Phosphate treated silicate phosphor

Details Phosphate treated silicate phosphor Phosphate treated silicate phosphor

1999-09-09

2001-10-16

Koslow, C. Melissa (Department: 1755)

Compositions

Inorganic luminescent compositions

Compositions containing halogen; e.g., halides and oxyhalides

C252S30140P, C252S30160F, C252S30160P

Reexamination Certificate

active

06303051

ABSTRACT:

TECHNICAL FIELD
This invention relates to silicate-based phosphors, and especially to lead activated barium disilicate (BaSi
2
O
5
:Pb), used in fluorescent lighting applications. More particularly, it relates to improved maintenance of silicate phosphors in fluorescent lamps.
BACKGROUND OF THE INVENTION
Typical silicate phosphors used in fluorescent lighting applications include BaSi
2
O
5
:Pb, Zn
2
SiO
4
:Mn and CaSiO
3
:Pb,Mn. Of particular interest is BaSi
2
O
5
:Pb which is used as the long-wavelength UV (347 nm) phosphor in fluorescent suntanning lamps. Its preparation and use have been described in U.S. Pat. Nos. 2,597,631, 3,043,781, and 5,234,625 which are incorporated herein by reference. A well-known drawback to the use of this phosphor, and silicate phosphors in general, is that lumen maintenance in fluorescent lamps is poor relative to other fluorescent lamp phosphors. That is, fluorescent lamps employing silicate phosphors exhibit a relatively rapid decrease in brightness over time.
It has been demonstrated, however, that the life of silicate phosphors can be extended considerably by applying a protective coating to the phosphor particles. In particular, U.S. Pat. Nos. 5,223,341 and 4,710,674 describe an A
2
O
3
coating which improves the maintenance of silicate phosphors in fluorescent lamps. The protective alumina coating is applied via a CVD method in a fluidized bed using pyrophoric organometallic compounds. While effective, the prior art method requires relatively complex coating equipment and hazardous chemicals. Thus, it would be advantageous to have a simpler, more economical method for protecting silicate phosphors and improving their maintenance in fluorescent lamps.
SUMMARY OF THE INVENTION
It is an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to provide a silicate phosphor having improved lumen maintenance in fluorescent lamps.
It is a further object of the invention to provide a method of treating silicate phosphors to improve their lumen maintenance in fluorescent lamps.
In accordance with one aspect the invention, there is provided a phosphate treated silicate phosphor having a protective phosphate-containing surface layer.
In accordance with another aspect of the invention, there is provided a method for treating a silicate phosphor comprising mixing the phosphor in an aqueous phosphate solution for a time sufficient to induce the formation of phosphate-containing surface layer, separating the phosphor from the solution, and annealing the phosphor to form a protective phosphate-containing surface layer.


REFERENCES:
patent: 3634886 (1988-04-01), None
Derwent Abstract 1973-04364U, abstract for CA 950956, pub. Jul. 9, 1974.

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