Title of Invention	A PROCESS FOR THE SYNTHESIS OF NEW BLUE EMITTING CE3+ ACTIVATED BORATE PHOSPHORS FOR USE IN FLUORESCENT LAMPS AND TV TUBES
Abstract	A Process for the synthesis of new blue emitting Ce3+ activated borate phosphors for use in fluorescent lamps and TV tubes, having the formula A6Mi-xCexM1(BO3)6 wherein A=La, Sr; M = La, Y, Gd, Lu; and M1 = Mg, Al, Ga, and x ranging from 0.001 -1 and the said synthesis is carried out by the solid state reaction using at least four of the ingredients from the group consisting of SrC03 (5.5 - 6.5 mole), La203 or Gd203 or Lu203 (0.001 - 1.0 mole), MgO (0.85 - 1.1 mole) [or AI(N03)39H20], Ce02 (0.001 - 1.1 mole ) and H3B03 (5.5 - 6.5 mole) comprising the followings steps: (i) mixing and grinding of the ingredients selected in suitable proportions, for about 15-45 minutes in an agate mortar with acetone, (ii) subjecting the ground ingredients to a pre-firing in air at temperatures ranging from 150-300°C for a period of time ranging from 2-10 hr. and (iii) subjecting the pre-heated powders obtained from step (ii) to a final heat treatment under reducing atmosphere at temperatures ranging from 750-1050°C for a period ranging from 6-30 hours, to obtain the desired phosphors useful as blue components in low pressure mercury vapour lamps, deluxe lamps and in television tubes, when excited with UV radiation of wavelengths 254 and 355 nm

Title of Invention

A PROCESS FOR THE SYNTHESIS OF NEW BLUE EMITTING CE3+ ACTIVATED BORATE PHOSPHORS FOR USE IN FLUORESCENT LAMPS AND TV TUBES

Abstract

A Process for the synthesis of new blue emitting Ce3+ activated borate phosphors for use in fluorescent lamps and TV tubes, having the formula A6Mi-xCexM1(BO3)6 wherein A=La, Sr; M = La, Y, Gd, Lu; and M1 = Mg, Al, Ga, and x ranging from 0.001 -1 and the said synthesis is carried out by the solid state reaction using at least four of the ingredients from the group consisting of SrC03 (5.5 - 6.5 mole), La203 or Gd203 or Lu203 (0.001 - 1.0 mole), MgO (0.85 - 1.1 mole) [or AI(N03)39H20], Ce02 (0.001 - 1.1 mole ) and H3B03 (5.5 - 6.5 mole) comprising the followings steps: (i) mixing and grinding of the ingredients selected in suitable proportions, for about 15-45 minutes in an agate mortar with acetone, (ii) subjecting the ground ingredients to a pre-firing in air at temperatures ranging from 150-300°C for a period of time ranging from 2-10 hr. and (iii) subjecting the pre-heated powders obtained from step (ii) to a final heat treatment under reducing atmosphere at temperatures ranging from 750-1050°C for a period ranging from 6-30 hours, to obtain the desired phosphors useful as blue components in low pressure mercury vapour lamps, deluxe lamps and in television tubes, when excited with UV radiation of wavelengths 254 and 355 nm

Full Text	The present invention relates to a process for the synthesis of new blue emitting Ce3+ activated borate phosphors for use in fluorescent lamps and TV tubes. More particularly, the invention relates to a process for the synthesis of new blue emitting Ce3+ activated borate phosphors having the formula A6M1-xCexM(BO3)6 wherein A=La,Sr; M = La,Y, Gd, Lu; and M1 =Mg, Al, Ga, and x ranging from 0.001-1. Phosphors for fluorescent lamps [low pressure mercury vapour (Ipmv) lamps, excited by mercury discharge at low pressure corresponding to radiation of wavelength 254 nm] range from the conventional halophosphates [Cas(PO4)3F : Sb3+, Mn2+; with a color rendering index (CRI) ~ 70 and an efficacy 65 Im/W], to tricolor blend of rare earth phosphors (with an improved CRI of 90 and an efficacy ~ 85 Im/W). The CRI of halophosphates can be increased without altering the lumen output by adding a blue emitter (broad band) to it, which covers the whole of the blue region. The phosphor Ca5(PO4)3F : Sb (emission maximum at 480 nm) satisfies this requirement. In the case of high efficiency tricolor (trichromatic) fluorescent lamps based on rare-earth phosphors, where a blend of three different inorganic compounds each emitting in different regions viz., blue (450 nm), green (540 nm) and red (610 nm) mixes upon to give out white light, when excited by mercury discharge at low pressure corresponding to radiation of wavelength 254 nm, further improvement of CRI is not a serious requirement. Still higher value of CRI (95) is achieved in the case of super-deluxe lamps (efficacy only 65 Im/W). This is possible by having a blend of a broad band emitting red with a broad band emitting blue as well as a line emitting green. The phosphor Sr4Al14O25 : Eu2+ (emission maximum at 490 nm) and Sr2p207 : Eu2+ (emission maximum at 420 nm) act as blue components in deluxe lamps. In general, narrow band (or line) emitters help to increase the efficacy while broad band emitters increase the CRI in Ipmv lamps. The requirements of all these components for use in Ipmv lamps are mainly strong emission in the required regions when excited with 254 nm wavelength and thus strong absorption of 254 nm radiation. In addition, it must be easily synthesizeable and must be stable [the inorganic dopant(s) present in the phosphor should not undergo any change in its valence state when heated to high temperatures ≥ 600° C, one of the essential conditions required during the process of lamp manufacturing (baking), and the phosphor should not degrade at ordinary and at high temperatures (≥ 900° C) and on continuous irradiation by light of wavelength 254 nm]. Hitherto, the blue components have been either calcium tungstate (CaWO4, emission at 420 nm) or calcium halophosphate (Ca5(PO4)3F) doped with antimony (Sb3+) in the case of conventional halophosphate system, or barium magnesium aluminate (BaMgAl10On) and strontium chloroapatite (Sr5(PO4)3Cl) doped with divalent europium (Eu2+) in the tricolor phosphor blend, or strontium aluminate (Sr2Al6O11) and strontium pyrophosphate (S^PaO?) doped with divalent europium (Eu2+) in deluxe lamps. Eventhough, these phosphors emit in the required region with high intensity, the phosphates and aluminates require very high temperatures (≥ 1200° C for phosphates and ≥ 1500° C for aluminates) for their synthesis. In addition, they require a strong reducing atmosphere (N2: H2 or Ffe gas flow) to reduce Eu3+ to Eu2+, at that temperatures. In the case of cathode-ray phosphors used in conventional televisions (CTV), the phosphor ZnS : Ag+ is the blue component. Here, the phosphor needs to get excited with long wavelength UV (355 nm) which is compatible with the cathode-ray excitation. For the beam-index phosphor used in television tubes, a short decay time is necessary to avoid afterglow or persistence. The life time of an electron in the excited state of Ce3+ ion, when doped in any inorganic crystal lattice is very short. Hence, the Ce3+ ion-doped lattices are preferred to avoid afterglow. Eventhough the silicate phosphors Y2Si2O7: Ce3+ (emission maximum at 375 nm) and Y2SiO5: Ce3+ (emitting in the blue region) are known as beam-index phosphors, the silicate phosphors not only require very high temperatures for their synthesis but also require repeated firing at high temperatures with several intermittent grindings. The main object of the present invention is to provide a process for the synthesis of new blue emitting Ce3+activated borate phosphors for use in fluorescent lamps and TV tubes, which obviates the drawbacks as detailed above. These borate phosphors can be synthesized easily at lower temperatures than those required for the synthesis of the existing aforementioned commercial blue phosphors and can be excited with radiation of wavelength 254 and 355 nm. In addition, these compounds emit a broad band (blue region) with very high intensity under both excitations. The above objectives may be accomplished, by using new borate phosphors of the type Sr6M1-xCexM'(BO3)6 with M = La, Gd, Lu and M1 = Ga ; La1. xCexSr5YMg(BO3)6 where 0.001  x  1 in both ; and SreY1-xCexAl(BO3)6 where 0.001  x  0.3, with a Rhombohedral-hexagonal structure. In these compounds, so far no attempts have been made to study the Ce3+ luminescence properties. In addition, when x = 1 in the above series of compounds, we get the new borate phosphors Sr6CeGa(BO3)6 and CeSr5YMg(BO3)6. In Fig.l (a = ZnS : Ag ; b = CaWO4 ; c - Sr2P2O7 : Eu2+ ; d = Sr6(LaCe)Ga(BO3)6) of the drawings accompanying this specification, the excitation spectra of various compounds are given along with our borate phosphors for comparison. When scanned for excitation by keeping the emission maximum (em) at 420 nm, the excitation band is found to be a broad band (220 - 375 nm) with a peak extending from 316-330nm and a side band at 355 nm, as shown in Fig. Id of the drawings accompanying this specification for a particular composition I which corresponds to Sr6CeGa(BO3)6(M = Ce ; M1 = Ga ; and x = 1.0). The excitation bands of other standard commercial phosphors are shown (Fig. l(a, b, c) of the drawings accompanying this specification) for comparison. Hence, it is clear that these borate phosphors can be excited efficiently with radiation of wavelength 254 as well as 355 nm In Fig.2 (a = ZnS : Ag ; b = Ca5(PO4)3F : Sb3*; c = CaWO4; d = Sr2P2O7 : Eu2+ ; e = Sr6CeGa(BO3)6 and f = Sr6Lao. 99Ceo.oiGa(BO3)6) of the drawings accompanying this specification, the emission spectra of various compounds (em = 254 nm) are given along with our borate phosphors for comparison. When excited with radiation of wavelength 254 nm(em) , these materials are found to emit a broad band (340 - 480 nm) with a peak in the range 410 - 420 nm for high Ce3+ concentrations and in the range 400 - 408 nm for low Ce3+ concentrations as shown in Fig. 2(e, f) of The drawings accompanying this specification In fig. 3 ( a = ZnS : Ag; b = Sr2P207 : Eu2+; c = SreCeGa(B03)6) of the drawings accompanying this specification, the emission spectra of various compounds (ex C = 355 nm) are given along with our borate phosphors for comparison. When excited with radiation of wavelength 355 nm, these borate phosphors are found to give a broad band which peaks at 420 nm as shown in Fig. 3c of the drawings accompanying this specification for the composition I. Proper comparison is made with the standard commercial phosphors Sr5(P04)3 Cl : Eu2+, Sr2P207: Eu2+ (obtained from Nichia Co., Japan), Ca5(P04)3F : Sb, CaW04 and ZnS : Ag (home made ) and our compounds are found to emit in the region as shown in Fig. 2 and Fig. 3 of the drawings accompanying this specification for various excitation wavelength. Accordingly, the present invention provides a A Process for the synthesis of new blue emitting Ce3+ activated borate phosphors for use in fluorescent lamps and TV tubes, having the formula AeM1-xCexM1(BO3)6 wherein A=La, Sr; M = La, Y, Gd, Lu; and M1 = Nig, Al, Ga, and x ranging from 0.001 -1 and the said synthesis is carried out by the solid state reaction using at least four of the ingredients from the group consisting of SrC03 (5.5 - 6.5 mole), La203 or Gd203 or Lu203 (0.001 - 1.0 mole), MgO (0.85 - 1.1 mole) [or AI(N03)39H20], Ce02 (0.001 - 1.1 mole ) and H3B03 (5.5 - 6.5 mole) comprising the followings steps: (i) mixing and grinding of the ingredients selected in suitable proportions, for about 15-45 minutes in an agate mortar with acetone, (ii) subjecting the ground ingredients to a pre-firing in air at temperatures ranging from 150-300°C for a period of time ranging from 2-10 hr. and (iii) subjecting the pre-heated powders obtained from step (ii) to a final heat treatment under reducing atmosphere at temperatures ranging from 750-1050°C for a period ranging from 6-30 hours, to obtain the desired phosphors useful as blue components in low pressure mercury vapour lamps, deluxe lamps and in television tubes, when excited with UV radiation of wavelengths 254 and 355 nm. In our co-pending application no. 53/del/99 we have described and claimed a process for the synthesis of new green emitting Tb3+ activated borate phosphor for use in low pressure mercury vapour lamps. In an embodiment of the invention, the synthesis of the borate phosphors is carried out under reducing atmosphere created by either activated charcoal or H2 gas flow. According to a feature of the invention, the synthesized borate phosphors have particle sizes in the range of 5-15 µrn According to the another feature of the invention, the synthesized borate phosphors show intense blue emission in the region A. = 400 - 420 nm. According to yet another feature of the invention, the synthesized borate phosphors are directly excited with radiation of wavelengths at 254 nm and 355 nm. According to the present invention, new borate phosphors have been synthesized by solid state reaction using the ingredients SrCO3, Ln2O3 (Ln = La, Y, Gd, Lu), M2O3 (M = Al, Ga), MgO, CeO2 and H3BO3 at about 750 - 1050° C under reducing atmosphere. Since the dopant cerium was required to yield the necessary luminescence by undergoing excitation-emission processes, it has been added as oxide along with the other raw materials. In an experiment, SrCO3 was mixed with H3BO3, La2O3, Ga2O3 and CeO2 in an agate mortar, ground thoroughly with acetone and allowed to dry in air. The mixture was then kept inside an alumina crucible (~ 20 ml capacity) and pre-fired in air at 150 - 300° C for 5 - 10 hrs. It was ground and kept in the same crucible over which ashless filter paper was placed so as to cover the sample fully. This crucible was then placed inside a big alumina crucible (75 - 100 ml capacity) containing 20 - 30 gm of activated charcoal at the bottom to create a non-oxidizing atmosphere in the crucible. The big crucible was then covered with a lid and placed — inside a muffle furnace. The furnace was then set to reach 750 - 10500 C and kept for 5-30 hours. The sample was cooled inside the furnace/quenched in air to room temperature. The final product obtained is a white powder. The experiments were repeated separately with H2 gas flow as the non-oxidizing/reducing medium instead of activated charcoal. The results obtained showed that, the average particle size of these powders was found to be in the range of 3-28 µm. The phase purity of these compounds was confirmed from powder X-ray data. The following Examples are given by way of illustrations of the present invention and should not be construed to limit the scope of the present invention. Example 1: Ingredients used in measures SrCO3 - 1.476 gm (0.01 mole) H3BO3 = 0.618 gm (0.01 mole) La2O3 = 0.269 gm (0.000825 mole) Ga2O3 = 0.156 gm (0.000832 mole) CeO2 = 0.003 gm (0.0000174 mole) Procedure used Pre-firng temperature : 300 0C; Duration : 10 hr. 0 Final heating temperature : 900 C ; Duration : 8 hr. Firing atmosphere : reducing atm. created by burning activated charcoal Results Composition of the finally formed product: Sr6Lao.99Ceo.o1Ga(BO3)6 Colour of the final product : White Density : 4.34 gm/cc (theor: 4.46 gm/cc) Particle size : 3 - 28 µm See also Fig.l & Fig. 2 of the drawings for luminescence properties. Example 2: Ingredients used in measures SrCO3 = 1.476 gm (0.01 mole) H3BO3 = 0.618 gm (0.01 mole) Ga2O3 = 0.156 gm (0.000832 mole) CeO2 = 0.287 gm (0.001667 mole) Procedure used Pre-firng temperature : 300 0C ; Duration : 10 hr. Final heating temperature : 900 C ; Duration : 8 hr. Firing atmosphere : reducing atm. created by H2 gas flow Results Composition of the finally formed product: Sr6CeGa(BO3)6 Colour of the final product : White weight of the final product : 1.76 gm (theor : 1.81 gm) Particle size : 3 - 28 µm See also Fig. 1, Fig.2 & Fig.3 of the drawings for luminescence properties. Example 3: Ingredients used in measures SrCO3 = 1.230 gm (0.00833 mole) H3BO3 = 0.618 gm (0.01 mole) Y2O3 = 0.188 gm (0.00083 mole) MgO = 0.067 gm (0.00166 mole) CeO2 = 0.287 gm (0.00166 mole) Procedure used Final heating temperature : 1050 0C ; Duration : llhr. Firing atmosphere : reducing atm. created by burning activated charcoal Results Composition of the finally formed product: CeSr5YMg(BO3)6 Colour of the final product : White Density : 4.26 gm/cc (theor : 4.35 gm/cc) Particle size : 2 - 28µm The main advantages of the present invention are: 1. The borate phosphors presently studied contain only Ce3+ ion as the activator which substitutes for the ion present at the M site in the formula Sr6MM'(BO3)6 (where M = La, Gd, Lu ; M1 = Ga) and at the La site in LaSr5YMg(BO3)6. 2. The borate phosphors presently studied can be synthesized easily at lower temperatures than those required for the existing commercial blue phosphors. 3. These borate phosphors can be excited efficiently with radiation of wavelength 254 and 355 nm. 4. Both a high emission intensity (light output comparable to or greater than the commercial blue phosphors) as well as a high value of CRI can be possible with these borate phosphors. 5. These borate phosphors can be used (as a blue phosphor) in Ipmv and super-deluxe lamps and ( as a beam-index phosphor) in television tubes because of their efficient emission under various excitation wavelength (254 and 355 nm). We Claim: 1. A Process for the synthesis of new blue emitting Ce3+ activated borate phosphors for use in fluorescent lamps and TV tubes, having the formula A6M1-xCexM1(B03)6 wherein A=l_a, Sr; M = La, Y, Gd, Lu; and M1 = Mg, Al, Ga, and x ranging from 0.001 - 1 and the said synthesis is carried out by the solid state reaction using at least four of the ingredients from the group consisting of SrC03 (5.5 - 6.5 mole), La203 or Gd203 or Lu203 (0.001 - 1.0 mole), MgO (0.85 - 1.1 mole) [or AI(N03)39H20], Ce02 (0.001 - 1.1 mole ) and H3B03 (5.5 - 6.5 mole) comprising the fallowings steps: (i) mixing and grinding of the ingredients selected in suitable proportions, for about 15-45 minutes in an agate mortar with acetone, (ii) subjecting the ground ingredients to a pre-firing in air at temperatures ranging from 150-300°C for a period of time ranging from 2-10 hr. and (iii) subjecting the pre heated powders obtained from step (ii) to a final heat treatment under reducing atmosphere at temperatures ranging from 750-1050°C for a period ranging from 6 - 30 hours, to obtain the desired phosphors useful as blue components in low pressure mercury vapour lamps, deluxe lamps and in television tubes, when excited with UV radiation of wavelengths 254 and 355 nm. 2. A process as claimed in claim 1 wherein the synthesis of the borate phosphors are carried out under reducing atmosphere created by either activated charcoal or H2 gas flow. 3. A process as claimed in claims 1 & 2 wherein the synthesized borate phosphors have particle sizes in the range of 5 - 15 µm. 4. A process as claimed in claims 1 & 2 wherein the synthesized borate phosphors show intense blue emission in the region A = 400 - 420 nm. 5. A process as claimed in claim 1&2 wherein the synthesized borate phosphors are directly excited with radiation of wavelengths at 254 nm and 355 nm. 6. A process for the synthesis of new blue emitting Ce3+ activated borate phosphors for fluorescent lamps and TV tubes substantially as herein described with reference to the examples and drawings accompanying this specification.

Full Text

The present invention relates to a process for the synthesis of new blue emitting Ce3+ activated borate phosphors for use in fluorescent lamps and TV tubes. More particularly, the invention relates to a process for the synthesis of new blue emitting Ce3+ activated borate phosphors having the formula A6M1-xCexM(BO3)6 wherein A=La,Sr; M = La,Y, Gd, Lu; and M1 =Mg, Al, Ga, and x ranging from 0.001-1.
Phosphors for fluorescent lamps [low pressure mercury vapour (Ipmv) lamps, excited by mercury discharge at low pressure corresponding to radiation of wavelength 254 nm] range from the conventional halophosphates [Cas(PO4)3F : Sb3+, Mn2+; with a color rendering index (CRI) ~ 70 and an efficacy 65 Im/W], to tricolor blend of rare earth phosphors (with an improved CRI of 90 and an efficacy ~ 85 Im/W). The CRI of halophosphates can be increased without altering the lumen output by adding a blue emitter (broad band) to it, which covers the whole of the blue region. The phosphor Ca5(PO4)3F : Sb (emission maximum at 480 nm) satisfies this requirement. In the case of high efficiency tricolor (trichromatic) fluorescent lamps based on rare-earth phosphors, where a blend of three different inorganic compounds each emitting in different regions viz., blue (450 nm), green (540 nm) and red (610 nm) mixes upon to give out white light, when excited by mercury discharge at low pressure corresponding to radiation of wavelength 254 nm, further improvement of CRI is not a serious requirement. Still higher value of CRI (95) is achieved in the case of super-deluxe lamps (efficacy only 65 Im/W). This is possible by having a blend of a broad band emitting red with a broad band emitting blue as well as a line emitting green. The phosphor Sr4Al14O25 : Eu2+ (emission maximum at 490 nm) and Sr2p207 : Eu2+ (emission maximum at 420 nm) act as blue components in deluxe lamps. In general, narrow band (or line) emitters help to increase the efficacy while broad band emitters increase the CRI in Ipmv lamps. The requirements of all these components for use in Ipmv lamps are mainly strong emission in the required regions when excited with 254 nm wavelength and thus strong absorption of 254 nm radiation. In addition, it must be easily synthesizeable and must be stable [the inorganic dopant(s) present in the phosphor should not undergo any change in its valence state when heated to high

temperatures ≥ 600° C, one of the essential conditions required during the process of lamp manufacturing (baking), and the phosphor should not degrade at ordinary and at high temperatures (≥ 900° C) and on continuous irradiation by light of wavelength 254 nm]. Hitherto, the blue components have been either calcium tungstate (CaWO4, emission at 420 nm) or calcium halophosphate (Ca5(PO4)3F) doped with antimony (Sb3+) in the case of conventional halophosphate system, or barium magnesium aluminate (BaMgAl10On) and strontium chloroapatite (Sr5(PO4)3Cl) doped with divalent europium (Eu2+) in the tricolor phosphor blend, or strontium aluminate (Sr2Al6O11) and strontium pyrophosphate (S^PaO?) doped with divalent europium (Eu2+) in deluxe lamps. Eventhough, these phosphors emit in the required region with high intensity, the phosphates and aluminates require very high temperatures (≥ 1200° C for phosphates and ≥ 1500° C for aluminates) for their synthesis. In addition, they require a strong reducing atmosphere (N2: H2 or Ffe gas flow) to reduce Eu3+ to Eu2+, at that temperatures.
In the case of cathode-ray phosphors used in conventional televisions (CTV), the phosphor ZnS : Ag+ is the blue component. Here, the phosphor needs to get excited with long wavelength UV (355 nm) which is compatible with the cathode-ray excitation. For the beam-index phosphor used in television tubes, a short decay time is necessary to avoid afterglow or persistence. The life time of an electron in the excited state of Ce3+ ion, when doped in any inorganic crystal lattice is very short. Hence, the Ce3+ ion-doped lattices are preferred to avoid afterglow. Eventhough the silicate phosphors Y2Si2O7: Ce3+ (emission maximum at 375 nm) and Y2SiO5: Ce3+ (emitting in the blue region) are known as beam-index phosphors, the silicate phosphors not only require very high temperatures for their synthesis but also require repeated firing at high temperatures with several intermittent grindings.
The main object of the present invention is to provide a process for the synthesis of new blue emitting Ce3+activated borate phosphors for use in fluorescent lamps and TV tubes, which obviates the drawbacks as detailed above. These borate phosphors can be synthesized easily at lower temperatures than those

required for the synthesis of the existing aforementioned commercial blue phosphors and can be excited with radiation of wavelength 254 and 355 nm. In addition, these compounds emit a broad band (blue region) with very high intensity under both excitations.
The above objectives may be accomplished, by using new borate phosphors of the type Sr6M1-xCexM'(BO3)6 with M = La, Gd, Lu and M1 = Ga ; La1. xCexSr5YMg(BO3)6 where 0.001  x  1 in both ; and SreY1-xCexAl(BO3)6 where 0.001  x  0.3, with a Rhombohedral-hexagonal structure. In these compounds, so far no attempts have been made to study the Ce3+ luminescence properties. In addition, when x = 1 in the above series of compounds, we get the new borate phosphors Sr6CeGa(BO3)6 and CeSr5YMg(BO3)6.
In Fig.l (a = ZnS : Ag ; b = CaWO4 ; c - Sr2P2O7 : Eu2+ ; d = Sr6(LaCe)Ga(BO3)6) of the drawings accompanying this specification, the excitation spectra of various compounds are given along with our borate phosphors for comparison. When scanned for excitation by keeping the emission maximum (em) at 420 nm, the excitation band is found to be a broad band (220 - 375 nm) with a peak extending from 316-330nm and a side band at 355 nm, as shown in Fig. Id of the drawings accompanying this specification for a particular composition I which corresponds to Sr6CeGa(BO3)6(M = Ce ; M1 = Ga ; and x = 1.0). The excitation bands of other standard commercial phosphors are shown (Fig. l(a, b, c) of the drawings accompanying this specification) for comparison. Hence, it is clear that these borate phosphors can be excited efficiently with radiation of wavelength 254 as well as 355 nm In Fig.2 (a = ZnS : Ag ; b = Ca5(PO4)3F : Sb3*; c = CaWO4; d = Sr2P2O7 : Eu2+ ; e = Sr6CeGa(BO3)6 and f = Sr6Lao. 99Ceo.oiGa(BO3)6) of the drawings accompanying this specification, the emission spectra of various compounds (em = 254 nm) are given along with our borate phosphors for comparison. When excited with radiation of wavelength 254 nm(em) , these materials are found to emit a broad band (340 - 480 nm) with a peak in the range 410 - 420 nm for high Ce3+ concentrations and in the range 400 - 408 nm for low Ce3+ concentrations as shown in Fig. 2(e, f) of

The drawings accompanying this specification In fig. 3 ( a = ZnS : Ag; b = Sr2P207 : Eu2+; c = SreCeGa(B03)6) of the drawings accompanying this specification, the emission spectra of various compounds (ex C = 355 nm) are given along with our borate phosphors for comparison. When excited with radiation of wavelength 355 nm, these borate phosphors are found to give a broad band which peaks at 420 nm as shown in Fig. 3c of the drawings accompanying this specification for the composition I. Proper comparison is made with the standard commercial phosphors Sr5(P04)3 Cl : Eu2+, Sr2P207: Eu2+ (obtained from Nichia Co., Japan), Ca5(P04)3F : Sb, CaW04 and ZnS : Ag (home made ) and our compounds are found to emit in the region as shown in Fig. 2 and Fig. 3 of the drawings accompanying this specification for various excitation wavelength.
Accordingly, the present invention provides a A Process for the synthesis of new blue emitting Ce3+ activated borate phosphors for use in fluorescent lamps and TV tubes, having the formula AeM1-xCexM1(BO3)6 wherein A=La, Sr; M = La, Y, Gd, Lu; and M1 = Nig, Al, Ga, and x ranging from 0.001 -1 and the said synthesis is carried out by the solid state reaction using at least four of the ingredients from the group consisting of SrC03 (5.5 - 6.5 mole), La203 or Gd203 or Lu203 (0.001 - 1.0 mole), MgO (0.85 - 1.1 mole) [or AI(N03)39H20], Ce02 (0.001 - 1.1 mole ) and H3B03 (5.5 - 6.5 mole) comprising the followings steps: (i) mixing and grinding of the ingredients selected in suitable proportions, for about 15-45 minutes in an agate mortar with acetone, (ii) subjecting the ground ingredients to a pre-firing in air at temperatures ranging from 150-300°C for a period of time ranging from 2-10 hr. and (iii) subjecting the pre-heated powders obtained from step (ii) to a final heat treatment under reducing atmosphere at temperatures ranging from 750-1050°C for a period ranging from 6-30 hours, to obtain the desired phosphors useful as blue components in low pressure mercury vapour lamps, deluxe lamps and in television tubes, when excited with UV radiation of wavelengths 254 and 355 nm.
In our co-pending application no. 53/del/99 we have described and claimed a process for the synthesis of new green emitting Tb3+ activated borate phosphor for use in low pressure mercury vapour lamps.

In an embodiment of the invention, the synthesis of the borate phosphors is carried out under reducing atmosphere created by either activated charcoal or H2 gas flow.
According to a feature of the invention, the synthesized borate phosphors have particle sizes in the range of 5-15 µrn
According to the another feature of the invention, the synthesized borate phosphors show intense blue emission in the region A. = 400 - 420 nm.
According to yet another feature of the invention, the synthesized borate phosphors are directly excited with radiation of wavelengths at 254 nm and 355 nm.
According to the present invention, new borate phosphors have been synthesized by solid state reaction using the ingredients SrCO3, Ln2O3 (Ln = La, Y, Gd, Lu), M2O3 (M = Al, Ga), MgO, CeO2 and H3BO3 at about 750 - 1050° C under reducing atmosphere. Since the dopant cerium was required to yield the necessary luminescence by undergoing excitation-emission processes, it has been added as oxide along with the other raw materials. In an experiment, SrCO3 was mixed with H3BO3, La2O3, Ga2O3 and CeO2 in an agate mortar, ground thoroughly with acetone and allowed to dry in air. The mixture was then kept inside an alumina crucible (~ 20 ml capacity) and pre-fired in air at 150 - 300° C for 5 - 10 hrs. It was ground and kept in the same crucible over which ashless filter paper was placed so as to cover the sample fully. This crucible was then placed inside a big alumina crucible (75 - 100 ml capacity) containing 20 - 30 gm of activated charcoal at the bottom to create a non-oxidizing atmosphere in the crucible. The big crucible was then covered with a lid and placed
—
inside a muffle furnace. The furnace was then set to reach 750 - 10500 C and kept for 5-30 hours. The sample was cooled inside the furnace/quenched in air to room temperature. The final product obtained is a white powder. The experiments were repeated separately with H2 gas flow as the non-oxidizing/reducing medium instead of activated charcoal. The results obtained showed that, the average particle size of these powders was found to be in the range of 3-28 µm. The phase purity of these compounds was confirmed from powder X-ray data.

The following Examples are given by way of illustrations of the present invention and should not be construed to limit the scope of the present invention.
Example 1: Ingredients used in measures
SrCO3 - 1.476 gm (0.01 mole)
H3BO3 = 0.618 gm (0.01 mole)
La2O3 = 0.269 gm (0.000825 mole)
Ga2O3 = 0.156 gm (0.000832 mole)
CeO2 = 0.003 gm (0.0000174 mole)
Procedure used
Pre-firng temperature : 300 0C; Duration : 10 hr.
0
Final heating temperature : 900 C ; Duration : 8 hr.
Firing atmosphere : reducing atm. created by burning activated charcoal
Results
Composition of the finally formed product: Sr6Lao.99Ceo.o1Ga(BO3)6
Colour of the final product : White
Density : 4.34 gm/cc (theor: 4.46 gm/cc)
Particle size : 3 - 28 µm
See also Fig.l & Fig. 2 of the drawings for luminescence properties.
Example 2: Ingredients used in measures
SrCO3 = 1.476 gm (0.01 mole) H3BO3 = 0.618 gm (0.01 mole) Ga2O3 = 0.156 gm (0.000832 mole) CeO2 = 0.287 gm (0.001667 mole) Procedure used

Pre-firng temperature : 300 0C ; Duration : 10 hr.

Final heating temperature : 900 C ; Duration : 8 hr.
Firing atmosphere : reducing atm. created by H2 gas flow
Results
Composition of the finally formed product: Sr6CeGa(BO3)6
Colour of the final product : White
weight of the final product : 1.76 gm (theor : 1.81 gm)
Particle size : 3 - 28 µm
See also Fig. 1, Fig.2 & Fig.3 of the drawings for luminescence properties.
Example 3: Ingredients used in measures
SrCO3 = 1.230 gm (0.00833 mole) H3BO3 = 0.618 gm (0.01 mole) Y2O3 = 0.188 gm (0.00083 mole) MgO = 0.067 gm (0.00166 mole) CeO2 = 0.287 gm (0.00166 mole) Procedure used

Final heating temperature : 1050 0C ; Duration : llhr.
Firing atmosphere : reducing atm. created by burning activated charcoal
Results
Composition of the finally formed product: CeSr5YMg(BO3)6
Colour of the final product : White
Density : 4.26 gm/cc (theor : 4.35 gm/cc)
Particle size : 2 - 28µm
The main advantages of the present invention are:
1. The borate phosphors presently studied contain only Ce3+ ion as the activator which substitutes for the ion present at the M site in the formula Sr6MM'(BO3)6 (where M = La, Gd, Lu ; M1 = Ga) and at the La site in LaSr5YMg(BO3)6.

2. The borate phosphors presently studied can be synthesized easily at lower
temperatures than those required for the existing commercial blue phosphors.
3. These borate phosphors can be excited efficiently with radiation of wavelength 254
and 355 nm.
4. Both a high emission intensity (light output comparable to or greater than the
commercial blue phosphors) as well as a high value of CRI can be possible with these
borate phosphors.
5. These borate phosphors can be used (as a blue phosphor) in Ipmv and super-deluxe
lamps and ( as a beam-index phosphor) in television tubes because of their efficient
emission under various excitation wavelength (254 and 355 nm).

We Claim:
1. A Process for the synthesis of new blue emitting Ce3+ activated borate phosphors
for use in fluorescent lamps and TV tubes, having the formula A6M1-xCexM1(B03)6
wherein A=l_a, Sr; M = La, Y, Gd, Lu; and M1 = Mg, Al, Ga, and x ranging from
0.001 - 1 and the said synthesis is carried out by the solid state reaction using at
least four of the ingredients from the group consisting of SrC03 (5.5 - 6.5 mole),
La203 or Gd203 or Lu203 (0.001 - 1.0 mole), MgO (0.85 - 1.1 mole) [or
AI(N03)39H20], Ce02 (0.001 - 1.1 mole ) and H3B03 (5.5 - 6.5 mole) comprising
the fallowings steps: (i) mixing and grinding of the ingredients selected in suitable
proportions, for about 15-45 minutes in an agate mortar with acetone, (ii)
subjecting the ground ingredients to a pre-firing in air at temperatures ranging from
150-300°C for a period of time ranging from 2-10 hr. and (iii) subjecting the pre
heated powders obtained from step (ii) to a final heat treatment under reducing
atmosphere at temperatures ranging from 750-1050°C for a period ranging from 6 -
30 hours, to obtain the desired phosphors useful as blue components in low
pressure mercury vapour lamps, deluxe lamps and in television tubes, when excited
with UV radiation of wavelengths 254 and 355 nm.
2. A process as claimed in claim 1 wherein the synthesis of the borate phosphors are
carried out under reducing atmosphere created by either activated charcoal or H2
gas flow.
3. A process as claimed in claims 1 & 2 wherein the synthesized borate phosphors
have particle sizes in the range of 5 - 15 µm.
4. A process as claimed in claims 1 & 2 wherein the synthesized borate phosphors
show intense blue emission in the region A = 400 - 420 nm.
5. A process as claimed in claim 1&2 wherein the synthesized borate phosphors are
directly excited with radiation of wavelengths at 254 nm and 355 nm.
6. A process for the synthesis of new blue emitting Ce3+ activated borate phosphors
for fluorescent lamps and TV tubes substantially as herein described with reference
to the examples and drawings accompanying this specification.

Documents:

52-del-1999-abstract.pdf

52-del-1999-claims.pdf

52-del-1999-correspondence-others.pdf

52-del-1999-correspondence-po.pdf

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

52-del-1999-drawings.pdf

52-del-1999-form-1.pdf

52-del-1999-form-19.pdf

52-del-1999-form-2.pdf

52-del-1999-form-3.pdf

52-del-1999-petition-138.pdf

« Previous Patent

Next Patent »

Patent Number

217394

Indian Patent Application Number

52/DEL/1999

PG Journal Number

15/2008

Publication Date

11-Apr-2008

Grant Date

26-Mar-2008

Date of Filing

12-Jan-1999

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001,

Inventors:

#	Inventor's Name	Inventor's Address
1	GUNDLAPALLI VENKATA SUBBA RAO	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-630006,
2	RAMAKRISHAN SANKAR , SENIOR RESEARCH	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-630006,CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI-630006,

PCT International Classification Number

C09K 11/63

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA