Title of Invention	''A PROCESS FOR PREPARING A NOVEL POLYCRYSTALLINE CERAMIC PHOSPHOR COMPOSITION USEFUL AS A LIGHT EMITTTING MATERIAL."
Abstract	This invention relates to a process for preparing a novel polycrystalline ceramic phosphor composition useful in luminescent display screen and compact fluorescent lamps.The novel phosphor composition of the present invention can generate simultaneously both red and green intense luminescence upon excitation either with UV light or with energetic electrons from a cathode ray-tube and is useful as a light emitting material of a fluorescent lamp and a visual display screen. Process steps are : preparing a homogeneous mixture of 30-50 mole % phosphorous pentoxide (P2O5) and 25-50 mole % of aluminium ion (Al+3) either in the form of oxide or nitrate or phosphate or halide, adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO) or halide (MX) or a mixture thereof where M= Ca, Mg, Sr, Ba, adding to the mixture 0-12 mole % of any one of the oxide from La2O3, Y2O3, Zr2O3, adding Eu+3 ion in the mixture in an overall concentration range of 3-7 mole %, firing the reaction mixture in the range of temperature of 200-1200° C, crushing the reaction product in to powder followed by crystallising the powder into micro crystals of uniform particle size by heat treating at a temperature range of 800 - 1200° C for 5-12 hours under inert atmosphere.

Title of Invention

''A PROCESS FOR PREPARING A NOVEL POLYCRYSTALLINE CERAMIC PHOSPHOR COMPOSITION USEFUL AS A LIGHT EMITTTING MATERIAL."

Abstract

This invention relates to a process for preparing a novel polycrystalline ceramic phosphor composition useful in luminescent display screen and compact fluorescent lamps.The novel phosphor composition of the present invention can generate simultaneously both red and green intense luminescence upon excitation either with UV light or with energetic electrons from a cathode ray-tube and is useful as a light emitting material of a fluorescent lamp and a visual display screen. Process steps are : preparing a homogeneous mixture of 30-50 mole % phosphorous pentoxide (P2O5) and 25-50 mole % of aluminium ion (Al+3) either in the form of oxide or nitrate or phosphate or halide, adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO) or halide (MX) or a mixture thereof where M= Ca, Mg, Sr, Ba, adding to the mixture 0-12 mole % of any one of the oxide from La2O3, Y2O3, Zr2O3, adding Eu+3 ion in the mixture in an overall concentration range of 3-7 mole %, firing the reaction mixture in the range of temperature of 200-1200° C, crushing the reaction product in to powder followed by crystallising the powder into micro crystals of uniform particle size by heat treating at a temperature range of 800 - 1200° C for 5-12 hours under inert atmosphere.

Full Text	This invention relates to a process for preparing a novel polycrystalline ceramic phosphor composition useful as a light emitting material. The novel phosphor composition of the present invention can generate simultaneously both red and green intense luminescence upon excitation either with UV light or with energetic electrons from a cathode ray-tube and is useful as a light emitting material of a fluorescent lamp and a visual display screen. Such materials are known in the art as phosphor materials and have been used in a variety of applications namely in fluorescent lighting, radiation sensing and CRT-display. Some of the earliest materials that have been used, as lamp or display phosphors are transition metal ion doped halo phosphates and oxides. At present, rare earth doped different polycrystalline ceramic are being increasingly used for this purposes e.g. in compact fluorescent lamps (CFL) in particular, for their higher colour rendition index and greater thermal stability. Possibility of use of rare earth ions as luminescence source in a lamp-phosphor was first suggested by Koedam and Opsteten. Reference may be made to their paper in Light Research Technol, 3(1971)265 wherein line emission of Eu(III), Tb(III), Dy(III) and Sm(III) were found to be particularly useful for this purpose. Later such ions were indeed, used for preparation of tri-band phosphor for use in compact fluorescent lamps. Reference may be made to the paper of Verstegen in J. Of Electro Chem. Soc. 121(1974)1627, wherein it has been shown how a proportionate mixture of three different phosphors activated with different rare earth ions and emitting respectively in the blue, green and red region can be used to generate white light for illumination purposes. Although, the performance of a phosphor material is mainly related to the presence of ions or atoms serving as activator, the efficiency of the emission varies with the variation of host composition, the method of preparation and many other factors. Preparation of Eu(III) activated phosphors using hosts like Yttrium oxide (Y2O3), Yttrium silicate (Y2Si2O5) and Yttrium vanadate (Y2V2O5) is well known. Each of these phosphors is known to emit strongly in the red and is used in CFL in conjunction with blue and green components to create white light for illumination. One of the draw backs of use of tri-chromatic mixture for white light generation is that the hosts of activator ions of different luminescence (blue, red and green) in most cases are different and behave in a different way to the excitation UV radiation causing a reduction in the efficiency of white light illumination. Moreover, the hosts (namely Y2O3, Y2Si2O5, Y2V2O5) which are usually used to prepare these phosphors are very expensive and require strict control on their purity. So in the recent studies, a considerable effort has been made to prepare phosphor of different colours Utilising a single host. Bivalent europium is known to emit with a broad band due to its 4f55d → 4f7 transition. And depending on the nature of the host, Eu(II) ions can emit from blue to the red region of light. Reference may be made to the paper of G. D. Dirksen et al in J. Solid State Chem. 92(1991)591. There are reports of generating Eu(II) ions from Eu(III) ions in a host matrix by codoping europium with alumina and then reducing the former with hydrogen. Reference may be made to the US patent No. 4,814,105 by Gerrit Oversluizen et al also to the papers of M. Nogami et al in Appl. Phys. Letts 69(1996)3776 and of A. Biswas et al in the J. of Non cryst. Solids, 261(2000)9. But main drawback of such materials is that in most cases , majority of the europium ions get reduced and hence emission from Eu(II) ions becomes dominant. Moreover, the reduced Eu(II) ions get back to the trivalent state when the phosphor is exposed to air. The main object of the present invention is to provide a process for preparing a novel polycrystalline ceramic phosphor composition useful in luminescent display screen and compact fluorescent lamps which obviates the above noted drawbacks. Another object of the present invention is to provide an Eu(III) ions activated ceramic phosphor which involves a host of relatively cheaper ingredients and is easy to prepare. Yet another object of the present invention is to provide a technique of crystallisation of the phosphor which enables the product to emit simultaneously both in the red and green with comparable efficiency. Accordingly, the present invention provides a process for preparing a novel polycrystalline ceramic phosphor composition useful as a light emitting material which comprises: preparing a homogeneous mixture of 30-50 mole % phosphorous pentoxide (P2O5) and 25-50 mole % of aluminium ion (Al+3) either in the form of oxide or nitrate or phosphate or halide, adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO) or halide (MX) or a mixture thereof where M= Ca, Mg, Sr, Ba, adding to the said mixture 0-12 mole % of any one of the oxide from La2O3, Y2O3, Zr2O3, adding Eu+3 ion in the mixture in an overall concentration range of 3-7 mole %, firing the reaction mixture in the range of temperature of 200-1200° C, crushing the reaction product in to powder followed by crystallising the powder into micro crystals of uniform particle size by heat treating at a temperature range of 800 -1200° C for 5-12 hours under inert atmosphere to obtain the product. In an embodiment of the present invention the phosphorous pentaoxide used, may be taken either as it is or in the form of a precursor like Phosphoric acid, ammonium di-hydrogen phosphate, di-ammonium hydrogen phosphate etc. In another embodiment of the present invention the Eu(III) ion may be added in the form of compounds such as europium oxide, chloride, nitrate etc. In yet another embodiment of the present invention, the firing of the reaction mixture can be effected in stepwise manner such as initially heating for 1-3 hours at temperature range 200-600° C, then firing the resulting mass for 1-4 hours in the temperature range 700-800° C and finally sintering the mass in temperature range of 900-1200° C. In another embodiment of the present invention, the gas or gas mixture used for creating inert atmosphere may be chosen from gases like nitrogen, argon, helium. The detailed process steps of the present invention are: 1) preparing a homogeneous mixture of 30-50 mole % phosphorous pentoxide (P2O5) wherein phosphorous pentaoxide used, may be taken either as it is or in the form of a precursor like Phosphoric acid, ammonium di-hydrogen phosphate, di-ammonium hydrogen phosphate etc., and 25-50 mole % of aluminium ion (Al+3) either in the form of oxide or nitrate or phosphate or halide. 2) adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO) or halide (MX) or a mixture of both where M= Ca, Mg, Sr, Ba, 3) further adding to the mixture 0-12 mole % of any one of the oxide from La2O3, ¥2O3, Zr2O3, 4) adding Eu+3 ion in the mixture in an overall concentration range of 3-7 mole % wherein Eu(III) ion is added in the form of compounds such as europium oxide, chloride, nitrate etc. 5) firing the reaction mixture in the range of temperatures of 200-1200° C where firing of the reaction mixture is effected in a stepwise manner such as initially heating for 1-3 hours at temperature range 200- 600° C, then firing the resulting mass for 1-4 hours in the temperature range 700-800° C and finally sintering the mass in temperature range of 900-1200° C 6) crushing the reaction product in to powder followed by crystallising the powder into microcrystals of uniform particle size by heat treating at a temperature range of 800 - 1200° C for 5-12 hours under inert atmosphere where the gas or gas mixture used for creating inert atmosphere is chosen from gases like nitrogen, argon, helium, etc. Novelty of the present invention lies in providing an europium ion activated new phosphor composition which can emit simultaneously in two chromatic region namely red and green of the visible light with comparable intensity producing a near white light fluorescence. This is as against the conventional trichromatic lamp phosphor where a mixture of three components of three different emission namely blue, green and red are used to generate the white light. The inventive steps includes (1) using of aluminium ion (Al+3) as one of the ingredients of the host to induce Eu ion to emit simultaneously both in the blue and red upon UV excitation (2) crystallising the reaction product into particles of uniform size through heat treatment under inert atmosphere. •The following examples provided below are by way of illustrations only and should not be construed to limit the scope of the invention. Example 1 The phosphor was prepared by making a mixture of 0.08 mole of aluminium meta phosphate and 0.02 mole of lanthanum oxide - adding to the mixture 0.1 mole of CaO and 0.06 mole of barium chloride and adding further to it 0.009 mole of Europium oxide reacting the resultant mixture with .06 mole of P205. finally heating the mixture in a furnace at 500°C for 1 hour then at 750°C for further period of 1 hour and finally at 1100°C for 2 hours. The porous mass obtained was crushed to powder and crystallised to particles by slow heat treatment at 900° C for 8 hours under the atmosphere of nitrogen. Example 2 The phosphor was also prepared by using a mixture of 0.05 mole of aluminium orthophosphate, 0.04 mole of strontium fluoride, 0.075 mole of barium oxide and 0.03 mole of zirconium oxide - adding to the mixture 0.021 mole of europium chloride - reacting the resultant mixture with 0.14 mole of concentrated orthophosphoric acid and finally heating the reaction mass in a furnace first at 200° C for nearly 1 hour and then up to 900°C for 3-4 hours. The resulting porous mass was crushed and then crystallised to uniform particle by heating slowly up to 800° C for 10 hours in nitrogen atmosphere. Example 3 The phosphor was also prepared by dissolving a mixture of 0.025 mole of strontium chloride, 0.080 mole of barium oxide, 0.055 mole of alumina and 0.035 mole of europium chloride 0.18 mole of phosphoric acid - mixing the ingredients in to a homogeneous mixture - heating the mixture at stages first at 200° C for 1 hour then 550-600° C for 2 hours and finally heating up to 1100°C. The partially crystallised porous product was then recrystallised slowly heating upto 900° C for 5 hours in an argon atmosphere. Example 4 Another method of preparing the phosphor was making of a mixture of 0.06 mole of aluminium orthophosphate, 0.09 mole calcium fluoride and 0.0045 mole of europium oxide - digesting the mixture with 0.06 mole of concentrated phosphoric acid - to heat the homogeneous reaction mass in a furnace at stages 250° C for 2 hours then at 700° C for 1 hour and finally up to 1150° C. The lumpy product was crushed to powder and then crystallised to uniform particles by heating slowly up to 800° for 8 hours under nitrogen atmosphere. • All the phosphors thus prepared give strong green-red luminescence upon excitation both at 254 nm and 390 nm. This is shown in Figure-1 of the drawing accompanying this specification. The luminescence efficiency of the phosphors was measured relative to the intensity of emission of a commercially available Philips 'True light phosphor' under 393 nm excitation, taking the latter's intensity value as 100. The intensity values of the present products were found to lie within 90-110 %. For TV-display purposes, the material needs to be deposited on the inner wall of the display screen and annealed into an envelope to provide fluorescent properties to a television screen. For use as the green and red component of a tri-chromatic mixture of a white light phosphor, an appropriate quantity of the material depending on the desired output colour temperature of the emission is to be mixed with the blue component of the desired mixture. The main advantages of the invention are: 1) In contrast to the emission properties of conventional rare earth phosphors which independently can emit only in a single chromatic region, the present phosphor can emit simultaneously in two chromatic regions namely green and red and hence it alone can serve the function of two phosphors of a tri-chromatic phosphor mixture of a fluorescent lamp. 2) The process of preparation of the phosphor is relatively simple and easy to carry out. 3) The cost of preparation is much lower compared to the commercially available similar rare earth doped phosphors. claim: 1. A process for preparing a novel polycrystalline ceramic phosphor composition useful as a light emitting material which comprises: preparing a homogeneous mixture of 30-50 mole % phosphorous pentoxide (P2O5) and 25-50 mole % of aluminium ion (Al+3) either in the form of oxide or nitrate or phosphate or halide, adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO) or halide (MX) or a mixture thereof where M= Ca, Mg, Sr, Ba, adding to the said mixture 0-12 mole % of any one of the oxide from La2O3, Y2O3, Zr2O3, adding Eu+3 ion in the mixture in an overall concentration range of 3-7 mole %, firing the reaction mixture in the range of temperature of 200-1200° C, crushing the reaction product in to powder followed by crystallising the powder into micro crystals of uniform particle size by heat treating at a temperature range of 800 - 1200° C for 5-12 hours under inert atmosphere to obtain the product. 2. A process as claimed in claim 1 wherein the phosphorous pentoxide used is either as it is or in the form of a precursor like phosphoric acid, ammonium di hydrogen phosphate, di ammonium hydrogen phosphate etc. 3. A process as claimed in claim-1& 2 wherein the Eu(III) ion is added using europium compounds like europium oxide, europium chloride, europium nitrate etc. 4. A process as claimed in claim 1 -3 wherein firing of the reaction mixture is effected in a stepwise manner such as initially heating for 1-3 hours at temperature range 200-600° C, then firing the resulting mass for 1-4 hours in the temperature range 700-800° C and finally sintering the mass in temperature range of 900-1200° C 5. A process as claimed in claim 1-4 wherein the inert atmosphere is provided by gases selected from Argon, nitrogen, helium. 6. A process for preparing a novel polycrystalline ceramic phosphor composition useful as a light emitting material substantially as herein described with reference to examples and drawing accompanying the specification.

Full Text

This invention relates to a process for preparing a novel polycrystalline ceramic phosphor composition useful as a light emitting material.
The novel phosphor composition of the present invention can generate simultaneously both red and green intense luminescence upon excitation either with UV light or with energetic electrons from a cathode ray-tube and is useful as a light emitting material of a fluorescent lamp and a visual display screen.
Such materials are known in the art as phosphor materials and have been used in a variety of applications namely in fluorescent lighting, radiation sensing and CRT-display. Some of the earliest materials that have been used, as lamp or display phosphors are transition metal ion doped halo phosphates and oxides. At present, rare earth doped different polycrystalline ceramic are being increasingly used for this purposes e.g. in compact fluorescent lamps (CFL) in particular, for their higher colour rendition index and greater thermal stability. Possibility of use of rare earth ions as luminescence source in a lamp-phosphor was first suggested by Koedam and Opsteten. Reference may be made to their paper in Light Research Technol, 3(1971)265 wherein line emission of Eu(III), Tb(III), Dy(III) and Sm(III) were found to be particularly useful for this purpose. Later such ions were indeed, used for preparation of tri-band phosphor for use in compact fluorescent lamps. Reference may be made to the paper of Verstegen in J. Of Electro Chem. Soc. 121(1974)1627, wherein it has been shown how a proportionate mixture of three different phosphors activated with different rare earth ions and emitting respectively in the blue, green and red region can be used to generate white light for illumination purposes.
Although, the performance of a phosphor material is mainly related to the presence of ions or atoms serving as activator, the efficiency of the emission varies with the variation of host composition, the method of preparation and many other factors.
Preparation of Eu(III) activated phosphors using hosts like Yttrium oxide (Y2O3), Yttrium silicate (Y2Si2O5) and Yttrium vanadate (Y2V2O5) is well known. Each of these phosphors is known to emit strongly in the red and is used in CFL in conjunction with blue and green components to create white light for illumination. One of the draw backs of use of tri-chromatic mixture for white light generation is that the hosts of activator ions of different luminescence (blue, red and green) in most cases are different and behave in a different way to the excitation UV radiation causing a reduction in the efficiency of white light illumination. Moreover, the hosts (namely Y2O3, Y2Si2O5, Y2V2O5) which are usually used to prepare these phosphors are very expensive and require strict control on their purity.
So in the recent studies, a considerable effort has been made to prepare phosphor of different colours Utilising a single host. Bivalent europium is known to emit with a broad band due to its 4f55d → 4f7

transition. And depending on the nature of the host, Eu(II) ions can emit from blue to the red region of light. Reference may be made to the paper of G. D. Dirksen et al in J. Solid State Chem. 92(1991)591. There are reports of generating Eu(II) ions from Eu(III) ions in a host matrix by codoping europium with alumina and then reducing the former with hydrogen. Reference may be made to the US patent No. 4,814,105 by Gerrit Oversluizen et al also to the papers of M. Nogami et al in Appl. Phys. Letts 69(1996)3776 and of A. Biswas et al in the J. of Non cryst. Solids, 261(2000)9. But main drawback of such materials is that in most cases , majority of the europium ions get reduced and hence emission from Eu(II) ions becomes dominant. Moreover, the reduced Eu(II) ions get back to the trivalent state when the phosphor is exposed to air.
The main object of the present invention is to provide a process for preparing a novel polycrystalline ceramic phosphor composition useful in luminescent display screen and compact fluorescent lamps which obviates the above noted drawbacks.
Another object of the present invention is to provide an Eu(III) ions activated ceramic phosphor which involves a host of relatively cheaper ingredients and is easy to prepare.
Yet another object of the present invention is to provide a technique of crystallisation of the phosphor which enables the product to emit simultaneously both in the red and green with comparable efficiency.
Accordingly, the present invention provides a process for preparing a novel polycrystalline ceramic phosphor composition useful as a light emitting material which comprises: preparing a homogeneous mixture of 30-50 mole % phosphorous pentoxide (P2O5) and 25-50 mole % of aluminium ion (Al+3) either in the form of oxide or nitrate or phosphate or halide, adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO) or halide (MX) or a mixture thereof where M= Ca, Mg, Sr, Ba, adding to the said mixture 0-12 mole % of any one of the oxide from La2O3, Y2O3, Zr2O3, adding Eu+3 ion in the mixture in an overall concentration range of 3-7 mole %, firing the reaction mixture in the range of temperature of 200-1200° C, crushing the reaction product in to powder followed by crystallising the powder into micro crystals of uniform particle size by heat treating at a temperature range of 800 -1200° C for 5-12 hours under inert atmosphere to obtain the product.
In an embodiment of the present invention the phosphorous pentaoxide used, may be taken either as it is or in the form of a precursor like Phosphoric acid, ammonium di-hydrogen phosphate, di-ammonium hydrogen phosphate etc.
In another embodiment of the present invention the Eu(III) ion may be added in the form of compounds such as europium oxide, chloride, nitrate etc.
In yet another embodiment of the present invention, the firing of the reaction mixture can be effected in
stepwise manner such as initially heating for 1-3 hours at temperature range 200-600° C, then firing the resulting mass for 1-4 hours in the temperature range 700-800° C and finally sintering the mass in temperature range of 900-1200° C.
In another embodiment of the present invention, the gas or gas mixture used for creating inert atmosphere may be chosen from gases like nitrogen, argon, helium. The detailed process steps of the present invention are:
1) preparing a homogeneous mixture of 30-50 mole % phosphorous pentoxide (P2O5) wherein
phosphorous pentaoxide used, may be taken either as it is or in the form of a precursor like Phosphoric
acid, ammonium di-hydrogen phosphate, di-ammonium hydrogen phosphate etc., and 25-50 mole %
of aluminium ion (Al+3) either in the form of oxide or nitrate or phosphate or halide.
2) adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO) or halide (MX) or
a mixture of both where M= Ca, Mg, Sr, Ba,
3) further adding to the mixture 0-12 mole % of any one of the oxide from La2O3, ¥2O3, Zr2O3,
4) adding Eu+3 ion in the mixture in an overall concentration range of 3-7 mole % wherein Eu(III) ion is
added in the form of compounds such as europium oxide, chloride, nitrate etc.

5) firing the reaction mixture in the range of temperatures of 200-1200° C where firing of the reaction
mixture is effected in a stepwise manner such as initially heating for 1-3 hours at temperature range 200-
600° C, then firing the resulting mass for 1-4 hours in the temperature range 700-800° C and finally
sintering the mass in temperature range of 900-1200° C
6) crushing the reaction product in to powder followed by crystallising the powder into microcrystals of
uniform particle size by heat treating at a temperature range of 800 - 1200° C for 5-12 hours under inert
atmosphere where the gas or gas mixture used for creating inert atmosphere is chosen from gases like
nitrogen, argon, helium, etc.
Novelty of the present invention lies in providing an europium ion activated new phosphor composition which can emit simultaneously in two chromatic region namely red and green of the visible light with comparable intensity producing a near white light fluorescence. This is as against the conventional trichromatic lamp phosphor where a mixture of three components of three different emission namely blue, green and red are used to generate the white light. The inventive steps includes (1) using of aluminium ion (Al+3) as one of the ingredients of the host to induce Eu ion to emit simultaneously both in the blue and red upon UV excitation (2) crystallising the reaction product into particles of uniform size through heat treatment under inert atmosphere.
•The following examples provided below are by way of illustrations only and should not be construed to limit the scope of the invention.
Example 1
The phosphor was prepared by making a mixture of 0.08 mole of aluminium meta phosphate and 0.02 mole of lanthanum oxide - adding to the mixture 0.1 mole of CaO and 0.06 mole of barium chloride and adding further to it 0.009 mole of Europium oxide reacting the resultant mixture with .06 mole of P205. finally heating the mixture in a furnace at 500°C for 1 hour then at 750°C for further period of 1 hour and finally at 1100°C for 2 hours. The porous mass obtained was crushed to powder and crystallised to particles by slow heat treatment at 900° C for 8 hours under the atmosphere of nitrogen.
Example 2
The phosphor was also prepared by using a mixture of 0.05 mole of aluminium orthophosphate, 0.04 mole of strontium fluoride, 0.075 mole of barium oxide and 0.03 mole of zirconium oxide - adding to the mixture 0.021 mole of europium chloride - reacting the resultant mixture with 0.14 mole of concentrated orthophosphoric acid and finally heating the reaction mass in a furnace first at 200° C for nearly 1 hour and then up to 900°C for 3-4 hours. The resulting porous mass was crushed and then crystallised to uniform particle by heating slowly up to 800° C for 10 hours in nitrogen atmosphere.
Example 3
The phosphor was also prepared by dissolving a mixture of 0.025 mole of strontium chloride, 0.080 mole of barium oxide, 0.055 mole of alumina and 0.035 mole of europium chloride 0.18 mole of phosphoric acid - mixing the ingredients in to a homogeneous mixture - heating the mixture at stages first at 200° C for 1 hour then 550-600° C for 2 hours and finally heating up to 1100°C. The partially crystallised porous product was then recrystallised slowly heating upto 900° C for 5 hours in an argon atmosphere.
Example 4
Another method of preparing the phosphor was making of a mixture of 0.06 mole of aluminium orthophosphate, 0.09 mole calcium fluoride and 0.0045 mole of europium oxide - digesting the mixture with 0.06 mole of concentrated phosphoric acid - to heat the homogeneous reaction mass in a furnace at stages 250° C for 2 hours then at 700° C for 1 hour and finally up to 1150° C. The lumpy product was crushed to powder and then crystallised to uniform particles by heating slowly up to 800° for 8 hours under nitrogen atmosphere.
• All the phosphors thus prepared give strong green-red luminescence upon excitation both at 254 nm and 390 nm. This is shown in Figure-1 of the drawing accompanying this specification. The luminescence efficiency of the phosphors was measured relative to the intensity of emission of a commercially available Philips 'True light phosphor' under 393 nm excitation, taking the latter's intensity value as 100. The intensity values of the present products were found to lie within 90-110 %.
For TV-display purposes, the material needs to be deposited on the inner wall of the display screen and annealed into an envelope to provide fluorescent properties to a television screen. For use as the green and red component of a tri-chromatic mixture of a white light phosphor, an appropriate quantity of the material depending on the desired output colour temperature of the emission is to be mixed with the blue component of the desired mixture.
The main advantages of the invention are:
1) In contrast to the emission properties of conventional rare earth phosphors which independently
can emit only in a single chromatic region, the present phosphor can emit simultaneously in two
chromatic regions namely green and red and hence it alone can serve the function of two phosphors
of a tri-chromatic phosphor mixture of a fluorescent lamp.
2) The process of preparation of the phosphor is relatively simple and easy to carry out.
3) The cost of preparation is much lower compared to the commercially available similar rare earth
doped phosphors.

claim:
1. A process for preparing a novel polycrystalline ceramic phosphor composition useful as a light
emitting material which comprises: preparing a homogeneous mixture of 30-50 mole % phosphorous
pentoxide (P2O5) and 25-50 mole % of aluminium ion (Al+3) either in the form of oxide or nitrate or
phosphate or halide, adding 30-45 mole % of an alkaline earth metal ion either in the form of oxide (MO)
or halide (MX) or a mixture thereof where M= Ca, Mg, Sr, Ba, adding to the said mixture 0-12 mole %
of any one of the oxide from La2O3, Y2O3, Zr2O3, adding Eu+3 ion in the mixture in an overall
concentration range of 3-7 mole %, firing the reaction mixture in the range of temperature of 200-1200°
C, crushing the reaction product in to powder followed by crystallising the powder into micro crystals of
uniform particle size by heat treating at a temperature range of 800 - 1200° C for 5-12 hours under inert
atmosphere to obtain the product.
2. A process as claimed in claim 1 wherein the phosphorous pentoxide used is either as it is or in the form
of a precursor like phosphoric acid, ammonium di hydrogen phosphate, di ammonium hydrogen
phosphate etc.
3. A process as claimed in claim-1& 2 wherein the Eu(III) ion is added using europium compounds like
europium oxide, europium chloride, europium nitrate etc.
4. A process as claimed in claim 1 -3 wherein firing of the reaction mixture is effected in a stepwise
manner such as initially heating for 1-3 hours at temperature range 200-600° C, then firing the resulting
mass for 1-4 hours in the temperature range 700-800° C and finally sintering the mass in temperature
range of 900-1200° C
5. A process as claimed in claim 1-4 wherein the inert atmosphere is provided by gases selected from
Argon, nitrogen, helium.
6. A process for preparing a novel polycrystalline ceramic phosphor composition useful as a light
emitting material substantially as herein described with reference to examples and drawing accompanying
the specification.

Documents:

611-del-200-abstract.pdf

611-del-2000-claims.pdf

611-del-2000-correspondence-others.pdf

611-del-2000-correspondence-po.pdf

611-del-2000-description (complete).pdf

611-del-2000-drawings.pdf

611-del-2000-form-1.pdf

611-del-2000-form-19.pdf

611-del-2000-form-2.pdf

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Patent Number

216736

Indian Patent Application Number

611/DEL/2000

PG Journal Number

13/2008

Publication Date

31-Mar-2008

Grant Date

19-Mar-2008

Date of Filing

23-Jun-2000

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH,

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	GOURKRISHNA DAS MAHAPATRA,	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032,
2	RADHABALLABH DEBNATH,	CENTRAL GLASS & RESEARCH INSTITUTE, CALCUTTA 700 032,
3	RAMPADA SAHOO	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032,
4	AHINDRA KUMAR CHAUDHURI,	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700032,

PCT International Classification Number

C09K 11/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA