Title of Invention	"A PROCESS FOR THE PREPARATION IMPROVED LONG DECAY IUMINESCENT POWDER USING A NOVEL COMPOSITION"
Abstract	A process for the preparation of improved long decay luminescent powder using a novel composition. The process related to the present invention involves the selection of a host material from group IIB-VIA compounds of periodic table either singly or a mixture of two or more, for example, oxides, sulphides, selenides, tellurides of zinc, cadmium and mercury, each of 99.99% purity, of size less than 100µm depending upon the application and the process of device application. The activators are selected from group IB or VIIB elements of the periodic table which can be copper, silver, gold and manganese, of 99.9% purity in the range of 1 -1000 ppm based on the required emission colour of the long decay luminescent powder.

Title of Invention

"A PROCESS FOR THE PREPARATION IMPROVED LONG DECAY IUMINESCENT POWDER USING A NOVEL COMPOSITION"

Abstract

A process for the preparation of improved long decay luminescent powder using a novel composition. The process related to the present invention involves the selection of a host material from group IIB-VIA compounds of periodic table either singly or a mixture of two or more, for example, oxides, sulphides, selenides, tellurides of zinc, cadmium and mercury, each of 99.99% purity, of size less than 100µm depending upon the application and the process of device application. The activators are selected from group IB or VIIB elements of the periodic table which can be copper, silver, gold and manganese, of 99.9% purity in the range of 1 -1000 ppm based on the required emission colour of the long decay luminescent powder.

Full Text	The present invention relates to a process for preparation of improved long decay luminescent powders using a novel composition Long decay luminescent powders also known as long decay phosphor have the unique property of light emission in the visible range for a quite long time from few seconds to several hours after having been excited by higher energy radiations for short times of the order of one second or less. Applications of these phosphors are almost limitless. To highlight a few, one may include emergency signs and low level lighting escape systems during general power failures or intentional power cuts, military applications, textile printing and textile fibres, lighting apparatus and switches, exit sign boards, electronic instrument dial pads etc. We are not aware of any "standard method" which may be used for the preparation of Long decay luminescent powders although some research papers and patents are available as described in US patents Nos. 5376303, 5650094 and 5859496. Long decay phosphors are based on compositions involving complicated compositions of divalent metals with oxides, aluminates and titanates. Copper activated zinc sulfide phosphor was one of the earliest reported in the series. Typical procedures are described in the literature but the preparative details are not disclosed. The process for the preparation of Long decay luminescent zinc sulphide powder essentially involves mixing of impurities known as activators in high purity zinc sulphide powder, incorporation of impurities in the latter by high temperature firing and classification of particles in the required particle size range. According to Van Gool and his co workers as described in Philips Res. Rept. 15, 238-253, 1960; Philips Research Rept. 15, 254-274, 1960, Philips Res. Rept. Suppt. 3, 1-119, 1961, the starting material for the preparation of luminescent powder is precipitated zinc sulphide powder which is first wetted with a standard solution of the activator. The amount of solution used is determined by the concentration of the activator required. Concentration of the activator is responsible for intensity of the emitted light as well as the decay tune of the emission also known as after glow. Incorporation of the activator through the process of diffusion is achieved by firing the material at high temperatures in silica container at temperatures in the range of 800-1200 °C in hydrogen sulphide gas atmospheres for a time duration ranging from a few minutes to 2-3 hrs. the material so obtained is suitably washed and classified for different sizes. The material is well dried before putting to use for making device. A large number investigators have studied the decay characteristics of the luminescence in zinc sulphide type phosphors as for example by G.F.J. Garlick as reported in Tans, electrochem. Soc. Vol 96, 90-113, 1949; d. Curie in "Luminescence in Crysrtals" . Methuen, London, 1963; S. Shionoya et. al, Phys. Chem. Solids 26, 697-710, 1965). The addition of second impurity which is referred to as a co-activator has also been reported in the literature. Such a co-activator in the first instance affect the colour of the emission. It is also known to affect the intensity of emission of the phosphor material and after glow of the emission after the excitation source is removed. It has been experienced that its effective role may depend on the amount of primary activator present and the precise manner in which the co activator is incorporated into the lattice of starting material. Thus the number of preparative parameters is very large. This complicated situation is also responsible for much of the apparently contradictory information found in the abovementioned literature. Therefore, it has been found that published data gives information about basic raw materials and activators to be used but, regarding parameters for the preparation which includes detailed process of incorporation of activators, nature and concentration of co-activators and types of salt to be used , no information is yet available. The long decay luminescent powder obtained on the basis of limited information is poorly crystalline and agglomerated type which has broad particle size distribution and lower brightness. The main object of the present invention is to provide a composition useful for the preparation of an improved long decay luminescent powder. Another object is to provide a process for the preparation of improved long decay luminescent powder using the composition of the present invention. Yet another object of the present invention is to provide a long decay luminescent powder which is free flowing and has narrow particle size distribution. Still another object is to provide a long decay luminescent powder having low energy excitation. Another object is to provide a long decay luminescent powder capable of providing varied emission colours. host material selected from group IIB-VIA compounds of periodic table either singly or a mixture of two or more, 1-1000 ppm of activator (s) selected from group IB, VIIB of the elements of the periodic table either singly or a mixture of two or more; and 50 -1000 ppm of co-activator (s) selected from group IA, IIA, IIIA/VIIA elements of the periodic table either singly or a mixture of two or more,.'! In an embodiment of the present invention, the host material, IIB-VIA compounds, used may be selected from oxides, sulphides, selenides, tellurides of zinc, cadmium and mercury of 99.99% purity and of size less than 100 µrn. In yet another embodiment of the present invention, the host material may also contain another compound selected from IIB-VIA compounds in the range of 1 to 50% wt. In still another embodiment of the present invention the activator(s) to be used may be selected from compounds of copper, silver, gold and manganese of 99.99% purity. In another embodiment of the present invention the co-activator(s) used may be a compound of aluminum, gallium, barium, magnesium, indium, chlorine, fluorine, bromine and iodine of 99.99% purity. The improved composition of the present invention which is useful for the preparation of long decay luminescent powder is not a mere admixture but a synergistic mixture having properties which are different from the aggregated properties of the individual components. Accordingly, the present invention provides a process for the preparation of improved long decay luminescent powder using a novel composition Comprising which comprises: firing the novel composition, at a temperature in the range of 600° - 1300°C for a period of 10 minutes to 20 hours, in a gaseous atmosphere containing a group VIA element, a mixture of group VIA element and one of the VIIA elements such as described herein, wherein the ratio of group VIA and VIIA in the gaseous atmosphere are in a ratio in the range of 1:0.1 to 1:1 by volume washing the resultant material obtained followed by grinding, sieving and drying by conventional methods to obtain improved long decay luminescent powder. In an embodiment of the present invention, the firing of the composition may be effected using a container selected from ceramic, quartz, host material, zinc oxide or any other refractory materials. In another embodiment of the present invention, the firing may be effected in a gaseous atmosphere containing group VIA element and/or group VIA element corresponding to the group VI element of the host material admixed with an inert gas. In yet another embodiment of the present invention, the elements of group VIA and VIIA in the gaseous atmosphere may be in a ratio in the range of 1:0.1 to 1:1 by volume. In another embodiment of the present invention, the firing may be effected at a temperature in the range of 800 - 1200°C. In still other embodiment of the present invention, the firing is effected for a time duration in the range of 30 minutes to 3 hours. The process related to the present invention involves the selection of a host material from group IIB-VIA compounds of periodic table either singly or a mixture of two or more, for example, oxides, sulphides, selenides, tellurides of zinc, cadmium and mercury, each of 99.99% purity, of size less than 100µm depending upon the application and the process of device application. The activators are selected from group IB or VIIB elements of the periodic table which can be copper, silver, gold and manganese, of 99.9% purity in the range of 1 - 1000 ppm based on the required emission colour of the long decay luminescent powder. The co-activator is selected from group IA, IIA, IIIA and VIIA elements of the periodic table which may be added singly or in combination in the form of compounds of aluminium, gallium, barium, magnesium, indium, chlorine, fluorine, bromine and iodine of 99.9% purity and in the range of 50-10000 ppm on the basis of the host material as selected above so that the charge compensation of the host material is taken care of and incorporation of activator is efficient. The above composition is thoroughly mixed. The above powder is filled in a ceramic/quartz/zinc oxide container and put in a ceramic enclosure both of which could be heated up to 1600 C and which is impervious to gases. It is advantageous to use processing container made out of zinc oxide or host material. It helps in the incorporation of trace additions of activators and co-activators quite effectively and has longer life thereby reducing the cost per piece considerably. The mixture is heated at a temperature in the range of 600-1300° C in a gaseous atmosphere containing a mixture of group VIA and/or group VIIA halogen elements. These gases can be admixed with an inert gas. The two elements of the group VIA and VIIA in the gases can be in ratio of 1:0.1 to 1:1 by volume respectively. The time duration of the firing is in the range of 10 minutes to 24 hours. The thorough blending of activators and co activators distributes these uniformly on the grains of host material. High temperature firing in atmosphere of gases described above at temperature in the range of 600- 1300°C melts the surface of the grain of the host material, dissolves and diffuses the activator/co-activators sinters the grains and recrystallization takes place. The washing and grinding of the fired material is done to get the desired particle size. The material is well dried in an electric oven at 60-150 °C to obtain long decay luminescent powder. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention. Example 1 10 g of zinc sulphide (ZnS) powder of 99.99% purity or better of size less than lOOµm is taken, to this 3 ml of activator cupric chloride (CuCl2.2H2O) solution of concentration 10"3g of Cu/ml is added. Then different co-activators are added as given in the following : Barium chloride (BaCl2) 1 gm, magnesium chloride (MgCl2) 0.4 gm, calcium chloride (CaCl2) 0.6 gm, potassium bromide (Kbr) 1 gm, potassium iodide (KI) 0.2 gm, sulfur (S) 1 gm. Some de-ionised/distilled water is added to make a uniform paste. The above wet mixture is dried in an electrical oven set at a temperature of 80 °C. The dried powder is further ground gently to make the mixture more uniform. The above powder is put in a covered alumina container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere in the enclosure is that of air or nitrogen. The temperature is raised to 800°C. The temperature is maintained for 3 hours. The material is then allowed to cool up to room temperature. The fired material is washed 3 times in hot de-ionised water and dried hi the oven set at 80°C. We thus get a green emitting long decay luminescent powder. Example 2 10 g of zinc sulfide (ZnS) powder of 99.99% purity of size less than lOOµm is taken, to this 3 ml of activator cupric chloride (CuCl2.2H2O) solution of concentration 10-3 g of Cu/ml is added. Then different co-activators are added as given in the following : Barium chloride (BaCl2) 1 gm, magnesium chloride (MgCl2) 0.4 gm, calcium chloride (CaCl2) 0.6 gm, potassium bromide (Kbr) 1 gm, potassium iodide (KI) 0.2 gm, sulfur (S) 1 gm. Some de-ionised/distilled water is added to make a uniform paste. The above wet mixture is dried in an electrical oven set at a temperature of 80°C. The dried powder is further ground gently to make the mixture more uniform. The above powder is put in a covered zinc oxide container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere in the enclosure is that of air or nitrogen. The temperature is raised to 800°C. The temperature is maintained for 3 hours. The material is then allowed to cool up to room temperature. The fired material is washed 3 times in hot de-ionised water and dried in the oven set at 80°C. We thus get a green emitting long decay luminescent powder. Example 3 10 g of zinc sulfide (ZnS) powder of 99.99% purity of size less than lOOµm is taken. To this 10 ml of activator cupric chloride (CuCl2.2H2O) solution of concentration 10-3 g of Cu/ml is added. Also 2 gm of sodium chloride (NaCl) is added to it. To this some de-ionised/distilled water is added to make a uniform paste. The above wet mixture is dried in an electrical oven set at a temperature of 80°C. The dried powder is further ground gently to make the mixing more uniform. The above powder is put in a quartz container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere within the enclosure is flushed clear of air with a mixture of hydrogen sulphide and hydrogen bromide gas in the ratio of 10:1 by volume. The temperature is raised to 1100°C while maintaining the above-mentioned gaseous atmosphere. The temperature and atmosphere is maintained for 30 minutes. The material is then allowed to cool up to 200 °C. The material is further cooled to room temperature in air. The fired material is washed 3 times in hot de-ionised water and dried in the oven set at 80°C. We thus get a green emitting long decay luminescent powder. Example 4 g of zinc sulfide (ZnS) powder and 2 g of cadmium sulfide (CdS) of 99.99% purity or better of size less than 100 µm is taken. To this 20 mg of activator cupric chloride (CuCl2-2H2O) and 1 g sodium chloride (NaCl) are added. Then 90 mg each of co-activators aluminum chloride (A1C13.6H2O), gallium chloride (GaCl3) and scandium chloride (ScCl3) are added. 1 mg of cobalt chloride (CoCl3) is also added to it. The above mixture is ground and thoroughly mixed. The above powder is put in a quartz container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere within the enclosure is flushed clear of air with a mixture of hydrogen sulphide and hydrogen chloride gas in the ratio of 9:1 by volume. The temperature is raised to 1000°C while maintaining the above-mentioned gaseous atmosphere. The temperature and atmosphere is maintained for 1 hour. The material is then allowed to cool up to 200°C. The material is further cooled to room temperature in air. The fired material is washed 3 times in hot de-ionised water and dried in the oven set at 80°C. We thus get a yellow emitting long decay luminescent powder. The above improved process with the composition described, thus yields a luminescent powder with long persistence ranging from a few second to a few hours. It gives out light of wavelength depending on the composition used when subjected to radiation's ranging from ultra-violet to visible light. The brightness of the emitted light shall be dependent on intensity and wavelength of ultra-violet radiation. The luminescent powder obtained is well crystalline, free flowing and of narrow particle size distribution between 5 to 70 µm. Decay time is of the order of several minutes which is a prerequisite for location, risk and control markings. The composition of the present invention is novel and the inventive step involved in the process of the present invention is in the use of a container of host material or an activator for processing of the composition. The advantages of the present invention are 1. Free fiowability and narrow particle size distribution of the powders in device fabrication when the powder is mixed with binders and highly uniform coatings are required. Sign displays and markings of the desired colours are obtained by choice of composition. 2.The application possibilities of such a powder are use in Exit sign boards, Emergency signs and low level lighting escape systems, Firemen's equipment, Outdoor path markings, Textile printing and Textile fibres etc. _3.the powder produced is excitable with ultraviolet and visible radiation in the range of 200 -5 50 nm. 4. The powder produced has a persistence (decay) time of ranging from a fraction of second to a few hour after removal of excitation source . We Claim: 1. A process for the preparation of improved long decay luminescent powder using a novel composition comprising host material selected from group IIB-VIA compounds of periodic table selected from oxides, sulphides, selenidies, telluride's of zinc, cadmium and mercury either singly or a mixture of two or more in the range of 1 - 50% wt. 1-1000 ppm of activator (s) selected from group IIB, VIIB of the elements of the periodic table such as herein described, either singly or a mixture of two or more; and 50 -1000 ppm of co-activator (s) selected from group IA, 11 A, IIIAA/VIIA elements of the periodic table selected from compound of aluminium, gallium, barium, magnesium, indium, chlorine, fluorine, bromine and iodine either singly or a mixture of two or more , said process comprising the steps of : firing the novel composition, at a temperature in the range of 600° - 1300°C for a period of 10 minutes to 20 hours, in a gaseous atmosphere containing a group VIA element, a mixture of group VIA element and one of the VIIA elements such as described herein, wherein the ratio of group VIA and VIIA in the gaseous atmosphere are in a ratio in the range of 1:0.1 to 1:1 by volume washing the resultant material obtained followed by grinding, sieving and drying by conventional methods to obtain improved long decay luminescent powder. 2. A process as claimed in claim 1, wherein the IIB/VIA compounds used are having of 99.99% purity and of size less than 100 urn. 3. A process as claimed in claims 1-3, wherein the activator(s) used are selected from compounds of copper, silver, gold and manganese of 99.99% purity. 4. A process as claimed in claims 1-4, wherein the firing of the composition is effected fusing a container selected from ceramic, quartz, host material, zinc oxide or any other refractory materials. 5. A process as claimed in claims 1 and 5, wherein the firing is effected in a gaseous atmosphere containing group VIA element and/or group VIIA element corresponding to the group VI element of the host material such as herein described , admixed with an inert gas. 6. A process as claimed in claims 1-6, wherein the firing is effected for a time duration of 30 minutes to 3 hours. 7. A process for the preparation of improved long decay luminescent powder using a novel composition substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for preparation of improved long decay luminescent powders using a novel composition
Long decay luminescent powders also known as long decay phosphor have the unique property of light emission in the visible range for a quite long time from few seconds to several hours after having been excited by higher energy radiations for short times of the order of one second or less.
Applications of these phosphors are almost limitless. To highlight a few, one may include emergency signs and low level lighting escape systems during general power failures or intentional power cuts, military applications, textile printing and textile fibres, lighting apparatus and switches, exit sign boards, electronic instrument dial pads etc.
We are not aware of any "standard method" which may be used for the preparation of Long decay luminescent powders although some research papers and patents are available as described in US patents Nos. 5376303, 5650094 and 5859496. Long decay phosphors are based on compositions involving complicated compositions of divalent metals with oxides, aluminates and titanates. Copper activated zinc sulfide phosphor was one of the earliest reported in the series. Typical procedures are described in the literature but the preparative details are not disclosed. The process for the preparation of Long decay luminescent zinc sulphide powder essentially involves mixing of impurities known as activators in high purity zinc sulphide powder, incorporation of impurities in the latter by high temperature firing and classification of particles in the required particle size range. According to Van Gool and his co workers as described in Philips Res. Rept. 15, 238-253, 1960; Philips Research Rept. 15, 254-274, 1960, Philips Res. Rept. Suppt. 3, 1-119, 1961, the starting material for the preparation of luminescent powder is precipitated zinc sulphide powder which is first wetted with a standard solution of the activator. The amount of solution used is determined by the concentration of the activator required. Concentration of the activator is responsible for intensity of the emitted light as well as the decay tune of the

emission also known as after glow. Incorporation of the activator through the process of diffusion is achieved by firing the material at high temperatures in silica container at temperatures in the range of 800-1200 °C in hydrogen sulphide gas atmospheres for a time duration ranging from a few minutes to 2-3 hrs. the material so obtained is suitably washed and classified for different sizes. The material is well dried before putting to use for making device. A large number investigators have studied the decay characteristics of the luminescence in zinc sulphide type phosphors as for example by G.F.J. Garlick as reported in Tans, electrochem. Soc. Vol 96, 90-113, 1949; d. Curie in "Luminescence in Crysrtals" . Methuen, London, 1963; S. Shionoya et. al, Phys. Chem. Solids 26, 697-710, 1965). The addition of second impurity which is referred to as a co-activator has also been reported in the literature. Such a co-activator in the first instance affect the colour of the emission. It is also known to affect the intensity of emission of the phosphor material and after glow of the emission after the excitation source is removed. It has been experienced that its effective role may depend on the amount of primary activator present and the precise manner in which the co activator is incorporated into the lattice of starting material. Thus the number of preparative parameters is very large. This complicated situation is also responsible for much of the apparently contradictory information found in the abovementioned literature. Therefore, it has been found that published data gives information about basic raw materials and activators to be used but, regarding parameters for the preparation which includes detailed process of incorporation of activators, nature and concentration of co-activators and types of salt to be used , no information is yet available. The long decay luminescent powder obtained on the basis of limited information is poorly crystalline and agglomerated type which has broad particle size distribution and lower brightness.
The main object of the present invention is to provide a composition useful for the preparation of an improved long decay luminescent powder.
Another object is to provide a process for the preparation of improved long decay luminescent powder using the composition of the present invention.

Yet another object of the present invention is to provide a long decay luminescent powder which is free flowing and has narrow particle size distribution.
Still another object is to provide a long decay luminescent powder having low energy excitation.
Another object is to provide a long decay luminescent powder capable of providing varied emission colours.
host material selected from group IIB-VIA compounds of periodic table either singly or a mixture of two or more, 1-1000 ppm of activator (s) selected from group IB, VIIB of the elements of the periodic table either singly or a mixture of two or more; and 50 -1000 ppm of co-activator (s) selected from group IA, IIA, IIIA/VIIA elements of the periodic table either singly or a mixture of two or more,.'!
In an embodiment of the present invention, the host material, IIB-VIA compounds, used may be selected from oxides, sulphides, selenides, tellurides of zinc, cadmium and mercury of 99.99% purity and of size less than 100 µrn.
In yet another embodiment of the present invention, the host material may also contain another compound selected from IIB-VIA compounds in the range of 1 to 50% wt.
In still another embodiment of the present invention the activator(s) to be used may be selected from compounds of copper, silver, gold and manganese of 99.99% purity.
In another embodiment of the present invention the co-activator(s) used may be a compound of aluminum, gallium, barium, magnesium, indium, chlorine, fluorine, bromine and iodine of 99.99% purity.
The improved composition of the present invention which is useful for the preparation of long decay luminescent powder is not a mere admixture but a synergistic mixture having properties which are different from the aggregated properties of the individual components.
Accordingly, the present invention provides a process for the preparation of improved
long decay luminescent powder using a novel composition Comprising which

comprises: firing the novel composition, at a temperature in the range of 600° - 1300°C for a period of 10 minutes to 20 hours, in a gaseous atmosphere containing a group VIA element, a mixture of group VIA element and one of the VIIA elements such as described herein, wherein the ratio of group VIA and VIIA in the gaseous atmosphere are in a ratio in the range of 1:0.1 to 1:1 by volume washing the resultant material obtained followed by grinding, sieving and drying by conventional methods to obtain improved long decay luminescent powder.
In an embodiment of the present invention, the firing of the composition may be effected using a container selected from ceramic, quartz, host material, zinc oxide or any other refractory materials.
In another embodiment of the present invention, the firing may be effected in a gaseous atmosphere containing group VIA element and/or group VIA element corresponding to the group VI element of the host material admixed with an inert gas.
In yet another embodiment of the present invention, the elements of group VIA and VIIA in the gaseous atmosphere may be in a ratio in the range of 1:0.1 to 1:1 by volume.
In another embodiment of the present invention, the firing may be effected at a temperature in the range of 800 - 1200°C.
In still other embodiment of the present invention, the firing is effected for a time duration in the range of 30 minutes to 3 hours.
The process related to the present invention involves the selection of a host material from group IIB-VIA compounds of periodic table either singly or a mixture of two or more, for example, oxides, sulphides, selenides, tellurides of zinc, cadmium and mercury, each of 99.99% purity, of size less than 100µm depending upon the application and the process of device application. The activators are selected from group IB or VIIB elements of the periodic table which can be copper, silver, gold and manganese, of 99.9% purity in the range of 1 - 1000 ppm based on the required emission colour of the long decay luminescent powder.

The co-activator is selected from group IA, IIA, IIIA and VIIA elements of the periodic table which may be added singly or in combination in the form of compounds of aluminium, gallium, barium, magnesium, indium, chlorine, fluorine, bromine and iodine of 99.9% purity and in the range of 50-10000 ppm on the basis of the host material as selected above so that the charge compensation of the host material is taken care of and incorporation of activator is efficient. The above composition is thoroughly mixed. The above powder is filled in a ceramic/quartz/zinc oxide container and put in a ceramic enclosure both of which could be heated up to 1600 C and which is impervious to gases. It is advantageous to use processing container made out of zinc oxide or host material. It helps in the incorporation of trace additions of activators and co-activators quite effectively and has longer life thereby reducing the cost per piece considerably. The mixture is heated at a temperature in the range of 600-1300° C in a gaseous atmosphere containing a mixture of group VIA and/or group VIIA halogen elements. These gases can be admixed with an inert gas. The two elements of the group VIA and VIIA in the gases can be in ratio of 1:0.1 to 1:1 by volume respectively. The time duration of the firing is in the range of 10 minutes to 24 hours. The thorough blending of activators and co activators distributes these uniformly on the grains of host material. High temperature firing in atmosphere of gases described above at temperature in the range of 600- 1300°C melts the surface of the grain of the host material, dissolves and diffuses the activator/co-activators sinters the grains and recrystallization takes place. The washing and grinding of the fired material is done to get the desired particle size. The material is well dried in an electric oven at 60-150 °C to obtain long decay luminescent powder.
The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.
Example 1
10 g of zinc sulphide (ZnS) powder of 99.99% purity or better of size less than lOOµm is taken, to this 3 ml of activator cupric chloride (CuCl2.2H2O) solution of concentration 10"3g of Cu/ml is added. Then different co-activators are added as given

in the following : Barium chloride (BaCl2) 1 gm, magnesium chloride (MgCl2) 0.4 gm, calcium chloride (CaCl2) 0.6 gm, potassium bromide (Kbr) 1 gm, potassium iodide (KI) 0.2 gm, sulfur (S) 1 gm. Some de-ionised/distilled water is added to make a uniform paste. The above wet mixture is dried in an electrical oven set at a temperature of 80 °C. The dried powder is further ground gently to make the mixture more uniform. The above powder is put in a covered alumina container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere in the enclosure is that of air or nitrogen. The temperature is raised to 800°C. The temperature is maintained for 3 hours. The material is then allowed to cool up to room temperature. The fired material is washed 3 times in hot de-ionised water and dried hi the oven set at 80°C. We thus get a green emitting long decay luminescent powder.
Example 2
10 g of zinc sulfide (ZnS) powder of 99.99% purity of size less than lOOµm is taken, to this 3 ml of activator cupric chloride (CuCl2.2H2O) solution of concentration 10-3 g of Cu/ml is added. Then different co-activators are added as given in the following : Barium chloride (BaCl2) 1 gm, magnesium chloride (MgCl2) 0.4 gm, calcium chloride (CaCl2) 0.6 gm, potassium bromide (Kbr) 1 gm, potassium iodide (KI) 0.2 gm, sulfur (S) 1 gm. Some de-ionised/distilled water is added to make a uniform paste. The above wet mixture is dried in an electrical oven set at a temperature of 80°C. The dried powder is further ground gently to make the mixture more uniform. The above powder is put in a covered zinc oxide container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere in the enclosure is that of air or nitrogen. The temperature is raised to 800°C. The temperature is maintained for 3 hours. The material is then allowed to cool up to room temperature. The fired material is washed 3 times in hot de-ionised water and dried in the oven set at 80°C. We thus get a green emitting long decay luminescent powder.
Example 3
10 g of zinc sulfide (ZnS) powder of 99.99% purity of size less than lOOµm is taken. To this 10 ml of activator cupric chloride (CuCl2.2H2O) solution of concentration 10-3

g of Cu/ml is added. Also 2 gm of sodium chloride (NaCl) is added to it. To this some de-ionised/distilled water is added to make a uniform paste. The above wet mixture is dried in an electrical oven set at a temperature of 80°C. The dried powder is further ground gently to make the mixing more uniform. The above powder is put in a quartz container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere within the enclosure is flushed clear of air with a mixture of hydrogen sulphide and hydrogen bromide gas in the ratio of 10:1 by volume. The temperature is raised to 1100°C while maintaining the above-mentioned gaseous atmosphere. The temperature and atmosphere is maintained for 30 minutes. The material is then allowed to cool up to 200 °C. The material is further cooled to room temperature in air. The fired material is washed 3 times in hot de-ionised water and dried in the oven set at 80°C. We thus get a green emitting long decay luminescent
powder.
Example 4
g of zinc sulfide (ZnS) powder and 2 g of cadmium sulfide (CdS) of 99.99% purity or better of size less than 100 µm is taken. To this 20 mg of activator cupric chloride (CuCl2-2H2O) and 1 g sodium chloride (NaCl) are added. Then 90 mg each of co-activators aluminum chloride (A1C13.6H2O), gallium chloride (GaCl3) and scandium chloride (ScCl3) are added. 1 mg of cobalt chloride (CoCl3) is also added to it. The above mixture is ground and thoroughly mixed. The above powder is put in a quartz container and the container is put in a ceramic enclosure of a heating equipment. The atmosphere within the enclosure is flushed clear of air with a mixture of hydrogen sulphide and hydrogen chloride gas in the ratio of 9:1 by volume. The temperature is raised to 1000°C while maintaining the above-mentioned gaseous atmosphere. The temperature and atmosphere is maintained for 1 hour. The material is then allowed to cool up to 200°C. The material is further cooled to room temperature in air. The fired material is washed 3 times in hot de-ionised water and dried in the oven set at 80°C. We thus get a yellow emitting long decay luminescent powder.

The above improved process with the composition described, thus yields a luminescent powder with long persistence ranging from a few second to a few hours. It gives out light of wavelength depending on the composition used when subjected to radiation's ranging from ultra-violet to visible light. The brightness of the emitted light shall be dependent on intensity and wavelength of ultra-violet radiation. The luminescent powder obtained is well crystalline, free flowing and of narrow particle size distribution between 5 to 70 µm. Decay time is of the order of several minutes which is a prerequisite for location, risk and control markings.
The composition of the present invention is novel and the inventive step involved in the process of the present invention is in the use of a container of host material or an activator for processing of the composition. The advantages of the present invention are
1. Free fiowability and narrow particle size distribution of the powders in device fabrication when the powder is mixed with binders and highly uniform coatings are required. Sign displays and markings of the desired colours are obtained by choice of composition.
2.The application possibilities of such a powder are use in Exit sign boards, Emergency signs and low level lighting escape systems, Firemen's equipment, Outdoor path markings, Textile printing and Textile fibres etc.
_3.the powder produced is excitable with ultraviolet and visible radiation in the range of 200 -5 50 nm.
4. The powder produced has a persistence (decay) time of ranging from a fraction of second to a few hour after removal of excitation source .

We Claim:
1. A process for the preparation of improved long decay luminescent powder using a novel composition comprising host material selected from group IIB-VIA compounds of periodic table selected from oxides, sulphides, selenidies, telluride's of zinc, cadmium and mercury either singly or a mixture of two or more in the range of 1 - 50% wt. 1-1000 ppm of activator (s) selected from group IIB, VIIB of the elements of the periodic table such as herein described, either singly or a mixture of two or more; and 50 -1000 ppm of co-activator (s) selected from group IA, 11 A, IIIAA/VIIA elements of the periodic table selected from compound of aluminium, gallium, barium, magnesium, indium, chlorine, fluorine, bromine and iodine either singly or a mixture of two or more , said process comprising the steps of : firing the novel composition, at a temperature in the range of 600° - 1300°C for a period of 10 minutes to 20 hours, in a gaseous atmosphere containing a group VIA element, a mixture of group VIA element and one of the VIIA elements such as described herein, wherein the ratio of group VIA and VIIA in the gaseous atmosphere are in a ratio in the range of 1:0.1 to 1:1 by volume washing the resultant material obtained followed by grinding, sieving and drying by conventional methods to obtain improved long decay luminescent powder.

2. A process as claimed in claim 1, wherein the IIB/VIA compounds used
are having of 99.99% purity and of size less than 100 urn.
3. A process as claimed in claims 1-3, wherein the activator(s) used are
selected from compounds of copper, silver, gold and manganese of
99.99% purity.
4. A process as claimed in claims 1-4, wherein the firing of the
composition is effected fusing a container selected from ceramic,
quartz, host material, zinc oxide or any other refractory materials.
5. A process as claimed in claims 1 and 5, wherein the firing is effected in
a gaseous atmosphere containing group VIA element and/or group
VIIA element corresponding to the group VI element of the host
material such as herein described , admixed with an inert gas.
6. A process as claimed in claims 1-6, wherein the firing is effected for
a time duration of 30 minutes to 3 hours.
7. A process for the preparation of improved long decay luminescent
powder using a novel composition substantially as herein described
with reference to the examples.

Documents:

445-del-1999-abstract.pdf

445-del-1999-claims.pdf

445-del-1999-correspondence-others.pdf

445-del-1999-correspondence-po.pdf

445-del-1999-description (complete).pdf

445-del-1999-form-1.pdf

445-del-1999-form-19.pdf

445-del-1999-form-2.pdf

445-del-1999-petition-138.pdf

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Patent Number

215878

Indian Patent Application Number

445/DEL/1999

PG Journal Number

12/2008

Publication Date

21-Mar-2008

Grant Date

05-Mar-2008

Date of Filing

19-Mar-1999

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	PRADEEP KUMAR GHOSH	NATIONAL PHYSICAL LABORATORY NEW DELHI.
2	HARISH CHANDER	NATIONAL PHYSICAL LABORATORY NEW DELHI.
3	PARMANAND	NATIONAL PHYSICAL LABORATORY NEW DELHI.`
4	VIRENDRA SHANKAR	NATIONAL PHYSICAL LABORATORY NEW DELHI.

PCT International Classification Number

C09Q 11/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA