CA1145132A - Ultraviolet emitting aluminate phosphor and fluorescent suntanning lamps utilizing same - Google Patents

Abstract

ABSTRACT
Alkaline earth substituted cerium magnesium aluminate phosphors represented by the molar formula:
Ce0.90Ba0.05Mg1.0Al11O18.925 exhibit optimum energy output within the WA (sun-tanning) region of the electromagnetic spectrum and minimal energy output within the UVB (sunburning) region of the elctromagnetic spectrum, and accordingly are useful in fluorescent lamps for artificial suntanning applications.

Description

ULTRAVIOLET EMITTING ALUMINATE PHOSPHOR
AND FLUORESCENT SUNTANNING LAMPS
UTILIZING SAME
TECHNICAL FIELD
This invention relates to aluminate phosphors .
emitting in the ultraviolet region of the electro-magnetic spectrum, and more particularly relates to - such phosphors containing cerium and alkaline earths, - 5 and to fluorescent lamps incorporating them.
BACKGROUND ART
Philips Electronics Associated Industries in British patent 1,452,083 disclosed an ultraviolet emitting fluorescent lamp phosphor having the com-position CeMgAlllOlg and the magneto plumbite struc-ture. H.F. Ward of Thorn Industries, in British patent -~
1,194,014 disclosed a:phosphor having the composition CeAlllO18 and the magneto plumbite structure. Although CeAlllO18 and CeMgAlllOlg havè similar crystal struc-~ ~tures, incorporation of magnesium shifts the uv-excited emission peak from about 460 nanometers in CeAlllOl9 to ab:out 370 na~ometers in CeMgAlllOlg. These phosphors are self-activated by the Ce ion.
: R.W. Wole,,while investigating aluminates with the magneto plumbite or B-alumina structure, dis-covered that by partially replacing cerium with barium, s~trontium or-calcium, the temperature dependence of the~emission of the cerium magnesium aluminates could be~greatly improved. Therefore, the alkaline earth-~ 2~5 : substituted cerium~magnesium aluminates are more 22~270 , ; - ~ ~ ,i ~.

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ll~Si32 effective than the cerium magnesium aluminates in highly loaded fluorescent lamps operating at wall temperatures within the range 200C to 400C. Such alkaline earth-substituted cerium magnesium aluminates are claimed in U.S. patent 4,088,922, issued May 9, 1978, and assigned to the present assignee.
U.S. patent 4,153,572, issued May 8, 1979, also to R.W. Wolfe and assigned to the present assignee, ! describes uv emitting yttrium-substituted magnesium aluminate phosphors having optimum emissions for ,l psoriasis treatment.
It is known that certain ions such as Fe3+ and Ti4+ when introduced into the soda-lime bulb glass for fluorescent lamps cause absorption of harmful sun-burning radiation emitted in the W B region, therefore permitting the use of certain phosphors in such lamps which would otherwise be discarded because of their undesirably high energy output in this region. How-ever, such energy absorbers in the glass also tend to absorb energy from the W A region, therefore diminishing - the overall suntanning power of the lamp.

DISCLOSURE O.F THE INVENTION
In accordance with the invention it has been dis-covered that certain alkaline earth-substituted cerium magnesium aluminate phosphors exhibit optimum energy i output within the UVA region and minimum energy output - within the W B region, thus making these phosphors useful in fluorescent lamps for suntanning applica-tions. Such phosphors may be represented by the molar formula:
cexRy(Mgl-gzng)zAlllol6~5~3/2(x+y)+
where R - Ba, Sr, or Ca x = 0.80-0.95 y = 0.02-0.15, z = 0.80-1.0, and B = 0-0.5 .
.~ , 22,270 .,. . ,~.

114S132 ' Lamps incorporating these phosphors exhibit improved energy output in the UVA region and decreased energy output in the W B region when compared to lamps in- !
corporating the phosphor compositions of the prior art.
Current emphasis is upon the development of new phosphors which would exhibit maximum energy output in the suntanning region of the electromagnetic spectrum, that is, 315 to 400 nanometers, and referred to as the UVA region, as opposed to energy outputs in the sunburning region below 315 nanometers, the so-called UVB region. A commercially available phosphor currently used for suntanning applications is BaSi205:Pb. However, phosphors having higher output in the W A region and better lamp maintenance are sought.
BEST MODE FOR CARRYING OUT THE INVENTION
For a better understanding of the invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above description of some of the aspects of the invention.
Phosphors of this invention may be prepared readily by blending the required amounts of appropriate starting materials and firing in a reducing atmosphere at an elevated temperature for a-moaest time interval. Time, temperature and reducing atmosphere are not critical, but a mixture of nitrogen and hydrogen or hydrogen are preferred, a temperature range from 1450C to 1750C
is also preferred, at a time interval of from 1 to 5 hours. The particular starting materials are not critical, but æhould of course be chosen so that they yield during firing the required composition. Com-pounds which upon heating decompose to oxides, such as hydroxides, carbonates, sulfates, nitrates, etc. are : "

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acceptable. Preferred starting materials are Al(OH)3, MgO, BAO, or BaF2, CeO2 or CeF3. The currently es-pecially preferred composition has the approximate molar formula:
CeO 9O BaO 05 ~Igl,o A11118~925 Example Preparation of CeO goBao~osMgl.oAlllol8 92~

2.330 grams of CeO2, 0.632 grams of MgO, and 0.135 grams of BaF2 are mixed with 13.470 grams of Al(OH)3.
The mixture is fired at 1550C for 4 hours in a dis-sociated ammonia atmosphere (75 volume percent ~J2, 25 volume percent H2). The resulting phosphor of the above molar composition is essentially in the hexagonal magneto plumbite phase, and when incorporated into a standard 40 watt fluorescent lamp has an emission in-tensity peak at about 349 nanometers. Energy output of the lamp after 100 hours operating time is as follows:
Watts output less than 315 nm (UVB)-0.15 Watts output between 315 and 400 nm (W A)-11.20 100 Hour Maintenance (%) - 97.9 ' Maintenance is defined as the ratio of the energy output in the W A region of the lamp divided by the initial energy output of the lamp. For example, 100 Hour Maintenance (%) =
i 25 Ener~y Output at 100 hours x 100 Energy Output at U Hours Table I lists ~amp data or this and other phosphors of this invention when compared to prior art phosphor compositions,. All lamp data is for low pressure mercury vapor (LPMV) lamps whose lamp glass spectral transmission decreases from about ~0 percent at about 350 nanometers to almost zero at about 270 nanometers.
Thus, it is understood that some of the W A energy and a substantial part of the UVB energy of the phosphor is absorbed by the lamp glass, and that the reported , values are for the lamps, not the phosphors.
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There are several points in the Table which warrant discussion. First, the phosphors prepared according to this invention show energy output in the UVA region after 100 hours of operation ranging from comparable to superior relative to the high temperature phosphors of U.S. patent 4,088,922, however, the high temperature phosphors which exhibit comparable W A energy output also exhibit undesirably high energy output in the W B
(sunburning) region. Second, the phosphors of this invention show superior energy output in the W A region over the remaining prior art phosphors tested, in-cluding the yttrium-substituted cerium magnesium - alu~inate of U.S. patent 4,153,572, the cerium magnesium aluminate o~ British patent 1,452,083, and the standard lead activated barium silicate commercial phosphor.
Third, the phosphors of the invention show superior lamp maintenance after 100 hours of operation over the cerium magnesium aluminate of British patent 1,452,083 and the standard lead-activated barium silicate commercial phosphor.
While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the in- '¦
vention as defined by the appended claims.
INDUSTRIA~ APPLICA~ILITY
The al~aline earth substituted cer,ium ,magnesium aluminate phosphors of this invention have optimum energy o,utput ln the UVA (suntanning) region of the electromagnetic spectrum and minimum energy output in the UVB (sunburning) region of the electro-magnetic spectrum, and accordingly are useful in fluorescent lamps for artificial suntanning applications.

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Claims (2)

CLAIMS:

1. Alkaline earth substituted cerium magnesium aluminate phosphor exhibiting a hexagonal magneto plumbite structure and having the molar formula:
CexRy(Mg1-BZnB)zAl11O16+3/2(x+y)+z, where x = 0.80 - 0.95 y = 0.02 - 0.15 z = 0.80 - 1.0 B = 0-0.5, and where R is selected from the group consisting of Ba, Sr, and Ca.

2. The phosphor of Claim 1 having the molar formula of approximately:
Ce0.90Ba0.05Mg1.0Al11O18.925, ?22,270