A series of LaP

3

O

9

:Ce

Gd

Tb phosphors have been prepared by a solution-precipitation method. X-ray structural analysis showed that they are fairly pure LaP

3

O

9

phase

with a cyclic-(PO

3

)

3

-structure

belonging to orthorhombic syngong;with cell parameters

a

=11.19

b

=8.54

c

=7.28

Their excitation and emission spectra

relative brightness and the luminescence lifetime of Ce

3+

have been measured. It was observed that the spectra of Ce

3+

overlaps with that of Gd

showing that there is some interaction in energy between these two ion;and Ce

3+

can effectively sensitize Tb

3+

so as to enhance the emission of Tb

3+

significantly. LaP

3

O

9

:Ce

Tb might be a new high efficient green emitting phosphor. Adding a small amount of Gd to Ce

Tb codoped LaP

3

O

9

led to the lowering of the emission brightness to a certain extent. This might be due to the competition absoption by Gd

3+

. From the luminescence lifetime of Ce

3+

it can be inferred that the energy transfer from Ce

3+

to Gd

3+

is weak

whereas that from Ce

3+

to Tb

3+

is very efficient.