It has been reported recently that some Eu

3+

doped nanocrystalline silicate and oxide were with higher quenching concentrations in comparison with the corresponding bulk materials. Computer simulation has shown that the size confinement and the existence of high density surface states affected significantly the quenching processes of the rare earth dopants in nanoparticles. To understand the feature of the energy transfer process in rare earth doped nanoparticles is important for further seeking applicable nano phosphors. This paper reported

the preparation of a series of Y

2

O

2

S:Tb

3+

nanocrystals with uniform sizes and varied Tb

3+

concentrations. The mean size of all the samples prepared was evaluated

based on the X-ray diffraction pattern

to be about 20nm. Emission spectra of Tb

3+

in nanocrystalline Y

2

O

2

S with different Tb

3+

concentrations were measured under 257nm excitation. With increasing Tb

3+

concentration

the luminescence intensity of both the

5

D

4

→

7

F

J

and

5

D

3

→

7

F

J

transitions increases at first and then decreases. Emission intensities reach their maximum at the Tb

3+

concentration of 0.6% for the

5

D

3

emission and of 6.4% for the

5

D

4

emission. The lifetime of the

5

D

3

level is 0.31ms in the sample with 0.065% Tb concentration

comparably shorter than 0.78ms in bulk Y

2

O

2

S:0.3%Tb. This fact indicates that the surface states do act as the quenching centers for the luminescence

and the increasing of quenching concentration comes probably from the lower quantum efficiency of the nanocrystals. The dependences of the intensity on Tb concentration and the decay curves of both

5

D

3

and

5

D

4

emissions fit with theory. The quenching of the

5

D

3

state is governed by dipole dipole interaction

while that of the

5

D

4

state by exchange interaction. Both the intensity and temporal analyses coincide and result in the same conclusion. Similar to bulk material

concentration quenching of the

5

D

3

state is due to cross relaxation. The mechanism of the concentration quenching of the

5

D

4

state is that the energy migrates among the Tb ions and is trapped finally by quenching centers

most likely

the surface states.