The semiconductor ZnO has grained substantial interests in the research community in part because of its wide direct band gap (3.3 eV) and large exciton binding energy (60 meV). It is a well-known piezoelectric and electro-optic material with potential applications such as optoelectronic and luminescent devices as well as chemical sensors. Even though the research focusing on ZnO goes back to several decades

one of the renewed interests is fueled by the observation of ferromagnetic behavior in transition metals doped ZnO which is called diluted magnetic semiconductors (DMS). DMS could be served as ideal material for exploiting spin in addition to charge in semiconductor devices. Much attention has been paid to the magnetic properties of ZnO-based DMS. In this paper we focused on the optical properties of Co-doped ZnO films. Highly (002) orientated Zn

0.95

Co

0.05

O films were deposited on Si (100) substrate using inductively coupled plasma enhanced physical vapor deposition (ICP-PVD) with magnetic confinement. X-ray diffraction pattern and typical Raman spectrum show that Zn

0.95

Co

0.05

O film has a wurtzite structure. Transmittance spectrum indicates that the Zn

0.95

Co

0.05

O film has an average transparency of over 80% in the visible and infrared wavelength. The band gap of Zn

0.95

Co

0.05

O film (3.11 eV) is less than that of pure ZnO

which is due to sp-d exchange interactions between the band electrons in ZnO and the localized d electrons of the Co

2+

ions. Three obvious absorption peaks around 660

615 and 560 nm are found. They are ascribed to derive from d-d transitions of tetrahedrally coordinated Co

2+

and attributed to the

4

A

2

(

4

F)→

2

E(

2

G)

4

A

2

(

4

F)→

4

T

1

(

4

P)

and

4

A

2

(

4

F)→

4

A

1

(

4

G) transitions. The photoluminescence spectrum shows broad blue and green emission from the Zn

0.95

Co

0.05

O film at room temperature. On the other hand

no luminescence is found in the ultraviolet region near 380 nm.