Trivalent europium-activated Y

2

O

3

has attracted much attention as red emitting phosphor in commercial application on fluorescent lighting and displaying. With the development of nanotechnology

the optical properties of nanocrystalline (NC) Y

2

O

3

:Eu

3+

have also been investigated extensively for its potential application on high resolution images and for fundamental researches such as local environment probing because Eu

3+

is supersensitive to its surroundings. As well known

Y

2

O

3

:Eu

3+

phosphor can absorb the UV light through a charge transfer band (CTB) or host excitation band and then generates red color fluorescence peaking at 611 nm. Some investigations on CTB of bulk and NC Y

2

O

3

:Eu

3+

have been reported. There exist S

6

and C

2

crystallographic sites in cubic Y

2

O

3

. The S

6

site has inversion symmetry center in which electric dipole transition is forbidden. Due to the absence of the inversion symmetry center

the C

2

site makes dominant contribution to the 611 nm emission which corresponds to the electronic dipole transition of

5

D

0

→

7

F

2

in Y

2

O

3

:Eu

3+

. Hence

the generally observed CTB and host excitation band in the excitation spectra by monitoring the red color fluorescence from

5

D

0

→

7

F

2

transition merely corresponds to the C

2

site. Although the S

6

site has almost no contribution to the red color fluorescence

it possibly competes with the C

2

site for energies under UV excitation. To our knowledge

there is no report on the UV excitation properties of the S

6

site in bulk and nanocrystalline Y

2

O

3

:Eu

3+

. The S

6

site allows the magnetic dipole transition

5

D

0

→

7

F

1

of Eu

3+

which provides the possibility to study the UV excitation properties of the S

6

site. The CTB and host excitation band for Eu

3+

at the S

6

site in bulk and nanocrystalline Y

2

O

3

:Eu

3+

is mainly investigated. The NC Y

2

O

3

:0.01 Eu

3+

was prepared by fast thermal decomposition of metal nitrate solution. The advantage of this method is that pure cubic phased Y

2

O

3

:Eu

3+

nanocrystals can be obtained at a relatively lower temperature than by any other methods. The particle sizes were determined to be 7 nm from a survey of the transmission electron microscopy micrographs. The bulk Y

2

O

3

:0.01 Eu

3+

powders was formed by annealing as-prepared corresponding nanoparticles at (1250)℃ in air. It was determined to be 2～3 μm by field-emission scanning electron microscopy (FE-SEM). Both the samples were identified as cubic structure from XRD. The spectra were carried out at room temperature with a Hitachi F-4500 florescence spectrometer using a Xe lamp as the excitation source. Increases of emission intensities for Eu

3+

at the S

6

site relative to that at the C

2

site have been observed as UV excitation wavelength decreases from 200～300 nm in both bulk and nanocrystalline cubic Y

2

O

3

:Eu

3+

. It indicates that the two kinds of sites have different charge transfer states and host lattice excitation responds. Decomposition of excitation spectra shows that the charge transfer band(CTB) of Eu

3+

at the S

6

site is located at the high-energy side of the C

2

site and the host prefers transferring energy to the S

6

site. Compared with the bulk material

the CTBs for the two sites both shift toward the red and the number ratio of S

6

to C

2

sites is smaller in nanocrystalline Y

2

O

3

:Eu

3+

. Above results are discussed.