the film density rate is measured under standard conditions (primary voltage of the X-ray tube; distance of the X-ray tubè from the screen and the filmi filters). The fluorohalide prepar-ed by the method according to the invention proves to have a rate which is 7 times that of the known CaWO~.
The afterglow level of the fluorohalide also is measured and compared with that of CaW04. For this purpose the screens are exposed to X-rays for some time (under standard conditions). One minute after cessation of the excitation a photographic film is placed on the screen and held in contact with it for 5 minutes.
The film density measured, which is a measure of the afterglow level, proves to be equal for the fluoro-halide and for the CaW04.
Example 2 Example 1 is repeated with the difference that the amount of 1.374g of EuC13 is added to the suspension and dissolved in it. The product obtained is equal to that of Example 1 and has substantially the same luminescence properties.
Example 3 Example 1 is repeated with the difference that the temperature treatment in the weakly reducing 1~59747 atmosphere is performed at 850C for 1 hour. The density rate of the obtained material is found to be 6.3 times that of CaW04 whilst the afterglow level is found to be about twice that of CaW04.
Example 4.
Example 1 is repeated with the difference that the temperature treatment in the weakly reducing atmos-phere is performed at 950C for 1 hour. The density rate of the resulting material is 5.2 times that of CaW04 and the afterglow level is about equal to that of CaW04.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Method of preparing a luminescent alkaline earth metal fluorohalide activated by bivalent europium and defined by the formula Me1-pEupFX, where Me repre-sents at least one of the alkaline earth metals Ba and Sr whilst up to 20 mole percent of these metals can be replaced by Ca, X represents at least one of the halogens Cl, Br and I and 0.001 ? p ? 0.20, char-acterized in that an aqueous suspension of MeF2 is made which contains 1 mole of MeX2 in dissolved form per mole of MeF2 and further may contain europium in the form of a europium halide in an amount at most equal to the amount desired in the fluorohalide, in that the suspension is evaporated to dryness at a temperature of 50°C to 250°C, the obtained product is mixed with the amount of europium halide which still may be required, the mixture is subjected to at least one temperature treatment at 600°C to 1000°C
in a weakly reducing atmosphere and the obtained reac-tion product, after cooling, is subjected to a final heating at 600°C to 850°C in an inert or weakly reduc-ing atmosphere.
in a weakly reducing atmosphere and the obtained reac-tion product, after cooling, is subjected to a final heating at 600°C to 850°C in an inert or weakly reduc-ing atmosphere.
2. Method as claimed in claim 1, characterized in that the suspension does not contain europium, p moles of EuX3 per mole of MeFX being added to the MeFX obtained by evaporation to dryness.
3. Method as claimed in Claim 1 or 2, characterized in that the reaction product is ground prior to the final heating.
4. Method as claimed in Claim 1, characterized in that a fluorohalide defined by the formula Ba1-pEupFCl is prepared.
5. Method as claimed in Claim 4, characterized in that the evaporation to dryness takes place at a temperature of 160°C to 180°C.
6. Method as claimed in Claim 4, characterized in that the temperature treatment is performed at a temperature of 800°C to 950°C in nitrogen containing 0.1 to 1 volume %
of hydrogen.
of hydrogen.
7. Method as claimed in Claim 4, 5 or 6, characterized in that the final heating is effected at a temperature of 700°C to 800°C in nitrogen.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7412917A NL176581C (en) | 1974-10-01 | 1974-10-01 | METHOD FOR PREPARING A LUMINESCENT NATURAL-POTASSIUM FLUORIDE HALOGENIDE ACTIVATED WITH Bivalent EUROPE ROENTGEN IMAGE REINFORCEMENT SCREEN. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1059747A true CA1059747A (en) | 1979-08-07 |
Family
ID=19822201
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA236,769A Expired CA1059747A (en) | 1974-10-01 | 1975-09-30 | Method of producing a luminescent alkaline earth metal fluorohalide activated by bivalent europium |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS573603B2 (en) |
| BE (1) | BE833978A (en) |
| CA (1) | CA1059747A (en) |
| DE (1) | DE2541748C3 (en) |
| FR (1) | FR2286872A1 (en) |
| GB (1) | GB1514785A (en) |
| IT (1) | IT1042928B (en) |
| NL (1) | NL176581C (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5944333B2 (en) * | 1978-07-12 | 1984-10-29 | 富士写真フイルム株式会社 | Radiographic image conversion method |
| JPS6090286A (en) * | 1983-10-24 | 1985-05-21 | Fuji Photo Film Co Ltd | Method for converting radiation image |
| FR2554122B1 (en) * | 1983-11-02 | 1987-03-20 | Rhone Poulenc Spec Chim | NOVEL COMPOSITION FOR MARKING DOCUMENTS AND METHOD FOR VERIFYING THE AUTHENTICITY OF SUCH DOCUMENTS |
| DE3347207A1 (en) * | 1983-12-27 | 1985-07-11 | Siemens AG, 1000 Berlin und 8000 München | X-RAY IMAGE STORAGE SCREEN |
| JPS60161478A (en) * | 1983-12-28 | 1985-08-23 | Fuji Photo Film Co Ltd | Fluorescent material and radiation image conversion panel using same |
| EP0168057B1 (en) * | 1984-07-13 | 1989-12-27 | Fuji Photo Film Co., Ltd. | Phosphor, radiation image recording and reproducing method and radiation image storage panel |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1555624A (en) * | 1967-09-14 | 1969-01-31 |
-
1974
- 1974-10-01 NL NL7412917A patent/NL176581C/en not_active IP Right Cessation
-
1975
- 1975-09-19 DE DE19752541748 patent/DE2541748C3/en not_active Expired
- 1975-09-26 IT IT2772475A patent/IT1042928B/en active
- 1975-09-26 GB GB3952475A patent/GB1514785A/en not_active Expired
- 1975-09-27 JP JP11599875A patent/JPS573603B2/ja not_active Expired
- 1975-09-29 BE BE160511A patent/BE833978A/en not_active IP Right Cessation
- 1975-09-30 CA CA236,769A patent/CA1059747A/en not_active Expired
- 1975-10-01 FR FR7530053A patent/FR2286872A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| NL176581B (en) | 1984-12-03 |
| GB1514785A (en) | 1978-06-21 |
| DE2541748C3 (en) | 1978-10-19 |
| FR2286872A1 (en) | 1976-04-30 |
| NL176581C (en) | 1985-05-01 |
| DE2541748A1 (en) | 1976-04-08 |
| JPS573603B2 (en) | 1982-01-22 |
| JPS5161499A (en) | 1976-05-28 |
| DE2541748B2 (en) | 1978-02-09 |
| BE833978A (en) | 1976-03-29 |
| IT1042928B (en) | 1980-01-30 |
| NL7412917A (en) | 1976-04-05 |
| FR2286872B1 (en) | 1979-09-07 |
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