Alkaline earth sulfides(AES) are excellent and versatile phosphor hosts

hold promise use for many fields.However

these phosphors are easy to hydrolysis in humidity air

and they are easy to dissociate and degrade under high-energy charge

which limit their applications.All of these problems can be solved by using appropriate protective coatings on the surface of phosphor to prevent from the reacting with the atmosphere around the phosphors.Chemical vapor deposition(CVD) method was used extensively

but this CVD process requires elaborate instrumentation

the cost is expensive.A simply wet method was firstly used to coat the unstable AES based phosphor in this paper.The phosphor was added into precursors solution of oxides(usually their soluble salts solution)

and then their hydroxides were precipitated on the surface of phosphors through changing the value of pH.The coated phosphors were separated from the liquor resulting and dried at sufficiently high temperature(300～500℃)for a sufficient time(1～2h) to remove water.During this process

part hydrolysis of the surface plays an important role

which make the oxide coating particles adhered better on the phosphor surface.A layer of oxide coating(such as Al

2

O

3

SiO

2

MgO

ZnO)was covered on the surface of alkaline earth sulfides based phosphor Ca

0.8

Sr

0.2

S:Eu

2+

Tm

3+

in aqueous medium.XRD

SEM and EDS were used to characterize the coating and the ideal model of coated phosphor and bonding between oxide coating particles and the surface of phosphor were discussed.The stability and optical properties of coated or uncoated phosphor were measured at room temperature.The results indicate that a layer of much smaller oxide coating particles indeed covered on the surface of phosphor

and the stability of coated phosphor has been enhanced to great extent; but oxide coating has no remarkable effects on their emission spectra except a little decrease of their PL intensities within the permitted range.Encapsulated with a layer of oxide coating is a good method to enhance the stability of alkaline earth sulfide based phosphor

and our method is simply and easy to carry out.