The Sr

2

MgSi

2

O

7

:Eu

2+

Dy

3+

is an excellent blue long afterglow phosphor.Its afterglow can last longer than 20 h.But the mechanism of the afterglow luminescence is not clear so far.In order to study the physical process of the afterglow luminescence

Eu

2+

Dy

3+

singly doped or co-doped silicate:Sr

2

MgSi

2

O

7

:Eu

2+

Sr

2

MgSi

2

O

7

:Dy

3+

Sr

2

MgSi

2

O

7

:Eu

2+

Dy

3+

and Sr

2

MgSi

2

O

7

were prepared and their VUV-UV excitation properties and temperature dependence were studied with synchrotron radiation VUV light.In emission spectrum of Sr

2

MgSi

2

O

7

:Eu

2+

Dy

3+

under 300 nm excitation

a broad band emission around 465 nm due to(4f

6

5d4f

7

)transition of Eu

2+

.Its excitation band lied around 360 nm.But under excitation at 172 nm

(besides)the broad band emission of Eu

2+

a relative low line emission peaked at 575 nm can also be seen.Compared with the emission spectrum of Sr

2

MgSi

2

O

7

:Dy

3+

it could be assigned to 4f-4f transition of Dy

3+

.This implied that Dy

3+

acted as not only traps

but luminescent centers also in the phosphor.In excitation spectra of Sr

2

MgSi

2

O

7

:Dy

3+

and Sr

2

MgSi

2

O

7

we could see that both host and Dy

3+

excitation band were in VUV range.So when Sr

2

MgSi

2

O

7

:Eu

2+

Dy

3+

was excited in UV-Vis range

only Eu

2+

emission 465 nm band can be recorded and no Dy

3+

and host emission existed.The phosphor is excited by daylight in applications

thus only the useful Eu

3+

emission can be observed.These results made the long afterglow phosphor Sr

2

MgSi

2

O

7

:Eu

2+

Dy

3+

very suitable for practical use.