GB2053953A - Ultraviolet emitting aluminate phosphor and fluorescent suntanning lamps utilizing same - Google Patents

Abstract

Alkaline earth substituted cerium magnesium aluminate phosphors exhibiting a hexagonal magneto plumbite structure have the general formula:- CexRy(Mg1-BZnB)ZAl11O16+3/2(x+y)+z wherein 0.8 </= x </= 0.95; 0.02 </= y </= 0.15; 0.8 </= z </= 1; 0 </= B </= 0.5 and R is Ca, Sr or Ba, A typical example is Ce0.90Ba0.05Mg1.0Al11O18.925 which exhibits optimum energy output within the UVA (suntanning) region of the electromagnetic spectrum and minimal energy output within the UVB (sunburning) region of the electromagnetic spectrum, and accordingly are useful in fluorescent lamps for artificial suntanning applications.

Description

SPECIFICATION Ultraviolet emitting aluminate phosphor and fluorescent suntanning lamps utilizing same This invention relates to aluminate phosphors emitting in the ultraviolet region of the electromagnetic spectrum, and more particularly relates to such phosphors containing cerium and alkaline earths, and to fluorescent lamps incorporating them.

Phillips Electronics Associated Industries in British Patent No 1 ,452,083 disclosed an ultraviolet emitting fluorescent lamp phosphor having the composition CeMgAI,,O,g and the magneto plumbite structure. H.F. Ward of Thorn Industries, in British Patent No. 1,194,014 disclosed a phQsphor having the composition CeAI"0,8 and the magneto plumbite structure. Although CeAI"0,8 and CeMgAI,,O,g have similar crystal structures, incorporation of magnesium shifts the uv-excited emission peak from about 460 nanometers in CeAI"018 to about 370 nanometers in CeMgA111019. These phosphors are self-activated by the Ce3+ ion.

R.W. Wolfe, whilst investigating aluminates with the magneto plumbite or B-alumina structure, discovered that by partially replacing cerium with barium, strontium or calcium, the temperature dependence of the emission of the cerium magnesium aluminates could be greatly improved. Therefore, the alkaline earth-substituted cerium magnesium aluminates are more effective than the cerium magnesium aluminates in highly loaded fluorescent lamps operating at wall temperatures within the range 2000C to 4000C. Such alkaline earth-substituted cerium magnesium aluminates are claimed in U.S. Patent No. 4,088,922, issued May 9th, 1978 and assigned to the present Assignee.

U.S. Patent No. 4,153,572, issued May 8th, 1979, also to R.W. Wolfe and assigned to the present assignee, described UV emitting yttrium-substituted magnesium aluminate phosphors having optimum emisions for psorisis treatment.

It is known that certain ions such as Fe3+ and Ti4+ when introduced into the soda-lime bulbglass for fluorescent lamps cause absorption of harmful sunburning radiation emitted in the UVB region, therefore permitting the use of certain phosphors in such lamps which would otherwise be discarded because of their undersirably high energy output in this region. However, such energy absorbers in the glass also tend to absorb energy from the UVA region, therefore diminishing the overall suntanning power of the lamp.

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 31 5 nanometers, the so-called UVB region. A commercially avaliable phosphor currently used for suntanning applications is BaSi205:Pb. However, phosphors having higher output in the UVA region and better lamp maintenance are sought.

In accordance with the invention it has been discovered that certain alkaline earth-substituted cerium magnesium aluminate phosphors exhibit optimum energy output within the UVA region and minimum energy output within the UVB region, thus making these phosphors useful in fluorescent lamps for suntanning applications. Such phosphors may be represented by the molar formula: CexRy(Mg1~BznB)zAl11o16w5+3l2{x+Yl+z where R = Ba, Sr, or Ca x = 0.80--0.95 y = 0.20-0.15, z = 0.80--1.0, and B = 0--0.5.

Lamps incorporating these phosphors exhibit improved energy output in the UVA region and decreased energy output in the UVB region when compared to lamps incorporating the phosphor compositions of the prior art.

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 modest 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 1450 C to 17500C is also preferred, at a time interval of from 1 to 5 hours. The particular starting materials are not critical, but should of course be chosen so that they yield during firing the required composition. Compounds which upon heating decompose to oxides, such as hydroxides, carbonates, sulfates, nitrates, etc. are acceptable. Preferred starting materials are Al(OH)3, MgO, BAO, or BaF2, CeO2or CeF3.The currentiy especially preferred composition has the approximate molar formula: Ce0.90 Ba0.05 Mg1.0 Al11O18.925 EXAMPLE Preparation of Ce0.90Ba0.05Mg1.0Al11O18,925 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 1 5500C for 4 hours in a dissociated ammonia atmosphere (75 volume percent N2, 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 intensity peak at about 349 nanometers.Energy output of the lamp after 100 hours operating time is as follows: Watts ouput less than 315 nm (UVB)-O.1 5 Watts ouput between 315 and 400 (UVA)-1 1.20 100 Hour Maintenance (%)97.9 maintenance is defined as the ratio of the energy output in the UVA region of the lamp divided by the initial energy output of the lamp. For example, 100 Hour Maintenance (%) = Energy Output at 100 hours x 100 Energy Output at O Hours Table I lists lamp data for this and other phosphors of this invention when compared to prior art phosphor compositions. All lamp data is for low pressure mercury vapour (LPMV) lamps whose lamp glass spectral transmission decreases from about 90 percent at about 350 nanometers to almost zero at about 270 nanometers.Thus, it is understood that some of the UVA 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.

TABLE 1 Composition and 40 Watt LPMV Lamp Data for Various Suntanning Phosphors Energy in Watts at 100 hrs. Lamp Maintenance Emission (UVB) (UVA) Source Composition Peak(nm) 315nm 315-400nm 100 hrs.

invention Ce.90@Sr.05Mg1.0Al11O18.9 349 .14 10.2 96.6 " Ce.90Ca.05Mg1.0Al11O18.9 349 .14 10.5 96.9 " Ce.90Ba.05Mg1.0Al11O18.9 349 .15 11.2 97.9 " Ce.95Ba.05Mg1.0Al11O19@0 349 .15 10.5 96.9 U.S. 4,088,922 Ce.49Sr.3Mg.61Al11O18.1 340 .64 10.7 94.3 "Ce.74Ba.05Mg.79Al11O18.4 344 .23 10.9 96.0 " Ce.61 Mg.61AL11O18.0 349 .15 8.9 97.0 "Ce.79Mg.79Al11O18.4 362 .12 7.2 93.3 U.S. 4,153,572 Ce.71Y1.14Mg.61Al11O18.2 348 .12 9.3 96.1 British Patent 1,452,083 Ce1.0Mg1.0Al11O19 365 .06 5.5 90.0 Standard Commercial Suntanning Phosphor BaSl2O5:Pb 350 .15 8.4 76.9 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 reiative to the high temperature phosphors of U.S.Patent No. 4,088,922, however, the high temperature phosphors which exhibit comparable UVA energy output also exhibit undesirably high energy output in the UVB (sunburning) region. Second, the phospors of this invention shown superior energy output in the UVA region over the remaining prior art phosphors tested, including the yttrium-substituted cerium magnesium aluminate of U.S. Patent No. 4,153,572, the cerium magnesium aluminate of British Patent No. 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 No.1,452,083 and the standard lead-activated barium silicate commercial phosphor.

The alkaline earth substitutesd cerium magnesium aluminate phosphors of this invention have optimum energy output in the UVA (suntanning) region of the electromagnetic spectrum and minimum energy output in the UVB (sunburning) region of the electromagnetic spectrum, and accordingly are useful in fluorescent lamps for artificial suntanning applications.

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 inventions as defined by appended Claims.

Claims (5)

1. An alkaline earth substituted cerium magnesium aluminate phosphor exhibiting a hexagonal magneto plumbite structure and having the molar formula: where x = 0.800.95 y = 0.02-0.15 z = 0.80-1.0 B = 0--0.5, and where R is Ba, Sr or Ca.

2. A phosphor as claimed in Claim 1, having the molar formula of approximately: Ce0.80Ba0.05Mg1.0Al11O18,925.

3. A phosphor as claimed in Claim 1, substantially as described herein.

4. A fluorescent lamp incorporating an ultraviolet emitting phosphor as claimed in any one of Claims 1-3.

5. The features as herein described, or their equivalents, in any novel selection.