GB2124243A - A green-emitting phosphor and a low pressure mercury vapor lamp employing this phosphor - Google Patents

A green-emitting phosphor and a low pressure mercury vapor lamp employing this phosphor Download PDF

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GB2124243A
GB2124243A GB08320036A GB8320036A GB2124243A GB 2124243 A GB2124243 A GB 2124243A GB 08320036 A GB08320036 A GB 08320036A GB 8320036 A GB8320036 A GB 8320036A GB 2124243 A GB2124243 A GB 2124243A
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phosphor
low pressure
envelope
mercury vapor
pressure mercury
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Katsuo Murakami
Saburo Umeda
Hitoshi Yamazaki
Norihiko Tanaka
Hiroshi Ito
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Mitsubishi Electric Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/38—Devices for influencing the colour or wavelength of the light
    • H01J61/42—Devices for influencing the colour or wavelength of the light by transforming the wavelength of the light by luminescence
    • H01J61/46—Devices characterised by the binder or other non-luminescent constituent of the luminescent material, e.g. for obtaining desired pouring or drying properties
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/7777—Phosphates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/7777—Phosphates
    • C09K11/7778—Phosphates with alkaline earth metals
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/7777—Phosphates
    • C09K11/7778—Phosphates with alkaline earth metals
    • C09K11/7779—Phosphates with alkaline earth metals with halogens
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/778—Borates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/38—Devices for influencing the colour or wavelength of the light
    • H01J61/42—Devices for influencing the colour or wavelength of the light by transforming the wavelength of the light by luminescence
    • H01J61/44—Devices characterised by the luminescent material

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Luminescent Compositions (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)

Abstract

A green-emitting phosphor for a low pressure mercury vapor discharge lamp has a monoclinic monazite-type crystal structure and comprises a phosphate of cerium, terbium, and possibly lanthanum, yttrium, gadolinium or lutetium. It is significantly different from green- emitting phosphors of the prior art in that it further comprises at least one element selected from the alkali metals, fluorine, indium, and boron. Because of the addition of these elements, the decrease in powder brightness of the present phosphor after heating in air at 600 DEG C (the temperature at which phosphors are heated during the baking step of lamp manufacture) is much less than for conventional green-emitting phosphors. The decrease in brightness of the present phosphor after irradiation by ultraviolet light at 185 nm is also much less than for conventional phosphors. It is accordingly most appropriate for use in discharge lamps. The low pressure mercury vapor discharge lamp using the present phosphor is of high efficiency and has excellent colour rendering.

Description

SPECIFICATION A green-emitting phosphor and a low pressure mercury vapor lamp employing this phosphor BACKGROUND OF THE INVENTION The present invention relates to a novel type of green-emitting phosphor, and also to low pressure mercury vapor discharge lamps using this type of phosphor. Green-emitting phosphors using terbium (Tb) as an activator have many practical applications, being widely used in low pressure mercury vapor discharge lamps, high pressure mercury vapor discharge lamps, cathode-ray tubes, and other devices.
For example, Japanese Patent Publication No. 48--221 17 discloses a mixture of blue, green, and redorange-emitting phosphors of relatively narrow spectral distribution for use in a 3-band fluorescent lamp. Also, Japanese Patent Laid Open No. 50-61 887 discloses a green-emitting fluorescent lamp for copy machines.
A number of terbium-activated phosphors exist in the prior art. Terbium-activated cerium orthophosphate phosphors [(Ce, Tb) PO4] were introduced in "The Journal of Chemical Physics" (Volume 51, 1969 No. 8, p.3252). Also, terbium-activated lanthanum cerium orthophosphate phosphors [(Cew, La, Tb)PO4] were disclosed in Japanese Patent Laid Open No. 54-56086. The cerium (Ce) in these phosphors absorbs ultraviolet radiation. The absorbed energy is transmitted to terbium, and green light is emitted by terbium, the emission spectrum of which has a peak in the vicinity of 545 nm.
However, when these orthophosphate phosphors are used in mercury vapor discharge lamps the resulting lamps have emission outputs far lower than would be expected based on the power brightness of the phosphors. As a result of experiments upon which the present invention is based, it became clear that there are 2 main causes for low emission output by orthophosphate phosphor mercury vapor discharge lamps. One is that heating in air causes the cerium in the phosphors to become easily oxidized (changing from a valency of 3 to a valency of 4), and therefore, at the time of lamp manufacture, heating during the backing step produces a significant decrease in brightness.The other cause for low emission output is that in low pressure mercury vapor lamps, irradiation by ultraviolet light at 1 85 nm produced by the discharge causes a decrease in brightness in an extremely short time.
SUMMARY OF THE INVENTION The object of the present invention is to solve the above-described problems of the prior art and provide a phosphor which suffers but little deterioration in its qualities during the baking step and which exhibits only a small decrease in brightness when used in mercury vapor discharge lamps.
It is a further object of the present invention to provide a low pressure mercury vapor lamp using this phosphor which has a high emission output combined with high efficiency and high color rendition.
These and other objects of the present invention will become clear upon reading the following description and upon studying the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the emission spectrum of a phosphor according to the present invention as set forth in Example 8.
Figure 2 is a cross-sectional view of one embodiment of a low pressure mercury vapor lamp using a phosphor according to the present invention.
Figure 3 shows the spectral distribution of the emission from a fluorescent lamp employing a phosphor according to the present invention as set forth in Example 45.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The phosphor according to the present invention comprises a phosphate of the Group Ill B elements cerium and terbium, or of cerium, terbium, and at least one other element of Group III B of the Periodic Table selected from the group consisting of lanthanum, yttrium, gadalinium, and lutetium, and further comprises at least one element selected from the alkali metals, fluorine, indium, and boron.
This phosphor is further characterized by having a monoclinic monazite-type crystal structure. A low pressure mercury vapor discharge lamp according to the present invention is characterized in that either all or part of the phosphor layers in the lamp are composed of this phosphor. A low pressure mercury vapor lamp according to the present invention has one or more phosphor layers, each of which includes a red-orange-emitting phosphor and the above-described phosphor according to the present invention or a red-orange-emitting phosphor, the phosphor according to the present invention, and a blueemitting phosphor.
The above described, well-known terbium-activated cerium orthophosphate phosphor and the terbium-activated lanthanum cerium orthophosphate phosphor both possess monoclinic monazite -type crystal structures. The phosphor according to the present invention possesses this same type of crystal structure. Also, like the phosphors of the prior art, the phosphor according to the present invention is a phosphate comprising cerium, terbium, and possibly lanthanum. However, it is essentially different from the prior art phosphors in that it contains at least one element selected from the alkali metals, fluorine, indium, and boron.
The introduction of these elements minimizes the decrease in brightness due to heating, decreases the reduction in brightness resulting from irradiation with ultraviolet light at 1 85 nm, and increases the powder brightness. Accordingly, the phosphor according to the present invention is extremely appropriate for use in mercury vapor discharge lamps. This phosphor can be excited no only by ultraviolet light but also by electrons, and thus can be used in cathode-ray tubes and similar devices.
Hereinafter, a number of examples of phosphors according to the present invention will be described in order to show the effects of changes in composition on the characteristics of the phosphor as weli as to show the preferred composition of the phosphor.
EXAMPLE 1 Lanthanum oxide (La2O3), cerium nitrate [Ce(N03)3.6H2O], and terbium oxide (Tb4O7) were dissolved in nitric acid to prepare a 10 1 solution containing 0.65 gram atoms of lanthanum, 0.15 gram atoms of cerium, and 0.20 gram atoms of terbium. This solution was gradually added dropwise into a 10 1 solution containing 2.4 moles of oxalic acid and reaction was carried out at approximately 800C.
The resulting precipitate of oxalate was filtered and dried. This oxalate was heated at 1 0000C-1 100 C for approximately 1 hour to change it into an oxide. The oxide was then thoroughly mixed with 0.90 moles of diammonium hydrogen phosphate [(NH4)2HPO4] and 0.10 moles of boric acid (H3BO3) and then baked at 1 2000C for 1 hour in a reducing atmosphere (nitrogen containing 5% hydrogen). The baked product wa pulverized and then sieved to obtain a phosphor.
The composition of this phosphor was (LaO 65CeO,l5TbO,20)203 0 90P205 0 1 B203 When excited by ultraviolet light at 254 nm, it strongly emitted green light and produced an emission spectrum with a peak in the vicinity of 545 nm. The power brightness was 100, the same as for the well-known phosphor (LaO 65CeO 15Tbo 20)PO4. However, after reheating in air at 6000C for 15 minutes, (almost the same conditions as used in the baking step), the powder brightness of the prior art phosphor decreased by 25%, while the phosphor according to the present invention decreased by but 7%.
To measure their endurance under ultraviolet light at 1 85 nm, both of the phosphors were irradiated for 30 minutes in a nitrogen atmosphere by a low pressure mercury vapor discharge lamp consisting of a quartz tube radiating ultraviolet light at 185 nm and 254 nm. After 30 minutes, the powder brightness of the prior art phosphor decreased by 7%, but that of the phosphor according to the present invention by only 4%.
To investigate the emission output of these phosphors, they were incorporated by standard methods into 40 watt fluorescent lamps (FL40S). The output using the prior art phosphor was 4350 lumens, while the output using the present phosphor was 4750 lumens.
EXAMPLES 2-7 Using the same technique as for Example 1, the boron content of the phosphor was gradually varied. The composition and characteristics of the phosphors are shown in Table 1.
TABLE 1
%Decrease in Brightness Lamp After UV Emission Example Powder lrradiation Output Number Phosphor Brightness After Heating at 185 nm (lumens) 1 (La0.65Ce0.15Tb0.20)2O3 # 0.9OP2O5 # 0.10B2O3 100 7 4 4760 2 (La0.65Ce0.15Tb0.20)2O3 # 0.95P2O5 # 0.05B2O3 100 20 6 4500 3 (La0.65Ce0.15Tb0.20)2O3 # 0.80P2O5 # 0.20B2O3 100 7 4 4760 4 (La0.65Ce0.15Tb0.20)2O3 # 0.65P2O5 # 0.35B2O3 99 16 6 4510 5 (La0.65Ce0.15Tb0.20)2O3 # 0.50P2O5 # 0.50B2O3 95 19 7 4430 6 (La0.65Ce0.15Tb0.20)2O3 # 0.40P2O5 # 0.60B2O3 97 21 7 4410 7 (La0.65Ce0.15Tb0.20)2O3 # 0.20P2O5 # 0.80B2O3 90 20 7 4310 Comparative Example 1 (La0.65Ce0.15Tb0.20)BO3 80 10 3 4300 Comparative Example 2 (La0.65Ce0.15Tb0.20)PO4 100 25 7 4350 The X-ray diffraction patterns of Examples 1-6 greatly resemble those of monoclinic monazites (i.e. they greatly resemble the diffraction pattern of Comparative Example 2). The X-ray diffraction pattern of Example 7 appears as an overlap of the diffraction pattern of a monoclinic monazite and of Comparative Example 1, and thus can be thought of as a mixture of the two.
From the point of view of lamp properties, when boron alone is used, the boron content per 1 gram atom of Group Ill B elements (i.e. the total of lanthanum, cerium, and terbium) is desirably no more than 0.6 gram atoms and preferably no more than 0.35 by no less than 0.05 gram atoms.
In the above examples, the effect of boron is not to accelerate the reaction at the time of synthesizing. Rather, boron can be thought of as displacing phosphorous in the phosphor and exerting some sort of action on the base crystal of the phosphor, based on the fact that when the phosphors of the above examples are dispersed in water, substantially no boron dissolves. Further, even if the amount of boron in the phosphor is increased to as high as 0.6 gram atoms, a very large quantity, the X-ray diffraction pattern highly resembles that produced by monoclinic monazites.
EXAMPLE 8 Using the same technique as for Example 1, an oxalate precipitate containing 0.65 gram atoms of lanthanum, 0.1 5 grams atoms of cerium, and 0.20 gram atoms of terbium was produced. The precipitate was heated at 1000-11 1 000C for approximately 1 hour to obtain oxides. These oxides were thoroughly mixed with 1.00 moles of diammonium hydrogen phosphate, 0.01 moles of lithium carbonate(Li2CO3), and 0.04 moles of boric acid, then baked, pulverized, and sieved under the same conditions as for Example 1 to obtain a phosphor having the composition.
(La0.65Ce0.15Tb0.20)2O3#P2O5#0.02Li2O3#0.04B2O3.
When excited by ultraviolet light at 254 nm, this phosphor exhibited strong emission of green light.
Figure 1 shows the emission spectrum of this phosphor. It had a powder brightness of 110, which decreased by 5% after heating in air at 6000 C. Irradiation by ultraviolet light at 185 nm produced at 2% decrease in the brightness degree. The lamp emission output using this phosphor was 51 50 lumens, and it has an X-ray diffraction pattern highly resembling that of monoclinic monazites. The characteristics of this phosphor are shown in Table 2.
TABLE 2
%Decrease in Brightness Lamp After UV Emission Example Powder lrradiation Output Number Phosphor Brightness After heating at 185 nm (lumens) 8 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.02Li2O # 04B2O3 110 5 2 5150 9 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.005Li2O # 0.01B2O3 107 4 2 5100 10 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.04Li2O # 0.08B2O3 113 8 3 5150 11 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.10Li2O # 0.10B2O3 110 15 4 4800 12 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.20Li2O # 0.20B2O3 101 24 7 4430 13 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.01Li2O # 0.07B2O3 113 6 2 5150 14 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.03Li2O # 0.02B2O3 110 5 2 5150 15 (La0.65Ce0.15Tb0.20)2O3 # 1.02P2O5 # 0.02Li2O # 0.04B2O3 110 5 2 5150 16 (La0.65Ce0.15Tb0.20)2O3 # 0.96P2O5 # 0.02Li2O # 0.04B3O3 115 7 7 5050 17 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.02Li2O 105 10 2 4860 TABLE 2 (Cont'd.)
%Decrease in Brightness Lamp After UV Emission Example Powder lrradiation Output Number Phosphor Brigtness After heating at 185 nm (lumens) 18 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.02Na2O 103 13 3 4700 19 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.02K2O 100 15 4 4620 20 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.01Cs2O 99 13 4 4570 21 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.01Rb2O 98 13 4 4540 22 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2P5 # 0.01Li2O # 0.10K2O # 0.04B2O3 103 10 3 4800 23 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.01Cs2O # 0.04B2O3 101 9 3 4770 24 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.01ln2O3 100 4 6 4800 25 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.03ln2O3 98 3 7 4760 26 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.10ln2O3 80 3 7 4430 27 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.01ln2O3 # ono1B2O3 100 3 7 4810 EXAMPLES 9-27 Using the same technique as for Example 8, the phosphors shown in Table 2 were prepared to determine the effects of various elements in various concentrations.Of the phosphors shown in this table, those containing an alkali metal were prepared by using a carbonate of the alkali metal as a starting material, while those containing indium were prepared by using indium nitrate trihydrate [In(NO3)3 3H2O] as a starting material.
Upon excitation by ultraviolet light at 254 nm, all of the phosphors in Table 2 exhibited strong emission of green light. In addition, their X-ray diffraction patterns were very similar to those of monoclinic moazites.
Comparison of the characteristics of the phosphors in Tables 1 and 2 clearly shows that the simultaneous incorporation of boron and an alkali metal produces extremely beneficial effects. The power brightness, the decrease in brightness after heating in air at 6000C, and the decrease in brightness after irradiation by ultraviolet light at 185 nm were all very satisfactory. In addition, an extremely high lamp emission output was obtained. Among the alkali metals used, lithium was particularly effective in producing these desirable results.
As can be seen from Examples 8-12, for each gram atom of Group Ill B elements (the total of lanthanum, cerium, and terbium), it is desirable that the amount of alkali metal be no more than 0.2 gram atoms. Comparison of Tables 1 and 2 also shows that the desirable amount of boron is much lower for phosphors containing both boron and an alkali metal than for phosphors containing only boron. As Example 9 indicates, even a boron content as low as 0.01 gram atoms produces fully satisfactory characteristics. The inclusion of indium is particularly effective in minimizing the percent decrease in brightness due to heating in air at 6000C. For each gram atom of Group III B elements (the total of lanthanum, cerium, and terbium), an indium content of no more than 0.1 gram atoms is desirable.
EXAMPLE 28 Using the same technique as for Example 1, an oxalate precipitate comprising 0.65 gram atoms of lanthanum, 0.15 gram atoms of cerium, and 0.20 gram atoms of terbium was produced. Oxides were obtained by heating the resultant oxalate at 1000-11 000C for approximately one hour. These oxides were thoroughly mixed with 1.00 mole of diammonium hydrogen phosphate and 0.025 moles of lithium fluoride (LiF). After being baked, pulverized, and sieved under the same conditions as for Example 1, a phosphor was obtained having the composition (LaO 6sCeO HTbo.2o)203 1 .OOP 2O5.0.05LiF.
Excitation of this phosphor by ultraviolet light at 254 nm produced strong emission of green light. It has a powder brightness of 109, which decreased by 6% after heating in air at 6000C and which decreased by 2% after irradiation by ultraviolet light at 1 85 nm. A lamp incorporating this phosphor had an emission output of 5100 lumens, and the phosphor has an X-ray diffraction pattern highly resembling that of monoclinic monazites.
EXAMPLES 29-32 The same technique was employed as for Example 28, using either lithium fluoride or lanthanum fluoride in various concentrations as a starting material. The contents and characteristics of the phosphors thus formed are shown in Table 3.
TABLE 3
%Decrease in Brightness Lamp After UV Emission Example Powder lrradiation Output Number Phosphor Brigtness After Heating at 185 nm (lumens) 28 (La0.65Ce0.15Tb0.20)2O3 # 1.00~2O5 # 0.05LiF 109 6 2 5100 29 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.02LiF 110 8 2 5100 30 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.05LiF # 0.02B2O3 108 4 2 5150 31 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.20LiF 80 0 2 4450 32 (La0.65Ce0.15Tb0.20)2O3 # 1.00P2O5 # 0.02LaF3 100 10 2 4700 All of these phosphors have X-ray diffraction patterns greatly resembling those of monoclinic monazites. Excitation by ultraviolet light at 254 nm produced strong emission of greeen light. For each gram atom of Group III B elements (the total of lanthanum, cerium, and terbium), a fluorine content of no more than 0.1 gram atoms is desirable.
EXAMPLES 33-43 Using the same technique as for Example 1, oxalates were formed containing various amounts of lanthanum, cerium, terbium, yttrium, and lutetium. Then, using the same technique as for Example 8, a number of phosphors were obtained. The results are shown in Table 4.
TABLE 4
%Decrease in Brightness Lamp After UV Emission Example Powder lrradiation Output Numbrer Phosphor Brightness After Heating at 185 nm (lumens) 33 (La0.80Ce0.05Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 101 5 0.5 4900 34 (La0.70Ce0.15Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 109 5 2 5100 35 (La0.56Ce0.30Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 110 5 4 5054 36 (La0.35Ce0.50Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 111 5 7 5000 37 (La0.05Ce0.80Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 110 5 10 4890 38 (Ce0.85Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 107 5 14 4740 39 (La0.65Ce0.30Tb0.05)2O3 # 1.00P2O5 # 0.02Li2O#0.04B2O3 90 5 4 4500 40 (La0.40Ce0.30Tb0.30)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 95 5 4 4610 41 (La0.45Gd0.10Ce0.30Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 107 5 4 4950 42 (La0.45Y0.10Ce0.30Tb0.15)2O3 # 1.00p2O5 # 0.02Li2O # 0.04B2O3 105 7 5 4810 43(La0.50Lu0.05Ce0.30Tb0.15)2O3 # 1.00P2O5 # 0.02Li2O # 0.04B2O3 107 7 5 4860 The X-ray diffraction patterns of Examples 33-43 greatly resemble those of monoclinic monazites.
Excitation by ultraviolet light at 254 nm produces strong emission of green light. As the cerium content increases, the decrease in brightness due to irradiation by ultraviolet light at 185 nm also increases. For this reason, even though the powder brightness is a maximum for a relatively high cerium content, the lamp emission output is a maximum for a relatively low cerium content. For each gram atom of Group III B elements in the phosphor (the total of lanthanum, cerium, and terbium), the content of cerium is desirably no less tha 0.05 and no greter than 0.8 gram atoms. For each gram atom of Group III B elements, if the content of terbium is 0.05 to 0.3 gram atoms, a bright phosphor can be obtained.
Examples 41-43 show that it is also possible to incorporate into the phosphate tie Group III E elements gadolinium, yttrium, and lutetium.
Now, a low pressure mercury vapor discharge lamp according to the present invention will be described. The embodiment of this lamp shown in Figure 2 is a 40 watt discharge lamp. It will be noted that the structure of this lamp is perfectly conventional. It comprises a sealed elongated light transmitting envelope 1, a pair of discharge electrodes 2 and 3 positioned at opposite ends of the envolope 1 , a filling 4 comprising mercury enclosed within the envelope 1 , and a phosphor layer or layers 5 coated on the inner surface of the envelope 1.
The unique feature of the present lamp is the composition of the phophor layer or layers, which comprises a phosphor according to the present invention. The following examples show the characteristics of various embodiments of this low pressure mercury vapor discharge lamps employing the phosphor according to the present invention.
EXAMPLE 44 The inner surface of the glass envelope 1 of a lamp like the one shown in Figure 2 was coated with the phosphor of Example 8. The initial luminous flux of this lamp was 5150 lumens. Even after 100 hours of operation, the luminous flux decreased by only 2% to 5050 lumens. A lamp using Comparative Example 2 of Table 1, a terbium-activated lanthanum cerium orthophosphate phosphor, had an initial luminous flux of 4350 lumens, which after 100 hours of operation decrease by 5% to 4130 lumens.
EXAMPLE 45 50% by weight of thb .1osphr of Example 8, 26% by weirs; of a europium-activated yttrium oxide phosphor (a red-orange-emitting phosphor having an emission peak at 611 nm), and 24% by weight of a europium-activated strontium barium chlorophosphate phosphor (a blue-emitting phosphor with an emission peak at approximately 445 nm) were mixed and then coated on the inner surface of the glass envelope 1 of a 40 watt low pressure mercury vapor discharge lamp like the one shown in Figure 2. The resulting lamp was a 3-band fluorescent lamp of high efficiency and high color rendition.
The color temperature of the lamp was 50000 K, the general color rendering index was 84, and it had an initial luminous flux of 3750 lumens. When Comparative Example 2 of Table 1 (a terbium-activated lanthanum cerium orthophosphate phosphor) was incorporated into the lamp as a green-emitting phosphor, there was no change in the color temperature or the general color rendering index, but the initial luminous flux was reduced to 3200 lumens. The spectral distribution of Examples 45 is shown in Figure 3.
EXAMPLE 46 To obtain a 3-band fluorescent lamp of low color temperature, 45% by weight of the phosphor of example 8 and 55% by weight of a europium-activated yttrium oxide phosphor were mixed and then coated on the glass envelope 1 of a discharge lamp like the one shown in Figure 2. The resulting lamp was of high efficiency and high color rendition, with a color temperature of 27000K. The emitted light was very similar to that of an incandescent lamp, with a general color rendering index of 87, and an initial luminous flux of 3600 lumens.
EXAMPLE 47 48% by weight of the phosphor of Example 1 5, 25% by weight of a europium-activated yttrium oxide phosphor, and 27% by weight of a europium-activated barium magnesium aluminate phosphor (a blue-emitting phosphor with an emission peak at approximately 450 nm) were mixed and then coated on the glass evelope 1 of a lamp like the one shown in Figure 2 to obtain a 3-band fluorescent lamp.
This lamp had a color temperature of 50000K, a general color rendering index of 84, and an initial luminous flux of 3680 lumens.
EXAMPLE 48 50% by weight of the phosphor of Example 36, 24% by weight of a europium-activated yttrium oxide phosphor, and 26% by weight of a europium-activated strontium calcium chlorophosphate phosphor (a blue-emitting phosphor with an emission peak at approximately 450 nm) were mixed and then coated on the glass envelope 1 of a discharge lamp like the one shown in Figure 2 to obtain a 3band fluorescent lamp. This lamp had a color temperature of 50000 K, a general color rendering index of 84, and an initial liminous flux of 3679 lumens.
EXAMPLE 49 36% by weight of the phosphor of Example 29, 18% by weight of a europium-activated yttrium oxide phosphor, 18% by weight of a europium-activated strontium calcium barium chlorophosphate phosphor (a blue-emitting phosphor with an emission peak at approximately 450 nm), and 28% by weight of an antimony manganese-activated calcium halophosphate phosphor were mixed and then coated on the glass envelope 1 of a discharge lamp like the one shown in Figure 2 to obtain a 3-band fluorescent lamp. This lamp had a color temperature of 50000 K, a general color rendering index of 81, and an initial luminous flux of 3580 lumens.
EXAMPLE 50 A 3-band fluorescent lamp having a plurality of phosphate layers was fabricated. First, an antimony manganese-activated calcium halophosphate phosphor was coated on the inner surface of the glass envelope 1 of a lamp like the one shown in Figure 2. On top of this layer, a mixture containing the phosphors of Example 45 was coated. This lamp, which allows a saving in the amount of phosphor mixture used, had a color temperature of 50000K, a general color rendering index of 83, and an initial luminous flux of 3700 lumens.

Claims (9)

1. A phosphor having a monoclinic monazite-type crystal structure comprising: a phosphate of the Group III B elements cerium and terbium or of cerium, terbium, and at least one other element of Group III B of the Periodic Table selected from the group consisting of lanthanum, yttrium, gadolinium, and lutetium; and at least one element selected from the alkali metals, fluorine, indium, and boron.
2. A phosphor as claimed in claim 1, wherein said phosphor contains at most 0.2 gram atoms of an alkali metal, at most 0.1 gram atoms of fluorine, at most 0.1 gram atoms of indium, and at most 0.6 gram atoms of boron per each gram atom of Group III B elements contained in said phosphor.
3. A phosphor as claimed in claim 1 or claim 2, wherein said phosphor contains the alkali metal lithium.
4. A phosphor as claimed in claim 1, 2, or 3, wherein the amount of cerium per gram atom of Group Ill B elements contained in said phosphor is at least 0.05 and at most 0.8 gram atoms.
5. A phosphor as claimed in claim 1 and substantially as set forth in any of the foregoing Examples.
6. A low pressure mercury vapor discharge lamp comprising: a sealed elongated light-transmitting envelope; a pair of discharge electrodes positioned at opposite ends of said envelope; a filling enclosed within said envelope comprising mercury; and a phosphor layer coated on the inner surface of said envelope, said phosphor layer comprising a phosphor as claimed in any of claims 1 to 5.
7. A low pressure mercury vapor discharge lamp comprising: a sealed elongate light-transmitting envelope; a pair of discharge electrodes positioned at opposite ends of said envelope; a filling enclosed within said envelope comprising mercury; and one or more phosphor layers coated on the inner surface of said envelope, each of said phosphor layers comprising a red-orange-emitting phosphor and a green-emitting phosphor and optionally a blueemitting phosphor, said green-emitting phosphor being a phosphor as claimed in any of claims 1 to 5.
8. A low pressure mercury vapor discharge lamp as claimed in claim 7, wherein said red-orange emitting phosphor is a europium-activated yttrium oxide phosphor.
9. A low pressure mercury vapor discharge lamp as claimed in claim 7 or 8, wherein said blueemitting phosphor comprises at least one phosphor selected from the group consisting of europiumactivated alkali earth metal chlorophosphate phosphors and europium-activated barium magnesium aluminate phosphors.
GB08320036A 1982-07-26 1983-07-26 A green-emitting phosphor and a low pressure mercury vapor lamp employing this phosphor Expired GB2124243B (en)

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US4764301A (en) * 1986-02-25 1988-08-16 Mitsubishi Denki Kabushiki Kaisha Phosphor
US5116532A (en) * 1990-05-14 1992-05-26 Gte Products Corporation Method of making lanthanum cerium terbium phosphate phosphor
US5132042A (en) * 1990-05-14 1992-07-21 Gte Products Corporation Method of making lanthanum cerium terbium phosphate phosphor with improved brightness
FR2672281A1 (en) * 1991-02-04 1992-08-07 Rhone Poulenc Chimie MIXED PHOSPHATE OF LANTHANE, TERBIUM AND CERIUM, PROCESS FOR PRODUCTION THEREOF
US5580490A (en) * 1991-07-19 1996-12-03 Rhone-Poulenc Chimie Crystallites of cerium/lanthanum/terbium phosphates from insoluble rare earth salts
US5989454A (en) * 1998-07-06 1999-11-23 Matsushita Electric Industrial Co., Ltd. Method for making small particle blue emitting lanthanum phosphate based phosphors
EP0581622B2 (en) † 1992-07-29 2002-05-02 Rhodia Chimie Process for preparation of rare earth phosphates and products obtained thereby
WO2003046935A2 (en) * 2001-11-28 2003-06-05 Koninklijke Philips Electronics N.V. Plasma display screen comprising a green phosphor
US7179402B2 (en) * 2004-02-02 2007-02-20 General Electric Company Phosphors containing phosphate and/or borate of metals of group IIIA, group IVA, and lanthanide series, and light sources incorporating the same
US7288215B2 (en) 2005-03-30 2007-10-30 Osram Sylvania Inc. Method of making narrow-band UVB-emitting phosphors
EP1676900A3 (en) * 2004-12-28 2008-03-05 Osram Sylvania Inc. Single-component UV-emitting phosphor
FR2938526A1 (en) * 2008-11-20 2010-05-21 Rhodia Operations CERIUM AND / OR TERBIUM PHOSPHATE, POSSIBLY WITH LANTHANE, LUMINOPHORE FROM THIS PHOSPHATE AND PROCESSES FOR THE PREPARATION THEREOF
FR2938525A1 (en) * 2008-11-20 2010-05-21 Rhodia Operations CERIUM AND / OR TERBIUM PHOSPHATE, POSSIBLY WITH LANTHANE, LUMINOPHORE FROM THIS PHOSPHATE AND PROCESSES FOR THE PREPARATION THEREOF
WO2010108860A1 (en) * 2009-03-24 2010-09-30 Rhodia Operations Composition containing a core/shell cerium and/or terbium phosphate, phosphor from said composition, and methods for preparing same
WO2011094937A1 (en) * 2010-02-04 2011-08-11 海洋王照明科技股份有限公司 Terbium doped phosphate-based green luminescent material and preparation method thereof
EP2370544A1 (en) * 2008-11-20 2011-10-05 Rhodia Opérations Cerium and/or terbium phosphate optionally with lanthanum, phosphor resulting from said phosphate and method for preparing same
EP2384309A1 (en) * 2008-11-20 2011-11-09 Rhodia Opérations Cerium and/or terbium phosphate optionally with lanthanum, phosphor resulting from said phosphate and method for preparing same
US20120241672A1 (en) * 2009-07-29 2012-09-27 Rhodia Operations Composition comprising a cerium and/or terbium phosphate and sodium, of core/shell type, phosphor resulting from this composition and methods for preparing same
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DE3729711A1 (en) * 1987-09-04 1989-03-23 Patent Treuhand Ges Fuer Elektrische Gluehlampen Mbh MERCURY LOW PRESSURE DISCHARGE LAMP FOR UV RADIATION
FR2694299B1 (en) * 1992-07-29 1994-09-09 Rhone Poulenc Chimie New green phosphors based on mixed lanthanum phosphate, cerium and terbium, their precursor and synthesis processes.
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Publication number Priority date Publication date Assignee Title
US4764301A (en) * 1986-02-25 1988-08-16 Mitsubishi Denki Kabushiki Kaisha Phosphor
US5116532A (en) * 1990-05-14 1992-05-26 Gte Products Corporation Method of making lanthanum cerium terbium phosphate phosphor
US5132042A (en) * 1990-05-14 1992-07-21 Gte Products Corporation Method of making lanthanum cerium terbium phosphate phosphor with improved brightness
US5562889A (en) * 1991-02-04 1996-10-08 Rhone-Poulenc Chimie Cerium/lanthanum/terbium mixed phosphates
EP0498689A1 (en) * 1991-02-04 1992-08-12 Rhone-Poulenc Chimie Mixed lanthanum terbium and cerium phosphate, process for its preparation
US5340556A (en) * 1991-02-04 1994-08-23 Rhone-Poulenc Chimie Cerium/lanthanum/terbium mixed phosphates
FR2672281A1 (en) * 1991-02-04 1992-08-07 Rhone Poulenc Chimie MIXED PHOSPHATE OF LANTHANE, TERBIUM AND CERIUM, PROCESS FOR PRODUCTION THEREOF
US5580490A (en) * 1991-07-19 1996-12-03 Rhone-Poulenc Chimie Crystallites of cerium/lanthanum/terbium phosphates from insoluble rare earth salts
EP0581622B2 (en) † 1992-07-29 2002-05-02 Rhodia Chimie Process for preparation of rare earth phosphates and products obtained thereby
US5989454A (en) * 1998-07-06 1999-11-23 Matsushita Electric Industrial Co., Ltd. Method for making small particle blue emitting lanthanum phosphate based phosphors
WO2003046935A2 (en) * 2001-11-28 2003-06-05 Koninklijke Philips Electronics N.V. Plasma display screen comprising a green phosphor
WO2003046935A3 (en) * 2001-11-28 2003-10-16 Koninkl Philips Electronics Nv Plasma display screen comprising a green phosphor
US7179402B2 (en) * 2004-02-02 2007-02-20 General Electric Company Phosphors containing phosphate and/or borate of metals of group IIIA, group IVA, and lanthanide series, and light sources incorporating the same
EP1676900A3 (en) * 2004-12-28 2008-03-05 Osram Sylvania Inc. Single-component UV-emitting phosphor
US7288215B2 (en) 2005-03-30 2007-10-30 Osram Sylvania Inc. Method of making narrow-band UVB-emitting phosphors
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FR2537151A1 (en) 1984-06-08
JPS5920378A (en) 1984-02-02
JPH0119720B2 (en) 1989-04-12
FR2537151B1 (en) 1987-02-20
DE3348146C2 (en) 1992-01-30
GB2124243B (en) 1985-12-04
CA1211781A (en) 1986-09-23
NL8302657A (en) 1984-02-16
DE3326921C2 (en) 1987-09-03
GB8320036D0 (en) 1983-08-24
DE3326921A1 (en) 1984-02-02
NL188756C (en) 1992-09-16

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