Lead-activated BaSi

2

O

5

(BaSi

2

O

5

:Pb

BSP)is used as the long wavelength UV phosphor in suntanning lamps

as well as speciality lamps for diazo-printing reprography

lithography

insect traps

photoche-mical and curing processes.A well-known problem with the use of this material is that its radiance maintenance is poor.That is

lamps employing the BaSi

2

O

5

:Pb phosphor exhibit a large decrease in radiant output over time.Presently

the stabilization of the light output of tanning lamps is achieved by the application of an Al

2

O

3

coating onto the surface of BSP particles.This measure requires a gas phase process

since the wet chemical precipitation of Al(OH)

3

has to be performed at an acidic pH

i.e

.in an environment which is hazardous to BSP.It is an object to provide a solution based method for BSP that can be performed at a high pH and is thus harmless to the phosphor

and further object to improve the lamp maintenance of BSP phosphor.The method involves adding an amount of a silicate phosphor to a salt solution containing a cation

such as Ba

2+

stirring the solution for a time sufficient to cause the cation to attach to the phosphor surface

separating the cation-treated phosphor from the solution

and annealing the phosphor at a temperature for a time sufficient to increase radiance maintenance of the cation-treated phosphor.The surface morphology and the surface component of cation-treated BSP phosphor were investigated by means of SEM and XPS

respectively.The luminescent performances of the lamps using the cation-treated phosphor and untreated phosphor were tested.The results demonstrate that cation-treated phosphor shows a decrease in the ratio of Si/Ba surface atoms

and lighting test indicates that lamp employing the cation-treated phosphor has a significant improvement in radiance maintenance.